Sestrin2 Phosphorylation by ULK1 Induces Autophagic Degradation of Mitochondria Damaged by Copper-Induced Oxidative Stress

Abstract

Selective autolysosomal degradation of damaged mitochondria, also called mitophagy, is an indispensable process for maintaining integrity and homeostasis of mitochondria. One well-established mechanism mediating selective removal of mitochondria under relatively mild mitochondria-depolarizing stress is PINK1-Parkin-mediated or ubiquitin-dependent mitophagy. However, additional mechanisms such as LC3-mediated or ubiquitin-independent mitophagy induction by heavy environmental stress exist and remain poorly understood. The present study unravels a novel role of stress-inducible protein Sestrin2 in degradation of mitochondria damaged by transition metal stress. By utilizing proteomic methods and studies in cell culture and rodent models, we identify autophagy kinase ULK1-mediated phosphorylation sites of Sestrin2 and demonstrate Sestrin2 association with mitochondria adaptor proteins in HEK293 cells. We show that Ser-73 and Ser-254 residues of Sestrin2 are phosphorylated by ULK1, and a pool of Sestrin2 is strongly associated with mitochondrial ATP5A in response to Cu-induced oxidative stress. Subsequently, this interaction promotes association with LC3-coated autolysosomes to induce degradation of mitochondria damaged by Cu-induced ROS. Treatment of cells with antioxidants or a Cu chelator significantly reduces Sestrin2 association with mitochondria. These results highlight the ULK1-Sestrin2 pathway as a novel stress-sensing mechanism that can rapidly induce autophagic degradation of mitochondria under severe heavy metal stress.

SESTRINs: Emerging Dynamic Stress-Sensors in Metabolic and Environmental Health

“…Recent studies indicate that Sestrin2 activates the autophagic clearance of damaged mitochondria through Parkin-ULK1-Beclin1 activation (Kumar and Shaha, 2018b) and also induces mitophagy in macrophages and renal tubular cells (Ishihara et al, 2013;Kim et al, 2016). ULK1 phosphorylates Sestrin2 at S73 and S254 to induce mitophagy upon copper-catalyzed oxidative stress (Kim H. et al, 2020). Although recent study suggests that Sestrin2 is colocalized with mitochondria and regulates some mitochondrial functions (Kovaleva et al, 2020), its direct translocation into mitochondria and involvement in maintaining mitochondrial antioxidant enzymes function and ROS level remain unknown.…”

“…However, Sesn3 is somewhat redundant to Sesn2 in metabolic function and autophagy induction in liver and colon tissues (Lee et al, 2012;Ro et al, 2016). Although ectopically expressed Sestrin2 protein is mostly found in cytoplasm (Parmigiani et al, 2014), recent studies suggest that Sestrin2 is associated with mitochondria (Kim H. et al, 2020;Kovaleva et al, 2020), nucleus (Tu et al, 2018;Wang L.X. et al, 2020), and endoplasmic reticulum (ER) (Wang L.X.…”

“…Exercise increases the same phosphorylation profile of Sestrin2 and improves skeletal muscle metabolism (Zeng et al, 2017(Zeng et al, , 2018b. ULK1 also phosphorylates S73 and S254 to activate the autophagic clearance of mitochondria in response to copperinduced oxidative stress (Kim H. et al, 2020). L261 and E451 are identified as essential residues for leucine binding in HEK293 cells (Lee et al, 2016;Saxton et al, 2016a,b;Wolfson et al, 2016).…”

Oxidative Stress-Induced Protein of SESTRIN2 in Cardioprotection Effect

“…Even more fascinating is new research demonstrating that ULK1 directly phosphorylates Ser-73 and Ser-254 residues of the SESN-A structural domain. These findings highlight the ULK1-SESTRIN2 pathway as an optimal route for inducing mitophagy quickly [46].…”

The Roles of Post-Translational Modifications on mTOR Signaling

“…Emerging studies demonstrate that phosphorylation and ubiquitination of Sestrin2 play a critical role in regulating mTORC1 signaling. ULK1-mediated phosphorylation of Sestrin2 at S73/S254 enhances its interaction with GATOR2, leading to mTORC1 inhibition and autophagy induction [ 134 , 135 ]. The RING-type E3 ligase RNF186 promotes ubiquitination and degradation of Serstrin2, leading to hyperactivation of the mTORC1 pathway [ 136 ].…”