Effects of Butyrate and Glucocorticoids on γ- to β-Globin Gene Switching in Somatic Cell Hybrids

Abstract

Butyrate and its analogs have been shown to induce fetal hemoglobin in humans and primates and in erythroid cell cultures. To obtain insights concerning the cellular mechanisms of butyrate action, we analyzed the effects of butyrate on human globin gene expression in hybrids produced by fusing mouse erythroleukemia cells (MEL) with human fetal erythroid cells (HFE). These hybrids initially express human fetal hemoglobin but subsequently switch to adult globin expression after several weeks in culture. We found that α-aminobutyric acid, a butyrate analog which does not induce terminal maturation, strikingly delays the rate of the γ- to β-globin gene (γ-to-β) switch in the HFE × MEL hybrids. The effect of butyrate on globin expression is transient, with the result that the delay of globin gene switching requires the continuous presence of this compound in culture. Furthermore, butyrate fails to induce fetal hemoglobin expression in hybrids which have switched, suggesting that the effect of this compound on γ-globin expression is due to inhibition of γ gene silencing rather than to induction of γ gene transcription. Since in other cellular systems, glucocorticoids antagonize the action of butyrate, the effect of dexamethasone on the γ-to-β switch in HFE × MEL hybrids was examined. Dexamethasone strikingly accelerated the γ-to-β switch, and its effect was irreversible. The effects of dexamethasone and butyrate on the γ-to-β switch of the HFE × MEL hybrids appear to be codominant. These results indicate that steroids can have a direct effect on globin gene switching in erythroid cells.