Abstract 4834: Energy-dependent AMPK association with the ULK1-mTORC1 complex regulates autophagy

Abstract Autophagy is an intracellular catabolic process through which bulky cytosolic components are sequestered for lysosomal degradation. Recent evidence suggests that mTOR suppresses autophagy through direct interaction with the ULK1-Atg13-FIP200 complex. However, the mechanism by which mTOR is controlled to activate ULK1 activity for autophagy induction is not yet well elucidated. Using tandem affinity purification (TAP) assay, we screened for ULK1 binding proteins and identified several additional ULK1 binding proteins that mediate the pro-autophagic activity of ULK1. Here we report AMP-activated protein kinase (AMPK), which is known to be a highly-conserved cellular energy sensor that is activated under conditions of low intracellular ATP, as a new ULK1 binding protein. We found that AMPK binds to the PS domain of ULK1 in an energy-dependent manner, whereas mTOR associates with ULK1 through raptor interaction with the kinase domain of ULK1 independently of nutrient availability. Mechanistically, AMPK inhibits the mTOR activity by recruiting 14-3-3 to the mTORC1 through phosphorylation of raptor in response to energy stress. Importantly, activation of AMPK by 5-amino-4-imidazolecarboxamide ribose (AICAR) is able to suppress the mTORC1 and induce autophagy in TSC2-deficient cells with wild-type raptor but not the mutant raptor (S722A/S792A) lacking AMPK phosphorylation sites. Our study indicates, therefore, that AMPK-mediated raptor phosphorylation plays an important role in the activation of ULK1 to induce autophagy under energy stress conditions. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4834.