The hypersensmvity of fanconi anemia hematopoietic progenitor cells to interferon-γ involves the activation of caspases 3 and 8, but not caspase 1

Hematopoietic progenitor cells (HPC) from mice nullizygous at the Fanconi anemia (FA) Group C locus (FAC -/-) and children with the Ccomplementation group are hypersensitive to rnitotic inhibitory factors, including interferon-y (IFN-y) Low doses of Interferon that have no effects on normal bone marrow cells profoundly suppress clonal growth, induce both fas and Interferon response factor-1 (IRF-1) gene expression, and induce apoptosis via the fas pathway. Because fasmadiated programmed cell death in many cells involves sequential activation of caspases, we sought to test the hypothesis that programmed cell death in hematopoietic progenitor cells from mice and children with Fanconi anemia of the group C type involves the ordered activation of specific caspase molecules. HSC536N E8Vtransformed lymphoblasls treated with an agonistic fas antibody (100 ng/ml) and IFN-y (1 ng/ml) contain activated caspase 3 [CPP32, Apopaln, YAMA] by 60 minutes and PARP cleavage products by 180 minutes, as determined by immunoblot analysis. The apoptotic effect of fas agonists in IFN-γ-treated FA-C CD34⁺ cells and HSC536N EBVtransformed lymphoblasts was blocked when the cells were pretreated with a tetrapeptide aldehyde inhibitor of caspase 3 (ac-DEVD-cho)(50 iM). Treatment with an inhibitor of caspase 1 [interteukin-1 p converting enzyme, (ICE)] (ac-YVAD-cho)(50 nM) did not block apoptosis. Murine FA-C -/- HPC primed with IFN-γ (SO units/ml) consistently showed an increase in clonal growth in response to the addition of an inhibitor of caspase 3. Caspase 1 was not cleaved by fas antibody treatment of either IFN-γ primed murine or human cells and the caspase 1 inhibitor did not prevent caspase 3 cleavage in these same cells. An inhibitor of caspase 8 [FLICE](ac-IETD-cho)(50 uM), however, did supress caspase 3 cleavage in the lymphoblast cells. We conclude that fas-induced apoptosis in Fanconi anemia progenitor cells of the C type involves the activation of caspase 8, which is involved in caspase 1 independent activation of caspase 3.