Effect of heme on globin messenger RNA synthesis

Erythroid spleen cells from anemic mice were incubated with various inhibitors of heme synthesis. All the effective inhibitors of heme synthesis decreased the incorporation of labelled leucine into protein in spleen erythroid cells. Hemin completely restored protein synthesis to the control levels in isonicotinic acid hydrazide (INH) and penicillamine treated erythroid cells. These two specific inhibitors of heme synthesis were used for the study of the effect of heme on globin mRNA synthesis. Newly synthesized [3H]-uridine labelled globin mRNA was isolated by hybridization to globin cDNA covalently bound to the cellulose column. INH and penicillamine inhibited [3H] uridine incorporation into globin mRNA. The addition of hemin to INH or penicillamine treated cells almost completely restored globin mRNA synthesis. Moreover, hemin alone slightly increased the incorporation of [3H] uridine into globin mRNA. Similar results were obtained in experiments with Friend erythroleukemia cells of the Fw line. These cells are deficient in ferrochelatase enzyme activity and heme synthesis is not significantly increased after induction of differentiation by chemical inducers. The cells induced by butyric acid were incubated for 2 h with or without 100 muM hemin. The incorporation of [3H] uridine into globin mRNA was measured. A 38% increase in globin mRNA synthesis was seen in cells incubated with hemin as compared with cells incubated without hemin. These results seem to indicate that heme affects transcription or processing of globin mRNA precursors. Heme inhibitors also reduce [3H] uridine incorporation into other poly(A)-containing RNA in erythroid spleen cells incubated in vitro. In agreement with these results hemin causes increase of synthesis of some other poly(A)-containing RNA in Friend cells described above.