Proteasome inhibition of C1498 and Renca by PS-341. C1498 (A) and Renca (B) cells were incubated for 2 hours (⋄) or 18 hours (▵) in the presence or absence of various concentrations of PS-341. Cells were washed, and proteasome enzymatic activity (± SEM) was determined as described in “Materials and methods.”