(c) Energetic stress, but not Aicar treatment, stimulates Sesn2 expression in MEF

(c) Energetic stress, but not Aicar treatment, stimulates Sesn2 expression in MEF. homeostasis. Eukaryotic organisms rely on glucose as a critical source for ATP production when metabolized via glycolysis and mitochondrial respiration. Glucose is also a substrate for glycosylation, a post-translational modification that occurs primarily in the endoplasmic reticulum (ER)1. Glucose starvation activates at least two mechanisms of the stress response: one senses energy availability via activation of 5-AMP-activated protein kinase (AMPK)2, and another is activated through accumulation of unfolded and unprocessed proteins in the ER and induction of ER stress followed by a program called the unfolded protein response (UPR)3,4. The UPR activates three pathways mediated by: protein kinase (PKR)-like ER kinase (PERK1), activating transcription factor 6 (ATF6) and inositol-requiring enzyme 1 (IRE1)3,5. PERK1 directly phosphorylates and inhibits eukaryotic translation initiation factor 2 alpha (eIF2), causing suppression of global protein synthesis; however, it also re-directs the translational machinery toward translation of specific mRNAs involved in the UPR4,5. The major function of the PERK1-eIF2 pathway is to Clemastine fumarate activate transcription factor 4 (ATF4)3, which is induced via a translation-dependent mechanism. ATF4 is a master regulator of numerous genes involved in the UPR6. Some of these genes, such as transcription factor CHOP, induce cell death, while others protect cell viability through suppression of cell death machinery and relief of ER stress, or by regulating metabolism4. Another important target of PERK is the master regulator of antioxidant response and metabolism Nuclear factor (erythroid-derived 2)-like 2 (NRF2)7. Under non-stressed conditions NRF2 is constantly bound to its partner Kelch like-ECH-associated protein 1 (Keap1) which retains NRF2 in the cytoplasm and stimulates its degradation. Under stress conditions, PERK directly phosphorylates NRF2 leading to its dissociation from Keap1 and translocation to the nucleus where it activates Clemastine fumarate the transcription of its target genes via recognition of antioxidant responsive elements (ARE)8. We have identified and characterized Clemastine fumarate the Sestrin (SESN) family of stress-responsive genes9,10 composed of and genes in mammals while only one Sestrin ortholog has been found in invertebrates10. Sestrins are activated by multiple insults including oxidative stress, DNA damage, hypoxia, growth factor depletion and ER stress11. We demonstrated that protein products of Sestrin genes work Hepacam2 as antioxidant proteins suppressing oxidative DNA damage and mutagenesis12,13. Furthermore, Sestrins also inhibit mammalian target of rapamycin (mTOR) complex 1 (mTORC1) kinase, a critical regulator of cell growth and metabolism14,15,16. Sestrins inhibit mTORC1 in a manner dependent on AMPK and tuberous sclerosis complex (TSC), which, in turn, inhibits the small GTPase Rheb, a critical activator of mTORC114,15,17,18,19. We and others have also described a parallel mechanism of mTORC1 inhibition by Sestrins mediated by small Rag GTPases20,21,22. Active forms of RagA/B:RagC/D heterodimers bring mTORC1 to the lysosomes where it interacts with Rheb23. The RagA/B activity is inhibited by its GTPase activated protein (GAP) – GATOR1 protein complex, which is in turn inhibited by GATOR2 protein complex. Sestrins interact with GATOR2 and inhibit mTORC1 lysosomal localization20,21. In our previous publications, we demonstrated that SESN2 is activated in response to some metabolic stress factors and is involved in the regulation of cell viability9,24; however, the precise role of SESN2 in the regulation of cell death is not well established. Here Clemastine fumarate we show that glucose starvation stimulates SESN2 via induction of ER stress and that SESN2 protects cells from necrotic cell death through the support of cell metabolism, ATP production and mitochondrial function. Results SESN2 is activated in response to energy stress in a manner similar to the UPR induction Different inducers of energy stress such as an inhibitor of glucose metabolism – 2-deoxyglucose (2DG), an inhibitor of complex I of the mitochondrial electron transport chain -.