The basic helix-loop-helix-zipper domain of TFE3 mediates enhancer-promoter interaction.
Binding sites for three families of sequence-specific DNA-binding proteins, microE3, C/EBP, and OCT, are found in both the promoters and the intronic enhancer of the immunoglobulin heavy-chain gene. We have used a cotransfection system to investigate how proteins binding these sites may participate in enhancer-promoter interactions. Basic helix-loop-helix-zipper (BHLHZIP) proteins TFE3 and TFEB activate from a distance in this assay, but the basic zipper (BZIP) protein NF-IL6 and endogenous OCT-binding proteins do not. Our results suggest that remotely bound TFE3 is recruited to the initiation site by association with proximally bound TFE3; this interaction is mediated by the BHLHZIP domain and not by activation domains of TFE3. The BZIP domain of Ig/EBP lacks this activity, revealing an important functional difference between these structurally related dimerization domains. We also show that TFE3 can exist as a tetramer in solution and that tetramerization is determined by the HLHZIP domain. These data support a model in which protein-protein interactions between proximally and remotely bound TFE3 recruit TFE3 to the initiation site for activation. The IgH gene is the first example of a cellular gene in which proximal and distal binding sites are found for a protein capable of mediating enhancer-promoter interaction.
Department of Microbiology, Columbia University College of Physicians and Surgeons, New York, New York 10032.
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Artandi
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Cooper
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Shrivastava
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Calame
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D018257:Helix-Loop-Helix Motifs; D007143:Immunoglobulin Heavy Chains / Q000235:genetics; D016350:Leucine Zippers; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011994:Recombinant Proteins; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D007143:Immunoglobulin Heavy Chains; D046911:Macromolecular Substances; D009687:Nuclear Proteins; D011994:Recombinant Proteins; C069203:TFE3 protein, human; D014157:Transcription Factors