Gbetagamma activation of Src induces caveolae-mediated endocytosis in endothelial cells

Caveolae-mediated endocytosis in endothelial cells is stimulated by the binding of albumin to gp60, a specific albumin-binding protein localized in caveolae. The activation of gp60 induces its cell surface clustering and association with caveolin-1, the caveolar-scaffolding protein. This interaction leads to G(i)-induced Src kinase activation, which in turn signals dynamin-2-mediated fission and directed migration of caveolae-derived vesicles from apical to basal membrane. In this study, we investigated the possible role of the Gbetagamma heterodimer in signaling G(i)-induced Src activation and subsequent caveolae-mediated endocytosis. We observed using rat lung microvascular endothelial cells that expression of the C terminus of beta-adrenergic receptor kinase (ct-betaARK), an inhibitor Gbetagamma signaling, prevented gp60-dependent Src activation as well as caveolae-mediated endocytosis and transcellular transport of albumin and uptake of cholera toxin subunit B, a specific marker of caveolae internalization. Expression of ct-betaARK also prevented Src-mediated tyrosine phosphorylation of caveolin-1 and dynamin-2 and the resultant phosphorylation-dependent association of dynamin-2 and caveolin-1. Also, the direct activation of Gbetagamma using a specific cell-permeant activating peptide (myristoylated-SIRKALNILGYPDYD) simulated the effects of gp60 in inducing Src activation, caveolin-1, and dynamin-2 phosphorylation as well as caveolae-mediated endocytosis of cholera toxin subunit B. The myristoylated-SIRKALNILGYPDYD peptide-induced responses were inhibited by the expression of ct-betaARK. Taken together, our results demonstrate that Gbetagamma activation of Src signals caveolae-mediated endocytosis and transendothelial albumin transport via transcytosis.