title: Human papillomavirus type 45 E7 is a transforming protein inducing retinoblastoma protein degradation and anchorage-independent cell cycle progression.
abstract: High-risk human papillomaviruses (HPV) cause cervical cancer. The biological properties of HPV-45, the third most prevalent high-risk HPV-genotype, are unknown. We demonstrate here that the HPV-45 E7 protein transforms immortalized NIH3T3 fibroblasts, while mutations in either the conserved LXCXE sequence (C28G) or the carboxyl-terminus (Delta87LQQLF91) significantly abolish this activity. To address the mechanisms underlying cell transformation by HPV-45 E7, we investigated its impact on the cell cycle. We show that HPV-45 E7 associates with the hypophosphorylated form of the retinoblastoma protein (pRb) and induces a significant reduction in the pRb half-life which can be blocked by epoxomicin. Moreover, HPV-45 E7 induces anchorage-independent cell cycle progression of NIH3T3 cells and extends the lifespan of primary human keratinocytes. HPV-45 E7C28G did not bind pRb and could neither induce pRb-proteolysis nor promote cell cycle progression. HPV-45 E7Delta87LQQLF91 had intermediate pRb-binding affinity and retained a residual activity to induce the degradation of pRb but lost the capability to promote cell cycle progression in suspension. Another carboxyl-terminal mutant, HPV-45 E7Delta81AEDL84, showed a trend to reduced transforming activity, had reduced pRb-binding activity and lost the capability to induce pRb-degradation; however, this mutant could induce anchorage-independent cell cycle progression with the same efficiency as HPV-45 E7 wild type. In summary, these data suggest that HPV-45 E7 is a transforming protein and that abrogation of cell cycle control contributes to its oncogenic potential.
authors.affiliation: Cell Metabolism and Differentiation Research Group, Institute for Biomedical Aging Research of the Austrian Academy of Sciences, Rennweg 10, A-6020 Innsbruck, Austria.
authors.forename: Dieter
authors.initials: D
authors.lastname: Morandell
authors.forename: Ursula
authors.initials: U
authors.lastname: Rostek
authors.forename: Veronique
authors.initials: V
authors.lastname: Bouvard
authors.forename: Beatriz
authors.initials: B
authors.lastname: Campo-Fernández
authors.forename: Marc
authors.initials: M
authors.lastname: Fiedler
authors.forename: Pidder
authors.initials: P
authors.lastname: Jansen-Dürr
authors.forename: Werner
authors.initials: W
authors.lastname: Zwerschke
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D002472:Cell Transformation, Viral; D002478:Cells, Cultured; D005260:Female; D005347:Fibroblasts / Q000821:virology; D006801:Humans; D015603:Keratinocytes / Q000821:virology; D051379:Mice; D008958:Models, Molecular; D020125:Mutation, Missense; D027383:Papillomaviridae / Q000502:physiology*; D050725:Papillomavirus E7 Proteins / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D016160:Retinoblastoma Protein / Q000378:metabolism*; D016415:Sequence Alignment; D017384:Sequence Deletion
chemical_list: D050725:Papillomavirus E7 Proteins; D016160:Retinoblastoma Protein; C514514:oncogene protein E7, human papilloma virus type 45