Phosphorylation at Ser724 of the ER stress sensor IRE1α governs its activation state and limits ER stress–induced hepatosteatosis

Abstract

Inositol-requiring enzyme 1 (IRE1) is an evolutionarily conserved sensor of endoplasmic reticulum (ER) stress and mediates a key branch of the unfolded protein response in eukaryotic cells. It is an ER-resident transmembrane protein that possesses Ser/Thr protein kinase and endoribonuclease (RNase) activities in its cytoplasmic region. IRE1 is activated through dimerization/oligomerization and autophosphorylation at multiple sites, acting through its RNase activity to restore the functional capacity of the ER. However, it remains poorly defined in vivo how the autophosphorylation events of endogenous IRE1 govern its dynamic activation and functional output. Here, we generated a mouse model harboring a S724A knock-in mutation (Ern1S724A/S724A) and investigated the importance of phosphorylation at Ser724 within the kinase activation loop of murine IRE1α. We found that in mouse embryonic fibroblast cells and in primary hepatocytes, S724A mutation resulted in markedly reduced IRE1α autophosphorylation in parallel with blunted activation of its RNase activity to catalyze X-box binding protein 1 (Xbp1) mRNA splicing. Furthermore, ablation of IRE1α phosphorylation at Ser724 exacerbated ER stress–induced hepatic steatosis in tunicamycin-treated Ern1S724A/S724A mice. This was accompanied by significantly decreased hepatic production of spliced XBP1 protein but increased CCAAT-enhancer–binding protein homologous protein (CHOP) level, along with suppressed expression of key metabolic regulators of fatty acid β-oxidation and lipid secretion. These results demonstrate a critical role of phosphorylation at Ser724 of IRE1α in dynamically controlling its kinase activity, and thus its autophosphorylation state, which is coupled to activation of its RNase activity in counteracting hepatic steatosis under ER stress conditions. Inositol-requiring enzyme 1 (IRE1) is an evolutionarily conserved sensor of endoplasmic reticulum (ER) stress and mediates a key branch of the unfolded protein response in eukaryotic cells. It is an ER-resident transmembrane protein that possesses Ser/Thr protein kinase and endoribonuclease (RNase) activities in its cytoplasmic region. IRE1 is activated through dimerization/oligomerization and autophosphorylation at multiple sites, acting through its RNase activity to restore the functional capacity of the ER. However, it remains poorly defined in vivo how the autophosphorylation events of endogenous IRE1 govern its dynamic activation and functional output. Here, we generated a mouse model harboring a S724A knock-in mutation (Ern1S724A/S724A) and investigated the importance of phosphorylation at Ser724 within the kinase activation loop of murine IRE1α. We found that in mouse embryonic fibroblast cells and in primary hepatocytes, S724A mutation resulted in markedly reduced IRE1α autophosphorylation in parallel with blunted activation of its RNase activity to catalyze X-box binding protein 1 (Xbp1) mRNA splicing. Furthermore, ablation of IRE1α phosphorylation at Ser724 exacerbated ER stress–induced hepatic steatosis in tunicamycin-treated Ern1S724A/S724A mice. This was accompanied by significantly decreased hepatic production of spliced XBP1 protein but increased CCAAT-enhancer–binding protein homologous protein (CHOP) level, along with suppressed expression of key metabolic regulators of fatty acid β-oxidation and lipid secretion. These results demonstrate a critical role of phosphorylation at Ser724 of IRE1α in dynamically controlling its kinase activity, and thus its autophosphorylation state, which is coupled to activation of its RNase activity in counteracting hepatic steatosis under ER stress conditions. In eukaryotic cells, the endoplasmic reticulum (ER) is a continuous membrane network that performs a variety of crucial functions, including the synthesis, folding, and processing of nearly one-third of the cellular proteome. Excess accumulation of unfolded or misfolded proteins within the ER lumen results in ER stress, triggering the activation of the adaptive cellular response referred to as the unfolded protein response (UPR) (1Ron D. Walter P. Signal integration in the endoplasmic reticulum unfolded protein response.Nat. Rev. Mol. Cell Biol. 2007; 8: 519-529Crossref PubMed Scopus (4703) Google Scholar, 2Walter P. Ron D. The unfolded protein response: from stress pathway to homeostatic regulation.Science. 2011; 334: 1081-1086Crossref PubMed Scopus (3654) Google Scholar, 3Hetz C. Zhang K. Kaufman R.J. Mechanisms, regulation and functions of the unfolded protein response.Nat. Rev. Mol. Cell Biol. 2020; 21: 421-438Crossref PubMed Scopus (396) Google Scholar). Three ER-resident transmembrane signal transducers, PKR-like endoplasmic reticulum kinase (PERK), activating transcription factor 6, and inositol-requiring enzyme 1 (IRE1), constitute the three canonical UPR signaling branches to manage ER stress and restore cellular homeostasis (1Ron D. Walter P. Signal integration in the endoplasmic reticulum unfolded protein response.Nat. Rev. Mol. Cell Biol. 2007; 8: 519-529Crossref PubMed Scopus (4703) Google Scholar, 2Walter P. Ron D. The unfolded protein response: from stress pathway to homeostatic regulation.Science. 2011; 334: 1081-1086Crossref PubMed Scopus (3654) Google Scholar). A great number of studies have demonstrated the pivotal roles of the UPR pathways in cell fate decisions (4Hetz C. Papa F.R. The unfolded protein response and cell fate control.Mol. Cell. 2018; 69: 169-181Abstract Full Text Full Text PDF PubMed Scopus (642) Google Scholar) as well as their implications in many pathological conditions including cancer and metabolic disorders (5Wang M. Kaufman R.J. Protein misfolding in the endoplasmic reticulum as a conduit to human disease.Nature. 2016; 529: 326-335Crossref PubMed Scopus (791) Google Scholar, 6Cubillos-Ruiz J.R. Bettigole S.E. Glimcher L.H. Tumorigenic and immunosuppressive effects of endoplasmic reticulum stress in cancer.Cell. 2017; 168: 692-706Abstract Full Text Full Text PDF PubMed Scopus (409) Google Scholar, 7Hotamisligil G.S. Endoplasmic reticulum stress and the inflammatory basis of metabolic disease.Cell. 2010; 140: 900-917Abstract Full Text Full Text PDF PubMed Scopus (2003) Google Scholar, 8Lee J. Ozcan U. Unfolded protein response signaling and metabolic diseases.J. Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). IRE1 is an UPR sensor that is conserved from to including Walter P. of endoplasmic reticulum proteins a transmembrane protein Full Text PDF PubMed Scopus Google Scholar, K. J. A transmembrane protein with a kinase activity is signaling from the ER to the Full Text PDF PubMed Scopus Google Scholar, Kaufman R.J. A stress response pathway from the endoplasmic reticulum to the a protein in PubMed Scopus Google Scholar). It possesses the ER proteins and the cytoplasmic with Ser/Thr protein kinase and endoribonuclease (RNase) activities its functional Papa F.R. Walter P. the of unfolded protein in the endoplasmic U. PubMed Scopus Google Scholar, C. Walter P. The transmembrane kinase is a that mRNA in the unfolded protein Full Text Full Text PDF PubMed Scopus Google Scholar, C. D. Glimcher L.H. The unfolded protein response: stress through the stress sensor Rev. 2011; PubMed Scopus Google Scholar). ER stress, IRE1 RNase is activated through dimerization/oligomerization and J. D. of human IRE1 a conserved activation of the unfolded protein U. PubMed Scopus Google Scholar, M. D. C. of the enzyme the basis and regulation in Full Text Full Text PDF PubMed Scopus Google Scholar, J. Zhang C. unfolded protein response through of PubMed Scopus Google Scholar, of the autophosphorylation and implications the unfolded protein J. 2011; PubMed Scopus Google the of the mRNA X-box binding protein 1 to a spliced transcription factor K. K. signaling pathways the unfolded protein response and C. Full Text Full Text PDF PubMed Scopus Google Scholar, K. XBP1 mRNA is by and spliced by IRE1 in response to ER stress to a transcription Full Text Full Text PDF PubMed Scopus Google Scholar, M. endoplasmic reticulum to capacity by processing the PubMed Scopus Google Scholar). The pathway a key UPR expression that the protein capacity of the ER and the of proteins (4Hetz C. Papa F.R. The unfolded protein response and cell fate control.Mol. Cell. 2018; 69: 169-181Abstract Full Text Full Text PDF PubMed Scopus (642) Google Scholar, C. D. Glimcher L.H. The unfolded protein response: stress through the stress sensor Rev. 2011; PubMed Scopus Google Scholar, J. Kaufman R.J. of transcription in the unfolded protein 2017; PubMed Scopus Google Scholar, at a endoplasmic Rev. Mol. Cell Biol. PubMed Scopus Google Scholar, P. protein and Cell Biol. PubMed Scopus Google Scholar, J. in the endoplasmic and UPR 2018; Full Text Full Text PDF PubMed Scopus Google Scholar). of the RNase activity of IRE1 is the of of or in a J. of endoplasmic the unfolded protein PubMed Scopus Google Scholar, J. Walter P. of in Cell Biol. PubMed Scopus Google Scholar, M. J. of IRE1 in cell fate Full Text Full Text PDF PubMed Scopus Google Scholar, D. ER stress to of PubMed Scopus Google Scholar, Zhang K. Inositol-requiring enzyme 1 through 2017; PubMed Scopus Google Scholar). of have demonstrated that in IRE1α a critical role in with ER stress but as a in response to stress and metabolic C. Zhang K. Kaufman R.J. Mechanisms, regulation and functions of the unfolded protein response.Nat. Rev. Mol. Cell Biol. 2020; 21: 421-438Crossref PubMed Scopus (396) Google Scholar, in metabolic 2011; Full Text Full Text PDF PubMed Scopus Google Scholar, roles the ER stress sensor in metabolic regulation and Biol. Full Text Full Text PDF PubMed Scopus Google Scholar). A of and have to the activation of IRE1α signaling in metabolic roles the ER stress sensor in metabolic regulation and Biol. Full Text Full Text PDF PubMed Scopus Google but the as well as the with to its activation and functional have to is a key of IRE1 activation in response to ER stress, and its RNase activity is to its kinase activity Walter P. and phosphorylation of the kinase signaling from the endoplasmic reticulum to the J. PubMed Scopus Google Scholar, Kaufman R.J. The unfolded protein response pathway in and of kinase Biol. Full Text Full Text PDF PubMed Scopus Google Scholar, K. Kaufman R.J. The endoribonuclease activity of IRE1 its mRNA and is the unfolded protein PubMed Scopus Google Scholar). studies of the cytoplasmic of IRE1 have that M. D. C. of the enzyme the basis and regulation in Full Text Full Text PDF PubMed Scopus Google Scholar) or J. Zhang C. unfolded protein response through of PubMed Scopus Google Scholar) the kinase at multiple sites, to a J. Zhang C. unfolded protein response through of PubMed Scopus Google Scholar). is to the binding and its or to activating its RNase processing M. D. C. of the enzyme the basis and regulation in Full Text Full Text PDF PubMed Scopus Google Scholar, J. Zhang C. unfolded protein response through of PubMed Scopus Google Scholar). of the cytoplasmic of human IRE1α to a with the of its kinase activation and found to poorly of the autophosphorylation and implications the unfolded protein J. 2011; PubMed Scopus Google Scholar). phosphorylation of three and within conserved kinase activation in from cytoplasmic of human IRE1α protein M. of RNase PubMed Scopus Google and phosphorylation of its RNase activity mRNA as well as of mRNA M. of RNase PubMed Scopus Google Scholar, M. J. branches of the unfolded protein response cell Cell. 2018; Full Text Full Text PDF PubMed Scopus Google Scholar). However, IRE1α proteins that phosphorylation of the activation loop is mRNA and phosphorylation at Ser724 and but an its RNase activity M. of RNase PubMed Scopus Google Scholar). a that phosphorylation at of endogenous IRE1α in cells or mouse multiple cells and by and the but by ER as of IRE1 at in cells and production Cell Biol. 2018; PubMed Scopus Google Scholar). In phosphorylation was to mRNA activity of IRE1α in cells, and it a its activity in However, it is knock-in mutation the kinase activity of IRE1α in response to stress in cells of IRE1 at in cells and production Cell Biol. 2018; PubMed Scopus Google Scholar). phosphorylation of sites, the three within the kinase activation loop of to stress that the phosphorylation events to govern the activation of its RNase the in of the in with to the of it remains phosphorylation within its kinase activation loop is in the dynamic regulation of endogenous IRE1α activation ER stress in phosphorylation at Ser724 IRE1α activation in response to a variety of stress under or pathological conditions. we generated a mouse model (Ern1S724A/S724A) the S724A knock-in mutation to phosphorylation at and investigated the importance of Ser724 of the dynamic activation of IRE1α protein ER stress and its functional in vivo in the of ER stress–induced hepatic the functional of phosphorylation at Ser724 the activation of endogenous IRE1α in we a knock-in mouse in which the Ser724 was by within the the of Ern1S724A/S724A at with in to their as their the at we IRE1α phosphorylation at from primary from but from their Ern1S724A/S724A ER stress by or the ER This the of IRE1α phosphorylation at Ser724 within its kinase activation loop in Ern1S724A/S724A knock-in mice. 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Papa F.R. The unfolded protein response and cell fate control.Mol. Cell. 2018; 69: 169-181Abstract Full Text Full Text PDF PubMed Scopus (642) Google Scholar). results from cells and demonstrate an role of phosphorylation at Ser724 in the kinase activity of IRE1α its which is coupled to the activation of its RNase of phosphorylation at of the kinase activation loop is to in the of IRE1α to at sites, which to its activation to the the phosphorylation at that to and its activity of IRE1 at in cells and production Cell Biol. 2018; PubMed Scopus Google phosphorylation at Ser724 of IRE1α a its activation ER stress, which its functional RNase mRNA and of It is the cell of activity its phosphorylation an in the in of cells. In phosphorylation at Ser724 of IRE1α cell effects cell under ER ER stress is a key in hepatic steatosis and fatty P. M. Endoplasmic reticulum in hepatic Rev. 2016; PubMed Scopus Google Scholar, C. D. C. Endoplasmic reticulum stress and the of fatty 2018; 69: Full Text Full Text PDF PubMed Scopus Google Scholar, The unfolded protein response and hepatic lipid in fatty PubMed Scopus Google and the pathway in the of many of hepatic lipid including fatty acid and lipid M. C. metabolic adaptive through the PubMed Scopus Google Scholar, Glimcher L.H. of hepatic by the transcription factor PubMed Scopus Google Scholar, Zhang D. J. is an Biol. 2016; Full Text Full Text PDF PubMed Scopus Google Scholar, J. J. expression to activity hepatic and lipid Full Text Full Text PDF PubMed Scopus Google Scholar). that IRE1α was to have a role in ER stress–induced steatosis K. J. J.R. unfolded protein response ER hepatic J. 2011; PubMed Scopus Google Scholar, C. Zhang factor is by the branch of the unfolded protein response and endoplasmic reticulum hepatic Biol. 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