title: Human papillomavirus E6 and Myc proteins associate in vivo and bind to and cooperatively activate the telomerase reverse transcriptase promoter.
abstract: The papillomavirus E6 protein binds and directs the ubiquitin-dependent degradation of the p53 tumor suppressor protein. Independent of this p53-degradative function, however, E6 induces cellular telomerase activity. This increase in enzyme activity reflects E6-enhanced transcription of the human telomerase reverse transcriptase (hTERT) catalytic subunit, but the molecular basis for this transactivation is unknown. In the present study, we demonstrate that E6/Myc interactions regulate hTERT gene expression. Mad protein, a specific antagonist of Myc, repressed E6-mediated transactivation of the hTERT promoter and this repression was relieved by Myc overexpression. The proximal Myc/ Max-binding element (E-box) in the hTERT promoter was the major determinant of both E6 and Myc responsiveness in keratinocytes. E6 did not alter Myc protein expression or Myc/Max association, and the induction of hTERT by Myc/E6 was independent of Myc phosphorylation at Thr-58/Ser-62 within the transactivation domain. However, immunoprecipitation studies demonstrated that endogenous Myc protein coprecipitated with E6 protein and chromatin immunoprecipitation analyses demonstrated that both E6 and Myc proteins bound to a minimal 295-bp hTERT promoter. Only the "high-risk" E6 proteins bound to the hTERT promoter, consistent with their preferential ability to induce telomerase. The observation that E6 associates with Myc complexes and activates a Myc-responsive gene identifies a mechanism by which this oncogene can modulate cell proliferation and differentiation.
authors.affiliation: Department of Pathology, Georgetown University Medical School, Washington, DC 20007, USA.
authors.forename: Tim
authors.initials: T
authors.lastname: Veldman
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Liu
authors.forename: Hang
authors.initials: H
authors.lastname: Yuan
authors.forename: Richard
authors.initials: R
authors.lastname: Schlegel
mesh_terms: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D001665:Binding Sites; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology; D004790:Enzyme Induction; D016259:Genes, myc; D006367:HeLa Cells; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D009856:Oncogene Proteins, Viral / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D027383:Papillomaviridae / Q000235:genetics / Q000502:physiology*; D050725:Papillomavirus E7 Proteins; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012045:Regulatory Sequences, Nucleic Acid; D012097:Repressor Proteins; D019098:Telomerase / Q000096:biosynthesis / Q000235:genetics*; D014157:Transcription Factors; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C068651:E6 protein, Human papillomavirus type 16; C499330:MAX protein, human; C079439:MXD1 protein, human; C067850:Myc associated factor X; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C059731:oncogene protein E7, Human papillomavirus type 16; D004247:DNA; D019098:Telomerase