Nonenzymatic Role for WRN in Preserving Nascent DNA Strands after Replication Stress

Abstract

Summary WRN, the protein defective in Werner Syndrome (WS), is a multifunctional nuclease involved in DNA damage repair, replication and genome stability maintenance. It was assumed that the nuclease activities of WRN were critical for these functions. Here, we report a non-enzymatic role for WRN in preserving nascent DNA strands following replication stress. We found that lack of WRN led to shortening of nascent DNA strands after replication stress. Further, we discovered that the exonuclease activity of MRE11 was responsible for the shortening of newly replicated DNA in the absence of WRN. Mechanistically, the N-terminal FHA domain of NBS1 recruits WRN to replication-associated DNA double-stranded breaks to stabilize Rad51 and to limit the nuclease activity of its C-terminal binding partner MRE11. Thus, the previously unrecognized non-enzymatic function of WRN in the stabilization of nascent DNA strands sheds light on the molecular reason for the origin of genome instability in WS individuals.

Class I Histone Deacetylase HDAC1 and WRN RECQ Helicase Contribute Additively to Protect Replication Forks upon Hydroxyurea-induced Arrest

“…Consistent with these results, our new data demonstrate that WRN depletion reduces the association of RAD51 with stalled forks. This reduction could reflect decreased recruitment to or increased loss of RAD51 from forks and is consistent with the phenotype recently reported in camptothecin-treated cells where chromatinbound RAD51 was reduced in the absence of WRN (42). However, other recent findings suggest that RAD51 may function upstream of WRN (47,53) and provide the WRN/DNA2 complex with a regressed fork as a substrate (54).…”

“…Parallel to HDAC1-Our previous studies (15) and findings by Su et al (42) suggest that WRN may affect fork recovery by functioning upstream of RAD51. HDAC1 (and -2) are thought to affect recruitment of RAD51 in double strand break repair (43).…”

Rad51 recombinase prevents Mre11 nuclease-dependent degradation and excessive PrimPol-mediated elongation of nascent DNA after UV irradiation

“…After HU and APH treatment, Rad51 loaders, such as BRCA2, prevent Mre11-dependent nucleolytic degradation of nascent DNA at stalled replication forks (6,7,(9)(10)(11)(12)(13)(14)38). We therefore treated Rad51-depleted and control samples with mirin, a specific inhibitor of the exonuclease activity of Mre11 (39).…”

“…Over the past few years, it has become evident that Rad51 escorts ongoing replication forks regardless of the presence of DSBs (3)(4)(5). Specifically, Rad51 protects persistently stalled replication forks from Mre11-mediated nucleolytic degradation and facilitates replication fork restart when the replication-halting agent hydroxyurea (HU) or aphidicolin (APH) is removed (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Such novel functions of Rad51 require many HRR factors, including BCRA2, FANCD2 (Fanconi Anemia Complementation group protein D2), CtIP, BRCA1, and the WRN helicase, but are independent of HRR effectors, such as Rad54 (6,7).…”

Protection or resection: BOD1L as a novel replication fork protection factor

“…In analogous fashion, the helicase/nuclease WRN is thought to protect nascent DNA by stabilizing RAD51 nucleofilaments, through a mechanism independent of its enzymatic activity. 7,8 Similarly, the TLS polymerase REV1 has recently been reported to prevent fork resection, again through its ability to promote RAD51 loading/foci formation. 9 Interestingly, PARP-1 has also been implicated in facilitating RAD51-mediated protection of stalled replication forks, 10 although it is unclear whether this is mediated through the poly-ADP ribose (PAR) chain-dependent recruitment of protective factors to stalled forks or via an alternative mechanism.…”