title: Destabilization of Rb by human papillomavirus E7 is cell cycle dependent: E2-25K is involved in the proteolysis.
abstract: The HPV oncoprotein E7 promotes proteasomal degradation of the tumor suppressor protein Rb. In this study, we analyzed the regulation of E7-induced Rb proteolysis in HPV-containing Caski cervical cancer cells. We show that the Rb proteolysis is cell cycle dependent; in S phase Rb is stable while in post-mitotic early G1 phase cells and in differentiated cells, Rb is unstable. Similarly, the in vivo Rb/E7 interaction is not detected in S-phase cells, but is readily detected in differentiating Caski cells. The ubiquitinating enzymes involved in Rb proteolysis have not been identified. We find that the E3 ligase MDM2 is not involved in the Rb proteolysis in Caski cells. An in vivo analysis using multiple catalytic site mutant dominant negative E2 enzymes show that the C92A E2-25K most effectively blocks E7-induced Rb proteolysis. Taken together, these results show that E7 induces Rb proteolysis in growth-arrested cells and E2-25K is involved in the proteolysis.
authors.affiliation: Center for Molecular Biology of Oral Diseases, University of Illinois at Chicago, Chicago, IL 60612, USA.
authors.forename: Kwang-Jin
authors.initials: KJ
authors.lastname: Oh
authors.forename: Anna
authors.initials: A
authors.lastname: Kalinina
authors.forename: Srilata
authors.initials: S
authors.lastname: Bagchi
mesh_terms: D002453:Cell Cycle; D002460:Cell Line; D006801:Humans; D009856:Oncogene Proteins, Viral / Q000502:physiology*; D050725:Papillomavirus E7 Proteins; D046988:Proteasome Endopeptidase Complex / Q000502:physiology; D051736:Proto-Oncogene Proteins c-mdm2 / Q000502:physiology; D016160:Retinoblastoma Protein / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000502:physiology*
chemical_list: D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D016160:Retinoblastoma Protein; D025801:Ubiquitin; C059731:oncogene protein E7, Human papillomavirus type 16; C100879:UBE2K protein, human; D044763:Ubiquitin-Conjugating Enzymes; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2; D046988:Proteasome Endopeptidase Complex