Fanconi anemia proteins and the s phase checkpoint

DNA interstrand crosslinks (ICLs) repair represents a formidable task for mammalian cells. Indeed, such DNA lesions, bridging both opposite DNA helices, function as a road-block for every DNA transaction, in particular DNA replication. The eight Fanconi anemia (FA) proteins interact in a common pathway that is thought to be central in ICLs sensing/repair. Interestingly, FA cells, either mutated in one of the proteins composing the FA core complex or in the downstream FA protein FANCD2, exhibited a partial intra-S checkpoint defect in response to crosslinked DNA. Most importantly, the FA proteins work in the ATR-NBS1 branch of the ICL-induced checkpoint pathway as demonstrated by knocking-down CHK1 or MRE11 expression in a FA background. Even though our data disclose a clear functional role for the FA proteins in the intra-S checkpoint response it does not give a definite answer on what FA proteins do in this process and how they participate in the suppression/restart of DNA synthesis. It seems conceivable that FA proteins participate in the process involved in the recovery of stalled replication forks, a common event in proliferating cells, possibly ensuring correct replication fork repair by homologous recombination.