BH3-only proteins are part of a regulatory network that control the sustained signalling of the unfolded protein response sensor IRE1α

et al.Adaptation to endoplasmic reticulum (ER) stress depends on the activation of the unfolded protein response (UPR) stress sensor inositol-requiring enzyme 1α(IRE1α), which functions as an endoribonuclease that splices the mRNA of the transcription factor XBP-1 (X-box-binding protein-1). Through a global proteomic approach we identified the BCL-2 family member PUMA as a novel IRE1αinteractor. Immun oprecipitation experiments confirmed this interaction and further detected the association of IRE1αwith BIM, another BH3-only protein. BIM and PUMA double-knockout cells failed to maintain sustained XBP-1 mRNA splicing after prolonged ER stress, resulting in early inactivation. Mutation in the BH3 domain of BIM abrogated the physical interaction with IRE1α, inhibiting its effects on XBP-1 mRNA splicing. Unexpectedly, this regulation required BCL-2 and was antagonized by BAD or the BH3 domain mimetic ABT-737. The modulation of IRE1αRNAse activity by BH3-only proteins was recapitulated in a cell-free system suggesting a direct regulation. Moreover, BH3-only proteins controlled XBP-1 mRNA splicing in vivo and affected the ER stress-regulated secretion of antibodies by primary B cells. We conclude that a subset of BCL-2 family members participates in a new UPR-regulatory network, thus assuming apoptosis-unrelated functions. © 2012 European Molecular Biology Organization.This work was supported by the FONDECYT no. 1100176, FONDAP grant no. 15010006, Millennium Institute no. P09-015-F, Muscular Dystrophy Association, Michael J Fox Foundation, Alzheimer’s Association, ALS Therapy Allianze and North American Spine Society (to CH); FONDECYT no. 3100033 (to DRG); Ligue nationale contre le cancer, and Agence Nationale pour la Recherche (to GK), National Institute of Health no. R01CA125562 and American Caner Society no. RSG-10-030-01-CCG (to EC); P&F award from Nutrition and Obesity Research Center (to TV); Grant SAF2008-00350 from Ministerio de Ciencia e Innovación, and Grant 200720I026 from CSIC (to FPM), Fondecyt 1095089 and ICM P05-001-F (to CG). Grant SAF2008-00350 from Ministerio de Ciencia e Innovación (Spanish Government). ML is the holder of a JAE-Doc postdoctoral fellowship (Spain) co-funded by the European Social Fund. DRR, HU and FL are funded by a CONICYT PhD fellowship.Peer Reviewe

BH3-only proteins are part of a regulatory network that control the sustained signalling of the unfolded protein response sensor IRE1 alpha

Adaptation to endoplasmic reticulum (ER) stress depends on the activation of the unfolded protein response (UPR) stress sensor inositol-requiring enzyme 1α(IRE1α), which functions as an endoribonuclease that splices the mRNA of the transcription factor XBP-1 (X-box-binding protein-1). Through a global proteomic approach we identified the BCL-2 family member PUMA as a novel IRE1αinteractor. Immun oprecipitation experiments confirmed this interaction and further detected the association of IRE1αwith BIM, another BH3-only protein. BIM and PUMA double-knockout cells failed to maintain sustained XBP-1 mRNA splicing after prolonged ER stress, resulting in early inactivation. Mutation in the BH3 domain of BIM abrogated the physical interaction with IRE1α, inhibiting its effects on XBP-1 mRNA splicing. Unexpectedly, this regulation required BCL-2 and was antagonized by BAD or the BH3 domain mimetic ABT-737. The modulation of IRE1αRNAse activity by BH3-only proteins was recapitulated in a cell