Caspase-8 proteolytic activity is not required for cytoplasmic dsRNA-induced signaling. (A). FLIP-/- MEFs were left untreated (lane 1), or treated with LF/poly(I:C) for 2 hours (lane 2), or pretreated for 1 hr with z-VAD-fmk (100 μM) followed by treatment with LF/poly(I:C) for 2 hours (lane 3). The cell lysates were then analyzed for procaspase-8 processing by immunoblot. (B). FLIP-/- MEFs were either left untreated or pretreated for 1 hr with z-VAD-fmk (100 μM) followed by LF/poly(I:C). After 4 hours the cells were analyzed by RT-PCR for expression of il-6, ifnb or ifna4 relative to gapdh. The data are representative of three experiments with similar findings.