title: Control of the replicative life span of human fibroblasts by p16 and the polycomb protein Bmi-1.
abstract: The polycomb protein Bmi-1 represses the INK4a locus, which encodes the tumor suppressors p16 and p14(ARF). Here we report that Bmi-1 is downregulated when WI-38 human fibroblasts undergo replicative senescence, but not quiescence, and extends replicative life span when overexpressed. Life span extension by Bmi-1 required the pRb, but not p53, tumor suppressor protein. Deletion analysis showed that the RING finger and helix-turn-helix domains of Bmi-1 were required for life span extension and suppression of p16. Furthermore, a RING finger deletion mutant exhibited dominant negative activity, inducing p16 and premature senescence. Interestingly, presenescent cultures of some, but not all, human fibroblasts contained growth-arrested cells expressing high levels of p16 and apparently arrested by a p53- and telomere-independent mechanism. Bmi-1 selectively extended the life span of these cultures. Low O(2) concentrations had no effect on p16 levels or life span extension by Bmi-1 but reduced expression of the p53 target, p21. We propose that some human fibroblast strains are more sensitive to stress-induced senescence and have both p16-dependent and p53/telomere-dependent pathways of senescence. Our data suggest that Bmi-1 extends the replicative life span of human fibroblasts by suppressing the p16-dependent senescence pathway.
authors.affiliation: Life Sciences Division, Lawrence Berkeley National Laboratory, California 94720, USA.
authors.forename: Koji
authors.initials: K
authors.lastname: Itahana
authors.forename: Ying
authors.initials: Y
authors.lastname: Zou
authors.forename: Yoko
authors.initials: Y
authors.lastname: Itahana
authors.forename: Jose-Luis
authors.initials: JL
authors.lastname: Martinez
authors.forename: Christian
authors.initials: C
authors.lastname: Beausejour
authors.forename: Jacqueline J L
authors.initials: JJ
authors.lastname: Jacobs
authors.forename: Maarten
authors.initials: M
authors.lastname: Van Lohuizen
authors.forename: Vimla
authors.initials: V
authors.lastname: Band
authors.forename: Judith
authors.initials: J
authors.lastname: Campisi
authors.forename: Goberdhan P
authors.initials: GP
authors.lastname: Dimri
mesh_terms: D002455:Cell Division / Q000235:genetics; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology*; D019077:Helix-Turn-Helix Motifs; D006801:Humans; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D063150:Polycomb Repressive Complex 1; D063146:Polycomb-Group Proteins; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins; D016160:Retinoblastoma Protein / Q000235:genetics / Q000378:metabolism; D019098:Telomerase / Q000235:genetics / Q000378:metabolism; D016615:Telomere / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: C069077:BMI1 protein, human; D019941:Cyclin-Dependent Kinase Inhibitor p16; D009687:Nuclear Proteins; D063146:Polycomb-Group Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D063150:Polycomb Repressive Complex 1; D019098:Telomerase; D010100:Oxygen