We previously identified an
endo-exonuclease that is highly expressed in
cancer cells and plays an important role in
DSB repair mechanisms. A small molecular compound
pentamidine, which specifically inhibited nuclease activity of the isolated
endo-exonuclease from yeast as well as from mammalian cells, was capable of sensitizing
tumor cells to
DNA damaging agents. In this study, we investigated the effect of precisely silencing the
endo-exonuclease expression by
small interfering RNA (
siRNA) upon treatment with a variety of
DNA damaging agents in mouse B16F10
melanoma cells. A maximum of 3.6 to approximately 4-fold reduction in
endo-exonuclease mRNA expression was achieved, over a period of 48-72 h of post transfection with a concomitant reduction in
protein expression (approximately 4-5 fold), resulting in a substantial reduction (approximately 45-50%) of the corresponding nuclease activity. Suppressed
endo-exonuclease expression conferred significant decrease in cell survival, ranging from approximately 30 to approximately 50% cell killing, in presence of
DNA damaging drugs methyl methane sulfonate (MMS),
cisplatin, 5-fluoro
uracil (5-FU) and gamma-irradiation but not at varying dosages of ultra violet (UV) radiation. The data strongly support a role for the
endo-exonuclease in repairing
DNA damages, induced by MMS,
cisplatin,
5-FU and gamma irradiation but not by UV radiation. The results presented in this study suggest that the
endo-exonuclease siRNA could be useful as a therapeutic tool in targeting the
endo-exonuclease in
cancer therapy.