Topoisomerase II beta in the cellular response to DNA damage

我们的DNA，大约有30亿个碱基对，在细胞的生命周期中编码了所有结构和功能的“蓝图”。维持这种DNA的完整性和稳定性对细胞和整个生物体的生存至关重要。在每一次细胞分裂中，这些DNA必须被忠实地复制并均匀地分配到子细胞中。它还必须准备好应对任何破坏DNA的事件。如果不这样做，就会导致DNA突变的积累、细胞衰老或细胞死亡。令人震惊的是，生物体中的每个细胞每天都要承受成千上万次的DNA损伤。它们自发地产生于内源性（来自身体内部）和外源性（来自身体外部）来源。矛盾的是，氧气虽然对生命是绝对必需的，但它作为细胞代谢的副产物被转化为活性氧；它们可以以多种方式改变DNA，可能导致突变或DNA片段断裂。地壳中自然产生的辐射以及来自太空、航空旅行和医用x射线的暴露都会导致我们的DNA断裂。值得庆幸的是，已知有200多种哺乳动物基因参与DNA损伤的检测和修复。也许矛盾的是，其他对细胞功能至关重要的蛋白质可以对DNA损伤做出反应，并被困在DNA上。这是一个潜在的危险，因为这些蛋白质可能会增加损伤负担，或减缓损伤部位的修复。这些蛋白质行为的表征是一个深入研究的领域。这个应用程序通过研究一种酶，拓扑异构酶ii （TOP2ß）的这种行为，为该领域做出了贡献。

Our DNA, with ~3 billion base pairs, encodes the ‘blueprint’ for all the structures and functions of a cell over its lifespan. Maintaining the integrity and stability of this DNA is of paramount importance to survival of the cell and the entire organism. With each cell division, this DNA must be faithfully copied and equally distributed into daughter cells. It must also be prepared to react to any DNA damaging events. Failure to do so can lead to the accumulation of mutations in our DNA, cell aging or cell death. Astoundingly, each cell in a living organism endures tens of thousands of DNA insults every day. These arise spontaneously from both endogenous (from within the body) and exogenous (from outside the body) sources. Paradoxically, oxygen, although absolutely essential for life, is converted to reactive oxygen species as by-products of cell metabolism; these can alter DNA in numerous ways, potential leading to mutations or broken DNA fragments. Naturally occurring radiation found in the earth’s crust and exposure from space, airline travel and medical x-rays can lead to breaks in our DNA. Thankfully, over 200 mammalian genes are known to be involved in the detection and repair of DNA damage. Perhaps paradoxically, other proteins critical for cell function can react to DNA damage and become trapped on the DNA. This is a potential hazard, as these proteins could add to the damage burden, or slow the repair of damage sites. Characterization of these protein behaviours is an area of intense investigation. This application contributes to the field by investigating this behaviour for one enzyme, topoisomerase IIß (TOP2ß). The topoisomerases are an evolutionarily conserved family of enzymes that are involved in untangling and unwinding DNA to allow for its replication (copying) and segregation (separation) into daughter cells. They are found in all organisms, including bacteria, viruses, plants and animals. Although topoisomerases (including the TOP2ß form) have been extensively studied, emerging data from my laboratory points to an as yet uncharacterized role for this protein in the response to damage caused by radiation. In our laboratory, we have developed experimental tools that position us to determine the role TOP2ß plays in the cell’s response to radiation. Using these unique reagents, together with additional resources obtained through international collaborations, we will specifically investigate how TOP2ß becomes trapped on DNA. Using engineered mutant forms of TOP2ß, we will clarify the requirement for enzyme activity and study the kinetics of its movement. Deciphering how our cells respond to the DNA damage, and identification and characterization of new proteins that respond to this damage, is of importance in understanding DNA repair in a wide range of organisms and for identifying targets for the development of agents that can help preserve the long-term stability of our DNA.