Dg. Brooks et al., Mutant K-ras enhances apoptosis in embryonic stem cells in combination with DNA damage and is associated with increased levels of p19(ARF), ONCOGENE, 20(17), 2001, pp. 2144-2152
The roles of K-ras in neoplasia are not entirely understood, although there
is evidence that K-ras affects susceptibility to apoptosis, modulating sur
vival of DNA damaged cells which would otherwise be eliminated. In this stu
dy, we investigated the effects of mutant K-ras on apoptosis in vitro follo
wing DNA damage. To avoid complications resulting from mutations in other c
ancer-related genes and from the presence of endogenous K-ras, we derived K
-ras null embryonic stem cells. Expression of either wild-type or mutant K-
vas was reconstructed by stable plasmid transfection, The cell lines were t
reated with etoposide, cisplatin and UV radiation and apoptosis measured fl
ow cytometrically. Mutant K-ras potentiated the effect of etoposide-derived
DNA damage by increasing apoptosis, whereas absence of K-ras had the oppos
ite effect. This pattern was similar but less marked with cisplatin, wherea
s UV yielded no difference in apoptosis with regard to K-ras status, sugges
ting that the effect of K-ras on apoptosis is dependent on the nature of th
e DNA damage, To investigate possible mechanisms, we examined the expressio
n of p19(ARF) mRNA by RT-PCR, Cells expressing mutant K-ras produced elevat
ed levels of p19(ARF) mRNA, which could link K-ras status with p53 expressi
on and hence susceptibility to DNA damage-induced apoptosis.