Inhibitory effect of nitric oxide on chemically induced differentiation of human leukemic K562 cells

The effect of nitric oxide (NO) was investigated in the human K562 cell line during chemically induced erythroid differentiation. Butyric acid (BA) and the anthracycline antitumour drugs aclarubicin (ACLA) and doxorubicin (DOX) were used as differentiating agents. In all cases, cell hemoglobinization was dose dependently inhibited by NO donors such as sodium nitroprusside (SNP). A 50% inhibition of cell differentiation was obtained with 25 microM SNP, which generated less than 2 microM nitrite in 3-day culture media. Increasing SNP concentrations led to higher nitrite accumulation (up to 12 microM with 1 mM SNP) and total inhibition of cell hemoglobinization, but did not have a significant effect on cell proliferation. As shown by Northern blotting, high concentrations of SNP (1 mM) reduced the expression of gamma-globin and porphobilinogen deaminase, but did not change GATA-1 and NF-E2 mRNA levels in ACLA- and BA-treated cells. In contrast, hemin-induced erythroid differentiation was not affected by the presence of NO donors. Altogether, these results show that NO is able to inhibit cell differentiation induced by some (ACLA, DOX, BA), but not all (hemin), agents. The inhibitory effect of NO seems to take place downstream of the regulation of erythroid gene expression.