Evidence for G-protein-dependent and G-protein-independent activation of phospholipase D in lymphocytes

Previously we reported that tumor-promoting phorbol esters stimulate phospholipase D (PLD) independent of protein kinase C (PKC) activation in bovine lymph node lymphocytes. (Cao et al., Biochem. Biophys. Res. Commun. 171, 955-962, 1990; 217, 908-915, 1995). In the present study, we examined the effects of prostagladins (PGs), E(2), F-2 alpha, D-2, and H-2 On PLD activity as measured by conversion of [1-C-14] arachidonic acid-labeled phospholipids into phosphatidylethanol (PEt) in bovine lymph node lymphocytes. Prostaglandins stimulated the formation of PEt at an optimal concentration of 10 mu M with relative stimulatory effect on the order of PGE(2) > PGF(2 alpha) > PGH(2) > PGD(2). The PGE(2)-stimulated formation of PEt was dose-dependent in the range of 0.1 to 10 mu M and was not inhibited by PKC inhibitors staurosporine and K252a. When both PGE(2) and 12-O-tetradecanoylphorbol-13-acetate (TPA) were included, their effect on the PLD activation was additive. Furthermore, NaF, a G-protein activator, stimulated the PEt formation. Interestingly, the stimulatory effects of PGE, and NaF were not additive; however, the formation of PEt by NaF and TPA was additive. These results suggest that similar to TPA, PGs increase PLD activity independent of PKC and the stimulation by PGs and TPA in lymphocytes may involve both G-protein-dependent and G-protein-independent signaling pathways. (C) 1996 Academic Press, Inc.