title: Identification of a co-repressor that inhibits the transcriptional and growth-arrest activities of CCAAT/enhancer-binding protein alpha.
abstract: We used a yeast two-hybrid screening approach to identify novel interactors of CCAAT/enhancer-binding protein alpha (C/EBPalpha) that may offer insight into its mechanism of action and regulation. One clone obtained was that for CA150, a nuclear protein previously characterized as a transcriptional elongation factor. In this report, we show that CA150 is a widely expressed co-repressor of C/EBP proteins. Two-hybrid and co-immunoprecipitation analyses indicated that CA150 interacts with C/EBPalpha. Overexpression of CA150 inhibited the transactivation produced by C/EBPalpha and was also able to reverse the enhancing effect of the co-activator p300 on C/EBPbeta-mediated transactivation. Analysis of C/EBPalpha mutants indicated that CA150 interacts with C/EBPalpha primarily through a domain spanning amino acids 135-150. Chromatin immunoprecipitation assays showed that CA150 was present on a promoter that is repressed by C/EBPalpha but not present on a promoter that is activated by C/EBPalpha. Finally, we showed that in cells in which growth arrest had been induced by ectopic expression of C/EBPalpha, CA150 was able to release them from growth arrest. Interestingly, CA150 could not reverse the growth arrest produced by the minimal growth-arrest domain of C/EBPalpha (amino acids 175-217), suggesting that the effect of CA150 was directed at a region of C/EBPalpha outside of this minimal domain, consistent with our two-hybrid analysis. Taken together, these data indicate that CA150 is a co-repressor of C/EBP proteins and provides a possible mechanism for how C/EBPalpha can repress transcription of specific genes.
authors.affiliation: Department of Biochemistry, University of Saskatchewan, 107 Wiggins Road, Saskatoon, Saskatchewan S7N 5E5, Canada.
authors.forename: Pamela J
authors.initials: PJ
authors.lastname: McFie
authors.forename: Guo-Li
authors.initials: GL
authors.lastname: Wang
authors.forename: Nicholai A
authors.initials: NA
authors.lastname: Timchenko
authors.forename: Heather L
authors.initials: HL
authors.lastname: Wilson
authors.forename: Xiaobin
authors.initials: X
authors.lastname: Hu
authors.forename: William J
authors.initials: WJ
authors.lastname: Roesler
mesh_terms: D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics* / Q000378:metabolism*; D019556:COS Cells; D006528:Carcinoma, Hepatocellular; D002455:Cell Division / Q000502:physiology; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D015723:Gene Library; D006801:Humans; D008113:Liver Neoplasms; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D035602:Transcriptional Elongation Factors; D014162:Transfection; D020798:Two-Hybrid System Techniques
chemical_list: D022763:CCAAT-Enhancer-Binding Protein-alpha; D012097:Repressor Proteins; C108440:TCERG1 protein, human; D015534:Trans-Activators; D035602:Transcriptional Elongation Factors