The effect of the Saccharomyces cerevisiae endo-exonuclease NUD1 gene expression on the resistance of HeLa cells to DNA-damaging agents.

HeLa cells transiently transfected with a mammalian expression DNA vector expressing the Saccharomyces cerevisiae endo-exonuclease (EE) NUD1 gene have exhibited changes in cell survival frequencies after treatment with different DNA-damaging agents as compared to HeLa cells transfected with a control plasmid. The NUD1-transfected cells showed a dose-dependent increase in sensitivity to UV irradiation resulting in up to 58% decrease in cell survival. In response to gamma-irradiation NUD1 transfected cells featured an increased survival at doses equal to and greater than 2.0 Gy, reaching a maximum enhancement in survival frequency of 17%. At the same time, the NUD1-transfectants featured an increase in resistance to 0.25 microM-0.5 microM cis-platin (up to 58% increase in cell survival) and 1.0 mM EMS (11% increase). At higher concentrations of EMS NUD1 expression resulted in a decreased cell survival of the transfected cells (17% decrease for 2.5 mM EMS). No difference in cell survival frequencies between the NUD1-transfectants and the controls was observed after treatment with different concentrations of chlorambucil and mechlorethamine. These results suggest possible roles played by EEs in different DNA repair pathways--being stimulatory for the repair of certain types of DNA lesions, such as double strand breaks (DSBs), and interfering with the endogenous DNA repair systems for the repair of other types of lesions. Furthermore, these results also provide additional indirect evidence for the role of EEs in homologous recombination.