TRANSPOSASE PROTEIN METNASE IN LEUKEMIC DECATENATION

描述(申请人提供)：转座酶活性在人类中被认为已经灭绝，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，甚至可能是恶性的。我们分离到了一种人类转座酶蛋白，称为Metnase，它对超螺旋DNA具有优先的内切酶活性。因此，我们探索了它在解开纠缠的DNA中的作用。DNA复制导致相互缠绕的姐妹染色单体，在后期染色单体分离之前，这些染色单体必须解开或去掉。如果没有，可能会发生灾难性的染色单体断裂，多个断裂可能导致染色体间末端连接和随后的易位。因此，细胞主动监测相互缠绕的染色单体的破坏。在有丝分裂之前，连锁化DNA的存在通常会导致细胞周期停滞，称为去细胞周期检查点。此前已有研究表明，膀胱癌和肺癌在去细胞周期检查点不会被适当地阻止。我们还发现，急性白血病不会在十分之一的检查站被逮捕。当ATR感测到连锁的染色体，然后发出信号，让细胞在有丝分裂前停止时，十分之一的检查点就会被激活。TOPO II1是物理上解开染色单体所必需的去化酶。除此之外，人们对这种最近描述的现象的分子机制知之甚少。我们发现，Metnase不是调节DNA片段的移动，而是通过显著提高Topo II1对DNA的破坏速度来提高染色体的稳定性。Metnase水平的增加增加了对Topo II1抑制剂ICRF-193和VP-16的耐药性。基于这些基本发现，我们假设Metnase在造血细胞的去化中发挥作用，并协助通过去细胞周期检查点的进展。这项应用将通过解决三个问题来描述这种情况发生的机制：1)Metnase增强Topo II1降解活性的机制是什么？2)Metnase的降解活性是由磷酸化信号激活的吗？3)Metnase是否介导了白血病等血液系统恶性肿瘤的降解？破译Metnase在杀灭中的作用机制有助于深入了解白血病易位的机制，为什么白血病未能在杀灭检查点适当地阻止，以及一些白血病对Topo II1抑制剂的耐药性。与公共健康相关：我们已经分离出一种名为Metnase的新蛋白质，它可以帮助染色体解开，从而防止它们在细胞分裂过程中断裂。防止这种染色体断裂可以减少导致多种形式癌症的突变。然而，癌细胞可以颠覆Metnase，并用它来抵抗DNA破坏化疗的行为。

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. We isolated a human transposase protein termed Metnase that had preferential endonuclease activity for supercoiled DNA. We therefore explored its role in decatenating tangled DNA. DNA replication results in intertwined sister chromatids that must be untangled, or decatenated, before chromatid separation at anaphase. When absent, catastrophic chromatid breakage can occur, and the multiple breaks can result in inter- chromosomal end joining and subsequent translocation. Therefore, cells actively monitor the decatenation of intertwined chromatids. The presence of catenated DNA usually induces a cell cycle arrest, termed the decatenation check point, before mitosis. It has been previously shown that bladder and lung cancers do not properly arrest at the decatenation cell cycle checkpoints. We also found that acute leukemias do not arrest at the decatenation checkpoints. The decatenation checkpoints are activated when ATR senses catenated chromosomes and then signals for the cell to arrest before mitosis. Topo II1 is the essential decatenating enzyme for physically untangling chromatids. Beyond that, little is known about the molecular mechanism of this recently described phenomenon. We found that Metnase, rather than mediating the mobility of DNA segments, increased chromosome stability by markedly enhancing the rate of DNA decatenation by Topo II1. Increasing Metnase levels increased resistance to the Topo II1 inhibitors ICRF-193 and VP-16. Based on these fundamental findings, we hypothesize that Metnase plays a role in hematopoietic decatenation, and assists in progression through the decatenation cell cycle checkpoint. This application will characterize the mechanism by which this takes place by addressing three questions: 1) What is the mechanism by which Metnase enhances Topo II1 decatenation activity? 2) Is the decatenation activity of Metnase activated by phosphorylation signals?,3) Does Metnase mediate decatenation in hematopoietic malignancies such as leukemia? Deciphering the mechanism by which Metnase functions in decatenation could lend insight into the mechanism of leukemogenic translocations, why leukemia fails to appropriately arrest at the decatenation check points, and resistance of some leukemias to Topo II1 inhibitors. PUBLIC HEALTH RELEVANCE: We have isolated a novel protein termed Metnase that helps chromosomes untangle, and thereby prevents their breakage during cell division. Preventing such chromosome breakage can reduce the mutations that cause many forms of cancer. The cancer cell, however, can subvert Metnase, and use it to resist the actions of DNA damaging chemotherapy.