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

Abstract

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-