Resveratrol Inhibits mTOR Signaling by Promoting the Interaction between mTOR and DEPTOR

Abstract

Resveratrol (RSV) is a naturally occurring polyphenol that has been found to exert antioxidant, anti-inflammatory, and neuroprotective properties. However, how RSV exerts its beneficial health effects remains largely unknown. Here, we show that RSV inhibits insulin-and leucine-stimulated mTOR signaling in C2C12 fibroblasts via a Sirt1-independent mechanism. Treating C2C12 cells with RSV dramatically inhibited insulin-stimulated Akt, S6 kinase, and 4E-BP1 phosphorylation but had little effect on tyrosine phosphorylation of the insulin receptor and activation of the p44/42 MAPK signaling pathway. RSV treatment also partially blocked mTOR and S6 kinase phosphorylation in TSC1/2-deficient mouse embryonic fibroblasts, suggesting the presence of an inhibitory site downstream of TSC1/2. Knocking out PDK1 or suppressing AMP-activated protein kinase had little effect on leucine-stimulated mTOR signaling. On the other hand, RSV significantly increased the association between mTOR and its inhibitor, DEPTOR. Furthermore, the inhibitory effect of RSV on leucine-stimulated mTOR signaling was greatly reduced in cells in which the expression levels of DEPTOR were suppressed by RNAi. Taken together, our studies reveal that RSV inhibits leucinestimulated mTORC1 activation by promoting mTOR/DEP-TOR interaction and thus uncover a novel mechanism by which RSV negatively regulates mTOR activity. The naturally occurring polyphenol resveratrol (RSV)3 has received great attention during the past few years due to its beneficial roles in longevity, cardioprotection, and immune regulation. How RSV exerts its biological function remains to be fully elucidated, but activation of the NAD ϩ -dependent deacetylase Sirt1 has been suggested as an important mechanism for the life span extension and cancer prevention properties of RSV (1). Several targets of RSV such as AMP-activated protein kinase (AMPK), Akt, and NF-B have also been identified (2-4). However, it remains controversial as to whether activation of these signaling pathways is Sirt1-dependent and whether additional targets and mechanisms are involved in RSV-initiated beneficial function in cells.mTOR (mammalian target of rapamycin) is a member of the phosphatidylinositol 3-kinase (PI3K)-related protein kinase subfamily that plays a critical role in the regulation of various cellular events such as cell growth and proliferation (5, 6). mTOR exists in two distinct complexes, TORC1 and TORC2, which differ in subunit compositions and biological functions (7). The rapamycin-sensitive mTORC1, which consists of five components, including mTOR, Raptor (regulatory-associated protein of mTOR), mLST8 (mammalian lethal with Sec13 protein 8; also known as G␤L), PRAS40 (proline-rich Akt substrate of 40 kDa), and DEPTOR (DEP domain-containing and mTORinteractive protein) (8), regulates protein synthesis and cell growth by phosphorylating downstream target proteins such as p70 ribosomal S6K1 (S6 kinase 1) and the eukaryotic initiation factor 4E-BP1 (5, 9). The rapamycin-insensitive TORC2, which compr...

Resveratrol Inhibits Oesophageal Adenocarcinoma Cell Proliferation via AMP-activated Protein Kinase Signaling

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DEPTOR Is a Stemness Factor That Regulates Pluripotency of Embryonic Stem Cells

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AICAR-induced activation of AMPK negatively regulates myotube hypertrophy through the HSP72-mediated pathway in C2C12skeletal muscle cells

“…Therefore, RNAi could not completely inhibit basal AMPK activity. A previous study also did not show the upregulation of phosphorylation level of p70 S6K Thr 389 by RNAi-induced AMPK suppression in C 2 C 12 cells (23). On the contrary, transgenic knockout of AMPK induced myotube hypertrophy and upregulation of p70 S6K phosphorylation by using primary cultured myoblasts under nonstimulated condition (22).…”