title: Bypass of telomere-dependent replicative senescence (M1) upon overexpression of Cdk4 in normal human epithelial cells.
abstract: Many stimuli causing 'stress' or DNA damage in cells can produce phenotypes that overlap with telomere-based replicative senescence. In epithelial systems, the p16/RB pathway may function as a stress senescence-signaling pathway independent of telomere shortening. Overexpressing cyclin-dependent kinase 4 (Cdk4) in human epidermal keratinocytes and human mammary epithelial cells not only prevents the p16(INK4a)-associated premature growth arrest due to telomere-independent stress (e.g., inadequate culture conditions), but also bypasses the ensuing telomere-dependent senescence (M1). Overexpressed Cdk4 in epithelial cells induces a dramatic upregulation of p16(INK4a) and milder upregulation of p53 and p21(WAF1), which become unresponsive to UV irradiation. Despite the high levels of these checkpoint factors, Cdk4-overexpressing cells divide in an apparently normal regulated fashion, are able to respond to changes in calcium levels, retain the stem cell phenotype, and fully differentiate and stratify. These results suggest that the differentiation pathways in Cdk4-overexpressing cells remain intact.
authors.affiliation: Hamon Center for Therapeutic Oncology Research, The University of Texas Southwestern Medical Center, Dallas, TX 75390-8593, USA. ruben.ramirez@utsouthwestern.edu
authors.forename: Ruben D
authors.initials: RD
authors.lastname: Ramirez
authors.forename: Brittney-Shea
authors.initials: BS
authors.lastname: Herbert
authors.forename: Melville B
authors.initials: MB
authors.lastname: Vaughan
authors.forename: Ying
authors.initials: Y
authors.lastname: Zou
authors.forename: Kenia
authors.initials: K
authors.lastname: Gandia
authors.forename: Carmela P
authors.initials: CP
authors.lastname: Morales
authors.forename: Woodring E
authors.initials: WE
authors.lastname: Wright
authors.forename: Jerry W
authors.initials: JW
authors.lastname: Shay
mesh_terms: D000328:Adult; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation; D002455:Cell Division; D002478:Cells, Cultured; D016922:Cellular Senescence; D002869:Chromosome Aberrations; D056741:Cyclin D; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism; D004261:DNA Replication; D004268:DNA-Binding Proteins; D004847:Epithelial Cells / Q000378:metabolism* / Q000528:radiation effects; D005260:Female; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D012016:Reference Values; D019098:Telomerase / Q000235:genetics / Q000378:metabolism; D016615:Telomere / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D015854:Up-Regulation
chemical_list: C493956:CDKN1A protein, human; D056741:Cyclin D; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D019098:Telomerase; D002118:Calcium