Phosphorylation of FANCD2 Inhibits the FANCD2/FANCI Complex and Suppresses the Fanconi Anemia Pathway in the Absence of DNA Damage

Abstract

Summary: Interstrand crosslinks (ICLs) of the DNA helix are a deleterious form of DNA damage. ICLs can be repaired by the Fanconi anemia pathway. At the center of the pathway is the FANCD2/FANCI complex, recruitment of which to DNA is a critical step for repair. After recruitment, monoubiquitination of both FANCD2 and FANCI leads to their retention on chromatin, ensuring subsequent repair. However, regulation of recruitment is poorly understood. Here, we report a cluster of phosphosites on FANCD2 whose phosphorylation by CK2 inhibits both FANCD2 recruitment to ICLs and its monoubiquitination in vitro and in vivo. We have found that phosphorylated FANCD2 possesses reduced DNA binding activity, explaining the previous observations. Thus, we describe a regulatory mechanism operating as a molecular switch, where in the absence of DNA damage, the FANCD2/FANCI complex is prevented from loading onto DNA, effectively suppressing the FA pathway. : Lopez-Martinez et al. describe a regulatory switch in the Fanconi anemia pathway. Phosphorylation of FANCD2 reduces the DNA binding activity of the FANCD2/FANCI complex, thereby preventing spurious activation of the pathway in the absence of DNA damage. Keywords: Fanconi anemia, interstrand crosslink repair, ICL repair, FANCD2/FANCI, genome stability, DNA repair, CK2, casein kinase 2, phosphorylation, kinase