Effects of forskolin and phorbol-myristate-acetate on cytoskeleton, extracellular matrix and protein phosphorylation in human endothelial cells.

The role that the intracellular mediators, cAMP and Ca2+/phosphatidylserine-dependent protein kinase C, play in the regulation of endothelial cell (EC) motility was investigated. The adenylate cyclase activator, forskolin, at 10 microM induced rapid and reversible alterations in the shape of cultured human EC, disappearance of actin bundles and the concentration of F-actin at cell borders. Actin reorganization provoked by forskolin coincide with redistribution of vinculin to the cell periphery and rapid elimination of surface-associated fibronectin. A protein kinase C activator, phorbol 12-myristate 13-acetate (PMA) at 10-100 microM induced no visible alterations of cell shape, but enhanced the effect of forskolin. PMA stimulated formation of "stress fibers" and increased the number of vinculin plaques in central areas of the cell. A decrease in the amount of the surface-associated fibronectin in PMA-treated cells has also been observed, but, this effect was considerably slower than that produced by forskolin. Forskolin, but not PMA stimulated phosphorylation of the major intermediate filament protein, vimentin.