title: ZEB1 and CtBP form a repressive complex at a distal promoter element of the BCL6 locus.
abstract: BCL6 is essential for normal antibody responses and is highly expressed in germinal centre B-cells. Constitutive expression due to chromosomal translocations or mutations of cis-acting regulatory elements contributes to diffuse large B-cell lymphoma. BCL6 expression is therefore tightly regulated in a lineage- and developmental-stage-specific manner, and disruption of normal controls can contribute to lymphomagenesis. In order to discover potential cis-acting control regions we carried out DNase I-hypersensitive site mapping. Gel-shift assays and chromatin immunoprecipitation of the core region of a hypersensitive site 4.4 kb upstream of BCL6 transcription initiation (HSS-4.4) showed an E-box element-binding ZEB1 (zinc finger E-boxbinding homeobox 1) and the co-repressor CtBP (C-terminal binding protein). As compared with peripheral blood B-cells, ZEB1, a two-handed zinc finger transcriptional repressor, is expressed at relatively low levels in germinal centre cells, whereas BCL6 has the opposite pattern of expression. Transfection of ZEB1 cDNA caused a reduction in BCL6 expression and a mutated ZEB1, incapable of binding CtBP, lacked this effect. siRNA (small interfering RNA)-mediated knockdown of ZEB1 or CtBP produced an increase in BCL6 mRNA. We propose that HSS-4.4 is a distal promoter element binding a repressive complex consisting of ZEB1 and CtBP. CtBP is ubiquitously expressed and the results of the present study suggest that regulation of ZEB1 is required for control of BCL6 expression.
authors.affiliation: Department of Haematology, Imperial College London, Hammersmith Hospital, UK.
authors.forename: Vasiliki
authors.initials: V
authors.lastname: Papadopoulou
authors.forename: Antonio
authors.initials: A
authors.lastname: Postigo
authors.forename: Ester
authors.initials: E
authors.lastname: Sánchez-Tilló
authors.forename: Andrew C G
authors.initials: AC
authors.lastname: Porter
authors.forename: Simon D
authors.initials: SD
authors.lastname: Wagner
mesh_terms: D000429:Alcohol Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000235:genetics; D051560:Proto-Oncogene Proteins c-bcl-6; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D024363:Transcription Initiation Site; D000071799:Zinc Finger E-box-Binding Homeobox 1
chemical_list: C084103:BCL6 protein, human; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; D051560:Proto-Oncogene Proteins c-bcl-6; D034741:RNA, Small Interfering; D014157:Transcription Factors; C486307:ZEB1 protein, human; D000071799:Zinc Finger E-box-Binding Homeobox 1; D000429:Alcohol Oxidoreductases; C096794:C-terminal binding protein