Abstract
The structure and the function of telomere are controlled by various proteins. Although DNA-PK primarily plays an important role in rejoining DNA broken ends caused by DNA damaging agants, in telomere region, it has been thought to protect telomere DNA double strand ends from mis-rejoining. Previous study showed that DNA-PKcs, a component of DNA-PK, is important for telomere stability, however, it is still unknown whether the kinase activity is required for telomere maintenance. In this study, we investigated the effects of NU7026, a specific inhibitor of DNA-PK activity, on telomere stability.
The inhibitory effects of NU7026 were examined by immunostaining using anti-phosphorylated-DNA-PKcs and anti-phosphorylated- histone H2AX in 1Gy-irradiated AT2KY cells. The most induced foci disappeared in cells treated with 10 uM of NU7026, indicating that the DNA-PK activity was completely suppressed by NU7026 at the concentration of 10 uM. Then, NU7026 was continuously exposed to normal human cells, and the cell growth was decreased to approximately 1/2 with 20 uM NU7026. Because abnormal cell divisions were observed in treated cells, we analyzed metaphase chromosomes in cells cultured in 10 uM and 20 uM NU7026. Telomere associations, telomere end fusions, both chromosome- and chromatid-type, were observed more frequently than in the untreated cells, which may result in defective growth of treated cells. These results indicate that the kinase activity of DNA-PK is essential for the stability of telomere DNA double strand end.
