Expression of the human .gamma.-globin gene after retroviral transfer to transformed erythroid cells

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Abstract
Regulation of the human fetal (.gamma.) globin gene and a series of mutant .gamma.-globin genes was studied after retroviral transfer into erythroid cells with fetal or adult patterns of endogenous globin gene expression. Steady-state RNA from a virally transferred 1A.gamma.-globin gene with a normal promoter increased after induction of erythroid maturation of murine erythroleukemia cells and comprised from 2% to 23% of the mouse .beta.maj-globin RNA level. RNA expression from the virally transferred A.gamma.-globin gene comprised 23% of the endogenous G.gamma.- + A.gamma.-globin expression in K 562 cells after treatment with hemin. Expression from a virally transferred .gamma.- or .beta.-globin gene exceeded endogenous .gamma.- or .beta.-globin expression by a factor of 6 or more in the human erythroleukemia line KMOE, in which the endogenous globin genes are weakly inducible. In these experiments, no difference in expression was observed between the gene with the normal promoter and an A.gamma.-globin gene with a point mutation in its promoter (-196 C-to-T) that has been associated with hereditary persistence of fetal hemoglobin (HPFH). To test for cis-acting determinants located within the introns of the .gamma.-globin gene, expression was measured from a set of .gamma.-globin genes configured with either intron alone or with neither intron. In contrast to an intronless .beta.-globin gene, which is not expressed in MEL cells, the intronless .gamma.-globin gene was expressed in MEL cells at 24% of the level of an intron-containing gene. The data show that .gamma.-globin genes can be expressed at substantial levels in transformed erythroid cell lines after retroviral transfer and that fundamental differences exist in the extent to which introns influence expression of .gamma.- and .beta.-globin genes.