title: Regulation of TCF ETS-domain transcription factors by helix-loop-helix motifs.
abstract: DNA binding by the ternary complex factor (TCF) subfamily of ETS-domain transcription factors is tightly regulated by intramolecular and intermolecular interactions. The helix-loop-helix (HLH)-containing Id proteins are trans-acting negative regulators of DNA binding by the TCFs. In the TCF, SAP-2/Net/ERP, intramolecular inhibition of DNA binding is promoted by the cis-acting NID region that also contains an HLH-like motif. The NID also acts as a transcriptional repression domain. Here, we have studied the role of HLH motifs in regulating DNA binding and transcription by the TCF protein SAP-1 and how Cdk-mediated phosphorylation affects the inhibitory activity of the Id proteins towards the TCFs. We demonstrate that the NID region of SAP-1 is an autoinhibitory motif that acts to inhibit DNA binding and also functions as a transcription repression domain. This region can be functionally replaced by fusion of Id proteins to SAP-1, whereby the Id moiety then acts to repress DNA binding in cis. Phosphorylation of the Ids by cyclin-Cdk complexes results in reduction in protein-protein interactions between the Ids and TCFs and relief of their DNA-binding inhibitory activity. In revealing distinct mechanisms through which HLH motifs modulate the activity of TCFs, our results therefore provide further insight into the role of HLH motifs in regulating TCF function and how the inhibitory properties of the trans-acting Id HLH proteins are themselves regulated by phosphorylation.
authors.affiliation: School of Biological Sciences, Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK.
authors.forename: Julie
authors.initials: J
authors.lastname: Stinson
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Inoue
authors.forename: Paula
authors.initials: P
authors.lastname: Yates
authors.forename: Anne
authors.initials: A
authors.lastname: Clancy
authors.forename: John D
authors.initials: JD
authors.lastname: Norton
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Sharrocks
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017930:Genes, Reporter / Q000235:genetics; D018257:Helix-Loop-Helix Motifs / Q000235:genetics*; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1; D051797:Inhibitor of Differentiation Protein 2; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics; D050807:ets-Domain Protein Elk-1; D050808:ets-Domain Protein Elk-4
chemical_list: D004268:DNA-Binding Proteins; C494193:ELK4 protein, human; C497453:ID1 protein, human; C497450:ID2 protein, human; D051798:Inhibitor of Differentiation Protein 1; D051797:Inhibitor of Differentiation Protein 2; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D050808:ets-Domain Protein Elk-4