Mismatch repair and nucleotide excision repair proteins cooperate in the recognition of DNA interstrand crosslinks

DNA interstrand crosslinks (ICLs) are among the most cytotoxic types of DNA damage, thus ICL-inducing agents such as psoralen, are clinically useful chemotherapeutics. Psoralen-modified triplex-forming oligonucleotides (TFOs) have been used to target ICLs to specific genomic sites to increase the selectivity of these agents. However, how TFO-directed psoralen ICLs (Tdp-ICLs) are recognized and processed in human cells is unclear. Previously, we reported that two essential nucleotide excision repair (NER) protein complexes, XPA-RPA and XPC-RAD23B, recognized ICLs in vitro, and that cells deficient in the DNA mismatch repair (MMR) complex MutS beta were sensitive to psoralen ICLs. To further investigate the role of MutS beta in ICL repair and the potential interaction between proteins from the MMR and NER pathways on these lesions, we performed electrophoretic mobility-shift assays and chromatin immunoprecipitation analysis of MutS beta and NER proteins with Tdp-ICLs. We found that MutS beta bound to Tdp-ICLs with high affinity and specificity in vitro and in vivo, and that MutS beta interacted with XPA-RPA or XPC-RAD23B in recognizing Tdp-ICLs. These data suggest that proteins from the MMR and NER pathways interact in the recognition of ICLs, and provide a mechanistic link by which proteins from multiple repair pathways contribute to ICL repair.