title: The tumor suppressor protein HBP1 is a novel c-myc-binding protein that negatively regulates c-myc transcriptional activity.
abstract: c-Myc is an important transcription factor that regulates cellular proliferation, cell growth, and differentiation. A number of transcriptional co-factors for c-Myc have been described that have binding sites within highly conserved regions of the c-Myc transactivational domain (TAD). Given the importance of the c-Myc TAD, we set out to identify new proteins that interact with this region using a yeast two-hybrid assay. HBP1 was identified in our screen as a protein that interacts with full-length c-Myc but not a c-Myc mutant lacking the TAD. HBP1 is a transcriptional repressor and has been shown to negatively regulate the cell cycle. A correlation between HBP1 under-expression and breast cancer relapse has been described, suggesting that HBP1 may be an important tumor suppressor protein. We have found that HBP1 binds c-Myc in cells, and expression of HBP1 inhibits c-Myc transactivational activity at least partly by preventing c-Myc binding to target gene promoters. c-Myc binds to the C terminus of HBP1, a region lost in some breast tumors, and some HBP1 mutants found in breast cancer weakly interact with and/or no longer negatively regulate c-Myc. This work adds to our understanding of c-Myc regulation and mechanisms of tumor suppression by HBP1.
authors.affiliation: Department of Medical and Molecular Genetics, Oregon Health and Science University, Portland, Oregon 97239, USA.
authors.forename: Julienne R
authors.initials: JR
authors.lastname: Escamilla-Powers
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Daniel
authors.forename: Amy
authors.initials: A
authors.lastname: Farrell
authors.forename: Karyn
authors.initials: K
authors.lastname: Taylor
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Zhang
authors.forename: Sarah
authors.initials: S
authors.lastname: Byers
authors.forename: Rosalie
authors.initials: R
authors.lastname: Sears
mesh_terms: D015153:Blotting, Western; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D005786:Gene Expression Regulation / Q000235:genetics / Q000502:physiology; D006609:High Mobility Group Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D009154:Mutation; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000235:genetics / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000235:genetics / Q000528:radiation effects; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: C486328:HBP1 protein, human; D006609:High Mobility Group Proteins; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D012097:Repressor Proteins