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MTOR activates the VPS34-UVRAG complex to regulate autolysosomal tubulation and cell survival.

ABSTRACT: Lysosomes are essential organelles that function to degrade and recycle unwanted, damaged and toxic biological components. Lysosomes also act as signalling platforms in activating the nutrient-sensing kinase mTOR. mTOR regulates cellular growth, but it also helps to maintain lysosome identity by initiating lysosomal tubulation through a process termed autophagosome-lysosome reformation (ALR). Here we identify a lysosomal pool of phosphatidylinositol 3-phosphate that, when depleted by specific inhibition of the class III phosphoinositide 3-kinase VPS34, results in prolonged lysosomal tubulation. This tubulation requires mTOR activity, and we identified two direct mTOR phosphorylation sites on UVRAG (S550 and S571) that activate VPS34. Loss of these phosphorylation sites reduced VPS34 lipid kinase activity and resulted in an increase in number and length of lysosomal tubules. In cells in which phosphorylation at these UVRAG sites is disrupted, the result of impaired lysosomal tubulation alongside ALR activation is massive cell death. Our data imply that ALR is critical for cell survival under nutrient stress and that VPS34 is an essential regulatory element in this process.

SUBMITTER: Munson MJ

PROVIDER: S-EPMC4585463 | biostudies-literature | 2015 Sep

REPOSITORIES: biostudies-literature

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mTOR activates the VPS34-UVRAG complex to regulate autolysosomal tubulation and cell survival.

Munson Michael J MJ Allen George Fg GF Toth Rachel R Campbell David G DG Lucocq John M JM Ganley Ian G IG

The EMBO journal 20150702 17

Lysosomes are essential organelles that function to degrade and recycle unwanted, damaged and toxic biological components. Lysosomes also act as signalling platforms in activating the nutrient-sensing kinase mTOR. mTOR regulates cellular growth, but it also helps to maintain lysosome identity by initiating lysosomal tubulation through a process termed autophagosome-lysosome reformation (ALR). Here we identify a lysosomal pool of phosphatidylinositol 3-phosphate that, when depleted by specific in ...[more]

PMID: 26139536

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Project description:The mechanisms orchestrating recycling of lysosomes through autophagic lysosome reformation (ALR) is incompletely understood. Previous data show that genetic depletion of BLOC1S1/GCN5L1/BORCS1 increases autolysosome (AL) accumulation. We postulated that this phenotype may manifest due to perturbed ALR. We explored this in control and bloc1s1 liver-specific knockout (LKO) mouse hepatocytes, showing that in response to nutrient-deprivation LKO's fail to initiate ALR due to blunted lysosomal tubulation. As kinesin motor proteins and the intracellular cytoskeleton are requirements for tubular formation from ALs, we explored the interaction of BLOC1S1 with motor proteins and cytoskeletal factors. BLOC1S1 interacts with the ARL8B-KIF5B (GTPase and kinesin motor protein) complex to recruit KIF5B to ALs. Furthermore, BLOC1S1 interacts with the actin nucleation promoting factor WHAMM, which is an essential structural protein in the initiation of lysosomal tubulation (LT). Interestingly, the genetic reintroduction of BLOC1S1 rescues LT in LKO hepatocytes, but not when KIF5B is concurrently depleted. Finally, given the central role of MTORC1 signaling in ALR initiation, it was interesting that MTORC1 activity was increased despite the absence of LT in LKO hepatocytes. Concurrently, inhibition of MTORC1 abolished BLOC1S1 reconstitution-mediated rescue of LT in LKO hepatocytes. Taken together these data demonstrate that the functional interaction of BLOC1S1 with the kinesin binding complex and the actin cytoskeleton are a requirement for LT which, in parallel with MTORC1 signaling, initiate lysosome recycling via ALR.Abbreviations: 3-MA: 3-methyladenine; AL: autolysosome; ALR: autophagic lysosome reformation; ARL8B: ADP-ribosylation factor-like protein 8B; ARPC2: actin related protein 2/3 complex, subunit 2; ATAT1/αTAT1: alpha tubulin acetyltransferase 1; AVd: autophagic vacuoles, degradative; BLOC1S1/GCN5L1: biogenesis of lysosomal organelles complex-1, subunit 1; CQ: chloroquine; KIF5B: kinesin family member 5B; KLC1: kinesin light chain 1; LAMP1: lysosomal-associated membrane protein 1; LAMP2: lysosomal-associated membrane protein 2; LC3B-I: cytosolic form of LC3B; LC3B-II: lipidated form of LC3B; MAP1LC3B/LC3B: microtubule-associated protein 1 light chain 3 beta; LKO: liver-specific knockout; LIs: lysosome inhibitors; LT: lysosomal tubulation; Ly: lysosome; MTORC1: mechanistic target of rapamycin kinase complex 1; PLEKHM2/SKIP: pleckstrin homology domain containing, family M (with RUN domain) member 2; Snapin: SNAP-associated protein; SQSTM1/p62: sequestosome 1; SVPs: synaptic vesicle precursors; TFEB: transcription Factor EB; TFE3: transcription factor E3; WHAMM: WAS protein homolog associated with actin, golgi membranes and microtubules.

Project description:VPS34 complex II (VPS34CII) is a 386-kDa assembly of the lipid kinase subunit VPS34 and three regulatory subunits that altogether function as a prototypical class III phosphatidylinositol-3-kinase (PI3K). When the active VPS34CII complex is docked to the cytoplasmic surface of endosomal membranes, it phosphorylates its substrate lipid (phosphatidylinositol, PI) to generate the essential signaling lipid phosphatidylinositol-3-phosphate (PI3P). In turn, PI3P recruits an array of signaling proteins containing PI3P-specific targeting domains (including FYVE, PX, and PROPPINS) to the membrane surface, where they initiate key cell processes. In endocytosis and early endosome development, net VPS34CII-catalyzed PI3P production is greatly amplified by Rab5A, a small G protein of the Ras GTPase superfamily. Moreover, VPS34CII and Rab5A are each strongly linked to multiple human diseases. Thus, a molecular understanding of the mechanism by which Rab5A activates lipid kinase activity will have broad impacts in both signaling biology and medicine. Two general mechanistic models have been proposed for small G protein activation of PI3K lipid kinases. 1) In the membrane recruitment mechanism, G protein association increases the density of active kinase on the membrane. And 2) in the allosteric activation mechanism, G protein allosterically triggers an increase in the specific activity (turnover rate) of the membrane-bound kinase molecule. This study employs an in vitro single-molecule approach to elucidate the mechanism of GTP-Rab5A-associated VPS34CII kinase activation in a reconstituted GTP-Rab5A-VPS34CII-PI3P-PX signaling pathway on a target membrane surface. The findings reveal that both membrane recruitment and allosteric mechanisms make important contributions to the large increase in VPS34CII kinase activity and PI3P production triggered by membrane-anchored GTP-Rab5A. Notably, under near-physiological conditions in the absence of other activators, membrane-anchored GTP-Rab5A provides strong, virtually binary on-off switching and is required for VPS34CII membrane binding and PI3P production.

Dataset Information

MTOR activates the VPS34-UVRAG complex to regulate autolysosomal tubulation and cell survival.

Publications

mTOR activates the VPS34-UVRAG complex to regulate autolysosomal tubulation and cell survival.

Similar Datasets

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