Inhibition of DNA-PK activity by phosphorothioate oligonucleotides

硫代寡核苷酸和苏拉明与包括DNA聚合酶在内的肝素结合蛋白结合，并抑制其功能。在本研究中，我们报道了硫代寡核苷酸、苏拉明和肝素对DNA依赖蛋白激酶(DNA-PK)活性的抑制作用。硫代寡核苷酸对DNA-PK活性的抑制作用随时间的延长而增强，在36-mer时达到平台期。硫代双核苷酸的碱基组成不影响抑制作用，硫代寡脱氧胞苷36-聚体的抑制作用约为磷酸二酯脱氧胞苷36-聚体的200倍。纯化的DNA-PK也有抑制作用，提示DNA-PK与硫代寡核苷酸有直接的相互作用。DNA-PK与双链DNA和硫代寡聚脱氧胞苷36-聚体的结合位置不同，因为它们在DNA-PK的激活过程中不具有竞争性。苏拉明和肝素抑制DNA-PK活性的IC_(50)和IC_(50)分别为1.7μM和0.27μg/ml。苏拉明可显著抑制培养细胞的DNA-PK活性和DNA双链断裂(DSB)修复。我们目前的观察表明，苏拉明MAV可能通过使DNA-PK失活和DSBs修复受损而导致细胞对电离辐射的敏化。

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.