Four human FANCG polymorphic variants show normal biological function in hamster CHO cells

Fanconi anemia (FA) is a rare cancer predisposition disease caused by mutations in at least 12 genes encoding proteins that cooperate to maintain genomic integrity. Variants of FA genes, including FANCG, have been identified in human population screening, but their potential reduction in protein function and role in cancer susceptibility is unclear. To test for possible dysfunction, we constructed plasmids containing four FANCG polymorphisms found in the human population and introduced them in the Fancg-deficient (fancg) KO40 line derived from AA8 hamster CHO cells. Expression of wild-type human FANCG provided fancg cells with complete phenotypic correction as assessed by resistance to the DNA crosslinking agent mitomycin C (MMC), thus providing a sensitive test for detecting the degree of complementation activity for the FANCG variants. We found that all four variants conferred levels of mitomycin C resistance as well as restoration of monoubiquitination of Fancd2, a key indicator of a functional FA protein pathway, similar to those observed in wild-type transfectants. Under the same conditions, the L71P amino acid substitution mutant, identified in an FA patient, gave no complementation. Using this novel system for determining FANCG functionality, we detect no decrement in function of the human FANCG polymorphic variants examined.