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Supplementary Figure 1 from Selective Inhibition of Growth of Tuberous Sclerosis Complex 2–Null Cells by Atorvastatin Is Associated with Impaired Rheb and Rho GTPase Function and Reduced mTOR/S6 Kinase Activity

Inactivating mutations in the tuberous sclerosis complex 2 (TSC2) gene, which encodes tuberin, result in the development of TSC and lymphangioleiomyomatosis (LAM). The tumor suppressor effect of tuberin lies in its GTPase-activating protein activity toward Ras homologue enriched in brain (Rheb), a Ras GTPase superfamily member. The statins, 3-hydroxy-3-methylglutaryl CoA reductase inhibitors, have pleiotropic effects which may involve interference with the isoprenylation of Ras and Rho GTPases. We show that atorvastatin selectively inhibits the proliferation of Tsc2−/− mouse embryo fibroblasts and ELT-3 smooth muscle cells in response to serum and estrogen, and under serum-free conditions. The isoprenoids farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP) significantly reverse atorvastatin-induced inhibition of Tsc2−/− cell growth, suggesting that atorvastatin dually targets a farnesylated protein, such as Rheb, and a geranylgeranylated protein, such as Rho, both of which have elevated activity in Tsc2−/− cells. Atorvastatin reduced Rheb isoprenylation, GTP loading, and membrane localization. Atorvastatin also inhibited the constitutive phosphorylation of mammalian target of rapamycin, S6 kinase, and S6 found in Tsc2−/− cells in an FPP-reversible manner and attenuated the high levels of phosphorylated S6 in Tsc2-heterozygous mice. Atorvastatin, but not rapamycin, attenuated the increased levels of activated RhoA in Tsc2−/− cells, and this was reversed by GGPP. These results suggest that atorvastatin may inhibit both rapamycin-sensitive and rapamycin-insensitive mechanisms of tuberin-null cell growth, likely via Rheb and Rho inhibition, respectively. Atorvastatin may have potential therapeutic benefit in TSC syndromes, including LAM. [Cancer Res 2007;67(20):9878–86]

Rho kinase (ROCK) is implicated in the development of pulmonary arterial hypertension (PAH) in which abnormal pulmonary vascular smooth muscle (VSM) contractility and remodeling lead to right heart failure. Pharmacologic ROCK inhibitors block experimental pulmonary hypertension (PH) development in rodents but can have off-target effects and do not distinguish between the two ROCK forms, ROCK1 and ROCK2, encoded by separate genes. An earlier study using gene knock out (KO) in mice indicated that VSM ROCK2 is required for experimental PH development, but the role of ROCK1 is not well understood. Here we investigated the in vivo role of ROCK1 in PH development by generating a VSM-targeted homozygous ROCK1 gene KO mouse strain. Adult control mice exposed to Sugen5416 (Su)/hypoxia treatment to induce PH had significantly increased right ventricular systolic pressures (RVSP) and RV hypertrophy versus normoxic controls. In contrast, Su/hypoxia-exposed VSM ROCK1 KO mice did not exhibit significant RVSP elevation, and RV hypertrophy was blunted. Su/hypoxia-induced pulmonary small vessel muscularization was similarly elevated in both control and VSM ROCK1 KO animals. siRNA-mediated ROCK1 knock-down (KD) in human PAH pulmonary arterial SM cells (PASMC) did not affect cell growth. However, ROCK1 KD led to reduced AKT and MYPT1 signaling in serotonin-treated PAH PASMC. The findings suggest that like VSM ROCK2, VSM ROCK1 actively contributes to PH development, but in distinction acts via nonproliferative pathways to promote hypoxemia, and thus may be a distinct therapeutic target in PH.

Abnormalities that characterize pulmonary arterial hypertension include impairment in the structure and function of pulmonary vascular endothelial and smooth muscle cells. Aldosterone levels are elevated in human pulmonary arterial hypertension and in experimental pulmonary hypertension, while inhibition of the aldosterone-binding mineralocorticoid receptor attenuates pulmonary hypertension in multiple animal models. We explored the role of mineralocorticoid receptor in endothelial and smooth muscle cells in using cell-specific mineralocorticoid receptor knockout mice exposed to sugen/hypoxia-induced pulmonary hypertension. Treatment with the mineralocorticoid receptor inhibitor spironolactone significantly reduced right ventricular systolic pressure. However, this is not reproduced by selective mineralocorticoid receptor deletion in smooth muscle cells or endothelial cells. Similarly, spironolactone attenuated the increase in right ventricular cardiomyocyte area independent of vascular mineralocorticoid receptor with no effect on right ventricular weight or interstitial fibrosis. Right ventricular perivascular fibrosis was significantly decreased by spironolactone and this was reproduced by specific deletion of mineralocorticoid receptor from endothelial cells. Endothelial cell-mineralocorticoid receptor deletion attenuated the sugen/hypoxia-induced increase in the leukocyte-adhesion molecule, E-selectin, and collagen IIIA1 in the right ventricle. Spironolactone also significantly reduced pulmonary arteriolar muscularization, independent of endothelial cell-mineralocorticoid receptor or smooth muscle cell-mineralocorticoid receptor. Finally, the degree of pulmonary perivascular inflammation was attenuated by mineralocorticoid receptor antagonism and was fully reproduced by smooth muscle cell-specific mineralocorticoid receptor deletion. These studies demonstrate that in the sugen/hypoxia pulmonary hypertension model, systemic-mineralocorticoid receptor blockade significantly attenuates the disease and that mineralocorticoid receptor has cell-specific effects, with endothelial cell-mineralocorticoid receptor contributing to right ventricular perivascular fibrosis and smooth muscle cell-mineralocorticoid receptor participating in pulmonary vascular inflammation. As mineralocorticoid receptor antagonists are being investigated to treat pulmonary arterial hypertension, these findings support novel mechanisms and potential mineralocorticoid receptor targets that mediate therapeutic benefits in patients.

Tissue matrix remodeling and fibrosis leading to loss of pulmonary arterial and right ventricular compliance are important features of both experimental and clinical pulmonary hypertension (PH). We have previously reported that transglutaminase 2 (TG2) is involved in PH development while others have shown it to be a cross-linking enzyme that participates in remodeling of extracellular matrix in fibrotic diseases in general. In the present studies, we used a mouse model of experimental PH (Sugen 5416 and hypoxia; SuHypoxia) and cultured primary human cardiac and pulmonary artery adventitial fibroblasts to evaluate the relationship of TG2 to the processes of fibrosis, protein cross-linking, extracellular matrix collagen accumulation, and fibroblast-to-myofibroblast transformation. We report here that TG2 expression and activity as measured by serotonylated fibronectin and protein cross-linking activity along with fibrogenic markers are significantly elevated in lungs and right ventricles of SuHypoxic mice with PH. Similarly, TG2 expression and activity, protein cross-linking activity, and fibrogenic markers are significantly increased in cultured cardiac and pulmonary artery adventitial fibroblasts in response to hypoxia exposure. Pharmacological inhibition of TG2 activity with ERW1041E significantly reduced hypoxia-induced cross-linking activity and synthesis of collagen 1 and α-smooth muscle actin in both the in vivo and in vitro studies. TG2 short interfering RNA had a similar effect in vitro. Our results suggest that TG2 plays an important role in hypoxia-induced pulmonary and right ventricular tissue matrix remodeling in the development of PH.

The pathophysiology of pulmonary hypertension (PH) and heart failure (HF) includes fibrogenic remodeling associated with loss of pulmonary arterial (PA) and cardiac compliance. We and others have previously identified that transglutaminase 2 (TG2) as a participant in adverse fibrogenic remodeling. However, little is known about the biologic mechanisms that regulate TG2 function. We examined physiological mouse models of experimental PH, HF and type 1 diabetes that are associated with altered glucose metabolism/ glycolysis and report here that TG2 expression and activity are elevated in pulmonary and cardiac tissues under all these conditions. We additionally used PA adventitial fibroblasts to test the hypothesis that TG2 is an intermediary between enhanced tissue glycolysis and fibrogenesis. Our in vitro results show that glycolytic enzymes and TG2 are up-regulated in fibroblasts exposed to high glucose, which stimulates cellular glycolysis as measured by Seahorse analysis. We examined the relationship of TG2 to a terminal glycolytic enzyme, pyruvate kinase M2 (PKM2), and found that PKM2 regulates glucose -induced TG2 expression and activity as well as fibrogenesis. Our studies further show that TG2 inhibition blocks glucose-induced fibrogenesis and cell proliferation. Our findings support a novel role for glycolysis -mediated TG2 induction and tissue fibrosis associated with experimental PH, HF and hyperglycemia.

The ubiquitous α-catulin acts as a scaffold for distinct signalosomes including RhoA/ROCK; however, its function is not well understood. While α-catulin has homology to the cytoskeletal linkers α-catenin and vinculin, it appears to be functionally divergent. Here we further investigated α-catulin function in pulmonary vascular endothelial cells (VEC) on the premise that α-catulin has a unique cytoskeletal role. Examination of endogenous α-catulin intracellular localization by immunofluorescence revealed a highly organized cytosolic filamentous network suggestive of a cytoskeletal system in a variety of cultured VEC. Double-immunofluorescence analyses of VEC showed endogenous α-catulin co-localization with vimentin intermediate filaments. Similar to vimentin, α-catulin was found to distribute into detergent-soluble and -insoluble fractions. Treatment of VEC with withaferinA, an agent that targets vimentin filaments, disrupted the α-catulin network distribution and altered α-catulin solubility. Vimentin participates in cell migration, and withaferinA was found to inhibit VEC migration in vitro; similarly, α-catulin knock-down reduced VEC migration. Based on previous reports showing that ROCK modulates vimentin, we found that ROCK depletion attenuated VEC migration; furthermore, α-catulin depletion was shown to reduce ROCK-induced signaling. These findings indicate that α-catulin has a unique function in co-localization with vimentin filaments that contributes to VEC migration via a pathway that may involve ROCK signaling. J. Cell. Physiol. 231: 934-943, 2016. © 2015 Wiley Periodicals, Inc.

Contraction of human pulmonary artery smooth muscle cells (HPASMC) isolated from pulmonary arterial hypertensive (PAH) and normal (non-PAH) subject lungs was determined and measured with real-time electrical impedance. Treatment of HPASMC with vasoactive peptides, endothelin-1 (ET-1) and bradykinin (BK) but not angiotensin II, induced a temporal decrease in the electrical impedance profile mirroring constrictive morphological change of the cells which typically was more robust in PAH as opposed to non-PAH cells. Inhibition with LIMKi3 and a cofilin targeted motif mimicking cell permeable peptide (MMCPP) had no effect on ET-1 induced HPASMC contraction indicating a negligible role for these actin regulatory proteins. On the other hand, a MMCPP blocking the activity of caldesmon reduced ET-1 promoted contraction pointing to a regulatory role of this protein and its activation pathway in HPASMC contraction. Inhibition of this MEK/ERK/p90RSK pathway, which is an upstream regulator of caldesmon phosphorylation, reduced ET-1 induced cell contraction. While the regulation of ET-1 induced cell contraction was found to be similar in PAH and non-PAH cells, a key difference was the response to pharmacological inhibitors and to siRNA knockdown of Rho kinases (ROCK1/ROCK2). The PAH cells required much higher concentrations of inhibitors to abrogate ET-1 induced contractions and their contraction was not affected by siRNA against either ROCK1 or ROCK2. Lastly, blocking of L-type and T-type Ca2+ channels had no effect on ET-1 or BK induced contraction. However, inhibiting the activity of the sarcoplasmic reticulum Ca2+ ATPase blunted ET-1 and BK induced HPASMC contraction in both PAH and non-PAH derived HPASMC. In summary, our findings here together with previous communications illustrate similarities and differences in the regulation PAH and non-PAH smooth muscle cell contraction relating to calcium translocation, RhoA/ROCK signaling and the activity of caldesmon. These findings may provide useful tools in achieving the regulation of the vascular hypercontractility taking place in PAH.

Vimentin is a major intermediate filament protein in vascular endothelial cells which might be involved in their function as a barrier tissue. It is proposed to dynamically maintain integrity of the endothelium as a tightly regulated permeability barrier that is subjected to a variety of shear and contractile forces. The results described in this report demonstrate that vimentin plays that role through mechanisms that are dependent on its phosphorylation state. Withaferin A (WFA), a vimentin targeting drug is shown to disrupt endothelial barrier function through its effects on vimentin filament distribution and physical properties. These effects are related to WFA's ability to increase vimentin phosphorylation. Through overexpressing a non-phosphorylatable vimentin mutant we can block the effects of WFA on vimentin distribution and barrier permeability. The barrier augmentation effect appears to extend to endothelial cells that do not express detectable mutant vimentin which might suggest transmissible effects across cells. Blocking vimentin phosphorylation also protects the endothelial barrier against LPS endotoxin, implicating it as a target for drug development against pulmonary edema and acute respiratory distress syndrome (ARDS).

Previous studies in human patients and animal models have suggested that transglutaminase 2 (TG2) is upregulated in pulmonary hypertension (PH), a phenomenon that appears to be associated with the effects of serotonin (5-hydroxytryptamine; 5-HT) in this disease. Using chemical tools to interrogate and inhibit TG2 activity in vivo, we have shown that pulmonary TG2 undergoes marked post-translational activation in a mouse model of hypoxia-induced PH. We have also identified irreversible fluorinated TG2 inhibitors that may find use as non-invasive positron emission tomography probes for diagnosis and management of this debilitating, lifelong disorder. Pharmacological inhibition of TG2 attenuated the elevated right ventricular pressure but had no effect on hypertrophy of the right ventricle of the heart. A longitudinal study of pulmonary TG2 activity in PH patients is warranted.

This study aimed to characterize alterations in select eicosanoids in experimental and human pulmonary arterial hypertension (PAH) and to assess their potential utility as predictors of outcome. Using liquid chromatography-mass spectrometry, we performed targeted lipidomic analyses of the lungs and right ventricles (RVs) of chronically hypoxic rats and plasma of consecutive PAH patients and healthy controls. In rat lungs, chronic hypoxia was associated with significantly decreased lung prostacyclin (PGI2)/thromboxane B2 (TXB2) ratio and elevated lung 8-hydroxyeicosanoid (HETE) acid concentrations. RV eicosanoids did not exhibit any changes with chronic hypoxia. PAH treatment-naive patients had significantly increased plasma concentrations of TXB2 and 5-, 8-, 12-, and 15-HETE. The PGI2/TXB2 ratio was lower in PAH patients than in controls, especially in the treatment-naive cohort (median: 2.1, 0.3, and 1.3 in controls, treatment-naive, and treated patients, respectively, P = 0.001). Survival was significantly worse in PAH patients with 12-HETEhigh (≥57 pg/mL) and 15-HETEhigh (≥256 pg/mL) in unadjusted and adjusted analyses (hazard ratio [HR]: 2.8 [95% confidence interval (CI): 1.1-7.3], P = 0.04 and HR: 4.3 [95% CI: 1.6-11.8], P = 0.004, respectively; adjustment was performed with the REVEAL [Registry to Evaluate Early and Long-Term PAH Disease Management] risk score). We demonstrate significant alterations in eicosanoid pathways in experimental and human PAH. We found that 12- and 15-HETE were independent predictors of survival in human PAH, even after adjusting for the REVEAL score, suggesting their potential role as novel biomarkers.

Serotonin (5-hydroxytryptamine, 5-HT) is mitogenic for several cell types including pulmonary arterial smooth muscle cells (PASMC), and is associated with the abnormal vascular smooth muscle remodeling that occurs in pulmonary arterial hypertension. RhoA/Rho kinase (ROCK) function is required for 5-HT-induced PASMC mitogenesis, and 5-HT activates RhoA; however, the signaling steps are poorly defined. Rho guanine nucleotide exchange factors (Rho GEFs) transduce extracellular signals to Rho, and we found that 5-HT treatment of PASMC led to increased membrane-associated Lbc Rho GEF, suggesting modulation by 5-HT. Lbc knockdown by siRNA attenuated 5-HT-induced thymidine uptake in PASMC, indicating a role in PASMC mitogenesis. 5-HT triggered Rho-dependent serum response factor-mediated reporter activation in PASMC, and this was reduced by Lbc depletion. Lbc knockdown reduced 5-HT-induced RhoA/ROCK activation, but not p42/44 ERK MAP kinase activation, suggesting that Lbc is an intermediary between 5-HT and RhoA/ROCK, but not ERK. 5-HT stimulation of PASMC led to increased association between Lbc, RhoA, and the α-catulin scaffold. Furthermore, α-catulin knockdown attenuated 5-HT-induced PASMC thymidine uptake. 5-HT-induced PASMC mitogenesis was reduced by dominant-negative G(q) protein, suggesting cooperation with Lbc/α-catulin. These results for the first time define a Rho GEF involved in vascular smooth muscle cell growth and serotonin signaling, and suggest that Lbc Rho GEF family members play distinct roles. Thus, the Lbc/α-catulin axis participates in 5-HT-induced PASMC mitogenesis and RhoA/ROCK signaling, and may be an interventional target in diseases involving vascular smooth muscle remodeling.

Heterotrimeric Galpha12/13 signals induce cellular responses such as serum response element (SRE)-mediated gene transcription via Rho GTPase. Guanine nucleotide exchange factors (GEFs) are strong candidates for linking Galpha signals to Rho. For example, p115 RhoGEF transduces Galpha13 signals to Rho and inhibits Galpha12/13 signals via the RhoGEF LH domain which links to Galpha subunits. Here, we have evaluated the signaling capacity of Lbc RhoGEF in the context of Galpha12/13 signals. In vitro GEF assays indicate that baculoviral-expressed proto-Lbc has minimal exchange activity, implying that a stimulus is required for Lbc activity in vivo. Expression of a catalytically inactive proto-Lbc mutant in HEK293T cells attenuates Galpha12- and thrombin-induced activation of an SRE transcriptional reporter, and the levels of inhibition observed is similar to that obtained with an analogous p115 RhoGEF mutant. proto-Lbc mutant expression also led to decreased levels of Galpha12-induced RhoA activation in vivo. Complex formation between Galpha12 and Lbc forms was detected. Analysis of the Lbc peptide sequence reveals a previously undetected region which may link to Galpha subunit signals. These findings support a role for Lbc in Galpha12-induced signaling pathways to Rho.

The ubiquitous α-catulin acts as a scaffold for distinct signalosomes including RhoA/ROCK; however, its function is not well understood. While α-catulin has homology to the cytoskeletal linkers α-catenin and vinculin, it appears to be functionally divergent. Here we further investigated α-catulin function in pulmonary vascular endothelial cells (VEC) on the premise that α-catulin has a unique cytoskeletal role. Examination of endogenous α-catulin intracellular localization by immunofluorescence revealed a highly organized cytosolic filamentous network suggestive of a cytoskeletal system in a variety of cultured VEC. Double-immunofluorescence analyses of VEC showed endogenous α-catulin co-localization with vimentin intermediate filaments. Similar to vimentin, α-catulin was found to distribute into detergent-soluble and -insoluble fractions. Treatment of VEC with withaferinA, an agent that targets vimentin filaments, disrupted the α-catulin network distribution and altered α-catulin solubility. Vimentin participates in cell migration, and withaferinA was found to inhibit VEC migration in vitro; similarly, α-catulin knock-down reduced VEC migration. Based on previous reports showing that ROCK modulates vimentin, we found that ROCK depletion attenuated VEC migration; furthermore, α-catulin depletion was shown to reduce ROCK-induced signaling. These findings indicate that α-catulin has a unique function in co-localization with vimentin filaments that contributes to VEC migration via a pathway that may involve ROCK signaling. J. Cell. Physiol. 231: 934-943, 2016. © 2015 Wiley Periodicals, Inc.

Tissue transglutaminase 2 (TG2) is a multifunctional enzyme that cross-links proteins with monoamines such as serotonin (5-hydroxytryptamine, 5-HT) via a transglutamidation reaction, and is associated with pathophysiologic vascular responses. 5-HT is a mitogen for pulmonary artery smooth muscle cells (PASMCs) that has been linked to pulmonary vascular remodeling underlying pulmonary hypertension development. We previously reported that 5-HT-induced PASMC proliferation is inhibited by the TG2 inhibitor monodansylcadaverine (MDC); however, the mechanisms are poorly understood. In the present study we hypothesized that TG2 contributes to 5-HT-induced signaling pathways of PASMCs. Pre-treatment of bovine distal PASMCs with varying concentrations of the inhibitor MDC led to differential inhibition of 5-HT-stimulated AKT and ROCK activation, while p-P38 was unaffected. Concentration response studies showed significant inhibition of AKT activation at 50 μM MDC, along with inhibition of the AKT downstream targets mTOR, p-S6 kinase and p-S6. Furthermore, TG2 depletion by siRNA led to reduced 5-HT-induced AKT activation. Immunoprecipitation studies showed that 5-HT treatment led to increased levels of serotonylated AKT and increased TG2-AKT complex formations which were inhibited by MDC. Overexpression of TG2 point mutant cDNAs in PASMCs showed that the TG2 C277V transamidation mutant blunted 5-HT-induced AKT activation and 5-HT-induced PASMC mitogenesis. Finally, 5-HT-induced AKT activation was blunted in SERT genetic knock-out rat cells, but not in their wild-type counterpart. The SERT inhibitor imipramine similarly blocked AKT activation. These results indicate that TG2 contributes to 5-HT-induced distal PASMC proliferation via promotion of AKT signaling, likely via its serotonylation. Taken together, these results provide new insight into how TG2 may participate in vascular smooth muscle remodeling.

We previously reported that transglutaminase 2 (TG2) activity is markedly elevated in lungs of hypoxia-exposed rodent models of pulmonary hypertension (PH). Since vascular remodeling of pulmonary artery smooth muscle cells (PASMCs) is important in PH, we undertook the present study to determine whether TG2 activity is altered in PASMCs with exposure to hypoxia and whether that alteration participates in their proliferative response to hypoxia. Cultured distal bovine (b) and proximal human (h) PASMCs were exposed to hypoxia (3% O2) or normoxia (21% O2). mRNA and protein expression were determined by PCR and Western blot analyses. TG2 activity and function were visualized and determined by fluorescent labeled 5-pentylamine biotin incorporation and immunoblotting of serotonylated fibronectin. Cell proliferation was assessed by [3H]thymidine incorporation assay. At 24 h, both TG2 expression and activity were stimulated by hypoxia in bPASMCs. Activation of TG2 by hypoxia was blocked by inhibition of the extracellular calcium-sensing receptor or the transient receptor potential channel V4. In contrast, TG2 expression was blocked by inhibition of the transcription factor hypoxia-inducible factor-1α, supporting the presence of separate mechanisms for stimulation of activity and expression of TG2. Pulmonary arterial hypertension patient-derived hPASMCs were found to proliferate significantly more rapidly and respond to hypoxia more strongly than control-derived hPASMCs. Similar to bovine cells, hypoxia-induced proliferation of patient-derived cells was blocked by inhibition of TG2 activity. Our results suggest an important role for TG2, mediated by intracellular calcium fluxes and HIF-1α, in hypoxia-induced PASMC proliferation and possibly in vascular remodeling in PH.

Members of the Dbl-homology (DH) family of proteins promote guanine nucleotide exchange on Rho GTPases. Lbc, which specifically acts on Rho but not Rac or Cdc42, was isolated as a transforming oncogene and is composed of a DH and a Pleckstrin-homology (PH) domain. We show here that the Lbc DH domain alone is capable of stimulating new DNA synthesis in quiescent fibroblasts and Rho-dependent actin stress fiber assembly. However, the PH domain is required for subcellular localization of Lbc along actin stress fibers and for efficient transformation of NIH3T3 cells. The results show that, in contrast to other Dbl-homology proteins, the PH domain of Lbc is dispensable for activation of Rho in vivo. The PH domain-dependent subcellular localization of Lbc may, however, be important for growth factor activation of endogenous Lbc and for oncogenic transformation.

Vimentin is a major intermediate filament protein in vascular endothelial cells which might be involved in their function as a barrier tissue. It is proposed to dynamically maintain integrity of the endothelium as a tightly regulated permeability barrier that is subjected to a variety of shear and contractile forces. The results described in this report demonstrate that vimentin plays that role through mechanisms that are dependent on its phosphorylation state. Withaferin A (WFA), a vimentin targeting drug is shown to disrupt endothelial barrier function through its effects on vimentin filament distribution and physical properties. These effects are related to WFA's ability to increase vimentin phosphorylation. Through overexpressing a non-phosphorylatable vimentin mutant we can block the effects of WFA on vimentin distribution and barrier permeability. The barrier augmentation effect appears to extend to endothelial cells that do not express detectable mutant vimentin which might suggest transmissible effects across cells. Blocking vimentin phosphorylation also protects the endothelial barrier against LPS endotoxin, implicating it as a target for drug development against pulmonary edema and acute respiratory distress syndrome (ARDS).

Constitutive activation of growth factor receptor signaling pathways leads to uncontrolled growth, but why tumor cells become anchorage independent is less clear. The fact that integrins transmit signals required for cell growth suggests that constitutive activation of steps downstream from integrins mediates anchorage independence. Since the small GTPase Rho may mediate integrin signal transduction, the effects of serum and the Rho nucleotide exchange factor oncogenes dbl and lbc on cell growth and signaling pathways were examined. Our data show that these oncogenes induce anchorage-independent but serum-dependent growth and stimulation of signaling pathways. These results show, therefore, that anchorage-independent growth results from constitutive activation of integrin-dependent signaling events. They also support the view that Rho is a functionally important mediator of integrin signaling.

Engagement and clustering of integrins triggers a number of intracellular signaling events, including activation of the mitogen-activated protein (MAP) kinases Erk1 and Erk2. To investigate the mechanism by which integrins mediate the activation of MAP kinases upon binding of NIH 3T3 cells to fibronectin, we assessed the effects of both inhibiting and activating the small GTPase Rho. We observed that inhibition of Rho by the Rho-specific inhibitor C3 exoenzyme or by a dominant negative Rho A (RhoN19) inhibited MAP kinase activation. Conversely, activation of Rho by expression of an activated Rho A mutant (RhoQ63L), or the Rho-specific guanine nucleotide exchange factor lbc, enhanced and partially mimicked activation of Erk2 by plating on fibronectin. These results therefore show that Rho is involved in the integrin-dependent activation of MAP kinase.

Phenotypic abnormalities of melanocytes, germ cells, and hematopoietic cells of Steel mice demonstrate the critical role of stem cell factor (SCF) in development. Production of SCF in the hematopoietic microenvironment as either a membrane-associated or soluble factor leads to pleiotropic effects on hematopoietic stem and progenitor cells and significant effects on the production of erythroid cells. Although the production of these two forms of SCF is highly regulated, the physiologic role(s) of membrane-associated and soluble SCF remain unclear. We have demonstrated that the generation of soluble murine SCF by murine stromal cells derived from the fetal hematopoietic microenvironment is dependent on two distinct proteolytic cleavage sites. The primary site in exon 6 is preferentially utilized in these cells. The secondary site located in exon 7 is utilized only in the absence of the primary site. Proteolytic processing at this secondary site appears to be species-specific, since the human protein sequence diverges at this site, and protein expressed from the human cDNA encoding this site in murine stromal cells remains largely membrane-associated. Site-directed mutagenesis of the murine SCF cDNA encoding both proteolytic cleavage sites leads to the generation of membrane-associated and biologically active SCF on murine stromal cells. These results suggest that the regulation of processing of the secondary proteolytic cleavage site could play a critical role in the function of membrane-associated SCF protein.

Serotonin (5-HT) stimulates pulmonary artery smooth muscle cell proliferation and has been associated with pulmonary arterial hypertension (PAH). Bone morphogenetic protein receptor 2 (BMPR2) mutations similarly have been linked to PAH. However, possible crosstalk between 5-HT and BMPR signaling remains poorly characterized. We report here that 5-HT activates Smads 1/5/8 in bovine and human pulmonary artery smooth muscle cells (SMCs) and causes translocation of these Smads from cytoplasm to the nucleus. DN BMPR1A blocked 5-HT activation of Smads 1/5/8 by 5-HT and BMPR1A overexpression enhanced it. Activation of Smads by 5-HT occurred through the 5-HT 1B/1D receptor as it was blocked with the inhibitor GR 55562 but unaffected by inhibitors of the 5-HT transporter and a variety of 5-HT receptors. Activation of the Smads by 5-HT depended on Rho/Rho kinase signaling as it was blocked by Y27632, but unaffected by inhibitors of PI3K or MAPK. Transfection of cells with BMPR1A and ligation of the BMP receptor with BMP-2 also activated GTP-Rho A of these SMCs, while DN BMPR1A blocked the activation. 5-HT stimulated an increase in serine/threonine phosphorylation of BMPR1A, supporting the activation of BMPR1A by 5-HT in SMCs. Infusion of 5-HT into mice with miniosmotic infusion pumps caused activation of Smads 1/5/8 in lung tissue, demonstrating the effect in vivo. The studies support a unique concept that 5-HT transactivates the serine kinase receptor, BMPR 1A, to activate Smads 1/5/8 via Rho and Rho kinase in pulmonary artery SMCs. Rho and Rho kinase also participate in the activation of Smads by BMP.

The ubiquitous alpha(E)-catenin is an essential actin cytoskeletal linker. The transcription factor, serum response factor (SRF), induces transcription via binding to the serum response element (SRE) in gene promoters, and in many cases responds to actin dynamics. Here, we report that alpha(E)-catenin expression in HEK293 cells activates the SRE.L transcriptional reporter, a reporter containing the isolated SRF-binding site, and a stably integrated SRE.L reporter in fibroblasts. alpha-Catenin-induced reporter activity appears only partly dependent on RhoA GTPase and Rho kinase function. alpha-Catenin expression has no effect on RhoA activation or localization, and alpha-catenin-induced SRE.L reporter activation is insensitive to the actin-modulating agent latrunculin B. Ectopic alpha-catenin expression was not sufficient to induce actin filament assembly as measured by stress fiber formation. SRE.L reporter is activated by the C-terminal approximately 300 residue region of alpha(E)-catenin. These results suggest induction of SRF-mediated transcription by alpha(E)-catenin either downstream of RhoA or via a parallel pathway.

Inactivating mutations in the tuberous sclerosis complex 2 (TSC2) gene, which encodes tuberin, result in the development of TSC and lymphangioleiomyomatosis (LAM). The tumor suppressor effect of tuberin lies in its GTPase-activating protein activity toward Ras homologue enriched in brain (Rheb), a Ras GTPase superfamily member. The statins, 3-hydroxy-3-methylglutaryl CoA reductase inhibitors, have pleiotropic effects which may involve interference with the isoprenylation of Ras and Rho GTPases. We show that atorvastatin selectively inhibits the proliferation of Tsc2−/− mouse embryo fibroblasts and ELT-3 smooth muscle cells in response to serum and estrogen, and under serum-free conditions. The isoprenoids farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP) significantly reverse atorvastatin-induced inhibition of Tsc2−/− cell growth, suggesting that atorvastatin dually targets a farnesylated protein, such as Rheb, and a geranylgeranylated protein, such as Rho, both of which have elevated activity in Tsc2−/− cells. Atorvastatin reduced Rheb isoprenylation, GTP loading, and membrane localization. Atorvastatin also inhibited the constitutive phosphorylation of mammalian target of rapamycin, S6 kinase, and S6 found in Tsc2−/− cells in an FPP-reversible manner and attenuated the high levels of phosphorylated S6 in Tsc2-heterozygous mice. Atorvastatin, but not rapamycin, attenuated the increased levels of activated RhoA in Tsc2−/− cells, and this was reversed by GGPP. These results suggest that atorvastatin may inhibit both rapamycin-sensitive and rapamycin-insensitive mechanisms of tuberin-null cell growth, likely via Rheb and Rho inhibition, respectively. Atorvastatin may have potential therapeutic benefit in TSC syndromes, including LAM. [Cancer Res 2007;67(20):9878–86]

The HMG-CoA reductase inhibitors, statins, have pleiotropic effects which may include interference with the isoprenylation of Ras and Rho small GTPases. Statins have beneficial effects in animal models of pulmonary hypertension, although their mechanisms of action remain to be determined. Serotonin [5-hydroxytryptamine (5-HT)] is implicated in the process of pulmonary artery smooth muscle (PASM) remodeling as part of the pathophysiology of pulmonary hypertension. We examined the effect of atorvastatin on 5-HT-induced PASM cell responses. Atorvastatin dose dependently inhibits 5-HT-induced mitogenesis and migration of cultured bovine PASM cells. Inhibition by atorvastatin was reversed by mevalonate and geranylgeranylpyrophosphate (GGPP) supplement, suggesting that the statin targets a geranylgeranylated protein such as Rho. Concordantly, atorvastatin inhibits 5-HT-induced cellular RhoA activation, membrane localization, and Rho kinase-mediated phosphorylation of myosin phosphatase-1 subunit. Atorvastatin reduced activated RhoA-induced serum response factor-mediated reporter activity in HEK293 cells, indicating that atorvastatin inhibits Rho signaling, and this was reversed by GGPP. While 5-HT-induced ERK MAP and Akt kinase activation were unaffected by atorvastatin, 5-HT-induced ERK nuclear translocation was attenuated in a GGPP-dependent fashion. These studies suggest that atorvastatin inhibits 5-HT-induced PASM cell mitogenesis and migration through targeting isoprenylation which may, in part, attenuate the Rho pathway, a mechanism that may apply to statin effects on in vivo models of pulmonary hypertension.

Differentiation of fibroblasts into myofibroblasts is an important event in many conditions such as wound repair and fibrosis. For example, in pulmonary fibrosis (PF) myofibroblasts occur in areas of active fibrosis and are responsible for production and deposition of extracellular matrix proteins [Vyalov et al., 1993]. Myofibroblasts derive from fibroblasts through the action of growth factors, such as, TGFβ [Desmouliere et al., 1993; Ronnov-Jessen and Petersen, 1993; Yokozeki et al., 1997; Roy et al., 2001]. Several signaling pathways have been proposed to mediate the actions of TGFβ on fibroblasts including the MAP kinase p38. Furthermore inhibition of p38 reduced pulmonary [Underwood et al., 2000; Matsuoka et al., 2002] and renal [Stambe et al., 2004] fibrosis in animal models. Recently the role of differentiation of fibroblasts into myofibroblasts in the pathogenesis of pulmonary hypertension has also been highlighted [Stenmark et al., 2002; Short et al., 2004]. We launched this project to investigate the role of MAP kinase activated protein kinase 2 (MAPKAPK2 or MK2), which is a downstream effector of p38, in fibrosis, and the mechanism by which its activation by TGFβ leads to differentiation of myofibroblasts. PF can arise in response to drugs and asbestos but the interstitial idiopathic pulmonary fibrosis (IPF) variant of the disease arises by unknown mechanisms. It has long been postulated that an inflammatory reaction is an important component or initiator of fibrosis. Several cytokines have been shown to be altered in fibrosis in animal models as well as human patients. For example, TGFβ [Khalil et al., 1991], IL-1β and TNFα [Piguet et al., 1993; Pan et al., 1996] have been reported to be elevated in the lungs of IPF patients. The range of cytokines altered during fibrosis led researchers to propose that fibrosis is the result of an imbalance between pro-inflammatory and profibrotic cytokines, and hence a dysregulated rather than a simple inflammatory reaction [Wallace et al., 1995; Ando et al., 1999; Ziesche et al., 1999]. Nevertheless, the role of inflammation in fibrosis continues to be questioned based on the fact that fibrosis can arise without clear evidence of inflammation, and that the levels of altered cytokines cannot be correlated with severity of fibrosis. While the range of cytokines and factors that become altered in the development of fibrosis continues to be investigated, it is clear that some of these factors, such as TGFβ initiate responses in model systems that mimic the human disease. Indeed, the key to understanding the etiology of PF might evolve from a better understanding of signaling events in fibroblasts in response to factors such as TGFβ leading to myofibroblast differentiation. Myofibroblasts are identified by increased expression of smα, which is usually expressed in smooth muscle cells. Functionally, myofibroblasts are more contractile and structurally they are characterized by increased actin stress fibers both of which are believed to be due to the increased expression of smα (for review, see Hinz and Gabbiani [2003]). Thus the mechanism by which smα expression is regulated has received considerable attention. In this report we have focused on TGFβ, a classical profibrotic factor, which has been linked to remodeling. TGFβ belongs to large family of proteins that are important in a variety of diseases ranging from cancer to pulmonary hypertension. It has been shown to stimulate a pathway that proceeds from cell surface receptors to the nucleus through Smad proteins (for review, see Attisano and Wrana [2002]). Yet TGFβ can signal independently of Smad proteins by activating Ras and Erk [Hartsough and Mulder, 1995; Hartsough et al., 1996], Rho GTPase and JNK [Atfi et al., 1997], as well as p38 MAP kinase [Hanafusa et al., 1999]. The latter pathway has recently been shown to play an important role in mediating the effects of hypoxia on different cell types [Seko et al., 1997; Conrad et al., 1999, 2000; Kacimi et al., 2000; Carini et al., 2001; Das et al., 2001; Kayyali et al., 2001; Marais et al., 2001; Welsh et al., 2001]. We have previously described how p38 activation leads to actin stress fiber formation in hypoxic endothelial cells and demonstrated that it is mediated by MK2 and its substrate HSP27 [Kayyali et al., 2002]. p38 signaling leading to HSP27 phosphorylation has also been shown to mediate fibroblast-mediated wound contractions [Hirano et al., 2002]. In evaluating the role of the p38 pathway in mediating the effects of TGFβ on fibroblast differentiation we have focused on MK2, an immediate downstream effector of p38. This kinase has been shown to phosphorylate serum response factor (SRF) which activates smα expression [Heidenreich et al., 1999]. Using mouse embryonic fibroblasts (MEF) from wild-type (WT) mice and MK2−/− mice in which the expression of MK2 has been disrupted, we examined myofibroblast potential and responsiveness to TGFβ. Our results indicate that MK2 plays an important role in myofibroblast phenotypic expression. Fibroblasts that lack MK2 express very little smα at baseline or in response to TGFβ. Furthermore, disruption of MK2 expression reverses the responsiveness of fibroblasts to TGFβ, implicating its mediation of the effects of TGFβ under normal conditions and in disease processes such as fibrosis.

Hepatocellular carcinoma is highly resistant to chemotherapeutic agents, thus the need to discover effective therapeutic molecules to suppress cancer cell growth and to overcome drug resistance is urgent. The Rho GTPase is implicated in cancer and metastasis and is directly activated by the Lymphoid blast crisis (Lbc) protooncogene, a Rho guanine-nucleotide exchange factor. The aim of the study was to analyze the expression of Lbc in hepatocarcinoma and to determine the effect of Lbc-induced Rho signaling on expression, growth rate and resistance to genotoxic stress. We found, by immunohistochemical analysis of biopsy samples and Northern and Western blot analyses of cell lines, that Lbc is absent in normal adult liver but is abundantly expressed in hepatocarcinoma, implying an increased Rho pathway signaling. Lbc stably transfected hepatocarcinoma cells exhibit increased proliferation and levels of ERK and cyclin D1 activation, which are blocked by a Rho inhibitor. In contrast, AKT activation was not altered. Moreover, Lbc expression confers increased resistance to genotoxic stress induced by doxorubicin, which is associated with upregulation of Bcl-2 and BAD phosphorylation, and this is reversed by a Rho inhibitor. In conclusion, these data support a role for Rho in liver cancer progression and resistance to therapy and may provide a basis for developing effective treatment for hepatocarcinoma.

Alpha-catenin, an integral part of cadherin-catenin adhesion complexes, is a major binding partner of beta-catenin, a key component of the Wnt pathway, which activates T-cell factor (TCF)/lymphoid enhancer factor (LEF) transcription and is often upregulated in cancers. Recently, we identified an alpha-catenin-related protein, alpha-catulin, whose function is poorly understood, as part of a Rho GTPase signaling complex. Here, based on evidence suggesting that alpha-catulin may associate with a beta-catenin fraction, we investigated the role of alpha-catenin family members in beta-catenin-mediated signals. Expression of the full length or a 103-residue region of alpha-catenin strongly inhibits the induction of the TCF/LEF-responsive TOPFLASH reporter in HEK293T cells expressing activated beta-catenin or in cancer cells with constitutively upregulated Wnt signaling, whereas alpha-catulin expression had no effect. Interestingly, alpha-catulin expression attenuates the activation of the cyclin D1 promoter, a target of Wnt pathway signals. Alpha-catulin appears to inhibit Ras-mediated signals to the cyclin D1 promoter, rather than beta-catenin signals, and the synergy between Ras and beta-catenin required to fully activate this promoter. Data suggesting the involvement of Rho in this response are presented and discussed. These results suggest a novel function for alpha-catulin and imply that alpha-catenin and alpha-catulin have distinct activities that downregulate, respectively, beta-catenin and Ras signals converging on the cyclin D1 promoter.

The Rho GTPase signaling pathway is required for actin cytoskeletal organization and serum response factor-dependent gene transcription. Lbc is a Rho-specific guanine nucleotide exchange factor that contains a modulatory C-terminal region. To elucidate Lbc regulatory mechanism(s), a yeast two-hybrid screen for proteins that interact with the Lbc C-terminal region was carried out, resulting in multiple isolation of cDNAs encoding the same 734-amino acid Lbc interacting protein. The Lbc interacting protein has homology with the alpha-catenin cell adhesion component and is identical to the alpha-catenin-like alpha-catulin protein of unknown function. The human alpha-catulin gene (CTNNAL1) maps to 9q31-32. Here we identify the predicted endogenous alpha-catulin product, document alpha-catulin and Lbc co-expression in multiple human cell lines, and show alpha-catulin and Lbc subcellular co-fractionation and intracellular localization. The required regions for Lbc and alpha-catulin interaction were mapped, and complex formation between Lbc and alpha-catulin in mammalian cells was detected. Functionally, alpha-catulin co-expression leads to increased Lbc-induced serum response factor activation in vivo as measured by a transcriptional reporter assay. Furthermore, alpha-catulin co-expression enhances Lbc-induced GTP-Rho formation in vivo. These results support the concept that the recently identified alpha-catulin protein may modulate Rho pathway signaling in vivo by providing a scaffold for the Lbc Rho guanine nucleotide exchange factor.

Recent reports have shown that several heterotrimeric protein-coupled receptors that signal through Galpha(q) can induce Rho-dependent responses, but the pathways that mediate the interaction between Galpha(q) and Rho have not yet been identified. In this report we present evidence that Galpha(q) expressed in COS-7 cells coprecipitates with the Rho guanine nucleotide exchange factor (GEF) Lbc. Furthermore, Galpha(q) expression enhances Rho-dependent responses. Coexpressed Galpha(q) and Lbc have a synergistic effect on the Rho-dependent rounding of 1321N1 astrocytoma cells. In addition, serum response factor-dependent gene expression, as assessed by the SRE.L reporter gene, is synergistically activated by Galpha(q) and Rho GEFs. The synergistic effect of Galpha(q) on this response is inhibited by C3 exoenzyme and requires phospholipase C activation. Surprisingly, expression of Galpha(q), in contrast to that of Galpha(12) and Galpha(13), does not increase the amount of activated Rho. We also observe that Galpha(q) enhances SRE.L stimulation by activated Rho, indicating that the effect of Galpha(q) occurs downstream of Rho activation. Thus, Galpha(q) interacts physically and/or functionally with Rho GEFs; however this does not appear to lead to or result from increased activation of Rho. We suggest that Galpha(q)-generated signals enhance responses downstream of Rho activation.

Thrombin induces astrocytoma cell rounding through a Rho-dependent pathway (Majumdar, M., Seasholtz, T. M., Goldstein, D., de Lanerolle, P., and Brown, J. H. (1998) J. Biol. Chem. 273, 10099-10106). The involvement of the G(12) family of G proteins and the role of specific Rho exchange factors in transducing signals from the thrombin receptor to Rho-dependent cytoskeletal responses was examined. Microinjection of cDNAs for activated Galpha(12) or Galpha(13) induced cell rounding, and antibodies to Galpha(12) or Galpha(13) blocked the response to thrombin. In contrast, activation or inhibition of Galpha(q) function had relatively little effect. The cytoskeletal response to Galpha(12) was inhibited by microinjection of C3 exoenzyme, indicating Rho dependence. Two Rho-specific guanine nucleotide exchange factors (GEFs), oncogenic lbc and p115, increased the percentage of rounded cells 4-5-fold, and this was inhibited by C3. Mutant GEFs lacking the Dbl homology (DH) domain required for exchange factor activity failed to induce cell rounding. However, the DH mutants of lbc and p115 were efficacious inhibitors of rounding induced by thrombin or Galpha(12). The effects of lbc were dependent on an intact pleckstrin homology domain, which may be required for appropriate targeting of the Rho-GEF. These findings identify the Galpha(12) protein family as transducers of thrombin signaling to the cytoskeleton and provide the first evidence that a Rho-GEF transduces signals between G protein-coupled receptors and Rho-mediated cytoskeletal responses.

Long-term bone marrow cultures have been useful in determining gene expression patterns in pre-B cells and in the identification of cytokines such as interleukin 7 (IL-7). We have developed a culture system to selectively grow populations of B lineage restricted progenitors (pro-B cells) from murine bone marrow. Pro-B cells do not grow in response to IL-7, Steel locus factor (SLF), or a combination of the two. c-kit, the SLF receptor, and the IL-7 receptor are both expressed by pro-B cells, indicating that the lack of response is not simply due to the absence of receptors. Furthermore, SLF is not necessary for the growth of pro-B cells since they could be expanded on a stromal line derived from Steel mice that produces no SLF. IL-7 responsiveness in pre-B cells is associated with an increase in n-myc expression and is correlated with immunoglobulin (Ig) gene rearrangements. Although members of the ets family of transcription factors and the Pim-1 kinase are expressed by pro-B cells, n-myc is not expressed. Pro-B cells maintain Ig genes in the germline configuration, which is correlated with a low level of recombination activating genes 1 and 2 (Rag-1 and 2) mRNA expression, but high expression of sterile mu and terminal deoxynucleotidyl transferase. Pro-B cells are unable to grow separated from the stromal layer by a porous membrane, indicating that stromal contact is required for growth. These results suggest that pro-B cells are dependent on alternative growth signals derived from bone marrow stroma and can be distinguished from pre-B cells by specific patterns of gene expression.

The maintenance and differentiation of hematopoietic stem cells is influenced by cells making up the hematopoietic microenvironment (HM), including bone marrow-derived stromal cells. We and several other investigators have recently demonstrated the molecular basis of abnormal HM observed in the steel mutant mouse and cloned the normal cDNA products of this gene (termed SCF, KL, or MCF). In this report, we focus on the human counterpart of the mouse Steel (Sl) gene. Alternative splicing of the human SCF pre-mRNA transcript results in secreted and membrane-bound forms of the protein. To investigate the role of these two forms of human SCF, we targeted an immortalized stromal cell line derived from fetal murine homozygous (Sl/Sl) SCF-deficient embryos for gene transfer of various human cDNAs encoding SCF. We report that stable stromal cell transfectants can differentially process the two forms of human SCF protein product. We also demonstrate that both soluble SCF and membrane-bound SCF are active in increasing the number of human progenitor cells in the context of stromal cell cultures, although in a qualitatively different manner. Hence, the membrane-bound form of SCF may play an important role in the cell-cell interactions observed between stromal and hematopoietic cells both in vitro and in vivo.

Despite the importance of germ cells to the survival of species, surprisingly little is known about their embryological origin, proliferation, migration and entry into mitotic arrest or meiosis. Mutations in the murine Dominant White Spotting (W) and Steel genes, which respectively encode the c-kit tyrosine kinase receptor and the c-kit ligand (or Steel factor), impair the development of primordial germ cells (PGCs) in vivo, as well as haematopoietic stem cells and neural crest-derived melanoblasts. Here we use a monoclonal antibody against c-kit tyrosine kinase receptor and recombinant Steel factor to study the c-kit receptor-ligand system in cultured PGCs. In addition, we show that leukaemia inhibitory factor (also known as differentiation inhibitory activity), a factor secreted by STO fibroblasts, can stimulate proliferation of primordial germ cells in vitro.

These studies describe a liquid suspension culture system for normal myeloid cells derived from human foetal liver. A simple one-step fractionation procedure was employed to obtain a cell population capable of expanding into all stages of myeloid differentiation, including committed myeloid progenitor cells (GM-CFC). Cell proliferation in these cultures resulted in the maintenance of early myeloid populations for up to a month. In order to extend myeloid cell maintenance, a specific factor in the form of media conditioned by human endothelial cells (endo C.M.) was used. Addition of endo C.M. to foetal liver cultures resulted in increased myeloid proliferation coupled to extensive myeloid differentiation. Clonally derived foetal liver culture cells proliferated for up to 2 months in the presence of endo C.M. before maturing into macrophages. These results show that endo C.M. exert an extensive proliferative effect on early myeloid cells as well as inducing their differentiation. The large quantity of cells in early stages of myeloid differentiation provided by foetal liver cultures may be useful for biochemical and molecular biology studies of myelopoiesis. In addition, these cultures are a potential source from which to derive normal myeloid lines. The separation of the potent proliferative activity present in endo C.M. may yield an effector which maintains human myeloid cell proliferation.

Rho GTPase is required for actin filament assembly and serum response element (SRE)-dependent gene transcription. Certain G protein-coupled receptors (GPCRs) induce Rho-dependent responses, but the intermediary signaling steps are poorly understood. The heterotrimeric Galpha12 family can induce Rho-dependent responses. In contrast, there are conflicting reports on the role of the Galphaq family in Rho signaling. We report that expression of activated Galphaq members, or activation of endogenous Galphaq via GPCR stimulation, induces SRE reporter activation via Rho, and increased GTP-Rho levels. Moreover, microinjection of activated Galphaq in fibroblasts induces actin stress fiber formation via Rho. Galphaq functionally cooperates with Lbc Rho guanine nucleotide exchange factor. Overall, these findings indicate that Galphaq family signals are sufficient to induce Rho-dependent cellular responses.

Surface marker studies of human leukaemia cells argue in favour of a normal cell surface phenotype and that unique surface changes are not essential to malignancy. This has led to speculation that leukaemia may result “from a subtle uncoupling of the controls which integrate proliferation with maturation” [1]. Studies using in vitro assays for haemopoietic progenitor cells (for example, GM-CFUc assay) have shown that specific humoral factors regulate normal haemopoiesis (GM-CSFs). Thus, the process of differentiation can in part be explained in terms of the expression of discriminatory surface receptors which are essential to alter (or maintain) the maturation status of cells. However, in order to investigate the underlying set of intracellular regulatory mechanisms which integrate proliferation with maturation it will be necessary to (a) work with cloned populations of cells and (b) have convenient markers for structures which are essential to cell proliferation and maturation within a particular lineage.

In long-term marrow cultures haemopoiesis can be maintained in vitro for up to 6 months. Critical analysis of the cell populations produced has shown that the stem cells and their committed progeny have characteristics in common with the corresponding cell types in vivo. The maintenance of haemopoiesis in vitro is associated with the development of an appropriate inductive environment provided by bone marrow derived adherent cells. Analysis of the interactions between environmental and haemopoietic cells has been facilitated by the development of in vitro systems reproducing the naturally occurring genetic environmental defects and other systems where the development of a competent inductive environment shows a dependency upon corticosteroid hormones. Investigations have shown that stem cell proliferation may be controlled by production of opposing activities, one stimulatory for DNA synthesis, the other inhibitory. A model is proposed whereby modulation in the production of these factors is determined by the physical presence of stem cells in a proposed cellular milieu, within the adherent layer. The adherent layer, apart from acting at the level of stem cell proliferation, can also modify the response of differentiating cells (eg, GM-CFC) to exogenous stimulatory activities. Addition of GM-CSF or of CSF-antiserum has no effect on haemopoiesis in long-term cultures.

The continuous human promyeloid cell line HL60 may be induced to differentiate into neutrophils by the presence of 1.25% dimethylsulphoxide (DMSO) and related compounds [4]. When treated with 12- O -tetradecanoylphorbol-13-acetate (TPA), the cells exhibit many features characteristic of monocytes/macrophages [13]. In both cases, the induced HL60 cells lose their proliferative ability. The availability of this inducible cell line has led to an increasing number of studies aimed at dissecting the process of myeloid differentiation. However, the correct interpretation of such studies may only be reached through the use of appropriate cellular controls; specifically, variant HL60 cell lines which do not differentiate in response to the inducing agents. Here we report the isolation and characterization of two variant cell lines of HL60 which do not differentiate in the presence of 1.25% dimethylsulphoxide but still respond to TPA. Comparison of these HL60 variants with the parental line should facilitate the elucidation of molecular events which regulate myeloid differentiation.

In this study we describe a new approach to producing extremely cytotoxic monoclonal antibodies. A non-cytotoxic antibody BK19.45 was rendered cytotoxic by coupling the antibody to the radioisotope astatine 211. BK19.45 was chosen for this study since this antibody recognises an antigen which is uniformly distributed on human bone marrow leukocytes. Hence the ability of astatine labelled antibodies to specifically kill myeloid precursor cells (CFU-C) can be documented precisely. Bone marrow cells and the cell line HL60 were treated in suspension with increasing amounts of labelled BK19.45 or concanavalin A. Astatine has a short half life (7.2hr) and produces short range a particles. Therefore the radiation dose to the cells is limited to only those cells binding the antibody. The cytotoxicity of astatine labelled reagents was determined by growing colonies in semi-solid agar. D 37 values in the range 5-12 atoms/cell were obtained. In conclusion (1) the extreme toxicity (2) short half-life of the radioisotope and (3) consequentially the lack of residual long-term toxic effects of astatine labelled reagents provide a system which can be used to eliminate in vitro subpopulations of cells from bone marrow in analysing precursor cell antigens.