The E3 ubiquitin ligase RFWD3 is mutated in a patient with Fanconi anemia lacking known Fanconi mutations.

  • Major finding: The E3 ubiquitin ligase RFWD3 is mutated in a patient with Fanconi anemia lacking known Fanconi mutations.

  • Concept: A Rfwd3−/− mouse model phenocopies other Fanconi anemia mouse models.

  • Impact:RFWD3 may be a Fanconi anemia gene, with biallelic inactivation resulting in Fanconi anemia.

RFWD3 is a WD40-containing E3 ubiquitin ligase that polyubiquitinates the homologous recombination (HR) protein replication protein A (RPA) to allow for productive DNA repair by HR. Knies and colleagues found biallelic germline mutations in RFWD3 in a patient with Fanconi anemia, a rare genomic instability disease that predisposes to cancer. She was determined to have Fanconi anemia, but sequencing did not detect mutations in any of the known downstream Fanconi anemia genes. Whole-exome sequencing uncovered two mutations in different parental alleles of RFWD3: a 2-bp duplication resulting in premature translation termination (c.205_206dupCC), and a missense mutation (c.1916T>A), both of which are predicted to be deleterious. Expression of wild-type RFWD3 in cells with these mutations reversed the genomic instability and HR defects, consistent with a role for RFWD3 in inducing Fanconi anemia. Mechanistically, the RFWD3 mutations impaired HR by preventing RFWD3 localization to chromatin and disrupting its interaction with RPA. In vivo, Rfwd3 knockout mice had a phenotype similar to that of other mouse models of Fanconi anemia including subfertility, ovarian and testicular atrophy, and a reduced lifespan. Furthermore, Rfwd3−/− mouse embryonic fibroblasts (MEF) were hypersensitive to DNA cross-linking agents and exhibited enhanced chromosomal breakage, reduced cell survival, and increased G2 cell-cycle arrest, which are also characteristics of cells lacking Fanconi anemia genes. The identification of biallelic germline RFWD3 mutations in a patient with Fanconi anemia, together with the phenotypes of the Rfwd3−/− mouse model and Rfwd3−/− MEFs, suggests that RFWD3 may be a Fanconi anemia gene (the authors nominate it as FANCW). Further clinical studies are warranted to determine the frequency of RFWD3 mutations in Fanconi anemia and elucidate its potential role in cancer susceptibility.

Knies K, Inano S, Ramírez MJ, Ishiai M, Surrallés J, Takata M, et al. Biallelic mutations in the ubiquitin ligase RFWD3 cause Fanconi anemia. J Clin Invest 2017 Jul 10 [Epub ahead of print].

©2017 American Association for Cancer Research.
2017
American Association for Cancer Research.