title: Association of extended in vitro proliferative potential with loss of p16INK4 expression.
abstract: This study addresses the question of whether loss of p16INK4 expression contributes to the immortalization of human cells. In vitro immortalization usually proceeds through two phases. In the first phase (lifespan extension), cells continue proliferating and their telomeres continue shortening beyond the point at which normal cells become senescent. In the second phase (immortalization), the cells activate a telomere maintenance mechanism and acquire an unlimited proliferative potential. It has previously been shown that immortalized cells containing viral oncoproteins that bind and inactivate p110RB contain wild-type p16INK4; we therefore examined the p16INK4 status of cell lines that became immortalized in vitro in the absence of these oncoproteins. Three such lines were identified: III-CF/.2A1 and III-CF/E6A2 (both derived from Li-Fraumeni syndrome fibroblasts, probably by spontaneous immortalization) and MePV-231 (normal mesothelial cells transfected with HPV-16 E6/E7 genes that underwent deletion of these genes before immortalization). In each case p16INK4 expression was lost at or before immortalization. Further, a cell strain was identified that had an extended but finite lifespan associated with loss of p16INK4 (and p53) expression. Thus loss of p16INK4 expression was associated with extended in vitro lifespan but was not sufficient for immortalization, even in the absence of wild-type p53.
authors.affiliation: Children's Medical Research Institute, Sydney, NSW, Australia.
authors.forename: J R
authors.initials: JR
authors.lastname: Noble
authors.forename: E M
authors.initials: EM
authors.lastname: Rogan
authors.forename: A A
authors.initials: AA
authors.lastname: Neumann
authors.forename: K
authors.initials: K
authors.lastname: Maclean
authors.forename: T M
authors.initials: TM
authors.lastname: Bryan
authors.forename: R R
authors.initials: RR
authors.lastname: Reddel
mesh_terms: D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002455:Cell Division / Q000502:physiology; D002470:Cell Survival / Q000502:physiology; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004279:DNA, Viral / Q000235:genetics; D004789:Enzyme Activation; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D005814:Genes, Viral; D006801:Humans; D027383:Papillomaviridae / Q000235:genetics; D019098:Telomerase / Q000378:metabolism; D016615:Telomere / Q000502:physiology; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000502:physiology
chemical_list: D002352:Carrier Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004279:DNA, Viral; D016159:Tumor Suppressor Protein p53; D019098:Telomerase