Expression And Activities Of Rho Main Family Members In Gastrointestinal Carcinoma

AIM: With the research development in oncology, more and more evidences have established that carcinogenesis of gastric mucosa displays multiple genetic alterations including activation of oncogenes, inactivation of tumor suppressor genes, loss of heterozygonisity (LOH) in chromosomes, errors in DMA replication and so on. It has been found that mutation or amplification of oncogenes, such as c-ras, c-erbB-2, K-sam, c-met and c-myc and inactivation of tumour suppressor genes, such as p53, APC, DCC and RB, are related to the pathogenesis of gastric cancer. However, the precise mechanisms of molecular genetic changes that contribute to malignant phenotypes of gastric carcinoma remain unclear. Small GTP-binding proteins are important molecules in signal transduction and control a set of essential cellular functions such as reorganization of the actin cytoskeleton, gene expression, cell cycle progression and cell-cell adhesion, which can be structurally classified into at least five families: the Ras, Rho, Rab, Sar1/Arf, and Ran families. The small GTP-binding proteins especially Ras and Rho families have been shown to be correlated with several different tumors. Although theactivation of Ras caused by point mutations are shown to be associated with carcinogenesis in stomach (9), there are no available data on the role of Rho family members in gastric cancer. To determine whether Rho family members are involved in the carcinogenesis of gastric epithelium, progression and metastasis in gastric carcinoma, we investigated the mRNA expression levels of seven main Rho family members in gastric cancer tissues and cell lines. The activities of five main Rho family members in some gastric cancer cell lines was also studied.METHODS: Fifty-three tumor and adjacent non-tumorous tissue specimens from patients with gastric cancer who underwent gastric surgery or endoscopy in our hospital were included in this study. Gastric cancer cell lines XGC9811C, XGC9811, MKN28, MKN45, SGC7901, AGS and KATOIII, liver cancer cell lines HepG2, SMMC7721, and HCC, colorectal cancer cell lines HT-29, HR8348, immortal intestinal epithelial cell line HIEC and mouse fibroblast cell line NIH3T3 were used in this study. RNA and protein were extracted from gastric cancer tissues and cell lines. The mRNA expression levels of seven main members RhoA, RhoB, RhoC, Rac1, Rac2, Rac3 and Cdc42 of Rho family in gastric carcinoma tissues and gastrointestinal cancer cell lines were systemically investigated using semi-quantitative reverse transcription-PCR. The activities of RhoA, RhoB, RhoC, Rac1 and Cdc42 in five gastric cancer cell lines were examined by pull down assay. All data were analysed with the SPSS software package, and the difference was considered significant at P<0.05.RESULTS: The mean mRNA expression levels of RhoA and Rac1 in gastric cancer tissue specimens were significantly higher than those inthe adjacent non-tumorous tissue specimens (P<0.01). The higher expression of RhoA was significantly correlated with pooly differentiated histological type of gastric carcinoma (P<0.05). Rac1 and RhoA in most gastrointestinal cancer cell lines also have higher mRNA expression levels as compared with that in the controls of normal gastric mucosa and human intestinal epithelial cell line HIEC. Total protein levels of RhoA, Rac1 and Cdc42 are higher in gastric cancer cell lines than that in HIEC. Rac1 activity can be detected by pull down assay in gastric cancer cell lines but not in HIEC. CONCLUSION: These findings indicate that RhoA and Rac1 may play important roles in the carcinogenesis and progression of gastric carcinoma. The mechanisms of Rho family members in occurrence and development of gastric carcinoma need to be further investigated.