The level of mRNA encoding beta-globin was examined in dimethyl sulfoxide (DMSO)-sensitive (DS), and DMSO-resistant (DR) murine erythroleukemia (MEL) cells. DR cells lack erythroid-specific delta- aminolevulinate (ALA) synthase (AL-AS-E), and fail to undergo erythroid differentiation following treatment with DMSO. Treatment of cells with DMSO markedly increased ALAS-E mRNA in DS cells, while the same treatment downregulated the nonspecific ALA synthase (ALAS-N) mRNA levels in both DS and DR cells. The levels of beta-globin mRNA, heme content, and hemoglobin in DS cells increased, while those in DR cells decreased following treatment with DMSO. Treatment of DR cells with hemin caused an increase in beta-globin mRNA and hemoglobin, and partially restored the DMSO-mediated suppression of beta-globin mRNA and hemoglobin synthesis. DMSO treatment decreased heme oxygenase (HO) mRNA in hemin-treated DS cells, but not in hemin-treated DR cells. These findings indicate that heme is necessary for accumulation of the beta-globin transcript during erythroid differentiation, and that hemin- mediated HO induction becomes markedly downregulated in differentiated erythroid cells, presumably because less free heme is available for HO induction by a greater demand for the synthesis of hemoglobin.

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