title: Novel CTCF binding at a site in exon1A of BCL6 is associated with active histone marks and a transcriptionally active locus.
abstract: BCL6 is a zinc-finger transcriptional repressor, which is highly expressed in germinal centre B-cells and is essential for germinal centre formation and T-dependent antibody responses. Constitutive BCL6 expression is sufficient to produce lymphomas in mice. Deregulated expression of BCL6 due to chromosomal rearrangements, mutations of a negative autoregulatory site in the BCL6 promoter region and aberrant post-translational modifications have been detected in a number of human lymphomas. Tight lineage and temporal regulation of BCL6 is, therefore, required for normal immunity, and abnormal regulation occurs in lymphomas. CCCTC-binding factor (CTCF) is a multi-functional chromatin regulator, which has recently been shown to bind in a methylation-sensitive manner to sites within the BCL6 first intron. We demonstrate a novel CTCF-binding site in BCL6 exon1A within a potential CpG island, which is unmethylated both in cell lines and in primary lymphoma samples. CTCF binding, which was found in BCL6-expressing cell lines, correlated with the presence of histone variant H2A.Z and active histone marks, suggesting that CTCF induces chromatin modification at a transcriptionally active BCL6 locus. CTCF binding to exon1A was required to maintain BCL6 expression in germinal centre cells by avoiding BCL6-negative autoregulation. Silencing of CTCF in BCL6-expressing cells reduced BCL6 mRNA and protein expression, which is sufficient to induce B-cell terminal differentiation toward plasma cells. Moreover, lack of CTCF binding to exon1A shifts the BCL6 local chromatin from an active to a repressive state. This work demonstrates that, in contexts in which BCL6 is expressed, CTCF binding to BCL6 exon1A associates with epigenetic modifications indicative of transcriptionally open chromatin.
authors.affiliation: 1] Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC) and Departamento de Biología Molecular, Universidad de Cantabria, CSIC, SODERCAN, Santander, Spain [2] Servicio de Hematología, Hospital U. Marqués de Valdecilla, and IFIMAV-FMV, Santander, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Batlle-López
authors.affiliation: 1] Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC) and Departamento de Biología Molecular, Universidad de Cantabria, CSIC, SODERCAN, Santander, Spain [2] Servicio de Hematología, Hospital U. Marqués de Valdecilla, and IFIMAV-FMV, Santander, Spain.
authors.forename: M G
authors.initials: MG
authors.lastname: Cortiguera
authors.affiliation: Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC) and Departamento de Biología Molecular, Universidad de Cantabria, CSIC, SODERCAN, Santander, Spain.
authors.forename: M
authors.initials: M
authors.lastname: Rosa-Garrido
authors.affiliation: Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC) and Departamento de Biología Molecular, Universidad de Cantabria, CSIC, SODERCAN, Santander, Spain.
authors.forename: R
authors.initials: R
authors.lastname: Blanco
authors.affiliation: Servicio de Hematología, Hospital U. Marqués de Valdecilla, and IFIMAV-FMV, Santander, Spain.
authors.forename: E
authors.initials: E
authors.lastname: del Cerro
authors.affiliation: Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC) and Departamento de Biología Molecular, Universidad de Cantabria, CSIC, SODERCAN, Santander, Spain.
authors.forename: V
authors.initials: V
authors.lastname: Torrano
authors.affiliation: Department of Cancer Studies and Molecular Medicine and MRC Toxicology Unit, University of Leicester, Leicester, UK.
authors.forename: S D
authors.initials: SD
authors.lastname: Wagner
authors.affiliation: Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC) and Departamento de Biología Molecular, Universidad de Cantabria, CSIC, SODERCAN, Santander, Spain.
authors.forename: M D
authors.initials: MD
authors.lastname: Delgado
mesh_terms: D001402:B-Lymphocytes / Q000473:pathology; D001665:Binding Sites; D000076246:CCCTC-Binding Factor; D045744:Cell Line, Tumor; D018899:CpG Islands; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D044127:Epigenesis, Genetic; D005091:Exons; D006657:Histones / Q000378:metabolism*; D006801:Humans; D020014:K562 Cells; D008223:Lymphoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D010950:Plasma Cells / Q000473:pathology; D051560:Proto-Oncogene Proteins c-bcl-6; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: C084103:BCL6 protein, human; D000076246:CCCTC-Binding Factor; C000619697:CTCF protein, human; C000619698:Ctcf protein, mouse; D004268:DNA-Binding Proteins; D006657:Histones; D051560:Proto-Oncogene Proteins c-bcl-6; D012097:Repressor Proteins