THE tumour suppressor p53 is required to induce programmed cell death
(apoptosis) by DNA-damaging agents(1,2). As p53 is a transcriptional a
ctivator(3) that mediates gene induction after DNA damage(4), it has b
een proposed to be a genetic switch that activates apoptosis-mediator
genes(5). Here we evaluate the role of p53 in DNA-damage-induced apopt
osis by establishing derivatives of GHFT1 cells, that are somatotropic
progenitors immortalized by expression of SV40 T-antigen(6), which ex
press a temperature-sensitive p53 mutant(7). In these cells induction
of apoptosis by DNA damage depends strictly on p53 function. A shift t
o the permissive temperature triggers apoptosis following DNA damage,
but this is independent of new RNA or protein synthesis. The extent of
apoptotic DNA cleavage is directly proportional to the period during
which p53 is functional. These results do not support the proposal tha
t p53 is an activator of apoptosis-mediator genes but rather indicate
that p53 either represses genes necessary for cell survival(8) or is a
component of the enzymatic machinery for apoptotic cleavage or repair
of DNA(5).