Alcohol-derived DNA crosslinks are repaired by two distinct mechanisms

Acetaldehyde is a highly reactive, DNA-damaging metabolite that is produced upon alcohol consumption(1). Impaired detoxification of acetaldehyde is common in the Asian population, and is associated with alcohol-related cancers(1,2). Cells are protected against acetaldehyde-induced damage by DNA crosslink repair, which when impaired causes Fanconi anaemia (FA), a disease resulting in failure to produce blood cells and a predisposition to cancer(3,4). The combined inactivation of acetaldehyde detoxification and the FA pathway induces mutation, accelerates malignancies and causes the rapid attrition of blood stem cells(5-7). However, the nature of the DNA damage induced by acetaldehyde and how this is repaired remains a key question. Here we generate acetaldehyde-induced DNA interstrand crosslinks and determine their repair mechanism in Xenopus egg extracts. We find that two replication-coupled pathways repair these lesions. The first is the FA pathway, which operates using excision-analogous to the mechanism used to repair the interstrand crosslinks caused by the chemotherapeutic agent cisplatin. However, the repair of acetaldehyde-induced crosslinks results in increased mutation frequency and an altered mutational spectrum compared with the repair of cisplatin-induced crosslinks. The second repair mechanism requires replication fork convergence, but does not involve DNA incisions-instead the acetaldehyde crosslink itself is broken. The Y-family DNA polymerase REV1 completes repair of the crosslink, culminating in a distinct mutational spectrum. These results define the repair pathways of DNA interstrand crosslinks caused by an endogenous and alcohol-derived metabolite, and identify an excision-independent mechanism. DNA interstrand crosslinks induced by acetaldehyde are repaired by both the Fanconi anaemia pathway and by a second, excision-independent repair mechanism.