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,¶
* Department of Microbiology and Immunology,
Department of Medicine,
Department of Biochemistry and Molecular Biology, and
James Graham Brown Cancer Center, University of Louisville School of Medicine, Louisville, KY 40202; and
¶ Veterans Affairs Medical Center, Louisville, KY 40206
The targets of the p38 MAPK pathway responsible for regulation of neutrophil chemotaxis and exocytosis are unknown. One target of this pathway is the actin-binding protein, heat shock protein 27 (Hsp27). Therefore, we tested the hypothesis that Hsp27 mediates p38 MAPK-dependent chemotaxis and exocytosis in human neutrophils through regulation of actin reorganization. Sequestration of Hsp27 by introduction of anti-Hsp27 Ab, but not an isotype Ab, inhibited fMLP-stimulated chemotaxis, increased cortical F-actin in the absence of fMLP stimulation, and inhibited fMLP-stimulated exocytosis. Pretreatment with latrunculin A prevented actin reorganization and the changes in fMLP-stimulated exocytosis induced by Hsp27 sequestration. To determine the role of Hsp27 phosphorylation, wild-type, phosphorylation-resistant, or phosphorylation-mimicking recombinant Hsp27 was introduced into neutrophils by electroporation. The phosphorylation-resistant mutant significantly reduced migration toward fMLP, whereas none of the Hsp27 proteins affected fMLP-stimulated or TNF-
-stimulated exocytosis or actin polymerization. Endogenous Hsp27 colocalized with F-actin in unstimulated and fMLP-stimulated neutrophils, whereas phosphorylated Hsp27 showed cytosolic localization in addition to colocalization with F-actin. Our results suggest that Hsp27 regulates neutrophil chemotaxis and exocytosis in an actin-dependent, phosphorylation-independent manner. Phosphorylation of Hsp27 regulates chemotaxis, but not exocytosis, independent of regulation of actin reorganization.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work was supported by the National Institutes of Health (DK62389, to R.A.W. and K.R.M.), the Department of Veterans Affairs (Merit Review, to K.R.M.), an American Heart Association Scientist Development Grant (0335278N, to M.J.R.), and the Ohio Valley affiliate of the American Heart Association (Predoctoral Fellowship Grant, to N.R.J.).
2 Address correspondence and reprint requests to Dr. Kenneth R. McLeish, Baxter I Research Building, 570 South Preston Street, Louisville, KY 40202. E-mail address: k.mcleish{at}louisville.edu
3 Abbreviations used in this paper: MAPKAPK2, MAPK-activated protein kinase-2; Hsp27, heat shock protein 27.
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