title: Polycomb CBX7 has a unifying role in cellular lifespan.
abstract: In contrast to cancer cells and embryonic stem cells, the lifespan of primary human cells is finite. After a defined number of population doublings, cells enter in an irreversible growth-arrested state termed replicative senescence. Mutations of genes involved in immortalization can contribute to cancer. In a genetic screen for cDNAs bypassing replicative senescence of normal human prostate epithelial cells (HPrEC), we identified CBX7, a gene that encodes a Polycomb protein, as shown by sequence homology, its interaction with Ring1 and its localization to nuclear Polycomb bodies. CBX7 extends the lifespan of a wide range of normal human cells and immortalizes mouse fibroblasts by downregulating expression of the Ink4a/Arf locus. CBX7 does not inter-function or colocalize with Bmi1, and both can exert their actions independently of each other as shown by reverse genetics. CBX7 expression is downregulated during replicative senescence and its ablation by short-hairpin RNA (shRNA) treatment inhibited growth of normal cells though induction of the Ink4a/Arf locus. Taken together, these data show that CBX7 controls cellular lifespan through regulation of both the p16(Ink4a)/Rb and the Arf/p53 pathways.
authors.affiliation: Wolfson Institute for Biomedical Research, University College London, Gower Street, London WC1E 6BT, UK. jesus.gil@cancer.org.uk
authors.forename: Jesús
authors.initials: J
authors.lastname: Gil
authors.forename: David
authors.initials: D
authors.lastname: Bernard
authors.forename: Dolores
authors.initials: D
authors.lastname: Martínez
authors.forename: David
authors.initials: D
authors.lastname: Beach
mesh_terms: D020823:ADP-Ribosylation Factor 1 / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D001483:Base Sequence / Q000235:genetics; D002461:Cell Line, Transformed / Q000166:cytology / Q000378:metabolism*; D002470:Cell Survival / Q000235:genetics*; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D016922:Cellular Senescence / Q000235:genetics*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism; D018076:DNA, Complementary / Q000032:analysis / Q000235:genetics; D015536:Down-Regulation / Q000235:genetics; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D063150:Polycomb Repressive Complex 1; D063146:Polycomb-Group Proteins; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D012313:RNA / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012689:Sequence Homology, Nucleic Acid
chemical_list: C069077:BMI1 protein, human; C489421:Bmi1 protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D018076:DNA, Complementary; D009687:Nuclear Proteins; D063146:Polycomb-Group Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D012313:RNA; D063150:Polycomb Repressive Complex 1; D020823:ADP-Ribosylation Factor 1