NVP-LAQ824 inhibits proteasome activity. (A) Whole-cell extracts were analyzed for levels of polyubiquitin conjugates by Western blot. Polyubiquitin conjugates were significantly increased at 10 hours, indicating inhibition of the 26S proteasome. (B) NVP-LAQ824 induced a time-dependent decrease in 20S proteasome activity, as determined by chymotrypsin-like proteasome activity at 10 hours (P = .001) and 24 hours (P = .0003). (C-D) NVP-LAQ824 inhibits NF-κB activation in a dose-dependent fashion, determined by EMSA and measured by densitometry. (E) There was no change in the levels of β5 proteasome subunits, even after 24-hour incubation with NVP-LAQ824, as determined by Western blot.