The role of heme in the maturation of erythroblasts: the effects of inhibition of pyridoxine metabolism

The role of heme in the maturation of erythroblasts and in globin gene expression was investigated with two in vitro erythroid cell culture systems, T3-CI2 murine erythroleukemia cells (MELC) and primary cells from mouse fetal liver (MFL). The accumulation and/or rates of synthesis of globin protein, heme, and globin mRNA were assayed in cells in which endogenous heme biosynthesis was reduced by the tuberculostatic drug isonicotinic acid hydrazide (INH). Under conditions in which heme synthesis was reduced 2-4-fold in dimethylsulfoxide (Me2SO) treated MELC and 5-10-fold in MFL erythroblasts, the levels of globin protein were reduced 10-fold and 2-fold, respectively. The rates of synthesis of globin protein were reduced to similar extents without a concomitant decrease in total protein synthesis. The levels of globin mRNA in INH-treated MELC and MFL cells were 2-7-fold lower than those in untreated cells. In MELC cells cultured with both INH and hemin, the globin protein and mRNA levels were the same as in cells cultured with hemin alone. The globin mRNA content of cells cultured with Me2SO plus INH was low but increased within 5 hr after the addition of hemin. Thus, hemin overcame the inhibitory effects of INH. These data are consistent with the hypothesis that heme affects globin gene expression at the pretranslational, as well as the translational level.