Regulation of GRIP1 and CBP Coactivator activity by Rho GDI modulates estrogen receptor transcriptional enhancement

Antitumor and antimetastatic activities of a novel benzothiazole-2-thiol derivative in a murine model of breast cancer

The prognosis of metastatic breast cancer is always very poor. Thus, it is urgent to develop novel drugs with less toxicity against metastatic breast cancer. A new drug (XC-591) derived from benzothiazole-2-thiol was designed and synthesized in our lab. In this study, we tried to assess effects of XC-591 treatment on primary breast cancer and pulmonary metastasis in 4T1 mice model. Furthermore, we tried to discover its possible molecular mechanism of action. MTT experiment showed XC-591 had significant anti-cancer activity on diverse cancer cells. Furthermore, XC-591 significantly suppressed the proliferation of 4T1 cells by colony formation assay. The in vivo results displayed that XC-591 could inhibit the growth and metastasis in 4T1 model. Moreover, histological analysis revealed that XC-591 treatment increased apoptosis, inhibited proliferation and angiogenesis in vivo. In addition, XC-591 did not contribute to obvious drug associated toxicity during the whole study. Molecular mechanism showed XC-591 could inhibit RhoGDI, activate caspase-3 and decrease phosphorylated Akt. The present data may be important to further explore this kind of new small-molecule inhibitor.

Role of Rho-specific guanine nucleotide dissociation inhibitor α regulation in cell migration

Cell migration is a vital process for many physiological and pathological events, and Rho GTPases have been confirmed as key factors in its regulation. The most studied negative regulator of Rho GTPases, Rho-specific guanine nucleotide dissociation inhibitor α (RhoGDIα), mediates cell migration through altering the overall expression and spatiotemporal activation of Rho GTPases. The RhoGDIα-Rho GTPases dissociation can be mediated by signal pathways targeting RhoGDIα directly. This review summarizes the research about the regulation of RhoGDIα during cell migration, which can be in a Rho GTPases association independent manner. Non-kinase proteins regulation, phosphorylation, SUMOylation and extracellular environmental factors are classified to discuss their direct signal regulations on RhoGDIα, which provide varied signal pathways for selective activation of Rho GTPases in cell migration.

RhoGDIα downregulates androgen receptor signaling in prostate cancer cells

INTRODUCTION

Treatment of primary prostate cancer (CaP) is the withdrawal of androgens. However, CaP eventually progresses to grow in a castration-resistant state due to aberrant activation of androgen receptor (AR). Understanding the mechanisms leading to the aberrant activation of AR is critical to develop effective therapy. We have previously identified Rho GDP Dissociation Inhibitor alpha (GDIα) as a novel suppressor in prostate cancer. In this study, we examine the effect of GDIα on AR signaling in prostate cancer cells.

METHODS

GDIα was transiently or stably transfected into several prostate cancer cell lines including LNCaP, C4-2, CWR22Rv1, and DU145. The regulation of AR expression by GDIα was analyzed by qRT-PCR and Western blot. AR activity was measured by luciferase reporter assays and electrophoretic mobility shift analysis (EMSA). Immunofluorescence assay was performed to study AR nuclear translocation. The interaction between GDIα and AR was examined by co-immunoprecipitation assays.

RESULTS

In this study, we have identified GDIα as a negative regulator of AR signaling pathway. Overexpression of GDIα downregulates AR expression at both mRNA and protein levels. Overexpression of GDIα is able to prevent AR nuclear translocation and inhibit transactivation of AR target genes. Co-immunoprecipitation assays showed that GDIα physically interacts with the N-terminal domain of AR.

CONCLUSIONS

GDIα suppresses AR signaling through inhibition of AR expression, nuclear translocation, and recruitment to androgen-responsive genes. GDIα regulatory pathway may play a critical role in regulating AR signaling and prostate cancer growth and progression.

Downregulation of RhoGDIα increased migration and invasion of ER (+) MCF7 and ER (-) MDA-MB-231 breast cancer cells

Rho GDP dissociation inhibitors (RhoGDIs) can inhibit cell motility, invasion, and metastasis in cancer by inactivating the RhoGTPases. A member of RhoGDI family has been consistently shown to interact with estrogen receptor (ER), and change its transcriptional activity. ER is a receptor known to be inversely correlated with cell motility and invasion in breast cancer. The consequence of RhoGDIα activity on migration and invasion of ER (+) and ER (-) breast cancers is not clear. The aim of our study was to investigate the possible opposing effect of RhoGDIα on the migration and invasion of ER (+) MCF7 and ER (-) MDA-MB-231 breast cancer cells. RhoGDIα was downregulated using short interfering RNA (siRNA) and upregulated using GFP-tagged ORF clone of RhoGDIα, and their ability for migration and invasion was assayed using transwell chambers. It was found that the silencing of RhoGDIα in MCF7 and MDA-MB-231 cells significantly increased migration and invasion of these cells into the lower surface of porous membrane of the chambers. Overexpression of RhoGDIα in MCF7 cells suppressed their migration and invasion, but no significant effect was found on MDA-MB-231 cells. Our results indicate that the downregulation of RhoGDIα similarly affects the in vitro migration and invasion of ER (+) MCF7 and ER (-) MDA-MB-231 cells. However, our assays are differently affected by the upregulation of RhoGDIα in these two cell lines and this may be due to the differences in ER expression, primary invasive ability and/or other molecules between these two cell line models which warrant further investigation.

Possible role of Efnb1 protein, a ligand of Eph receptor tyrosine kinases, in modulating blood pressure

Eph kinases constitute the largest receptor tyrosine kinase family, and their ligands, ephrins (Efns), are also cell surface molecules. Although they are ligands, Efns can transduce signals reversely into cells. We have no prior knowledge of the role played by any members of this family of kinases or their ligands in blood pressure (BP) regulation. In the present studies, we investigated the role of Efnb1 in vascular smooth muscle cell (VSMC) contractility and BP regulation. We revealed that reverse signaling through Efnb1 led to a reduction of RhoA activation and VSMC contractility in vitro. Consistent with this finding, ex vivo, there was an increase of RhoA activity accompanied by augmented myosin light chain phosphorylation in mesenteric arteries from mice with smooth muscle-specific conditional Efnb1 gene knock-out (KO). Small interfering RNA knockdown of Grip1, a molecule associated with the Efnb1 intracellular tail, partially eliminated the effect of Efnb1 on VSMC contractility and myosin light chain phosphorylation. In support of these in vitro and ex vivo results, Efnb1 KO mice on a high salt diet showed a statistically significant heightened increment of BP at multiple time points during stress compared with wild type littermates. Our results demonstrate that Efnb1 is a previously unknown negative regulator of VSMC contractility and BP and that it exerts such effects via reverse signaling through Grip1.

Receptor tyrosine kinase Ephb6 regulates vascular smooth muscle contractility and modulates blood pressure in concert with sex hormones

Eph kinases constitute the largest receptor tyrosine kinase family, and their ligands, ephrins (Efns), are also cell surface molecules. Our study is the first to assess the role of Ephb6 in blood pressure (BP) regulation. We observed that EphB6 and all three of its Efnb ligands were expressed on vascular smooth muscle cells (VSMC) in mice. We discovered that small arteries from castrated Ephb6 gene KO males showed increased contractility, RhoA activation, and constitutive myosin light chain phosphorylation ex vivo compared with their WT counterparts. Consistent with this finding, castrated Ephb6 KO mice presented heightened BP compared with castrated WT controls. In vitro experiments in VSMC revealed that cross-linking Efnbs but not Ephb6 resulted in reduced VSMC contractions, suggesting that reverse signaling through Efnbs was responsible for the observed BP phenotype. The reverse signaling was mediated by an adaptor protein Grip1. Additional experiments demonstrated decreased 24-h urine catecholamines in male Ephb6 KO mice, probably as a compensatory feedback mechanism to keep their BP in the normal range. After castration, however, such compensation was abolished in Ephb6 KO mice and was likely the reason why BP increased overtly in these animals. It suggests that Ephb6 has a target in the nervous/endocrine system in addition to VSMC, regulating a testosterone-dependent catecholamine compensatory mechanism. Our study discloses that Ephs and Efns, in concert with testosterone, play a critical role in regulating small artery contractility and BP.

RhoGDI signaling provides targets for cancer therapy

Rho GDP-Dissociation Inhibitors (RhoGDIs) are important regulators of the Rho family of small GTPases. The expression of RhoGDIs is altered in a variety of cancers and they have been shown to mediate several processes during tumorigenesis and cancer progression. Using examples of RhoGDI-mediated signaling and expression patterns in endothelial cells as well as pancreatic, breast, and bladder cancer, the multitude of potential cancer therapeutic targets presented by a better understanding of their function is illustrated. Several novel therapeutic strategies are proposed for intervening in RhoGDI signaling, and potential complications arising from their implementation are discussed.

Repression of the estrogen receptor-alpha transcriptional activity by the Rho/megakaryoblastic leukemia 1 signaling pathway

Although involved in processes leading to the emergence and development of hormone-dependent breast cancers, the estrogen receptor alpha (ERalpha) also prevents transformed cells from progressing toward a more aggressive phenotype. The transcriptional activity of ERalpha is mediated through two transactivation functions, called activation function 1 and 2, whose respective involvement varies in a cell-specific manner. Here, we identify the Rho/megakaryoblastic leukemia 1 (MKL1) signaling pathway as a main actor in controlling the cell-specific activity of both transactivation functions of ERalpha. Notably, we show that, when the coregulator MKL1 is sequestered in an inactive form by unpolymerized actin, the transcriptional activity of ERalpha mainly relies on the activation function 1. The activation of MKL1, which results from its dissociation from unpolymerized actin, promoted by the ability of Rho to support polymeric actin accumulation, silences the activation function 1 of ERalpha and allows the receptor to mainly act through its activation function 2. Importantly, this switch in the respective contribution exerted by both transactivation functions is correlated with an impaired ability of ERalpha to efficiently transactivate estrogen-regulated reporter genes. MKL1 is further shown to be present on estrogen-responsive genes in vivo. Interestingly, the Rho/MKL1 signaling pathway is activated during the epithelial-mesenchymal transition. A reduced transactivation efficiency of ERalpha, resulting from the activation of this pathway, may therefore suppress the protective role exerted by ERalpha toward tumor progression and invasiveness.

X chromosome gene expression in human tissues: male and female comparisons

About 25% of X-linked genes may escape inactivation at least to some degree. However, in vitro results from somatic cell hybrids may not reflect what happens in vivo. Therefore, we analyzed the female/male (F/M) gene fold expression ratio for 299 X-linked and 7795 autosomal genes from 11 different tissues from an existing in vivo microarray database. On average 5.1 and 4.9% of genes showed higher expression in females compared with 7.4 and 7.9% in males, respectively, for X-linked and autosomal genes. A trend was found for F/M gene fold ratios greater than 1.5 for several X-linked genes indicating overexpression in females among multiple tissues. Nine X-linked genes showed overexpression in females in at least 3 of the 11 studied tissues. Of the 9 genes, 6 were located on the short arm and 3 on the long arm of the X chromosome. Six of the 9 genes have previously been reported to escape X inactivation. However, in general, no consistent pattern was seen for the expression of X-linked genes between in vitro and in vivo systems. This study indicates that factors other than the X-inactivation process may impact on the expression of X-linked genes resulting in an overall similar gender expression for both X-linked and autosomal genes.

Genes invoked in the ovarian transition to menopause

Menopause and the associated declines in ovarian function are major health issues for women. Despite the widespread health impact of this process, the molecular mechanisms underlying the aging-specific decline in ovarian function are almost completely unknown. To provide the first gene-protein analysis of the ovarian transition to menopause, we have established and contrasted RNA gene expression profiles and protein localization and content patterns in healthy young and perimenopausal mouse ovaries. We report a clear distinction in specific mRNA and protein levels that are noted prior to molecular evidence of steroidogenic failure. In this model, ovarian reproductive aging displays similarities with chronic inflammation and increased sensitivity to environmental cues. Overall, our results indicate the presence of mouse climacteric genes that are likely to be major players in aging-dependent changes in ovarian function.

Expression of plexin-B1 in the mouse ovary and its possible role in follicular development

OBJECTIVE

To study the expression of plexin-B1 in the mouse ovary and its possible role in follicular development.

DESIGN

Controlled laboratory study.

SETTING

Research laboratory, Ha'Emek Medical Center.

PATIENT(S)

ICR female mice (n = 36) were studied.

MAIN OUTCOME MEASURE(S)

Plexin-B1 expression by immunohistochemistry, Western blot analysis, and reverse transcriptase-polymerase chain reaction. Microscopic morphometric and morphologic analysis for the evaluation of mouse follicular growth and E2, P, and T secretion from the developed follicles.

RESULT(S)

Plexin-B1 was expressed in the mouse ovary mostly in the granulosa cells. Plexin-B1 gene expression increased significantly by 126.8% +/- 38% in the pregnant mare serum gonadotropin-treated group and increased by 98.7% +/- 15.2 and 262.2% +/- 65.4% in the hCG-treated group 6 h and 24 h after injection, respectively (ANOVA; P < .05). Comparison of the maximum diameters of the control and study groups on day 9 of the culture period revealed a significant difference between the two groups (P < .001). In the control group, the mean maximum diameter was 191 +/- 2.6 microm compared with 136 +/- 5.13 microm in the presence of neutralizing antibodies against plexin-B1. Neutralizing antibody against plexin-B1 decreases E2 and P secretion.

CONCLUSION(S)

This study shows for the first time the expression of plexin-B1 in the mouse ovary. A possible role for plexin-B1 in follicular growth and steroidogenesis, most likely via the granulosa cells, is suggested.

Développement des inhibiteurs de farnésyl transférase comme agents anticancéreux

Ras proteins belong to the monomeric GTPases familly. They control cell growth, differentiation, proliferation, and survival. Ras mutations are frequently found in human cancers and play a fundamental role in tumorigenesis. Ras requires localization to the plasma membrane to exert its oncogenic effects. This subcelllular localization is dependent of protein farnesylation which is a post translational modification catalysed by the farnesyl transferase enzyme. Farnesyl transferase Inhibitors (FTI) were then designed ten to twelve years ago to inhibit ras processing and consequently the growth of ras mutated tumor. Preclinical data show that FTIs inhibit cell proliferation and survival in vitro and in vivo of a wide range of cancer cell lines, many of which contain wild type ras suggesting that mutated Ras is not the only target of the FTIs effects. Four FTIs went then through clinical trials and three of then are still developed in the clinic. Phase I et II clinical trials confirmed a relevant antitumor activity and a low toxicity. Phase III clinical trials are currently undergoing for both solid and hematologic tumors. The expected results should allow to define the position of FTIs as anticancer drugs, particularly in combination with conventional chemotherapy, hormone therapy, radiotherapy or any other new targeted compound.

G protein-coupled receptor 30 down-regulates cofactor expression and interferes with the transcriptional activity of glucocorticoid

G protein-coupled receptor 30 (GPR30) has previously been described to be important in steroid-mediated growth and to inhibit cell proliferation. Here we investigated whether the effect of GPR30 on cell growth is dependent on steroid hormone receptors. We stably introduced GPR30 in immortalized normal mammary epithelial (HME) cells using retroviruses for gene delivery. GPR30 inhibited the growth and proliferation of the cells. They expressed glucocorticoid receptor, but not estrogen or progesterone receptor. GPR30 down-regulated the expression of cofactor transcription intermediary factor 2 (TIF2) analyzed using quantitative RT-PCR analysis, and also diminished the expression of TIF2 at protein level analyzed by Western blotting using nuclear extracts from mammary epithelial cells. When HME cells were transiently transfected with the glucocorticoid response element MMTV-luc reporter plasmid, stable expression of GPR30 resulted in the abolition of ligand-induced transactivation of the promoter. In COS cells, transient transfection of GPR30 with glucocorticoid receptor alpha resulted in an abrogation of the MMTV-luc and GRE-luc reporter activities induced by dexamethasone. The results suggest a novel mechanism by which membrane-initiated signaling interferes with steroid signaling.

Transcriptional regulation of human UGT1A1 gene expression: activated glucocorticoid receptor enhances constitutive androstane receptor/pregnane X receptor-mediated UDP-glucuronosyltransferase 1A1 regulation with glucocorticoid receptor-interacting protein 1

UDP-glucuronosyltransferase (UGT) 1A1 glucuronidates endogenous metabolites, such as bilirubin, and exogenous substances, and plays a critical role in their detoxification and excretion. In a previous article, we described the phenobarbital response activity to a 290-base pair (bp) distal enhancer sequence (-3499/-3210) of the human UGT1A1 gene that is activated by the constitutive androstane receptor (CAR). Here, we show that dexamethasone at submicromolar concentrations enhances the pregnane X receptor (PXR) activator-mediated expression of the UGT1A1 gene and protein in HepG2 cells. We investigated the molecular mechanism of UGT1A1 induction by glucocorticoids at submicromolar concentrations and PXR activators and the functional cross-talk between the glucocorticoid receptor (GR) and CAR/PXR. The glucocorticoid-response element (GRE) was characterized by cotransfection experiments, site-directed mutagenesis, and electrophoretic mobility shift assays. Analysis of the human UGT1A1 promoter revealed GREs at -3404/-3389 and -3251/-3236 close to the CAR/PXR response element gtNR1 (-3382/-3367). Furthermore, in an in vitro reporter gene assay, dexamethasone effectively enhanced CAR/PXR-mediated transactivation of the 290-bp distal enhancer module in HepG2 cells and CV-1 cells in the presence of exogenously expressed GR and glucocorticoid receptor-interacting protein 1 (GRIP1). In glutathione S-transferase pull-down experiments, CAR and PXR interacted with GRIP1. Together, these results demonstrate a rational mechanistic basis for UGT1A1 induction by glucocorticoids and PXR activators, showing that activated GR enhances CAR/PXR-mediated UGT1A1 regulation with the transcriptional cofactor GRIP1 and that GR may be involved synergistically in the xenobiotic-responsive regulation of UGT1A1 by CAR/PXR.

Prenylation inhibitors stimulate both estrogen receptor alpha transcriptional activity through AF-1 and AF-2 and estrogen receptor beta transcriptional activity

Introduction

We showed in a previous study that prenylated proteins play a role in estradiol stimulation of proliferation. However, these proteins antagonize the ability of estrogen receptor (ER) α to stimulate estrogen response element (ERE)-dependent transcriptional activity, potentially through the formation of a co-regulator complex. The present study investigates, in further detail, how prenylated proteins modulate the transcriptional activities mediated by ERα and by ERβ.

Methods

The ERE-β-globin-Luc-SV-Neo plasmid was either stably transfected into MCF-7 cells or HeLa cells (MELN cells and HELN cells, respectively) or transiently transfected into MCF-7 cells using polyethylenimine. Cells deprived of estradiol were analyzed for ERE-dependent luciferase activity 16 hours after estradiol stimulation and treatment with FTI-277 (a farnesyltransferase inhibitor) or with GGTI-298 (a geranylgeranyltransferase I inhibitor). In HELN cells, the effect of prenyltransferase inhibitors on luciferase activity was compared after transient transfection of plasmids coding either the full-length ERα, the full-length ERβ, the AF-1-deleted ERα or the AF-2-deleted ERα. The presence of ERα was then detected by immunocytochemistry in either the nuclei or the cytoplasms of MCF-7 cells. Finally, Clostridium botulinum C3 exoenzyme treatment was used to determine the involvement of Rho proteins in ERE-dependent luciferase activity.

Results

FTI-277 and GGTI-298 only stimulate ERE-dependent luciferase activity in stably transfected MCF-7 cells. They stimulate both ERα-mediated and ERβ-mediated ERE-dependent luciferase activity in HELN cells, in the presence of and in the absence of estradiol. The roles of both AF-1 and AF-2 are significant in this effect. Nuclear ERα is decreased in the presence of prenyltransferase inhibitors in MCF-7 cells, again in the presence of and in the absence of estradiol. By contrast, cytoplasmic ERα is mainly decreased after treatment with FTI-277, in the presence of and in the absence of estradiol. The involvement of Rho proteins in ERE-dependent luciferase activity in MELN cells is clearly established.

Conclusions

Together, these results demonstrate that prenylated proteins (at least RhoA, RhoB and/or RhoC) antagonize the ability of ERα and ERβ to stimulate ERE-dependent transcriptional activity, potentially acting through both AF-1 and AF-2 transcriptional activities.

RhoA/ROCK activation by growth hormone abrogates p300/histone deacetylase 6 repression of Stat5-mediated transcription

We demonstrate here that growth hormone (GH) stimulates the activation of RhoA and its substrate Rho kinase (ROCK) in NIH-3T3 cells. GH-stimulated formation of GTP-bound RhoA requires JAK2-dependent dissociation of RhoA from its negative regulator p190 RhoGAP. Inactivation of RhoA does not affect GH-stimulated JAK2 tyrosine phosphorylation nor p44/42 MAPK activity. However, RhoA and ROCK activities are required for GH-stimulated, Stat5-mediated transcription. RhoA-dependent enhancement of GH-stimulated, Stat5-mediated transcription is due to repression of histone deacetylase 6 activity recruited by transcription cofactor p300 that negatively regulates GH-stimulated, Stat5-mediated transcription. We also demonstrate that RhoA is the pivot for cAMP-dependent protein kinase inhibition of GH-stimulated, Stat5-mediated transcription as a consequence of cAMP-dependent protein kinase inactivation of RhoA through serine residue 188 of RhoA. We have therefore provided a novel mechanism by which a Ras-like small GTPase, RhoA, can regulate Stat5-mediated transcription.