Rd. Meng et al., P53-independent increase in E2F-1 expression enhances the cytotoxic effects of etoposide and of adriamycin, INT J ONCOL, 14(1), 1999, pp. 5-14
The transcription factor E2F-1 drives cell cycle progression at the G(1)- t
o S-phase boundary; however, over-expression of E2F-1 can induce apoptosis.
We show here that E2F-1 protein levels increase in human medulloblastoma,
glioma, lung, colon, and bladder cancer cell lines (n=7) following treatmen
t with the DNA damaging agents adriamycin etoposide. This induction of E2F-
1 occurs independently of Rb or p53 status and involves new protein synthes
is. Although E2F-1 protein levels increase following DNA damage, several ge
nes transcriptionally targeted by E2F-1 are not similarly induced. Rather,
induction of E2F-1 in the tumor cells correlates with their sensitivity to
adriamycin or to etoposide. Correspondingly, fibroblasts from E2F-1 knockou
t mice are more resistant to DNA damage than cells from normal mice. Overex
pression of E2F-1 protein in tumor cell lines infected with an adenovirus e
ncoding wild-type E2F-1 leads to enhanced cytotoxicity following exposure t
o DNA damaging agents, which results from enhanced apoptosis. The results o
f this study implicate a role for E2F-1 in p53-independent cytotoxicity of
chemotherapy and provide a pharmacological tool for increasing levels of th
e apoptosis-inducing E2F-1 protein.