title: The ansamycin antibiotic, rifamycin SV, inhibits BCL6 transcriptional repression and forms a complex with the BCL6-BTB/POZ domain.
abstract: BCL6 is a transcriptional repressor that is over-expressed due to chromosomal translocations, or other abnormalities, in ∼40% of diffuse large B-cell lymphoma. BCL6 interacts with co-repressor, SMRT, and this is essential for its role in lymphomas. Peptide or small molecule inhibitors, which prevent the association of SMRT with BCL6, inhibit transcriptional repression and cause apoptosis of lymphoma cells in vitro and in vivo. In order to discover compounds, which have the potential to be developed into BCL6 inhibitors, we screened a natural product library. The ansamycin antibiotic, rifamycin SV, inhibited BCL6 transcriptional repression and NMR spectroscopy confirmed a direct interaction between rifamycin SV and BCL6. To further determine the characteristics of compounds binding to BCL6-POZ we analyzed four other members of this family and showed that rifabutin, bound most strongly. An X-ray crystal structure of the rifabutin-BCL6 complex revealed that rifabutin occupies a partly non-polar pocket making interactions with tyrosine58, asparagine21 and arginine24 of the BCL6-POZ domain. Importantly these residues are also important for the interaction of BLC6 with SMRT. This work demonstrates a unique approach to developing a structure activity relationship for a compound that will form the basis of a therapeutically useful BCL6 inhibitor.
authors.affiliation: Department of Biochemistry, University of Leicester, Leicester, United Kingdom; Department of Cancer Studies and Molecular Medicine and MRC Toxicology Unit, University of Leicester, Leicester, United Kingdom.
authors.forename: Sian E
authors.initials: SE
authors.lastname: Evans
authors.affiliation: Department of Biochemistry, University of Leicester, Leicester, United Kingdom.
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Goult
authors.affiliation: Department of Biochemistry, University of Leicester, Leicester, United Kingdom.
authors.forename: Louise
authors.initials: L
authors.lastname: Fairall
authors.affiliation: Department of Chemistry, University of Leicester, Leicester, United Kingdom.
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Jamieson
authors.affiliation: Section of Experimental Therapeutics, Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom.
authors.forename: Paul
authors.initials: P
authors.lastname: Ko Ferrigno
authors.affiliation: Section of Experimental Therapeutics, Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom.
authors.forename: Robert
authors.initials: R
authors.lastname: Ford
authors.affiliation: Department of Biochemistry, University of Leicester, Leicester, United Kingdom.
authors.forename: John W R
authors.initials: JW
authors.lastname: Schwabe
authors.affiliation: Department of Cancer Studies and Molecular Medicine and MRC Toxicology Unit, University of Leicester, Leicester, United Kingdom.
authors.forename: Simon D
authors.initials: SD
authors.lastname: Wagner
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D056985:Nuclear Receptor Co-Repressor 2 / Q000737:chemistry / Q000378:metabolism*; D060066:Protein Interaction Maps / Q000187:drug effects; D017434:Protein Structure, Tertiary; D051560:Proto-Oncogene Proteins c-bcl-6; D012097:Repressor Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D017828:Rifabutin / Q000737:chemistry / Q000494:pharmacology*; D012294:Rifamycins / Q000737:chemistry / Q000494:pharmacology*; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; C084103:BCL6 protein, human; D004268:DNA-Binding Proteins; D056985:Nuclear Receptor Co-Repressor 2; D051560:Proto-Oncogene Proteins c-bcl-6; D012097:Repressor Proteins; D012294:Rifamycins; D017828:Rifabutin; C023808:rifamycin SV