Phosphorylation of FANCA on S1449 is important for Fanconi anemia (FA) pathway function

Fanconi anemia (FA) is a rare genetic disorder characterized by congenital defects, aplastic anemia, and a predisposition to cancer. Cells from FA patients display genome instability and a hypersensitivity to DNA crosslinking agents such as mitomycin C (MMC). Exact functions of the proteins involved in the FA pathway remain elusive, but several lines of evidence suggest that FA proteins are involved in the cellular response to DNA damage. Previous work has shown that the FA protein, FANCA, is phosphorylated after DNA damage and localized to chromatin, but the site and significance of this phosphorylation were previously unknown. Mass spectrometry of FANCA revealed one phosphopeptide with phosphorylation on Serine 1449. Mutation of this residue to alanine (S1449A) abolished a slower mobility form of FANCA seen after MMC treatment. Furthermore, the S1449A mutant failed to completely correct the MMC hypersensitivity of FA‐A mutant cells, demonstrating that S1449 is a functionally important phosphorylation site. In addition, S1449A mutant cells displayed lower than wild‐type levels of FANCD2 monoubiquitination following DNA damage, further indicating impaired FA pathway function. The DNA damage response is, in large part, coordinated by phosphorylation events initiated by apical kinases ATM and ATR. S1449 is found in a consensus ATM site, therefore studies are underway to determine if ATM or ATR is the kinase responsible for FANCA phosphorylation at S1449. Phosphorylation is a crucial process in transducing the DNA damage response, and phosphorylation of FA proteins appears critical to both localization and function of the proteins. Understanding how phosphorylation marks are placed on FANCA will give insight into the role of FANCA in the DNA damage response.