Thymocyte apoptosis induced by p53-dependent and independent pathways.
Death by apoptosis is characteristic of cells undergoing deletion during embryonic development, T- and B-cell maturation and endocrine-induced atrophy. Apoptosis can be initiated by various agents and may be a result of expression of the oncosuppressor gene p53 (refs 6-8). Here we study the dependence of apoptosis on p53 expression in cells from the thymus cortex. Short-term thymocyte cultures were prepared from mice constitutively heterozygous or homozygous for a deletion in the p53 gene introduced into the germ line after gene targeting. Wild-type thymocytes readily undergo apoptosis after treatment with ionizing radiation, the glucocorticoid methylprednisolone, or etoposide (an inhibitor of topoisomerase II), or after Ca(2+)-dependent activation by phorbol ester and a calcium ionophore. In contrast, homozygous null p53 thymocytes are resistant to induction of apoptosis by radiation or etoposide, but retain normal sensitivity to glucocorticoid and calcium. The time-dependent apoptosis that occurs in untreated cultures is unaffected by p53 status. Cells heterozygous for p53 deletion are partially resistant to radiation and etoposide. Our results show that p53 exerts a significant and dose-dependent effect in the initiation of apoptosis, but only when it is induced by agents that cause DNA-strand breakage.
Clarke
A R
AR
Department of Pathology, University Medical School, Edinburgh, UK.
Purdie
C A
CA
Harrison
D J
DJ
Morris
R G
RG
Bird
C C
CC
Hooper
M L
ML
Wyllie
A H
AH
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002478:Cells, Cultured; D004247:DNA / Q000187:drug effects; D005047:Etoposide / Q000494:pharmacology; D005260:Female; D005720:Gamma Rays; D017353:Gene Deletion; D016158:Genes, p53 / Q000502:physiology*; D006579:Heterozygote; D006720:Homozygote; D015759:Ionomycin / Q000494:pharmacology; D008297:Male; D008775:Methylprednisolone / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013950:Thymus Gland / Q000166:cytology* / Q000187:drug effects / Q000528:radiation effects
D015759:Ionomycin; D005047:Etoposide; D004247:DNA; D013755:Tetradecanoylphorbol Acetate; D008775:Methylprednisolone