Interferon-gamma-induced apoptotic responses of Fanconi anemia group C hematopoietic progenitor cells involve caspase 8-dependent activation of caspase 3 family members

Hematopoietic progenitor cells (HPC) from mice nullizygous at the Fanconi a nemia (FA) group C locus and children with Fanconi anemia group C (FA-C) ar e hypersensitive to interferon-gamma (IFN-gamma) and tumor necrosis factor- alpha. This hypersensitivity results, in part, from the capacity of these c ytokines to prime the fas pathway. Because fas-mediated programmed cell dea th in many cells involves sequential activation of specific caspases, we te sted the hypothesis that programmed cell death in FA HPC involves the order ed activation of specific caspase molecules. Lysates from lymphoblasts trea ted with both agonistic anti-fas antibody and IFN-gamma contained activated caspase 3 family members (caspases 3, 6, and 7), as well as caspase 8, whe reas activation of caspases 1, 2, 4, 9, and 10 was not detected. The apopto tic effects of fas agonists in IFN-gamma -treated human and murine FA-C cel ls were blocked when pretreated with inhibitors (ac-DEVD-cho, CP-DEVD-cho, Z-DEVD-FMK) of the caspase 3 protease. Inhibitors (ac-YVAD cho, CP-YVAD-cho , Z-YVAD-FMK) of caspase 1 did not block apoptosis or caspase 3 activation. Treatment of FA cells with the fluoromethyl ketone tetrapeptide caspase 8 inhibitor (ac-IETD-FMK) did suppress caspase 3 activation. A 4-fold greater fraction of IFN-induced FA-C cells expressed caspase 3 than FA-C cells com plemented by retroviral-mediated transfer of FANCC. Therefore fas-induced a poptosis in Fanconi anemia cells of the C type involves the activation of c aspase 8, which controls activation of caspase 3 family members and one dir ect or indirect function of the FANCC protein is to suppress apoptotic resp onses to IFN-gamma upstream of caspase 3 activation. (C) 2000 by The Americ an Society of Hematology.