Formation of diacylglycerol, inositol phosphates, arachidonic acid and its metabolites in macrophages

Treatment of macrophages with zymosan, 4β‐phorbol 12‐myristate 13‐acetate (PMA) and fluoride but not with A 23187 or arachidonic acid (ΔAch) leads to a generation of diacylglycerol (acyl 2 Gro). Formation of inositol phosphates is achieved with zymosan, only. An elevation of intracellular calcium is obtained with zymosan and A 23187 but not with PMA, fluoride or ΔAch. Prior treatment of the cells with phorbol ester for 3 h which has been shown recently to result in a down regulation of protein kinase (PK) C‐β but not PKC‐δ [Duyster, J., Schwende, H., Fitzke, E., Hidaka H. & Dieter P. (1993) Biochem. J. 292 , 203–207] has no effect on the zymosan‐induced formation of acyl 2 Gro or inositol phosphates but inhibits the PMA‐induced generation of acyl 2 Gro. Down regulation of PKC‐δ by prior phorbol ester treatment for 24 h augments the zymosan‐induced generation of acyl 2 Gro and inositol phosphates. The acyl 2 Gro lipase inhibitor RG 80267 inhibits the PMA‐induced and fluoride‐induced generation of prostaglandin (PG) E 2 , reduces the zymosan‐induced release of PGE 2 by 50% but has no effect on PGE 2 formation of unstimulated, A 23187 treated or ΔAch‐treated cells. Furthermore, RG 80267 enhances accumulation of ΔAch‐labeled acyl 2 Gro in response to zymosan, PMA and fluoride. These data indicate that zymosan activates a phosphatidylinositol 4,5‐bisphosphate‐specific phospholipase (PL) C, that generation of acyl 2 Gro by PMA and fluoride occurs via hydrolysis of other phospholipids, that PKC‐β is involved in the PMA‐induced generation of acyl 2 Gro and PKC‐δ negatively modulates the zymosan‐induced activation of PLC and PMA and fluoride induce a liberation of ΔAch from acyl 2 Gro, A 23187 activates the PLA 2 pathway and zymosan stimulates both, the acyl 2 Gro‐ and PLA 2 ‐pathway.