The Sec61 translocon limits IRE1α signaling during the unfolded protein response

Abstract

IRE1α is an endoplasmic reticulum (ER) localized endonuclease activated by misfolded proteins in the ER. Previously, we demonstrated that IRE1α 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 IRE1α complexes in cells with blue native PAGE immunoblotting. We find that IRE1α forms a hetero-oligomeric complex with the Sec61 translocon that is activated upon ER stress with little change in the complex. In addition, IRE1α oligomerization, activation, and inactivation during ER stress are regulated by Sec61. Loss of the IRE1α-Sec61 translocon interaction as well as severe ER stress conditions causes IRE1α to form higher-order oligomers that exhibit continuous activation and extended cleavage of XBP1u mRNA. Thus, we propose that the Sec61-IRE1α complex defines the extent of IRE1α activity and may determine cell fate decisions during ER stress conditions.DOI: http://dx.doi.org/10.7554/eLife.27187.001

An Improved Human smORF Annnotation Workflow Combining De Novo Transcriptome Assembly and Ribo-Seq

“…Xtail uses Ribo-Seq data to measure changes in translation while accounting for changes in transcript abundance using RNA-Seq data to quantify the magnitude and statistical significance of differential translation efficiency (TE) genome-wide. Both TG and TM induced higher TE for ATF4, IFRD1, and SEC61G, which have been shown to be regulated during ER stress 51–53 , as well as several other genes (Fig. 3c).…”

IRE1β negatively regulates IRE1α signaling in response to endoplasmic reticulum stress

“…Further in vitro and structural studies are needed to define the molecular interface mediating the IRE1-IRE1 interaction. Likewise, other ER lumenal and membrane proteins, such as BiP (Bertolotti et al, 2000), ERdj4 (Amin-Wetzel et al, 2017), Hsp47 (Sepulveda et al, 2018), and Sec61 (Sundaram et al, 2017) regulate IRE1 activity, and we have not studied how IRE1 may affect these interactions. And, we do not measure IRE1dependent RIDD activity (Hollien et al, 2009;Hollien and Weissman, 2006).…”

A Molecular Mechanism for Turning off IRE1α Signaling During Endoplasmic Reticulum Stress

“…On the other hand, hyperactivated IRE1α can produce excess of XBP1 transcription factor, which can be beneficial for tumor cell growth in a hostile environment (Cubillos-Ruiz et al, 2017). Recent studies have identified many IRE1α interacting proteins that have been shown to regulate IRE1α activation and inactivation during ER stress (Eletto et al, 2014; Sundaram et al, 2017; Sepulveda et al, 2018). One of the key factors that regulate IRE1α activity is the luminal Hsp70 like chaperone BiP ATPase (Bertolotti et al, 2000; Okamura et al, 2000; Pincus et al, 2010; Amin-Wetzel et al, 2017).…”

“…However, it is unclear how the luminal protein BiP is efficiently recruited to the membrane-localized IRE1α in cells. Our previous studies have shown that IRE1α interaction with the Sec61 translocon is essential to regulate its oligomerization and RNase activity in cells (Sundaram et al, 2017). However, the molecular mechanism by which the Sec61 translocon limits IRE1α activity is unclear.…”

“…We have previously shown that IRE1α forms a complex with the Sec61 translocon to cleave its substrate mRNAs (Plumb et al, 2015). This complex also regulates IRE1α activation dynamics during ER stress in cells (Sundaram et al, 2017), but the underlying mechanism is unclear. Here, we show that Sec63 is a subunit of the IRE1α/Sec61 translocon complex.…”