title: A KRAB-related domain and a novel transcription repression domain in proteins encoded by SSX genes that are disrupted in human sarcomas.
abstract: SSX genes show extensive nucleotide sequence conservation but little is known of their function. Disruption of SSX1 or SSX2, by chromosome translocation and 'in-frame' fusion to SYT, is a consistent feature of synovial sarcomas. The resulting SYT-SSX1/SSX2 proteins are activators of transcription; transactivation function is located in SYT. Unrearranged SSX1 can repress transcription, and this has been attributed to a putative Krüppel associated box (KRAB) repression domain at the N-terminus. Here we isolated SSX-KRAB domains to specifically measure repression activity, using a previously characterized KOX1-KRAB domain as a control. In our repressor assay SSX1- and SSX2-KRAB domains down-modulated the transactivation of a reporter gene by threefold, compared with 83-fold repression achieved by KOX1-KRAB in the assay. Yeast two-hybrid analysis showed that SSX1-KRAB, unlike KOX1-KRAB, fails to interact with the KRAB co-repressor TIF1beta. These results raise questions about the evolutionary and functional relationship of SSX-KRAB and typical KRAB domains of Krüppel zinc finger genes. We found that full-length SSX1 showed potent (74-fold) repression in our repressor assay, indicating the existence of a repression domain distinct from SSX-KRAB. By assaying deletion constructs of SSX1 we localized repression activity to 33 amino acids at the C-terminus. This novel domain is conserved between SSX family members, and, unlike the KRAB-related domain, is retained on fusion with SYT. This has important implications in understanding the mechanism by which the SYT-SSX fusion protein could contribute to neoplasia.
authors.affiliation: Department of Cancer Medicine, Imperial College of Science, Technology and Medicine, Hammersmith campus, London, UK.
authors.forename: F L
authors.initials: FL
authors.lastname: Lim
authors.forename: M
authors.initials: M
authors.lastname: Soulez
authors.forename: D
authors.initials: D
authors.lastname: Koczan
authors.forename: H J
authors.initials: HJ
authors.lastname: Thiesen
authors.forename: J C
authors.initials: JC
authors.lastname: Knight
mesh_terms: D000595:Amino Acid Sequence; D004268:DNA-Binding Proteins; D006801:Humans; D051741:Kruppel-Like Transcription Factors; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics*; D012509:Sarcoma / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
chemical_list: D004268:DNA-Binding Proteins; D051741:Kruppel-Like Transcription Factors; D009363:Neoplasm Proteins; D012097:Repressor Proteins; C109484:ZNF10 protein, human; C093962:synovial sarcoma X breakpoint proteins