title: Elevated p16 at senescence and loss of p16 at immortalization in human papillomavirus 16 E6, but not E7, transformed human uroepithelial cells.
abstract: CDKN2/p16 inhibits the cyclin D/cyclin-dependent kinase complexes that phosphorylate pRb, thus blocking cell cycle progression. We previously reported that p16 levels are low to undetectable in normal human uroepithelial cells (HUCs) and in immortalized uroepithelial cells with functional pRb, whereas p16 levels are markedly elevated in immortal HUCs with altered pRb (T. Yeager et al., Cancer Res., 55: 493-497, 1995). We now report that elevation of p16 levels occurs at senescence in HUCs, including HUCs transformed by human papillomavirus 16 E7 or E6, whose oncoprotein products lead to functional loss of pRb and p53, respectively. We also report that six of six independently immortalized E7 HUCs show high levels of p16 similar to those observed at HUC senescence, whereas p16 is undetectable in five of five immortal E6 HUCs. Four of the five independent E6 HUCs that lost p16 at immortalization showed hemizygous deletion of the 9p21 region. However, no homozygous CDKN2 deletions were detected, and only one CDKN2 mutation was identified. For the first time, these data associate elevated p16 with senescence in human epithelial cells. These data also suggest that a component of immortalization may be abrogation, either by pRb inactivation (as in the E7-transformed HUCs) or by p16 inactivation (as in the E6-transformed HUCs), of a p16-mediated senescence cell cycle block.
authors.affiliation: Department of Human Oncology, Clinical Science Center, University of Wisconsin, Madison 53792, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Reznikoff
authors.forename: T R
authors.initials: TR
authors.lastname: Yeager
authors.forename: C D
authors.initials: CD
authors.lastname: Belair
authors.forename: E
authors.initials: E
authors.lastname: Savelieva
authors.forename: J A
authors.initials: JA
authors.lastname: Puthenveettil
authors.forename: W M
authors.initials: WM
authors.lastname: Stadler
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology / Q000528:radiation effects; D002472:Cell Transformation, Viral / Q000502:physiology*; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology / Q000528:radiation effects; D002899:Chromosomes, Human, Pair 9; D019941:Cyclin-Dependent Kinase Inhibitor p16; D017353:Gene Deletion; D006801:Humans; D009154:Mutation; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000502:physiology*; D027383:Papillomaviridae / Q000235:genetics / Q000502:physiology*; D050725:Papillomavirus E7 Proteins; D012097:Repressor Proteins; D016160:Retinoblastoma Protein / Q000378:metabolism; D014551:Urinary Tract / Q000166:cytology
chemical_list: D002352:Carrier Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; C068651:E6 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; D050725:Papillomavirus E7 Proteins; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; C059731:oncogene protein E7, Human papillomavirus type 16