EGF modulation of the ras-related rhoB gene expression in human breast-cancer cell lines

Study on Allele Specific Expression of Long-Term Residents in High Altitude Areas

In diploid organisms, half of the chromosomes in each cell come from the father and half from the mother. Through previous studies, it was found that the paternal chromosome and the maternal chromosome can be regulated and expressed independently, leading to the emergence of allele specific expression (ASE). In this study, we analyzed the differential expression of alleles in the high-altitude population and the normal population based on the RNA sequencing data. Through gene cluster analysis and protein interaction network analysis, we found some changes occurred at the gene level, and some negative effects. During the study, we realized that the calmodulin homology domain may have a certain correlation with long-term survival at high altitude. The plateau environment is characterized by hypoxia, low air pressure, strong ultraviolet radiation, and low temperature. Accordingly, the genetic changes in the process of adaptation are mainly reflected in these characteristics. High altitude generation living is also highly related to cancer, immune disease, cardiovascular disease, neurological disease, endocrine disease, and other diseases. Therefore, the medical system in high altitude areas should pay more attention to these diseases.

RhoB as a tumor suppressor: It’s all about localization

The small GTPase RhoB is distinguished from other Rho proteins by its unique subcellular localization in endosomes, multivesicular bodies, and nucleus. Despite high sequence homology with RhoA and RhoC, RhoB is mainly associated with tumor suppressive function, while RhoA and RhoC support oncogenic transformation in most malignancies. RhoB regulates the endocytic trafficking of signaling molecules and cytoskeleton remodeling, thereby controlling growth, apoptosis, stress response, immune function, and cell motility in various contexts. Some of these functions may be ascribed to RhoB's unique subcellular localization to endocytic compartments. Here we describe the pleiotropic roles of RhoB in cancer suppression in the context of its subcellular localization, and we discuss possible therapeutic avenues to pursue and highlight priorities for future research.

The RAS-related GTPase RHOB confers resistance to EGFR-tyrosine kinase inhibitors in non-small-cell lung cancer via an AKT-dependent mechanism

Although lung cancer patients harboring EGFR mutations benefit from treatment with EGFR‐tyrosine kinase inhibitors (EGFR‐TKI), most of them rapidly relapse. RHOB GTPase is a critical player in both lung carcinogenesis and the EGFR signaling pathway; therefore, we hypothesized that it could play a role in the response to EGFR‐TKI. In a series of samples from EGFR‐mutated patients, we found that low RHOB expression correlated with a good response to EGFR‐TKI treatment while a poor response correlated with high RHOB expression (15.3 versus 5.6 months of progression‐free survival). Moreover, a better response to EGFR‐TKI was associated with low RHOB levels in a panel of lung tumor cell lines and in a lung‐specific tetracycline‐inducible EGFR^L858R transgenic mouse model. High RHOB expression was also found to prevent erlotinib‐induced AKT inhibition in vitro and in vivo. Furthermore, a combination of the new‐generation AKT inhibitor G594 with erlotinib induced tumor cell death in vitro and tumor regression in vivo in RHOB‐positive cells. Our results support a role for RHOB/AKT signaling in the resistance to EGFR‐TKI and propose RHOB as a potential predictor of patient response to EGFR‐TKI treatment.

Use of synthetic isoprenoids to target protein prenylation and Rho GTPases in breast cancer invasion

Dysregulation of Ras and Rho family small GTPases drives the invasion and metastasis of multiple cancers. For their biological functions, these GTPases require proper subcellular localization to cellular membranes, which is regulated by a series of post-translational modifications that result in either farnesylation or geranylgeranylation of the C-terminal CAAX motif. This concept provided the rationale for targeting farnesyltransferase (FTase) and geranylgeranyltransferases (GGTase) for cancer treatment. However, the resulting prenyl transferase inhibitors have not performed well in the clinic due to issues with alternative prenylation and toxicity. As an alternative, we have developed a unique class of potential anti-cancer therapeutics called Prenyl Function Inhibitors (PFIs), which are farnesol or geranyl-geraniol analogs that act as alternate substrates for FTase or GGTase. Here, we test the ability of our lead PFIs, anilinogeraniol (AGOH) and anilinofarnesol (AFOH), to block the invasion of breast cancer cells. We found that AGOH treatment effectively decreased invasion of MDA-MB-231 cells in a two-dimensional (2D) invasion assay at 100 µM while it blocked invasive growth in three-dimensional (3D) culture model at as little as 20 µM. Notably, the effect of AGOH on 3D invasive growth was phenocopied by electroporation of cells with C3 exotransferase. To determine if RhoA and RhoC were direct targets of AGOH, we performed Rho activity assays in MDA-MB-231 and MDA-MB-468 cells and found that AGOH blocked RhoA and RhoC activation in response to LPA and EGF stimulation. Notably, the geranylgeraniol analog AFOH was more potent than AGOH in inhibiting RhoA and RhoC activation and invasive growth. Interestingly, neither AGOH nor AFOH impacted 3D growth of MCF10A cells. Collectively, this study demonstrates that AGOH and AFOH dramatically inhibit breast cancer invasion, at least in part by blocking Rho function, thus, suggesting that targeting prenylation by using PFIs may offer a promising mechanism for treatment of invasive breast cancer.

RhoB modifies estrogen responses in breast cancer cells by influencing expression of the estrogen receptor

INTRODUCTION

RhoB has been reported to exert positive and negative effects on cancer pathophysiology but an understanding of its role in breast cancer remains incomplete. Analysis of data from the Oncomine database showed a positive correlation between RhoB expression and positivity for both estrogen receptor alpha (ERα) and progesterone receptor (PR).

METHODS

This finding was validated by our analysis of a tissue microarray constructed from a cohort of 113 patients and then investigated in human cell models.

RESULTS

We found that RhoB expression in tissue was strongly correlated with ERα and PR expression and inversely correlated with tumor grade, tumor size and count of mitosis. In human breast cancer cell lines, RhoB attenuation was associated with reduced expression of both ERα and PR, whereas elevation of RhoB was found to be associated with ERα overexpression. Mechanistic investigations suggested that RhoB modulates ERα expression, controlling both its protein and mRNA levels, and that RhoB modulates PR expression by accentuating the recruitment of ERα and other major co-regulators to the promoter of PR gene. A major consequence of RhoB modulation was that RhoB differentially regulated the proliferation of breast cancer cell lines. Interestingly, we documented crosstalk between RhoB and ERα, with estrogen treatment leading to RhoB activation.

CONCLUSION

Taken together, our findings offer evidence that in human breast cancer RhoB acts as a positive function to promote expression of ERα and PR in a manner correlated with cell proliferation.

RhoB controls endothelial cell morphogenesis in part via negative regulation of RhoA

Recent studies have suggested a role for the small GTPase RhoB in the control of processes required for angiogenesis. However, the mechanisms whereby RhoB exerts control over these processes are not well understood. Given the role of vascular endothelial growth factor (VEGF) in pathological angiogenesis, we were interested in examining whether RhoB contributed to VEGF-induced angiogenic processes. To assess this, RhoB was specifically depleted in human umbilical vein endothelial cells (HUVEC), using siRNA-targeted strategies. The effects of RhoB depletion on VEGF-induced angiogenic activities were assessed using a variety of standard in vitro angiogenesis assays to assess endothelial cell viability, migration and capillary morphogenesis. Effects of RhoB depletion on signaling from other Rho family member proteins was also assessed using specific activity assays for RhoA and RhoC. We observed that although RhoB appeared dispensable for HUVEC viability, RhoB was required for endothelial cell migration, sprouting, and capillary morphogenesis. We also observed that siRNA-mediated depletion of RhoB in HUVEC resulted in increased RhoA activation in response to VEGF stimulation. This increased RhoA activation contributed to the cellular morphogenesis defects observed in RhoB-depleted cells, as inhibition of RhoA activity using C3 transferase, or inhibition of the activity of the downstream RhoA effectors Rho-dependent kinases I and II (ROCK I and II) led to a partial restoration of capillary morphogenesis in the absence of RhoB. Thus our data indicate that RhoB plays a significant role in VEGF-induced endothelial cell morphogenesis in part by negatively regulating the activity of RhoA and the RhoA/ROCK pathway.

miR-21 targets the tumor suppressor RhoB and regulates proliferation, invasion and apoptosis in colorectal cancer cells

It has become increasingly clear that microRNAs play an important role in many human diseases including cancer. Here, we show that expression of miR-21 in HEK293 and several colorectal cancer cells was found inversely correlated with ras homolog gene family, member B (RhoB) expression. miR-21 expression significantly suppressed RhoB 3' UTR luciferase-reporter activity, but the inhibitory effect was lost when the putative target sites were mutated. Exogenous miR-21 over-expression mimicked the effect of RhoB knockdown in promoting proliferation and invasion and inhibiting apoptosis, whereas anti-miR-21 or RhoB expression yielded opposite effects, in colorectal cancer cells. These results suggest that miR-21 is a regulator of RhoB expression and RhoB could be a useful target in exploring the potential therapeutic benefits of miR-21 mediated tumor cell behaviors in colorectal cancer.

The nuclear guanine nucleotide exchange factors Ect2 and Net1 regulate RhoB-mediated cell death after DNA damage

Commonly used antitumor treatments, including radiation and chemotherapy, function by damaging the DNA of rapidly proliferating cells. However, resistance to these agents is a predominant clinical problem. A member of the Rho family of small GTPases, RhoB has been shown to be integral in mediating cell death after ionizing radiation (IR) or other DNA damaging agents in Ras-transformed cell lines. In addition, RhoB protein expression increases after genotoxic stress, and loss of RhoB expression causes radio- and chemotherapeutic resistance. However, the signaling pathways that govern RhoB-induced cell death after DNA damage remain enigmatic. Here, we show that RhoB activity increases in human breast and cervical cancer cell lines after treatment with DNA damaging agents. Furthermore, RhoB activity is necessary for DNA damage-induced cell death, as the stable loss of RhoB protein expression using shRNA partially protects cells and prevents the phosphorylation of c-Jun N-terminal kinases (JNKs) and the induction of the pro-apoptotic protein Bim after IR. The increase in RhoB activity after genotoxic stress is associated with increased activity of the nuclear guanine nucleotide exchange factors (GEFs), Ect2 and Net1, but not the cytoplasmic GEFs p115 RhoGEF or Vav2. Importantly, loss of Ect2 and Net1 via siRNA-mediated protein knock-down inhibited IR-induced increases in RhoB activity, reduced apoptotic signaling events, and protected cells from IR-induced cell death. Collectively, these data suggest a mechanism involving the nuclear GEFs Ect2 and Net1 for activating RhoB after genotoxic stress, thereby facilitating cell death after treatment with DNA damaging agents.

Phosphorylation of RhoB by CK1 impedes actin stress fiber organization and epidermal growth factor receptor stabilization

RhoB is a small GTPase implicated in cytoskeletal organization, EGF receptor trafficking and cell transformation. It is an immediate-early gene, regulated at many levels of its biosynthetic pathway. Herein we show that the serine/threonine protein kinase CK1 phosphorylates RhoB in vitro but not RhoA or RhoC. With the use of specific CK1 inhibitors, IC261 and D4476, we show that the kinase phosphorylates also RhoB in HeLa cells. Mass spectrometry analysis demonstrates that RhoB is monophosphorylated by CK1, in its C-terminal end, on serine 185. The substitution of Ser185 by Ala dramatically inhibited the phosphorylation of RhoB in cultured cells. Lastly we show that the inhibition of CK1 activates RhoB and promotes RhoB dependent actin fiber formation and EGF-R level. Our data provide the first demonstration of RhoB phosphorylation and indicate that this post-translational maturation would be a novel critical mechanism to control the RhoB functions.

Cytokeratin KRT8/18 expression differentiates distinct subtypes of grade 3 invasive ductal carcinoma of the breast

Invasive ductal carcinomas of the breast (IDC) are routinely assessed on hematoxylin and eosin stained paraffin sections, with limited use of immunohistochemistry (IHC). Most IDC are regarded as a single diagnostic entity, IDC of no special type (IDC-NST), which is subdivided further only by grading. However, recent research suggests that there is high clinical relevance in differentiating IDC subtypes. Here, we ascertain whether tumor histology alone can predict basal or luminal cell phenotype in high-grade IDC-NST, and whether IHC and molecular characteristics are associated with the observed morphologies. A total of 29 grade 3 IDC-NST samples were studied, 10 tumors from a selected pilot cohort A and 19 tumors from an unselected validation cohort B. Along with histopathological assessment, the expression of ESR1, PGR, ERBB2 (HER-2), the basal/myoepithelial marker TP73L (p63), cytokeratins 5/6 (KRT5/6) and 14 (KRT14), and the luminal-specific cytokeratins 8/18 (KRT 8/18) and 19 (KRT19) was assessed by IHC. Hierarchical cluster analysis of clinicopathological variables and, separately, microarray expression profiles showed that the phenotypically distinctive basaloid and luminal tumors of cohort A fell into two main groups, defined by heterogeneous or uniformly positive expression of KRT8/18. The 38 genes differentially expressed between these two classes included ERBB2, KRT8, and six other genes previously associated with ERBB2-positive or luminal phenotypes. Tumor histology was not predictive for validation cohort B, but quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed two molecularly defined clusters that again aligned with the KRT8/18 staining phenotypes. Metaphase comparative genomic hybridization revealed 10q, 16q, and 20q copy-number imbalances that associated recurrently with KRT8/18 staining patterns.

Phase I Trial of Tipifarnib (R115777) Concurrent With Radiotherapy in Patients with Glioblastoma Multiforme

PURPOSE

To conduct a Phase I trial to determine the maximally tolerated dose (MTD) of tipifarnib in combination with conventional three-dimensional conformal radiotherapy (RT) for patients with glioblastoma multiforme.

METHODS AND MATERIALS

After resection or biopsy, tipifarnib was given 1 week before and then continuously during RT (60 Gy), followed by adjuvant administration until progression. The tipifarnib dose during RT was escalated in cohorts of 3 starting at 200 mg/day.

RESULTS

Thirteen patients were enrolled, and 12 were evaluable for MTD. Of these patients, 7 had undergone biopsy, 4 had partial resection, and 1 had gross total resection. No dose-limiting toxicity (DLT) was observed during the concomitant treatment at 200 mg. All 3 patients at 300 mg experienced DLT during the concomitant treatment: 1 with sudden death and 2 with acute pneumonitis. The MTD was reached at 300 mg. The adjuvant treatment was suppressed from the protocol after a case of pneumonitis during this treatment. Six additional patients were included at 200 mg/day of the new protocol, confirming the safety of this treatment. Of the 9 evaluable patients, 1 had partial response, 4 had stable disease, and 3 had rapid progression; the patient with gross total resection was relapse-free after 21 months. Median survival of the evaluable patients was 12 months (range, 5.2-21 months).

CONCLUSION

Tipifarnib (200 mg/day) concurrent with standard radiotherapy is well tolerated in patients with glioblastoma. Preliminary efficacy results are encouraging.

Epidermal growth factor receptor-induced circadian-time-dependent gene regulation in suprachiasmatic nucleus

A significant functional role for epidermal growth factor receptor (EGFR) in the suprachiasmatic nucleus is suggested by recent findings that epidermal growth factor receptor and its ligand transforming growth factor-alpha are highly expressed in the suprachiasmatic nucleus. Recent studies indicate that epidermal growth factor receptor activation induces behavioral and physiological effects, strengthening the notion that epidermal growth factor receptor can modulate suprachiasmatic nucleus neural function and behavior. A global transcriptional profiling study is performed to investigate the gene expression response to epidermal growth factor receptor activation in the suprachiasmatic nucleus. The results indicate that all of the observed gene expression response is circadian-time dependent. The response included several genes encoding different neuropeptide receptors, ion channels and kinases. In order to hypothesize the transcription factors underlying the epidermal growth factor receptor response, different circadian-time-dependent gene expression groups were analyzed for enriched transcriptional regulatory elements in the promoters. The results indicate that several transcription factors such as Elk1 and cAMP-responsive element binding protein/activating transcription factor family, known to be 'input points' to the core clock network, are playing a role. Together, these results indicate that epidermal growth factor receptor has a circadian-time-dependent neuromodulatory function in the suprachiasmatic nucleus.

RhoB is frequently downregulated in non-small-cell lung cancer and resides in the 2p24 homozygous deletion region of a lung cancer cell line

Identification of a homozygous deletion in cancer cells provides strong evidence for the location of a tumor suppressor gene (TSG). We analyzed the 2p24 homozygous deletion of a non-small-cell lung cancer (NSCLC) cell line, NCI-H2882, and found that the deletion size was 3.7 Mbp. Since RhoB, which has been suggested to be a candidate TSG, was located in this region, we analyzed RhoB for alterations in NSCLC. Although we found no mutations in 48 cell lines including 20 NSCLCs, a loss of heterozygosity (LOH) analysis in 128 primary NSCLCs showed that 25 of 62 informative samples had LOH at the RhoB locus. Northern blot analysis of 28 cell lines (including 15 NSCLCs) indicated that RhoB expression was downregulated in 27. We analyzed RhoB expression in 112 primary NSCLCs with immunohistochemistry and found no or a weak RhoB expression in 33 (42%) of 78 adenocarcinomas, whereas we found it in 29 (94%) of 31 squamous cell carcinomas. No or a weak expression of RhoB was more frequently observed in poorly- or moderately-differentiated adenocarcinomas than in well-differentiated ones (p = 0.0014). Furthermore, no or a weak expression of RhoB indicated a tendency to poor patient prognosis. Although hypermethylation was not found at the promoter region, the RhoB expression in NSCLC cell lines was induced by histone deacetylase inhibition, suggesting that RhoB downregulation may be due to histone modification. The present study demonstrates that RhoB expression is frequently downregulated in NSCLCs by multiple mechanisms, suggesting that RhoB is a candidate TSG for NSCLC.

RhoB protects human keratinocytes from UVB-induced apoptosis through epidermal growth factor receptor signaling

Exposure of the skin to UVB light results in the formation of DNA photolesions that can give rise to cell death, mutations, and the onset of carcinogenic events. Specific proteins are activated by UVB and then trigger signal transduction pathways that lead to cellular responses. An alteration of these signaling molecules is thought to be a fundamental event in tumor promotion by UVB irradiation. RhoB, encoding a small GTPase has been identified as a DNA damage-inducible gene. RhoB is involved in epidermal growth factor (EGF) receptor trafficking, cytoskeletal organization, cell transformation, and survival. We have analyzed the regulation of RhoB and elucidated its role in the cellular response of HaCaT keratinocytes to relevant environmental UVB irradiation. We report here that the activated GTP-bound form of RhoB is increased rapidly within 5 min of exposure to UVB, and then RhoB protein levels increased concomitantly with EGF receptor (EGFR) activation. Inhibition of UVB-induced EGFR activation prevents RhoB protein expression and AKT phosphorylation but not the early activation of RhoB. Blocking UVB-induced RhoB expression with specific small interfering RNAs inhibits AKT and glycogen synthase kinase-3beta phosphorylation through inhibition of EGFR expression. Moreover, down-regulation of RhoB potentiates UVB-induced cell apoptosis. In contrast, RhoB overexpression protects keratinocytes against UVB-induced apoptosis. These results indicated that RhoB is regulated upon UVB exposure by a two-step process consisting of an early EGFR-independent RhoB activation followed by an EGFR-dependent induction of RhoB expression. Moreover, we have demonstrated that RhoB is essential in regulating keratinocyte cell survival after UVB exposure, suggesting its potential role in photocarcinogenesis.

Geranylgeranylated, but not farnesylated, RhoB suppresses Ras transformation of NIH-3T3 cells

RhoB is a low molecular weight GTPase that is both farnesylated (RhoB-F) and geranylgeranylated (RhoB-GG) in cells. Based on data from rodent cell models, it has been suggested that RhoB displays differential effects on cell transformation, according to the nature of its prenylation. To test directly this hypothesis, we generated GTPase-deficient RhoB mutants that are exclusively either farnesylated or geranylgeranylated. We show that in Ras-transformed murine NIH-3T3 cells, RhoB-F enhances, whereas RhoB-GG and RhoB (F/GG) suppresses anchorage-dependent and -independent cell growth as well as tumor growth in nude mice. We then demonstrate that Ras constitutive activation of the tumor survival pathways Akt and NF-kappa B are blocked by RhoB-GG, but not by RhoB-F, providing further support for the opposing role of RhoB-F and RhoB-GG in Ras malignant transformation in NIH-3T3 cells. In addition, both RhoB (F/GG) and RhoB-GG induce apoptosis in Ras-transformed NIH-3T3 cells whereas RhoB-F has no effect. Our data demonstrate that RhoB-F and RhoB-GG which differ only by a 5-carbon isoprene behave differently in rodent cells highlighting the important role of prenyl groups in protein function and emphasize the potency of RhoB to regulate negatively the oncogenic signal.

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.

Relevance of breast cancer cell lines as models for breast tumours: an update

The number of available breast cancer cell (BCC) lines is small, and only a very few of them have been extensively studied. Whether they are representative of the tumours from which they originated remains a matter of debate. Whether their diversity mirrors the well-known inter-tumoural heterogeneity is another essential question. While numerous similarities have long been found between cell lines and tumours, recent technical advances, including the use of micro-arrays and comparative genetic analysis, have brought new data to the discussion. This paper presents most of the BCC lines that have been described in some detail to date. It evaluates the accuracy of the few of them widely used (MCF-7, T-47D, BT-474, SK-BR-3, MDA-MB-231, Hs578T) as tumour models. It is concluded that BCC lines are likely to reflect, to a large extent, the features of cancer cells in vivo. The importance of oestrogen receptor-alpha (gene ESR1 ) and Her-2/ neu ( ERBB2 ) as classifiers for cell lines and tumours is underlined. The recourse to a larger set of cell lines is suggested since the exact origin of some of the widely used lines remains ambiguous. Investigations on additional specific lines are expected to improve our knowledge of BCC and of the dialogue that these maintain with their surrounding normal cells in vivo.

Additive effects of tamoxifen and the farnesyl transferase inhibitor FTI-277 on inhibition of MCF-7 breast cancer cell-cycle progression

The efficacy of tamoxifen in the hormonal therapy of breast cancer is well established, but therapeutic resistance is inevitable. FTIs are a new class of anticancer drugs that are in phase III clinical evaluation. Since the mechanisms of action of these 2 classes of drugs are different, we tested the combination of tamoxifen and FTI-277 on inhibiting proliferation of hormone-dependent MCF-7 human breast cancer cells. An additive effect on cell proliferation was demonstrated, accompanied by an additive G(0)/G(1) arrest. The major effect of the combination of the 2 drugs was to maintain p21(waf/cip1) at an intermediate level, higher than that observed in the presence of tamoxifen alone. This was associated with an additive effect on inactivation of cyclin E-Cdk2 complexes and decreased phosphorylation of pRb and p130 pocket proteins. These effects were accompanied by increased association of 2 CDIs, p27(kip1) and p21(waf/cip1), with cyclin E-Cdk2 complexes. These data demonstrate that the additive effect is likely predominantly due to the recruitment of p27(kip1) and, to a lesser extent, p21(waf/cip1) into the cyclin E-Cdk2 complexes. Together, these results suggest that the combination of FTI and tamoxifen may increase the antitumor effect of either drug alone in breast cancer.

RhoB controls the 24 kDa FGF-2-induced radioresistance in HeLa cells by preventing post-mitotic cell death

Farnesylated Ras oncoprotein induces a cellular resistance to ionizing radiation that can be reversed by farnesyltransferase inhibitors (FTI). We previously demonstrated that, expression of the 24 kDa FGF2 isoform in wild type ras bearing HeLa cells, induced radioresistance which was also reversed by FTI. We tested the hypothesis that wild type Ras or RhoB, which has been proposed as a potential FTI target, could control the FGF-2-induced radioresistance mechanisms. For this, we expressed inducible dominant negative forms of Ras (RasN17) and Rho (RhoBN19) in 24 kDa FGF2 transfected HeLa cells and analysed their survival after irradiation. While no cell survival modification was observed after RasN17 induction, the expression of RhoBN19 induced a radiosensitization of FGF2 radioresistant HeLa cells in the same range as the one observed after a 48 h treatment with the specific FTI, R115777. Moreover, we showed that activated RhoB but not RhoA induced radioresistance in NIH3T3 cells. The radiosensitizer effect of RhoBN19 expression was due to the induction of the radiation induced post-mitotic cell death. Taken together, these data demonstrate that 24 kDa FGF-2-induced radioresistance is controlled by Rho pathways and suggest that RhoB should be a major determinant in cellular resistance to ionizing radiation.

Farnesyltransferase inhibitor, R115777, reverses the resistance of human glioma cell lines to ionizing radiation

We investigated for the first time the ability of farnesyltransferase inhibitors (FTI) to radiosensitize human glioma. For this, human glioma cell lines were treated with the specific FTI, R115777, 48 hr prior to a 2Gy irradiation. The treatment with R115777 decreased by 45% the SF2 value of the more radioresistant glioma cell lines (SF763 and U87) without any significant effect on the radioresistance of the radiosensitive ones (SF767 and U251-MG). This radiosensitizer effect was due to the induction of post-mitotic necrotic cell death. We then tested the hypothesis that wild-type Ras or RhoB, which has been proposed as potential FTI target, could control the glioma radioresistance. For this, we expressed inducible dominant negative forms of Ras (RasN17) and RhoB (RhoBN19) in radioresistant U87 glioma cell line and analyzed the survival after irradiation of the obtained clones. While blocking Ras pathways by expression of RasN17 did not affect the SF2 value of the U87 glioma cell line, the expression of RhoBN19 dramatically reduced the cell survival after irradiation of these cells. Taken together, these data demonstrated that RhoB, but not Ras, is implicated in glioma radioresistance. Furthermore, the R115777 differential radiosensitizer effect underlines the potential therapeutic interest of using this drug as a radiosensitizer of human glioma.

Overexpression of RhoA mRNA is associated with advanced stage in testicular germ cell tumour

OBJECTIVE

To clarify the role of Rho small GTP-binding protein (Rho) in the progression of testicular germ cell tumour (GCT), by examining the expression levels of mRNAs of Rho genes in testicular GCT.

PATIENTS AND METHODS

The mRNA levels of the RhoA, RhoB and RhoC genes were analysed in the surgical specimens of testicular GCT tissues from 45 consecutive Japanese patients, and in the corresponding unaffected tissue originating from the same patient, using reverse transcription-polymerase chain reaction. The expression levels in tumour tissues were compared with those in unaffected tissues and the relationship between their expression levels in tumours and tumour stage evaluated. The expression levels of mRNAs of the Rho genes were also evaluated between tumours with seminoma only, and mixed tumours with seminoma and nonseminoma.

RESULTS

The mRNA levels of RhoA were greater in tumour tissues than in unaffected tissues of the resected testis (P < 0.01); the mRNAs of RhoB and RhoC were not detected in either tissue. The increase in RhoA mRNA levels was related to tumour stage (P < 0.05). The mRNA levels of RhoA in seminomatous and nonseminomatous areas where both were present were higher than those in tumours with seminoma only (P < 0.05).

CONCLUSIONS

These results suggest that RhoA is involved in testicular germinal epithelial carcinogenesis and progression in testicular GCT, indicating that RhoA may be a useful prognostic marker for progression in testicular GCT.

Activation of protein kinase C by phorbol esters modulates alpha2beta1 integrin on MCF-7 breast cancer cells

Cellular adhesions to other cells and to the extracellular matrix play crucial roles in the malignant progression of cancer. In this study, we investigated the role of protein kinase C (PKC) in the regulation of cell-substratum adhesion by the breast adenocarcinoma cell line MCF-7. A PKC activator, 12-O-tetradecanoylphorbol-l, 3-acetate (TPA), stimulated cell adhesion to laminin and collagen I in a dose-dependent manner over a 1- to 4-h interval. This enhanced adhesion was mediated by alpha2beta1 integrin, since both anti-alpha2 and anti-beta1 blocking antibodies each completely abrogated the TPA-induced adhesion. FACS analysis determined that TPA treatment does not change the cell surface expression of alpha2beta1 integrin over a 4-h time interval. However, alpha2beta1 levels were increased after 24 h of TPA treatment. Thus, the enhanced avidity of alpha2beta1-dependent cellular adhesion preceded the induction of alpha2beta1 cell surface expression. Northern blot analysis revealed that mRNA levels of both alpha2 and beta1 subunits were increased after exposure to TPA for 4 h, indicating that the induction of alpha2beta1 mRNA preceded that of its cell surface expression. This further suggested that the TPA-induced avidity of alpha2beta1 was independent of increased expression of alpha2beta1. Pretreatment of cells with the PKC inhibitor calphostin C partially antagonized the TPA-induced increase in expression of alpha2beta1 integrin expression and of alpha2beta1-mediated cellular adhesion. To identify a possible mechanism by which TPA could be acting to promote the rapid induction of alpha2beta1 adhesion, we treated the cells with the Rho-GTPase inhibitor Clostridium botulinumexotoxin C3. C3 inhibited TPA-induced adhesion to laminin and collagen I in a dose-dependant manner, suggesting a likely role for Rho in TPA-induced adhesion. Together, these results suggest that PKC can modulate the alpha2beta1-dependent adhesion of MCF-7 cells by two distinct mechanisms: altering the gene expression of integrins alpha2 and beta1 and altering the avidity of the alpha2beta1 integrin by a Rho-dependant mechanism.

RhoB is stabilized by transforming growth factor beta and antagonizes transcriptional activation

Transforming growth factor beta (TGF-beta) is the prototype for an evolutionarily conserved superfamily of secreted factors implicated in diverse biological phenomena. The pleiotropic responses to TGF-beta are initiated by a heteromeric receptor complex that binds and phosphorylates downstream effectors. Among these, the Smads have been extensively studied. However, less attention has been directed toward alternative downstream effectors and their participation in TGF-beta signal transduction. We show that TGF-beta promotes accumulation of the labile monomeric GTPase RhoB by antagonizing its normal proteolytic destruction, presumably via the 26 S proteasome. RhoB accumulates in its isoprenylated form. Transient overexpression of wild type RhoB but not its dominant negative mutant RhoB-N19 antagonizes TGF-beta-mediated transcriptional activation. These results suggest a novel mechanism of regulation by TGF-beta and implicate RhoB as a negative regulator of TGF-beta signal transduction.

Analysis of differential protein expression in normal and neoplastic human breast epithelial cell lines

High-resolution two-dimensional gel electrophoresis (2-DE) and database analysis was used to establish protein expression patterns for cultured normal human mammary epithelial cells and thirteen breast cancer cell lines. The Human Breast Epithelial Cell database contains the 2-DE protein patterns, including relative protein abundances, for each cell line, plus a composite pattern that contains all the common and specifically expressed proteins from all the cell lines. Significant differences in protein expression, both qualitative and quantitative, were observed not only between normal cells and tumor cells, but also among the tumor cell lines. Eight percent (56/727) of the consistently detected proteins were found in significantly (P< 0.001) variable levels among the cell lines. Eight proteins present in normal cultured breast epithelial cells were not detected in any of the tumor cell lines. We identified a subset of the differentially expressed proteins using a combination of immunostaining, protein sequencing, comigration, and subcellular fractionation. These identified proteins include the intermediate filament components vimentin and cytokeratins. The cell lines can be classified into four distinct groups based on their intermediate filament protein profile. We also identified heat shock proteins; hsp27 and hsp60 varied in abundance and in some cases in the relative phosphorylation levels among the cell lines. Many of the differentially expressed proteins we identified have roles in cellular proliferation and differentiation, including annexin V, elongation initiation factor 5A, Rho GDP dissociation inhibitor, and prohibitin. We identified inosine-5-monophosphate dehydrogenase in each of the cell lines, and found the levels of this enzyme in the tumor cell lines elevated 2- to 20-fold relative to the levels in normal cells. These results expand the human breast epithelial cell protein database (http:// www.anl.gov/CMB/PMG) which is being built to assist researchers with the identification of abnormal patterns of expression and pathways associated with malignancy.

Prevention of EGF-modulated adhesion of tumor cells to matrix proteins by specific EGF receptor inhibition

The adhesion of tumor cells to various extracellular matrix (ECM) proteins is influenced by epidermal growth factor (EGF). Maximal effects are obtained at low EGF concentrations, at which mostly the cytoskeleton-associated high-affinity EGF receptors (EGFRs) are saturated. Tumor cells expressing EGFR either endogenously (MDA MB 231, MTLn3) or, for the human EGFR, ectopically (MTC HER1/1) in intermediate amounts exhibited, upon EGF addition, increased cellular adhesion to various ECM proteins, such as fibronectin, collagens and vitronectin. In contrast, human A431 and MDA MB 468 cells, over-expressing EGFR, demonstrated reduced attachment in similar experimental conditions. Both increased as well as reduced EGF-dependent adhesion could be blocked using either ligand-blocking monoclonal antibody 14E1 or the potent EGFR tyrosine kinase inhibitor PD 153035. Our data indicate that signals downstream of EGFR activation are responsible for the opposing effects of EGF on cellular adhesion since both can be prevented by EGFR inhibition. Thus, the integration of EGFR- and integrin-dependent signals can be different in carcinoma cell lines and might be influenced by EGFR numbers.

Overexpression of the rhoC gene correlates with progression of ductal adenocarcinoma of the pancreas

It has been reported that the rho genes, which consist of a ras-related small GTPase protein family, regulate cytoskeletal structures and have the potential to transform cultured cells. To investigate the biological relevance of the rho genes in pancreatic carcinogenesis, we examined expressions of the rhoA, B and C genes by polymerase chain reaction after reverse transcription (RT-PCR) in 33 cases of ductal adenocarcinoma of the pancreas. In addition, mutations of the K-ras, rhoA, B and C genes were studied in the same series of tumour tissues to correlate with rho gene expressions. The expression levels of the rhoC gene were significantly higher in tumours than in non-malignant portions (P < 0.001). Metastatic lesions overexpressed the rhoC gene compared with primary tumours (P < 0.05). Carcinoma tissues with perineural invasion and lymph node metastasis exhibited significantly higher expressions of the rhoC gene than tumours without these manifestations (P < 0.001 and P < 0.05 respectively). Overexpression of the rhoC gene significantly correlated with poorer prognosis of patients with pancreatic adenocarcinoma (P < 0.05). In contrast, the expression levels of the rhoA and B genes showed no significant relationship with clinicopathological findings. Mutation was not found either in the rhoA, B or C gene sequences examined. K-ras gene mutation, detected in 27 out of 33 (81.8%) cases, did not affect the expression levels in any of the rho genes. These suggest that elevated expression of the rhoC gene may be involved in the progression of pancreatic carcinoma independent of K-ras gene activation.

Gene expression of the small GTP-binding proteins RhoA, RhoB, Rac1, and Cdc42 in adult rat brain

GTPases of the Rho subfamily, i.e. Rho, Rac and Cdc42, are molecular switches in various signaling pathways. Best characterized are their functions in the regulation of the actin cytoskeleton. In neuronal cell lines they are involved in the mechanisms leading to synapse formation and plasticity. It is still unknown whether they have respective functions in the mammalian CNS. In this case, they should be present in the adult brain, especially in areas known for their synaptic remodeling. We have studied the expression of the Rho GTPases in adult rat brain with in situ hybridization and Western blot analysis. High amounts of RhoA, RhoB, Rac1 and Cdc42 mRNAs were detected in neurons of the hippocampus, i.e. in pyramidal cells of the CA1-CA4 regions as well as in granule cells of the dentate gyrus and in hilar cells. Also in cerebellum, Purkinje and granular cells expressed the four mRNAs. Strong gene expression was also found in brainstem, thalamus and neocortex. Using Western blot analysis, RhoA and Cdc42 proteins were detected in hippocampus, cerebellum, thalamus and neocortex. It is concluded that GTPases of the Rho family play a role in the regulation of cellular functions in the adult brain.

Activity of retinoic acid receptor-gamma selectively binding retinoids alone and in combination with interferon-gamma in breast cancer cell lines

Retinoids modulate several cell functions and especially inhibit the growth of a wide variety of cells including breast cancer. Retinoic acid receptor-gamma (RAR-gamma) has been shown to mediate the antiproliferative activity of retinoids. To further test this hypothesis we examined the effects of different RAR-gamma selectively binding retinoids (CD2325, CD2247, CD666 and CD437) on breast cancer cell lines. With exception of CD2247, all retinoids inhibited proliferation of MCF-7, SKBR-3, T47D and ZR-75-1 breast cancer cell lines, similar to the natural compound all-trans retinoic acid (ATRA). In addition, all 4 compounds were able to act synergistically with interferon-gamma (IFN-gamma) in all breast cancer cell lines including the retinoid-resistant BT-20 and 734-B lines. In functional transactivation assays we demonstrated that only in the MCF-7 cell line, TPA-mediated AP-1 activity was suppressed only by ATRA and CD2325, whereas in SKBR-3, another RA-sensitive breast cancer cell line, it was not. The synergistic antiproliferative activity involving retinoids and IFN-gamma could not be explained by an enhanced anti-AP-1 activity. No correlation was found between expression of RARs and cellular retinoic acid binding proteins (CRABPs) and antiproliferative effects of the retinoids. RAR-gamma selectively binding retinoids are potent inhibitors of breast cancer cell proliferation, alone and in combination with IFN-gamma. For this reason and because of a possible low toxicity, as compared with retinoic acid, we speculate that these RAR-gamma selective binding retinoids might be of clinical importance.

Isolation of a novel human cDNA (rhoHP1) homologous to rho genes

A novel full-length cDNA showing homology with rho genes was isolated from a human placenta cDNA library. Sequencing of a total of 1086 nucleotides of this clone revealed an open reading frame of 630 nucleotides (210 amino acids). In view of its degree of homology to members of the Rho family of molecules (50-54% identical amino acids, 60-63% identical nucleotides within the coding region), the predicted product was designated RhoHP1(Rho-related protein HP1). Northern analysis indicated that a message about 1.2-kb long is expressed in human heart, placenta, liver, skeletal muscle, and pancreas and, with weaker intensity, in several other tissues.

Combined analysis of in situ hybridization, cell cycle and structural markers using reflectance and immunofluorescence confocal microscopy

A method for the simultaneous detection of mRNA by reflectance in situ hybridization (RISH), cell cycle and structural markers by immunofluorescence using confocal laser scanning microscopy is presented. The mRNA expression of two ras-related genes rhoB and rhoC was analysed in human breast cancer cell lines and human histological specimens (breast cancer tissues and skin biopsies). In breast cancer cell lines, the conditions were optimized to detect RNA-RNA hybrids and DNA synthesis after pulse-labelling with bromodeoxyuridine. Endonuclease-exonuclease digestion, which allows the accessibility to specific antibodies of halogenated pyrimidine molecules, was carried out following ISH. Finally, cytokeratin or vimentin staining was performed. The detection of signals, arising from 1-nm colloidal gold particles without silver enhancement, by reflectance confocal laser scanning microscopy is described. Bromodeoxybiridine DNA markers and cytokeratin/vimentin staining were detected concomitantly using different fluorochromes. To allow comparative expression of two related genes, the mRNA of rhoB and rhoC were detected using digoxigenin- or biotin-labelled riboprobes and, after 3-D imaging, a detailed analysis by optical horizontal (x, y) and vertical (x, z) sectioning was undertaken. The subsequent bromodeoxyuridine detection procedure permitted to us explore the specific transcription of these two genes during S and non-S phases. This method allows the identification and localization of several subcellular components in cells within a complex tissue structure and makes it possible to analyse further transcript localization in relation to the function of the encoded protein and to the cell cycle.