Differential Regulation of Retinoic Acid Signaling in Fanconi Anemia

Abstract

Fanconi anemia (FA) is a rare genetic disease characterized by heterogeneous congenital defects, and increased risk for early‐onset bone marrow failure and cancer. Biallelic mutations in any one of 23 genes leads to FA. In vitro experiments have established a coordinated role for the FA gene network in the repair of DNA interstrand crosslinks (ICLs). However, the endogenous source(s) of DNA damage and chromosome instability in FA patients remain largely unknown. Recent studies have suggested that the FA proteins may play an important role in the repair of DNA damage caused by genotoxic reactive aldehydes produced during cellular metabolism, e.g., acetaldehyde and formaldehyde. To discover novel metabolic pathways linked to FA, we recently performed RNA‐seq analysis on telomerase‐immortalized mutant and functionally complemented FA‐D2 (FANCD2‐/‐) patient cells. Gene ontology enrichment analysis uncovered dysregulation of retinoid metabolism and retinoic acid signaling in mutant FA‐D2 (FANCD2‐/‐) cells. For example, we observed increased expression of the retinoid metabolism genes RDH10, ALDH1A1, and CYP26B1, in the absence of FANCD2. RDH10 converts retinol to retinaldehyde; ALDH1A1 converts retinaldehyde to retinoic acid; CYP26B1 degrades excess retinoic acid. In addition, we observed altered expression of multiple retinoic acid regulated genes including RARA, EGR1, and TGM2, and several members of the HOX, PAX, and SOX gene families. Using immunoblotting and qPCR, we have validated differential expression of many of these genes. We have also observed altered retinoid metabolism in Fancd2‐/‐ mouse cells. Furthermore, in preliminary flow cytometry experiments, we have determined that FA‐D2 (FANCD2‐/‐) patient cells exhibit increased aldehyde dehydrogenase activity. These findings are potentially highly significant and suggest that dysregulated retinoid metabolism and retinoic acid signaling ‐ as well as retinaldehyde‐associated genotoxicity ‐ might be key molecular features of FA. Further characterization of this newly discovered link could pave the way for the discovery of new therapeutic targets for FA patients.