Figure 5.

X/XO induces a concentration-dependent increase in mature IL-1β secretion and enhances ICE cleavage in differentiated mutant SOD1-positive cells. (a) After exposure of the cells to three different concentrations of X/XO for 4 hr at 37°C, secreted IL-1β was determined by ELISA and expressed as pg/ml per cell number. Each column of the histogram represents the mean ± SEM value of released IL-1β obtained from 9–12 single determinations. As shown by ∗, a statistical difference between untreated and X/XO-treated groups is observed only in mutant SOD1-expressing cells (P < 0.05). (b) Differentiated cells expressing either the WT hSOD1 or mutant hSOD1 were exposed to X/XO (100 μM X, 10 milliunits/ml XO). After 4 hr, the processing of ICE was detected by Western blotting using a polyclonal antibody against the p20 subunit. In WT-expressing cells, the antibody recognized only the p45 proactive form of ICE. The cleavage product (p20) is present in G37R-, G41D-, and G85R-positive cells after treatment with X/XO. In G41D- and G85R-expressing cells, the p20 product is also present without X/XO treatment and slightly increases after X/XO.