Cohesin Is Limiting for the Suppression of DNA Damage–Induced Recombination between Homologous Chromosomes

Brandeis University, United States of America
PLoS Genetics (Impact Factor: 7.53). 07/2010; 6(7):e1001006. DOI: 10.1371/journal.pgen.1001006
Source: PubMed


Double-strand break (DSB) repair through homologous recombination (HR) is an evolutionarily conserved process that is generally error-free. The risk to genome stability posed by nonallelic recombination or loss-of-heterozygosity could be reduced by confining HR to sister chromatids, thereby preventing recombination between homologous chromosomes. Here we show that the sister chromatid cohesion complex (cohesin) is a limiting factor in the control of DSB repair and genome stability and that it suppresses DNA damage-induced interactions between homologues. We developed a gene dosage system in tetraploid yeast to address limitations on various essential components in DSB repair and HR. Unlike RAD50 and RAD51, which play a direct role in HR, a 4-fold reduction in the number of essential MCD1 sister chromatid cohesion subunit genes affected survival of gamma-irradiated G(2)/M cells. The decreased survival reflected a reduction in DSB repair. Importantly, HR between homologous chromosomes was strongly increased by ionizing radiation in G(2)/M cells with a single copy of MCD1 or SMC3 even at radiation doses where survival was high and DSB repair was efficient. The increased recombination also extended to nonlethal doses of UV, which did not induce DSBs. The DNA damage-induced recombinants in G(2)/M cells included crossovers. Thus, the cohesin complex has a dual role in protecting chromosome integrity: it promotes DSB repair and recombination between sister chromatids, and it suppresses damage-induced recombination between homologues. The effects of limited amounts of Mcd1and Smc3 indicate that small changes in cohesin levels may increase the risk of genome instability, which may lead to genetic diseases and cancer.

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    • "One possible explanation for this ‘hyper-rec’ phenotype associated with the replication checkpoint mutants is a role for Mrc1 in promoting sister chromatid cohesion in S. cerevisiae (54). As sister chromatid cohesion limits recombination between homologous chromosomes (55), disrupting sister chromatid cohesion through such mutations could facilitate increased levels of interchromosomal GC. "
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    ABSTRACT: DNA double-strand breaks (DSBs) can cause chromosomal rearrangements and extensive loss of heterozygosity (LOH), hallmarks of cancer cells. Yet, how such events are normally suppressed is unclear. Here we identify roles for the DNA damage checkpoint pathway in facilitating homologous recombination (HR) repair and suppressing extensive LOH and chromosomal rearrangements in response to a DSB. Accordingly, deletion of Rad3ATR, Rad26ATRIP, Crb253BP1 or Cdc25 overexpression leads to reduced HR and increased break-induced chromosome loss and rearrangements. We find the DNA damage checkpoint pathway facilitates HR, in part, by promoting break-induced Cdt2-dependent nucleotide synthesis. We also identify additional roles for Rad17, the 9-1-1 complex and Chk1 activation in facilitating break-induced extensive resection and chromosome loss, thereby suppressing extensive LOH. Loss of Rad17 or the 9-1-1 complex results in a striking increase in break-induced isochromosome formation and very low levels of chromosome loss, suggesting the 9-1-1 complex acts as a nuclease processivity factor to facilitate extensive resection. Further, our data suggest redundant roles for Rad3ATR and Exo1 in facilitating extensive resection. We propose that the DNA damage checkpoint pathway coordinates resection and nucleotide synthesis, thereby promoting efficient HR repair and genome stability.
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    • "Particularly relevant is exposure of cells to DNA damage, which can activate dormant cohesin molecules (Strom et al. 2004, 2007; Unal et al. 2004, 2007, 2008). Since cohesin mutants show defects in homologous recombination (Covo et al. 2010; Sjogren and Strom 2010) and since defects in resolution of recombination intermediate can lead to chromosome gain (Ho et al. 2010; Rodrigue et al. 2012) the effects of DNA damage and the role of homologous recombination on chromosome gain in WT and SCC defective strains were studied. We examined chromosome gain following growth of diploid MATa/MATa cells on plates containing a low level of the recombinogen methyl methanesulfonate (MMS; 1 mM). "
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    • "This growth advantage was not observed in the diploid, supporting the contention that it is indeed a function of tetraploid-specific pathway activation. Previously, three regulatory processes were shown to be essential specifically in tetraploids – homologous recombination, kinetochore function, and spindle chromatid cohesion [27,62], and our findings suggest that the CWI pathway is a fourth essential process. "
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