title: Activation of Wnt signaling pathway by human papillomavirus E6 and E7 oncogenes in HPV16-positive oropharyngeal squamous carcinoma cells.
abstract: We sought to determine the role of human papillomavirus (HPV) E6 and E7 oncogenes in nuclear beta-catenin accumulation, a hallmark of activated canonical Wnt signaling pathway. We used HPV16-positive oropharyngeal cancer cell lines 147T and 090, HPV-negative cell line 040T, and cervical cell lines SiHa (bearing integrated HPV16) and HeLa (bearing integrated HPV18) to measure the cytoplasmic and nuclear beta-catenin levels and the beta-catenin/Tcf transcriptional activity before and after E6/E7 gene silencing. Repression of HPV E6 and E7 genes induced a substantial reduction in nuclear beta-catenin levels. Luciferase assay showed that transcriptional activation of Tcf promoter by beta-catenin was lower after silencing. The protein levels of beta-catenin are tightly regulated by the ubiquitin/proteasome system. We therefore performed expression analysis of regulators of beta-catenin degradation and nuclear transport and showed that seven in absentia homologue (Siah-1) mRNA and protein levels were substantially upregulated after E6/E7 repression. Siah-1 protein promotes the degradation of beta-catenin through the ubiquitin/proteasome system. To determine whether Siah-1 is important for the proteasomal degradation of beta-catenin in HPV16-positive oropharyngeal cancer cells, we introduced a Siah-1 expression vector into 147T and 090 cells and found substantial reduction of endogenous beta-catenin in these cells. Thus, E6 and E7 are involved in beta-catenin nuclear accumulation and activation of Wnt signaling in HPV-induced cancers. In addition, we show the significance of the endogenous Siah-1-dependent ubiquitin/proteasome pathway for beta-catenin degradation and its regulation by E6/E7 viral oncoproteins in HPV16-positive oropharyngeal cancer cells.
authors.affiliation: Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: Theodore
authors.initials: T
authors.lastname: Rampias
authors.forename: Eleni
authors.initials: E
authors.lastname: Boutati
authors.forename: Eirini
authors.initials: E
authors.lastname: Pectasides
authors.forename: Clarence
authors.initials: C
authors.lastname: Sasaki
authors.forename: Panteleimon
authors.initials: P
authors.lastname: Kountourakis
authors.forename: Paul
authors.initials: P
authors.lastname: Weinberger
authors.forename: Amanda
authors.initials: A
authors.lastname: Psyrri
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000378:metabolism / Q000821:virology; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D020868:Gene Silencing / Q000502:physiology; D005822:Genetic Vectors / Q000235:genetics; D006367:HeLa Cells; D052162:Human papillomavirus 16 / Q000235:genetics*; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D009856:Oncogene Proteins, Viral / Q000235:genetics*; D009959:Oropharyngeal Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000821:virology; D050725:Papillomavirus E7 Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics; D051822:T Cell Transcription Factor 1 / Q000235:genetics / Q000378:metabolism; D014161:Transduction, Genetic / Q000379:methods; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D051153:Wnt Proteins / Q000235:genetics* / Q000378:metabolism; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism; D000098563:Seven in Absentia Proteins
chemical_list: C068651:E6 protein, Human papillomavirus type 16; D009687:Nuclear Proteins; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D012097:Repressor Proteins; D051822:T Cell Transcription Factor 1; D051153:Wnt Proteins; D051176:beta Catenin; C059731:oncogene protein E7, Human papillomavirus type 16; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins; D046988:Proteasome Endopeptidase Complex