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Molecular and Cellular Biology, September 2008, p. 5223-5237, Vol. 28, No. 17
0270-7306/08/$08.00+0     doi:10.1128/MCB.00431-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Chaperone Hsp27, a Novel Subunit of AUF1 Protein Complexes, Functions in AU-Rich Element-Mediated mRNA Decay ^,

Kristina S. Sinsimer, Frances M. Gratacós, Anna M. Knapinska, Jiebo Lu, Christopher D. Krause, Alexandria V. Wierzbowski, Lauren R. Maher, Shannon Scrudato, Yonaira M. Rivera, Swati Gupta, Danielle K. Turrin, Mary Pauline De La Cruz, Sidney Pestka, and Gary Brewer^*

Department of Molecular Genetics, Microbiology and Immunology, UMDNJ-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5635

Received 15 March 2008/ Returned for modification 19 May 2008/ Accepted 11 June 2008

Controlled, transient cytokine production by monocytes depends heavily upon rapid mRNA degradation, conferred by 3' untranslated region-localized AU-rich elements (AREs) that associate with RNA-binding proteins. The ARE-binding protein AUF1 forms a complex with cap-dependent translation initiation factors and heat shock proteins to attract the mRNA degradation machinery. We refer to this protein assembly as the AUF1- and signal transduction-regulated complex, ASTRC. Rapid degradation of ARE-bearing mRNAs (ARE-mRNAs) requires ubiquitination of AUF1 and its destruction by proteasomes. Activation of monocytes by adhesion to capillary endothelium at sites of tissue damage and subsequent proinflammatory cytokine induction are prominent features of inflammation, and ARE-mRNA stabilization plays a critical role in the induction process. Here, we demonstrate activation-induced subunit rearrangements within ASTRC and identify chaperone Hsp27 as a novel subunit that is itself an ARE-binding protein essential for rapid ARE-mRNA degradation. As Hsp27 has well-characterized roles in protein ubiquitination as well as in adhesion-induced cytoskeletal remodeling and cell motility, its association with ASTRC may provide a sensing mechanism to couple proinflammatory cytokine induction with monocyte adhesion and motility.

Published ahead of print on 23 June 2008.

Supplemental material for this article may be found at http://mcb.asm.org/.

Present address: Department of Molecular Biology, Princeton University, Princeton, NJ 08544.

Present address: Pharmanet Inc., 504 Carnegie Center, Princeton, NJ 08540.