title: p53 is preferentially recruited to the promoters of growth arrest genes p21 and GADD45 during replicative senescence of normal human fibroblasts.
abstract: Replicative senescence is the terminal growth arrest that most normal human cells enter into after a fixed number of divisions in vitro, limiting the proliferative potential of a cell and preventing genomic instability caused by critically short telomeres. Thus, senescence presents a tumor-suppressive mechanism and a barrier to tumor formation. However, senescent cells are inherently resistant to apoptosis and, as they accumulate in aging tissues, may contribute to organ dysfunction and promote tumor progression as part of the stromal environment. Replicative life span in normal human cells can be extended by inactivation of the tumor suppressor gene p53 or its direct target, the cyclin-dependent kinase inhibitor p21, suggesting a direct role for this pathway in senescence. However, p53 recruitment to promoters of target genes during replicative senescence has not been shown in live cells. In this study, we used chromatin immunoprecipitation to determine that p53 preferentially occupied the promoters of growth arrest genes p21 and GADD45 in senescent normal human diploid fibroblasts but not the promoters of other target genes that recruited p53 following doxorubicin-induced DNA damage, such as apoptosis regulators TNFRSF10b, TNFRSF6, and PUMA. This differential recruitment of p53 in senescent versus doxorubicin-treated fibroblasts was accompanied by differences in post-translational modification of p53. These data provide mechanisms for both the growth arrest mediated by p53 and the resistant nature of senescent cells to apoptosis despite p53 activity.
authors.affiliation: University of Texas Health Science Center at San Antonio, Department of Cellular and Structural Biology, Sam and Ann Barshop Institute for Longevity and Aging Studies, San Antonio, TX 78245-3207, USA. jacksonjg@uthscsa.edu
authors.forename: James G
authors.initials: JG
authors.lastname: Jackson
authors.forename: Olivia M
authors.initials: OM
authors.lastname: Pereira-Smith
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000235:genetics*; D002455:Cell Division; D016922:Cellular Senescence; D004261:DNA Replication; D004171:Diploidy; D004317:Doxorubicin / Q000494:pharmacology; D005347:Fibroblasts / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D052816:Foreskin / Q000166:cytology / Q000502:physiology; D016158:Genes, p53; D006801:Humans; D008297:Male; D009154:Mutation; D009369:Neoplasms / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics*; D015689:Oncogene Protein p21(ras) / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011499:Protein Processing, Post-Translational; D000097642:GADD45 Proteins
chemical_list: D018797:Cell Cycle Proteins; D004317:Doxorubicin; D009687:Nuclear Proteins; D015689:Oncogene Protein p21(ras); C439070:GADD45A protein, human; D000097642:GADD45 Proteins