Targeting mTORC2 component rictor inhibits cell proliferation and promotes apoptosis in gastric cancer

The mammalian target of rapamycin (mTOR) kinase acts downstream of phosphoinositide 3-kinase/Akt and plays an important role in tumor growth and progression of gastric cancer. It is well characterized that mTOR complex1 (mTORC1) controls cell metabolism and proliferation, whereas the contribution of mTOR complex2 (mTORC2) and its key component, Rictor, remains poorly understood. Therefore, we investigated clinical significance of Rictor expression by immunohistochemical analysis of 391 tissue samples from gastric cancer patients. In addition, the roles of Rictor in cell proliferation, apoptosis, migration and invasion in vitro were evaluated by RNA interference. The results showed that over expression of Rictor was associated with increased tumor size, depth of tumor invasion, lymph node metastasis and advanced TNM stage, together with poorer overall and relapse-free survival. Stable sh-RNA mediated down-regulation of Rictor significantly inhibited SGC7901 and MGC803 gastric cancer cells proliferation, migration and invasion. Furthermore, Rictor knockdown attenuated cell cycle progression and enhanced apoptosis, synergistic with treatment of mTORC1 inhibitor rapamycin owing to abrogating the feedback activation of Akt. Our findings identify Rictor as an important mediator of tumor progression and metastasis, providing the rationale for targeting both mTORC1 and mTORC2 as part of therapeutic strategy for gastric cancer.