Roles of Human Tyrosyl-DNA Phosphodiesterases in Processing Topoisomerase Cleavable Complexes

• Main Authors: Shih-Yun Huang, 黃詩勻
• Other Authors: Tsai-Kun Li
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/76596139450892864519

碩士 === 國立臺灣大學 === 微生物學研究所 === 100 === Topoisomerases (TOP1/2/3) can solve the topological problems of DNA through transient breakage and religation reactions and has become excellent targets of anticancer drugs. Drugs targeting topoisomerases induce the formation of topoisomerase cleavable complex (TOPcc) in a special form of protein-embedded, phosphotyrosyl-linked DNA breakage and hence blocking the accessibility of signaling and repair proteins. During the formation of TOPcc, TOP1 and TOP2 covalently links to DNA though a 3’-phosphotyrosyl bond and 5’-phosphotyrosyl bond, respectively. Tyrosyl-DNA phosphodiesterases (TDP1/2) have recently been reported to process the hidden DNA breakage in TOPcc into uncovered DNA lesions by mediating the cleavage of enzyme-DNA phosphotyrosyl linkage. However, the specificity to 3’- and 5’-phosphotyrosyl linkage and corresponding functions of hTDP1/2 in processing of TOP1/2cc remain ill defined. Toward this aim, we used RNA interference (RNAi) technology and overexpression system to investigate the roles of hTDP1/2 in the TOP1/2cc-mediated DNA breakage and DNA damage responses (DDR). In addition, the potential relationship among hTDP1/2, transcription- and replication-initiated processing (TIP and RIP) pathways are also studied. We found that hTDP1 contributes to the repair of TOP1cc while hTDP1 and hTDP2 both participate in the repair of TOP2cc in human cells. Moreover, our results also suggest that hTDP1/2 are involved in TOP2cc-mediated DDR that are activated by transcription- and replication-initiated processing pathway. Consistently, both hTDP1- and hTDP2-deficient cells are hypersensitive to TOP2-targeting drugs. Together, our studies not only demonstrated the distinctive roles of hTDP1/2 in the processing of TOP1/2cc but also suggest a novel combination therapeutic strategy of using TOP1/2- and TDP1/2-targeting agents.