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. 2015 Dec 21;16(12):30405–30421. doi: 10.3390/ijms161226238

Figure 6.

Figure 6

Inhibition of the 26S proteasome and sub-lethal irradiation can enhance sensitivity to killing through FAS and TRAIL receptors in colorectal carcinoma cells, but not in CCD-18Co cells. Tumor cells were mock-irradiated (0 Gy) or irradiated with 5 Gy and cultured for 24 h. Following incubation, mock-irradiated or irradiated cells were treated with 10 nM bortezomib and incubated for an additional 24 h. The tumor cells were then incubated for 3 h with agonistic anti-Fas antibody (FASL) or recombinant TRAIL protein. Control cells were incubated with IgM isotype control antibody. Cells were subsequently fixed and permeabilized before being stained for intracellular active caspase-3 with a PE-labeled monoclonal antibody. The level of activated caspase-3 was evaluated by flow cytometry. Isotype control stained cells were analyzed for each treatment group individually and set to 5% positive. Graph shows average of three independent experiments, with error bars denoting SEM * p < 0.05, *** p < 0.0005. Percentage of active caspase-3 in (A) CCD-18Co, (B) SW620, (C) and HTC116 cells inhibition sensitizes tumor cells to Fas or TRAIL mediated killing possibly through enhancing cell surface expression of death receptors, which sensitizes tumor cells to killing by their ligands.