NITRIC-OXIDE ALTERS THE EXPRESSION OF GAMMA-GLOBIN, H-FERRITIN, AND TRANSFERRIN RECEPTOR IN HUMAN K562 CELLS AT THE POSTTRANSCRIPTIONAL LEVEL

Cellular iron metabolism is altered during chronic inflammatory states , leading to reticuloendothelial iron sequestration and an associated anemia. To study the effects of nitric oxide (NO) on the expression of three genes involved in erythroid cell iron metabolism (gamma-globin, H-ferritin, and transferrin receptor [TfR]), we developed a series of human K562 erythroleukemic cell clones retrovirally transduced with i nducible nitric oxide synthase (NOS-2) and producing different steady- state levels of NO. gamma-Globin and H-ferritin protein expression was reduced in NO-producing cells in relation to the amount of NO produce d. Conversely, cell surface TfR expression increased in NO-producing c lones. Both the inhibitory effects of NO on gamma-globin and H-ferriti n expression and the stimulatory effect on TfR were reversed by the NO S inhibitor N-G-methyl-L-arginine (N(G)MMA). gamma-Globin and H-ferrit in mRNA levels were unaffected by NO production. In the case of TfR, N O appeared to stabilize mRNA in that the half life of TfR mRNA decreas ed from approximately 15 hours to less than 3 hours when NO production by NOS-transduced clones was inhibited. Thus, NO can regulate express ion of these genes at the posttranscriptional level, an effect that is likely mediated by the known effect of NO on the RNA binding activity of iron regulatory protein-1 (Pantopoulos and Hentze, Proc Natl Acad Sci USA 92:1267, 1995). Furthermore, our findings suggest a mechanism for the observed relationship between NO production and the pathophysi ology of the anemia of chronic disease.