title: Loss of retinoblastoma but not p16 function allows bypass of replicative senescence in human fibroblasts.
abstract: Current models envision replicative senescence to be under dual control by the p53 and retinoblastoma (RB) tumour-suppressor pathways. The role of the p16(INK4a)-RB pathway is controversial, and the function of RB in human cells has not been tested directly. We used targeted homologous recombination to knock out one copy of RB in presenescent human fibroblasts. During entry into senescence, RB+/- cells underwent spontaneous loss of heterozygosity and the resultant RB-/- clones bypassed senescence. The extended lifespan phase was eventually terminated by a crisis-like state. The same phenotype was documented for p21(CIP1/WAF1) and p53 heterozygous cells, indicating that loss of function of all three genes results in failure to establish senescence. By contrast, the abolition of p16 function by the expression of a p16-insensitive cyclin-dependent kinase 4 protein or siRNA-mediated knockdown provided only minimal lifespan extension that was terminated by senescence. We propose that p53, p21 and RB act in a linear genetic pathway to regulate cell entry into replicative senescence.
authors.affiliation: Department of Molecular Biology, Cell Biology & Biochemistry, Brown University, Providence, Rhode Island 02912, USA.
authors.forename: Wenyi
authors.initials: W
authors.lastname: Wei
authors.forename: Utz
authors.initials: U
authors.lastname: Herbig
authors.forename: Shan
authors.initials: S
authors.lastname: Wei
authors.forename: Annie
authors.initials: A
authors.lastname: Dutriaux
authors.forename: John M
authors.initials: JM
authors.lastname: Sedivy
mesh_terms: D016922:Cellular Senescence / Q000502:physiology*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics* / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D004261:DNA Replication / Q000502:physiology*; D005347:Fibroblasts / Q000502:physiology; D006801:Humans; D016160:Retinoblastoma Protein / Q000235:genetics* / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016160:Retinoblastoma Protein