Abstract
Several proteins in the BRCA-Fanconi anemia (FA) pathway, such as FANCJ, BRCA1, and FANCD2, interact with mismatch repair (MMR) pathway factors, but the significance of this link remains unknown. Unlike the BRCA-FA pathway, the MMR pathway is not essential for cells to survive toxic DNA interstrand crosslinks (ICLs), although MMR proteins bind ICLs and other DNA structures that form at stalled replication forks. We hypothesized that MMR proteins corrupt ICL repair in cells that lack crosstalk between BRCA-FA and MMR pathways. Here, we show that ICL sensitivity of cells lacking the interaction between FANCJ and the MMR protein MLH1 is suppressed by depletion of the upstream mismatch recognition factor MSH2. MSH2 depletion suppresses an aberrant DNA damage response, restores cell cycle progression, and promotes ICL resistance through a Rad18-dependent mechanism. MSH2 depletion also suppresses ICL sensitivity in cells deficient for BRCA1 or FANCD2, but not FANCA. Rescue by Msh2 loss was confirmed in Fancd2-null primary mouse cells. Thus, we propose that regulation of MSH2-dependent DNA damage response underlies the importance of interactions between BRCA-FA and MMR pathways.
Highlights
DNA interstrand crosslinks (ICLs) induce a range of cellular responses, including recruitment of DNA repair proteins to the lesion and/or a stalled replication fork
To test the idea that MMR is toxic in the absence of coordination with the BRCA-Fanconi anemia (FA) pathway, we tested whether the ICL sensitivity of FANCJ-deficient cells is due to MMR factors
By analyzing the percent of G2/ M cells following aphidicolin release, we found that MSH2 depletion effectively restored cell cycle progression to the FANCJK141/142Aexpressing FA-J cells (Fig 5E) consistent with MSH2 interfering with the restart of stalled replication forks when cells lack the FANCJ– MLH1 interaction
Summary
DNA interstrand crosslinks (ICLs) induce a range of cellular responses, including recruitment of DNA repair proteins to the lesion and/or a stalled replication fork. Cells derived from Fanconi anemia (FA) patients or BRCA1/2-associated tumors that lack the BRCA-FA pathway (BRCA-FA cells) are extremely sensitive to agents such as mitomycin C (MMC) that induce ICLs (Moldovan & D’Andrea, 2009; Muniandy et al, 2010) This interstrand crosslink (ICL) sensitivity and associated chromosomal aberrations are key determinants to diagnosing genetic deficiency in the BRCA-FA pathway, which has up to 16 components (Sharma & Canman, 2012). Loss of the BRCA-FA proteins BRCA1 and FANCD2 leads to defects in recombination-directed repair This has been attributed to non-homologous end-joining (NHEJ) proteins that occupy the ends of broken DNA and interfere with DNA end-processing required for HR (Bunting & Nussenzweig, 2010; Aly & Ganesan, 2011). Loss of 53BP1 overcomes early embryonic lethality in BRCA1-nullizigous mice (Cao et al, 2009; Bouwman et al, 2010; Bunting et al, 2012), suggesting that 53BP1 underlies the proliferation defect in BRCA1 mice
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