Tumor promoters stimulate the formation of 1,2-diacylglycerol in murine peritoneal macrophages: a possible mechanism for stimulating superoxide anion radical production.

The formation of 1,2-diacylglycerol (DAG), a known stimulator of superoxide anion radical (O2-.) production in inflammatory cells, was assessed in murine peritoneal macrophages following treatment in vitro with tumor promoters. Addition of phorbol-12-myristate-13-acetate (PMA, 1-100 ng/ml) to resident peritoneal macrophage cultures from CD-1 female mice resulted in a 3- to 7-fold increase in [3H]DAG formation. The response was observed from 15 min to 2 h following the addition of PMA. At concentrations at which they stimulate O2-. production, PMA and other tumor promoters such as mezerein, phorbol-12,13-dibutyrate and 4-O-methyl-PMA stimulated the formation of [3H]DAG. Similar results were obtained when thioglycollate-elicited macrophages were used. Concurrent with the formation of [3H]DAG was a release of [3H]choline equivalents from the resident peritoneal macrophages treated with tumor promoters. The calcium ionophore A23187 did not stimulate O2-. production of [3H]DAG formation in resident peritoneal macrophages. These results demonstrate that tumor promoters stimulate the accumulation of DAGs in murine peritoneal macrophages at concentrations at which they stimulate O2-. production and suggest a mechanism by which tumor promoters such as mezerein, which are weak activators of protein kinase C, may indirectly stimulate O2-. production.