Inhibition of DNA-PK activity by phosphorothioate oligonucleotides

硫代磷酸寡核苷酸和苏拉明结合肝素结合蛋白，包括DNA聚合酶，并抑制其功能。在本研究中，我们报告了DNA依赖性蛋白激酶（DNA-PK）活性的抑制硫代磷酸酯磷脂，苏拉明和肝素。硫代磷酸寡核苷酸对DNA-PK活性的抑制作用随着长度的增加而增加，并在36聚体处达到平台。硫代磷酸寡脱氧胞苷36聚体的抑制作用可以是磷酸二酯寡脱氧胞苷36聚体的抑制作用的约200倍。用纯化的DNA-PK也观察到抑制作用，这表明DNA-PK和硫代磷酸寡核苷酸之间的直接相互作用。DNA-PK对双链DNA和硫代寡脱氧胞苷36聚体的结合位置不同，因为它们在DNA-PK活化中不具有竞争性。苏拉明和肝素对DNA-PK活性有抑制作用，IC_2<50>分别为1.7 μM和0.27 μg/ml。苏拉明在体内处理可显著抑制培养细胞的DNA-PK活性和DNA双链断裂（DSB）修复。我们的观察结果表明，苏拉明可能通过使DNA-PK失活和损伤DSB修复而导致细胞对电离辐射的增敏。

Phosphorothioate oligonudeotides and suramin bind to heparin binding proteins including DNA polymerases, and inhibit their functions. In the present study, we report inhibition of DNA-dependent protein kinase (DNA-PK) activity by phosphorothioate oiigonucleotides, suramin and heparin. Inhibitory effect of phosphorothioate oligonudeotides on DNA-PK activity was increased with length and reached a plateau at 36-mer. The base composition of phosphorothioate digonucleotides did not affect the inhibitory effect The inhibitory effect by phosphorothioate oligodeoxycytidine 36-mer can be about 200-fold greater than that by the phosphodiester oligodeoxycytidine 36-mer. The inhibitory effect was also observed with purified DNA-PK, which suggests direct interaction between DNA-PK and phosphorothioate oligonucleotides. DNA-PK will have different binding positions for double-stranded DNA and phosphorothioate oligodeoxycytidine 36-mer because they were not competitive in DNA-PK activation. Suramin and heparin inhibited DNA-PK activity with IC_<50> of 1.7 μM and 0.27 μg/ml respectively. DNA-PK activities and DNA double-stranded breaks (DSBs) repair in cultured cells were significantly suppressed by the treatment with suramin in vivo. Our present observations suggest that suramin mav possibly result in sensitization of cells to ionizing radiation bv inactivation of DNA-PK and the impairment of DSBs repair.