A tuberous sclerosis complex signalling node at the peroxisome regulates mTORC1 and autophagy in response to ROS

Abstract

Subcellular localization is emerging as an important mechanism for mTORC1 regulation. We report that the tuberous sclerosis complex (TSC) signaling node, TSC1, TSC2 and Rheb, localizes to peroxisomes, where it regulates mTORC1 in response to reactive oxygen species (ROS). TSC1 and TSC2 were bound by PEX19 and PEX5, respectively, and peroxisome-localized TSC functioned as a Rheb GAP to suppress mTORC1 and induce autophagy. Naturally occurring pathogenic mutations in TSC2 decreased PEX5 binding, abrogated peroxisome localization, Rheb GAP activity, and suppression of mTORC1 by ROS. Cells lacking peroxisomes were deficient in mTORC1 repression by ROS and peroxisome-localization deficient TSC2 mutants caused polarity defects and formation of multiple axons in neurons. These data identify a role for TSC in Users may view, print, copy, download and text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use: http://www.nature.com/authors/editorial_policies/license.html#terms COMPETING FINANCIAL INTERESTSThe authors declare that they have no competing financial interests. HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript responding to ROS at the peroxisome, and identify the peroxisome as a signaling organelle involved in regulation of mTORC1.Tuberous sclerosis complex (TSC) is a hereditary hamartoma syndrome caused by defects in either the TSC1 or TSC2 genes 1, 2 . The TSC tumor suppressor is a heterodimer comprised of tuberin (TSC2), a GTPase activating protein (GAP), and its activation partner hamartin (TSC1), which localizes the TSC tumor suppressor to endomembranes and protects TSC2 from proteasomal degradation 3,4 . TSC inhibits the activity of the small GTPase Rheb to repress mammalian target of rapamycin complex 1 (mTORC1) signaling, a negative regulator of autophagy [5][6][7][8][9][10][11][12] . mTORC1 is regulated by a variety of cellular stimuli including amino acids, mitogens such as insulin, glucose, and energy stress [13][14][15] . In the case of amino acids, which do not signal through TSC-Rheb pathway 15 , mTORC1 activity is regulated by the Rag GTPases, which form the Ragulator complex that localizes mTORC1 to the late endosome or lysosome compartment of cells [13][14][15][16][17][18] . We recently reported that TSC functions in a signaling node downstream of ataxia telangiectasia mutated (ATM) to repress mTORC1 in response to reactive oxygen species (ROS) 19 . However, identification of the specific subcellular compartment(s) in which the TSC tumor suppressor functions to regulate mTORC1 in response to ROS has heretofore remained elusive.Peroxisomes, carry out key metabolic functions in the cell including β-oxidation of fatty acids, and are a major source of cellular ROS 20,21 . Like mitochondria, peroxisomes are autonomously replicating organelles. Peroxisome biogenesis requires peroxin (PEX) proteins, which are essential for assembly of functional peroxisomes 22 . Specific PEX pro...

Cross-cancer profiling of molecular alterations within the human autophagy interaction network

“…[64][65][66] Suppressed autophagy is implicated in the progression of polycystic kidney disease (PKD), where it promotes the growth of kidney cysts, 67 and patients with acquired cystic kidney disease are at a higher risk for KIRC. 68 Hypoxia also plays an important role in cyst expansion in PKD through the upregulation of HIF1A in cyst epithelium; 69 however, HIF1A has been shown to increase autophagic flux in a rat proximal tubular cell line.…”

Peroxisomal protein PEX 13 functions in selective autophagy

“…Since the peroxisome biogenesis function of PEX13 depends on other peroxin family members, we evaluated whether other peroxins are required for mitophagy and general autophagy. Of note, PEX5 and PEX19 are involved in ROS‐induced general autophagy 3, and we previously identified PEX3 as a candidate selective autophagy factor 16. Using pools of four siRNAs targeting each gene, we knocked down PEX3 , PEX5 , PEX13 , PEX14 , or PEX19 in HeLa cells (Fig 5A).…”

“…Our observation that PEX13 did not colocalize with markers of the early autophagosome (WIPI2) or with the selective autophagic cargo (TOMM20) during basal and mitophagy conditions suggests it does not function as an autophagy receptor. Given the precedent of peroxisome‐associated proteins functioning as signaling platforms 3, 4, we speculate that PEX13 may regulate selective autophagy as a peroxisomal membrane‐associated signaling node, leading to downstream posttranslational modifications (such as ubiquitylation 28 or phosphorylation 29, 30) and activation of other yet‐to‐be identified selective autophagy regulators. Unbiased proteomics approaches will be helpful to interrogate this pathway.…”

“…Peroxisomal membrane proteins have also been implicated as signaling platforms involved in reactive oxygen species (ROS)‐induced autophagy 3 and antiviral immunity 4. Similar to other PEX genes, PEX13 was originally identified and has been best studied in the context of its role in peroxisome biogenesis and ZSS 5, 6.…”

Rheb in neuronal degeneration, regeneration, and connectivity

“…In the presence of insulin, Akt-mediated phosphorylation of TSC complex causes its dissociation from the lysosomes, hence promoting Rheb and mTORC1 activation ( Benjamin and Hall, 2014;Menon et al, 2014;Dibble and Cantley, 2015). Interestingly, mTORC1 can also be activated at other endo-membranes including peroxisomes and Golgi complex (Flinn et al, 2010;Zhang et al, 2013).…”