Molecular Mechanism Of TFIP11 In Genome Stability Mainteance

The accurate and complete replication of DNA is vital for maintaining genomic integrity.However,DNA replication is constantly challenged by a variety of endogenous and exogenous sources of stress,which may lead to replication fork stalling,genome instability,eventually resulting in tumorigenesis.Replication fork reversal has emerged as one of the most important cellular response to various kinds of replication stress in higher eukaryotic cells.It has been demonstrated to be required for stabilizing and timely restarting stalled replication forks.Many important proteins associating with DNA damage repair are also involved in replication fork reversal,including RAD51 and BLM.The RAD51 recombinase is an essential factor of homologous recombination(HR)that plays crucial roles in the repair of DNA double-strand breaks(DSBs)and in safeguarding genome integrity.RAD51 is also involved in promoting replication fork reversal in response to replication stress.It has been proposed that RAD51 acts together with DNA translocases to catalyze the initiate fork reversal step.To date,precisely how RAD51 activity at stalled forks is controlled in cells remains poorly understood.Bloom syndrome is a rare hereditary chromosomal instability disorder caused by mutations in the gene encoding the BLM helicase.It is characterized by growth retardation,hypersensitivity to sunlight,immunodeficiency and high cancer predisposition.BLM,a member of the highly conserved Rec Q helicase family,has been implicated in promoting restart of stalled replication forks,but the underlying mechanism and dynamic regulation mechanism remain poorly understood.In the present study,depletion or overexpression of BLM resulted in a dramatic decrease in the percentage of HU-induced reversed forks,suggesting that BLM mediated fork reversal is a highly controlled process.Interestingly,we found that TFIP11 interacted with BLM and thus antagonized the recruitment of BLM at stalled forks.Hence,we propose that TFIP11 may regulate replication fork reversal through regulating the recruitment of BLM at stalled replication forks.TFIP11 was originally identified as a binding partner of tuftelin,including TIP＿N,G-patch and GCFC domains.TFIP11 and its homologs have been implicated in several key biological processes,such as RNA splicing,non-homologous end-joining(NHEJ)-mediated DSB repair,and telomere metabolism.In addition,whether TFIP11 participates in the cellular response to replication stress remains to be investigated.Here,we showed that TFIP11 accumulated at stalled forks upon replication stress by its intrinsic GCFC DNA binding domain.Furthermore,TFIP11 competed with the BLM helicase for association with stalled replication forks and thereby facilitated RAD51-mediated stalled fork reversal.Consequently,loss of TFIP11 resulted in aberrant accumulation of BLM at stalled forks,which in turn compromised RAD51 recruitment,impaired replication stressinduced fork reversal,enhanced chromosomal instability and hypersensitized cells to replication stress-inducing agents.Overall,these findings reveal a previously unidentified regulatory mechanism of TFIP11-BLM-RAD51 axis in fork reversal,which provides new insights into the precise regulation of replication fork reversal and represents novel therapeutic targets to potentiate cancer therapy by genotoxic agents.