Tumor necrosis factor-α inversely regulates prostaglandin D2 and prostaglandin E2 production in murine macrophages

Abstract

Increased synthesis of insulin-like growth factor-1 is induced in murine macrophages by prostaglandin E2 (PGEs) and tumor necrosis factor-α (TNFα). Accordingly, we have investigated mechanisms regulating synthesis of PGE2 that might contribute to autocrine/paracrine effects on insulin-like growth factor-1 production. In response to zymosan, TNFα specifically induced a 5- fold increase in PGE2 synthesis, at the same time decreasing PGD2 production in a reciprocal fashion. Activators of cyclic AMP-dependent protein kinase (PKA), such as PGE2 itself or dibutyryl cyclic AMP, did not modify PGE2 production by themselves but potentiated the TNFα-induced increase in PGE2; this effect required both RNA and protein synthesis. No significant change in arachidonate release or production of other eicosanoids was observed. The inducible form of cyclooxygenase-2 (COX2) but not of the constitutive form COX1 was implicated in the generation of both PGE2 and PGD2 in these cells by use of specific inhibitors and effects of dexamethasone. Neither COX1 nor COX2 protein levels were affected by TNFα or PKA activators used alone, whereas in association, marked up-regulation of COX2 mRNA and protein was observed. Incubations of cells carried out with PGH2 demonstrated that PGE2 synthase activity was increased after a TNFα pretreatment. Taken together, our results suggest that TNFα induced a switch from the PGD2 to PGE2 synthesis pathway by regulating PGE2 synthase expression and/or activity and that activators of PKA markedly potentiated the TNFα-induced increase in PGE2 through up-regulation of COX2 gene expression.