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CTCF and the global effects of distinct histone marks on BCL6 expression in lymphoma cells

AuthorsRosa-Garrido, Manuel ; Delgado, M. Dolores
Issue Date2012
CitationEACR 22 (2012)
Abstract[Introduction]: BCL6 is a transcrIpIionaI repressor highly expressed in germinal centre B-cells and it is required for germinal centres' formation and T-dependent antibody responses. Within the germinal centres, BCL6 is involved in the control of lymphocyte activation, differentiation and apoptosis by repressing a broad spectrum of genes. BCL6 deregulation due to transIocations is delected in diflerent B-ceIl Iymphoma types and BCL6 overexpression induces Iymphomas in mice. However, BCL6 regulatory mechanisms are largely unknown. Our aim was to investigate BCL6 regulation by CTCF, a multifunctional chromatin regulator that has key roles in inducing and supporting chromatin Interactions and in the epigenetic regulation of a number of genes. [Material and Methods]: Gel retardatlon and chromatin immunoprecipitation (ChiP) assays were performed to study the CTCF binding to the BCL6 regulatory region. The presence of histone marks upon silencing of CTCF was analyzed by ChiP. Protein and mRNA Ievels were analyzed by western bIot and qRT-PCR, respectiveIy. [Results]: We identífy a CTCF bindlng site in exon lA of BCL6 within a CpG Island, which is unmethylated in cell lines and primary Iymphoma samples. CTCF binding in vitro and occupation in vivo to the BCL6 regulatory region was observad. Variant histone H2A.Z and marks of active chromatin such as H3K4me2 and H3ac, are present at the CTCF blnding site in BCL6 expressing Iymphoma cells. On the contrary, much Iower chromatln enrichment was found for repressive histones. H3K9me3 arld H3K27me3. Silencing of CTCF with a shRNA vector reduces BCL6 mRNA and protein levels. These changes were accompanied with Ioss of active histone rnarks and incorporatlon of repressive marks at the BCL6 exon 1A regulatory region. [Conclusions]: Our data suggest that CTCF protects BCL6 regulatory region against repressive histone marks and induces chromatin modificatlons at the BLC6 Iocus. Overall we have shown that CTCF binds to a novel site within the exon 1A of the transcriptionally active BCL6 Iocus and may contribute to maintain transcription.
DescriptionTrabajo presentado al "22th Biennial Congress of the European Association for Cancer Research" celebrado en Barcelona del 7 al 10 de julio de 2012.-- et al.
Appears in Collections:(IBBTEC) Comunicaciones congresos
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