Inhibition of mTORC2 but not mTORC1 Up-Regulates E-Cadherin Expression and Inhibits Cell Motility by Blocking HIF-2α Expression in Human Renal Cell Carcinoma

Purpose: Molecular targeted drugs, such as mTORC1 inhibitors, have been clinically popularized for advanced renal cell carcinoma treatment but metastasis is still a serious concern. mTORC2 has several important functions, including HIF-2 alpha activation in malignant cells. HIF-2 alpha suppresses E-cadherin expression, which is associated with tumor invasion and metastasis. We investigated whether mTORC2 regulates E-cadherin expression and controls cell motility during HIF-2 alpha down-regulation in renal cell carcinoma cells. Materials and Methods: We used PP242, a dual inhibitor of mTORC1/mTORC2 and the mTORC1 specific inhibitor rapamycin. E-cadherin expression in 786-O cells was examined using real-time polymerase chain reaction, Western blot and immunocytochemical staining. Cell motility was analyzed by time-lapse microscopy and wound healing assay. Results: High E-cadherin expression was found in RCC4/VHL cells but low levels were found in VHL defective RCC4 and 786-O cells. HIF-2 alpha expression was suppressed only in RCC4/VHL cells. In 786-O cells HIF-2 alpha inhibition induced by the dual mTORC1/C2 inhibitor PP242 (0.05 to 0.5 mu mol/L) resulted in a dose dependent increase in E-cadherin expression and the restored E-cadherin was localized at cell-to-cell junctions. Treatment with the mTORC1 inhibitor rapamycin resulted in no significant change. The migration of PP242 treated cells was significantly suppressed compared with those treated with rapamycin. Conclusions: Results show that mTORC2 might regulate E-cadherin expression and suppress cell motility by controlling the mTORC2-HIF-2 alpha signaling pathway. The dual inhibitor of mTORC1/C2 as a cadherin regulatory agent may be a novel therapeutic strategy with tumoricidal agents for advanced renal cell carcinoma.