NF-kappa B activity is required for the deregulation of c-myc expression by the immunoglobulin heavy chain enhancer.
The c-myc gene is translocated to one of the immunoglobulin genes in Burkitt's lymphoma resulting in deregulated expression of c-myc. Several enhancers have been shown to be important for expression of the immunoglobulin heavy chain gene. Four enhancer regions (murine-hypersensitive sites (MHS) 1, 2, 3, and 4) located 3' of the murine immunoglobulin heavy chain gene play a role in activating expression of the translocated c-myc gene. The enhancer regions also result in a shift in transcriptional initiation from the P2 promoter to P1 that is characteristic of the translocated c-myc allele. We found that the most 3' enhancer region (MHS4) activated the c-myc promoter by 46-fold in the Raji Burkitt's lymphoma cell line, and it was the most active enhancer in these cells. The addition of enhancer regions MHS1,2 and 3 to MHS4 increased c-myc transcription by an additional 3-fold and resulted in the full promoter shift from P2 to P1. By deletion analysis of enhancer region MHS4, we located a region that was critical for the transcriptional activity of MHS4. Electrophoretic mobility shift assay analysis revealed that NF-kappaB/Rel family members bound to this region. Mutation of the NF-kappaB binding site abolished both the enhancer activity and the promoter shift activity of MHS4. An active NF-kappaB site was also identified in the human HS4 enhancer. Inhibition of c-myc promoter activity driven by the immunoglobulin enhancers was observed with expression of a super-repressor IkappaBalpha construct. These results indicate that the NF-kappaB/Rel transcription factors play an important role in the deregulation of the translocated c-myc gene in Burkitt's lymphoma and suggest that interference with NF-kappaB function may represent a new approach to the treatment of Burkitt's lymphoma.
Center for Molecular Biology in Medicine, Veterans Affairs Palo Alto Health Care System and the Department of Medicine, Stanford University School of Medicine, Stanford, California 94305, USA.
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Kanda
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Zhang
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Grandchamps
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Boxer
D000818:Animals; D001483:Base Sequence; D002051:Burkitt Lymphoma / Q000235:genetics*; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D016259:Genes, myc / Q000235:genetics*; D006801:Humans; D020672:I-kappa B Proteins; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D051379:Mice; D009154:Mutation / Q000235:genetics; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D052002:NF-kappa B p50 Subunit; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D051996:Transcription Factor RelA; D014162:Transfection; D014178:Translocation, Genetic / Q000235:genetics; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D007143:Immunoglobulin Heavy Chains; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; C000606204:NFKBIA protein, human; C000606205:Nfkbia protein, mouse; D012333:RNA, Messenger; D012097:Repressor Proteins; D051996:Transcription Factor RelA; D000072000:NF-KappaB Inhibitor alpha; D004247:DNA