NITRIC-OXIDE-RELEASING AGENTS AND CGMP ANALOGS INHIBIT MURINE ERYTHROLEUKEMIA CELL-DIFFERENTIATION AND SUPPRESS ERYTHROID-SPECIFIC GENE-EXPRESSION - CORRELATION WITH DECREASED DNA-BINDING OF NF-E2 AND ALTERED C-MYB MESSENGER-RNA EXPRESSION

Differentiation of murine erythroleukemia (MEL) cells induced by hexam ethylene bisacetamide (HMBA) and DMSO was inhibited by several structu rally unrelated nitric oxide (NO)-releasing agents and two membrane-pe rmeable cCMP analogues. Since the effect of the NO-releasing agents wa s augmented by a cCMP phosphodiesterase inhibitor, at least some of th eir effect appeared to be mediated by activation of cytosolic guanylat e cyclase. The drugs did not globally block differentiation since hemi n-induced differentiation was undisturbed. In HMBA-treated cells, the NO-releasing agents and cGMP analogues reduced beta-globin and delta-a minolevulinate synthetase mRNA expression and inhibited the late down- regulation of c-myb mRNA that is required for HMBA-induced differentia tion of MEL cells; the regulation of c-myc mRNA was not changed by the drugs. Nuclear run-off analyses showed that the drugs inhibited HMBA- induced changes in beta-globin and c-myb transcription rates, and tran sient transfection of a reporter gene construct demonstrated that the drugs inhibited the HMBA-inducible enhancer function of the alpha-glob in control region, which contains binding sites for the erythroid tran scription factors NF-E2 and GATA-1. The NO-releasing agents and cCMP a nalogues largely prevented HMBA-induced increases in DNA binding of NF -E2, whereas DNA binding of CATA-1 and SP-1 was not affected. The inhi bition of erythroid gene expression by NO and cCMP analogues may be ph ysiologically important under conditions of high NO production by endo thelial cells and macrophages, i.e., during acute or chronic inflammat ion.