Phosphorylation-dependent regulation of phospholipase D2 by protein kinase C delta in rat pheochromocytoma PC12 cells

Abstract

Many studies have shown that protein kinase C (PKC) is an important physiological regulator of phospholipase D (PLD). However, the role of PKC in agonist-induced PLD activation has been mainly investigated with a focus on the PLD1, which is one of the two PLD isoenzymes (PLD1 and PLD2) cloned to date. Since the expression of PLD2 significantly enhanced phorbol 12-myristate 13-acetate (PMA)- or bradykinin-induced PLD activity in rat pheochromocytoma PC12 cells, we investigated the regulatory mechanism of PLD2 in PC 12 cells. Two different PKC inhibitors, GF109203X and Ro-318220, completely blocked PMA-induced PLD2 activation. In addition, specific inhibition of PKCdelta by rottlerin prevented PLD2 activation in PMA-stimulated PC12 cells. Concomitant with PLD2 activation, PLD2 became phosphorylated upon PMA or bradykinin treatment of PC12 cells. Moreover, rottlerin blocked PMA- or bradykinin-induced PLD2 phosphorylation in PC 12 cells. Expression of a kinase-deficient mutant of PKCdelta using adenovirus-mediated gene transfer inhibited the phosphorylation and activation of PLD2 induced by PMA in PC12 cells, suggesting the phosphorylation-dependent regulation of PLD2 mediated by PKCdelta kinase activity in PC12 cells. PKCdelta co-immunoprecipitated with PLD2 from PC 12 cell extracts, and associated with PLD2 in vitro in a PMA-dependent manner. Phospho-PLD2 immunoprecipitated from PMA-treated PC12 cells and PLD2 phosphorylated in vitro by PKCdelta were resolved by two-dimensional phosphopeptide mapping and compared. At least seven phosphopeptides co-migrated, indicating the direct phosphorylation of PLD2 by PKCdelta inside the cells. Immunocytochemical studies of PC12 cells revealed that after treatment with PMA, PKCdelta was translocated from the cytosol to the plasma membrane where PLD2 is mainly localized. These results suggest that PKCS-dependent direct phosphorylation plays an important role in the regulation of PLD2 activity in PC12 cells.