The present study demonstrates that even brief inhibition of degradation by the 26S proteasome inhibits global protein synthesis, mediated through increased phosphorylation of eIF2α (eukaryotic translational initiation factor 2α) by the HRI (haem-regulated inhibitor) kinase. Exposure of COS-7 cells to the proteasome inhibitor MG-132 (the proteasome inhibitor carbobenzoxy-L-leucyl-L-leucyl-leucinal) for 4 h resulted in a 55–60% decrease in protein synthesis rate compared with control cells. This repression of protein synthesis after treatment with MG-132 is not due to induction of apoptosis, which is known to occur after longer periods of 26S inhibition. Instead, we observed a significantly increased phosphorylation of eIF2α, which is known to repress global protein synthesis. In three MEF (mouse embryonic fibroblast) knockout cell lines lacking one of the four kinases known to phosphorylate eIF2α, increased phosphorylation of eIF2α still occurred after inhibition of the 26S proteasome. These three cell lines included a deletion of the PKR (double-stranded-RNA-dependent protein kinase); a deletion of the PERK (PKR-like endoplasmic reticulum resident kinase); or a deletion of the GCN2 (positive general control of transcription-2) kinase, indicating that none of these kinases was primarily responsible for the observed phosphorylation of eIF2α. In contrast, in a fourth MEF knockout cell line, HRI−/− cells lacking the HRI kinase failed to increase eIF2α phosphorylation upon proteasome inhibitor treatment (MG-132 or various doses of Bortezomib), indicating that the HRI kinase is the primary kinase activated by brief treatment of MEFs with 26S proteasome inhibitors.
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Research Article|
May 28 2008
Phosphorylation of eIF2α in response to 26S proteasome inhibition is mediated by the haem-regulated inhibitor (HRI) kinase
Azmi Yerlikaya;
Azmi Yerlikaya
*Department of Biology, Faculty of Science and Arts, University of Dumlupinar, Kutahya, Turkey
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Scot R. Kimball;
Scot R. Kimball
†Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, U.S.A.
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Bruce A. Stanley
Bruce A. Stanley
1
‡The Pennsylvania State University College of Medicine, Section of Research Resources, Hershey, PA 17033, U.S.A.
1To whom correspondence should be addressed (email bstanley@psu.edu).
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Publisher: Portland Press Ltd
Received:
February 12 2008
Revision Received:
February 12 2008
Accepted:
February 21 2008
Accepted Manuscript online:
February 21 2008
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© The Authors Journal compilation © 2008 Biochemical Society
2008
Biochem J (2008) 412 (3): 579–588.
Article history
Received:
February 12 2008
Revision Received:
February 12 2008
Accepted:
February 21 2008
Accepted Manuscript online:
February 21 2008
Connected Content
A correction has been published:
Phosphorylation of eIF2α in response to 26S proteasome inhibition is mediated by the haem-regulated inhibitor (HRI) kinase
Citation
Azmi Yerlikaya, Scot R. Kimball, Bruce A. Stanley; Phosphorylation of eIF2α in response to 26S proteasome inhibition is mediated by the haem-regulated inhibitor (HRI) kinase. Biochem J 15 June 2008; 412 (3): 579–588. doi: https://doi.org/10.1042/BJ20080324
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