TRANSPOSASES IN ETOPOSIDE RESISTANCE

描述（由申请人提供）：转座酶活性被认为在人类中已经灭绝，因为DNA运动在高等生物中可能是有害的，导致基因组不稳定和可能的恶性肿瘤。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。发现它与DNA连接酶IV相互作用，与其NHEJ修复活性一致。甲基化酶也是一种优先用于超卷曲DNA的内切酶。因此，我们探讨了甲基化酶在消去复制染色单体中的作用。Metnase与Topoisomerase II （Topo II）相互作用，增强了其在体外和细胞内DNA十烷化的活性。在Metnase转座酶结构域内的核酸酶活性是Topo II十烷化活性充分增强的必要条件。Metnase提高了Topo II对DNA进行十烷化的速率，并增强了Topo II抵抗十烷化抑制剂ICRF-193的能力。Metnase可改善Topo II对ICRF-193的耐药性，这一发现激发了对其是否介导对临床相关Topo II抑制剂依托泊苷的耐药性的研究。我们发现Metnase在体外阻止依托泊苷对Topo II十烷磺酸的抑制，并介导细胞对依托泊苷的抗性，促进依托泊苷存在下的增殖。Metnase也促进了依托泊苷诱导的DSB更快的清除。因此，Metnase似乎介导了对依托泊苷诱导的DNA损伤和细胞周期阻滞的抗性。这是一种尚未探索的依托泊苷耐药新机制。本申请通过提出三个问题来定义Metnase介导对依托泊苷抗性的机制：1)调节Metnase减少依托泊苷dsb能力的上游信号是什么？2) Metnase还原依托泊苷dsb的下游途径是什么？3) Metnase水平是否预示人类恶性肿瘤对依托泊苷的临床耐药？

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?