RhoB, not RhoA, represses the transcription of the transforming growth factor beta type II receptor by a mechanism involving activator protein 1

Actin Cytoskeleton and Regulation of TGFβ Signaling: Exploring Their Links

Human tissues, to maintain their architecture and function, respond to injuries by activating intricate biochemical and physical mechanisms that regulates intercellular communication crucial in maintaining tissue homeostasis. Coordination of the communication occurs through the activity of different actin cytoskeletal regulators, physically connected to extracellular matrix through integrins, generating a platform of biochemical and biomechanical signaling that is deregulated in cancer. Among the major pathways, a controller of cellular functions is the cytokine transforming growth factor β (TGFβ), which remains a complex and central signaling network still to be interpreted and explained in cancer progression. Here, we discuss the link between actin dynamics and TGFβ signaling with the aim of exploring their aberrant interaction in cancer.

RhoB deficiency in thymic medullary epithelium leads to early thymic atrophy

RhoB, a member of the Rho subfamily of small GTPases, mediates diverse cellular functions, including cytoskeletal organization, cell transformation and vesicle trafficking. The thymus undergoes progressive decline in its structure and function after puberty. We found that RhoB was expressed in thymic medullary epithelium. To investigate a role of RhoB in the regulation of thymic epithelial organization or thymocyte development, we analyzed the thymi of RhoB-deficient mice. RhoB-deficient mice were found to display earlier thymic atrophy. RhoB deficiency showed significant reductions in thymus weight and cellularity, beginning as early as 5 weeks of age. The enhanced expression of TGF-β receptor type II (TGFβRII) in thymic medullary epithelium was observed in RhoB-null mice. In addition, the expression of fibronectin, which is shown to be regulated by TGF-β signaling, was accordingly increased in the mutant thymic medulla. Since there is no age-related change of RhoB expression in the thymus, it is unlikely that RhoB in thymic epithelium directly contributes to age-related thymic involution. Nevertheless, our findings strongly support a physiological role of RhoB in regulation of thymus development and maintenance through the inhibition of TGF-β signaling in thymic medullary epithelium.

JNK-mediated transcriptional upregulation of RhoB is critical for apoptosis of HCT-116 colon cancer cells by a novel diarylsulfonylurea derivative

Diarylsulfonylureas are potent antitumor agents that have been tested in clinical trials. However, detailed mechanisms of their apoptotic activity remain unclear. Here, we report a new diarylsulfonylurea derivative, LB2A, that upregulates RhoB, thereby inducing potent apoptosis in HCT-116 human colon cancer cells independently of p53 status. LB2A decreased procaspase-3, increased phospho-JNK, and cleaved PARP, leading to apoptosis of HCT-116 cells. Prior treatment of HCT-116 cells with the JNK inhibitor SP600125 and the RNA synthesis inhibitor DRB blocked apoptosis, implying that JNK activation and mRNA production are important for apoptosis by LB2A. Western blotting, RT-PCR, and RhoB-promoter luciferase reporter assays revealed that LB2A increased RhoB via JNK-mediated transcriptional activation. LB2A decreased HDAC1 and increased acetyl-H3, both of which activate the RhoB promoter and were blocked by SP600125. Ectopic expression of RhoB induced apoptosis of HCT-116 cells, suggesting that RhoB is critical for the anti-cancer activity of LB2A in human colon cancer cells. LB2A also exhibited potent tumor growth inhibition of HCT-116 cells in vivo using a mouse xenograft assay. Taken together, these results show that LB2A induces apoptosis of HCT-116 cells via JNK-mediated transcriptional upregulation of RhoB and may therefore provide a potential therapy for human colon cancer.

Mammalian Rho GTPases: new insights into their functions from in vivo studies

Rho GTPases are key regulators of cytoskeletal dynamics and affect many cellular processes, including cell polarity, migration, vesicle trafficking and cytokinesis. These proteins are conserved from plants and yeast to mammals, and function by interacting with and stimulating various downstream targets, including actin nucleators, protein kinases and phospholipases. The roles of Rho GTPases have been extensively studied in different mammalian cell types using mainly dominant negative and constitutively active mutants. The recent availability of knockout mice for several members of the Rho family reveals new information about their roles in signalling to the cytoskeleton and in development.

MAP1A light chain-2 interacts with GTP-RhoB to control epidermal growth factor (EGF)-dependent EGF receptor signaling

Rho GTPases have been implicated in the control of several cellular functions, including regulation of the actin cytoskeleton, cell proliferation, and oncogenesis. Unlike RhoA and RhoC, RhoB localizes in part to endosomes and controls endocytic trafficking. Using a yeast two-hybrid screen and a glutathione S-transferase pulldown assay, we identified LC2, the light chain of the microtubule-associated protein MAP1A, as a novel binding partner for RhoB. GTP binding and the 18-amino acid C-terminal hypervariable domain of RhoB are critical for its binding to MAP1A/LC2. Coimmunoprecipitation and immunofluorescence experiments showed that this interaction occurs in U87 cells. Down-regulation of MAP1A/LC2 expression decreased epidermal growth factor (EGF) receptor expression and modified the signaling response to EGF treatment. We concluded that MAP1A/LC2 is critical for RhoB function in EGF-induced EGF receptor regulation. Because MAP1A/LC2 is thought to function as an adaptor between microtubules and other molecules, we postulate that the RhoB and MAP1A/LC2 interactions facilitate endocytic vesicle trafficking and regulate the trafficking of signaling molecules.

Interleukin-1beta impairment of transforming growth factor beta1 signaling by down-regulation of transforming growth factor beta receptor type II and up-regulation of Smad7 in human articular chondrocytes

OBJECTIVE

Extracellular matrix deposition is tightly controlled by a network of regulatory cytokines. Among them, interleukin-1beta (IL-1beta) and transforming growth factor beta1 (TGFbeta1) have been shown to play antagonistic roles in tissue homeostasis. The purpose of this study was to determine the influence of IL-1beta on TGFbeta receptor type II (TGFbetaRII) regulation and TGFbeta1 responsiveness in human articular chondrocytes.

METHODS

TGFbeta1-induced gene expression was analyzed through plasminogen activator inhibitor 1 and p3TP-Lux induction. Receptor-activated Smad (R-Smad) phosphorylation, TGFbeta receptors, and Smad expression were determined by Western blotting and real-time reverse transcription-polymerase chain reaction techniques. Signaling pathways were investigated using specific inhibitors, messenger RNA (mRNA) silencing, and expression vectors.

RESULTS

IL-1beta down-regulated TGFbetaRII expression at both the protein and mRNA levels and led to inhibition of the TGFbeta1-induced gene expression and Smad2/3 phosphorylation. Moreover, IL-1beta strongly stimulated the expression of inhibitory Smad7. TGFbetaRII overexpression abolished the loss of TGFbeta1 responsiveness induced by IL-1beta. The decrease in TGFbetaRII required de novo protein synthesis and involved both the NF-kappaB and JNK pathways.

CONCLUSION

We demonstrate that IL-1beta impairs TGFbeta1 signaling through down-regulation of TGFbetaRII, which is mediated by the p65/NF-kappaB and activator protein 1/JNK pathways, and secondarily through the up-regulation of Smad7. These findings show that there is cross-talk in the signaling of 2 regulatory cytokines involved in inflammation.

Complexity in interpretation of embryonic epithelial-mesenchymal transition in response to transforming growth factor-beta signaling

Epithelial-mesenchymal transition (EMT) is a highly conserved and fundamental process that governs morphogenesis in development and may also contribute to cancer metastasis. Transforming growth factor (TGF-beta) is a potent inducer of EMT in various developmental and tumor systems. The analysis of TGF-beta signal transduction pathways is now considered a critically important area of biology, since many defects occur in these pathways in embryonic development. The complexity of TGF-beta signal transduction networks is overwhelming due to the large numbers of interacting constituents, complicated feedforward, feedback and crosstalk circuitry mechanisms that they involve in addition to the cellular kinetics and enzymatics that contribute to cell signaling. As a result of this complexity, apparently simple but highly important questions remain unanswered, that is, how do epithelial cells respond to such TGF-beta signals? System biology and cellular kinetics play a crucial role in cellular function; omissions of such a critical contributor may lead to inaccurate understanding of embryonic EMT. In this review, we identify and explain why certain conditions need to be considered for a true representation of TGF-beta signaling in vivo to better understand the controlled, yet delicate mechanism of embryonic EMT.

Inhibition of Rho-kinase attenuates nephrosclerosis and improves survival in salt-loaded spontaneously hypertensive stroke-prone rats

OBJECTIVES

We examined whether the Rho/Rho-kinase pathway is involved in the pathogenesis of nephrosclerosis in severely hypertensive rats and assessed the effects of long-term treatment with a Rho-kinase inhibitor, fasudil, on kidney function, histological findings, gene expressions, and survival. We also attempted to elucidate the mechanisms involved.

METHODS

We studied the following four groups: control Wistar-Kyoto rats (WKY), untreated salt-loaded spontaneously hypertensive stroke-prone rats (SHR-SP), low-dose fasudil (15 mg/kg per day)-treated SHR-SP, and high-dose fasudil (30 mg/kg per day)-treated SHR-SP. After 8 weeks' treatment, the effects of fasudil were examined.

RESULTS

Untreated SHR-SP were characterized by increased blood pressure without circadian variation, decreased kidney function, abnormal renal morphological findings, and increased messenger RNA expression levels of transforming growth factor beta, collagen I, collagen III, p40phox, p47phox, plasminogen activator inhibitor 1, and intracellular adhesion molecule 1 in the renal cortex, compared with WKY. Long-term high-dose fasudil treatment significantly improved renal function (serum creatinine -32%, creatine clearance +39%), proteinuria (-92%) and histological findings (glomerular injury score -57%, arteriolar injury score -55%, fibrous area -40%, ED-1-positive cells -43%) without changing blood pressure or circadian variation, compared with untreated SHR-SP. In addition, fasudil significantly improved increased mRNA expression levels in the renal cortex. Furthermore, high-dose fasudil significantly prolonged survival time compared with untreated SHR-SP (P < 0.01). Low-dose fasudil treatment improved these variables slightly, but did not affect most significantly.

CONCLUSION

The Rho/Rho-kinase pathway participates in the pathogenesis of nephrosclerosis in SHR-SP independently of blood pressure-lowering activity, partly by upregulation of the gene expressions of extracellular matrix, oxidative stress, adhesion molecules, and antifibrinolysis.

Molecular pathways triggering glioma cell invasion

The efficacy of treating malignant gliomas with adjuvant therapies remains largely unsuccessful due to the inability to effectively target invading cells. Although our understanding of glioma oncogenesis has steadily improved, the molecular mechanisms that mediate glioma invasion are still poorly understood. It is clear that genetic alterations in malignant gliomas affect cell proliferation and cell cycle control, which are the targets of most chemotherapeutic agents. However, effective therapy against cell invasion has been less successful. Future treatment protocols must incorporate pharmacotherapeutic strategies that target resistant infiltrative glioma cells as well as proliferating ones. Thus, delineating the point of convergence of signaling pathways, which mediate glioma invasion, proliferation and apoptosis, may identify novel targets that can serve as possible points of therapeutic intervention. The optimization of novel strategies will require reliable preclinical testing using an in vivo animal model of brain invasion. Current applications of existing animal models are not currently optimized or characterized for use in glioma invasion research. As such, the development of a bona fide brain invasion model in vivo must be established. Progress in understanding molecular mechanisms driving glioma invasion will be critical to the success of managing and improving the outcome of patients with this grave disease.

Long-term administration of rho-kinase inhibitor ameliorates renal damage in malignant hypertensive rats

We have shown recently that fasudil, a Rho-kinase inhibitor, has renoprotective effects in salt-sensitive hypertensive rats. We hypothesized that activation of Rho-kinase is involved in the pathogenesis of glomerulosclerosis in malignant hypertensive rats. To test this hypothesis, we studied the following 4 groups: control Wistar-Kyoto rats, untreated deoxycorticosterone-acetate salt spontaneously hypertensive rats (DOCA-SHR), low-dose fasudil-treated DOCA-SHR, and high-dose fasudil-treated DOCA-SHR. After 3 weeks of treatment, the effects of fasudil were examined. DOCA-SHR was characterized by increased blood pressure (BP); increased kidney weight; decreased renal function; increased proteinuria; abnormal histological findings; increased monocyte/macrophage infiltration; increased urinary 8-isoprostran levels; increased gene expression of collagen I, collagen III, transforming growth factor-beta, and reduced nicotinamide-adenine dinucleotide phosphate oxidase subunits (p40phox, p47phox, and p67phox); and decreased gene expression of endothelial NO synthase (eNOS) in the renal cortex as compared with Wistar-Kyoto rats. Long-term high-dose fasudil treatment significantly improved renal function and histological findings without changing BP, as compared with untreated DOCA-SHR. Interestingly, long-term fasudil treatment significantly decreased monocyte/macrophage infiltration and urinary 8-isoprostran excretion, in association with decreased mRNA levels of transforming growth factor-beta, collagen I, collagen III, and NADPH oxidase subunits (p40phox, p47phox, and p67phox), and increased mRNA levels of eNOS in the renal cortex. Long-term low-dose fasudil treatment tended to improve these variables slightly but did not affect most of them significantly. Our results suggest that long-term fasudil treatment provides renoprotective effects independent of BP-lowering activity. These renoprotective effects are associated with inhibition of extracellular matrix gene expression, monocyte/macrophage infiltration, oxidative stress, and upregulation of eNOS gene expression.

E-cadherin transcriptional downregulation by promoter methylation but not mutation is related to epithelial-to-mesenchymal transition in breast cancer cell lines

Using genome-wide expression profiling of a panel of 27 human mammary cell lines with different mechanisms of E-cadherin inactivation, we evaluated the relationship between E-cadherin status and gene expression levels. Expression profiles of cell lines with E-cadherin (CDH1) promoter methylation were significantly different from those with CDH1 expression or, surprisingly, those with CDH1 truncating mutations. Furthermore, we found no significant differentially expressed genes between cell lines with wild-type and mutated CDH1. The expression profile complied with the fibroblastic morphology of the cell lines with promoter methylation, suggestive of epithelial–mesenchymal transition (EMT). All other lines, also the cases with CDH1 mutations, had epithelial features. Three non-tumorigenic mammary cell lines derived from normal breast epithelium also showed CDH1 promoter methylation, a fibroblastic phenotype and expression profile. We suggest that CDH1 promoter methylation, but not mutational inactivation, is part of an entire programme, resulting in EMT and increased invasiveness in breast cancer. The molecular events that are part of this programme can be inferred from the differentially expressed genes and include genes from the TGFβ pathway, transcription factors involved in CDH1 regulation (i.e. ZFHX1B, SNAI2, but not SNAI1, TWIST), annexins, AP1/2 transcription factors and members of the actin and intermediate filament cytoskeleton organisation.

Molecular Mechanisms and Therapeutic Strategies of Chronic Renal Injury: Renoprotective Effect of Rho-Kinase Inhibitor in Hypertensive Glomerulosclerosis

Among the GTP-binding proteins, Rho is known to function as a molecular switch in various cellular functions. Among the Rho effectors, the cellular function and signal transduction of Rho-kinase have been extensively studied. However, information about its in vivo functions is still limited. With the recent development of a specific Rho-kinase inhibitor such as Y-27632 and fasudil, the understanding of the role of the Rho/Rho-kinase pathway in vitro and in vivo has advanced. However, to date, there have been few studies investigating the role of Rho-kinase in renal disease. Recent studies have shown that Rho-kinase inhibitor significantly attenuated the tubulointerstitial fibrosis in kidney induced by unilateral ureteral obstruction. However, there have been few studies investigating the role of the Rho/Rho-kinase pathway in hypertensive glomerular sclerosis. In this review, we described the role of the Rho/Rho-kinase pathway in the progression of renal glomerulosclerosis in several forms of hypertensive rats. Our results suggest that chronic inhibition of the Rho-kinase pathway may be a new therapeutic approach for hypertensive glomerulosclerosis. Our results also suggest that the mechanism of the renoprotective effect of Rho-kinase inhibitor is partly mediated via inhibition of extracellular matrix gene expression, monocytes/macrophages infiltration, oxidative stress, and upregulation of eNOS gene expression.

Initial molecular characterization of a novel Rho-type GTPase RhoH in the filamentous ascomycete Ashbya gossypii

The organization of the actin cytoskeleton is of central importance in determining cell shape and morphogenesis. Rho-type GTP-binding proteins are known for their role to activate downstream effector proteins that act as scaffolds and direct the assembly of actin filaments. We have identified a novel Rho-type GTPase, RHOH, in the filamentous ascomycete Ashbya gossypii and also in one of its closest relatives, Holleya sinecauda both species belonging to the genus Eremothecium. RHOH is a paralog of AgRHO1 and was generated by tandem duplication in an evolutionary ancestor but is not found in Saccharomyces cerevisae. Deletion of RHOH was carried out in both A. gossypii and H. sinecauda and showed that this gene is non-essential. However, a cell wall defect was observed that led to increased cell lysis at the hyphal tip and an increased sensitivity against the cell wall agents calcofluor and SDS in the AgrhoH strain. These results suggested at least partially overlapping functions between RhoH and Rho1 without excluding any spilt functions of these proteins. Deletion of both the RHOH and RHO1 genes in A. gossypii exacerbated the mutant rho1 phenotype and resulted in germination deficient spores. This suggests that Rho1/RhoH -in contrast to Cdc42- are required at the early steps of spore germination.

Activation of RalA is critical for Ras-induced tumorigenesis of human cells

RalGEFs were recently shown to be critical for Ras-mediated transformed and tumorigenic growth of human cells. We now show that the oncogenic activity of these proteins is propagated by activation of one RalGEF substrate, RalA, but blunted by another closely related substrate, RalB, and that the oncogenic signaling requires binding of the RalBP1 and exocyst subunit effector proteins. Knockdown of RalA expression impeded, if not abolished, the ability of human cancer cells to form tumors. RalA was also commonly activated in a panel of cell lines from pancreatic cancers, a disease characterized by activation of Ras. Activation of RalA signaling thus appears to be a critical step in Ras-induced transformation and tumorigenesis of human cells.

Palmitoylated cysteine 192 is required for RhoB tumor-suppressive and apoptotic activities

RhoA and RhoB share 86% amino acid sequence identity, yet RhoA promotes whereas RhoB suppresses malignant transformation. Amino acids 29, 100, 116, 123, 129, 140-143, 141, 146, 152, 154, 155, 173, 181, 183-187, 189, 190, 191, 192, and 193 in RhoB were mutated to the corresponding RhoA residues to determine those critical for RhoB tumor-suppressive activity. Of all the mutants made, only the cysteine 192 (one of two palmitoylation sites) and cysteine 193 (the prenylation site) point mutations abolish RhoB functions. In contrast, mutation of the other palmitoylation site, cysteine 189, did not affect RhoB functions. Moving cysteine 192 to position 190 did not affect RhoB function either. Mutation of cysteine 192 to glycine, alanine, or serine blocks the ability of RhoB to suppress transforming growth factor beta type II receptor, p2lwaf, and AP-1 promoter transcriptional activities. Furthermore, mutations of cysteines 192 and 193, but not 189, mislocalize RhoB and prevent RhoB from inhibiting anchorage-dependent and anchorage-independent tumor growth and colony formation as well as prevent it from inducing apoptosis. The cysteine 192 RhoB mutant is farnesylated and geranylgeranylated as efficiently as wild type RhoB. A RhoA-(1-180)/RhoB-(181-196) chimera inhibited tumor cell proliferation and induced apoptosis as efficiently as RhoB. These results demonstrate that the presence of neither cysteine 193 nor cysteine 192 alone is sufficient and that both palmitoylated cysteine 192 and prenylated cysteine 193, but not palmitoylated cysteine 189, are required for RhoB tumor-suppressive and proapoptotic activities.

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.

Fasudil, a Rho-kinase inhibitor, attenuates glomerulosclerosis in Dahl salt-sensitive rats

OBJECTIVE

The present study was designed to clarify whether the Rho-Rho-kinase pathway is involved in the process of hypertensive glomerulosclerosis and to assess the therapeutic effect of fasudil, a specific Rho-kinase inhibitor.

METHOD AND RESULTS

Dahl salt-sensitive rats (DS) and Dahl salt-resistant rats (DR) were fed a high-salt diet at 6 weeks of age. Fasudil (30 mg/kg per day) was administered for 7 weeks to DS starting at the age of 11 weeks. After 7 weeks, untreated DS were characterized by decreased kidney function, increased proteinuria, abnormal morphological findings, increased adrenomedullin and atrial natriuretic peptide (ANP) levels, and increased renal messenger RNA expression of RhoB, Rho-kinasealpha, Rho-kinasebeta, collagen I and collagen III, and transforming growth factor-beta (TGF-beta) in the renal cortex compared with DR. Chronic fasudil treatment significantly improved renal function (serum creatinine, -26%; blood urea nitrogen, -41%; creatinine clearance, +42%), proteinuria (-24%) and histological findings (glomerular injury score, -49%; afferent arteriolar injury score, -17%) without changing blood pressure compared with untreated DS. Interestingly, long-term fasudil treatment decreased the plasma adrenomedullin (-25%) and ANP (-49%), but did not change the plasma renin or aldosterone. Furthermore, fasudil significantly decreased the messenger RNA expression of TGF-beta (-20%), collagen I (-23%), and collagen III (-24%) in the renal cortex. However, there were still significant differences in the aforementioned parameters between DR and fasudil-treated DS.

CONCLUSION

These results suggest that the Rho-Rho-kinase pathway may be partly responsible for the pathogenesis of hypertensive glomerulosclerosis independently of blood pressure in DS, and that chronic inhibition of the Rho-Rho-kinase pathway may be a new strategy for treating hypertensive nephrosclerosis.

Increased long-term potentiation in the CA1 region of rat hippocampus via modulation of GTPase signalling or inhibition of Rho kinase

There is accumulating evidence that Ras, and Ras-related GTPases of the Rho family, such as RhoA, RhoB and Rac1, are involved in synaptic plasticity in brain regions such as the hippocampus. We have recently shown that Rho family GTPases are activated by synaptic transmission in the CA1 region of the hippocampus. Since the function of these GTPases is dependent on post-translational isoprenylation by either farnesyl or geranylgeranyl transferases, we tested the hypothesis that inhibition of isoprenylation would modify long-term potentiation (LTP). Farnesyl transferase inhibition, which suppressed activation of RhoB and Ras but not RhoA or Rac1, reduced the magnitude of LTP, while geranylgeranyl transferase inhibition, which inhibited RhoA and Rac1 but not RhoB, increased the magnitude of LTP. In addition, Y-27632, a specific inhibitor of a downstream effector of Rho GTPases-Rho-kinase-also increased the magnitude of LTP. This provides strong evidence that GTPases are important mediators of synaptic plasticity, and demonstrates that Rho-kinase acts to reduce the degree of plasticity at hippocampal synapses during LTP. Rho-kinase inhibitors have the unusual property of increasing the magnitude of LTP, and so may be potential cognitive enhancers.

Rho and Rac take center stage

Many features of cell behavior are regulated by Rho family GTPases, but the most profound effects of these proteins are on the actin cytoskeleton and it was these that first drew attention to this family of signaling proteins. Focusing on Rho and Rac, we will discuss how their effectors regulate the actin cytoskeleton. We will describe how the activity of Rho proteins is regulated downstream from growth factor receptors and cell adhesion molecules by guanine nucleotide exchange factors and GTPase activating proteins. Additionally, we will discuss how there is signaling crosstalk between family members and how various bacterial pathogens have developed strategies to manipulate Rho protein activity so as to enhance their own survival.

TGFbeta3 signaling activates transcription of the LEF1 gene to induce epithelial mesenchymal transformation during mouse palate development

Epithelial mesenchymal transformation (EMT) of the medial edge epithelial (MEE) seam creates palatal confluence. This work aims to elucidate the molecular mechanisms by which TGFβ₃ brings about palatal seam EMT. We collected mRNA for PCR analysis from individual transforming MEE cells by laser microdissection techniques and demonstrated that TGFβ₃ stimulates lymphoid-enhancing factor 1 (LEF1) mRNA synthesis in MEE cells. We show with antisense β-catenin oligonucleotides that up-regulated LEF1 is not activated by β-catenin in palate EMT. We ruled out other TGFβ₃ targets, such as RhoA and MEK1/2 pathways, and we present evidence using dominant-negative Smad4 and dominant-negative LEF1 showing that TGFβ₃ uses Smads both to up-regulate synthesis of LEF1 and to activate LEF1 transcription during induction of palatal EMT. When phospho-Smad2 and Smad4 are present in the nucleus, LEF1 is activated without β-catenin. Our paper is the first to show that the Smad2,4/LEF1 complex replaces β-catenin/LEF1 during activation of EMT in vivo by TGFβ₃.

Activation of Rho GTPases by synaptic transmission in the hippocampus

Ras-related GTPases of the Rho family, such as RhoA and RhoB, are well-characterised mediators of morphological change in peripheral tissues via their effects on the actin cytoskeleton. We tested the hypothesis that Rho family GTPases are involved in synaptic transmission in the CA1 region of the hippocampus. We show that GTPases are activated by synaptic transmission. RhoA and RhoB were activated by low frequency stimulation, while the induction of long-term potentiation (LTP) by high frequency stimulation was associated with specific activation of RhoB via NMDA receptor stimulation. This illustrates that these GTPases are potential mediators of synaptic transmission in the hippocampus, and raises the possibility that RhoB may play a role in plasticity at hippocampal synapses during LTP.

Androgen control of cell proliferation and cytoskeletal reorganization in human fibrosarcoma cells: role of RhoB signaling

We recently generated an HT-1080-derived cell line called HT-AR1 that responds to dihydrotestosterone (DHT) treatment by undergoing cell growth arrest in association with cytoskeletal reorganization and induction of neuroendocrine-like cell differentiation. In this report, we show that DHT induces a dose-dependent increase in G0/G1 growth-arrested cells using physiological levels of hormone. The arrested cells increase in cell size and contain a dramatic redistribution of desmoplakin, keratin 5, and chromogranin A proteins. DHT-induced cytoskeletal changes were also apparent from time lapse video microscopy that showed that androgen treatment resulted in the rapid appearance of neuronal-like membrane extensions. Expression profiling analysis using RNA isolated from DHT-treated HT-AR1 cells revealed that androgen receptor activation leads to the coordinate expression of numerous cell signaling genes including RhoB, PTGF-beta, caveolin-2, Egr-1, myosin 1B, and EHM2. Because RhoB has been shown to have a role in tumor suppression and neuronal differentiation in other cell types, we investigated RhoB signaling functions in the HT-AR1 steroid response. We found that steroid induction of RhoB was DHT-specific and that newly synthesized RhoB protein was post-translationally modified and localized to endocytic vesicles. Moreover, treatment with a farnesyl transferase inhibitor reduced DHT-dependent growth arrest, suggesting that prenylated RhoB might function to inhibit HT-AR1 cell proliferation. This was directly shown by transfecting HT-AR1 cells with RhoB coding sequences containing activating or dominant negative mutations.

Transforming growth factor beta1 receptor II is downregulated by E1A in adenovirus-infected cells

Transforming growth factor beta1 (TGF-beta1) signaling is compromised in many tumors, thereby allowing the tumor to escape the growth-inhibitory and proapoptotic activities of the cytokine. Human adenoviruses interfere with a number of cellular pathways involved in cell cycle regulation and apoptosis, initially placing the cell in a "tumor-like" state by forcing quiescent cells into the cell cycle and also inhibiting apoptosis. We report that adenovirus-infected cells resemble tumor cells in that TGF-beta1 signaling is inhibited. The levels of TGF-beta1 receptor II (TbetaRII) in adenovirus-infected cells were decreased, and this decrease was mapped, by using virus mutants, to the E1A gene and to amino acids 2 to 36 and the C-terminal binding protein binding site in the E1A protein. The decrease in the TbetaRII protein was accompanied by a decrease in TbetaRII mRNA. The decrease in TbetaRII protein levels in adenovirus-infected cells was greater than the decrease in TbetaRII mRNA, suggesting that downregulation of the TbetaRII protein may occur through more than one mechanism. Surprisingly in this context, the half-lives of the TbetaRII protein in infected and uninfected cells were similar. TGF-beta1 signaling was compromised in cells infected with wild-type adenovirus, as measured with 3TP-lux, a TGF-beta-sensitive reporter plasmid expressing luciferase. Adenovirus mutants deficient in TbetaRII downregulation did not inhibit TGF-beta1 signaling. TGF-beta1 pretreatment reduced the relative abundance of adenovirus structural proteins in infected cells, an effect that was potentiated when cells were infected with mutants incapable of modulating the TGF-beta signaling pathway. These results raise the possibility that inhibition of TGF-beta signaling by E1A is a means by which adenovirus counters the antiviral defenses of the host.

Transforming growth factor beta-regulated gene expression in a mouse mammary gland epithelial cell line

Background

Transforming growth factor beta (TGF-β) plays an essential role in a wide array of cellular processes. The most well studied TGF-β response in normal epithelial cells is growth inhibition. In some cell types, TGF-β induces an epithelial to mesenchymal transition (EMT). NMuMG is a nontransformed mouse mammary gland epithelial cell line that exhibits both a growth inhibitory response and an EMT response to TGF-β, rendering NMuMG cells a good model system for studying these TGF-β effects.

Method

A National Institutes of Aging mouse 15,000 cDNA microarray was used to profile the gene expression of NMuMG cells treated with TGF-β1 for 1, 6, or 24 hours. Data analyses were performed using GenePixPro and GeneSpring software. Selected microarray results were verified by northern analyses.

Results

Of the 15,000 genes examined by microarray, 939 were upregulated or downregulated by TGF-β. This represents approximately 10% of the genes examined, minus redundancy. Seven genes previously not known to be regulated by TGF-β at the transcriptional level (Akt and RhoB) or not at all (IQGAP1, mCalpain, actinin α3, Ikki, PP2A-PR53), were identified and their regulation by TGF-β verified by northern blotting. Cell cycle pathway examination demonstrated downregulation of cyclin D₂, c-myc, Id2, p107, E2F5, cyclin A, cyclin B, and cyclin H. Examination of cell adhesion-related genes revealed upregulation of c-Jun, α-actinin, actin, myosin light chain, p120cas catenin (Catns), α-integrin, integrin β5, fibronectin, IQGAP1, and mCalpain.

Conclusion

Using a cDNA microarray to examine TGF-β-regulated gene expression in NMuMG cells, we have shown regulation of multiple genes that play important roles in cell cycle control and EMT. In addition, we have identified several novel TGF-β-regulated genes that may mediate previously unknown TGF-β functions.

Epigenetic regulation of ARHI in breast and ovarian cancer cells

ARHI (Ras homologue member I) encodes a 26-kDa GTPase with 50-60% amino acid homology to Ras and Rap. ARHI and Ras share similar GTP/GDP binding domains, but exert opposite functions. ARHI is one of the first reported tumor suppressors in the ras superfamily. ARHI is expressed consistently in normal breast and ovarian epithelial cells, but not in breast or ovarian cancers. The loss of ARHI can be related to tumor progression. Reexpression of ARHI induces apoptosis of breast and ovarian cancer cells by a caspase-independent, calpain-dependent pathway. ARHI is consistently expressed in normal breast and ovarian epithelial cells but is dramatically downregulated in more then 70% of breast and ovarian cancers. ARHI is maternally imprinted with methylation of the three CpG islands in the maternal allele of normal cells. ARHI is expressed only from the paternal allele whose three CpG islands are not methylated. Loss of ARHI expression can occur through a genetic event, with loss of heterozygosity observed in 40% of breast, ovarian, and pancreatic cancers; but it can also occur through epigenetic mechanisms, including DNA methylation, histone deacetylation, histone methylation, and transcriptional regulation. Our data suggest that acetylation and methylation of chromatin associated with the ARHI promoter leads to loss of both ARHI expression and the ability to suppress tumor growth. Changes in chromatin that silence ARHI may be driven by methylation-dependent and -independent pathways. Reactivation of both the silenced paternal and imprinted maternal alleles can be achieved by demethylation and inhibition of histone deacetylation.

Rap1 reverses transcriptional repression of TGF-beta type II receptor by a mechanism involving AP-1 in the human pancreatic cancer cell line, UK Pan-1

The TGF-beta signaling pathway has potent anti-mitogenic effects in epithelial cells and loss of negative growth regulation is often associated with increased tumorigenicity. The human pancreatic ductal adenocarcinoma cell line, UK Pan-1, which expresses DPC4, is not highly responsive to TGF-beta due to transcriptional repression of TGF-beta type II receptor (RII). Here, we show that UK Pan-1 cells transfected with a plasmid to overexpress rap1 protein (UK/rap1) causes an increase in RII transcription and restores sensitivity to TGF-beta growth inhibition. The overexpression of rap1 was associated with diminished ras signaling as measured by ras binding domain (RBD)-binding assays. Electrophoretic mobility shift assays (EMSA) analysis revealed increased binding of nuclear proteins to a previously identified positive regulatory element (PRE1) of the RII promoter in rap1 transfected cells. Competition with an oligo containing the AP-1 consensus site was able to inhibit this binding of nuclear proteins to the PRE1 region. Further EMSA analysis using antibodies to various AP-1 components revealed that junB antibodies partially depleted the increase in binding to the PRE1 seen in UK/rap1 cells while antibodies to other AP-1 constituents such as c-jun, c-fos, and ATF-1 had no effect on binding. Consistent with this data, transient transfection of UK Pan-1 cells with junB resulted in greater RII transcription (twofold) as measured by RII-luciferase assay. Mutation of the AP-1 site inhibited junB-mediated or rap1-mediated increases in RII promoter activity. These data suggest that rap1 signaling may mediate an increase in RII transcription via increased binding of nuclear factors including junB to the PRE1 region of the RII promoter.

Acetaldehyde stimulates the activation of latent transforming growth factor-beta1 and induces expression of the type II receptor of the cytokine in rat cultured hepatic stellate cells

Acetaldehyde, the major active metabolite of alcohol, induces the activation of hepatic stellate cells (HSC), leading to over-production of alpha1(I) collagen and ultimately causing hepatic fibrosis. The underlying mechanisms of this process remain largely unknown. Transforming growth factor-beta1 (TGF-beta1) is a potent inducer of alpha1(I) collagen production. Accumulating evidence has shown a potential role for TGF-beta1 in alcohol-induced hepatic fibrogenesis. The aims of this study were to determine the effect of acetaldehyde on TGF-beta signalling, to elucidate the underlying mechanisms as well as to evaluate its role in expression of alpha1(I) collagen gene in cultured HSC. It was hypothesized that acetaldehyde activated TGF-beta signalling by inducing the expression of elements in the TGF-beta signal transduction pathway, which might contribute to alpha1(I) collagen gene expression in cultured HSC. Initial results revealed that acetaldehyde activated TGF-beta signalling in cultured HSC. Additional studies demonstrated that acetaldehyde stimulated the secretion and activation of latent TGF-beta1, and induced the expression of the type II TGF-beta receptor (Tbeta-RII). Further experiments found cis - and trans -activating elements responsible for Tbeta-RII gene expression induced by acetaldehyde. Activation of TGF-beta signalling by acetaldehyde contributed to alpha1(I) collagen gene expression in cultured HSC. In summary, this report demonstrated that acetaldehyde stimulated TGF-beta signalling by increasing the secretion and activation of latent TGF-beta1 as well as by inducing the expression of Tbeta-RII in cultured HSC. Results from this report provided a novel insight into mechanisms by which acetaldehyde stimulated the expression of alpha1(I) collagen in HSC and a better understanding of effects of alcohol (or acetaldehyde) on hepatic fibrogenesis.

Farnesyltransferase inhibitors: novel compounds in development for the treatment of myeloid malignancies

The farnesyltransferase inhibitors (FTIs) have been shown in early clinical trials to elicit antitumor actions in a broad range of solid and hematologic malignancies. The mechanism of FTI action involves blockade of farnesyltransferase, an enzyme implicated in multiple cell-signaling pathways involved in proliferation, angiogenesis, or decreased apoptosis. Of the four main classes of FTIs, two orally bioavailable FTIs have advanced farthest in clinical development. ZARNESTRA (formerly R115777, Ortho Biotech Oncology, Raritan, NJ) and Sarasar (formerly SCH66336, Schering-Plough, Kenilworth, NJ) have demonstrated biologic and clinical activity in a range of solid tumors, and Zarnestra phase I trials have documented clinical responses in approximately 30% of patients with high-risk leukemias or myelodysplastic syndrome (MDS). The main across-class toxicities associated with the use of FTIs are myelosuppression and fatigue. Certain toxicities, such as the QTc abnormalities associated with L-778,123, do not appear to be class related. As results of phase II trials with FTIs in acute and chronic myeloid leukemias and in MDS become available, clinicians will learn more about the potential role of this class of targeted anticancer drugs-and possibly about the clinical distinctions among members of this class.