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 PC12 cells. Two different PKC inhibitors,
GF109203X and
Ro-31-8220, completely blocked PMA-induced PLD2 activation. In addition, specific inhibition of PKC delta 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 PC12 cells. Expression of a
kinase-deficient mutant of PKC delta 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 PKC delta
kinase activity in PC12 cells. PKC delta co-immunoprecipitated with PLD2 from PC12 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 PKC delta were resolved by two-dimensional
phosphopeptide mapping and compared. At least seven
phosphopeptides co-migrated, indicating the direct phosphorylation of PLD2 by PKC delta inside the cells. Immunocytochemical studies of PC12 cells revealed that
after treatment with PMA, PKC delta was translocated from the cytosol to the plasma membrane where PLD2 is mainly localized. These results suggest that PKC delta-dependent direct phosphorylation plays an important role in the regulation of PLD2 activity in PC12 cells.