Platelet interaction with CNBr peptides from type II collagen via integrin α2β1

Adhesion of blood platelets to fibrillar collagens plays a crucial role in haemostasis. Collagen type II is a homotrimeric member of the fibrillar collagen family, whose ability to interact with platelets has been poorly investigated. In this work, we analysed platelet adhesion to the whole collagen type II molecule, as well as to its CNBr peptides. We found that collagen type II is as efficient as collagen type I in supporting platelet adhesion. Platelet binding sites on collagen type II were identified in two different CNBr-derived peptides, CB8 and CB11. The ability of these peptides to support platelet adhesion required the triple helical conformation. Interaction of platelets with CB8 and CB11 peptides was totally dependent on the presence of Mg2+ ions, and was completely inhibited by the anti-integrin α2β1 antibody P1E6. Upon adhesion to CB8 and CB11, a significant increase in intracellular protein tyrosine phosphorylation was observed. The pattern of tyrosine phosphorylated proteins in CB8- and CB11-adherent platelets was very similar to that observed in platelets adherent to the whole collagen molecule. By immunoprecipitation experiments, we identified two substrates that were tyrosine phosphorylated in adherent platelets as the tyrosine kinase Syk and the PLCγ2 isozyme. By contrast, platelet adhesion to CB8 and CB11 did not promote tyrosine phosphorylation of FcR γ-chain. Finally, we found that collagen type II, but not the CNBr-derived peptides, was able to induce cell aggregation associated to protein tyrosine phosphorylation when added to a platelet suspension. These results identify the CNBr peptides from collagen type II CB8 and CB11 as ligands for platelet integrin α2β1, and recognise their ability to support platelet adhesion and activation. © 2003 Elsevier Science B.V. All rights reserved.