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Here, we demonstrated that DNA-PKcs is over-expressed in multiple human renal cell carcinoma (RCC) tissues and in primary/established human RCCs. Pharmacological or genetic inhibition of DNA-PKcs suppressed proliferation of RCC cells. DNA-PKcs was in the complex of mTOR and SIN1, mediating mTORC2 activation and HIF-2α expression in RCC cells. Inhibiting or silencing DNA-PKcs suppressed AKT Ser-473 phosphorylation and HIF-2α expression. In vivo, DNA-PKcs knockdown or oral administration of the DNA-PKcs inhibitor NU-7441 inhibited AKT Ser-473 phosphorylation, HIF-2α expression and 786-0 RCC xenograft growth in nude mice. We showed that miRNA-101 level was decreased in RCC tissues/cells, which could be responsible for DNA-PKcs overexpression and DNA-PKcs mediated oncogenic actions in RCC cells. We show that DNA-PKcs over-expression regulates mTORC2-AKT activation, HIF-2α expression and RCC cell proliferation.

The expression and biological function of Grb2-associated binding 2 (Gab2) in renal cell carcinoma (RCC) cells was tested here. We showed that Gab2 expression was significantly elevated in human RCC tissues and RCC cells. It was correlated with over-activation of Akt and downregulation of microRNA-302c-3p (“miR-302c-3p”), a putative Gab2-targeting microRNA. Knockdown of Gab2 inhibited Akt activation and 786-O RCC cell proliferation. Reversely, forced over-expression of Gab2 led to Akt hyper-activation to facilitate 786-O cell proliferation. Exogenous expression of miR-302c caused Gab2 downregulation, Akt inhibition and 786-O cell proliferation inhibition. On the other hand, miR-302c-3p depletion by expressing its anti-sense (“antagomiR-302c”) led to Gab2 upregulation, Akt activation and increased 786-O cell proliferation. Significantly, miR-302c-3p failed to affect the proliferation of 786-O cells with shRNA-depleted Gab2. Together, we suggest that miR-302c-3p depletion in human RCC cells leads to Gab2 over-expression, Akt hyper-activation and cell proliferation.