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Ayele Nigatu, Wondossen Sime, Gezahegn Gorfu, Tarekegn Geberhiwot, Ingegerd Andurn, Sulev Ingerpuu, Masayuki Doi, Karl Tryggvason, Paul Hjemdahl, Manuel Patarroyo
Megakaryocytic cells synthesize and platelets secrete 5-laminins, and the endothelial laminin isoform laminin 10 (511) strongly promotes adhesion but not activation of platelets
Following vascular injury, basement membrane (BM) components of the blood vessels are exposed to circulating cells and may contribute to hemostasis and/or thrombosis. Laminins 8 (LN-8) (411) and 10 (LN-10) (511) are major laminin isoforms of the endothelial BM, and LN-8 is also secreted by activated platelets. In the present study, we demonstrate synthesis of 5-laminins LN-10 and LN-11 (521) by megakaryocytic cells, and intracellular expression of these laminin isoforms in blood platelets. In contrast to platelet LN 4 chain that had an apparent molecular weight of 180 kDa and associated mostly to LN1 chain, platelet LN5 consisted of 300/350 kDa polypeptides and associated mainly to LN2. Both 4- and 5-laminins were secreted by platelets following stimulation. When compared to recombinant human (rh) LN-8, rhLN-10 was much more adhesive to platelets, though adhesion to both proteins was largely mediated via 61 integrin. In spite of their adhesive properties, rhLN-8 and rhLN-10 induced neither P-selectin expression nor cell aggregation, two signs of platelet activation. This study demonstrates synthesis/expression of heterotrimeric 5-laminins in hematopoietic/blood cells, and provides evidence for the adhesive, but not activating, role of endothelial laminin isoforms in platelet biology.
Thrombosis and Haemostasis, Schattauer
Print ISSN: 0340-6245
Volume: 95, 01/2006
Pages: 85 - 93