ATP-Competitive Partial Antagonists—'PAIR's—Segregate IRE1α’s RNase-Mediated Biological Outputs
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ABSTRACT: During mammalian cell growth and differentiation, the unfolded protein response (UPR) homeostatically adjusts endoplasmic reticulum (ER) protein-folding capacity to match changing cellular secretory demands. However, under high/chronic ER stress conditions the UPR triggers apoptosis. This dichotomy is promoted in part by differential activation levels of the ER transmembrane kinase/endoribonuclease (RNase) IRE1a. IRE1a kinase auto-phosphorylation operates as a rheostat to control downstream RNase-induced outputs that either sustain adaptive ER protein-folding or cause apoptosis. We have previously shown that IRE1a’s RNase activity can be activated or fully inactivated by ATP-competitive kinase inhibitors. Here we developed a new class of ATP-competitive kinase inhibitors that partially antagonize the RNase of IRE1a at full occupancy. An atomic level resolution co-crystal structure shows that these small molecule partial antagonists—which we named ‘PAIR’s for (Partial Antagonists of IRE1a RNase)—occupy the ATP-binding site of IRE1a and partially displace a helix (helix aC) in the kinase domain that forms part of a dimeric interface. In insulin-producing beta cells, PAIRs permit adaptive XBP1 mRNA splicing, while quelling destructive/terminal outputs from extra-XBP1 mRNA endonucleolytic decay, thus preventing apoptosis. Preservation of XBP1 splicing by PAIRs permits B lymphocytes to differentiate into immunoglobulin-producing plasma cells. In summary, we propose that an intermediate RNase-inhibitory “sweet spot,” achieved by PAIR-bound IRE1a, may capture a structural conformation naturally available to IRE1a that could represent a desirable therapeutic state for drugging this master UPR sensor/effector.
ORGANISM(S): Rattus norvegicus
PROVIDER: GSE164496 | GEO | 2021/06/01
REPOSITORIES: GEO
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