Dual inhibition by S6K1 and Elf4E is essential for controlling cellular growth and invasion in bladder cancer

Abstract Purpose We investigated how dual inhibition of the molecular mechanism of mammalian target of rapamycin (mTOR) downstream of S6K1 and the eukaryotic initiation factor 4E (eIF4E) can lead to suppression of proliferation and progression of urothelial carcinoma. Materials and methods We characterized the molecular mechanism of the mTOR pathway in the T24 and 5637 urothelial carcinoma cell lines by interfering with different molecular components using rapamycin and short interfering (siRNA) technology (S6K1 or elF4E) and analyzed the effects on molecular activation status, cell growth, proliferation, and invasion. Results A high concentration of rapamycin (10 μM) blocked both S6K1 and elF4E phosphorylation and inhibited cell proliferation in T24 and 5637 cells. The inhibition of both S6K1 and elF4E phosphorylation by rapamycin reduced cell viability and proliferation more than transfection of siRNA against S6K1 or elF4E in 5637 and T24 cells. Cells silenced for S6K1 or elF4E expression exhibited significantly reduced cell migration and invasion compared with those of the control but inhibition of both S6K1 and elF4E phosphorylation by rapamycin reduced cell migration and invasion more than siRNA transfection against S6K1 or elF4E in 5637 and T24 cells. Conclusion These findings suggest that both the mTOR pathway downstream of eukaryotic initiation factor 4E and S6K1 can be successfully inhibited, therefore, the recurrence of bladder cancer can be prevented by high-dose rapamycin only, suggesting that 4E-BP1 might be still under mTORC1.