title: Tetrameric oligomerization mediates transcriptional repression by the BRCA1-dependent Kruppel-associated box-zinc finger protein ZBRK1.
abstract: The Kruppel-associated box (KRAB)-zinc finger protein ZBRK1 has been implicated in the transcriptional regulation of DNA damage-response genes that function in cell growth control and survival. Recently, we described a novel BRCA1-dependent C-terminal transcriptional repression domain (CTRD) within ZBRK1, the mode of repression of which is functionally distinguishable from that of the N-terminal KRAB repression domain within ZBRK1. The identification of BRCA1 binding-competent but repression-defective CTRD mutants further revealed that BRCA1 binding is necessary, but not sufficient, for ZBRK1 CTRD function. During an unbiased search for possible co-regulators of the CTRD, we identified ZBRK1 itself, suggesting that ZBRK1 can oligomerize through its CTRD. Herein we explore the physical and functional requirements for ZBRK1 oligomerization in ZBRK1-directed transcriptional repression. Protein interaction analyses confirmed that ZBRK1 can homo-oligomerize both in vitro and in vivo and further mapped the ZBRK1 oligomerization domain to the CTRD C terminus. Biochemical analyses, including protein cross-linking and gel filtration chromatography, revealed that ZBRK1 homo-oligomers exist as tetramers in solution. Functionally, ZBRK1 oligomerization facilitates ZBRK1-directed transcriptional repression through ZBRK1 response elements; requirements for oligomerization-dependent repression include the ZBRK1 CTRD and KRAB repression domains but not the DNA binding activity of ZBRK1. These observations suggest that higher order oligomers of ZBRK1 may assemble on target ZBRK1 response elements through both protein-DNA and CTRD-dependent protein-protein interactions. These findings thus reveal an unanticipated dual function for ZBRK1 in both DNA binding-dependent and -independent modes of transcriptional repression and further establish the CTRD as a novel protein interaction surface responsible for directing homotypic and heterotypic interactions necessary for ZBRK1-directed transcriptional repression.
authors.affiliation: Department of Molecular Medicine and Institute of Biotechnology, University of Texas Health Science Center at San Antonio, 15355 Lambda Drive, San Antonio, TX 78245-3207.
authors.forename: Wei
authors.initials: W
authors.lastname: Tan
authors.forename: Seokjoong
authors.initials: S
authors.lastname: Kim
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Boyer
mesh_terms: D019313:BRCA1 Protein / Q000378:metabolism; D045744:Cell Line, Tumor; D002850:Chromatography, Gel; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004247:DNA / Q000737:chemistry; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000737:chemistry* / Q000502:physiology; D017353:Gene Deletion; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D047468:Immunoprecipitation; D016296:Mutagenesis; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000737:chemistry* / Q000502:physiology; D020218:Response Elements; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D019313:BRCA1 Protein; D003432:Cross-Linking Reagents; D004268:DNA-Binding Proteins; D012097:Repressor Proteins; C422407:ZNF350 protein, human; D004247:DNA