The Molecular Adapter SLP-76 Relays Signals from Platelet Integrin αIIbβ3 to the Actin Cytoskeleton*

By A. Obergfell, B. A. Judd, M. A. del Pozo, M. Schwartz, G. Koretzky, S. Shattil. Journal of Biological Chemistry, 2001

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Platelet adhesion to fibrinogen through integrin αIIbβ3 triggers actin rearrangements and cell spreading. Mice deficient in the SLP-76 adapter molecule bleed excessively, and their platelets spread poorly on fibrinogen. Here we used human platelets and a Chinese hamster ovary (CHO) cell expression system to better define the role of SLP-76 in αIIbβ3 signaling. CHO cell adhesion to fibrinogen required αIIbβ3 and stimulated tyrosine phosphorylation of SLP-76. SLP-76 phosphorylation required coexpression of Syk tyrosine kinase and stimulated association of SLP-76 with the adapter, Nck, and with the Rac exchange factor, Vav1. SLP-76 expression increased lamellipodia formation induced by Syk and Vav1 in adherent CHO cells (p < 0.001). Although lamellipodia formation requires Rac, SLP-76 functioned downstream of Rac by potentiating adhesion-dependent activation of PAK kinase (p < 0.001), a Rac effector that associates with Nck. In platelets, adhesion to fibrinogen stimulated the association of SLP-76 with the SLAP-130 adapter and with VASP, a SLAP-130 binding partner implicated in actin reorganization. Furthermore, SLAP-130 colocalized with VASP at the periphery of spread platelets. Thus, SLP-76 functions to relay signals from αIIbβ3 to effectors of cytoskeletal reorganization. Therefore, deficient recruitment of specific adapters and effectors to sites of adhesion may explain the integrin phenotype of SLP-76−/− platelets.

Subfields: Hematology, Immunology and Allergy, Pathology and Forensic Medicine

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