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Blood, 15 February 2006, Vol. 107, No. 4, pp. 1405-1412.
Prepublished online as a Blood First Edition Paper on October 11, 2005; DOI 10.1182/blood-2005-06-2406.
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HEMOSTASIS, THROMBOSIS, AND VASCULAR BIOLOGY
Laminin stimulates spreading of platelets through integrin 6 1dependent activation of GPVI
Osamu Inoue,
Katsue Suzuki-Inoue,
Owen J. T. McCarty,
Masaaki Moroi,
Zaverio M. Ruggeri,
Thomas J. Kunicki,
Yukio Ozaki, and
Steve P. Watson
From the Department of Clinical and Laboratory Medicine, University of Yamanashi, Japan; Centre for Cardiovascular Sciences, Institute of Biomedical Research, University of Birmingham, United Kingdom; Department of Protein Biochemistry, Institute of Life Science, Kurume University, Fukuoka, Japan; and Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA.
The extracellular matrix protein, laminin, supports platelet adhesion through binding to integrin 6 1 In the present study, we demonstrate that human laminin, purified from placenta, also stimulates formation of filopodia and lamellipodia in human and mouse platelets through a pathway that is dependent on 6 1 and the collagen receptor GPVI. The integrin 6 1 is essential for adhesion to laminin, as demonstrated using an 6-blocking antibody, whereas GPVI is dispensable for this response, as shown using "knockout" mouse platelets. On the other hand, lamellipodia formation on laminin is completely inhibited in the absence of GPVI, although filopodia formation remains and is presumably mediated via 6 1 Lamellipodia and filopodia formation are inhibited in Syk-deficient platelets, demonstrating a key role for the kinase in signaling downstream of GPVI and integrin 6 1 GPVI was confirmed as a receptor for laminin using surface plasmon resonance spectroscopy and by demonstration of lamellipodia formation on laminin in the presence of collagenase. These results identify GPVI as a novel receptor for laminin and support a model in which integrin 6 1 brings laminin to GPVI, which in turn mediates lamellipodia formation. We speculate that laminin contributes to platelet spreading in vivo through a direct interaction with GPVI.

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