Interplay between oncogenic K-Ras and wild-type H-Ras in Caco2 cell transformation

Mutation of RAS genes is one of the most common oncogenic alterations in cancer and acquisition of activating RAS mutations has been demonstrated to cause progression of colorectal adenoma to cancer. The aim of this study was to identify changes in the proteome of the intermediate-stage colorectal cancer cell line Caco2, induced by ectopic expression of two distinct RAS proteins, KRAS(V12) and HRAS(V12), in their mutated, constitutively active form. Using 2D-gel electrophoresis, followed by LC-MS/MS we identified almost 200 differentially expressed proteins in pair-wise comparisons of Caco2 vs Caco2-KRAS(V12) and Caco2 vs Caco2-HRAS(V12). Although many of the affected proteins were unique for each pair, there were also substantial similarities. Interestingly, transformation by the mutant KRAS(V12) gene resulted in elevated expression levels and activity of endogenous H-ras protein. Silencing the latter with a specific RNAi reversed several proteomic changes observed in KRAS(V12)-transformed cells, suggesting that oncogenic K-ras partly exerts its effects through endogenous H-ras activation. Alterations in the expression of cytoskeletal and cell adhesion proteins, caused by HRAS siRNA treatment, correlated with a reduction in the invasive properties of Caco2-KRAS(V12) cells. Our data suggest a novel interplay between K-ras and H-ras, with possible implications for colorectal carcinogenesis.