Role of Src-induced dynamin-2 phosphorylation in caveolae-mediated endocytosis in endothelial cells

Albumin transcytosis, a determinant of transendothelial permeability, is mediated by the release of caveolae from the plasma membrane. We addressed the role of Src phosphorylation of the GTPase dynamin-2 in the mechanism of caveolae release and albumin transport. Studies were made in microvascular endothelial cells in which the uptake of cholera toxin subunit B, a marker of caveolae, and (125)I-albumin was used to assess caveolae-mediated endocytosis. Albumin binding to the 60-kDa cell surface albumin-binding protein, gp60, induced Src activation (phosphorylation on Tyr(416)) within 1 min and resulted in Src-dependent tyrosine phosphorylation of dynamin-2, which increased its association with caveolin-1, the caveolae scaffold protein. Expression of kinase-defective Src mutant interfered with the association between dynamin-2, which caveolin-1 and prevented the uptake of albumin. Expression of non-Src-phosphorylatable dynamin (Y231F/Y597F) resulted in reduced association with caveolin-1, and in contrast to WT-dynamin-2, the mutant failed to translocate to the caveolin-rich membrane fraction. The Y231F/Y597F dynamin-2 mutant expression also resulted in impaired albumin and cholera toxin subunit B uptake and reduced transendothelial albumin transport. Thus, Src-mediated phosphorylation of dynamin-2 is an essential requirement for scission of caveolae and the resultant transendothelial transport of albumin.