SGK1 sensitivity of platelet migration

Recent observations pointed to the ability of platelets to migrate and thus to invade the inflamed vascular wall. Platelet migration could be stimulated by stromal cell-derived factor-1 (SDF-1), an effect dependent on phosphatidylinositide-3-kinase (PI3K) and paralleled by activation and phosphorylation of Wiskott-Aldrich syndrome protein (WASP). Migration is inhibited by vinculin, which is similarly regulated by phosphorylation. PI3K-sensitive kinases include the serum- and glucocorticoid-inducible kinase 1 (SGK1). The present study explored whether SGK1 modifies WASP and vinculin phosphorylation in murine platelets and participates in the regulation of platelet migration. Platelets were isolated from gene-targeted mice lacking SGK1 (sgk1(-/-)) and from their wild type littermates (sgk1(+/+)). Platelet migration stimulated with SDF-1 was significantly less pronounced in sgk1(-/-)platelets than in sgk1(+/+) platelets. Moreover, SDF-1 significantly induced WASP phosphorylation, an effect again reduced in platelets lacking SGK1. Phosphorylation of vinculin was significantly enhanced in sgk1(-/-)platelets and was significantly reduced following treatment of platelets with Ca(2+) chelator BAPTA. Immunohistochemical analysis of in vivo experiments in intestinal vessels after vascular inflammation revealed that transmigration of platelets into inflamed vessel walls was significantly less pronounced in sgk1(-/-)than in sgk1(+/+) mice. In conclusion, SGK1 is a powerful regulator of platelet migration.