Role of double-stranded RNA-dependent protein kinase in mediating hypersensitivity of Fanconi anemia complementation group C cells to interferon gamma, tumor necrosis factor-alpha, and double-stranded RNA

Hematopoietic cells bearing inactivating mutations of Fanconi anemia group C (FANCC) are excessively apoptotic and demonstrate hypersensitivity not on ly to cross-linking agents but also to interferon gamma (IFN-gamma) and tum or necrosis factor-alpha. Seeking essential signaling pathways for this phe notype, this study quantified constitutive and induced RNA-dependent protei n kinase (PKR) activation in Fanconi anemia cells of the C complementation group (FA-C). PKR was constitutively phosphorylated and exhibited an increa sed binding affinity for double-stranded RNA (dsRNA) in FANCC(-/-) cells. F ANCC(-/-) cells were hypersensitive to both dsRNA and the combination of ds RNA and IFN-gamma in that these agents induced a higher fraction of apoptos is in FANCC(-/-) cells than in normal cells. Overexpression of wild-type PK R-sensitized FANCC(-/-) cells to apoptosis induced by IFN-gamma and dsRNA. Conversely, inhibition of PKR function by enforced expression of a dominant -negative inhibitory mutant of PKR (PKR Delta6) substantially reduced the I FN and dsRNA hypersensitivity of FANCC(-/-) cells. Two PKR target molecules , I kappaB-alpha and IRF-1, were not differentially activated in FANCC(-/-) cells, but enforced expression of a nonphosphorylatable form of eukaryotic translation initiation factor-2 alpha reversed the PKR-mediated block of m essenger RNA translation and partially abrogated the PKR-mediated apoptosis in FANCC(-/-) cells. Because no evidence was found of a PKR/FANCC complex in normal cells, it was concluded that an essential function of FANCC is to suppress, indirectly, the activity of PKR and that FANCC inactivation resu lts in IFN hypersensitivity, at least in part, because this function of FAN CC is abrogated. (Blood. 2001;97: 1644-1652) (C) 2001 by The American Socie ty of Hematology.