Nutrient starvation elicits an acute autophagic response mediated by Ulk1 dephosphorylation and its subsequent dissociation from AMPK. Proc Natl Acad Sci USA

Howard Hughes Medical Institute and Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 03/2011; 108(12):4788-93. DOI: 10.1073/pnas.1100844108
Source: PubMed


Macroautophagy (herein referred to as autophagy) is an evolutionarily conserved self-digestive process cells adapt to starvation and other stress responses. Upon starvation, autophagy is induced, providing cells with needed nutrient supplies. We report here that Unc-51-like kinase 1 (Ulk1), a key initiator for mammalian autophagy, undergoes dramatic dephosphorylation upon starvation, particularly at serine 638 and serine 758. Phosphorylations of Ulk1 are mediated by mammalian target-of-rapamycin (mTOR) kinase and adenosine monophosphate activated protein kinase (AMPK). AMPK interacts with Ulk1 in a nutrient-dependent manner. Proper phosphorylations on Ulk1 are crucial for Ulk1/AMPK association, as a single serine-to-alanine mutation (S758A) at Ulk1 impairs this interaction. Compared to the wild-type ULK1, this Ulk1-S758A mutant initiates starvation-induced autophagy faster at an early time point, but does not alter the maximum capacity of autophagy when starvation prolongs. This study therefore revealed previously unnoticed acute autophagy response to environmental changes.

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    • "ULK1 is a kinase which itself is controlled by phosphorylation events and phosphorylates its substrates for modulating their activity (Bononi et al., 2011; Wu et al., 2014). Hence, detection of phosphorylation sites in ULK1 may unravel important functional aspects regarding its involvement in various disorders (Olsen et al., 2010; Wang et al., 2010; Shang et al., 2011). The NetPhos algorithm (Blom et al., 1999) was used for the prediction of phosphorylation sites at serine (S), threonine (T) and tyrosine (Y) residues in the ULK1 amino acid sequence. "
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    ABSTRACT: Autophagy is a degradation pathway involving lysosomal machinery for degradation of damaged organelles like endoplasmic reticulum, mitochondria etc. into their building blocks to maintain homeostasis within the cell. ULK1, a serine/threonine kinase, is conserved across species, from yeasts to mammals, and plays a central role in autophagy pathway. It receives signals from upstream modulators such as TIP60, mTOR and AMPK and relays them to its downstream substrates like Ambra1 and ZIP kinase. The activity of this complex is regulated through protein-protein interactions and post-translational modifications. Applying in silico analysis we identified (i) conserved patterns of ULK1 that showed its evolutionary relationship between the species which were closely related in a family compared to others. (ii) total 23 TFBS distributed throughout ULK1 and nuclear factor (erythroid-derived) 2 (NFE2) is of utmost significance because of its high importance rate. NEF2 has already been shown experimentally to play role autophagy pathway. Most of these were of Zinc coordinating class and we suggest that this information could be utilized to modulate this pathway by modifying interactions of these TFs with ULK1. (iii) CATTT haplotype was prominently found with frequency 0.774 in the studied population and nsSNPs which could have harmful effect on ULK1 protein and these could further be tested. (iv) total 83 phosphorylation sites were identified; 26 are already known and 57 are new that include one at tyrosine residue which could further be studied for its involvement in ULK1 regulation and hence autophagy. Furthermore, 4 palmitoylation sites at positions 426, 927, 1003 and 1049 were also found which could further be studied for protein-protein interactions as well as in trafficking. Copyright © 2015. Published by Elsevier B.V.
    Gene 02/2015; 562(1). DOI:10.1016/j.gene.2015.02.056 · 2.14 Impact Factor
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    • "Mirroring these findings, phosphorylation at Ser2481 of mTOR, implicated to be an autophosphorylation site and indicative of TORC1 activity (Soliman et al., 2010), displays parallel changes to those in its substrates (data not shown). ULK-1, a positive regulator of autophagy, has been demonstrated to be inhibited when phosphorylated at Ser757/758 by mTOR (Kim et al., 2011; Shang et al., 2011). We also demonstrated that phosphorylation of Ser757 in ULK-1 is reduced by glucose deprivation in cardiomyocytes and decreased further by WT HK-II overexpression. "
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    Molecular cell 01/2014; 53(4). DOI:10.1016/j.molcel.2013.12.019 · 14.02 Impact Factor
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    • "Autophagy is a highly conserved evolutionary process that destroys cellular components producing ATP and macromolecules derived from the destroyed components. Stimuli such as hypoxia [21], infections caused by viruses and bacteria [22], oxidative stress [23], starvation [24] and DNA damage [25] are responsible for triggering autophagy. Both autophagy and the proteasome system are able to degrade proteins, but only autophagy is capable of degrading entire organelles. "
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    ABSTRACT: Many alkylating agents are used as chemotherapeutic drugs and have a long history of clinical application. These agents inflict a wide range of DNA damage resulting in a complex cellular response. After DNA damage, cells trigger a series of signaling cascades promoting cellular survival and cell cycle blockage which enables time for DNA repair to occur. More recently, induction of autophagy has been observed in cancer cells after treatment with different DNA- targeted anticancer drugs, including alkylating agents. Several studies have demonstrated that induction of autophagy after DNA damage delays apoptotic cell death and may therefore lead to chemoresistance, which is the limiting factor for successful chemotherapy. On the other hand, depending on the extent of damage and the cellular context, the induction of autophagy may also contribute to cell death. Given these conflicting results, many studies have been conducted to better define the role of autophagy in cancer cells in response to chemotherapy. In this review, we describe the main alkylating agents used in clinical oncology as well as the cellular response they evoke with emphasis on autophagy.
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