Implication of protein kinase C alpha in PAF-stimulated phospholipase D activation in Chinese hamster ovary (CHO) cells expressing PAF receptor.

Protein kinase C (PKC) isozyme(s) involved in regulation of platelet-activating factor (PAF)-induced phospholipase D (PLD) activation was investigated in CHO cells stably expressing cloned guinea-pig PAF receptor (WT-H cells). Three PKC isozymes, alpha, epsilon, and zeta, were identified by Western blotting, which displayed different kinetics of translocation from cytosol to membrane upon PAF stimulation. Cytosolic PKC alpha was rapidly translocated to membrane in response to PAF within 30 s and then returned to cytosol by 10 min. This kinetics was well correlated with PAF-induced transient PLD activation. Pretreatment of the cells with 100 nM 4 beta-phorbol 12-myristate 13-acetate (PMA) for 2 h resulted in down-regulation of PKC alpha, leaving PKC epsilon and zeta unchanged. Under the same conditions, PAF and PMA-mediated PLD activation were markedly reduced. These data suggest that PKC alpha is involved in the regulation of PAF-stimulated PLD activation in WT-H cells.