mTOR Complex 2 Is Involved in Regulation of Cbl-Dependent c-FLIP Degradation and Sensitivity of TRAIL-Induced Apoptosis

作者：Zhao Liqun; Yue Ping; Khuri Fadlo R; Sun Shi Yong^*

来源：Cancer Research, 2013, 73(6): 1946-1957.

DOI：10.1158/0008-5472.CAN-12-3710

The mTOR positively regulates cell proliferation and survival through forming 2 complexes with raptor (mTOR complex 1; mTORC1) or rictor (mTOR complex 2; mTORC2). Compared with the mTORC1, relatively little is known about the biologic functions of mTORC2. This study focuses on addressing whether mTORC2 regulates apoptosis, particularly induced by TRAIL (TNFSF10). Using the mTOR kinase inhibitor, PP242, as a research tool, we found that it synergized with TRAIL to augment apoptosis of cancer cells. PP242 reduced the abundance of the short form of c-FLIP (FLIPS, CFLAR(S)) and survivin (BIRC5). Enforced expression of ectopic FLIPS, but not survivin, attenuated augmented apoptosis induced by PP242 plus TRAIL. Thus, it is FLIPS downregulation that contributes to synergistic induction of apoptosis by PP242 plus TRAIL. PP242 decreased FLIPS stability, increased FLIPS ubiquitination, and facilitated FLIPS degradation. Moreover, knockdown of the E3 ligase Cbl (CBL) abolished PP242-induced FLIPS reduction. Thus, PP242 induces Cbl-dependent degradation of FLIPS, leading to FLIPS downregulation. Consistently, knockdown of rictor or mTOR, but not raptor, mimicked PP242 in decreasing FLIPS levels and sensitizing cells to TRAIL. Rictor knockdown decreased FLIPS stability, whereas enforced expression of rictor stabilized FLIPS. Moreover, silencing of Cbl abrogated FLIPS reduction induced by rictor knockdown. Collectively we conclude that it is mTORC2 inhibition that results in FLIPS downregulation and subsequent sensitization of TRAIL-induced apoptosis. Our findings provide the first evidence showing that mTORC2 stabilizes FLIPS, hence connecting mTORC2 signaling to the regulation of death receptor-mediated apoptosis. Cancer Res; 73(6); 1946-57.

• 出版日期2013-3-15