Department of Pharmacology and Penn State Hershey Cancer Institute, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America.
PLoS One. 2010 Nov 3;5(11):e15394. doi: 10.1371/journal.pone.0015394.
Autophagy is a highly orchestrated intracellular bulk degradation process that is activated by various environmental stresses. The serine/threonine kinase ULK1, like its yeast homologue Atg1, is a key initiator of autophagy that is negatively regulated by the mTOR kinase. However, the molecular mechanism that controls the inhibitory effect of mTOR on ULK1-mediated autophagy is not fully understood. Here we identified AMPK, a central energy sensor, as a new ULK1-binding partner. We found that AMPK binds to the PS domain of ULK1 and this interaction is required for ULK1-mediated autophagy. Interestingly, activation of AMPK by AICAR induces 14-3-3 binding to the AMPK-ULK1-mTORC1 complex, which coincides with raptor Ser792 phosphorylation and mTOR inactivation. Consistently, AICAR induces autophagy in TSC2-deficient cells expressing wild-type raptor but not the mutant raptor that lacks the AMPK phosphorylation sites (Ser722 and Ser792). Taken together, these results suggest that AMPK association with ULK1 plays an important role in autophagy induction, at least in part, by phosphorylation of raptor to lift the inhibitory effect of mTOR on the ULK1 autophagic complex.
自噬是一种高度协调的细胞内批量降解过程，可被多种环境应激激活。丝氨酸/苏氨酸激酶 ULK1 与其酵母同源物 Atg1 一样，是自噬的关键起始因子，受 mTOR 激酶的负调控。然而，控制 mTOR 对 ULK1 介导的自噬的抑制作用的分子机制尚未完全了解。在这里，我们确定 AMPK，一种中央能量传感器，为 ULK1 的新结合伙伴。我们发现 AMPK 与 ULK1 的 PS 结构域结合，这种相互作用是 ULK1 介导的自噬所必需的。有趣的是，AICAR 激活 AMPK 诱导 14-3-3 与 AMPK-ULK1-mTORC1 复合物结合，这与 raptor Ser792 磷酸化和 mTOR 失活一致。一致地，AICAR 诱导在表达野生型 raptor 但缺乏 AMPK 磷酸化位点（Ser722 和 Ser792）的突变体 raptor 的 TSC2 缺陷细胞中发生自噬。总之，这些结果表明，AMPK 与 ULK1 的关联在自噬诱导中起着重要作用，至少部分通过 raptor 的磷酸化来解除 mTOR 对 ULK1 自噬复合物的抑制作用。
