Differential induction of eicosanoid synthesis in monocytic cells treated with retinoic acid and 1,25-dihydroxy-vitamin D 3

Abstract

Synthesis and release of eicosanoids is characteristic to mature monocytes, while in undiffernetiated premonocytic cells arachidonic acid (AA) metabolism is barely detectable. Since some vitamins and cytokines induce differentiation of these cells to a more monocyte-like cell type, we evaluated the effect of retinoic acid (RA), 1,25(OH) 2-vitamin D 3 (1,25-D 3) and interferon-γ (IFN-γ) on AA metabolism in the human premonocytic cell lines U937 and THP-1. In U937 cells, differentiation with RA (1 μM) followed by stimulation with the calcium ionophore A23187 (10 μM) or platelet activating factor (PAF; 100 nM) significantly increased synthesis of immunoreactive 6-keto PGF 1α, TxB 2 and PGE 2 5- to 6-fold. Analysis of AA metabolism in RA-differentiated cells prelabelled with [ 3H]-AA revealed the formation of additional radioactive compounds which coeluted with standards for PGF 2α, PGD 2 and 12-hydroxyheptadecatrienoic acid (HHT). The structural identity of 6-keto PGF 1α, TxB 2, PGE 2 and HHT was confirmed by gas chromatography-mass spectrometry (GC-MS). In parallel, RA induced the expression of the monocytic surface antigen CD11b, but not CD14. Differentiation with 1,25-D 3 (10 nM) only marginally increased stimulated eicosanoid formation, while it more effectively induced expression of CD11b and CD14. Pretreatment with IFN-γ (100 IU/ml) slightly increased stimulus-dependent AA metabolism, but did not induce expression of CD11b or CD14. Induction of eicosanoid synthesis by RA was further confirmed in THP-1 cells. These data indicate that RA most effectively induced cyclooxygenase activity and stimulus-dependent eicosanoid formation in U937 and THP-1 cells. Furthermore, since expression of monocytic surface antigens differed between RA and 1,25-D 3, it is suggested that induction of cyclooxygenase activity may correlate to differentiation into distinct monocytic phenotypes.