title: BCL6 programs lymphoma cells for survival and differentiation through distinct biochemical mechanisms.
abstract: The BCL6 transcriptional repressor is the most commonly involved oncogene in diffuse large B-cell lymphomas (DLBCLs). Constitutive expression of BCL6 mediates lymphomagenesis through aberrant proliferation, survival, and differentiation blockade. Binding of BCL6 to the SMRT/N-CoR corepressors mediates the BCL6 survival effect in DLBCL. Although the basis for differentiation blockade is unknown in DLBCL, recent data suggest that BCL6 binding to the MTA3 corepressor might be involved. We report that BCL6 and MTA3 are coexpressed in normal germinal center B cells and DLBCL. Depletion of MTA3 in DLBCL cells induced a differentiation-related BCL6 target gene (PRDM1), but not target genes involved in survival. Accordingly, MTA3 and PRDM1 expression are mutually exclusive in germinal center B cells. We performed chromatin immunoprecipitation (ChIP)-on-chip mapping of the PRDM1 locus, identifying a novel BCL6 binding site on intron 3 of the PRDM1 gene, and show that BCL6 recruits MTA3 to this site. In DLBCL cells, MTA3 depletion induced plasmacytic differentiation but did not decrease viability of DLBCL cells. However, MTA3 depletion synergized with a specific BCL6 inhibitor that blocks SMRT/N-CoR binding to decrease DLBCL viability. Taken together, these results show that BCL6 regulates distinct transcriptional programs through the SMRT/N-CoR and MTA3 corepressors, respectively, and provides a basis for combinatorial therapeutic targeting of BCL6.
authors.affiliation: Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Samir
authors.initials: S
authors.lastname: Parekh
authors.forename: Jose M
authors.initials: JM
authors.lastname: Polo
authors.forename: Rita
authors.initials: R
authors.lastname: Shaknovich
authors.forename: Przemyslaw
authors.initials: P
authors.lastname: Juszczynski
authors.forename: Paola
authors.initials: P
authors.lastname: Lev
authors.forename: Stella M
authors.initials: SM
authors.lastname: Ranuncolo
authors.forename: Yingnan
authors.initials: Y
authors.lastname: Yin
authors.forename: Ulf
authors.initials: U
authors.lastname: Klein
authors.forename: Giorgio
authors.initials: G
authors.lastname: Cattoretti
authors.forename: Riccardo
authors.initials: R
authors.lastname: Dalla Favera
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Shipp
authors.forename: Ari
authors.initials: A
authors.lastname: Melnick
mesh_terms: D015153:Blotting, Western; D002454:Cell Differentiation; D002470:Cell Survival; D047369:Chromatin Immunoprecipitation; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007124:Immunoenzyme Techniques; D016393:Lymphoma, B-Cell / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D016403:Lymphoma, Large B-Cell, Diffuse / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056971:Nuclear Receptor Co-Repressor 1; D056985:Nuclear Receptor Co-Repressor 2; D020411:Oligonucleotide Array Sequence Analysis; D000074462:Positive Regulatory Domain I-Binding Factor 1; D051560:Proto-Oncogene Proteins c-bcl-6 / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D046888:Tissue Array Analysis; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; C486657:MTA3 protein, human; C539127:NCOR1 protein, human; C539130:NCOR2 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D056971:Nuclear Receptor Co-Repressor 1; D056985:Nuclear Receptor Co-Repressor 2; D051560:Proto-Oncogene Proteins c-bcl-6; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D014157:Transcription Factors; C087042:PRDM1 protein, human; D000074462:Positive Regulatory Domain I-Binding Factor 1