title: Repression of AP-1 function: a mechanism for the regulation of Blimp-1 expression and B lymphocyte differentiation by the B cell lymphoma-6 protooncogene.
abstract: The B cell lymphoma-6 (BCL-6) transcriptional repressor protein is an important regulator of B cell differentiation and is strongly implicated in the development of B cell lymphoma. Expression of the Blimp-1 transcription factor, which is critical for promoting B cell differentiation into plasma cells, is repressed by BCL-6. We have investigated the mechanism for how BCL-6 represses Blimp-1 transcription, and have found that BCL-6 regulates the Blimp-1 promoter through a novel mechanism involving AP-1 elements. Specifically, BCL-6 is a potent repressor of transcriptional activity mediated by AP-1 factors. We found that the zinc-finger region of BCL-6 interacts with c-Jun, JunB, and JunD proteins but does not bind c-Fos or Fra-2 proteins. An estrogen receptor ligand binding domain fusion with the BCL-6 zinc finger domain can act as a estrogen-inducible dominant negative protein and increase AP-1 activity in BCL-6(+) cells but not in BCL-6(-) cells, indicating that endogenous BCL-6 represses AP-1 activity. Additionally, we have confirmed a specific interaction between c-Jun and the zinc finger domain of BCL-6 in vivo using a mammalian two-hybrid assay. Repression of AP-1 function by BCL-6 may be a key mechanism for how BCL-6 regulates gene expression to control inflammation, lymphocyte differentiation, and lymphomagenesis.
authors.affiliation: Department of Microbiology and Immunology and The Walther Oncology Center, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
authors.forename: Farha H
authors.initials: FH
authors.lastname: Vasanwala
authors.forename: Saritha
authors.initials: S
authors.lastname: Kusam
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Toney
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Dent
mesh_terms: D001402:B-Lymphocytes / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D001483:Base Sequence; D002454:Cell Differentiation; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics*; D006801:Humans; D000074462:Positive Regulatory Domain I-Binding Factor 1; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D051560:Proto-Oncogene Proteins c-bcl-6; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism; D011519:Proto-Oncogenes; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques
chemical_list: D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D051560:Proto-Oncogene Proteins c-bcl-6; D016755:Proto-Oncogene Proteins c-jun; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D018808:Transcription Factor AP-1; D014157:Transcription Factors; C087042:PRDM1 protein, human; D004247:DNA; D000074462:Positive Regulatory Domain I-Binding Factor 1