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The role of nitric oxide (NO) in tumor biology remains controversial and poorly understood. While a few reports indicate that the presence of NO in tumor cells or their micro-environment is detrimental for tumor-cell survival, and consequently their metastatic ability, a large body of data suggests that NO promotes tumor progression. The purpose of this study was to identify the source of NO in the spontaneously metastasizing C3-L5 murine mammary-adenocarcinoma model, the role of tumor-derived NO in tumor-cell invasiveness, and the mechanisms underlying the invasion-stimulating effects of tumor-derived NO. The source of NO was established by immunocytochemical localization of NO synthase (NOS) enzymes in C3-L5 cells in vitro and transplanted tumors in vivo. An in vitro transwell Matrigel invasion assay was used to test the invasiveness of C3-L5 cells in the presence or the absence of NO blocking agents or iNOS inducers (IFN-γ and LPS). The mechanisms underlying the invasion-stimulating effects of tumor-derived NO were examined by measuring mRNA expression of matrix metalloproteinases (MMP)-2 and -9, and tissue inhibitors of metalloproteinases (TIMP) 1, 2 and 3 in C3-L5 cells in various experimental conditions. Results showed that C3-L5 cells expressed high level of eNOS protein in vitro, and in vivo, both in primary and in metastatic tumors. C3-L5 cells also expressed iNOS mRNA and protein when cultured in the presence of IFN-γ and LPS. Constitutively produced NO promoted tumor-cell invasiveness in vitro by down-regulating TIMP 2 and TIMP 3. In addition, there was up-regulation of MMP-2, when extra NO was induced by IFN-γ and LPS. In conclusion, NO produced by C3-L5 cells promoted tumor-cell invasiveness by altering the balance between MMP-2 and its inhibitors TIMP-2 and 3. Thus, our earlier observations of anti-tumor and anti-metastatic effects of NO inhibitors in vivo in this tumor model can be explained, at least in part, by reduced tumor-cell invasiveness. Int. J. Cancer 81:889–896, 1999. © 1999 Wiley-Liss, Inc.

Summary Extravillous trophoblast (EVT) cells of the human placenta proliferate, migrate and invade the decidua and its vasculature. By utilizing in vitro propagated normal first trimester human EVT cells in functional assays, we have shown that proliferative, migratory and invasive functions of these cells are stringently regulated in situ by numerous growth factors, their binding proteins and proteoglycans and extracellular matrix (ECM) components. Growth factors in the EGF family (EGF, TGFβ and amphiregulin), CSF-1, VEGF and PIGF all stimulate EVT cell proliferation without affecting migratory or invasive abilities, whereas IGF-II and its binding protein IGFBP-1 stimulate EVT cell migration and invasiveness without affecting proliferation. Finally, TGFβ a major decidual cell product, inhibits proliferation, migration and invasiveness of normal EVT cells, whereas choriocarcinoma cells defy the TGFβ mediated control. We have produced “premalignant” derivatives of normal EVT cells by SV40 Tag transfection, some of which are immortal (as opposed to normal EVT cells which senesce at 5–15 passages), hyperproliferative, hyperinvasive, resistant to antiproliferative and antiinvasive action of TGFβ and deficient in gap junctional intercellular communication, but are yet incapable of anchorage independent growth or tumorigenicity in nude mice. Transition of the normal EVT cell to the premalignant stage is associated with multiple genetic changes, e.g., a downregulation of connexins, TIMP-1, TIMP-2 and PAI-I, which partially account for the phenotypic changes. We have recently intruduced activated H-ras oncogene into a premalignant EVT cell line to induce malignant/metastatic phenotype. Normal, premalignant and malignant EVT cell lines derived from a single placenta provide us with an exquisite in vitro model for studies of stage-specific genetic changes responsible for trophoblastic tumor progression.

Placenta growth factor (PlGF) is a homodimeric glycoprotein, 46-50 kDa in size, belonging to the vascular endothelial growth factor (VEGF) sub-family. It exists as two isoforms, PlGF-1 and -2, the latter having a heparin-binding domain. Like VEGF, it is a potent angiogenic factor; however, PlGF homodimers interact with the VEGF receptor Flt-1 (fms-like tyrosine kinase), but not with the kinase domain-containing region (KDR). Since PlGF is made by the human placenta and extravillous trophoblast (EV-T) cells of the human placenta express Flt-1 in situ, these cells may be responsive to PlGF. Therefore, this study examined whether first trimester EVT cells propagated in vitro expressed the mRNA or the protein of Flt-1 and PlGF, and whether exogenous PlGF-1 had any effect on EVT cell proliferation, migration or invasiveness. Immunocytochemical and RT-PCR analyses revealed that both normal and SV40 Tag-immortalized EVT cells expressed the protein and mRNA for Flt-1, but not for PlGF-1 or -2. Exogenous PlGF-1 stimulated proliferation (measured by 3H-thymidine uptake) of normal EVT cells in a concentration-dependent manner, but only in the presence of excess heparan sulphate proteoglycans (HSPGs). These results raise two possibilities: that exogenous PlGF-1 (in spite of having a low affinity for heparin) was sequestered away from its receptor because of binding to heparan sulphate proteoglycans on the EVT cell surface or the ECM, or that HSPGs could modify the interaction between Flt-1 and PlGF. PlGF-1, in the presence or absence of HSPGs, however, had no effect on EVT migration or invasiveness, when measured with a transwell invasion (in the presence of Matrigel) or migration (in the absence of Matrigel) assay. These findings place PlGF amongst a large group of growth factors that promote EVT cell proliferation without influencing their migratory or invasive behaviours, and suggest that PlGF-Flt-1 interactions may be regulated by HSPGs in situ.

Vascular endothelial growth factor (VEGF) is a homodimeric glycoprotein that promotes angiogenesis and vascular hyperpermeability and interacts with two receptors, fms-like tyrosine kinase (Flt-1) and kinase domain-containing region (KDR). In situ localization in the pregnant human uterus revealed that VEGF mRNA is expressed primarily by the maternal decidua, whereas the receptor Flt-1 is expressed primarily by chorionic vascular endothelium and trophoblast cells-in particular, the extravillous trophoblast (EVT). We examined whether the mRNA and protein of VEGF and its receptors are expressed by invasive human first-trimester EVT cells propagated in culture and whether VEGF influences EVT cell proliferation, migration, and invasiveness. Proliferation was assessed by the uptake of [ 3 H]thymidine. Invasion and migration across transwells were assessed by the degree of cellular transgression of a Millipore membrane coated, respectively, with and without Matrigel. Results of immunocytochemical and reverse transcription-polymerase chain reaction analysis revealed that both protein and mRNA of VEGF, Flt-1, and KDR were expressed by cultured normal EVT cells as well as their premalignant derivative produced by SV-40 Tag-immortalization, and BeWo choriocarcinoma cells. Under serum-free conditions, exogenous VEGF 121 (the non-heparin-binding isoform) stimulated proliferation of all three cell lines in a concentration-dependent manner. The effects were abolished with a VEGF-neutralizing antibody. The same stimulatory effects on EVT cells were also seen with exogenous VEGF 165 (a heparin-binding isoform), only after a cleaving of the heparin-binding domain with plasmin or a blocking of heparin binding sites with excess soluble heparan sulphate proteoglycans (HSPGs), suggesting a regulatory role of HSPGs. However, VEGF 121 and VEGF 165 (with and without the HSPG pretreatment) had no effect on normal EVT cell migration or invasiveness. Thus, VEGF may provide a dual role in angiogenesis and EVT cell proliferation during normal placental development.

Poor gap junctional intercellular communication (GJIC) has been associated with uncontrolled cell growth and neoplasia. We have successfully propagated normal first trimester invasive extravillous trophoblast (EVT) cells, and have produced premalignant EVT lines after SV40 Tagtransformation: RSVT-2 is an uncloned line that is long-lived; RSVT2/C is a clonal line that is immortal. Both are hyperproliferative, hyperinvasive and variably refractory to the anti-proliferative and anti-invasive effects of transforming growth factor β (TGFβ). Possible changes in gap junctions during the transition of normal invasive EVT cells to the premalignant stage were examined by comparing expression of connexin proteins (by immunolabeling for Cx26, Cx32, Cx40, Cx43), and mRNA (by Northern blot with cDNA probes for Cx26, Cx32, Cx43), and functional GJIC (by dye transfer using the preloading method) in normal parental EVT cells and their SV40 Tag transformants. Results from immunofluorescence and Northern blot analysis revealed that, of the panel of connexins examined, only Cx43 was variably expressed in these cell lines in vitro. Expression of Cx43 protein and mRNA was abundant in normal EVT cell line HTR8, reduced in long-lived RSVT-2 cells and undetectable in immortalized RSVT2/C cells. GJIC, as measured by dye transfer between donor and recipient cells, was also similarly reduced in recipient RSVT-2 cells, and drastically reduced in RSVT2/C cells, irrespective of whether the dye donor was of the same cell type (homocellular coupling) or HTR8 cells (heterocellular coupling). Treatment with TGFβ reduced Cx43 mRNA expression as well as GJIC in normal EVT cells, but not in the SV40 Tag transformants. Our findings suggest that downregulation of connexins with the resultant impairment in GJIC is an early event in tumor progression, as observed in the premalignant SV40 Tag transformants. Int. J. Cancer77:440–448, 1998. © 1998 Wiley-Liss, Inc.

Invasion of the uterus by first trimester human placental extravillous trophoblast (EVT) cells depends on mechanisms shared by malignant cells. However, unlike tumor invasion, trophoblast invasion of the uterus is stringently controlled in situ by local molecules such as transforming growth factor (TGF)beta. Since EVT cells possess active invasion-associated genes but are nontumorigenic, our objective was to induce premalignant and then malignant phenotype into a normal EVT cell line in order to identify the molecular basis of tumor progression. Simian virus 40 large T antigen (SV40 Tag) was introduced into a normal human first trimester invasive EVT cell line, HTR8, established in our laboratory. Since the HTR8 line has a limited in vitro lifespan of 12-15 passages, SV40 Tag-transformed cells were selected on the basis of extended lifespan. A long-lived line, RSVT-2, was produced and an immortalized subclone, RSVT2/C, was further derived under a forced crisis regimen. We examined transformation-induced alterations in proliferative and invasive abilities, responses to the invasion and proliferation-regulating growth factor TGFbeta and changes in gene expression for invasion-associated enzymes or enzyme inhibitors. RSVT-2 and RSVT2/C cell lines were hyperproliferative and hyperinvasive when compared with the parental HTR8 cell line. They were also variably resistant to the anti-proliferative and anti-invasive signals from TGFbeta. Since both cell lines remained non-tumorigenic in nude mice, these properties indicate that they attained a premalignant phenotype. Both cell lines showed reduced expression of tissue inhibitor of metalloproteases (TIMP)-1, while TIMP-2 and plasminogen activator inhibitor (PAI)-I expression was was also reduced in RSVT2/C cells, thus contributing to their hyperinvasiveness. Their resistance to the anti-invasive action of TGFbeta was explained by the failure of TGFbeta to upregulate TIMPs and PAI-I, in contrast to the TGFbeta-induced upregulation noted in parental HTR8 cells.

Summary Human placentation involves proliferation, migration and invasion of the endometrium and its vasculature by the extravillous trophoblast (EVT). These trophoblast functions are highly regulated both spatially and temporally by numerous local growth factors (in an autocrine and/or paracrine manner), components of the extracellular matrix (ECM), as well as growth factor binding proteins and proteoglycans. For example, all EGF receptor ligands (EGF, TGFα, amphiregulin), as well as CSF-1, VEGF and PIGF stimulate EVT cell proliferation by autocrine, paracrine or juxtacrine pathways, with little or no effect on trophoblast invasion or migration. Decidua-derived TGFβ blocks functions of proliferation, invasion and migration. The invasion regulating effect is due to the upregulation of protease inhibitors TIMP-1 and PAI-1, downregulation of uPA, and suppression of trophoblast migratory ability, owing to an upregulation of integrins making the cells more adhesive to the ECM. Trophoblast derived IGF-II has no influence on EVT cell growth, but stimulates EVT cell invasiveness by promoting migration, an effect which is independent of IGF-I receptor. An IGF binding protein, IGFBP-1, produced by the decidua promotes trophoblast invasiveness by stimulating migration, which requires access to trophoblast α 5 β 1 integrin. A TGFβ-binding and inactivating proteoglycan, decorin, is colocalized with TGFβ in the first trimester decidual ECM, possibly serving as a storage mechanism for inactivated TGFβ. When activated by plasmin (at the invasive front of the trophoblast), the active TGFβ may control trophoblast hyperinvasion of the decedua. Both premalignant as well as malignant EVT cells show resistance to the invasion and proliferation regulating signals of TGFβ, indicating that defects in TGFβ signaling may represent early genetic events facilitating trophoblastic tumor progression.

Summary Development of the human placenta leads to two distinct trophoblast populations: the villous trophoblast primarily engaged in absorptive, exchange and endocrine functions, and the extravillous trophoblast (EVT) primarily engaged in remodeling the pregnant endometrium and its vasculature to achieve placental anchorage to the uterine wall and unhindered placental perfusion through low resistance uterine vessels. Both trophoblast populations arise by proliferation and differentiation of cytotrophoblast stem cells in the villus. Transforming growth factor (TGF)β, a homodimeric glycoprotein existing in several isoforms is a potent regulator of villous as well as extravillous trophoblast cell functions. This factor is produced by the placenta (primarily the syncytiotrophoblast), and more abundantly by the decidual cells. In the first trimester decidua, it is stored in the extracellular matrix, colocalized with a TGFβ binding and inactivating proteoglycan, decorin. The inactive decidual TGFβ can be activated by trophoblast derived proteases. TGFβ retards differentiation of the villous

The present study was designed to test the hypothesis that endogenous prostaglandin E (PGE) promotes the development, growth and metastasis of spontaneous mammary tumors in C3H/HeJ female retired breeder mice. The effect of chronic oral indomethacin (indo) therapy starting at 6 months of age was tested on these parameters as well as on animal survival, in comparison with control mice placed on 0.2% ethanol in drinking water for up to 25 months of age. Indo treatment delayed the initial (up to 27 weeks) development of primary tumors by 11-12 weeks; however, the subsequent rate of tumor appearance was unaffected (totaling 82% in indo-treated vs. 90% in controls by 25 months of age). Spontaneous regression of primary tumors (26% in controls) increased 2-fold (53%) with indo therapy. While the apparent reduction in the growth rate of primary tumors and the overall prolongation of animal survival were not significant, the lifespan of mice bearing multiple tumors was significantly prolonged by therapy. There was also a 2-fold reduction in the incidence of lung metastases in mice bearing detectable primary tumors, and this was more pronounced during the earlier phase of tumor development. Positive immunostaining for cyclooxygenase-2 enzyme (indicative of the cellular source of PGE) was exhibited by tumor cells, stromal cells and macrophages within the primary tumors. Tumors in indo-treated mice exhibited histological evidence of increased differentiation (acinar architecture), significant tumor cell death, mononuclear cell infiltration and reduction in vascularity, indicating that the beneficial effects of indo were due to multiple mechanisms, including improved immune response and reduced angiogenesis.

To address the inadequacy of current assays, we developed a directed in vivo lymphangiogenesis assay (DIVLA) by modifying an established directed in vivo angiogenesis assay. Silicon tubes (angioreactors) were implanted in the dorsal flanks of nude mice. Tubes contained either growth factor-reduced basement membrane extract (BME)-alone (negative control) or BME-containing vascular endothelial growth factor (VEGF)-D (positive control for lymphangiogenesis) or FGF-2/VEGF-A (positive control for angiogenesis) or a high VEGF-D-expressing breast cancer cell line MDA-MD-468LN (468-LN), or VEGF-D-silenced 468LN. Lymphangiogenesis was detected superficially with Evans Blue dye tracing and measured in the cellular contents of angioreactors by multiple approaches: lymphatic vessel endothelial hyaluronan receptor-1 (Lyve1) protein (immunofluorescence) and mRNA (qPCR) expression and a visual scoring of lymphatic vs blood capillaries with dual Lyve1 (or PROX-11 or Podoplanin)/Cd31 immunostaining in cryosections. Lymphangiogenesis was absent with BME, high with VEGF-D or VEGF-D-producing 468LN cells and low with VEGF-D-silenced 468LN. Angiogenesis was absent with BME, high with FGF-2/VEGF-A, moderate with 468LN or VEGF-D and low with VEGF-D-silenced 468LN. The method was reproduced in a syngeneic murine C3L5 tumor model in C3H/HeJ mice with dual Lyve1/Cd31 immunostaining. Thus, DIVLA presents a practical and sensitive assay of lymphangiogenesis, validated with multiple approaches and markers. It is highly suited to identifying pro-and anti-lymphangiogenic agents, as well as shared or distinct mechanisms regulating lymphangiogenesis vs angiogenesis, and is widely applicable to research in vascular/tumor biology. © 2013 USCAP, Inc. All rights reserved.

We had earlier shown that therapy with N G -nitro- L -arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, had antitumor and antimetastatic effects in C3-L5 mammary adenocarcinoma-bearing mice. When combined with interleukin-2 (IL-2) therapy, L-NAME augmented antitumor effects of IL-2. In the present study, we tested whether the L-NAME effects were due, at least in part, to a potentiation of antitumor cytotoxicity of host effector cells. We examined the effects of L-NAME on IL-2-induced generation of antitumor cytotoxicity in vivo and in vitro in splenocytes of healthy and C3-L5 tumor-bearing C3H/HeJ mice, using 51 Cr release assay. IL-2 treatment, in vivo or in vitro, markedly stimulated splenocyte tumoricidal activity against NK-sensitive (YAC-1) and -resistant (C3-L5) targets, accompanied with an increase in NO production measured in the serum or culture medium. Addition of L-NAME to IL-2 therapy blocked IL-2-induced NO production in vivo and improved IL-2-induced splenocyte cytotoxicity as well as tumor regression. Addition of L-NAME in vitro also reduced IL-2-induced NO production in the medium and enhanced IL-2-induced cytotoxicity of splenocytes of healthy but not tumor-bearing mice. These results reveal that IL-2-induced increase in NO production in vivo causes a suppression of LAK cell activation, which can be overcome by NO inhibition with L-NAME therapy. These findings, combined with our observation that L-NAME can mitigate IL-2-induced capillary leakage in healthy and tumor-bearing mice, suggest that L-NAME could be a valuable adjunct to IL-2 therapy of cancer and infectious diseases.

We tested whether treatment with an inhibitor of nitric oxide synthesis (N G-methyl-L-arginine, MeArg) can ameliorate interleukin-2(IL-2)-therapy-induced capillary leak syndrome in healthy or tumor-bearing mice without compromising the antitumor effects of IL-2 therapy. Healthy or C3-L5-mammary-adenocarcinoma-bearing C3H/HeJ mice were treated with one or two rounds of various doses of IL-2 (ten injections, i. p., every 8 h) or MeArg (ten injections s. c., every 8 h) or their combination. In an additional experiment, MeArg was given chronically in the drinking water, rather than s. c. to healthy mice subjected to one round of therapy as above. Mice were killed 1 h after their last IL-2 injection to measure the water content of the lungs and pleural cavities (markers of capillary leakage), NO production (given by NO2 – and NO3 – levels in the serum and pleural effusion), as well as the effect of therapies on the primary tumor size and number of spontaneous lung metastatic nodules. Results revealed that all doses of IL-2 (7500 – 35 000 Cetus U/injection), as well as both rounds of IL-2 therapy, caused capillary leakage. However, no pleural effusion was seen after the second round in any of the IL-2-treated groups. MeArg therapy, given subcutaneously (5 – 20 mg kg–1 injection–1 in healthy and 20 mg kg–1 injection–1 in tumor-bearing mice), did not ameliorate IL-2-induced capillary leakage in either group of mice, and did not compromise antitumor effects of IL-2. However, subcutaneous MeArg therapy alone reduced the growth of the primary tumors, the occurrence of spontaneous lung metastases and the amount of tumor-induced pulmonary edema. When MeArg therapy was given orally (1 mg/ml drinking water), a substantial drop in NO production, as well as reduction in capillary leakage was noted in IL-2-treated healthy mice. These findings suggest that NO inhibitors could be a valuable adjunct to IL-2 therapy of cancer and infectious diseases.

We tested whether NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, can prevent interleukin 2 (IL-2)-induced capillary leakage in tumour-bearing mice without compromising the therapeutic benefits of IL-2. C3H/HeJ female mice transplanted s.c. with 2.5 x 10(5) C3-L5 mammary carcinoma cells were treated with: nothing, IL-2 (ten injections of 15,000 Cetus units i.p. every 8 h), L-NAME (0.1, 0.5, or 1 mg ml-1 drinking water), IL-2 + L-NAME (0.1 or 0.5 or 1 mg ml-1 drinking water). Therapies were given in one round (IL-2, days 10-13; L-NAME, days 9-13) or in two rounds (IL-2, days 10-13 and 20-23; L-NAME, days 9-13 and days 19-23) after tumour transplantation. Capillary leakage was measured from the water contents of the pleural cavities, lungs, spleen and kidneys. Effects of the therapies on the primary tumour size and the number of spontaneous lung metastases were also recorded. NO production was measured as the nitrite + nitrate levels in the serum and in the pleural effusion. After the first round of therapies, addition of L-NAME significantly reduced IL-2-induced pulmonary oedema and water retention in the spleen in a dose-dependent manner. It also significantly reduced the IL-2-induced rise in NO levels in the serum and pleural fluid, but did not affect IL-2-induced pleural effusion or water retention in the kidney. At later stages of tumour growth (day 23), tumours themselves induced significant fluid retention in the lungs and the kidney, which was not aggravated further with the second round of IL-2 therapy. At this time, L-NAME therapy alone ameliorated tumour-induced pulmonary oedema. During both rounds of therapy different doses of L-NAME alone caused a reduction of primary tumour growth as well as spontaneous lung metastases, which improved further with the addition of IL-2. The combination therapy was at least as effective as IL-2 therapy. In summary, L-NAME had anti-tumour effects in vivo, reduced the severity of IL-2-induced capillary leakage in some organs and did not compromise anti-tumour efficacy of IL-2 therapy. Thus, L-NAME could be a valuable adjunct to IL-2-based cancer therapy.

We tested whether NG-nitro-L-arginine methyl ester (L-NAME), a potent inhibitor of NO synthesis, can prevent interleukin-2 (IL-2)-induced capillary leakage. Healthy C3H/HeJ female mice were treated with: nothing; IL-2 (10 injections; 35,000, 15,000, or 7,500 Cetus U i.p. every 8 h); IL-2 + L-NAME (0.01, 0.1, 0.5, and 1 mg/ml of drinking water starting 1 day before IL-2 therapy and ending with IL-2 therapy); or L-NAME alone. In the first series of experiments, mice were killed 1 h after last IL-2 injection to measure pleural effusion, and water content of the lungs, spleen, and kidney (markers of capillary leakage), as well as NO2- + NO3- levels in the serum and pleural effusion. In the two additional series, the survival of treated mice was followed. All doses of IL-2-induced capillary leak syndrome as indicated by pleural effusion, pulmonary edema, and fluid retention in the spleen and kidney. NO production was positively correlated with manifestation and severity of this syndrome. NO2- + NO3- levels in the pleural effusion were directly related to IL-2 dose, and L-NAME treatment reduced both the NO production and severity of capillary leakage, excepting fluid retention in the kidney. However, L-NAME therapy prevented IL-2-induced mortality only when combined with a middle range IL-2 dose (15,000 U/injection). In summary, oral L-NAME therapy effectively prevented IL-2-induced capillary leakage in healthy mice, suggesting its potential value as a supplement in IL-2-based immunotherapy of cancer and infectious diseases.

We developed a method of propagating pure first trimester human trophoblast cells growing out of primary explants of mechanically derived chorionic villus fragments (Yagel et al, 1989; Graham et al, 1992). We have now extensively characterized these cells during their initial outgrowth and in long-term culture, employing a variety of markers and techniques as outlined below. By double label immunofluorescence using epithelial (cytokeratin) and mesenchymal (vimentin) cell markers, we identified the chorionic villus migrant cell populations as pure trophoblast (39 per cent of outgrowths) or a mixture of trophoblast and fibroblast (61 per cent). Further phenotyping of the pure trophoblast outgrowths by double label immunostaining using anti-cytokeratin antibody and a panel of other primary antisera revealed that these cells exhibit a variety of markers characteristic of extravillous invasive trophoblast cells in situ: insulin-like growth factor (IGF)-II, NDOG-5, proliferating cell nuclear antigen (PCNA), human leucocyte antigen framework antigen (W6/32) and a distinct set of integrins including alpha 1, alpha 3, alpha 5, alpha v and beta 1 subunits and alpha v beta 3/beta 5 vitonectin receptor. They were negative for alpha 6 and beta 4 integrin subunits. Immunogold electron microscopy of explants grown on type IV collagen gel revealed the production of conventional and oncofetal types of fibronectin by mononucleate trophoblast cells and human placental lactogen by multinucleate cells. Immunolabelling, flow cytometry and immunoprecipitation revealed that this phenotypic profile was retained with complete fidelity in the long-term culture; thus, trophoblasts migrating out of first trimester chorionic villus explants and their propagated progeny belong to the invasive extravillous trophoblast of the placenta.

Cancer stem-like cells (SLC) resist conventional therapies, necessitating searches for SLC-specific targets. We established that cyclo-oxygenase(COX)-2 expression promotes human breast cancer progression by activation of the prostaglandin(PG)E-2 receptor EP4. Present study revealed that COX-2 induces SLCs by EP4-mediated NOTCH and WNT up-regulation. EP4 antagonist (EP4A) treatment ablated SLCs both in vitro and in vivo. Ectopic COX-2 over-expression in MCF-7 and SKBR-3 human breast cancer cell lines (named MCF-7-COX-2 and SKBR-3-COX-2) resulted in aggressive phenotypes: increased migration/invasion/proliferation, EMT, elevated SLCs, evidenced by spheroid formation for successive generations, increased ALDH activity and co-expression of COX-2/SLC markers. These changes were reversed with COX-2 inhibitor or EP4A, indicating dependence on COX-2/EP4 activities. COX-2 overexpression or EP4 agonist treatment of COX-2 low cells caused up-regulation of NOTCH/WNT pathway genes, blocked with PI3K/AKT inhibitors. Supporting above findings, micro-array analysis showed up-regulation of numerous SLC-regulatory and EMT-associated genes in MCF-7-COX-2 cells. MCF-7-COX-2 cells showed increased orthotopic tumorigenicity and spontaneous multi-organ metastases in NOD/SCID/IL-2Rγ-deficient mice for successive generations with limiting cell inocula. Orthotopic tumors showed significant up-regulation of VEGF-A/C/D, Vimentin and phospho-AKT, down-regulation of E-Cadherin and enrichment of SLC marker positive and spheroid forming cells. MCF-7-COX-2 cells also showed increased lung colonization in NOD/SCID/GUSB-null mice, an effect reversed with EP4 knockdown or EP4A treatment. COX-2, EP4 and ALDH1A expression in situ in human breast cancer tissues were highly correlated with one other, more marked in progressive stage of disease. High COX-2/EP4 expression was linked with poor survival. Thus EP4 represents a novel SLC-ablative target in human breast cancer. (Supported by a grant of the OICR to PKL and a TBCRU fellowship to MM) Citation Format: Mousumi Majumder, Xiping Xin, Ling Liu, Elena Tutunea-Fatan, Mauricio Rodriguez-Torres, Krista Vincent, Andrew Deweyert, Lynne-Marie Postovit, David Hess, Peeyush K. Lala. Breast cancer stem cell induction by COX-2 via EP4/PI3K-AKT/NOTCH-WNT axis: EP4 as therapeutic target. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3315.

Trophoblast invasion of the human uterus is stringently controlled by the microenvironment. Invasive extravillous trophoblast cells in situ as well as in culture express a selective repertoire of cell surface integrins. Since migration is a necessary step in the invasion cascade, we tested whether certain integrins or invasion-regulating molecules, i.e., TGF-beta, IGF-II, and IGFBP-1 produced at the fetomaternal interface had a functional role on trophoblast migration. Flow cytometric analysis of integrin expression and the use of an in vitro cell migration assay revealed that exogenous TGF-beta upregulates integrin expression and reduces migratory ability to the invasive trophoblast, whereas IGF-II has no effect on integrin expression but stimulates migration. Trophoblast migration was inhibited in the presence of alpha 5 and beta 1 integrin blocking antibodies, indicating its dependence on the expression of these subunits. Furthermore, IGFBP-1, which contains an RGD sequence recognizing certain integrins, stimulated migration, an effect that was blocked by pretreatment with anti-alpha 5 or -beta 1 blocking Abs. These studies demonstrate that the migration of first trimester invasive trophoblast in vitro (1) requires the expression of alpha 5 and beta 1 integrin subunits, (2) is inhibited by TGF-beta, possibly due to increased cell adhesiveness to the extracellular matrix, (3) is stimulated by IGF-II by an as yet undetermined mechanism, and (4) is stimulated by IGFBP-1, likely by interaction with the RGD binding site of the alpha 5 beta 1 integrin. The invasion-regulating effects of TGF-beta, IGF-II, and IGFBP-1 may thus, at least in part, be due to their migration-regulating effects on the invasive trophoblast.

Extravillous trophoblast (EVT) cells of the human placenta invade the uterine decidua and utero-placental arteries to establish an efficient exchange of key molecules between maternal and fetal blood. Trophoblast invasion is stringently regulated in situ both positively and negatively by a variety of factors at the fetal-maternal interface to maintain a healthy utero-placental homeostasis. One such factor, decorin, a transforming growth factor (TGF)-beta binding, leucine-rich proteoglycan produced by the decidua, negatively regulates EVT proliferation, migration, and invasiveness independent of TGF-beta. We reported that these decorin actions were mediated by its binding to multiple tyrosine kinase receptors, including vascular endothelial growth factor receptor (VEGFR)-2. The present study explores the mechanisms underlying decorin antagonism of VEGF (VEGF-A) stimulation of endovascular differentiation of EVT using our EVT cell line, HTR-8/SVneo. We observe that decorin inhibits VEGF-induced EVT cell migration and endothelial-like tube formation on matrigel. VEGF activates MAPKs (p38 MAPK, MEK3/6, and ERK1/2) in EVT cells, and the activation is blocked in both cases by decorin. Employing selective MAPK inhibitors, we show that both p38 and ERK pathways contribute independently to VEGF-induced EVT migration and capillary-like tube formation. VEGF upregulates the vascular endothelial (VE) markers VE-cadherin and beta-catenin in EVT and endothelial cells, and this upregulation is blocked by decorin and MAPK inhibitors. These results suggest that decorin inhibits VEGF-A stimulation of trophoblast migration and endovascular differentiation by interfering with p38 MAPK and ERK1/2 activation. Thus decorin-mediated dual impediment of endovascular differentiation of the EVT and angiogenesis may have implications for pathogenesis of preeclampsia, a hypoinvasive trophoblast disorder in pregnancy.

Extravillous trophoblast (EVT) cells of the human placenta invade the uterine decidua and utero-placental arteries to establish an efficient exchange of key molecules between maternal and fetal blood. Trophoblast invasion is stringently regulated in situ both positively and negatively by a variety of factors at the fetal-maternal interface to maintain a healthy utero-placental homeostasis. One such factor, decorin, a transforming growth factor (TGF)-beta binding, leucine-rich proteoglycan produced by the decidua, negatively regulates EVT proliferation, migration, and invasiveness independent of TGF-beta. We reported that these decorin actions were mediated by its binding to multiple tyrosine kinase receptors, including vascular endothelial growth factor receptor (VEGFR)-2. The present study explores the mechanisms underlying decorin antagonism of VEGF (VEGF-A) stimulation of endovascular differentiation of EVT using our EVT cell line, HTR-8/SVneo. We observe that decorin inhibits VEGF-induced EVT cell migration and endothelial-like tube formation on matrigel. VEGF activates MAPKs (p38 MAPK, MEK3/6, and ERK1/2) in EVT cells, and the activation is blocked in both cases by decorin. Employing selective MAPK inhibitors, we show that both p38 and ERK pathways contribute independently to VEGF-induced EVT migration and capillary-like tube formation. VEGF upregulates the vascular endothelial (VE) markers VE-cadherin and beta-catenin in EVT and endothelial cells, and this upregulation is blocked by decorin and MAPK inhibitors. These results suggest that decorin inhibits VEGF-A stimulation of trophoblast migration and endovascular differentiation by interfering with p38 MAPK and ERK1/2 activation. Thus decorin-mediated dual impediment of endovascular differentiation of the EVT and angiogenesis may have implications for pathogenesis of preeclampsia, a hypoinvasive trophoblast disorder in pregnancy.

Weekly injections of dimethylhydrazine (DMH) (25 mg/kg), or azoxymethane (AOM) (8 mg/kg) to young adult male CDI mice for 1-2 months produced generalized intestinal crypt hyperplasia, which we measured in duodenum in terms of number of interphase and mitotic cells present in crypts. As shown earlier, the crypts expanded because of the presence of a hyperproliferative "initiated" crypt subpopulation which was also sensitive to natural killer (NK) cells. Hyperplasia was thus present as long as NK activity was suppressed by the carcinogen treatment. After interruption of the treatment for periods of 1, 2, 3, 6 and 10 months in the various groups, hyperplasia soon regressed as a result of elimination of the subpopulation by the recovering NK cells. When NK activity was once again eliminated during the terminal days of these "interruption periods" (by injections of anti-asialo GM-I antibody, alpha AGM-I), the original hyperplasia was fully reconstituted, apparently from stem cells of the subpopulation which survived up to 10 months in their crypt base location. These "initiated stem cells" represented, then, the original carcinogenic insult during the pre-cancerous period. They also appeared to be the source of the eventual neoplasia, as treating the animals with mutagens during the interruption periods produced specific changes in crypt base histology: new "crypt base basophilic" (CBB) cells appeared which produced large accumulations as well as microscopic tumors when NK activity was suppressed (by alpha AGM-I). Some of the initiated stem cells were apparently transformed into neoplastic ones which remained under NK control, the NK cells preventing the establishment of their progeny. Further experiments indicated that, although the initiated stem cells are not eliminated by normal NK activity, activated NK cells can kill them, thereby eliminating the potential source of neoplasia.

Human placental trophoblast invasion of the uterus is a highly controlled event. We had shown that transforming growth factor-beta (TGF-beta) produced in the pregnant uterus controls invasiveness and reduces proliferation of first trimester placental trophoblasts in vitro. The anti-invasive effect of TGF-beta was due, at least in part, to induction of tissue inhibitor of metalloproteinases (TIMP)-1. In the present study we compared the effects of TGF-beta on proliferation ([3H]-TdR incorporation) and invasiveness (3-day Matrigel invasion assay) of JAR and JEG-3 choriocarcinoma cells vs normal first trimester human trophoblast cells. Transcripts of type IV collagenases (72- and 92-kDa enzymes, i.e., gelatinases A and B) and their inhibitors (TIMP-1 and TIMP-2) in these cells were measured by Northern analysis, and secretion of gelatinases and plasminogen activators (PAs) was evaluated by gel zymography. The results revealed that: (a) TGF-beta inhibited invasiveness and proliferation of normal trophoblast but not JAR and JEG-3 choriocarcinoma cells; (b) gelatinase A mRNA, expressed by the normal trophoblast and JAR cells, was upregulated in the presence of TGF-beta; (c) gelatinase B mRNA was not detected in the total RNA preparations of treated or untreated normal trophoblast or choriocarcinoma cells; (d) TGF-beta significantly upregulated the levels of TIMP-1 mRNA in the normal trophoblasts, but this transcript was very low in treated as well as untreated choriocarcinoma cells; TGF-beta also upregulated the 3.5-kb TIMP-2 message in the normal trophoblast; (e) gelatin zymography revealed a distinct band of approximately 68-kDa (gelatinase A) in the conditioned media of normal trophoblast and JAR cells; however, TGF-beta did not change the level of secretion of this gelatinase; and (f) the normal trophoblast also exhibited significant PA secretion (casein zymography) which was reduced in the presence of TGF-beta. PA secretion by the malignant trophoblast cells was low and unaffected by TGF-beta. These findings suggest that choriocarcinoma cells may become refractory to the mechanisms which control normal trophoblast proliferation and invasiveness. Concurrent resistance to antiproliferative and anti-invasive molecules such as TGF-beta may be highly relevant to tumor progression.

Summary By employing pure cultures of first trimester human trophoblast cells we have examined the effects of EGF and TGFα on trophoblast cell proliferation and invasiveness. Both exogenous EGF and TGFα were able to stimulate trophoblast proliferation ( 3 H-TdR incorporation). Anti-TGFα neutralizing Ab had no effect on proliferation indicating the lack of significant endogenous TGFα production in these cultures. Anti-EGF-receptor blocking Ab significantly decreased trophoblast proliferation indicating the presence of endogenous EGF or another EGF-receptor ligand, capable of binding to the EGF-receptor, and enhancing trophoblast growth. EGF and TGFα did not alter trophoblast invasiveness in a Matrigel invasion assay although an increase in the transcription of invasion regulating molecules, type IV collagenases and their inhibitors TIMP1 and TIMP2 was noted. Both growth factors may be required for normal placental growth in situ . These studies reveal that the two important biological processes, e.g., trophoblast proliferation and invasion required for placental development are not necessarily linked.

Extravillous trophoblasts (EVT) of the human placenta invade the uterine decidua and its arteries to ensure successful placentation. We previously identified two decidua-derived molecules, TGF-β and a TGF-β-binding proteoglycan decorin (DCN), as negative regulators of EVT proliferation, migration, and invasiveness and reported that DCN acts via multiple tyrosine kinase receptors [epidermal growth factor-receptor (EGF-R), IGF receptor-1 (IGFR1), and vascular endothelial growth factor 2 receptor (VEGFR-2)]. Because binding of DCN toVEGFR-2 has never been reported earlier, present study explored this binding, the approximate location of VEGFR-2-binding site in DCN, and its functional role in our human first trimester EVT cell line HTR-8/SVneo. Based on far-Western blotting and coimmunoprecipitation studies, we report that DCN binds both native (EVT expressed) and recombinant VEGFR-2 and that this binding is abrogated with a VEGFR-2 blocking antibody, indicating an overlap between the ligand-binding and the DCN-binding domains of VEGFR-2. We determined that 125I-labeled VEGF-E (a VEGFR-2 specific ligand) binds EVT with a dissociation constant (K d) of 566 pM, and DCN displaced this binding with an inhibition constant (K i) of 3.93-5.78 nM, indicating a 7- to 10-fold lower affinity of DCN for VEGFR-2. DCN peptide fragments derived from the leucine rich repeat 5 domain that blocked DCN-VEGFR-2 interactions or VEGF-E binding in EVT cells also blocked VEGF-A- and VEGF-E-induced EVT cell proliferation and migration, indicative of functional VEGFR-2-binding sites of DCN. Finally, DCN inhibited VEGF-E-induced EVT migration by interfering with ERK1/2 activation. Our findings reveal a novel role of DCN as an antagonistic ligand for VEGFR-2, having implications for pathophysiology of preeclampsia, a trophoblast hypoinvasive disorder in pregnancy, and explain its antiangiogenic function. © 2011 by The Endocrine Society.

Transforming growth factor alpha (TGF alpha) is an important growth regulatory molecule, the location and function of which at the human fetomaternal interface remain to be determined. The present study examined the presence of TGF alpha in the human placenta, decidua, and fetal membranes throughout gestation (from a total of 29 subjects) as well as its functional role in the proliferation of first trimester trophoblasts. The peptide was localized immunocytochemically with a monoclonal anti-TGF alpha antibody (Ab) (MF9) on paraffin-embedded tissues via the avidin-biotin complex-peroxidase technique with diaminobenzidine (DAB) as the chromogen. Omission or TGF alpha absorption of the primary Ab served as negative controls. Specific (cytoplasmic) staining was noted in typical stromal-type decidual cells, including cells of the decidua basalis and parietalis and chorionic decidua, throughout gestation. Villous trophoblast cells (syncytiotrophoblast and to a minor extent cytotrophoblast) at all gestational ages as well as extravillous cytotrophoblast cells (intermediate and cytotrophoblastic shell) also showed specific cytoplasmic staining. Chorionic trophoblasts showed variable staining, and little or no immunoreactivity was seen in the amniocytes. Second-passage first trimester human trophoblast cells (characterized by their expression of cytokeratin as well as other markers) were cultured in the presence of TGF alpha or neutralizing anti-TGF alpha Ab (TAb-1) or no additive for 18 h prior to exposure to 3H-TdR for 6 h to measure 3H-TdR uptake. TGF alpha (0-100 ng/ml) caused a dose-dependent stimulation of proliferation, reaching a near plateau at 6-100 ng/ml to slightly more than double the basal level. The presence of anti-TGF alpha Ab alone (25 micrograms/ml) did not significantly influence the proliferation of the cells, indicating the absence of significant endogenous TGF alpha in these cultures; however, the Ab was able to abolish the stimulatory function of exogenous TGF alpha. Exogenous TGF alpha also increased the number of trophoblast nuclei immunoreactive for proliferating cell nuclear antigen and reduced the incidence of multinucleate cells in culture. These results indicate that TGF alpha is present in the cells of the fetomaternal interface throughout human gestation and may function as a stimulator of trophoblastic growth in situ.

Women with anticardiolipin antibodies (ACLA) are at increased risk for fetal loss. One potential explanation for this outcome is that sera from these individuals contain antibodies reactive with trophoblast cells, which are involved in the establishment of the uteroplacental vasculature and maintenance of placental blood fluidity. To examine this hypothesis, we compared the incidence of trophoblast-reactive antibodies in 27 patients with ACLA and a history of fetal loss with that in 29 normal pregnant women. Sera from 20 patients, but only one control, contained trophoblast-reactive antibodies (P < .001). These antibodies were not directed against major histocompatibility class I antigens, and reacted with both term and first-trimester trophoblast cells. In most cases, sera from which ACLA were adsorbed by cardiolipin- containing liposomes maintained reactivity against cells. In addition, patient Ig fractions immunoprecipitated an approximately 62-kD protein from the trophoblast cell surface, stimulated the release of arachidonic acid and thromboxane A2 by trophoblasts, and inhibited the binding of prourokinase to trophoblast urokinase receptors. These observations show that sera from women with ACLA and a history of fetal loss contain antitrophoblast antibodies. These antibodies may be serologically distinct from ACLA, and may contribute to the pathogenesis of fetal demise.

We had earlier shown that tumor-bearing results in an inactivation of IL-2-dependent effector cells by host macrophage-derived PGE2, and that chronic indomethacin therapy (CIT) aimed at blocking prostaglandin synthesis, combined with multiple rounds of IL-2, can cure experimental metastases of a variety of tumors in mice. We have now tested the efficacy of this therapy on spontaneous as well as experimental metastasis of C3-L5 mammary adenocarcinoma in C3H/HeJ mice. Mice transplanted s.c. with C3-L5 cells (and showing visible spontaneous lung metastases between days 7 and 10) were given CIT starting on day 15, plus 2 5-day rounds of IL-2 or IL-2 alone. Mice injected i.v. with 10(4) C3-L5 cells (and showing lung micrometastases on day 5) were placed on CIT on day 5 and given 3 5-day rounds of IL-2 or treated with IL-2 alone. Control mice received vehicles alone. Results revealed that combined CIT + IL-2 therapy in the spontaneous metastasis model caused a regression of primary tumors, a marked reduction in lung metastases scored on days 25-35 and a marked prolongation of host survival (79% cured). Survivors rechallenged with 10(4) tumor cells i.v. on day 210 resisted tumor growth. In the experimental metastasis model, this therapy also markedly reduced lung metastases and prolonged animal survival (50% cured). In both models, the combination therapy led to the presence of highly active tumoricidal (for C3-L5 and YAC-1 lymphoma targets) lymphocytes with AGM-1+, Lyt-2- and Thy-1 +/- phenotype and macrophages in the spleen and the lungs, and ADCC-promoting activity in the serum. CIT + IL-2 therapy can thus effectively eradicate spontaneous and experimental mammary adenocarcinoma metastasis in mice. It activates natural effector cells in situ, generates ADCC-promoting activity in the serum and results in resistance to tumor take in this moderately immunogenic tumor model.

We established trophoblast cell cultures with extended lifespans by introducing into first trimester human trophoblasts the gene encoding simian virus 40 large T antigen. The transfected trophoblasts were characterized according to their expression of various morphological and functional markers. Both parental (HTR-8) and transfected (HTR-8/SVneo) lines were morphologically similar and positive for cytokeratin, confirming their epithelial (trophoblastic) identity. Whereas the parental cells senesced after 12-14 passages, the transfectants have been in culture for over 32 passages. Human chorionic gonadotrophin was detected only in the HTR-8/SVneo cells and not in the parental cells. Both lines required at least 5% serum in order to sustain growth in vitro and responded to transforming growth factor-beta (TGF-beta) with reduced [3H]-thymidine incorporation in a dose-dependent manner. Treatment with TGF-beta also resulted in decreased secretion of plasminogen activators (PAs) and reduced PA activity by both lines. Both cell lines secreted mostly 72-kDa type IV collagenase as determined by substrate gel zymography, but the level of secretion of this enzyme was not significantly affected by TGF-beta in either line. Even though both lines exhibited similar in vitro invasive abilities, only the invasiveness of the parental cells was reduced by TGF-beta. Neither parental or transfected cells were capable of growth in soft agar and no sign of tumor formation was evident more than 5 months after subcutaneous inoculation of the transfected cells into nude mice. These results indicate that apart from their ability to sustain prolonged growth in culture, the transfected HTR-8/SVneo cells share a number of phenotypic properties with the parental trophoblast cells. For this reason, these transfected trophoblasts may prove to be an important tool for the study of placental function and/or tumor progression.

Histamine type-2 receptor antagonists (H-2RA) have been used chronically to prevent dyspepsia in cancer patients subjected to immunotherapy with chronic indomethacin (Indo) and intermittent IL-2 in our cancer centre. We tested the effects of these agents during immunotherapy of C3H/HeJ mice transplanted s.c. with 5 x 10(5) C3L5 mammary adenocarcinoma cells. Tumor-transplanted mice were divided into groups receiving: (1) Indo (14 micrograms/ml); (2) H-2RA, i.e. (a) ranitidine at 28.6 micrograms/ml (Ran-lo) or 143 micrograms/ml (Ran-hi), or (b) famotidine (Fam) at 4.3 micrograms/ml, or (c) cimetidine (Cim) at 107 micrograms/ml, all in the drinking water on days 5-24; (3) IL-2 (1.5 x 10(3) Cetus U i.p. every 8 h on days 10-14 and 20-24); (4) combinations of H-2RA + Indo; or (5) combinations of H-2RA + Indo + IL-2. Animals were killed on day 24 for examination of primary s.c. tumor growth, secondary lung metastasis and splenocyte cytotoxicity against YAC-1 lymphoma cells (51Cr release assay). Results revealed: (1) primary tumor growth was reduced in mice treated with Fam + Indo, Indo + IL-2 and any of the H-2RA + Indo + IL-2 (no difference observed within the last two groups); (2) lung metastases decreased in mice treated with IL-2 alone, Indo + IL-2, and Indo + IL-2 + Ran-hi; (3) splenic cytotoxicity was suppressed in tumor-bearing controls, with partial restoration seen in Ran (both doses), Ran-lo + Indo, Ran-lo + Indo + IL-2, and Cim + Indo + IL-2 treated groups. Nearly complete restoration was seen in Cim, Cim + Indo, Indo + IL-2, Ran-hi + Indo + IL-2, and Fam + Indo + IL-2 groups. Thus, addition of H-2RA did not alter the overall therapeutic efficacy of the standard Indo + IL-2 tumor immunotherapy.

Summary In this study we have examined whether trophoblast invasiveness is aninherent property of these cells and, since in vitro placental invasion of the uterus is spatially and temporally restricted, whether loss of invasion is due to control by the decidual tissue. Using in vitro invasion assays we have shown that cultured first trimester as well as term human trophoblast cells, dissociated from the uterine microenvironment, are highly invasive. Conditioned media from first trimester human decidual cells (DCM) significantly reduced invasion of first trimester trophoblast cells. This suppression was prevented by addition of neutralizing anti-TGFβ antibody or neutralizing antibody to Tissue Inhibitor of Metalloproteinases-1 (TIMP-1) to the DCM, and mimicked by TGFβ1. We have previously reported a decrease in collagenase type IV activity in the conditioned media of first trimester trophoblast cultures when TGFβ1 was added to these cultures and that presence of neutralizing anti-TGFβ antibody in trophoblast cultures (to remove endogenous TGFβ activity) resulted in down regulation of TIMP-1 message. Here we show that removal of endogenous TGFβ in trophoblast and decidual cultures resulted in a decrease in TIMP activity in the conditioned media. These data, taken together, indicate that decidua-derived TGFβ exerts its anti-invasive action by up regulating TIMP levels in both the trophoblast and decidua. Another mechanism by which TGFβ exerts its anti-invasive role is by inducing the differentiation of invasive trophoblasts into non-proliferating, multinucleated, presumably non-invasive cells. Other mechanisms of control of trophoblast invasion remain to be determined.

The objective of the workshop was to illustrate how embryonic or trophoblast cells interact with a variety of factors in their microenvironment, via appropriate cell surface receptors, to activate intracellular signalling mechanisms responsible for a variety of cellular functions, e.g. proliferation, migration, invasion, differentiated functions such as secretion of functional molecules, cellular defense against stress, cell survival and programmed cell death (apoptosis). Since Dr John Gerhart (University of California, Berkeley) had already made a superb presentation on the general principles in ‘cell–cell signalling in development’ in a plenary lecture, this workshop was primarily focused on the signalling in the placental trophoblast. The workshop included five brief overviews with lively discussion and audience participation. Dr Peeyush Lala (University of Western Ontario) set the stage by talking about ‘Trophoblast microenvironment: key molecules modulating trophoblast function’. He made the point that there are a great variety of cells, which serve either as the sources or the targets for signal-inducing molecules operating at the fetal–maternal interface. The placenta and the endometrium, including the decidua, represent this interface. Within the placenta there are different trophoblast subsets (e.g. villous syncytiotrophoblast and cytotrophoblast, extravillous trophoblast) and other fetally derived cells within the villus core (e.g. mesenchymal cells, macrophages and endothelial cells). Within the endometrium/decidua, there are decidual cells, endometrial stromal cells, glandular epithelial cells, cells of the endometrial vasculature (endothelial cells and smooth muscle cells) and immigrant leukocytes of maternal origin (e.g. natural killer cells, T cells, B cells and macrophages). The most common mechanism for intracellular signal induction is the occupation of the cell surface receptors with the appropriate ligands, which may act in autocrine, juxtacrine and paracrine manners. The signal-inducing ligands typically include hormones, growth factors, growth factor-binding proteins (e.g. IGFBPs) and proteoglycans (e.g. heparan sulfate proteoglycan, Decorin) and components of the extracellular matrix (ECM)

The present study tested the hypothesis that the production of vascular endothelial growth factor C (VEGF-C), a key lymphangiogenic factor, by human breast cancer cells can be stimulated by human lectins, using plant lectins as controls.The effects of human galectins and five plant lectins reacting with distinct determinants of N- and O-glycans on the accumulation of VEGF-C in serum-free cell culture media of human breast cancer cells endowed with high (MDA-MB-231) and low (MCF7, T-47D, and SK-BR-3) VEGF-C-producing abilities were examined.All tested lectins stimulated VEGF-C production by MDA-MB-231 cells, albeit with different potency. Concanavalin A, but not galectins, was also able to stimulate VEGF-C production by low VEGF-C-producing cell lines MCF7 and T-47D. Both VEGF-C mRNA and protein were strongly up-regulated in SK-BR-3 cells by concanavalin A and wheat germ agglutinin, but not jacalin.The differential response of breast cancer cell lines separated by the endogenous level of VEGF-C production suggests that galectins may contribute to tumor-associated lymphangiogenesis in a cell-specific manner.

Trophoblast cells of the placenta in many species have acquired mechanisms to invade the uterus, inclusive of its blood vessels, to establish efficient fetomaternal exchange of molecules. This invasion is strictly controlled both spatially and temporally and, in humans, usually continues until midgestation. Key mechanisms underlying various steps in trophoblast invasion are (i) the attachment to the basement membrane, most likely by binding to laminin; (ii) the detachment from the basement membrane matrix, a process requiring the presence of complex-type oligosaccharides on the cell surface; and (iii) the breakdown of basement membrane components, mediated by secretion of metalloproteases (such as type IV collagenases) and serine proteases (plasminogen activator). Activation of trophoblast-derived metalloproteases appears to be plasmin dependent. Trophoblast invasiveness in situ is controlled by the microenvironment, owing to local production of anti-invasive factors by the decidual tissue of the uterus. One of these factors is TIMP (tissue inhibitor of metalloproteases), which neutralizes metalloproteases in an equimolar ratio. Another is TGF-β (transforming growth factor-β), which has a dual effect: it induces TIMP-1 secretion by the trophoblast and decidual cells and promotes differentiation of invasive trophoblast cells into multinucleated giant cells, which are presumably noninvasive. Thus, TGF-β provides the key control of trophoblast invasiveness in situ. This control is lost in certain choriocarcinomas. In contrast to the response shown by the normal trophoblast, JAR and JEG-3 choriocarcinoma cell invasiveness does not seem to be inhibited by TGF-β. In fact, in preliminary studies, JAR cells responded to TGF-β by increased invasiveness. The reasons for the differential effects of TGF-β on normal versus malignant trophoblast cell invasiveness are currently under study.Key words: trophoblast, invasion, control, choriocarcinoma, transforming growth factor-β.

The study reported here was designed to examine the in situ distribution and characteristics of hemopoietically derived decidual cells during normal pregnancy in mice prenatally reconstituted with bone marrow cells carrying a transgenic marker. Bone marrow cells from a transgenic CD-1 strain (CD-1 beta; carrying 1000 copies of beta-globin genes in tandem) were injected into the yolk sac of Day 17 conventional CD-1 embryos. The pregnant females were allowed to deliver normally, and the female offspring raised to puberty were mated with CD-1 males and then killed on Day 12 of gestation. The extent of chimerism in sections of their spleens, uteri, and other organs was evaluated by in situ hybridization of the sections with a biotinylated cDNA probe specific for the beta-globin genes followed by avidin-biotin-peroxidase staining. Tissue controls were provided by CD-1 beta and CD-1 mice, respectively. Tissues were also processed without the application of the probe or with the application of biotinylated lambda DNA as specificity controls. Reconstituted mice exhibited variable degrees of hemopoietic chimerism as indicated by labeling of their splenic lymphocytes (18-54%; mean 42%) as well as hemopoietic cells in other organs. Variable cellular labeling was also noted in their decidua basalis and metrial glands. Labeled cells in these tissues were identified as typical decidual cells, macrophages, and granulated metrial gland (GMG) cells. Labeling of typical decidual cells varied extensively among implantation sites in the same chimera, the average labeling ranging from 17% to 33% (mean 24%) in various chimeras. Labeling was also noted in GMG cells, lymphocytes, and some decidual cells migrating out of metrial gland explants after 24-h culture. The non-pregnant uterus of a chimeric mouse revealed significant labeling of endometrial stromal cells indicative of their hemopoietic origin. These results revealed a hemopoietic origin of certain typical decidual cells and GMG cells identified in situ during normal murine pregnancy and a hemopoietic origin of certain endometrial stromal cells that may represent precursors of decidual cells. The precise timing of the predecidual stem cell migration from the bone marrow to the uterus remains to be defined.

In situ hybridization and northern/slot blot analyses were used to quantify the expression of calcyclin (2A9, 5B10), osteopontin (opn, secreted phosphoprotein, 2ar) and calmodulin mRNAs in mouse tissues that support pregnancy. High-to-moderate levels of the mRNAs of all three genes were detected at discrete locations in the uterus, decidua and placenta as a function of gestation time. Calmodulin expression was constant in these tissues; calcyclin mRNA was high during early pregnancy and declined after day 8-9 of gestation; and opn mRNA was undetectable before day 7, with maximal levels on days 9-12 in each of these tissues. Calcyclin, but not opn, expression was also observed in the chorioamnion after day 12. Calcyclin was expressed throughout the decidua on day 8 but became restricted to the primary (antimesometrial) decidual zone and decidua lateralis on day 9, and the decidua capsularis after day 9. By contrast, opn mRNA was localized on day 9 to the mesometrial triangle, which contains a large population of granulated metrial gland cells, and to the decidua basalis. These two genes may serve as markers for the two types of decidual tissue. We suggest that one function of OPN, which may be an indicator of cells in the decidua that have a bone marrow genealogy, is to mediate the flux of calcium from the maternal circulation to the developing embryo.

The processes of implantation and placentation are both dependent on the invasion and remodeling of the uterine endometrium and vasculature by trophoblasts. Because the secretion and autocrine binding of urokinase (uPA) appears to be a common mechanism used by cells to facilitate plasmin-dependent tissue invasion, we measured the production of uPA and expression of uPA receptors by trophoblasts. Prourokinase bound specifically, reversibly, and with high affinity to cultured trophoblasts, via the uPA epidermal growth factor-like domain. Trophoblasts derived from two first-trimester placentae bound more prourokinase than cells isolated from term placentae. Furthermore, in vitro differentiation of cultured cytotrophoblasts into syncytiotrophoblasts was associated with diminished expression of urokinase receptors and a parallel decrease in the cellular content of uPA receptor mRNA. Trophoblasts also secreted prourokinase and plasminogen activator inhibitors types 1 and 2 (PAI-1 and PAI-2). Although prourokinase was secreted in amounts sufficient to endogenously saturate trophoblast uPA receptors, trophoblasts secreted greater amounts of PAI-1 and PAI-2 than uPA, and no net plasminogen activator activity was detected in trophoblast conditioned medium. In contrast, plasminogen added directly to cultured trophoblasts was readily converted to plasmin. Although the invasion and remodeling of uterine tissues by trophoblasts is a complex process dependent on several proteases of varying specificity, our findings suggest that the expression and modulation of urokinase receptors on the trophoblast cell surface may play an important role in this process.

We examined the localization of transforming growth factor (TGF)-beta in first-trimester and term human decidua and chorionic villi and explored the role of this factor on the proliferation and differentiation of cultured trophoblast cells. Two antibodies, 1D11.16.8, a mouse monoclonal neutralizing antibody capable of recognizing both TGF-beta 1 and TGF-beta 2 and CL-B1/29, a rabbit polyclonal antibody capable of recognizing TGF-beta 2, were used to immunolocalize TGF-beta in fixed, paraffin-embedded, or fixed, frozen sections of placenta and decidua, providing similar results. Intense labeling was observed in the extracellular matrix (ECM) of the first-trimester decidua and cytoplasm of term decidual cells. Syncytiotrophoblast cell cytoplasm as well as the ECM in the core of the chorionic villi of both first-trimester and term placentas exhibited a moderate degree of labeling. Strong cytoplasmic labeling was observed in the cytotrophoblastic shell of the term placenta. To examine the role of TGF-beta on trophoblast proliferation and differentiation, early passage cultures of first-trimester and primary cultures of term trophoblast cells were established and characterized on the basis of numerous immunocytochemical and functional markers. These cells expressed cytokeratin, placental alkaline phosphatase, urokinase-type plasminogen activator, and pregnancy-specific beta glycoprotein, but not factor VIII or 63D3; they also produced hCG and collagenase type IV. Exposure of first-trimester trophoblast cultures to TGF-beta 1 significantly inhibited proliferation in a dose-dependent manner. An antiproliferative effect was also noted in the presence of TGF-beta 2. These effects were abrogated in the presence of the neutralizing anti-TGF-beta antibody (1D11.16.8) in a concentration-dependent manner. In a 3-day culture, exogenous TGF-beta 1 stimulated formation of multinucleated cells by the first trimester as well as term trophoblast cells. Addition of neutralizing anti-TGF-beta antibody to first-trimester trophoblast cells stimulated proliferation beyond control levels in a 24-h culture and reduced formation of multinucleated cells in a 3-day culture, indicating the presence of endogenous TGF-beta activity. These results indicate that TGF-beta produced at the human fetal-maternal interface plays a major regulatory role in the proliferation and differentiation of the trophoblast.

We have previously shown that decidua is the major site of transforming growth factor-alpha (TGF-alpha) gene expression at the feto-maternal interface during the early stages of pregnancy in the rat. The present study was undertaken to determine whether the presence of TGF-alpha mRNA in the decidua was in direct response to a signal derived from the conceptus. We therefore used the model of pseudopregnancy in rat, inducing decidualization in the absence of a conceptus. TGF-alpha mRNA expression was examined using Northern blot analysis, and TGF-alpha peptide was localized using immunohistochemistry. Pseudopregnancy was produced through standard hormonal priming followed by an artificial stimulus of intrauterine sesame oil or PBS to induce decidualization. Northern blot analysis demonstrated TGF-alpha mRNA expression specifically in the deciduoma beginning on the day of decidual stimulus (Day 4), increasing on Day 6, and continuing through Day 14. In contrast to decidua of normal pregnancy, an additional transcript of 3.0 kb was present in the deciduoma. Immunohistochemistry of tissues from Day 9 of pseudopregnancy revealed specific cytoplasmic immunoreactivity in the majority of stromal type decidual cells of the antimesometrial area, whereas mesometrial decidual cells were not immunoreactive. The results indicate that the induction of decidual TGF-alpha gene expression is not in direct response to a signal derived from the conceptus but is a de novo event associated with the decidual reaction, and that the resulting TGF-alpha peptide is present in the majority of stromal type antimesometrial decidual cells. These findings also suggest that TGF-alpha could be playing a role in proliferation and/or differentiation of the decidua.

The authors evaluated magnetic resonance imaging (MRI) for monitoring orthotopic bladder tumour growth and treatment response to intravesical immunotherapy with the biological response modifiers (BRMs): recombinant tumour necrosis factor alpha (TNF-α), combination of TNF-α plus interferon gamma (IFN-γ) and interleukin-2 (IL-2). MRI demonstrated detection of early superficial murine bladder tumour (MBT-2) and accurate sequential assessment of the topography and depth of intravesical tumour involvement. Response to intravesical instillations with multiple doses ofBRMs was assessed against early stage MBT-2 bladder tumours (confirmed by MRI) 14 days after transurethral tumour implantation. Serial MRI scans of TNF-α treated mice revealed significant retardation of tumour growth which correlated well with corresponding histological examination of the whole mount bladder sections illustrating areas and depth of tumour regression. Intravesical instillation of combination TNF-α plus IFN-γ into tumour-bearing mice caused tumour growth inhibition up to 21 days following treatment; the results, however, were not superior to those noted with TNF-α alone. Sequential MR images of tumour-bearing bladders following intravesical treatment with IL-2 revealed tumour regression with no visible tumour from day 21 to 33 post tumour implant. Histological examination revealed foci of carcinoma in situ only. Control untreated bladders revealed deeply invasive transitional cell carcinoma. These results show that MRI offers a dependable tool for noninvasive monitoring of tumour growth and of the course of experimental bladder tumour during therapy.

Earlier studies from this laboratory revealed that killer lymphocyte lineages are inactivated in the tumor-bearing host by macrophage-derived PGE2. In this study, we examined whether tumor bearing causes a change in the density or affinity of PGE2 receptors on lymphocytes, making them more vulnerable to PGE2 action, and whether it enhances PGE2 production by host macrophages. PGE2 receptors were examined on both unfractionated and monocyte-macrophage-depleted splenocytes of normal or tumor-bearing C3H/HeJ mice (at 25 days following s.c. transplantation of 106 C3 mammary adenocarcinoma cells) using a [3H]PGE2 binding assay in the presence of increasing (up to 104-fold) concentrations of unlabeled PGE2 (or PGA or PGF2α as specificity controls) followed by a Scatchard analysis. PGE2 production by splenic macrophages was measured with a radio-immunoassay. Results revealed that splenocytes in normal and tumor-bearing mice bear specific receptors for PGE2, since splenocyte binding of [3H]PGE2 (10−9 M) was inhibited in the presence of excess unlabeled PGE2, but not 104-fold excess PGA or PGF2α. Tumor-bearing did not appear to cause an appreciable change in the affinity or density of these receptors, since Kd and Bmax values for PGE2 binding were similar for normal and tumor-bearing mice. However, specific PGE2-binding by splenocytes in vitro was reduced in tumor-bearing mice. Three types of evidence indicate that this resulted from a partial occupation of PGE2 receptors on lymphocytes with PGE2 produced by splenic macrophages of tumor-bearing hosts. First, depletion of monocyte-macrophages from the splenocyte population improved this binding in tumor-bearing but not normal mice. Second, pre-incubation of splenocytes with indomethacin (10−5 M, to block PG synthesis) led to a significant rise in specific PGE2 binding by unfractionated (and to only a minor extent, monocyte-macrophage-depleted) splenocytes from tumor-bearing, but not from normal mice. Third, tumor-bearing caused an enhancement of PGE2-production by splenic macrophages, this production increasing with increment in tumor burden. Thus PGE2-mediated suppression of lymphocyte activation in the tumor-bearing host results from excess PGE2 production in the lymphocyte microenvironment, without an alteration in lymphocyte binding ability for PGE2.

We have previously shown that first trimester human trophoblast cells share in vitro invasive properties with malignant cells. In this study we show that the in situ control of trophoblast invasion is provided by the uterine microenvironment. Trophoblast cells were labeled with 125I-deoxyuridine and examined for their ability to invade an epithelium-free human amniotic membrane in vitro under various conditions. The degree of invasion was determined as the percentage of the radioactivity retained within the membrane. Conditioned media from first trimester human decidual cells (DCM) suppressed invasion of trophoblast cells in the amnion invasion assay. This suppression was prevented by addition of neutralizing anti-TGF beta antibody or neutralizing antibody to tissue inhibitor of metalloproteinases (TIMP-1) to the DCM, and mimicked by TGF beta 1. These antibodies also augmented invasion beyond control levels, suggesting that trophoblast cells may also produce these factors. A bioassay for TGF beta activity, measured by antiproliferative effect on the mink lung epithelial cell line Mv 1 Lu, revealed that decidual cells produced this factor only in the latent form, whereas the active form was produced by the trophoblast. A decrease in collagenase type IV activity in the conditioned media of trophoblast cultures was observed when TGF beta 1 was added to these cultures. Removal of endogenous TGF beta in trophoblast cultures by addition of anti-TGF beta antibody resulted in down-regulation of TIMP message as determined by Northern analysis. These results indicate that a) decidua-derived (and to a minor extent trophoblast-derived) TGF beta is the prime mediator in the control of invasion by first trimester trophoblast, the latent form of TGF beta likely being activated by trophoblast-derived proteinases; b) induction of TIMP by TGF beta in both trophoblast and decidua is the final pathway in this control.

We have reported that down-modulation of tissue inhibitor of metalloproteinases (TIMP) by means of antisense RNA converts non-tumorigenic Swiss 3T3 cells into malignant cells capable of forming metastasizing tumors in nude mice [Science 243:947 (1989)]. We now describe changes in the expression of specific genes associated with tumor progression of two lines down-modulated with TIMP, LA1 and LA7. Six independent variant cell lines, generated from different primary tumors produced by LA1 and LA7, lacked (like LA1 and LA7) many characteristics of typical transformed cells. However, their tumorigenicity in nude mice was enhanced; tumors appeared with a shorter lag (1–3 weeks versus 8–10 weeks for the parental clones, LA1 and LA7) and grew very rapidly. Increases, substantial in some cases, in the expression of a cysteine proteinase, cathepsin L, and metalloproteinases homologous to rat transin (stromelysin) and transin-2 were characteristic of these variant clones. The mRNA levels encoding the transformation-associated secreted phosphoprotein (osteopontin) and the calcium-binding protein calcyclin were also augmented. No evidence for gene amplification was found, and we did not detect any change in the mRNA levels of the proto-oncogenes that were examined. These novel cell lines represent a new paradigm for the transformed cell. Our data suggest that a reduction in TIMP secretion enhances the cell's oncogenic capacity by altering the extracellular environment in a way conducive to further changes in gene expression necessary for tumor progression.

Decorin (DCN), a decidua-derived TGFbeta-binding proteoglycan, negatively regulates proliferation, migration, and invasiveness of human extravillous trophoblast (EVT) cells in a TGFbeta-independent manner. The present study examined underlying mechanisms, in particular possible roles of epidermal growth factor receptor (EGFR), IGF receptor (IGFR)-I, and vascular endothelial growth factor receptor (VEGFR)-2. EVT cell sprouting from first-trimester chorionic villus explants in the presence or absence of TGFbeta-neutralizing antibody was inhibited with DCN, suggesting its negative regulatory role in situ. Inhibition of migration of the human EVT cell line HTR-8/SVneo in transwells undercoated with fibronectin was stronger when cells were briefly preincubated with DCN at 4 C (known to retard dissociation of receptor-ligand complex) than at 37 C, suggesting possible DCN action by cell membrane binding. Pretreatment of cells with an IGFR-I blocking agent, but not two EGFR blocking agents or a VEGFR blocking agent, significantly abrogated migration inhibitory effects of DCN, suggesting the involvement of IGFR-I but not EGFR or VEGFR in migration inhibition by DCN. On the other hand, pretreatment with either of the EGFR blocking agents, or the VEGFR blocking agent but not the IGFR-I blocking agent, blocked proliferation inhibitory effects of DCN, indicating the roles of EGFR and VEGFR, but not IGFR-I in antiproliferative action of DCN. EVT cells expressed EGFR, IGFR-I, and VEGFR-2. IGFR-I and VEGF-R2 were phosphorylated in the presence of their natural ligands as well as DCN, and these events were blocked by pretreatment with respective receptor blocking agents indicating DCN-mediated activation of these receptors. In conclusion, DCN effects on EVT cells are mediated selectively by multiple tyrosine kinase receptors.

The invasion of maternal decidua and uterine spiral arteries by a trophoblast subpopulation called extravillous trophoblast (EVT) is essential for the establishment of a normal placenta and an adequate blood flow toward the fetus. Derangements in these processes underlie pregnancy-related diseases like preeclampsia and intrauterine growth restriction. Many growth factors, growth factor binding proteins, and extracellular matrix components can positively or negatively regulate the proliferation, migration, and/or invasiveness of these EVT cells. RHO GTPases, including RHOA, RAC1, and CDC42, are ubiquitous proteins that control cytoskeletal changes by forming stress fibers and projecting lamellipodia and filopodia during cellular migration. We had previously shown that prostaglandin (PG) E(2) produced in abundance by the decidua promotes the migration of first-trimester human EVTs by increasing the intracellular concentration of calcium and activating calpain. Using our well-characterized immortalized EVT cell line, HTR-8/SVneo, as well as villus explants from first-trimester placentae, this study examined the role of RHO GTPases RAC1 and CDC42 in PGE(2)-mediated migratory responses of these cells. Though a RAC1 inhibitor, NSC23766 as well as RAC1 knockdown by siRNA decreased the migration of HTR-8/SVneo cells in a Transwell migration assay, this inhibition could not be restored by PGE(2) or 17-phenyl trinor PGE(2) (PGE receptor PTGER1 agonist) or PGE(1) Alcohol (PGE receptor PTGER4 agonist). Similar results were noted for EVT cell spreading in villus explants. Furthermore, CDC42 silencing using siRNA inhibited PGE(2)-induced migration of HTR-8/SVneo cells. Finally, the treatment of EVT cells with PGE(2), PTGER1 agonist, or PTGER4 agonist activated RAC1 and CDC42 at 10 min, suggesting that RAC1 and CDC42 play an essential role in PGE(2)-mediated migration of human EVTs.

Objective: Aberrant expression of developmentally regulated genes during placental development could affect fetal growth and contribute to preeclampsia. Expression of serine protease HtrA1 is developmentally regulated with the highest expression in decidua capsularis, compared with ectoplacental cone, and with the highest expression during later stages of pregnancy, compared with early stages. This study was designed to determine the expression of HtrA1 in placental tissues from control and preeclamptic pregnancies and to determine the effect of HtrA1 expression in trophoblast cell migration and invasion. Study Design: HtrA1 expression was assessed by immunohistochemistry in placentas from gestational age-matched preeclamptic and control pregnancies. HtrA1 expression in extravillous trophoblast cells, HTR-8/SVneo, was assessed by immunoblotting and immunofluorescence microscopy. Finally, the effect of ectopic expression of HtrA1 on cell migration and invasion was determined in HTR-8/SVneo cells. Results: Higher expression of HtrA1 was detected in placental tissues collected from patients with early-onset preeclampsia, compared with those from gestational age-matched control samples. Moreover, ectopic expression of HtrA1 significantly attenuates HTR-8/SVneo cell migration and invasion. Conclusion: Higher expression of HtrA1 is associated with early-onset preeclampsia and may affect trophoblast cell migration and invasion. © 2008 Mosby, Inc. All rights reserved.

We examined the relationship of l-A expression by normal murine macrophages to their immunoregulatory role on natural killer cell activity. Macrophages were isolated on the basis of plastic adherence; characterized on the basis of conventional markers such as phagocytic ability, cytoplasmic non-specific esterase activity, surface MAC-1 and F4/80 antigen expression; and then used for functional studies relative to their expression of surface l-A. Two functional macrophage subsets were identified: NK-stimulatory and NK-suppressive subsets. The former function was associated with splenic macrophages, which were predominantly l-A+ as identified with a radioautographic immunolabeling technique; the latter function with peritoneal macrophages which were predominantly l-A-. Loss of macrophage l-A expression in vitro was delayed in the presence of indomethacin and enhanced in the presence of PGE2, indicating that PGE2 down-regulates l-A expression on macrophages. The NK stimulatory function of l-A+ macrophages was attributable to a soluble mediator, identified as IFN-γ, since the stimulatory ability was abrogated with an anti-IFN-γ antibody. l-A expression appears to be important for the stimulatory function, since some interference with this function was noted in the presence of anti-I-A antibody. The NK-suppressor function of I-A- macrophages was attributable to the soluble mediator PGE2, since this function was abrogated with indomethacin or anti-PGE2 antibody. These results are relevant to the understanding of normal in vivo immunoregulation by macrophages.

Previous studies from this laboratory have demonstrated a large influx of null lymphocytes into the murine decidua during pregnancy. We had also shown that trophoblast cells of the murine placenta bear target structures recognized by NK cells. Since NK lineage cells belong to the null category of lymphocytes, we examined whether cells of this lineage appear in the murine decidua, and if so, whether their activity is locally regulated by NK suppressor cells. We further investigated the identity of the suppressor cells as well as their suppressor products. NK lineage cells, irrespective of their activation status, were identified morphologically in radioautographic preparations as the non-T, non-B (null) lymphocytes capable of binding YAC-1 lymphoma targets. NK activity of nucleated cells was measured with a 4-hr 51Cr-release assay against labeled YAC-1 targets. Studies with outbred CD1 mice, and to a smaller extent, inbred CBA mice revealed that the incidence of NK lineage cells remained fairly constant within the decidua throughout pregnancy, but their activity decreased steadily to negligible levels by Day 12-14 of gestation. This was found to result from an inactivation caused by NK-suppressor cells in the decidua. A mixing of Ficoll-Paque-separated nucleated cells of the decidua with normal splenic effector cells (at 1:1 ratio) led to a suppression of their NK activity tested immediately or after a 20-hr coculture. This suppression was MHC unrestricted. Suppressor cells were identified both in plastic nonadherent fraction highly enriched for typical decidual cells as well as in the plastic adherent fraction containing decidual cells and macrophages. Addition of indomethacin (10(-5) M), an inhibitor of prostaglandin synthesis, or anti PGE2 antibody, revived the NK activity in the mixed population, as well as in the decidua, suggesting a PGE2-mediated suppression. High levels of PGE2 were detectable in decidual cell supernatants with a sensitive radioimmunoassay. Addition of pure PGE2 (10(-7)-10(-6) M) but not PGF2 alpha (10(-6) M) during the NK assay or to the effector cells for a 20-hr period prior to the assay led to an inhibition of NK activity. These results reveal that NK cells appearing in the murine decidua are progressively inactivated by PGE2 produced by decidual cells and decidual macrophages.

Nodal, a member of the transforming growth factor-beta superfamily, is known to play critical roles in early vertebrate development, but its functions in extraembryonic tissues are unclear. ALK7 is a type I receptor for Nodal. Recently, we demonstrated that Nodal mRNA and several ALK7 transcripts are expressed in human placenta throughout pregnancy (Roberts, H. J., Hu, S., Qiu, Q., Leung, P. C. K., Cannigia, I., Gruslin, A., Tsang, B., and Peng, C. (2003) Biol. Reprod. 68, 1719-1726). In this study, we determined the role of Nodal and ALK7 in trophoblast cell proliferation and apoptosis. Overexpression of Nodal in normal trophoblast cells (HTR8/SVneo) and several choriocarcinoma cell lines resulted in a significant decrease in the number of metabolically active cells. The effect of Nodal could be mimicked by constitutively active ALK7 (ALK7-ca), but was blocked by kinase-deficient ALK7. The growth inhibitory effect of Nodal was also blocked by dominant-negative Smad2/3. Overexpression of Nodal and ALK7-ca induced apoptosis in trophoblast cells as determined by Hoechst staining, flow cytometry, and caspase-3 Western blotting. In addition, Nodal and ALK7-ca decreased the number of proliferating cells as measured by bromodeoxyuridine assays. Furthermore, overexpression of Nodal or ALK7-ca increased p27 expression, but reduced the levels of Cdk2 and cyclin D(1). Taken together, this study demonstrates for the first time that Nodal, acting through ALK7 and Smad2/3, inhibits proliferation and induces apoptosis in human trophoblast cells. Our findings also suggest that the Nodal-ALK7 pathway inhibits cell proliferation by inducing G(1) cell cycle arrest and that this effect is mediated in part by the p27-cyclin E/Cdk2 pathway.