Effects of PS-341 on NF-κB activity. Cells were transfected with either the pTATA-luc or the pNF-κB-luc plasmids. After a recovery period of 36 hours, transfectants were treated with various concentrations of PS-341 (20 nM), SN50 (50 μg/mL), or Helenalin (5 μM) for 2 hours followed by a further 4 hours in the presence or absence of TRAIL (1 μg/mL). Relative levels of NF-κB—driven promoter activity in C1498 (A) or A20 (B) were then calculated (± SEM) as previously described in “Materials and methods.”