Platelet adhesion to extracellular matrices and platelet aggregation are key mechanisms by which platelets participate in hemostasis and thrombosis. These processes are in part mediated by the binding of adhesive proteins including fibrinogen, fibronectin, and von Willebrand Factor to adhesion receptors belonging to the integrin superfamily. In particular, the platelet glycoprotein IIb-IIIa (GPIIb-IIIa) is the most prominent integrin on platelets and recognizes the Arg-Gly-Asp (RGD) sequence present in these adhesive proteins. As a consequence of cellular stimulation and adhesive protein binding to GPIIb-IIIa, the integrin receptor becomes attached to the platelet cytoskeleton which appears to mediate clot retraction. By RGD affinity chromatography, we found that several cytoskeletal proteins were co-purified with GPIIb-IIIa suggesting that these proteins provide linkages between the adhesion receptor and the platelet cytoskeleton. Our immediate research goal focuses on the identification of these proteins in order to elucidate the mechanism mediating GPIIb-IIIa/cytoskeleton interactions. This will be accomplished by immunochemical and protein sequencing studies. Furthermore, by biochemical and molecular engineering techniques, we aim to identify determinants of the cytoplasmic domains of GPIIb-IIIa involved in cytoskeletal attachment. Another major interest in my laboratory is based on recent findings that adhesive protein bindings to GPIIb-IIIa induce tyrosine phosphorylation of a series of intracellular proteins. We aim to identify kinases and phosphatases regulating these signal transduction processes, and their functional significance on cell-cell as well as cell-extracellular matrix interactions.
Publications:
1. Lam, S.C.-T. Isolation and characterization of a chymotryptic fragment of platelet glycoprotein IIb-IIIa retaining Arg-Gly-Asp binding activity. Journal of Biological Chemistry, 267(8):5649-5655, 1992.
2. Wencel-Drake, J.D., Frelinger III, A.L., Dieter, M.G. and Lam, S.C.-T. Arg-Gly-Asp dependent occupancy of GPIIb/IIIa by applaggin: Evidence for internalization and cycling of a platelet integrin. Blood, 81(1):62-69, 1993.
3. Wencel-Drake, J.D., Dieter, M.G. and Lam, S.C.-T. Immunolocalization of ß1 integrins in platelets and platelet derived microvesicles. Blood, 82(4):1197-1203, 1993.
4. Knezevic, I., Leisner, T.M. and Lam, S.C.-T. Direct binding of the platelet integrin alpha-IIb-Beta3 (GPIIb-IIIa) to talin: Evidence that interactionis mediated through the cytoplasmic domains of both Alpha-IIb and Beta3. Journal of Biological Chemistry, 271(27):16416-16421, 1996.