Vascular endothelial growth factor induces protein kinase C (PKC)-dependent Akt/PKB activation and phosphatidylinositol 3'-kinase-mediates PKC delta phosphorylation: role of PKC in angiogenesis.

Activation of the protein kinase Akt/PKB mediates VEGF-dependent endothelial cell survival and eNOS activation. Here we examined the role of PKC in mediating VEGF-induced Akt activation. The PKC inhibitors GF109203X and calphostin C inhibited VEGF-induced Akt activation. Rottlerin and Go6976, inhibitors with specificities for PKC delta and alpha, respectively, also strongly inhibited VEGF-induced Akt activation. VEGF-induced Akt activation was prevented by down-regulation of PKC induced by prolonged pretreatment with the phorbol ester, PMA. VEGF induced phosphorylation of PKC delta at Thr 505 in the activation loop, and this phosphorylation was inhibited by LY294002, suggesting that modulation of PKC delta activation by VEGF occurs distal to phosphatidylinositol 3'-kinase. PKC and PI3K inhibitors both strongly reduced the stimulation of branching tubulogenesis by VEGF in vitro. The finding that PKC mediates VEGF-induced Akt activation identifies a novel signal transduction pathway through which Akt can be regulated by growth factors acting through receptor protein tyrosine kinases, and indicates that PKC-mediated Akt activity may play an essential role in VEGF-stimulated angiogenesis.