A role for the ribosome-associated complex in activation of the IRE1 branch of UPR

The ubiquitous ribosome-associated complex (RAC) is a chaperone that spans ribosomes, making contacts near both the polypeptide exit tunnel and the decoding center, a position prime for sensing and coordinating translation and folding. Loss of RAC is known to result in growth defects and sensitization to translational and osmotic stresses. However, the physiological substrates of RAC and the mechanism(s) by which RAC is involved in responding to specific stresses in higher eukaryotes remain obscure. The data presented here uncover an essential function of mammalian RAC in the unfolded protein response (UPR). Knockdown of RAC sensitizes mammalian cells to endoplasmic reticulum (ER) stress and selectively interferes with IRE1 branch activation. Higher-order oligomerization of the inositol-requiring enzyme 1 alpha (IRE1 alpha) kinase/endoribonuclease depends upon RAC. These results reveal a surveillance function for RAC in the UPR, as follows: modulating IRE1 alpha clustering as required for endonuclease activation and splicing of the substrate Xbp1 mRNA.

Automated summary

The study reveals an essential role of mammalian RAC in the unfolded protein response (UPR) and its involvement in modulating IRE1 branch activation. RAC is shown to regulate the clustering of IRE1 alpha, which is crucial for endonuclease activation and splicing of Xbp1 mRNA substrate.