Modulation of the IgH enhancer's cell type specificity through a genetic switch.
Using defined regions of the immunoglobulin heavy-chain enhancer linked to minimal promoters and cDNAs that encode the two helix-loop-helix transcription factors ITF-1 and TFE3, we demonstrate that activity of an otherwise repressed enhancer can be stimulated in nonlymphoid cells. Repression in non-B cells is mediated by the microE5 motif. Derepression occurs at two levels. First, overexpression of ITF-1, and E12/E47-related protein that binds the microE5 motif, leads to transcriptional activation itself. Second, binding of ITF-1 physically displaces a repressor that normally blocks the stimulatory activity of TFE3, which binds the neighboring microE3 motif. TFE3 can only stimulate enhancer activity in the presence of ITF-1 or in the absence of a microE5 motif. Hence, one component of the enhancer's cell type specificity can be artificially modulated through a "genetic switch" in which activity is dictated by the relative levels of ITF-1 and a competing repressor.
Ruezinsky
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Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia 19104-6148.
Beckmann
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Kadesch
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D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics; D004742:Enhancer Elements, Genetic; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D008969:Molecular Sequence Data; D010957:Plasmids; D011401:Promoter Regions, Genetic; D013379:Substrate Specificity; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic; D014162:Transfection
D051792:Basic Helix-Loop-Helix Proteins; D004247:DNA; D007143:Immunoglobulin Heavy Chains; D014157:Transcription Factors; C407909:TCF3 protein, human