BRCA1 Promotes Unloading of the CMG Helicase from a Stalled DNA Replication Fork

Long, David T.; Joukov, Vladimir; Budzowska, Magda; Walter, Johannes C.

doi:10.1016/j.molcel.2014.08.012

Cited by 109 publications

(124 citation statements)

References 60 publications

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“…CMG complexes from both replication forks unload from both leading strands, as previously described (Long et al , 2014; Zhang et al , 2015) which enables one nascent leading strand to gradually progresses to 1 nt from the ICL (“0” position; step b‐ii) as previously described (Raschle et al , 2008; Zhang et al , 2015). The structure that arises at this stage is inhibitory for XPF‐ERCC1.…”

Section: Discussionmentioning

confidence: 97%

“…Both nascent leading strands initially stall ~20–40 nt from the ICL (“−20” position) due to steric hindrance imposed by the CMG helicase complexes (Fu et al , 2011). BRCA1‐dependent eviction of the CMG helicase at the replication forks enables the subsequent extension of one nascent leading strand to immediately adjacent to the crosslinked nucleotides (“approach” to “−1” position; Long et al , 2014). Subsequently, ubiquitylated FANCD2‐FANCDI facilitates the cleavage flanking the ICL by a nuclease(s) resulting in “unhooking” of the ICL.…”

Section: Introductionmentioning

confidence: 99%

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RPA activates the XPF ‐ ERCC 1 endonuclease to initiate processing of DNA interstrand crosslinks

et al. 2017

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During replication‐coupled DNA interstrand crosslink (ICL) repair, the XPF‐ERCC1 endonuclease is required for the incisions that release, or “unhook”, ICLs, but the mechanism of ICL unhooking remains largely unknown. Incisions are triggered when the nascent leading strand of a replication fork strikes the ICL. Here, we report that while purified XPF‐ERCC1 incises simple ICL‐containing model replication fork structures, the presence of a nascent leading strand, modelling the effects of replication arrest, inhibits this activity. Strikingly, the addition of the single‐stranded DNA (ssDNA)‐binding replication protein A (RPA) selectively restores XPF‐ERCC1 endonuclease activity on this structure. The 5′–3′ exonuclease SNM1A can load from the XPF‐ERCC1‐RPA‐induced incisions and digest past the crosslink to quantitatively complete the unhooking reaction. We postulate that these collaborative activities of XPF‐ERCC1, RPA and SNM1A might explain how ICL unhooking is achieved in vivo.

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Section: Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

RPA activates the XPF ‐ ERCC 1 endonuclease to initiate processing of DNA interstrand crosslinks

et al. 2017

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“…During ICL repair, helicase eviction is dependent on BRCA1 (16), a well-established tumor suppressor with multiple DNA repair functions (25). Although BRCA1 has been traditionally described as a recombination protein (26-29), growing evidence indicates that members of the BRCA pathway also play an important role in managing replication stress and resolving stalled forks (16,30,31).CMG unloading and fork resolution are also central events in …”

mentioning

confidence: 99%

“…1B, step i), which is required to initiate repair (14). The leading strands of the converging forks initially stall ϳ20 to 40 nucleotides from the cross-link ("arrival") due to steric hindrance from the CMG replicative helicase (15,16), which is comprised of Cdc45, MCM2-7, and GINS (17). Removal of the helicase complex is followed by the extension of leading strands to within 1 nucleotide of the cross-link ("approach") (Fig.…”

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confidence: 99%

p97 Promotes a Conserved Mechanism of Helicase Unloading during DNA Cross-Link Repair

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Rycenga

Gruber

et al. 2016

Molecular and Cellular Biology

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Interstrand cross-links (ICLs) are extremely toxic DNA lesions that create an impassable roadblock to DNA replication. When a replication fork collides with an ICL, it triggers a damage response that promotes multiple DNA processing events required to excise the cross-link from chromatin and resolve the stalled replication fork. One of the first steps in this process involves displacement of the CMG replicative helicase (comprised of Cdc45, MCM2-7, and GINS), which obstructs the underlying crosslink. Here we report that the p97/Cdc48/VCP segregase plays a critical role in ICL repair by unloading the CMG complex from chromatin. Eviction of the stalled helicase involves K48-linked polyubiquitylation of MCM7, p97-mediated extraction of CMG, and a largely degradation-independent mechanism of MCM7 deubiquitylation. Our results show that ICL repair and replication termination both utilize a similar mechanism to displace the CMG complex from chromatin. However, unlike termination, repair-mediated helicase unloading involves the tumor suppressor protein BRCA1, which acts upstream of MCM7 ubiquitylation and p97 recruitment. Together, these findings indicate that p97 plays a conserved role in dismantling the CMG helicase complex during different cellular events, but that distinct regulatory signals ultimately control when and where unloading takes place. Interstrand cross-links (ICLs) are extremely toxic DNA lesions that covalently couple both strands of the DNA duplex. Replicating cells are particularly sensitive to ICLs, which disrupt the strand separation required for DNA replication and transcription (1). Repair of ICLs is initiated primarily during S phase when a replication fork collides with the cross-link (2-4). Fork stalling triggers a damage response that involves multiple DNA processing events that promote excision of the ICL from chromatin and resolution of the stalled replication fork (5). Defects in ICL repair are associated with delays in cell cycle progression, increased chromosomal breakage, and severe sensitivity to DNA cross-linking agents. The cellular symptoms of deficient or aberrant repair are thought to underlie the molecular basis of several cancer predisposition syndromes (6), including Fanconi anemia (FA) and hereditary breast and ovarian cancer.Fanconi anemia is a rare chromosomal instability disorder caused by mutations in 1 of at least 16 different genes (7). Four of the FA genes are classified as breast/ovarian cancer susceptibility (BRCA) genes (FANCD1/BRCA2, FANCJ/BRIP1, FANCN/ PALB2, FANCO/RAD51C) (8), with recent evidence also supporting classification of BRCA1 as a new FA subtype (FANCS) (9). Together, the FA/BRCA proteins and associated factors form a multifunctional network that plays a critical role in managing various forms of DNA damage and replication stress (10). Although both FA and BRCA proteins are required for ICL repair, each pathway also supports nonoverlapping functions (11, 12) that play different roles in how cells respond to treatment with DNA cross-linking agents.Xenop...

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“…RAP80 is recruited during the initial stages of ICL recognition in a ubiquitin-dependent manner, possibly implicating its function in the BRCA1-dependent CMG clearance. This step in ICL repair is important for subsequent ICL recognition by the FANCD2-I complex (Long et al 2014).…”

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confidence: 99%

MERIT40 cooperates with BRCA2 to resolve DNA interstrand cross-links

et al. 2015

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MERIT40 is an essential component of the RAP80 ubiquitin recognition complex that targets BRCA1 to DNA damage sites. Although this complex is required for BRCA1 foci formation, its physiologic role in DNA repair has remained enigmatic, as has its relationship to canonical DNA repair mechanisms. Surprisingly, we found that Merit40 −/− mice displayed marked hypersensitivity to DNA interstrand cross-links (ICLs) but not whole-body irradiation. MERIT40 was rapidly recruited to ICL lesions prior to FANCD2, and Merit40-null cells exhibited delayed ICL unhooking coupled with reduced end resection and homologous recombination at ICL damage. Interestingly, Merit40 mutation exacerbated ICL-induced chromosome instability in the context of concomitant Brca2 deficiency but not in conjunction with Fancd2 mutation. These findings implicate MERIT40 in the earliest stages of ICL repair and define specific functional interactions between RAP80 complex-dependent ubiquitin recognition and the Fanconi anemia (FA)-BRCA ICL repair network.

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BRCA1 Promotes Unloading of the CMG Helicase from a Stalled DNA Replication Fork

Cited by 109 publications

References 60 publications

RPA activates the XPF ‐ ERCC 1 endonuclease to initiate processing of DNA interstrand crosslinks

RPA activates the XPF ‐ ERCC 1 endonuclease to initiate processing of DNA interstrand crosslinks

p97 Promotes a Conserved Mechanism of Helicase Unloading during DNA Cross-Link Repair

MERIT40 cooperates with BRCA2 to resolve DNA interstrand cross-links

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