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The autophagy initiating kinase ULK1 is regulated via opposing phosphorylation by AMPK and mTOR

Molecular and Cell Biology Laboratory, Dulbecco Center for Cancer Research, University of California at San Diego, La Jolla, USA.
Autophagy (Impact Factor: 11.42). 06/2011; 7(6):643-4. DOI: 10.4161/auto.7.6.15123
Source: PubMed

ABSTRACT The serine/threonine kinase ULK1 is a mammalian homolog of Atg1, part of the Atg1 kinase complex, which is the most upstream component of the core autophagy machinery conserved from yeast to mammals. In budding yeast, activity of the Atg1 kinase complex is inhibited by TORC1 (target of rapamycin complex 1), but how the counterpart ULK1 complex in mammalian cells is regulated has been unknown. Our laboratories recently discovered that AMPK associates with, and directly phosphorylates, ULK1 on several sites and this modification is required for ULK1 activation after glucose deprivation. In contrast, when nutrients are plentiful, the mTORC1 complex phosphorylates ULK1, preventing its association and activation by AMPK. These studies have revealed a molecular mechanism of ULK1 regulation by nutrient signals via the actions of AMPK and mTORC1.

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    • "While AMPK activates ULK1 by phosphorylating at least four sites (Egan et al., 2011a), mTORC1 inactivates ULK1 by phosphorylating a single site, Ser757 (Kang et al., 2013; Kim et al., 2011). As several physiological stresses result in both AMPK activation and mTOR inhibition, ULK1 activation proceeds through positive signals from AMPK and loss of inhibitory signals from mTORC1 (Egan et al., 2011a). It is notable, however, that mTORC1 is inactivated by many stresses beyond just those affecting AMPK, and the data to date suggest that pharmacological suppression of mTORC1 is sufficient to induce ULK1 kinase activity (Russell et al., 2013). "
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    ABSTRACT: Many tumors become addicted to autophagy for survival, suggesting inhibition of autophagy as a potential broadly applicable cancer therapy. ULK1/Atg1 is the only serine/threonine kinase in the core autophagy pathway and thus represents an excellent drug target. Despite recent advances in the understanding of ULK1 activation by nutrient deprivation, how ULK1 promotes autophagy remains poorly understood. Here, we screened degenerate peptide libraries to deduce the optimal ULK1 substrate motif and discovered 15 phosphorylation sites in core autophagy proteins that were verified as in vivo ULK1 targets. We utilized these ULK1 substrates to perform a cell-based screen to identify and characterize a potent ULK1 small molecule inhibitor. The compound SBI-0206965 is a highly selective ULK1 kinase inhibitor in vitro and suppressed ULK1-mediated phosphorylation events in cells, regulating autophagy and cell survival. SBI-0206965 greatly synergized with mechanistic target of rapamycin (mTOR) inhibitors to kill tumor cells, providing a strong rationale for their combined use in the clinic. Copyright © 2015 Elsevier Inc. All rights reserved.
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    • "j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / c a n l e t response to nutrient depletion leads to ULK1 activation and autophagy induction [17] [18] [19] [20]. Therefore, since the Rottlerin uncoupling effects have been documented in different cancer cells [21] [22] [23], we hypothesized that AMPK could be the Rottlerin target responsible for MCF-7 autophagic death. "
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    • "Although autophagy has been associated with prodeath mechanisms, it provides a pro-survival function during metabolic stress (Poels et al. 2009). ATP depletion or increased ROS levels during excitotoxicity may induce autophagy , through AMPK-mTOR-ULK signalling (Egan et al. 2011; Kim et al. 2011). Whether autophagy activation during excitotoxicity is pro-survival or pro-apoptotic remains to be fully elucidated (Poels et al. 2009; Ginet et al. 2014). "
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