A role for the Fanconi anemia C protein in maintaining the DNA damage-induced G2 checkpoint

Fanconi anemia ( FA) is a complex, heterogeneous genetic disorder composed of at least 11 complementation groups. The FA proteins have recently been found to functionally interact with the cell cycle regulatory proteins ATM and BRCA1; however, the function of the FA proteins in cell cycle control remains incompletely understood. Here we show that the Fanconi anemia complementation group C protein (Fancc) is necessary for proper function of the DNA damage-induced G(2)/M checkpoint in vitro and in vivo. Despite apparently normal induction of the G(2)/M checkpoint after ionizing radiation, murine and human cells lacking functional FANCC did not maintain the G(2) checkpoint as compared with wild-type cells. The increased rate of mitotic entry seen in Fancc -/- mouse embryo fibroblasts correlated with decreased inhibitory phosphorylation of cdc2 kinase on tyrosine 15. An increased inability to maintain the DNA damage-induced G(2) checkpoint was observed in Fancc -/-; Trp53 -/- cells compared with Fancc -/- cells, indicating that Fancc and p53 cooperated to maintain the G(2) checkpoint. In contrast, genetic disruption of both Fancc and Atm did not cooperate in the G(2) checkpoint. These data indicate that Fancc and p53 in separate pathways converge to regulate the G(2) checkpoint. Finally, fibroblasts lacking FANCD2 were found to have a G(2) checkpoint phenotype similar to FANCC-deficient cells, indicating that FANCD2, which is activated by the FA complex, was also required to maintain the G(2) checkpoint. Because a proper checkpoint function is critical for the maintenance of genomic stability and is intricately related to the function and integrity of the DNA repair process, these data have implications in understanding both the function of FA proteins and the mechanism of genomic instability in FA.