ABSTRACTObjective: To determine if the novel cyclooxygenase, COX II, was induced by acidic fibroblast growth factor (aFGF) in rabbit cardiac muscle microvessel (RCME) endothelial cells and to determine the role of protein kinase C (PKC) activation in the mediation of the aFGF induction of COX activity.Methods: Cultured RCME cells were treated with aFGF (200 ng/ml). Induction of COX II activity was assessed by determination of COX activity (PGE2production), by immunoprecipitation of metabolically labeled COX II, and by Northern analyses. The role of PKC was assessed using phorbol myristate acetate and PKC inhibitors and by determination of PKC activity in cytosol and membrane fractions of RCME cells treated with aFGF and phorbol myristate acetate.Results: aFGF selectively induced COX II protein and mRNA. Protein kinase C activation was implicated in the transduction of the effects of aFGF for the following reasons: (1) phorbol myristate acetate (PMA), a direct activator of protein kinase C, was a potent inducer of COX II mRNA, COX activity and synthesis of COX II protein. (2) H‐7, an inhibitor of PKC, but not the inactive control, HA‐1004, blocked aFGF induction of COX II mRNA, COX II protein synthesis, and COX activity. Two additional inhibitors of PKC, calphostin C and staurosporine, also inhibited aFGF induction of COX activity. (3) Downregulation of PKC by overnight incubation with 1 μM PMA blocked subsequent induction of COX II protein synthesis by aFGF. (4) aFGF treatment of RCME cells resulted in the translocation of PKC activity from the cytosol to the membrane fraction. However, aFGF, at concentrations that elicited COX II, neither induced Ca2+mobilization from intracellular stores nor increased the accumulation of inositol phosphates.Conclusion: aFGF induces COX II in RCME and this response in mediated, at least in part, by protein kinase C activation. However, aFGF mediated activation of PKC activation must stimulate this kinase through a pathway of signal transduction distinct from inositol phospholipid accumulation or elevation of intracellular