Cellular processes that maintain the integrity of our genome are crucial to prevent genetic diseases such as cancer. The main interest of our laboratory is to decipher the molecular details of these processes. Currently, we focus on understanding: 1) how toxic DNA lesions, called interstrand crosslinks (ICLs), are repaired, and 2) how stable secondary DNA structures (G-quadruplexes) are resolved. We study these processes in the context of active DNA replication and make use of Xenopus egg extracts that support highly regulated vertebrate DNA replication in vitro.

In this seminar I will focus on the mechanism of repair of specific DNA interstrand crosslinks that are formed endogenously. One of the most well-known pathways in ICL repair is the Fanconi anemia pathway. This pathway currently consists of 21 proteins, and a defect in any of these causes the cancer predisposition disorder Fanconi anemia (FA). The FA pathway repairs DNA ICLs through an intricate mechanisms involving endonucleases, translesion polymerases and homologous recombination. Recently, a second ICL repair route was identified that involves the glycosylase Neil3. While the FA pathway has been shown to repair cisplatin and nitrogen mustard-induced ICLs, it is currently unclear what is the endogenous source of DNA lesions that causes FA. Recently, genetic studies have shown a clear link between reactive aldehydes and FA. However, these cellular metabolites induce various DNA lesions, including ICLs. To prove that endogenous aldehyde-induced ICLs can cause FA, it is crucial to show that the FA pathway acts on these lesions. 

Using a sequence-specific acetaldehyde-derived ICL (AA-ICL) situated on a plasmid, in combination with Xenopus egg extract, we examined AA-ICL repair. Surprisingly, we found that two different replication-dependent pathways can process this ICL. In agreement with the genetics, one repair route depends on the Fanconi anemia pathway. The other repair route shows some similarities with the recently described glycosylase pathway, but it does not depend on Neil3. Consistent with this, FANCL deficient cells are sensitive to acetaldehyde but additional loss of Neil3 does not enhance this sensitivity.

This data has two important implications: First, it shows that acetaldehyde-induced ICLs are repaired by the Fanconi anemia pathway. This strongly indicates that reactive aldehydes are the endogenous source of ICLs that can lead to Fanconi anemia. Second, in addition to the incision and glycosylase pathways, a third replication-dependent ICL repair pathway exists.