EIF4EBP1 and renal cell carcinoma: However, as shown in Fig. 2d, 4EBP1 and S6RP expression and phosphorylation aberrantly increased in RCC cells but not in normal kidney tissues and a renal tubular cell line, suggesting that GSK-3 as well as mTORC1 could be involved in the activation of mTORC1 downstream pathway in RCC.