NF-kappaB activates Bcl-2 expression in t(14;18) lymphoma cells.
The t(14;18) translocation, which is characteristic of follicular lymphoma, results in the overexpression of the bcl-2 gene dependent upon regulatory elements within the bcl-2 5' flanking region and the immunoglobulin heavy chain gene enhancers. Conflicting evidence exists on the effects of NF-kappaB expression on Bcl-2 levels in different cell types. Lymphoma cells with the t(14;18) translocation show high levels of nuclear NF-kappaB proteins. We observed decreased levels of endogenous Bcl-2 when the IkappaBalpha-super-repressor was expressed in a t(14;18) cell line. Deletion analysis of the bcl-2 promoter indicated that the repressive effect of the IkappaBalpha-super-repressor occurred through a region that contained no NF-kappaB consensus sequences. This highly active region contained a c-AMP response element (CRE) and several Sp1 binding sites. Chromatin immunoprecipitation assays with antibodies specific for the NF-kappaB and CREB/ATF family members, as well as Sp1, resulted in the isolation of this IkappaBalpha-super-repressor responsive region of the bcl-2 promoter. Mutation of the CRE and the two Sp1 sites in different combinations in bcl-2 reporter constructs resulted in the loss of bcl-2 promoter repression by the IkappaBalpha-super-repressor. We therefore conclude that the activation of bcl-2 by NF-kappaB in t(14;18) lymphoma cells is mediated through the CRE and Sp1 binding sites.
Heckman
Caroline A
CA
Center for Molecular Biology in Medicine, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94305, USA.
Mehew
John W
JW
Boxer
Linda M
LM
D017209:Apoptosis; D001665:Binding Sites; D015153:Blotting, Western; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism; D002883:Chromosomes, Human, Pair 14; D002887:Chromosomes, Human, Pair 18; D000242:Cyclic AMP / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D005822:Genetic Vectors; D006801:Humans; D015151:Immunoblotting; D008156:Luciferases / Q000378:metabolism; D008223:Lymphoma / Q000378:metabolism*; D008957:Models, Genetic; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016329:Sp1 Transcription Factor / Q000378:metabolism; D014162:Transfection; D014178:Translocation, Genetic; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D014466:Ultraviolet Rays
D002843:Chromatin; D016328:NF-kappa B; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D016329:Sp1 Transcription Factor; D014409:Tumor Necrosis Factor-alpha; D000242:Cyclic AMP; D008156:Luciferases