Expression and prognostic role of RhoA GTPases in hepatocellular carcinoma

A comparative anticancer analysis of iron oxide nanoparticles of Hippophae rhamnoides and Cichorium intybus found in the Karakoram Range of Gilgit Baltistan against liver cancer targeting the RhoA gene

OBJECTIVE

The current research work focused on the evaluation of of H. rhamnoides and C. intybus Fe2O3 NPs against liver cancer cell line (HepG2) by performing antiproliferative assay targeting the RhoA gene and apoptotic pathway genes and proteins.

METHODS

Fe2O3 NPs were synthesized using extracts of H. rhamnoides and C. intybus and characterized by UV-Vis spectroscopy, FTIR, SEM/EDS and XRD. MTT assay was used to study cytotoxicity against the HepG2 cells. Real-time qPCR and ELISA were used for the gene and protein analysis.

RESULTS

An absorbance peak at 300 nm for H. rhamnoides and 289 nm for C. intybus nanoparticles were observed by UV-Vis analysis. The FTIR bands of H. rhamnoide Fe2O3 NPs suggested the presence of aldehydes, alcohols and polyols whereas bands of C. intybus Fe2O3 NPs suggested the presence of carboxyl groups, hydroxyl groups, alkynes and amines. The size of Fe2O3 NPs was found to be 27 ± 5nm for H. rhamnoides and 84 ± 4nm for C. intybus. The IC50 value of 41.69 µM for H. rhmnoides and 71.04 µM for C. intybus Fe2O3 NPs compared to plant extract (78.10 and 96.03 µM for H. rhamnoides and C. intybus, respectively) were found against HepG2 cells. The gene expression and protein levels of RhoA were decreased whereas those of bax, caspase 3, caspase 8 and caspase 9 were found increased.

CONCLUSION

Nanoparticles and extract of H. rhamnoides were found more effective as compared to C. intybus, which was evident by the results of cytotoxicity and analysis of studied genes and proteins.

Platelets' RNA as biomarker trove for differentiation of early-stage hepatocellular carcinoma from underlying cirrhotic nodules

BACKGROUND & AIMS

Among the multiplicity of factors involved in rising incidence of hepatocellular carcinoma (HCC)-the second deadliest cancer, late diagnosis of early-stage HCC nodules originating from late-stage cirrhotic nodules is the most crucial. In recent years, Tumor-educated platelets (TEPs) have emerged as a strong multimodal tool to be used in liquid-biopsy of cancers because of changes in their mRNA content. This study assessed the reliability of selected mRNA repertoire of platelets as biomarkers to differentiate early HCC from late-stage cirrhotic nodules.

METHODS

Quantitative real time PCR (qRT-PCR) was used to evaluate expression levels of selected platelets-specific mRNA between HCC patients compared to cirrhosis patients. ROC curve analysis assessed the sensitivity and specificity of the biomarkers.

RESULTS

RhoA, CTNNB1 and SPINK1 showed a significant 3.3-, 3.2- and 3.18-folds upregulation, respectively, in HCC patients compared to cirrhosis patients while IFITM3 and SERPIND1 presented a 2.24-fold change. Strikingly, CD41+ platelets also demonstrated a marked difference of expression in HCC and cirrhosis groups.

CONCLUSIONS

Our study reports liquid biopsy-based platelets mRNA signature for early diagnosis of HCC from underlying cirrhotic nodules. Moreover, differential expression of CD41+ platelets in two groups provides new insights into a probable link between CD41 expression on platelets with the progression of cirrhosis to HCC.

RhoA and Rac1 in Liver Cancer Cells: Induction of Overexpression Using Mechanical Stimulation

Liver cancer, especially hepatocellular carcinoma (HCC), is an aggressive disease with an extremely high mortality rate. Unfortunately, no promising markers are currently available for the early diagnosis of this disease. Thus, a reliable biomarker reflecting the early behaviour of the tumour will be valuable for diagnosis and treatment. The Ras homologous (Rho) GTPases, which belong to the small guanosine triphosphate (GTP) binding proteins, have been reported to play an important role in mediating liver cancer based on their important function in cytoskeletal reorganisation. These proteins can be either oncogenic or tumour suppressors. They are also associated with the acquirement of malignant features by cancer cells. The overexpression of RhoA and Rac1, members of the Rho GTPases, have been linked with carcinogenesis and the progression of different types of cancer. In the quest of elucidating the role of mechanical stimulation in the mechanobiology of liver cancer cells, this paper evaluates the effect of stretching on the expression levels of RhoA and Rac1 in different types of liver cancers. It is shown that that stretching liver cancer cells significantly increases the expression levels of RhoA and Rac1 in HCC and cholangiocarcinoma cell lines. We hypothesise that this relatively simple and sensitive method could be helpful for screening biological features and provide suitable treatment guidance for liver cancer patients.

The diagnostic and prognostic role of RhoA in hepatocellular carcinoma

The aim of this study was to investigate the expression level of Ras homolog gene family, member A (RhoA) in patients with hepatocellular carcinoma (HCC) and to investigate the prognostic and diagnostic value of RhoA. Data mining from various data bases and wet experiments on samples from Peking Union Medical College Hospital showed that RhoA mRNA and protein expression were significantly higher in the HCC tissues than in the normal tissues. Higher expression at both the mRNA and protein levels was associated with a poorer prognosis. High sensitivity (92.5%) and specificity (90.0%) were observed in the diagnostic model based on protein level rather than mRNA level. RhoA expression was modulated by genetic amplification. The lysosome, pathogenic Escherichia coli infection, purine metabolism and pyrimidine metabolism pathways were mainly enriched in the high RhoA level group, while the hedgehog signaling, linoleic acid metabolism, olfactory transduction and taste transduction pathways were enriched in the low RhoA level group. RhoA is commonly upregulated in HCC tissues, and its expression at both the mRNA and protein levels is associated with poor prognosis. Notably, RhoA protein levels serve as a diagnostic biomarker for HCC.

Genomic landscape of gastric cancer: molecular classification and potential targets

Gastric cancer imposes a considerable health burden worldwide, and its mortality ranks as the second highest for all types of cancers. The limited knowledge of the molecular mechanisms underlying gastric cancer tumorigenesis hinders the development of therapeutic strategies. However, ongoing collaborative sequencing efforts facilitate molecular classification and unveil the genomic landscape of gastric cancer. Several new drivers and tumorigenic pathways in gastric cancer, including chromatin remodeling genes, RhoA-related pathways, TP53 dysregulation, activation of receptor tyrosine kinases, stem cell pathways and abnormal DNA methylation, have been revealed. These newly identified genomic alterations await translation into clinical diagnosis and targeted therapies. Considering that loss-of-function mutations are intractable, synthetic lethality could be employed when discussing feasible therapeutic strategies. Although many challenges remain to be tackled, we are optimistic regarding improvements in the prognosis and treatment of gastric cancer in the near future.

MicroRNA-142-3p and microRNA-142-5p are downregulated in hepatocellular carcinoma and exhibit synergistic effects on cell motility

MicroRNAs (miRNAs), an important class of small non-coding RNAs, regulate gene expression at the post-transcriptional level. miRNAs are involved in a wide range of biological processes and implicated in different diseases, including cancers. In this study, miRNA profiling and qRT-PCR validation revealed that miR-142-3p and miR-142-5p were significantly downregulated in hepatocellular carcinoma (HCC) and their expression levels decreased as the disease progressed. The ectopic expression of miR-142 significantly reduced HCC cell migration and invasion. Overexpression of either miR-142-3p or miR-142-5p suppressed HCC cell migration, and overexpression of both synergistically inhibited cell migration, which indicated that miR-142-3p and miR-142-5p may cooperatively regulate cell movement. miR-142-3p and miR-142-5p, which are mature miRNAs derived from the 3'- and 5'-strands of the precursor miR-142, target distinct pools of genes because of their different seed sequences. Pathway enrichment analysis showed a strong association of the putative gene targets of miR-142-3p and miR-142-5p with several cell motility-associated pathways, including those regulating actin cytoskeleton, adherens junctions, and focal adhesion. Importantly, a number of the putative gene targets were also significantly upregulated in human HCC cells. Moreover, overexpression of miR-142 significantly abrogated stress fiber formation in HCC cells and led to cell shrinkage. This study shows that mature miR-142 pairs collaboratively regulate different components of distinct signaling cascades and therefore affects the motility of HCC cells.

RhoGTPases - A novel link between cytoskeleton organization and cisplatin resistance

For more than three decades, platinum compounds have been the first line treatment for a wide spectrum of solid tumors. Yet, cisplatin resistance is a major impediment in cancer therapy, and deciphering the mechanisms underlying chemoresistance is crucial for the development of novel therapies with enhanced efficacy. The Rho subfamily of small GTPases plays a significant role in cancer progression, and a growing body of evidence points toward the involvement of these proteins in anticancer drug resistance, including cisplatin resistance. The cycling between active and inactive states, governed by the balance between their GEFs, GAPs and GDIs, RhoGTPases, acts as molecular switches with a pivotal role in actin cytoskeleton organization. The Rho subfamily of proteins is involved in many key cellular processes including adhesion, vesicular trafficking, proliferation, survival, cell morphology and cell-matrix interactions. Although RhoA, RhoB and RhoC are highly homologous and share some upstream regulators and downstream effectors, they each have different roles in cancer progression and chemoresistance. While RhoA and RhoC are upregulated in many tumors and can stimulate transformation, RhoB appears to exhibit tumor suppressor characteristics with proapoptotic effects. In the current review, we discuss the role of Rho subfamily of proteins in cancer, and focus on their involvement in intrinsic and acquired drug resistance.

MicroRNA-122 triggers mesenchymal-epithelial transition and suppresses hepatocellular carcinoma cell motility and invasion by targeting RhoA

The loss of microRNA-122 (miR-122) expression is strongly associated with increased invasion and metastasis, and poor prognosis of hepatocellular carcinoma (HCC), however, the underlying mechanisms remain poorly understood. In the present study, we observed that miR-122 over-expression in HCC cell lines Sk-hep-1 and Bel-7402 triggered the mesenchymal-epithelial transition (MET), as demonstrated by epithelial-like morphological changes, up-regulated epithelial proteins (E-cadherin, ZO-1, α-catenin, occludin, BVES, and MST4), and down-regulated mesenchymal proteins (vimentin and fibronectin). The over-expression of miRNA-122 also caused cytoskeleton disruption, RhoA/Rock pathway inactivation, enhanced cell adhesion, and suppression of migration and invasion of Sk-hep-1 and Bel-7402 cells, whereas, these effects could be reversed through miR-122 inhibition. Additional studies demonstrated that the inhibition of wild-type RhoA function induced MET and inhibited cell migration and invasion, while RhoA over-expression reversed miR-122-induced MET and inhibition of migration and invasion of HCC cells, suggesting that miR-122 induced MET and suppressed the migration and invasion of HCC cells by targeting RhoA. Moreover, our results demonstrated that HNF4α up-regulated its target gene miR-122 that subsequently induced MET and inhibited cell migration and invasion, whereas miR-122 inhibition reversed these HNF4α-induced phenotypes. These results revealed functional and mechanistic links among the tumor suppressors HNF4α, miR-122, and RhoA in EMT and invasive and metastatic phenotypes of HCC. Taken together, our study provides the first evidence that the HNF4α/miR-122/RhoA axis negatively regulates EMT and the migration and invasion of HCC cells.

Loss of ARHGDIA expression is associated with poor prognosis in HCC and promotes invasion and metastasis of HCC cells

Rho GTPases control a wide range of cellular processes and contribute to tumor invasion and metastasis. As a regulator of Rho activity, ARHGDIA is aberrantly expressed in several types of tumors and plays different roles in the tumor process. To elucidate the role of ARHGDIA in HCC, we investigated the patterns of its expression, prognosis and clinical profiles in HCC. Functional assays were performed to investigate whether the alteration of ARHGDIA has an effect on cell growth, migration and invasion, as well as the status of Rho GTPases. We found that ARHGDIA was frequently downregulated in HCC and associated with tumor invasion and metastasis. Moreover, ARHGDIA was significantly associated with OS and TTR of HCC patients. Low level of ARHGDIA exhibited a decreased postoperative OS and a shorter TTR compared those with high levels. Functional assays showed that loss of ARHGDIA promoted HCC cell migration and invasion in vitro and lung metastasis formation in vivo. We found that loss of ARHGDIA significantly induced Rac1 and RhoA activation which may contribute to invasion and metastasis of HCC. In conclusion, the present study has identified loss of ARHGDIA contributed to the processes of hepatic tumorigenesis, in particular invasion and metastasis which may provide a potential therapeutic target for HCC.

Rho GTPases and cancer

Rho GTPases are a family of small GTPases, which play an important role in the regulation of the actin cytoskeleton. Not surprisingly, Rho GTPases are crucial for cell migration and therefore highly important for cancer cell invasion and the formation of metastases. In addition, Rho GTPases are involved in growth and survival of tumor cells, in the interaction of tumor cells with their environment, and they are vital for the cancer supporting functions of the tumor stroma. Recent research has significantly improved our understanding of the regulation of Rho GTPase activity, the specificity of Rho GTPases, and their function in tumor stem cells and tumor stroma. This review summarizes these novel findings and tries to define challenging questions for future research.

Crosstalk of Ras and Rho: activation of RhoA abates Kras-induced liver tumorigenesis in transgenic zebrafish models

RAS and Rho small GTPases are key molecular switches that control cell dynamics, cell growth and tissue development through their distinct signaling pathways. Although much has been learnt about their individual functions in both cell and animal models, the physiological and pathophysiological consequences of their signaling crosstalk in multi-cellular context in vivo remain largely unknown, especially in liver development and liver tumorigenesis. Furthermore, the roles of RhoA in RAS-mediated transformation and their crosstalk in vitro remain highly controversial. When challenged with carcinogens, zebrafish developed liver cancer that resembles the human liver cancer both molecularly and histopathologically. Capitalizing on the growing importance and relevance of zebrafish (Danio rerio) as an alternate cancer model, we have generated liver-specific, Tet-on-inducible transgenic lines expressing oncogenic Kras(G12V), RhoA, constitutively active RhoA(G14V) or dominant-negative RhoA(T19N). Double-transgenic lines expressing Kras(G12V) with one of the three RhoA genes were also generated. Based on quantitative bioimaging and molecular markers for genetic and signaling aberrations, we showed that the induced expression of oncogenic Kras during early development led to liver enlargement and hepatocyte proliferation, associated with elevated Erk phosphorylation, activation of Akt2 and modulation of its two downstream targets, p21Cip and S6 kinase. Such an increase in liver size and Akt2 expression was augmented by dominant-negative RhoA(T19N), but was abrogated by the constitutive-active RhoA(G14V). Consequently, induced expression of the oncogenic Kras in adult transgenic fish led to the development of hepatocellular carcinomas. Survival studies further revealed that the co-expression of dominant-negative RhoA(T19N) with oncogenic Kras increased the mortality rate compared with the other single or double-transgenic lines. This study provides evidence of the previously unappreciated signaling crosstalk between Kras and RhoA in regulating liver overgrowth and liver tumorigenesis. Our results also implicate that activating Rho could be beneficial to suppress the Kras-induced liver malignancies.

A network-based maximum link approach towards MS identifies potentially important roles for undetected ARRB1/2 and ACTB in liver cancer progression

Hepatocellular Carcinoma (HCC) ranks among the deadliest of cancers and has a complex etiology. Proteomics analysis using iTRAQ provides a direct way to analyse perturbations in protein expression during HCC progression from early- to late-stage but suffers from consistency and coverage issues. Appropriate use of network-based analytical methods can help to overcome these issues. We built an integrated and comprehensive Protein-Protein Interaction Network (PPIN) by merging several major databases. Additionally, the network was filtered for GO coherent edges. Significantly differential genes (seeds) were selected from iTRAQ data and mapped onto this network. Undetected proteins linked to seeds (linked proteins) were identified and functionally characterised. The process of network cleaning provides a list of higher quality linked proteins, which are highly enriched for similar biological process gene ontology terms. Linked proteins are also enriched for known cancer genes and are linked to many well-established cancer processes such as apoptosis and immune response. We found that there is an increased propensity for known cancer genes to be found in highly linked proteins. Three highly-linked proteins were identified that may play an important role in driving HCC progression - the G-protein coupled receptor signalling proteins, ARRB1/2 and the structural protein beta-actin, ACTB. Interestingly, both ARRB proteins evaded detection in the iTRAQ screen. ACTB was not detected in the original dataset derived from Mascot but was found to be strongly supported when we re-ran analysis using another protein detection database (Paragon). Identification of linked proteins helps to partially overcome the coverage issue in shotgun proteomics analysis. The set of linked proteins are found to be enriched for cancer-specific processes, and more likely so if they are more highly linked. Additionally, a higher quality linked set is derived if network-cleaning is performed prior. This form of network-based analysis complements the cluster-based approach, and can provide a larger list of proteins on which to perform functional analysis, as well as for biomarker identification.

Overexpression of engulfment and cell motility 1 promotes cell invasion and migration of hepatocellular carcinoma

Engulfment and cell motility 1 (Elmo1) has been linked to the invasive phenotype of glioma cells. The use of Elmo1 inhibitors is currently being evaluated in hepato-cellular carcinoma (HCC), but the molecular mechanisms of their therapeutic effect have yet to be determined. Elmo1 expression in HCC tissue samples from 131 cases and in 5 HCC cell lines was determined by immunohistochemistry, quantitative RT-PCR and Western blotting. To functionally characterize Elmo1 in HCC, Elmo1 expression in the HCCLM3 cell line was blocked by siRNA. Cell migration was measured by wound healing and transwell migration assays in vitro. Elmo1 overexpression was significantly correlated with cell invasion and the poor prognosis of HCC. Elmo1-siRNA-treated HCCLM3 cells demonstrated a reduction in cell migration. The present study demonstrated for the first time that the suppression of Elmo1 expression inhibits cell invasion in HCC.

Rosuvastatin counteracts vessel arterialisation and sinusoid capillarisation, reduces tumour growth, and prolongs survival in murine hepatocellular carcinoma

Background and Aims. An arterial blood supply and phenotypic changes of the sinusoids characterise the liver vasculature in human hepatocellular carcinoma (HCC). We investigated the effects of rosuvastatin on liver vessel anomalies, tumour growth and survival in HCC. Methods. We treated transgenic mice developing HCC, characterized by vessel anomalies similar to those of human HCC, with rosuvastatin. Results. In the rosuvastatin group, the survival time was longer (P < .001), and liver weight (P < .01) and nodule surface (P < .01) were reduced. Rosuvastatin decreased the number of smooth muscle actin-positive arteries (P < .05) and prevented the sinusoid anomalies, with decreased laminin expression (P < .001), activated hepatic stellate cells (P < .001), and active Notch4 expression. Furthermore, rosuvastatin inhibited endothelial cell but not tumour hepatocyte functions. Conclusions. Rosuvastatin reduced the vessel anomalies and tumour growth and prolonged survival in HCC. These results represent new mechanisms of the effects of statin on tumour angiogenesis and a potential target therapy in HCC.

Integrin-linked kinase overexpression and its oncogenic role in promoting tumorigenicity of hepatocellular carcinoma

Background

Integrin-linked kinase (ILK) was first discovered as an integrin β1-subunit binding protein. It localizes at the focal adhesions and is involved in cytoskeleton remodeling. ILK overexpression and its dysregulated signaling cascades have been reported in many human cancers. Aberrant expression of ILK influenced a wide range of signaling pathways and cellular functions. Although ILK has been well characterized in many malignancies, its role in hepatocellular carcinoma (HCC) is still largely unknown.

Methodology/Principal Findings

Quantitative PCR analysis was used to examine ILK mRNA expression in HCC clinical samples. It was shown that ILK was overexpressed in 36.9% (21/57) of HCC tissues when compared to the corresponding non-tumorous livers. The overall ILK expression level was significantly higher in tumorous tissues (P = 0.004), with a significant stepwise increase in expression level along tumor progression from tumor stage I to IV (P = 0.045). ILK knockdown stable clones were established in two HCC cell lines, BEL7402 and HLE, and were subjected to different functional assays. Knockdown of ILK significantly suppressed HCC cell growth, motility and invasion in vitro and inhibited tumorigenicity in vivo. Western blot analysis revealed a reduced phosphorylated-Akt (pAkt) at Serine-473 expression in ILK knockdown stable clones when compared to control clones.

Conclusion/Significance

This study provides evidence about the clinical relevance of ILK in hepatocarcinogenesis. ILK was found to be progressively elevated along HCC progression. Here our findings also provide the first validation about the oncogenic capacity of ILK in vivo by suppressing its expression in HCC cells. The oncogenic role of ILK is implicated to be mediated by Akt pathway.

RhoGTPases and Rho-effectors in hepatocellular carcinoma metastasis: ROCK N'Rho move it

Hepatocellular carcinoma (HCC) is an intractable disease with an extremely high mortality rate. Metastasis is the major factor of liver failure, tumour recurrence and death in HCC patients. Unfortunately, no promising curative therapy for HCC metastasis is available as yet; therefore, treatment for advanced HCC still remains a formidable challenge. A large body of evidence has demonstrated that the RhoGTPases/Rho-effector pathway plays important roles in mediating HCC metastasis based on their foremost functions in orchestrating the cell cytoskeletal reorganization. This review will first discuss the general principles of cancer metastasis and cancer cell movement with a particular focus on HCC.We will then summarize the implications of various members in the RhoGTPases/Rho-effectors signalling cascade including the upstream RhoGTPase regulators RhoGTPases and Rho-effectors and their downstream targets in HCC metastasis. Finally, we will discuss the therapeutic insight of targeting the RhoGTPases/Rho-effector pathway in HCC. Taken together, the literature demonstrates the importance of the RhoGTPases/Rho-effector signalling pathway in HCC metastasis and marks the necessity to have a more thorough knowledge of this complicated signalling network in order to develop novel therapeutic strategies for HCC patients.

Noncanonical Wnt11 inhibits hepatocellular carcinoma cell proliferation and migration

The canonical Wnt signaling is frequently activated due to overexpression and/or mutations in components of this pathway in hepatocellular carcinoma (HCC). However, the biological role of noncanonical Wnt-mediated signaling in HCC with respect to the signaling pathways involved and their physiologic function is unknown. Here, we report the role of Wnt11, a member of the noncanonical cascade, in hepatic oncogenesis. The expression levels of Wnt11 mRNA and protein were significantly downregulated in human HCC tumors compared with the adjacent uninvolved liver as measured by quantitative real-time reverse transcription-PCR and Western blot analysis. In human HCC cell lines, overexpression of Wnt11 activated protein kinase C signaling. Protein kinase C antagonized the canonical signaling through phosphorylation of beta-catenin and reduced T-cell factor-mediated transcriptional activity, resulting in a decrease of cell proliferation. Furthermore, ectopic expression of Wnt11 promotes RhoA/Rho kinase activation. We found that activated Rho kinase inhibited Rac1 to reduce cell motility and migration. These observations suggest a novel role for Wnt11 as a tumor suppressor during hepatocarcinogenesis because loss of expression promotes the malignant phenotype via both canonical and noncanonical Wnt signaling pathways.

Rho-kinase 2 is frequently overexpressed in hepatocellular carcinoma and involved in tumor invasion

Deregulation of Rho family small guanosine triphosphatases has been implicated in human carcinogenesis. Rho-kinases are downstream effectors of Rho guanosine triphosphatases in the regulation of cytoskeletal reorganization and cell motility. However, their functions in human cancers remain elusive. In this study, we aimed to investigate the role of Rho-kinases in hepatocellular carcinoma (HCC) tumor progression and invasion. We first examined the expression of the two Rho-kinases (ROCK1 and ROCK2) in human HCC, and found that ROCK2 was frequently overexpressed in primary HCCs (22/41 [53.66%]). Clinico-pathological analysis revealed that overexpression of ROCK2 was significantly associated with the presence of tumor microsatellite formation (P = 0.005), suggesting that deregulation of ROCK2 may contribute to the intrahepatic metastasis of HCC. Consistently, we demonstrated that stable overexpression of ROCK2 significantly enhanced cell motility and invasiveness in HCC cells. Conversely, stable knockdown of ROCK2 by short hairpin RNA approach remarkably reduced HCC cell migration and invasion. Moreover, orthotopic liver xenograft models provided further support that stable knockdown of ROCK2 suppressed HCC invasion in vivo. Stable knockdown of ROCK2 in HCC cells significantly inhibited Golgi reorientation, myosin phosphatase phosphorylation, and formations of stress fibers, filopodia, and lamellipodia; these molecular and cellular events are crucial for cell motility and cancer invasion.

CONCLUSION

Our results indicate that ROCK2 was overexpressed in human HCCs, and this overexpression was associated with a more aggressive biological behavior. Our findings also demonstrate that ROCK2 played a significant role in regulating cytoskeletal events and contributed to the invasion of HCC.

Rho GTPase function in tumorigenesis

Malignant tumor cells display uncontrolled proliferation, loss of epithelial cell polarity, altered interactions with neighboring cells and the surrounding extracellular matrix, and enhanced migratory properties. Proteins of the Rho GTPase family regulate all these processes in cell culture and, for that reason, Rho GTPases, their regulators, and their effectors have been suggested to control tumor formation and progression in humans. However, while the tumor-relevant functions of Rho GTPases are very well documented in vitro, we are only now beginning to assess their contribution to cancer in human patients and in animal models. This review will give a very brief overview of Rho GTPase function in general and then focus on in vivo evidence for a role of Rho GTPases in malignant tumors, both in human patients and in genetically modified mice.

Rho GTPases in hepatocellular carcinoma

Rho GTPases are major regulators of signal transduction pathways and play key roles in processes including actin dynamics, cell cycle progression, cell survival and gene expression, whose deregulation may lead to tumorigenesis. A growing number of in vitro and in vivo studies using tumor-derived cell lines, primary tumors and animal cancer models strongly suggest that altered Rho GTPase signaling plays an important role in the initiation as well as in the progression of hepatocellular carcinoma (HCC), one of the deadliest human cancers in the world. These alterations can occur at the level of the GTPases themselves or of one of their regulators or effectors. The participation into the tumorigenic process can occur either through the over-expression of one of these components which presents an oncogenic activity as illustrated with RhoA and C or through the attenuation of the expression of a component presenting tumor suppressor activity as for Cdc42 or the RhoGAP, DLC-1. Consequently, these observations reflect the heterogeneity and the complexity of liver carcinogenesis. Recently, pharmacological approaches targeting Rho GTPase signaling have been used in HCC-derived models with relative success but remain to be validated in more physiologically relevant systems. Therefore, therapeutic approaches targeting Rho GTPase signaling may provide a novel alternative for anti-HCC therapy.

Simulation of crosstalk between small GTPase RhoA and EGFR-ERK signaling pathway via MEKK1

MOTIVATION

Small GTPase RhoA regulates cell-cycle progression via several mechanisms. Apart from its actions via ROCK, RhoA has recently been found to activate a scaffold protein MEKK1 known to promote ERK activation. We examined whether RhoA can substantially affect ERK activity via this MEKK1-mediated crosstalk between RhoA and EGFR-ERK pathway. By extending the published EGFR-ERK simulation models represented by ordinary differential equations, we developed a simulation model that includes this crosstalk, which was validated with a number of experimental findings and published simulation results.

RESULTS

Our simulation suggested that, via this crosstalk, RhoA elevation substantially prolonged duration of ERK activation at both normal and reduced Ras levels. Our model suggests ERK may be activated in the absence of Ras. When Ras is overexpressed, RhoA elevation significantly prolongs duration of ERK activation but reduces the amount of active ERK partly due to competitive binding between ERK and RhoA to MEKK1. Our results indicated possible roles of RhoA in affecting ERK activities via MEKK1-mediated crosstalk, which seems to be supported by indications from several experimental studies that may also implicate the collective regulation of cell fate and progression of cancer and other diseases.

DLC1 is a chromosome 8p tumor suppressor whose loss promotes hepatocellular carcinoma

Deletions on chromosome 8p are common in human tumors, suggesting that one or more tumor suppressor genes reside in this region. Deleted in Liver Cancer 1 (DLC1) encodes a Rho-GTPase activating protein and is a candidate 8p tumor suppressor. We show that DLC1 knockdown cooperates with Myc to promote hepatocellular carcinoma in mice, and that reintroduction of wild-type DLC1 into hepatoma cells with low DLC1 levels suppresses tumor growth in situ. Cells with reduced DLC1 protein contain increased GTP-bound RhoA, and enforced expression a constitutively activated RhoA allele mimics DLC1 loss in promoting hepatocellular carcinogenesis. Conversely, down-regulation of RhoA selectively inhibits tumor growth of hepatoma cells with disabled DLC1. Our data validate DLC1 as a potent tumor suppressor gene and suggest that its loss creates a dependence on the RhoA pathway that may be targeted therapeutically.

Mouse EP3 alpha, beta, and gamma receptor variants reduce tumor cell proliferation and tumorigenesis in vivo

Prostaglandin E(2), which exerts its functions by binding to four G protein-coupled receptors (EP1-4), is implicated in tumorigenesis. Among the four E-prostanoid (EP) receptors, EP3 is unique in that it exists as alternatively spliced variants, characterized by differences in the cytoplasmic C-terminal tail. Although three EP3 variants, alpha, beta, and gamma, have been described in mice, their functional significance in regulating tumorigenesis is unknown. In this study we provide evidence that expressing murine EP3 alpha, beta, and gamma receptor variants in tumor cells reduces to the same degree their tumorigenic potential in vivo. In addition, activation of each of the three mEP3 variants induces enhanced cell-cell contact and reduces cell proliferation in vitro in a Rho-dependent manner. Finally, we demonstrate that EP3-mediated RhoA activation requires the engagement of the heterotrimeric G protein G(12). Thus, our study provides strong evidence that selective activation of each of the three variants of the EP3 receptor suppresses tumor cell function by activating a G(12)-RhoA pathway.

Is autotaxin (ENPP2) the link between hepatitis C and hepatocellular cancer?

INTRODUCTION

Hepatitis C is the most significant risk factor for development of hepatocellular carcinoma. Inflammation, fibrosis, and liver cell proliferation may contribute to cancer development either through malignant hepatocyte transformation or extracellular matrix remodeling within the tumor microenvironment. The study objective was to investigate differences in gene expression between patients with Hepatitis C (+/- cancer) and normal that might explain the increased cancer risk.

METHODS

Liver tissue was collected from three patient groups: 1) healthy patients, 2) Hepatitis C patients without cancer, 3) patients with Hepatitis C and hepatocellular carcinoma. Microarray analysis was performed on samples from each group. Western blot and real-time polymerase chain reaction (PCR) analyses corroborated the microarray data. A p value of 0.05 was set as significant.

RESULTS

Microarray analysis showed overexpression of autotaxin in patients with cancer versus hepatitis patients or normal patients. Rho GTPase binding proteins (Cdc42s) associated with lysophosphatidic acid signaling were also overexpressed in cancer patients. Real-time polymerase chain reaction showed overexpression of several factors associated with autotaxin in patients with Hepatitis C (+/- cancer) versus normal patients.

CONCLUSIONS

Patients with Hepatitis C and hepatocellular carcinoma show differential expression of various components of the autotaxin pathway versus normal patients. This merits further investigation in the context of early diagnosis.