title: Human papillomavirus type 16 E7 oncoprotein inhibits apoptosis mediated by nuclear insulin-like growth factor-binding protein-3 by enhancing its ubiquitin/proteasome-dependent degradation.
abstract: The E7 protein encoded by the oncogenic human papillomavirus type 16 has been shown to bind and inactivate insulin-like growth factor-binding protein-3 (IGFBP-3), the pro-apoptotic product of a tumour suppressor gene; however, the molecular mechanism underlying E7-induced inactivation of IGFBP-3 remained uncertain. In this study, we map the IGFBP-3-binding domain for E7 to the nuclear localization signal in the conserved C-terminal domain of IGFBP-3. Moreover, we demonstrate that both proteins interact in the nucleus and that E7 induces polyubiquitination and proteasome-dependent proteolysis of nuclear IGFBP-3 in cervical cancer cells. This leads to a dramatic shortening of the half-life of nuclear IGFBP-3, whereas the stability of an E7-non-binding IGFBP-3 mutant is not affected by E7. Finally, we show that E7-mediated destruction of nuclear IGFBP-3 correlates with the inhibition of IGFBP-3-induced apoptotic cell death. These data are consistent with E7-induced ubiquitin/proteasome-dependent inactivation of nuclear IGFBP-3.
authors.affiliation: Cell Metabolism and Differentiation Research Group, Rennweg 10, 6020 Innsbruck, Austria.
authors.forename: Frédéric R
authors.initials: FR
authors.lastname: Santer
authors.forename: Barbara
authors.initials: B
authors.lastname: Moser
authors.forename: Gilles A
authors.initials: GA
authors.lastname: Spoden
authors.forename: Pidder
authors.initials: P
authors.lastname: Jansen-Dürr
authors.forename: Werner
authors.initials: W
authors.lastname: Zwerschke
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D005260:Female; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000502:physiology*; D050725:Papillomavirus E7 Proteins; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D025801:Ubiquitin / Q000378:metabolism*; D002583:Uterine Cervical Neoplasms