Author response: The Sec61 translocon limits IRE1α signaling during the unfolded protein response

Abstract

IRE1a is an endoplasmic reticulum (ER) localized endonuclease activated by misfolded proteins in the ER. Previously, we demonstrated that IRE1a forms a complex with the Sec61 translocon, to which its substrate XBP1u mRNA is recruited for cleavage during ER stress (Plumb et al., 2015). Here, we probe IRE1a complexes in cells with blue native PAGE immunoblotting. We find that IRE1a forms a hetero-oligomeric complex with the Sec61 translocon that is activated upon ER stress with little change in the complex. In addition, IRE1a oligomerization, activation, and inactivation during ER stress are regulated by Sec61. Loss of the IRE1a-Sec61 translocon interaction as well as severe ER stress conditions causes IRE1a to form higher-order oligomers that exhibit continuous activation and extended cleavage of XBP1u mRNA. Thus, we propose that the Sec61-IRE1a complex defines the extent of IRE1a activity and may determine cell fate decisions during ER stress conditions.