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© 2009 by The American Society for Biochemistry and Molecular Biology, Inc.
Ribosomal Protein S19 Interacts with Macrophage Migration Inhibitory Factor and Attenuates Its Pro-inflammatory Function*
Ana-Maria Filip
Abstract: Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that has been implicated in the pathogenesis of inflammatory disorders such as infection, sepsis, and autoimmune disease. MIF exists preformed in cytoplasmic pools and exhibits an intrinsic tautomerase and oxidoreductase activity. MIF levels are elevated in the serum of animals and patients with infection or different inflammatory disorders. To elucidate how MIF actions are controlled, we searched for endogenous MIF-interacting proteins with the potential to interfere with key MIF functions. Using in vivo biotin-tagging and endogenous co-immunoprecipitation, the ribosomal protein S19 (RPS19) was identified as a novel MIF binding partner. Surface plasmon resonance and pulldown experiments with wild type and mutant MIF revealed a direct physical interaction of the two proteins (KD = 1.3 x 10-6 M). As RPS19 is released in inflammatory lesions by apoptotic cells, we explored whether it affects MIF function and inhibits its binding to receptors CD74 and CXCR2. Low doses of RPS19 were found to strongly inhibit MIF-CD74 interaction. Furthermore, RPS19 significantly compromised CXCR2-dependent MIF-triggered adhesion of monocytes to endothelial cells under flow conditions. We, therefore, propose that RPS19 acts as an extracellular negative regulator of MIF.
Received for publication November 12, 2008. Revision received December 24, 2008. * This work was supported by Deutsche Forschungsgemeinschaft Grants Me 1323/2-4 (to A. M.) and SFB 542/TP A7 (J. B.) and a research grant of the University Medical Centre Giessen and Marburg (to A. M.). 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 To whom correspondence should be addressed: Dept. of Anatomy and Cell Biology, Justus-Liebig-University of Giessen, Aulweg 123, D-35385 Giessen, Germany. Tel.: 49-641-9947024; Fax: 49-641-9947029; E-mail: andreas.meinhardt{at}anatomie.med.uni-giessen.de.
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