TNF-α hypersensitivity of Fancc^-/- hematopoietic progenitors is dependent on Ask1 and p38. (A) TNF-α-induced apoptosis in c-kit⁺ cells. WT and Fancc^-/- c-kit⁺ cells were pretreated with SeMet or were cultured in normal conditions before 24-hour exposure to 10 ng/mL TNF-α. Cytospins of cells from each experimental group were made before apoptosis was analyzed using a TUNEL assay (n = 3; ^*P ≤ .006). (B) TNF-α sensitivity of hematopoietic progenitors. WT, Fancc^-/-, and Fancc^-/-; Ask1^-/- low-density BM cells were cultured in colony assays with increasing concentrations of TNF-α (n = 4 mice/genotype; ^*P ≤ .05). (C) TNF-α sensitivity of hematopoietic progenitors. WT and Ask1^-/- low-density BM cells were cultured in colony assays with increasing concentrations of TNF-α (n = 5 mice/genotype). (D) p38 inhibitor and progenitor assays. WT and Fancc^-/- low-density BM cells were cultured in colony assays with SB203580 or vehicle control and increasing concentrations of TNF-α (n = 6 mice/genotype; ^*P ≤ .001). All data points shown represent the mean of multiple experiments, and error bars represent SD.