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Cost and availability have often dictated the use of heterologous/alien prolactins in experiments, particularly in vivo. The assumption has been that what is initiated in the target cell is representative of the homologous hormone since many heterologous mammalian prolactins bind to and activate rodent receptors. Here, we examined gene expression in mouse liver in response to a 7-day treatment with recombinant mouse prolactin (mRecPRL), recombinant ovine prolactin (oRecPRL) and pituitary extract ovine prolactin (oPitPRL). Having established mouse ribosomal protein S9 as the most stable reference gene in the liver in the absence and presence of prolactin treatment, we examined expression of the two most highly expressed prolactin receptors (PRLRs) and three members of the Cyp3a group of cytochrome P450 isoenzymes by qRTPCR. For short form (SF) 3 PRLR, mRecPRL doubled expression while for oRecPRL and oPitPRL expression was only 1.3-fold control. For the long form (LF) PRLR, changes were similar to those seen for SF 3 PRLR, such that the SF3:LF PRLR ratio remained the same. Expression of the Cyp3as was also dependent on the prolactin origin and, although mRecPRL always stimulated, the other PRLs caused varying results. Compared to control, Cyp3a16 was stimulated 12-fold by mRecPRL, 3-fold by oRecPRL, and 6-fold by oPitPRL. For Cyp3a41, mRecPRL was 3.7-fold control, oRecPRL was without effect, and oPitPRL was 2-fold control. Importantly, for Cyp3a44, mRecPRL stimulated 2-fold, whereas both oRecPRL and oPitPRL had an opposite, inhibitory effect, with expression at 0.5-fold control. We conclude that homologous hormone had the largest stimulatory effect on expression of all measured genes and that by contrast heterologous hormone showed reduced activity, no activity, or opposite activity, depending on the gene being analyzed. Thus, experimentation using alien heterologous PRL may lead to inaccurate conclusions.

A proportion of secreted pituitary prolactin (PRL) is phosphorylated. However, because most commercial sources of PRL are recombinant proteins without posttranslational modification, the importance of PRL phosphorylation to the production of milk proteins is an understudied area. Here, we have examined the effect of PRL phosphorylation on expression of the milk protein, β-casein, using a phospho-stable mimic of the phosphorylated form (S179D-PRL) and analyzing promoter activation and mRNA stability over a 7-day treatment period in response to this and unmodified PRL. At equivalent concentrations, the phospho-mimic showed a superior ability to activate a −2300 → +490 region of the promoter, but not an artificial promoter consisting of three Stat5 consensus sites upstream of a minimal promoter. Unlike unmodified PRL, S179D-PRL was also able to stabilize β-casein mRNA. These effects of S179D-PRL were eliminated by incubation in the MAP kinase pathway inhibitor, U0126, bringing promoter activation down to the level seen with unmodified PRL and essentially eliminating the effect on mRNA stability. These results support an important role for the posttranslational phosphorylation of PRL and signaling through the MAP kinase pathway in the production of this milk protein.

Mouse model systems are unmatched for the analysis of disease processes because of their genetic manipulability and the low cost of experimental treatments. However, because of their small body size, some structures, such as the oviduct with a diameter of 200-400 μm, have proven to be relatively difficult to study except by immunohistochemistry. Recently, immunohistochemical studies have uncovered more complex differences in oviduct segments than were previously recognized; thus, the oviduct is divided into four functional segments with different ratios of seven distinct epithelial cell types. The different embryological origins and ratios of the epithelial cell types likely make the four functional regions differentially susceptible to disease. For example, precursor lesions to serous intraepithelial carcinomas arise from the infundibulum in mouse models and from the corresponding fimbrial region in the human fallopian tube. The protocol described here details a method for microdissection to subdivide the oviduct in such a way to yield a sufficient amount and purity of RNA necessary for downstream analysis such as reverse transcription-quantitative PCR (RT-qPCR) and RNA sequencing (RNAseq). Also described is a mostly non-enzymatic tissue dissociation method appropriate for flow cytometry or single cell RNAseq analysis of fully differentiated oviductal cells. The methods described will facilitate further research utilizing the murine oviduct in the field of reproduction, fertility, cancer, and immunology.

Highlights • Systemic knockdown of the long form prolactin receptor in vivo increases survival in an aggressive, immunocompetent model of stage IV, triple negative breast cancer. • Knockdown of the long form prolactin receptor reduces Treg recruitment to tumors by reducing tumor parenchymal production of CCL-17. • Those Tregs still recruited to primary tumors have a substantial reduction in their ability to promote epithelial to mesenchymal transition of tumor parenchyma. • For the Tregs in the primary tumor, there is transcript downregulation of components of the T cell receptor complex and CTLA-4. • Tregs outside of the tumor have normal ability to suppress T effector cell proliferation after 1–5 months of treatment. • Knockdown of the long form of the prolactin receptor therefore seems to have an intra-tumor immunotherapeutic effect without effect on peripheral Treg function., Previous work has shown systemic knockdown of the long form prolactin receptor (LFPRLR) in vivo markedly reduced metastasis in mouse models of breast cancer, but whether this translated to prolonged survival was unknown. Here we show that LFPRLR knockdown in the highly metastatic, immunocompetent 4T1 model prolonged survival and reduced recruitment of T regulatory cells (Tregs) to the tumor through effects on the production of CCL17. For the Tregs still recruited to the primary tumor, LFPRLR knockdown both directly and indirectly reduced their ability to promote tumor parenchymal epithelial to mesenchymal transition. Importantly, effects of prolactin on expression of mesenchymal genes by the tumor parenchyma were very different in the absence and presence of Tregs. While systemic knockdown of the LFPRLR downregulated transcripts important for immune synapse function in the remaining tumor Tregs, splenic Tregs seemed unaffected by LFPRLR knockdown, as demonstrated by their continued ability to suppress anti-CD3/CD28-stimulated effector cell proliferation at 1–5 months. These results demonstrate that knockdown of the LFPRLR achieves intra-tumor immunotherapeutic effects and suggest this occurs with reduced likelihood of peripheral inflammatory/autoimmune sequelae.

We have used the four core genotypes (FCG) mouse model, which allows a distinction between effects of gonadal secretions and chromosomal complement, to determine when sex differences in the immune system first appear and what influences their development. Using splenic T cell number as a measure that could be applied to neonates with as yet immature immune responses, we found no differences among the four genotypes at postnatal day 1, but by day 7, clear sex differences were observed. These sex differences were unexpectedly independent of chromosomal complement and similar in degree to gonadectomized FCG adults: both neonatal and gonadectomized adult females (XX and XY) showed 2-fold the number of CD4+ and 7-fold the number of CD8+ T cells versus their male (XX and XY) counterparts. Appearance of this long-lived sex difference between days 1 and 7 suggested a role for the male-specific perinatal surge of testicular testosterone. Interference with the testosterone surge significantly de-masculinized the male CD4+, but not CD8+ splenic profile. Treatment of neonates demonstrated elevated testosterone limited mature cell egress from the thymus, whereas estradiol reduced splenic T cell seeding in females. Neonatal male splenic epithelium/stroma expressed aromatase mRNA, suggesting capacity for splenic conversion of perinatal testosterone into estradiol in males, which, similar to administration of estradiol in females, would result in reduced splenic T cell seeding. These sex steroid effects affected both CD4+ and CD8+ cells and yet interference with the testosterone surge only significantly de-masculinized the splenic content of CD4+ cells. For CD8+ cells, male cells in the thymus were also found to express one third the density of sphingosine-1-phosphate thymic egress receptors per cell compared to female, a male characteristic most likely an indirect result of Sry expression. Interestingly, the data also support a previously unrecognized role for non-gonadal estradiol in the promotion of intra-thymic cell proliferation in neonates of both sexes. Microarray analysis suggested the thymic epithelium/stroma as the source of this hormone. We conclude that some immune sex differences appear long before puberty and more than one mechanism contributes to differential numbers and distribution of T cells.

Prolactin (PRL) is a pleiotropic hormone with multiple functions in several tissues and organs, including the brain. PRL decreases lesion-induced microgliosis and modifies gene expression related to microglial functions in the hippocampus, thereby providing a possible mechanism through which it might participate in neuroimmune modulatory responses and prevent neuronal cell damage. However, the direct contribution of microglial cells to PRL-mediated neuroprotection is still unclear and no studies have yet documented whether PRL can directly activate cellular pathways in microglial cells. The aim of this study is to elucidate in vitro actions of PRL on the immortalized SIM-A9 microglia cell line in basal and LPS-stimulated conditions. PRL alone induced a time-dependent extracellular signal-regulated kinase 1/2 (ERK1/2) activation. Pretreatment with PRL attenuated LPS (200 ng/ml) stimulated pro-inflammatory markers: nitric oxide (NO) levels, inducible nitric oxide synthase (iNOS), interleukins (IL)-6, -1β and tumor necrosis factor (TNF-α) expression at 20 nM dosage. PRL suppressed LPS-induced nuclear factor (NF)-κappaB (NF-κB) p65 subunit phosphorylation and its upstream p-ERK1/2 activity. In conclusion, PRL exhibits anti-inflammatory effects in LPS-stimulated SIM-A9 microglia by downregulating pro-inflammatory mediators corresponding to suppression of LPS-activated ERK1/2 and NF-κB phosphorylation.

The most common and most deadly form of “ovarian”cancer is High-Grade Serous Carcinoma (HGSC), now appreciated to arise from epithelial cells of the fallopian tube/oviduct. The serum analyte with the greatest specificity and sensitivity that correlates with the presence or absence of HGSC is prolactin (PRL). However, unknown is whether elevated PRL initiates disease or is the result of disease, although once cancer is present,it is clear that PRL promotes disease. In order to examine the potential for disease initiation in normal animals, it was first important to determine which cells in the mouse oviduct respond to PRL. In many cell types, the long form of the Prlr mediates increased survival, proliferation and migration, whereas the short forms have the opposite effect. After establishing equivalent efficiencies of primers for the long form (LF) and 3 short forms (SF1-3) of the murine Prlr and the endogenous control gene, Gapdh, the mRNA expression profiles of these forms of the receptor were followed by RT-qPCR as a function of stage of the estrous cycle (proestrus, estrus, metestrus, diestrus - determined by vaginal cytology) and region of the oviduct (isthmus, ampulla and fimbria). Expression of SF1 was not detected. SF2 was essentially consistently expressed throughout the oviduct and at all stages of the estrous cycle. By contrast, the ratio of LF to SF3 varied by region of the tube, with more SF3 towards the fimbria and more LF towards the isthmus. The epithelium of the oviduct is primarily composed of multi-ciliated cells and secretory cells, with more ciliated cells towards the fimbria and more secretory cells towards the isthmus. The RT-qPCR results therefore suggested the possibility that a greater proportion of LF Prlr was present on secretory cells and a greater proportion of SF3 Prlr on ciliated cells. Using antibodies raised against intracellular peptide regions specificto the LF (aa 309-325) and SF3 (aa 281-296), both receptor isoforms were localized by immunofluorescence to apical regions of both epithelial cell types,but the presence of receptors on cilia (clearly demonstrated by 3Dreconstruction and rotation) complicated analysis of relative fluorescence by microscopy. Only the LF Prlr signals via Stat5 and so it was anticipated thatStat5 activation could serve as a substitute marker of the relative presence ofLF Prlr. Following in vivo intraperitoneal injection of PRL (5μg/g, 30 min),activated Stat5 was localized to epithelial cells at the base of, and in between, mucosal folds, thereby suggesting a further regionality to receptor distribution. For the fimbrial region only, which is where HGSC is thought to arise, expression of both the LF and SF3 Prlr changed as a function of the stage of the estrous cycle, with highest mRNA expression at diestrus/proestrus. Ongoing work includes flow cytometry of epithelial subpopulations and spatialanalysis of gene expression.

Rationale B cell malignancies, including leukemia and lymphoma, are high-risk lymphoid neoplasms. B cell malignancies predispose to autoimmune diseases including systemic lupus erythematosus (SLE) which increase the risk of developing these malignancies by >5-fold. Increased prolactin (PRL) expression is known to exacerbate SLE and promote the survival of autoreactive B cells. Furthermore, PRL induces expression of the protooncogenes, MYC and BCL2, in lymphoid tissues. However, whether PRL drives the initiation and maintenance of B cell malignancies was not known. Results We first tested our hypothesis that PRL, specifically signaling through the pro-proliferative and anti-apoptotic long isoform (LF) of the PRL receptor (PRLR), drives the progression of SLE to B cell malignancies. To this end, we knocked down the LF PRLR in MRL-lpr mice predisposed to developing SLE using a splice-modulating oligomer (SMO) that blocks splicing to produce the LF PRLR without affecting the short isoforms. LF PRLR knockdown reduced splenic and circulating B cell numbers in MRL-lpr SLE mice (Fig.1a). Consistent with reduced B cell numbers, BCL2 expression in B cells of SLE mice was suppressed after LF PRLR knockdown, although MYC was unaltered (Fig.1b). By sequencing the immunoglobulin heavy chains (IGH), we compared the composition of the splenic B cell repertoire between control- and LF PRLR SMO-treated SLE mice. Control oligomer treated SLE mice accumulated splenic B cells with long complementary determining region 3 (CDR3) and B cells with non-functional IGH, characteristics of autoreactive B cells. Treatment with the LF PRLR SMO reduced both. We then measured the expression of enzymes known to induce malignant transformation of B cells, namely recombination activating genes 1/2 (RAG1/2) and activation-induced cytidine deaminase (AID), in B cells of SLE mice in controls versus LF PRLR knockdown. Importantly, LF PRLR knockdown significantly reduced RAG1 (Fig.1c) and AID expression in splenic B cells of SLE mice (Fig.1d,e). Our findings thus underscore a causal role for LF PRLR signaling in promoting of malignant transformation of B cells in SLE. Because PRL induces the expression of BCL2 and MYC in lymphocytes, we next determined whether LF PRLR promotes the survival of overt B cell malignancies that overexpress MYC and BCL2, including diffuse large B cell lymphoma (DLBCL) and B-cell acute lymphoblastic leukemia (B-ALL). We observed that B-lymphoblasts expressed significantly higher levels of PRL and the LF PRLR as compared to normal B cells (Fig.1f). We also found that higher expression of PRL at diagnosis predicts poor clinical outcome in DLBCL patients (P=0.0244), and that patients with MYC/BCL2-overexpressing ALLs with a poor prognosis had significantly higher expression of the LF PRLR compared to their MYC lowBCL2 low counterparts (P Knockdown of the LF PRLR using the LF PRLR SMO in MYC/BCL2-driven human B cell malignancies killed lymphoblasts and reduced MYC and BCL2 protein levels (Fig.1g). Because we previously showed that MYC-driven lymphoid malignancies are sensitive to natural killer (NK) cell-mediated immune clearance, we also examined whether LF PRLR knockdown synergized with NK cells in killing DLBCL. We found that LF PRLR knockdown enhanced NK cell-mediated killing of B-lymphoblasts (Fig.1h). Of note, no reductions were observed in NK cell viability or MYC levels within NK cells upon LF PRLR knockdown, suggesting that LF PRLR selectively kills B-lymphoblasts without negatively impacting NK homeostasis. Conclusion Our studies identify the specific knockdown of LF PRLR as a potentially safe and targeted strategy to prevent the onset of B cell malignancies in SLE patients and to treat flagrant DLBCL and B-ALL. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

We have previously demonstrated lactational transfer of T cell–based immunity from dam to foster pup. In the short term, a significant part of transferred immunity is passive cellular immunity. However, as time progresses, this is replaced by what we have described as maternal educational immunity such that by young adulthood, all immune cells responding to a foster dam immunogen are the product of the foster pup’s thymus. To reduce confounding factors, this original demonstration used congenic/syngeneic dam and foster pup pairs. In this study, we investigated lactational transfer of immunity to Mycobacterium tuberculosis in MHC class I–mismatched animals, as well as from Th1-biased dams to Th2-biased foster pups. Using immunized C57BL/6J dams, lactational transfer to nonimmunized BALB/cJ foster pups resulted in much greater immunity than direct immunization in 5-wk-old pups (ex vivo assay of pup splenocytes). At this age, 82% of immunogen-responding cells in the pup spleen were produced through maternal educational immunity. FVB/NJ nonimmunized foster recipients had a greater number of maternal cells in the spleen and thymus but a much larger percentage was Foxp3+, resulting in equivalent immunity to direct immunization. Depletion of maternal Foxp3+ cells from pup splenocytes illustrated a substantial role for lactationally transferred dam regulatory T cells in suppression of the ex vivo response in FVB/NJ, but not BALB/cJ, recipients. We conclude that lactational transfer of immunity can cross MHC class I barriers and that Th1 immunity can be imparted to Th2-biased offspring; in some instances, it can be greater than that achieved by direct immunization.

Prolactin promotes a variety of cancers by an array of different mechanisms. Here, we have investigated prolactin's inhibitory effect on expression of the cell cycle-regulating protein, p21. Using a miRNA array, we identified a number of miRNAs upregulated by prolactin treatment, but one in particular that was strongly induced by prolactin and predicted to bind to the 3′UTR of p21 mRNA, miR-106b. By creating a p21 mRNA 3′UTR-luciferase mRNA construct, we demonstrated degradation of the construct in response to prolactin in human breast, prostate and ovarian cancer cell lines. Increased expression of miR-106b replicated, and anti-miR-106b counteracted, the effects of prolactin on degradation of the 3′UTR construct, p21 mRNA levels, and cell proliferation in breast (T47D) and prostate (PC3) cancer cells. Increased expression of miR-106b also stimulated migration of the very epithelioid T47D cell line. By contrast, anti-miR-106b dramatically decreased expression of the mesenchymal markers, SNAIL-2, TWIST-2, VIMENTIN, and FIBRONECTIN. Using signaling pathway inhibitors and the 3′UTR construct, induction of miR-106b by prolactin was determined to be mediated through the MAPK/ERK and PI3K/Akt pathways and not through Jak2/Stat5 in both T47D and PC3 cells. Prolactin activation of MAPK/ERK and PI3K/Akt also activates ERα in the absence of an ERα ligand. 17β-estradiol promoted degradation of the construct in both cell lines and pre-incubation in the estrogen antagonist, Fulvestrant, blocked the ability of both prolactin and 17β-estradiol to induce the construct-degrading activity. Together, these data support a convergence of the prolactin and 17β-estradiol miR-106b-elevating signaling pathways at ERα.

Females have more robust immune responses than males, well-illustrated by the degree of inflammation elicited during delayed-type hypersensitivity (DTH) responses. Here, we have investigated underlying sex differences that may contribute to differential footpad DTH responses using wildtype and four core genotypes (FCG) mice and popliteal lymphnode cellularity and gene expression. DTH responses in XX and XY FCG females showed no role for almost all genes expressed on sex chromosomes. After then filtering-out genes differentially expressed between XX and XY females, only one gene was sexually differentially expressed in wildtype mice, glycosylation-dependent cell adhesion molecule 1 (Glycam1), expressed 7-fold higher in females. Glycam1 facilitates leukocyte entry through high endothelial venules. Consistent with greater Glycam1 expression, female nodes contained twice as many cells. While females had more memory T cells in their nodes, males had a higher percentage of T regulatory cells. This sexual dimorphism in wildtype animals manifested pre-pubertally, was enhanced post-pubertally, and was eliminated by castration. The formation of male gonads is determined by the expression of Sry. Sry overexpression, which does not affect testosterone levels, produced an exaggerated male phenotype. We conclude that Sry expression through formation of the male gonad indirectly negatively impacts the potential for local inflammation.

Immune cells in the mammary gland play a number of important roles, including protection against infection during lactation and, after passing into milk, modulation of offspring immunity. However, little is known about the mechanism of recruitment of immune cells to the lactating gland in the absence of infection. Given the importance of prolactin to other aspects of lactation, we hypothesized it would also play a role in immune cell recruitment. Prolactin treatment of adult female mice for a period equivalent to pregnancy and the first week of lactation increased immune cell flux through the mammary gland, as reflected in the number of immune cells in mammary gland-draining, but not other lymph nodes. Conditioned medium from luminal mammary epithelial HC11 cell cultures was chemo-attractive to CD4+ and CD8+ T cells, CD4+ and CD8+ memory T cells, B cells, macrophages, monocytes, eosinophils, and neutrophils. Prolactin did not act as a direct chemo-attractant, but through effects on luminal mammary epithelial cells, increased the chemo-attractant properties of conditioned medium. Macrophages and neutrophils constitute the largest proportion of cells in milk from healthy glands. Depletion of CCL2 and CXCL1 from conditioned medium reduced chemo-attraction of monocytes and neutrophils, and prolactin increased expression of these two chemokines in mammary epithelial cells. We conclude that prolactin is an important player in the recruitment of immune cells to the mammary gland both through its activities to increase epithelial cell number as well as production of chemo-attractants on a per cell basis.

Even though mutations in the tumor suppressor, BRCA1, markedly increase the risk of breast and ovarian cancer, most breast and ovarian cancers express wild type BRCA1. An important question is therefore how the tumor-suppressive function of normal BRCA1 is overcome during development of most cancers. Because prolactin promotes these and other cancers, we investigated the hypothesis that prolactin interferes with the ability of BRCA1 to inhibit the cell cycle. Examining six different cancer cell lines with wild type BRCA1, and making use of both prolactin and the growth-inhibiting selective prolactin receptor modulator, S179D PRL, we demonstrate that prolactin activation of Stat5 results in the formation of a complex between phospho-Stat5 and BRCA1. Formation of this complex does not interfere with nuclear translocation or binding of BRCA1 to the p21 promoter, but does interfere with the ability of BRCA1 to transactivate the p21 promoter. Overexpression of a dominant-negative Stat5 in prolactin-stimulated cells resulted in increased p21 expression. We conclude that prolactin inhibits a major tumor-suppressive function of BRCA1 by interfering with BRCA1's upregulation of expression of the cell cycle inhibitor, p21.

Small oligonucleotides (oligos) are increasingly being utilized as diagnostics or treatments for disease. An impediment to broader use is the ability to readily measure oligos in biological fluids. Here, we describe a very straightforward assay with detection in the sub-picomole range that does not require extraction from serum/plasma or polymerization chain reaction amplification. As a result, there are no losses or errors due to sample handling, and the assay can be used to measure oligos modified in a variety of ways that increase therapeutic efficacy. The enzyme-linked oligonucleotide hybridization assay (ELOHA) is based on competition with a detection oligo for hybridization to a capture oligo covalently linked to a solid substrate. The versatility of ELOHAs is demonstrated by application to the measurement of three oligos, including two morpholino-oligos with 3′-octaguanidine derivatization for efficient cell uptake. The third oligo is unmodified and has a DNA sequence equivalent to miR93. The assays have sensitivity as low as 0.28 pmol/sample reaction at 50% hybridization. Adding to clinical utility is the need for only a simple 96-well absorbance plate reader and the finding that neither EDTA nor heparin interferes with detection.

Matrix metalloproteinases (MMPs) are considered excellent targets for cancer therapy because of their important roles in multiple aspects of tumor growth and metastatic spread. However, not all MMPs, or even all activities of specific MMPs, promote cancer. Therefore, there is a need for highly specific inhibitors. Monoclonal antibodies provide the potential for the degree of specificity required, but the isolation of antibodies able to inhibit a specific protease with high selectivity is challenging. Proteolysis specificity lies in recognition of the substrate in or around the active site, which generally forms a concave cleft inaccessible by human IgGs. Inspired by camelid antibodies, which have convex paratopes, we have produced a recombinant human IgG, designated 3A2, which binds in the substrate cleft of MMP-14, inhibiting its activity, but not the activity of highly homologous MMPs. In the 4T1 highly metastatic, syngeneic, orthotopic model of breast cancer, IgG 3A2 markedly inhibited growth of the primary tumor, but more importantly reduced metastatic spread to the lungs and liver by 94%. Stem cells in the tumor population expressed twice as much MMP-14 mRNA as bulk tumor cells. In addition to reducing dissemination of tumor stem cells, as would be expected from inhibition of MMP-14's ability to degrade components of the extracellular matrix, IgG 3A2 also inhibited the ability of individual stem cells to proliferate and produce colonies. We conclude that it is possible to produce antibodies with sufficient specificity for development as therapeutics and that IgG 3A2 has therapeutic potential.

Controversy exists concerning the role of the long prolactin receptor (PRLR) in the progression of breast cancer. By targeting pre-mRNA splicing, we succeeded in knocking down only the long PRLR in vivo, leaving the short forms unaffected. Using two orthotopic and highly-metastatic models of breast cancer, one of which was syngeneic (mouse 4T1) to allow assessment of tumor-immune interactions and one of which was endocrinologically humanized (human BT-474) to activate human PRLRs, we examined the effect of long PRLR knockdown on disease progression. In both models, knockdown dramatically inhibited metastatic spread to the lungs and liver and resulted in increased central death in the primary tumor. In the syngeneic model, immune infiltrates in metastatic sites were changed from innate inflammatory cells to lymphocytes, with an increase in the incidence of tumor-specific cytotoxic T cells. Long PRLR knockdown in three-dimensional culture induced apoptosis of tumor-initiating/cancer stem cells (death of 95% of cells displaying stem cell markers in 15 days). We conclude that the long PRLR plays an important role in breast cancer metastasis.

A comprehensive understanding of prolactin's (PRL's) role in breast cancer is complicated by disparate roles for alternatively-spliced PRL receptors (PRLR) and crosstalk between PRL and estrogen signaling. Among PRLRs, the short form 1b (SF1b) inhibits PRL-stimulated cell proliferation. In addition to ligand-dependent PRLRs, constitutively-active varieties, missing the S2 region of the extracellular domain (ΔS2), naturally occur. Expression analysis of the ΔS2 version of SF1b (ΔS2SF1b) showed higher expression in histologically-normal contiguous tissue versus invasive ductal carcinoma. To determine the function of ΔS2SF1b, a T47D breast cancer line with inducible expression was produced. Induction of ΔS2SF1b blocked estrogen-stimulated cell proliferation. Unlike intact SF1b, induction of ΔS2SF1b had no effect on PRL-mediated activation of Stat5a. However induction inhibited estrogen's stimulatory effects on serine-118 phosphorylation of estrogen receptor α, serine-473 phosphorylation of Akt, serine-9 phosphorylation of GSK3β, and c-myc expression. In addition, induction of ΔS2SF1b increased expression of the cell cycle-inhibiting protein, p21. Thus, increased expression of ΔS2SF1b, such as we demonstrate occurs with the selective PRLR modulator, S179D PRL, would create a physiological state in which estrogen-stimulated proliferation was inhibited, but differentiative responses to PRL were maintained.

Prolactin (PRL) has many functions in the CNS, including neuroprotection. During lactation, the dorsal hippocampus is protected from excitotoxic kainic acid (KA)-induced cellular damage. We have previously reported that systemic pre-treatment with ovine PRL had similar protective effects in female rats. Here, we asked (1) whether intracerebral human PRL (hPRL) would have the same action, (2) because phosphorylated PRL is high in lactation, whether a mimic of phosphorylated hPRL, human prolactin in which the normally phosphorylated serine at position 179 is replaced with an aspartate (S179D-PRL), had similar activity, and (3) what signaling pathways mediated the protective effect. Female ovariectomized (OVX, 1 month) rats were implanted with micro-osmotic pumps connected to unilateral icv cannulae directed at the right lateral ventricle. The pumps delivered 0.10 ng/h of hPRL, S179D-PRL, a combination of hPRL+S179D-PRL, or saline vehicle for 7 days prior to a systemic dose of 7.5mg/kg of KA. Rats were sacrificed 48 h after KA injection. Immunostaining for neuronal nuclei (Neu-N) revealed a significant KA-induced decrease in cell number in the CA1, CA3, and CA4 hippocampal areas of rats (∼55% of control). Treatment with either hPRL or S179D-PRL or the combination prevented the damaging effect of KA in these hippocampal regions (∼95% of corresponding control), but was not completely effective at preventing early seizure-related behaviors such as staring and wet dog shakes. Analysis of signals generated by hPRL and S179D-PRL showed no activation of signal transducer and activation of transcription 5 (Stat5) or other signaling molecules in the hippocampus, but activation of extracellular-regulated kinase (ERK)1/2 in the amygdala. These results support a central protective effect of both PRL forms and suggest that PRL could be exerting its protective action by indirectly modulating input signals to the hippocampus and thus regulating excitability.

Using multiple murine foster-nursing protocols, thereby eliminating placental transfer and allowing a distinction between dam- and pup-derived cells, we show that foster nursing by an immunized dam results in development of CD8+ T cells in nonimmunized foster pups that are specific for Ags against which the foster dam was immunized (Mycobacterium tuberculosis or Candida albicans). We have dubbed this process “maternal educational immunity” to distinguish it from passive cellular immunity. Of the variety of maternal immune cells present in milk, only T cells were detected in pup tissues. Maternal T cells, a substantial percentage of which were CD4+MHC class II+, accumulated in the pup thymus and spleen during the nursing period. Further analysis of maternal cells in the pup thymus showed that a proportion was positive for maternal immunogen-specific MHC class II tetramers. To determine the outcome of Ag presentation in the thymus, the maternal or foster pup origin of immunogen-responding CD8+ cells in foster pup spleens was assessed. Whereas ∼10% were maternally derived in the first few weeks after weaning, all immunogen-responding CD8+ T cells were pup derived by 12 wk of age. Pup-derived immunogen-responsive CD8+ cells persisted until at least 1 y of age. Passive cellular immunity is well accepted and has been demonstrated in the human population. In this study, we show an arguably more important role for transferred immune cells: the direction of offspring T cell development. Harnessing maternal educational immunity through prepregnancy immunization programs has potential for improvement of infant immunity.

Lymphangioleiomyomatosis, a cystic lung disease of women, is characterized by proliferation of smooth muscle-like lymphangioleiomyomatosis cells, which possess mutations in the tuberous sclerosis complex genes, TSC1/TSC2. Growth factors involved in lymphangioleiomyomatosis cell proliferation are unknown. Prolactin, an important reproductive hormone in women, is known to promote cell proliferation and survival in other tissues.To determine the role of prolactin in signaling and proliferation in lymphangioleiomyomatosis.Prolactin levels in the sera of patients with lymphangioleiomyomatosis were correlated with clinical status. Components of prolactin signal transduction pathways were assessed in lymphangioleiomyomatosis lesions from human lung explants by real-time reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. Prolactin effects on proliferation and signaling were quantified in tuberin-deficient and tuberin-expressing rat cells in vitro.Higher prolactin levels in the sera of patients with lymphangioleiomyomatosis were associated with a faster rate of decline in FEV(1) and an increased history of pneumothorax (P0.01). Higher levels of prolactin and prolactin receptor mRNA and immunoreactivity were found in lymphangioleiomyomatosis lesions when compared with vascular smooth muscle cells in the same region of tissue. This was accompanied by evidence of activation of signal transducer and activator of transcription-1 (STAT1), STAT3, p44/42, and p38 mitogen-activated protein kinase. Tsc2(-/-) Eker rat embryonic fibroblasts expressed more prolactin receptor than did Tsc2(+/+) cells, and responded to prolactin with increased proliferation and activation of the same signaling pathways seen in vivo.Prolactin may be an important growth factor in the pathogenesis of lymphangioleiomyomatosis.

Dear Sir, Cutaneous melanoma is the most aggressive form of skin cancer and several families of receptor tyrosine kinases have been implicated in its development and progression, including the Eph receptor family (Hess et al., 2007; Smalley et al., 2009). Among Eph receptors, EphA2 has been most extensively studied in melanoma and linked to increased malignancy (Hess et al., 2007; Margaryan et al., 2009). The roles of other Eph receptors in melanoma progression, however, have not been extensively characterized. A recent study has shown that overexpression of EphB4 in murine B16 melanoma cells (which do not express the preferred EphB4 ligand, ephrin-B2) decreases the survival of ephrin-B2-positive tumor endothelial cells, suggesting that EphB4 may function as a tumor suppressor in melanoma by inhibiting angiogenesis (Huang et al., 2007). However, the widespread expression EphB4 in human cancers (Pasquale, 2010), including melanomas (Figure S1), suggests a possible positive role in tumor progression. Our previous work showed that EphB4 promotes the migratory ability of a series of murine melanoma cell lines (Yang et al., 2006). SW1 and C19 represent distinctive clones derived from the same parental cell line. The more aggressive SW1 cells express high levels of EphB4 and have high migratory ability, whereas the less aggressive C19 cells have low EphB4 levels and migrate poorly. The two cell lines similarly express the ephrin-B2 ligand. We previously reported that EphB4 endogenously co-expressed with ephrin-B2 in SW1 cells or transiently transfected in C19 cells promotes cell migration in vitro by activating the RhoA GTPase, thus inducing actin cytoskeleton reorganization. Here we show that EphB4 co-expression with ephrin-B2 also promotes SW1 and C19 cell growth in vitro and tumor growth in vivo. We generated 4 stable C19 clones overexpressing EphB4 (C19-EphB4) as well as SW1 and C19 clones expressing EGFP (SW1 and C19; Figures 1A and S2A) and examined their proliferation by measuring BrdU incorporation and apoptosis by Hoechst nuclear staining. SW1 cells, which express high levels of endogenous EphB4, proliferate faster and exhibit less apoptosis compared to C19 cells. The C19-EphB4 clones, where the transfected EphB4 is expressed at levels similar to those in the SW1 clones, have proliferation and apoptotic rates comparable to the SW1 cells (Figures 1B,C and S2B,C). These results show that coexpression of EphB4 with ephrin-B2 promotes melanoma cell proliferation and survival in vitro. To investigate the in vivo role of EphB4 in melanoma growth, we used the stable clones to generate tumors in a mouse xenograft model. The SW1 and C19-EphB4 tumors grew faster than the C19 tumors over a period of 4.7 weeks, while there was no significant difference in body weight between the 3 groups of mice (Figure S2D). Enhancement of melanoma tumor growth by EphB4 was confirmed by injecting a mixture of 3 additional SW1, C19 or C19-EphB4 clones and measuring tumor growth for 7.5 weeks (Figure 1D). Several lung metastases were observed at 7.5 weeks in the mice bearing SW1 tumors, but not in the ones with either C19 or C19-EphB4 tumors (data not shown), suggesting that high EphB4 expression alone may not be sufficient to promote the formation of detectable metastases. Figure 1 EphB4 promotes melanoma cell proliferation and inhibits apoptosis in vitro and promotes melanoma tumor growth in vivo. (A) EphB4 expression levels in 3 SW1, C19 and C19-EphB4 clones (data for clone #1 are shown in Figure S2). Lysates were probed by immunoblotting ... Figure 2 EphB4 upregulates Erk and Akt phosphorylation and Bcl-2 expression, and promotes blood vessel enlargement in melanoma tumors. (A) EphB4 immunoprecipitates from tumors grown for 7.5 weeks were probed for phosphotyrosine (pTyr) and reprobed for EphB4. The ... To investigate the signaling pathways that promote the growth of melanoma cells expressing high EphB4 levels, we first assessed EphB4 tyrosine phosphorylation as an indication of receptor activation. This revealed that EphB4 is substantially activated in the SW1 and C19-EphB4 tumors (Figure 2A), consistent with the reported expression of the ephrin-B2 ligand in both SW1 and C19 cells and the extensive cell-cell contacts present in the 3-dimensional tumor environment (Yang et al., 2006). We then examined the effects of EphB4 expression on the activation of the Erk1/2 and the Akt kinases, which are known to play a critical role in melanoma cell transformation, survival and proliferation (Gray-Schopfer et al., 2007; Lopez-Bergami et al., 2008). We detected significantly higher levels of Erk1/2 phosphorylation at threonine 202 and tyrosine 204 and Akt phosphorylation at serine 473 in SW1 and C19-EphB4 tumors compared to C19 tumors, indicating increased activation of Erk1/2 and Akt (Figure 2B,C). We also detected higher levels of the anti-apoptotic protein Bcl-2 in the SW1 and C19-EphB4 tumors than the C19 tumors (Figure 2D). The higher Erk1/2 and Akt activity (which are consistent with the EphB4-dependent activation of Akt previously observed in breast cancer and endothelial cells (Steinle et al., 2002; Kumar et al., 2006)) and the higher Bcl-2 expression, would all be expected to contribute to the faster growth of tumors expressing activated EphB4. Besides cell proliferation and apoptosis, angiogenesis is another important event that contributes to tumor progression. Given that EphB4 can activate reverse signaling through ephrin-B2 on adjacent endothelial cells to promote angiogenesis and blood vessel remodeling (Pasquale, 2010), we also examined the effects of EphB4 on tumor vascularization. Quantitative analysis of CD31-stained tumor sections revealed that the blood vessels were significantly larger in both SW1 and C19-EphB4 tumors than in C19 tumors at both 4.7 weeks and 7.5 weeks (Figures 2E and S3A). No significant difference was observed in blood vessel densities between the 3 groups, although more blood vessels were formed over the same time period in the tumors expressing EphB4, given the larger size of these tumors. To verify that the vascular differences observed were not due to the different tumor sizes, we also examined tumors of similar size, which were collected at different times after melanoma cell injection. SW1 and C19-EphB4 tumors similar in size to the C19 tumors also had larger blood vessels (Fig. S3B). These data suggest that EphB4 expression causes blood vessel growth and enlargement in SW1 and C19-EphB4 melanoma tumors. If increased vascularization in EphB4-expressing tumors supports faster growth of tumor cells, this would result in larger tumors with similar vascular densities (Kerbel and Folkman, 2002). Although EphB4 promotes SW1 and C19 melanoma cell malignancy, this receptor has been reported to suppress tumorigenicity in breast and colorectal cancer cells (Pasquale, 2010). These divergent activities may depend in part on whether the ephrin-B2 ligand is co-expressed and persistently activates the receptor and on other contextual factors. In addition, ephrin-B2 can also transduce signals through its cytoplasmic domain, which are known as reverse signals and are triggered by binding to Eph receptors (Pasquale, 2010; Meyer et al., 2005). Since both EphB4 and ephrin-B2 are present in SW1 and C19-EphB4 cells, we cannot exclude that some of the tumor promoting effects observed could be due to ephrin-B2 reverse signaling. In conclusion, we show that besides promoting RhoA-dependent migration (Yang et al., 2006), EphB4 can promote the growth of melanomas expressing the ephrin-B2 ligand by stimulating proliferation, survival and angiogenesis. Our findings suggest that upregulation of EphB4 receptor expression can play a role in melanoma progression, particularly in tumors where Erk and/or Akt are not highly activated by mutations.

S179D prolactin (S179D PRL) is a pseudophosphorylated form of human PRL which has potent antitumor and anti-angiogenic activities in vivo. This molecule binds to the same forms of the PRL receptor (PRLR) as unmodified PRL, yet this binding results in different intracellular signaling and biological end points. Since it is now clear that PRLRs are predimerized and therefore that ligand binding must initiate signaling by inducing a conformational change in the receptor dimer, we hypothesized that S179D PRL had an altered conformation compared to unmodified PRL. The conformation of the ligand-receptor ternary complex would therefore also have an altered conformation, and thus, different signaling molecules would be activated. Here we present evidence in support of this hypothesis by demonstrating, in contrast to unmodified PRL, that S179D PRL has reduced nickel and zinc binding capacity and a higher affinity for heparin and DEAE. Conformational changes have occurred since these features are counterintuitive on the basis of the simple substitution of a serine with a negatively charged aspartate residue. To demonstrate that these particular properties of S179D PRL were not due to misfolding of the molecule during production, S179D PRL was expressed in two different mammalian cell lines. Also investigated was the potential for production of S179D PRL as a soluble cytoplasmic, or secreted periplasmic, protein in Escherichia coli.

Using spacers between the C-termini of the long (LF) or short (SF) human prolactin receptors and luciferase/GFP such that bioluminescence resonance energy transfer (BRET) occurred minimally in intact versions of these receptors in the absence of ligand, we have monitored the BRET signal after deletion of regions of the extracellular domain (ECD). Deletion of S2 produced ligand-independent BRET for only those pairings normally occurring in the presence of ligand with the intact receptor. Deletion of the similarly sized S1, or S1 plus S2, produced no ligand-independent or -dependent BRET. When deleted receptors were transfected into human breast (T47D) or prostate (DU145) cancer cells incubated in the absence of added prolactin (PRL) and presence of anti-PRL, expression of the DeltaS2LF resulted in increased cell number, whereas expression of the intact receptor did not. When endogenous beta-casein expression was examined in T47D cells, the DeltaS2LF and DeltaS2F1a both showed ligand-independent activation of transcription, again not duplicated by the intact receptor. Paired with evidence in the literature for predimerization of PRLRs, these results demonstrate that altered ECD conformation, and not just a change in bulk, produces altered conformation of the intracellular signaling region of the receptors, supporting the concept that ligand binding to the ECD of intact predimerized receptors could initiate signaling. In addition, the current work supports a dual proliferative and differentiative role for the LF receptor, but only a differentiative role for the SF1a receptor. Naturally occurring DeltaS2 PRL receptors (PRLR) were also found in normal and cancerous human cells. This additionally suggests a heretofore unappreciated ligand-independent role for PRLRs.

The rabbit lacrimal gland undergoes an immunophysiological transformation during pregnancy, reminiscent of that of the mammary gland as it prepares to deliver secretory IgA into the nascent fluid product. The contents of TGF-beta and prolactin (PRL) within ductal epithelial cells increase, and their primary localizations shift from the apical to the basal cytoplasm, suggesting a transformation from exocrine to paracrine secretion. Studies with ex vivo acinar cell models demonstrated that elevated PRL suppresses traffic of secretory proteins into the regulated exocrine apparatus and directs them into a novel, induced, regulated paracrine apparatus [Wang, Y., Chiu, C.T., Nakamura, T., Walker, A.M., Petridou, B., Trousdale M.D., Hamm-Alvarez S.F., Schechter J.E., Mircheff A.K., 2007. Elevated prolactin redirects secretory vesicle traffic in rabbit lacrimal acinar cells. Am. J. Physiol. Endocrinol. Metab. 292, E1122-E1134]. However, it was not clear whether PRL itself entered the induced paracrine apparatus. In the present study, confocal immunofluorescence microscopy revealed that natively expressed PRL and over-expressed PRL co-localized with PRL receptors (PRLR); rab11, a marker for the recycling endosome; gamma-adaptin, a marker for the Golgi complex and trans-Golgi network; and rab7, a marker for the autophagic lysosomal apparatus. Natively expressed, over-expressed, and endocytosed PRL also co-localized with rab4 and rab5A, markers for the early endosome, and with rab3D, a marker for regulated exocrine secretory vesicles. Endocytosed PRL was stored in intact form and released in response to stimulation with carbachol. Subcellular fractionation analysis detected relative excesses of PRL over PRLR in fractions that contained fragments of the recycling endosome and fractions that contained both secretory vesicle fragments and prelysosomal and autolysosomal fragments. EM-gold microscopy demonstrated PRL within small vesicles, consistent with endosomes or secondary lysosomes, and in large vesicles, consistent with regulated secretory vesicles. The secretory vesicles were preponderantly localized in the apical cytoplasm of control cells, and in the basal cytoplasm of PRL over-expressing cells. These results indicate that when lacrimal epithelial cells synthesize PRL, and when they endocytose it from their ambient medium, they traffic it both into the endosomes that constitute the constitutive transcytotic paracrine apparatus and also into regulated secretory vesicles, which are associated with the exocrine apparatus at low PRL levels and with the induced paracrine apparatus at high PRL levels.

Glioblastoma multiforme is an extremely aggressive and invasive form of central nervous system tumor commonly treated with the chemotherapeutic drug Temozolomide. Unfortunately, even with treatment, the median survival time is less than 12 months. 2,9-Di- sec-butyl-1,10-phenanthroline (SBP), a phenanthroline-based ligand originally developed to deliver gold-based anticancer drugs, has recently been shown to have significant antitumor activity in its own right. SBP is hypothesized to initiate tumor cell death via interaction with non-DNA targets, and considering most glioblastoma drugs kill tumors through DNA damage processes, SBP was tested as a potential novel drug candidate against glial-based tumors. In vitro studies demonstrated that SBP significantly inhibited the growth of rodent GL-26 and C6 glioma cells, as well as human U-87, and SW1088 glioblastomas/astrocytomas. Furthermore, using a syngeneic glioma model in mice, in vivo administration of SBP significantly reduced tumor volume and increased survival time. There was no significant toxicity toward nontumorigenic primary murine and human astrocytes in vitro, and limited toxicity was observed in ex vivo tissues obtained from noncancerous mice. Terminal deoxynucleotidyl transferase dUTP nick end labeling staining and recovery assays suggest that SBP induces apoptosis in gliomas. This exploratory study suggests SBP is effective in slowing the growth of tumorigenic cells in the brain while exhibiting limited toxicity to normal cells and tissues and should therefore be further investigated for its potential in glioblastoma treatment.

We have demonstrated that S179D prolactin (PRL) is potently antiangiogenic in vivo. Here, we examined apoptosis in human endothelial cells, using procaspase-8 and cytochrome c release as markers of the extrinsic and intrinsic pathways, respectively. Both pathways converge at caspase-3, which is responsible for cleavage of DNA fragmentation factor (DFF45). A 3-d incubation in 50 ng/ml S179D PRL quadrupled the number of early apoptotic cells; this effect was doubled at 100 ng/ml and became maximal at 500 ng/ml. DFF45 and procaspase 8 cleavage were detectable at 100 ng/ml. Cytochrome c, however, was unaffected until 500 ng/ml. The p21 increased at 24 h, whereas a change in p53 required both triple the time and higher doses. The p21 promoter activity was maximal at 50 ng/ml, whereas 500 ng/ml were required to see a significant change in the Bax promoter (a measure of p53 activity). Because S179D PRL and basic fibroblast growth factor (bFGF) have both been shown to activate ERK, the effect of S179D PRL on bFGF-induced ERK signaling was examined. S179D PRL blocked ERK phosphorylation in response to bFGF, whereas continued coincubation caused a delayed and prolonged activation of ERK. PD98059 inhibited this delayed activation of ERK and effects of S179D PRL on all measures except p53 levels or activity of the Bax promoter. We conclude that S179D PRL blocks bFGF-induced ERK signaling and yet uses ERK in a different time frame to elevate p21 and activate the extrinsic pathway. Prolonged incubations and high concentrations additionally activate the intrinsic pathway using an alternate intracellular signal.

Increasing evidence suggests an important role for autocrine/paracrine prolactin in breast and prostate cancers and other disease states. Prolactin production in these extrapituitary sites is not governed by dopamine agonists, a finding that has spurred the production of prolactin receptor antagonists. This review focuses on one such antagonist, S179D prolactin, which was produced by mimicking a natural antagonist, phosphorylated prolactin. S179D prolactin is a very effective growth antagonist, partly because it inhibits signalling from unmodified prolactin and partly because it produces its own intracellular signal. This signal results in cell differentiation, cell-cycle arrest or apoptosis depending on dose, duration of treatment and cellular context. S179D prolactin is also a potent antiangiogenic and initial studies have shown it to be a potent anti-inflammatory agent. In light of these additional modes of action, it is suggested that S179D prolactin should now be more aptly referred to as a selective prolactin receptor modulator.

Prolactin (PRL) and GH have two distinct binding sites (site 1 with high affinity; site 2 with low affinity) that each interact with a PRL receptor (PRLR) to form a functional receptor dimer that activates signal transduction. The G129R mutation in PRL and the G120R mutation in GH disrupt the structural integrity of site 2 such that the ligands retain the ability to bind to the first receptor with high affinity, but act as receptor antagonists. In this study, we examined the ability of monomeric and dimeric forms of these ligands, human (h) PRL and hGH, and their antagonists (hPRL-G129R and hGH-G120R) to 1) bind to PRLRs; 2) induce conformational changes in PRLRs; 3) activate signaling pathways associated with the PRLR; and 4) mediate cell proliferation in vitro. In contrast to monomeric hPRL-G129R, homodimeric hPRL-G129R induced PRLR dimerization; activated Janus family of tyrosine kinases 2/signal transducer and activator of transcription 5, Ras/Raf/MAPK kinase/Erk, and phosphatidylinositol 3-kinase/Akt signaling; and stimulated Nb2 cell proliferation. Similarly, homodimeric hGH-G120R was able to mediate signaling via the PRLR and to stimulate Nb2 cell proliferation. These experiments demonstrate that a ligand must have two functional binding sites, but that these may be site 1 plus site 2 or two site 1’s, to elicit receptor-mediated signal transduction. The size of the ligand plays less of a role in receptor activation, suggesting that the extracellular portion of the PRLR (and possibly the GH receptor) is rather flexible and can accommodate larger ligands. These findings may have implications for designing multifunctional therapeutics that target this class of cytokine receptors.

S179D prolactin (PRL) is an experimentally useful mimic of naturally phosphorylated human prolactin. S179D PRL, but not unmodified PRL, was found to be anti-angiogenic in both the chorioallantoic membrane and corneal assays. Further investigation using human endothelial in vitro models showed reduced cell number, reduced tubule formation in Matrigel, and reduced migration and invasion, as a function of treatment with S179D PRL. Analysis of growth factors in human endothelial cells in response to S179D PRL showed: a decreased expression or release of endogenous PRL, heme-oxygenase-1, basic fibroblast growth factor (bFGF), angiogenin, epidermal growth factor and vascular endothelial growth factor; and an increased expression of inhibitors of matrix metalloproteases. S179D PRL also blocked signaling from bFGF in these cells. We conclude that this molecular mimic of a pituitary hormone is a potent anti-angiogenic protein, partly as a result of its ability to reduce utilization of several well-established endothelial autocrine growth loops, partly by its ability to block signaling from bFGF and partly because of its ability to decrease endothelial migration. These findings suggest that circulating levels of phosphorylated PRL may influence the progression of cancer and, furthermore, that S179D PRL may be a useful anti-angiogenic therapeutic.

Prolactin (PRL) is a hormone that contributes to both the growth and differentiation of mammary epithelial cells, activities likely to impact breast cancer in opposite ways. Whether PRL causes growth or differentiation has been solely attributed to the coexisting steroidal environment, with PRL stimulating mammary gland growth during pregnancy, and then milk production after the postpartum drop in estrogen and progesterone. However, previous work from our laboratory has shown that the form of PRL may also be an important factor. During pregnancy, unmodified PRL (U-PRL) promotes mammary growth, while an increase in phosphorylated PRL, or administration of a molecular mimic of phosphorylated PRL (S179D PRL), inhibits growth. Unknown, however, is whether these forms of PRL have opposite effects on growth in the absence of steroids and whether effects are directly on mammary epithelial cells. To mimic the glandular epithelium in vitro, we used contact-inhibited, differentiated cells and showed that even with these minimally growing cells that treatment with U-PRL caused increased expression of cyclin D1 and cyclin-dependent kinase 4, increased activity of both cdk4 and cdk2, while having no effect on the inhibitory protein, p21. S179D PRL, by contrast, had no effect on cyclin D1 and cdk4 expression, but increased p21 expression and expression of the vitamin D receptor (VDR). We conclude that increased U-PRL or decreased phosphorylated PRL can directly affect cell cycle control proteins in relatively differentiated mammary epithelial cells, thereby implicating the balance between these two forms of PRL in the early promotion of breast cancer.

The effects of two major forms of prolactin (PRL) were examined on delayed type hypersensitivity (DTH) responses to Candida albicans . Unmodified PRL (U-PRL) had no effect on the DTH response, whereas a molecular mimic of phosphorylated PRL (S179D PRL) significantly inhibited immune responses to this robust antigen. This effect of S179D PRL was not accompanied by gross alterations in splenic T cell numbers, CD4 / CD8 ratios, or T and B cell activation markers, but did produce a decrease in splenocyte apoptosis. Using gld animals, Fas ligand (FasL) was implicated in the suppressive effects of S179D PRL. Circulating IgG 1 and IgG 2 antibody levels were increased in response to treatment with both forms of PRL, but the effects of S179D PRL were most pronounced. Cytokine changes in the popliteal lymph nodes specific to S179D PRL treatment showed an inhibition of pro-inflammatory cytokines. In conclusion, mice treated with a molecular mimic of phosphorylated prolactin showed a profound inhibition of DTH responses to Candida correlating with an absence of GM-CSF, IL-4, and IL-13 production and a marked reduction in IL-12p70 synthesis.

In this study, we further investigated the mechanisms by which pseudophosphorylated prolactin (S179D PRL) inhibits the growth of human prostate cancer cells. When treated with S179D PRL for 3 days, LnCAP cells responded by increasing expression of the vitamin D receptor (VDR) and the cell cycle regulatory molecule, p21, whereas PC3 and DU145 cells did not. After 5 days of treatment, both PC3 and DU145 cells responded. Untreated LnCAP cells express the short 1b form (SF1b) of the human prolactin receptor, but DU145 and PC3 cells express only low amounts of this receptor until elevated by treatment with S179D PRL. DU145 and PC3 cells become sensitive to the negative effects of S179D PRL on cell number after induction of the SF1b. Transfection of either SF1b or SF1a into PC3 or DU145 cells made them sensitive to S179D PRL in the 3-day time frame, a finding that was not duplicated by transfection with the long form of the receptor. Treatment of LnCAP cells with S179D PRL increased long-term activation of extracellular signal-regulated kinase 1/2 (ERK1/2). This did not occur in PC3 and DU145 cells until transfection with SF1a/SF1b. Blockade of ERK signaling eliminated S179D PRL-stimulated expression of the VDR and p21 in LnCAP cells and transfected PC3 and DU145 cells. We conclude that initiation of alternative splicing to produce SF1b, and subsequent altered signaling, contribute to the growth inhibitory mechanisms of S179D PRL. This is the first indication of a role for short prolactin receptors in the regulation of cell proliferation.

Posttranslational modifications of prolactin (PRL), including phosphorylation, vary with physiologic state and alter biologic activity. In light of the growing evidence for a role for PRL in proliferation in mammary cancer, we examined the ability of a mimic of phosphorylated human PRL, S179D-PRL, to initiate signals to several pathways in mammary tumor cells alone and in combination with unmodified PRL. Unmodified PRL employed multiple pathways to increase cellular proliferation and cyclin D1 levels in PRL-deficient MCF-7 cells. S179D-PRL was a weak agonist compared with unmodified PRL with regard to cellular proliferation, cyclin D1 levels, and phosphorylation of signal transducer and activator of transcription 5 and ERKs. However, S179D-PRL was a potent antagonist of unmodified PRL to these endpoints. In contrast to the reduced levels of the long isoform of the PRL receptor observed in response to a 3-d incubation with unmodified PRL, S179D-PRL up-regulated expression of this isoform, 4-fold. These studies support the utility of this mutant as a PRL antagonist to proliferative signals in mammary epithelial cells, including a potential role in breast cancer therapeutics.

Previous work has shown that naturally phosphorylated prolactin antagonizes the growth-promoting activities of unmodified prolactin (U-PRL) and that this effect is duplicated by a molecular mimic, S179D PRL. At the same time, the S179D PRL is a superagonist with regard to expression of some PRL-regulated genes. We have asked whether the different activities of U-PRL and S179D PRL are the result of differential signaling. HC11 cells (a normal mouse mammary cell line) were grown to confluence, primed with hydrocortisone, and then exposed to the PRLs. A 15 min incubation of PRL-naive cells led to substantial tyrosine phosphorylation of Jak 2 and Stat 5a by U-PRL and an essentially equivalent Jak 2 activation by S179D PRL. The latter, however, was accompanied by reduced tyrosine phosphorylation of Stat 5a. EMSA analysis using a Stat 5 binding site showed both PRLs to cause equivalent binding of nuclear proteins and that most of what bound was complexed through Stat 5a. Phosphoamino acid analysis of Stat 5 showed S179D PRL to double the amount of serine phosphorylation versus that seen with U-PRL. Analysis of the MAP kinase pathway showed U-PRL capable of activation of ERKs 1 and 2 but that signaling via ERKs 1 and 2 was greater with S179D PRL. A 7-day incubation in either PRL increased beta-casein mRNA levels, but S179D PRL caused a 2-fold increase over that seen with U-PRL. The increase, over that seen with U-PRL, was blocked by the MAP kinase inhibitor, PD98059. After 7 days of treatment with S179D PRL, expression of the short PRL receptor was doubled, and signaling showed a greater dependence on the MAP kinase pathway (2.9-fold increase in ERK 1 and 2 activation). We conclude that although both PRLs use both pathways to some extent, U-PRL signals primarily through Jak 2-Stat 5 whereas S179D PRL signals primarily through the MAP kinase pathway especially after prolonged exposure. This is the first demonstration of differential involvement of signaling pathways by different forms of PRL.

There have been few studies aimed at determining the effects of maternal peptide hormones on the developing fetus and even fewer aimed at determining the long-term consequences of abnormalities in maternal hormone exposure. In this study, we have examined the effect of maternal prolactin (PRL) on the production, seeding and long-term function of a T lymphocyte subset for which the precursors are only present during fetal life. Using this system, we can determine long-term consequences of maternal hormone exposure without concern for the subsequent influence of the offspring's endocrine milieu. Recombinant versions of the two major forms of the pituitary hormone, PRL, were administered to rats throughout pregnancy. Administration of a molecular mimic of phosphorylated PRL (PP-PRL) resulted in a marked increase in the level of apoptosis in the thymus of newborn pups, an effect that was not duplicated by administration of unmodified PRL. The increased thymic apoptosis in the animals exposed to PP-PRL resulted in decreased epidermal seeding of gammadeltaT cells and a markedly decreased gammadeltaT cell-modulated epidermal response in the offspring. This decreased gammadeltaT cell modulated response persisted to adulthood. We conclude that maternal PRL composition during pregnancy can have a permanent effect on at least one component of the developing immune system.

We have investigated the individual roles of unmodified prolactin (U-PRL) and a mimic of phosphorylated PRL (S179D PRL) in mammary development. Recombinant versions of the PRLs were delivered to rats throughout pregnancy at a rate of 6 microg/24 h per rat and to non-pregnant females at a rate of 24 microg/24 h per rat. Measurement of progesterone, corticosterone, and estradiol showed no effect of the administered PRLs on the levels of these other mammotropic hormones. Histological and morphometric analysis showed U-PRL to cause mammary growth, whereas S179D PRL inhibited growth. Molecular analysis demonstrated decreased beta-casein expression in the mammary glands of the U-PRL-treated animals at term and increased beta-casein expression in the mammary glands of the S179D PRL-treated animals. Superior beta-casein gene expression in response to S179D PRL versus U-PRL was confirmed in HC11 cells. We conclude that U-PRL is important for growth, whereas S179D PRL promotes at least one measure of differentiated function in the mammary gland.

The clinical relevance and prognostic significance of tumor-infiltrating Tregs in different types of cancers makes them appealing therapeutic targets. However, targeting all Tregs initiates autoimmune disease. In the current study, we have found that knockdown of the long form of the prolactin receptor (LFPRLR) inhibits the function of tumor Tregs with no functional change in peripheral Tregs. Knockdown of the LFPRLR was by splice modulating oligomer (SMO), tested in the syngeneic 4T1-Balb/c immune-competent breast cancer model. Similar effects would be predicted to occur in prostate and ovarian cancer. Knockdown reduced tumor output of CCL17, a chemokine regulated by the major LFPRLR signaling Jak2/Stat5 pathway. Reduced CCL17 output in turn resulted in impaired Treg recruitment into tumors, allowing enhanced CD4+ and CD8+ T cell activities within the tumor and reducing metastasis to distal organs. Also observed was a reduction in Tregs at metastatic sites. RNAseq transcriptomic analysis of LFPRLR SMO-treated tumor Tregs revealed that among immune-suppressive cytokines, expression of IL-10 and TGF-β was not affected, but EBI3, a component of IL-35, became undetectable. Of cytokines known to promote metastasis, IL-6, IL23a and IL34 were reduced. When tumor Tregs, isolated from LFPRLR SMO-treated animals, were co-cultured with 4T1 breast cancer cells, they failed to drive epithelial to mesenchymal transition, while tumor Tregs isolated from control SMO-treated animals did transform 4T1 cells into a more mesenchymal phenotype. Although tumor T regs were reduced by treatment, other major components of the tumor microenvironment, including B cells, CD8+ T cells, macrophages, NK T cells, dendritic cells, myeloid-derived suppressor cells, and fibroblasts were not changed by LFPRLR knockdown, while effector CD4+ T cells were increased and tumor endothelial cells were decreased. Although the population of CD8+ T cells was not changed, their activity was enhanced, as determined by their production of IL-2 and IFN-γ when stimulated. Examination of splenic Tregs from animals treated with LFPRLR- or control SMO for 28 days showed normal suppressive activity of anti-CD3-stimulated T cell proliferation. In conclusion, systemic LFPRLR knockdown has direct and indirect effects on tumor Tregs that modify their cytokine profile and reduce their suppressive capability and ability to drive epithelial to mesenchymal transition of tumor cells. Citation Format: Kuan-Hui E. Chen, Ameae Walker. Phenotypic change specific to tumor-infiltrating regulatory T cells by LFPRLR knockdown [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-211. doi:10.1158/1538-7445.AM2017-LB-211

We have identified a new variant of human Stat5a, found at higher ratios to full-length Stat5a in invasive ductal carcinoma versus contiguous normal tissue. The variant, missing exon 5, inhibits p21 and Bax production and increases cell number. After prolactin stimulation, only full-length Stat5a interacts with the vitamin D and retinoid X receptors, whereas only Δ5 Stat5a interacts with activating protein 1–2 and specificity protein 1. Prolactin also oppositely regulates interaction of the two Stat5a forms with β-catenin. We propose that a change in splicing leading to upregulation of this new isoform is a pathogenic aspect of invasive ductal carcinoma.

Prolactin (PRL) is a pituitary polypeptide hormone characterized by multiple biological actions including stimulation of growth in the prostate and formation of secretory alveoli and stimulation of milk protein gene expression in the mammary gland. PRL exerts its effect by dimerizing its receptor (PRLR) on the plasma membrane and regulating gene expression through the JAK-Stat signal pathway. We have previously described a natural variant of the PRLR in which the S2 subdomain of the extracellular domain is missing (Delta S2). Delta S2 PRLRs are dimerized in the absence of PRL and have constitutive activity in the promotion of breast cancer cell growth. Enhancer of zeste homolog 2 (EZH2), as one of the histone-modifying enzymes, is a key factor regulating gene expression by epigenetic modification. We hypothesized that these constitutive activated Delta S2 PRLRs played a pathogenic role in breast cancer in part through alterations in the expression of EZH2 and the trimethylation of histone 3 on lysine 27 (H3K27Me3).In order to verify the clinical significance and to establish the link between Delta S2 PRLR expression and epigenetic change, EZH2, H3K27Me3, and Delta S2 PRLR were detected in both normal and cancerous human breast tissues. Also, overexpression of Delta S2 PRLR in breast epithelial cells was achieved by infection with adenovirus carrying the cDNA. Western blotting and chromatin immunoprecipitation (ChIP assay) and acid histone extraction were applied to detect the expression of EZH2 and the trimethylation of histone 3, respectively.In breast tissue, higher EZH2 expression and higher H3K27Me3 were found associated with higher Delta S2 expression in breast cancer samples. In breast epithelial cells, overexpression of Delta S2 PRLR increased EZH2 methyltransferase mRNA and protein, induced EZH2 methyltransferase recruitment to chromatin, increased the trimethylation of H3K27Me3, and decreased the expression of p53 gene.Delta S2 PRLR plays an important pathogenic role in breast cancer through epigenetic modification. Elevated expression of Delta S2 PRLR, achieved by alternate splicing of the pre-mRNA of the full-length form, is a new mechanism contributing to human breast cancer.