裂殖酵母Snf2家族蛋白Rrp2在依托泊苷诱导的DNA损伤应答中的作用

Etoposide is a commonly used antitumor drug. It causes DNA damage through inhibiting the topoisomerase Top2. It is not entirely clear how cells respond to etoposide-induced DNA damage and in particular how the covalent complex between Top2 and DNA (Top2 cleavage complex, Top2cc) is removed. Fission yeast is an important model organism for studying DNA damage response. Through screening the genome-wide fission yeast deletion mutant library, we found that the mutant lacking the Snf2-family protein Rrp2 is strongly sensitive to etoposide but not sensitive to other DNA damaging agents, suggesting that Rrp2 is specifically involved in etoposide-induced DNA damage response. Preliminary analyses indicate that the function of Rrp2 depends on its ATPase activity and appears to be intimately connected to sumoylation. We postulate that Rrp2 may interact with sumoylated Top2 and thereby inhibit the deleterious degradation of sumoylated Top2. The ATPase activity of Rrp2 may allow it to promote the cutting of the Top2cc-associated DNA strand by nucleases. We will test these hypotheses to gain new insights into the mechanisms of eukaryotic DNA damage response.

依托泊苷是一种常用的抗肿瘤药物。它通过抑制拓扑异构酶Top2诱导DNA损伤。细胞如何应答依托泊苷诱导的DNA损伤，特别是如何去除Top2与DNA的共价复合物（Top2 cleavage complex, Top2cc），目前仍不完全清楚。裂殖酵母是研究DNA损伤应答的重要模式生物。我们通过对裂殖酵母缺失突变体文库的筛选，发现一个Snf2家族蛋白Rrp2的缺失导致对依托泊苷的高度敏感性，但不引起对其它DNA损伤条件的敏感性，表明Rrp2特异地参与依托泊苷诱导的损伤应答。初步分析显示Rrp2的功能依赖于它的ATPase活力，并与苏素化修饰有密切关系。我们推测Rrp2可能与苏素化的Top2相互作用，从而抑制有不利后果的对苏素化Top2的降解。Rrp2的ATPase活力可能允许它促进核酸酶对Top2cc所在的DNA链的切割。我们将对这些假说进行检验，以期得到对真核生物DNA损伤应答机制的新认识。

DNA拓扑异构酶II（Top2）毒剂通过稳定Top2反应过程中形成的Top2与DNA共价连接的中间体，对基因组稳定性造成影响。一些Top2毒剂如依托泊苷等被应用于癌症的临床治疗。还有多种Top2毒剂以天然产物的形式在自然界和人们的日常饮食中广泛存在。因此研究细胞抵御Top2毒剂的机制有重要的理论和应用意义。我们的研究工作发现一个名为Rrp2的DNA移位酶通过阻止Top2的降解来避免Top2毒剂所造成的基因组损伤，从而揭示了一种真核生物中的新的基因组保护机制。