title: DNA-damaging agents induce both p53-dependent and p53-independent apoptosis in immature thymocytes.
abstract: Apoptosis in the immature thymus can be induced by both p53-dependent and -independent pathways, the former being activated by exposure to DNA-damaging agents and the latter being induced by glucocorticoids [Nature (Lond.) 362:847-849; Nature (Lond.) 362:849-852 (1993)]. We report that the DNA-damaging agents etoposide and gamma-radiation induced similar levels of apoptosis in both proliferatively enriched and quiescent immature rat thymocytes, as assessed by flow cytometry and the formation of both kilobase-pair and 180-bp integer fragments of DNA. However, a marked stabilization of p53 occurred exclusively in the proliferatively enriched population, which was also enriched for immature CD4- CD8- and mature CD4+ CD8-/CD4- CD8+ cells. In contrast, DNA damage-induced apoptosis in quiescent mature peripheral T cells was associated with an accumulation of p53. Our studies suggest that stabilization of p53 in thymocytes in response to DNA damage may be developmentally regulated. In immature thymocytes obtained from p53-null mice, DNA-damaging agents induced apoptosis at significantly lower levels and at later times than that seen in cells from p53 wild-type animals. These data support the hypothesis that DNA-damaging agents induce apoptosis primarily via a p53-dependent pathway in immature thymocytes as previously reported. We report here that DNA damage can also induce apoptosis by a p53-independent pathway in a particular subpopulation of immature thymocytes.
authors.affiliation: MRC Toxicology Unit, University of Leicester, UK. mm21@leic.ac.uk
authors.forename: M
authors.initials: M
authors.lastname: MacFarlane
authors.forename: N A
authors.initials: NA
authors.lastname: Jones
authors.forename: C
authors.initials: C
authors.lastname: Dive
authors.forename: G M
authors.initials: GM
authors.lastname: Cohen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D000945:Antigens, Differentiation, T-Lymphocyte / Q000032:analysis; D000972:Antineoplastic Agents, Phytogenic / Q000633:toxicity*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D002455:Cell Division / Q000502:physiology; D004247:DNA / Q000187:drug effects* / Q000378:metabolism / Q000528:radiation effects*; D004249:DNA Damage; D003907:Dexamethasone / Q000633:toxicity; D005047:Etoposide / Q000633:toxicity*; D005720:Gamma Rays; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D051381:Rats; D011916:Rats, Inbred F344; D013601:T-Lymphocytes / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D060265:Tetraspanin 25; D013950:Thymus Gland / Q000166:cytology* / Q000187:drug effects / Q000528:radiation effects; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis / Q000502:physiology*; D051028:bcl-2-Associated X Protein
chemical_list: D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D000972:Antineoplastic Agents, Phytogenic; C554895:Cd53 protein, mouse; C554896:Cd53 protein, rat; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D060265:Tetraspanin 25; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D005047:Etoposide; D003907:Dexamethasone; D004247:DNA