OBJECTIVE: To investigate the role for α4 in cell transformation induced by chemical carcinogens. METHODS:Immunoblotting was performed to examine the expression of α4 in chemical-transformed cells and tumor cell lines. Stable cell lines L02R-α4 and L02R-SHα4 were generated by infecting L02R cells with retroviral vectors encoding α4 or lentiviral α4 shRNA,respectively. Cell proliferation and anchorage-independent cell growth were examined in these cells. Immunoblotting analysis was applied to measure the phosphorylation status of p70S6K1 and 4E-BP1,which were the key members of mTOR pathway in established cells and transformed cell models L02RT-AFB1,HepG2,and SMMC with or without rapamycin treatment. RESULTS:The protein expression of α4 in chemical-transformed cells and tumor cell lines increased by 1.9-5.9 fold compared with non-transformed cells. Immunoblotting results verified that L02R-α4 and L02R SHα4 cells were successfully established. Ectopic expression of α4 promoted cell growth and led to cell transformation. Notable increased phosphorylation levels of S6K1 (Thr389) and 4E-BP1 (Thr37/46) were observed in transformed cells where α4 was overexpressed. Upon rapamycin treatment, phosphorylation of p70S6K1 and 4E-BP1 declined significantly in all cells. Particularly,the effects were more profound in L02R-SHα4 cells. CONCLUSION:Overexpression of α4 promoted cell proliferation and induced cell transformation via activation of mTOR signaling pathway.