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Elife. 2015 May 19;4. doi: 10.7554/eLife.05434.

Endoplasmic reticulum stress-independent activation of unfolded protein response kinases by a small molecule ATP-mimic.

Author information

1
Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States.
2
Fundación Ciencia & Vida, Santiago, Chile.
3
Department of Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States.

Abstract

Two ER membrane-resident transmembrane kinases, IRE1 and PERK, function as stress sensors in the unfolded protein response. IRE1 also has an endoribonuclease activity, which initiates a non-conventional mRNA splicing reaction, while PERK phosphorylates eIF2α. We engineered a potent small molecule, IPA, that binds to IRE1's ATP-binding pocket and predisposes the kinase domain to oligomerization, activating its RNase. IPA also inhibits PERK but, paradoxically, activates it at low concentrations, resulting in a bell-shaped activation profile. We reconstituted IPA-activation of PERK-mediated eIF2α phosphorylation from purified components. We estimate that under conditions of maximal activation less than 15% of PERK molecules in the reaction are occupied by IPA. We propose that IPA binding biases the PERK kinase towards its active conformation, which trans-activates apo-PERK molecules. The mechanism by which partial occupancy with an inhibitor can activate kinases may be wide-spread and carries major implications for design and therapeutic application of kinase inhibitors.

KEYWORDS:

E. coli; IPA; IRE1; PERK; biochemistry; cell biology; human; human cells; mouse; protein kinase

PMID:
25986605
PMCID:
PMC4436593
DOI:
10.7554/eLife.05434
[Indexed for MEDLINE]
Free PMC Article

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