RPS6KB1 and renal cell carcinoma: To examine the role of GSK-3 in the mTORC1 downstream signaling pathway and its effects on cell proliferation, we treated ACHN, Caki1, and A498 human RCC cells, with AR-A014418, an ATP-competitive and small-molecule inhibitor of GSK-3 [27], and examined its effects on the phosphorylation of 4EBP1, S6K, and S6RP (Fig. 2a).