Biology subjects

Appathurai, S.

Publications and source records attributed to Appathurai, S..

2 recordsLinked to original sources

bioRxiv2020

The Sec63/BiP complex suppresses higher-order oligomerization and RNase activity of IRE1α during ER stress

Misfolded proteins in the endoplasmic reticulum (ER) activate IRE1 endoribonuclease in mammalian cells, which mediates XBP1 mRNA splicing to produce an active transcription factor. This promotes the expression of specific genes to alleviate ER stress and thereby attenuating IRE1. Although sustained activation of IRE1 is linked to human diseases, it is not clear how IRE1 is attenuated during ER stress. Here, we identify that Sec63 is a subunit of the previously identified IRE1/Sec61 translocon complex. We find that Sec63 recruits and activates BiP ATPase through its luminal J-domain to bind onto IRE1. This leads to inhibition of higher-order oligomerization and attenuation of IRE1 RNase activity during prolonged ER stress. In Sec63 deficient cells, IRE1 remains activated for a long time despite the presence of excess BiP in the ER. Thus, our data suggest that the Sec61 translocon bridges IRE1 with Sec63/BiP to regulate the dynamics of IRE1 signaling in cells.

cell biology↗

bioRxiv2017

Dynamic changes in oligomeric complexes of UPR sensors induced by misfolded proteins in the ER

The endoplasmic reticulum (ER) localized unfolded protein response (UPR) sensors, IRE1, PERK, and ATF6, are activated upon accumulation of misfolded proteins caused by ER stress. It is debated whether these UPR sensors are activated either by the release of their negative regulator BiP chaperone or directly binding to misfolded proteins during ER stress. Here we simultaneously examined oligomerization and activation of all three endogenous UPR sensors. We found that UPR sensors existed as preformed oligomers even in unstressed cells, which shifted to large oligomers for PERK and small oligomers for ATF6, but little changed for IRE1 upon ER stress. Neither depletion nor overexpression of BiP had significant effects on oligomeric complexes of UPR sensors both in unstressed and stressed cells. Thus, our results find less evidence for the BiP-mediated activation of UPR sensors in mammalian cells and support that misfolded proteins bind and activate the preformed oligomers of UPR sensors.

cell biology↗