BRCA2 Regulates Homologous Recombination in Response to DNA Damage: Implications for Genome Stability and Carcinogenesis

Abstract

BRCA2 has been implicated in the maintenance of genome stability and RAD51-mediated homologous recombination repair of chromosomal double-strand breaks (DSBs), but its role in these processes is unclear. To gain more insight into its role in homologous recombination, we expressed wild-type BRCA2 in the well-characterized BRCA2-deficient human cell line CAPAN-1 containing, as homologous recombination substrates, either direct or inverted repeats of two inactive marker genes. Whereas direct repeats monitor a mixture of RAD51-dependent and RAD51-independent homologous recombination events, inverted repeats distinguish between these events by reporting RAD51-dependent homologous recombination, gene conversion, and crossover events only. At either repeats, BRCA2 decreases the rate and frequency of spontaneous homologous recombination, but following chromosomal DSBs, BRCA2 increases the frequency of homologous recombination. At direct repeats, BRCA2 suppresses both spontaneous gene conversion and deletions, which can arise either from crossover or RAD51-independent sister chromatid replication slippage (SCRS), but following chromosomal DSBs, BRCA2 highly promotes gene conversion with little effect on deletions. At inverted repeats, spontaneous or DSB-induced crossover events were scarce and BRCA2 does not suppress their formation. From these results, we conclude that (i) BRCA2 regulates RAD51 recombination in response to the type of DNA damage and (ii) BRCA2 suppresses SCRS, suggesting a role for BRCA2 in sister chromatids cohesion and/or alignment. Loss of such control in response to estrogeninduced DNA damage after BRCA2 inactivation may be a key initial event triggering genome instability and carcinogenesis. (Cancer Res 2005; 65(10): 4117-25)

Brca2/Pds5 complexes mobilize persistent meiotic recombination sites to the nuclear envelope

“…Considering that exchange between the chromatids requires their precise alignment over extensive regions around homologous recombination intermediates, it is tempting to speculate that the Brca2-mediated Pds5-Pds5 interactions might serve the simultaneous clamping of two cohesin rings around the homologs. Interestingly, DNA repair studies in mammals have provided evidence for a role of Brca2 in sister chromatid cohesion and/or alignment (Abaji et al, 2005;Brough et al, 2012).…”

Chronic Hypoxia Decreases Synthesis of Homologous Recombination Proteins to Offset Chemoresistance and Radioresistance

“…The CAPAN1 human pancreatic cancer cell lines (clones D2 and D2 B74) were grown in RPMI 1640 supplemented with 15% FCS, 10 mmol/L HEPES, 4.5 g/L dextrose, and 1 mmol/L pyruvic acid. These cells are isogenic for the expression and function of BRCA2 and are isogenic for functional HR as previously described (31).…”

Disruption of p53 by the Viral oncoprotein HPV16-E6 does not Deregulate Chromosomal Homologous Recombination in a Transcriptional Interference-Free Assay System

“…Recently, we found that in this assay system, the breast cancer susceptibility BRCA2 protein, which interacts with p53 and RAD51, 36 suppresses spontaneous HR but promotes HR following chromosomal DSBs. 37 We report here that, in this assay system, disruption of p53 by the human papilloma virus oncoprotein HPV16-E6 in two distinct human cell lines containing either direct or inverted repeats did not result in increased rates of spontaneous HR.…”