TRANSPOSASES IN ETOPOSIDE RESISTANCE

描述（由申请人提供）：转座酶活性被认为在人类中灭绝，因为DNA移动在高等生物中可能是有害的，导致基因组不稳定性和可能的恶性肿瘤。然而，我们分离出一种名为Metnase的人转座酶蛋白，它具有组蛋白甲基化酶和非同源末端连接（NHEJ）DNA修复活性。发现其与DNA连接酶IV相互作用，与其NHEJ修复活性一致。Metnase也是一种对超螺旋DNA优先的内切酶。因此，我们探讨了Metnase在去连锁复制染色单体中的作用。Metnase与拓扑异构酶II（Topo II），关键的脱连环酶，相互作用，并增强其在DNA脱连环，在体外和细胞内的活性。Metnase的转座酶结构域内的核酸酶活性是完全增强Topo II去连环化活性所必需的。Metnase提高了Topo II使DNA脱连环的速率，并增加了Topo II抵抗脱连环抑制剂ICRF-193的能力。Metnase改善Topo II对ICRF-193的抗性的发现刺激了对它是否可以介导对临床相关Topo II抑制剂依托泊苷的抗性的研究。我们发现，Metnase阻止抑制拓扑异构酶II decatenation依托泊苷在体外，并介导细胞耐药依托泊苷，促进增殖的依托泊苷的存在。Metnase也促进了更快的清除依托泊苷诱导的DSB。因此，Metnase似乎介导对依托泊苷诱导的DNA损伤和细胞周期停滞的抗性。这是一个新的机制，依托泊苷耐药，是未开发的。本申请提出通过提出三个问题来定义Metnase介导对依托泊苷的抗性的机制：1）调节Metnase减少依托泊苷DSB的能力的上游信号是什么？2)Metnase减少依托泊苷DSB的下游途径是什么？3)Metnase水平能预测人类恶性肿瘤对依托泊苷的临床耐药性吗？

DESCRIPTION (provided by applicant): Transposase activity was thought to be extinct in humans because DNA movement can be deleterious in higher organisms, resulting in genomic instability and perhaps malignancy. However, we isolated a human transposase protein termed Metnase that had histone methylase and non-homologous end-joining (NHEJ) DNA repair activity. It was found to interact with DNA Ligase IV, consistent with its NHEJ repair activity. Metnase also was an endonuclease preferential for supercoiled DNA. We therefore explored Metnase's role in decatenating replicated chromatids. Metnase interacted with Topoisomerase II (Topo II ), the critical decatenating enzyme, and enhanced its activity in DNA decatenation, both in vitro and intracellularly. The nuclease activity within the transposase domain of Metnase was required for full enhancement of Topo II decatenating activity. Metnase improved the rate at which Topo II decatenated DNA, and increased the ability of Topo II to resist the decatenation inhibitor ICRF-193. The finding that Metnase improved Topo II resistance to ICRF-193 stimulated an investigation into whether it could mediate resistance to the clinically relevant Topo II inhibitor etoposide. We found that Metnase prevented inhibition of Topo II decatenation by etoposide in vitro, and mediated cellular resistance to etoposide, promoting proliferation in the presence of etoposide. Metnase also promoted a more rapid clearance of etoposide-induced DSB. Thus, Metnase appeared to mediate resistance to etoposide-induced DNA damage and cell cycle arrest. This is a novel mechanism of etoposide resistance that is unexplored. This application proposes to define the mechanism by which Metnase mediates resistance to etoposide by asking three questions: 1) What are the upstream signals that regulate the ability of Metnase to reduce etoposide DSBs? 2) What is the downstream pathway by which Metnase reduces etoposide DSBs? 3) Do Metnase levels predic clinical resistance to etoposide in human malignancy?