Functional Identification Of Xrcc4, A Similar Factor (xlf)

Eukaryotic cells have developed a series of DNA damage response mechanisms,including the cell cycle checkpoint controls,DNA repair,and DNA damage-inuced apoptosis.DNA double-strand-breaks(DSBs) are the most serious DNA damage,which can be repaired mainly by the two pathways,namely homologous recombination repair(HR) and non-homologous-end-joining(NHEJ).NHEJ pathway is the major DSB repair pathway in mammalian cells.XLF(XRCC4-1ike factor) is a newly identified protein,whose loss-of-function mutations lead to human immunodeficiency with microcephaly.It has been reported that XLF facilitates the repair of replication-independent DSB damage induced by ironing radiations,and therefore increases the viability of the cells under this DNA damage condition.Werner syndrome is an autosomal recessive genetic disease with premature aging,its causative gene WRN plays an important role in both HR and NHEJ.In addition,it is also involved in telomere maintenance,and therefore prevents cells from senescence.This thesis research investigated functions of XLF in response to replication-dependent DNA damage.We found that downregulation of XLF impaired the ability of cells to repair DSBs induced by CPT(a topoisomerase I inhibitor),and increased the sensitivity of these cells to DNA replication stress conditions.We also found that WRN and XLF itself are positive transcriptional regulators of XLF.These results indicate that XLF not only plays key roles in the repair of replication-dependent DSBs,but also probably involves in other processes(e.g.,telomere maintenance and premature aging) mediated by WRN.