MxA overexpression reveals a common genetic link in four Fanconi anemia complementation groups

Fanconi anemia (FA) consists of a group of at least five autosomal recessive disorders that share both clinical (e.g., birth defects and hematopoietic failure) and cellular (e.g., sensitivity to cross-linking agents and predisposition to apoptosis) features with each other. However, a common pathogenetic link among these groups has not been established. To identify genetic pathways that are altered in FA and characterize shared molecular defects, we used mRNA differential display to isolate genes that have altered expression patterns in FA cells. Here, we report that the expression of an interferon-inducible gene, MxA, is highly upregulated in cells of FA complementation groups A, B, C, and D, but it is suppressed in FA group C cells complemented with wild-type FAC cDNA as well as in non-FA cells. A posttranscriptional mechanism rather than transcriptional induction appears to account for MxA overexpression. Forced expression of MxA in Hep3B cells enhances their sensitivity to mitomycin C and induces apoptosis, similar to the FA phenotype. Thus, MxA is a downstream target of FAC and is the first genetic marker to be identified among multiple FA complementation groups. These data suggest that FA subtypes converge onto a final common pathway, which is intimately related to the interferon signaling mechanism. Constitutive activity of this pathway may explain a number of the phenotypic features of FA, particularly the pathogenesis of bone marrow failure.