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J. Biol. Chem., Vol. 280, Issue 44, 36873-36882, November 4, 2005

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Two Functional Active Conformations of the Integrin 21, Depending on Activation Condition and Cell Type^*

Gerlinde R. Van de Walle, Karen Vanhoorelbeke1, Zsuzsa Majer, Eszter Illyés, Johan Baert¶, Inge Pareyn, and Hans Deckmyn2

From the Laboratories for Thrombosis Research and ^¶Histology, Interdisciplinary Research Centre, Katholieke Universiteit Leuven, Campus Kortrijk, 8500 Kortrijk, Belgium and the Department of Organic Chemistry, Eötvös Loránd University, 1518 Budapest, Hungary

For several integrins, the existence of multiple conformational states has been studied intensively. For the integrin 21, a major collagen receptor on platelets and other cell types, however, no such experimental data were available thus far. Recently, our group has developed a monoclonal antibody IAC-1 sensitive to the molecular conformation of 21 because it only binds to the activated state of 21 on platelets, induced upon inside-out signaling. By investigating IAC-1 binding in combination with collagen binding after inside-out stimulation and outside manipulation, we demonstrated the existence of three different conformations of 21 on platelets and Chinese hamster ovary cells as follows: (i) a nonactivated, resting state with no collagen nor IAC-1 binding; (ii) an intermediate state, induced by outside manipulation, with collagen but no IAC-1 binding; and (iii) a fully activated state, induced after inside-out stimulation, with both collagen and IAC-1 binding. Moreover, these different conformational states of 21 are dependent on the cell type where 21 is expressed, as IAC-1 binding to peripheral blood mononuclear cells and Jurkat cells could also be induced by outside manipulation, in contrast to platelets and 21-expressing Chinese hamster ovary cells. Finally, we revealed a functional relevance for these different conformational states because the conformation of 21, induced after outside manipulation, resulted in significantly more cell spreading on coated collagen compared with nonactivated or inside-out stimulated cells.

Received for publication, July 26, 2005

^* This work was supported by Grant GOA/2004/09 from the Katholieke Universiteit Leuven, the Hungarian Research Fund/OTKA Grant T037719, and a Bilateral Collaboration Grant BIL/04/36. 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 Postdoctoral fellow of the Fonds voor Wetenschappelijk Onderzoek Vlaanderen.

² To whom correspondence should be addressed: Laboratory for Thrombosis Research, Interdisciplinary Research Centre, Katholieke Universiteit Leuven, Campus Kortrijk, E. Sabbelaan 53, 8500 Kortrijk, Belgium. Tel.: 32-56246422; Fax: 32-56246997; E-mail: Hans.deckmyn{at}kulak.ac.be.

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