Pommier Y, Kohlhagen G, Wu C, Simmons D T
Laboratory of Molecular Pharmacology, National Cancer Institute, Bethesda, Maryland 20892-4255, USA.
Biochemistry. 1998 Mar 17;37(11):3818-23. doi: 10.1021/bi972067d.
DNA topoisomerase I (top1) is a ubiquitous enzyme that forms reversible DNA single-strand breaks (cleavage complexes) and plays a role in transcription, DNA replication, and repair. Top1 is the target of camptothecins which selectively trap top1 cleavage complexes and represent a novel class of anticancer drugs active against human solid tumors. The present study demonstrates that recombinant large T antigen (T-Ag), a virus encoded helicase with strong affinity for tumor suppressors and cell cycle- and replication-related proteins, suppresses top1 cleavage complexes and top1 catalytic activity. This top1 suppressive activity is probably not due to T-Ag binding to DNA, as a T-Ag truncation mutant containing only the first 246 amino acids and deficient in DNA binding also inhibited top1, and the inhibition was independent of ATP. T-Ag also antagonized and reversed the trapping of top1 cleavage complexes by camptothecin. These results demonstrate a functional interaction between T-Ag and top1: they also suggest the importance of top1-protein interactions for the regulation of DNA replication and modulation of camptothecin activity.
DNA拓扑异构酶I（top1）是一种普遍存在的酶，它能形成可逆的DNA单链断裂（切割复合物），并在转录、DNA复制和修复过程中发挥作用。Top1是喜树碱的作用靶点，喜树碱能选择性地捕获top1切割复合物，是一类对人类实体瘤有效的新型抗癌药物。本研究表明，重组大T抗原（T-Ag）是一种病毒编码的解旋酶，对肿瘤抑制因子以及细胞周期和复制相关蛋白具有很强的亲和力，它能抑制top1切割复合物和top1的催化活性。这种top1抑制活性可能不是由于T-Ag与DNA结合所致，因为一个仅包含前246个氨基酸且缺乏DNA结合能力的T-Ag截短突变体也能抑制top1，并且这种抑制作用与ATP无关。T-Ag还能拮抗并逆转喜树碱对top1切割复合物的捕获。这些结果证明了T-Ag与top1之间存在功能相互作用：它们还表明top1-蛋白质相互作用对于DNA复制调控和喜树碱活性调节的重要性。
