FIG. 4.
NF-κB-mediated upregulation of FLIP protects from Fas-induced apoptosis. HT1080 wt or I-κBmut cells were pretreated for 2 h with TNF at 50 ng/ml, washed with fresh medium, and subsequently incubated in the presence of cross-linked FasL at 100 ng/ml for 8 h. Apoptosis was quantified by Hoechst staining. FLIP and TRAF1 protein contents were analyzed by immunoblot assay. Compared to Fig. 2, a longer exposure time was chosen to reveal the cleavage of FLIPL into its p43 fragment upon treatment with FasL. The values beside the lower left-hand images are molecular sizes in kilodaltons.