Article

The Rad51 paralog complexes BCDX2 and CX3 act at different stages in the BRCA1-BRCA2 dependent homologous recombination pathway

Molecular Biology Program and Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, 10021, USA.
Molecular and Cellular Biology (Impact Factor: 4.78). 11/2012; 33(2). DOI: 10.1128/MCB.00465-12
Source: PubMed

ABSTRACT

The Rad51 paralogs are required for homologous recombination (HR) and the maintenance of genomic stability. The molecular
mechanisms by which the five vertebrate Rad51 paralogs regulate HR and genomic integrity remain unclear. The Rad51 paralogs
associate with one another in two distinct complexes: Rad51B-Rad51C-Rad51D-XRCC2 (BCDX2) and Rad51C-XRCC3 (CX3). We find that
the BCDX2 and CX3 complexes act at different stages of the HR pathway. In response to DNA damage, the BCDX2 complex acts downstream
of BRCA2 recruitment but upstream of Rad51 recruitment. In contrast, the CX3 complex acts downstream of Rad51 recruitment
but still has a marked impact on the measured frequency of homologous recombination. Both complexes are epistatic with BRCA2
and synthetically lethal with Rad52. We conclude that human Rad51 paralogs facilitate BRCA2-Rad51-dependent homologous recombination
at different stages in the pathway and function independently of Rad52.

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    • "Similarly, the BC subcomplex of the BCDX2 complex has been reported to have in vitro RAD51 mediator activity and the DX2 subcomplex has been reported to have strand exchange activity. However, the specific activities of the RAD51 paralog complexes and subcomplexes have not been defined in vivo [5] [6] [7]. "
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    ABSTRACT: Genetic polymorphisms in DNA repair genes may induce individual variations in DNA repair capacity, which may in turn contribute to the risk of cancer developing. Homologous recombination repair (HRR) plays a critical role in maintaining chromosomal integrity and protecting against carcinogenic factors. The aim of the present study was to evaluate the relationship between prostate cancer risk and the presence of single nucleotide polymorphisms (SNPs) in the genes involved in HRR, that is, RAD51 (rs1801320 and rs1801321), RAD51B (rs10483813 and rs3784099), XRCC2 (rs3218536), and XRCC3 (rs861539). Polymorphisms were analyzed by PCR-RFLP and Real-Time PCR in 101 patients with prostate adenocarcinoma and 216 age- and sex-matched controls. A significant relationship was detected between the RAD51 gene rs1801320 polymorphism and increased prostate cancer risk. Our results indicate that the RAD51 gene rs1801320 polymorphism may contribute to prostate cancer susceptibility in Poland.
    Full-text · Article · Sep 2015 · Analytical cellular pathology (Amsterdam)
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    • "Our observations, together with previously reported findings, suggest that Rad51 paralogs perform two distinct functions to promote HR: they protect Rad51-ssDNA filaments against disruption by antirecombinases (Liu et al., 2011a) and directly stimulate the intrinsic recombinase activity of Rad51 by remodeling pre-synaptic filaments to an active, ''open,'' flexible, and stable conformation primed for homology search and strand invasion . Importantly, the mechanism we have discovered for the Rad51 paralogs in stimulating HR is distinct from that proposed for other positive regulators of HR, which are epistatic to Rad51 paralogs, including BRCA2 and Rad54 (Chun et al., 2013; Jensen et al., 2010, 2013; Liu et al., 2010; Solinger et al., 2002; Thorslund et al., 2010). We therefore propose a model (Figure 7I) for HR, in photobleaches; histogram of FRET values collected from all molecules with a Gaussian fit are shown in red, where x 0 is the mean FRET, s is the distribution width, and c 2 quantifies the quality of the fit. "
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    ABSTRACT: Repair of DNA double strand breaks by homologous recombination (HR) is initiated by Rad51 filament nucleation on single-stranded DNA (ssDNA), which catalyzes strand exchange with homologous duplex DNA. BRCA2 and the Rad51 paralogs are tumor suppressors and critical mediators of Rad51. To gain insight into Rad51 paralog function, we investigated a heterodimeric Rad51 paralog complex, RFS-1/RIP-1, and uncovered the molecular basis by which Rad51 paralogs promote HR. Unlike BRCA2, which nucleates RAD-51-ssDNA filaments, RFS-1/RIP-1 binds and remodels pre-synaptic filaments to a stabilized, "open," and flexible conformation, in which the ssDNA is more accessible to nuclease digestion and RAD-51 dissociation rate is reduced. Walker box mutations in RFS-1, which abolish filament remodeling, fail to stimulate RAD-51 strand exchange activity, demonstrating that remodeling is essential for RFS-1/RIP-1 function. We propose that Rad51 paralogs stimulate HR by remodeling the Rad51 filament, priming it for strand exchange with the template duplex. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Full-text · Article · Jul 2015 · Cell
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    • "Our observations, together with previously reported findings, suggest that Rad51 paralogs perform two distinct functions to promote HR: they protect Rad51-ssDNA filaments against disruption by antirecombinases (Liu et al., 2011a) and directly stimulate the intrinsic recombinase activity of Rad51 by remodeling pre-synaptic filaments to an active, ''open,'' flexible, and stable conformation primed for homology search and strand invasion . Importantly, the mechanism we have discovered for the Rad51 paralogs in stimulating HR is distinct from that proposed for other positive regulators of HR, which are epistatic to Rad51 paralogs, including BRCA2 and Rad54 (Chun et al., 2013; Jensen et al., 2010, 2013; Liu et al., 2010; Solinger et al., 2002; Thorslund et al., 2010). We therefore propose a model (Figure 7I) for HR, in photobleaches; histogram of FRET values collected from all molecules with a Gaussian fit are shown in red, where x 0 is the mean FRET, s is the distribution width, and c 2 quantifies the quality of the fit. "

    Full-text · Article · Jul 2015 · Cell
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