Inhibition of TRAIL apoptosis by c-FLIP expression. (A) C1498 cells were transfected with a c-FLIP expression plasmid as described in “Materials and methods.” Cells were then cloned, and the levels of expression of the Flag-tagged c-FLIP and native c-FLIP in C1498 cells and representative clones 1, 2, and 3 were determined by Western blotting with an antibody to c-FLIP. (B) C1498 cells and clones 1, 2, and 3 were labeled with [¹¹¹In] Ox. Cells were then incubated with media (□), PS-341 at 10 nM (▦), or PS-341 at 10 nM for 2 hours prior to the addition of 200 ng/mL TRAIL (▪). After a further 16 hours, cell lysis (± SEM) was estimated as described in “Materials and methods.” *P < .001 by Student t test when compared with C1498 cells.