A role for protein kinase C‐α in zymosan‐stimulated eicosanoid synthesis in mouse peritoneal macrophages

A possible regulatory function of protein kinase C (PKC) isoenzymes in zymosan‐stimulated eicosanoid synthesis was studied in mouse peritoneal macrophages in culture. The addition of zymosan to intact cells labelled with [ 3 H]arachidonic acid stimulated a time‐dependent and concentration‐dependent release of the fatty acid. There was a simultaneous marked increase in the synthesis of prostaglandin E 2 and leukotriene C 4 . The protein‐kinase inhibitor K‐252a and the selective PKC inhibitor CGP41251 completely blocked zymosan‐triggered arachidonic acid release as well as prostaglandin E 2 and leukotriene C 4 synthesis. In contrast, an inactive staurosporine derivative, CGP42700, failed to inhibit any of the zymosan‐induced responses. The down‐regulation of PKC by long‐term treatment with phorbol 12‐myristate 13‐acetate eliminated zymosan‐stimulated arachidonic acid release and eicosanoid synthesis (after 4–6 h treatment). By using specific antibodies it was observed that mouse macrophages express five PKC isoenzymes, PKC‐α, ‐β, ‐δ, ‐ζ and ‐ζ. No PKC‐γ isoenzyme was detected. After exposure to phorbol 12‐myristate 13‐acetate, a complete depletion of PKC‐β was observed within 1 h and the complete depletion of PKC‐α and PKC‐δ isotypes was observed within 4 h. In contrast, PKC‐ε was only partially down‐regulated after a 24‐h treatment with phorbol 12‐myristate 13‐acetate and PKC‐ζ was not affected at all. These data indicate that PKC‐α and PKC‐δ isoenzymes are candidates for regulating prostaglandin and leukotriene production. From the potent inhibitory activities of K‐252a and CGP41251, two compounds that reportedly display a higher selectivity for PKC‐α compared to PKC‐δ, it is suggested that PKC‐α triggers arachidonic acid mobilization and eicosanoid synthesis in peritoneal macrophages.