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Vol. 18, Issue 7, 2603-2618, July 2007

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Inhibition of the Ubiquitin-Proteasome System Induces Stress Granule Formation

Rachid Mazroui^*, Sergio Di Marco^*, Randal J. Kaufman, and Imed-Eddine Gallouzi^*

*McGill University, Department of Biochemistry, Montreal, Quebec, H3G 1Y6, Canada; and Howard Hughes Medical Institute, University of Michigan Medical Center, Ann Arbor, MI 48109

Submitted December 6, 2006; Revised April 20, 2007; Accepted April 24, 2007
Monitoring Editor: A. Gregory Matera

The inhibition of the ubiquitin-dependent proteasome system (UPS) via specific drugs is one type of approach used to combat cancer. Although it has been suggested that UPS inhibition prevents the rapid decay of AU-rich element (ARE)-containing messages, very little is known about the cellular mechanisms leading to this effect. Here we establish a link between the inhibition of UPS activity, the formation of cytoplasmic stress granules (SGs), and mRNA metabolism. The assembly of the SGs requires the phosphorylation of the translation initiation factor eIF2 by a mechanism involving the stress kinase GCN2. On prolonged UPS inhibition and despite the maintenance of eIF2 phosphorylation, SGs disassemble and translation recovers in an Hsp72 protein-dependent manner. The formation of these SGs coincides with the disassembly of processing bodies (PBs), known as mRNA decay entities. As soon as the SGs assemble, they recruit ARE-containing messages such as p21^cip1 mRNA, which are stabilized under these conditions. Hence, our findings suggest that SGs could be considered as one of the players that mediate the early response of the cell to proteasome inhibitors by interfering temporarily with mRNA decay pathways.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Address correspondence to: Imed-Eddine Gallouzi (imed.gallouzi{at}mcgill.ca)

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