F-box DNA Helicase 1 (FBH1) Contributes to the Destabilization of DNA Damage Repair Machinery in Human Cancers

SIMPLE SUMMARY: Cancer cells are characterized by the accumulation of genetic mutations due to failures of the repair machinery. In some cases, excessive “repair” may cause DNA damage if the machinery runs amok and acts on DNA sequences that have not been damaged. In this report, we interrogate mutations in the FBH1 gene, which restrains homologous recombination, one mechanism of DNA double-strand break repair in eukaryotes. We find that mutations in FBH1 co-occur with mutations in the breast cancer susceptibility gene BRCA2 and other DNA damage repair genes. These findings suggest that FBH1 contributes to the general destabilization of the repair machinery in cancer cells. ABSTRACT: Homologous recombination (HR) is the major mechanism of rescue of stalled replication forks or repair of DNA double-strand breaks (DSBs) during S phase or mitosis. In human cells, HR is facilitated by the BRCA2-BRCA1-PALB2 module, which loads the RAD51 recombinase onto a resected single-stranded DNA end to initiate repair. Although the process is essential for error-free repair, unrestrained HR can cause chromosomal rearrangements and genome instability. F-box DNA Helicase 1 (FBH1) antagonizes the role of BRCA2-BRCA1-PALB2 to restrict hyper-recombination and prevent genome instability. Here, we analyzed reported FBH1 mutations in cancer cells using the Catalogue of Somatic Mutations in Cancers (COSMIC) to understand how they interact with the BRCA2-BRCA1-PALB2. Consistent with previous results from yeast, we find that FBH1 mutations co-occur with BRCA2 mutations and to some degree BRCA1 and PALB2. We also describe some co-occurring mutations with RAD52, the accessory RAD51 loader and facilitator of single-strand annealing, which is independent of RAD51. In silico modeling was used to investigate the role of key FBH1 mutations on protein function, and a Q650K mutation was found to destabilize the protein structure. Taken together, this work highlights how mutations in several DNA damage repair genes contribute to cellular transformation and immortalization.