Figure 4.

Inhibition of the proteasome activity by the pro-drug form of lovastatin and lactacystin. Cell extracts were prepared from either MDA-MB-157 cells (A) without drug treatment or (B) treated with either lovastatin (lov) (40 μM), pro-drug (40 μM), or lactacystin (lact) (1 μM) in the presence or absence of mevalonate (mev) (5 mM) for 36 hr and assayed for proteasome enzyme activity. The extracts in A were incubated in the presence of the indicated concentrations of the drugs for 20 min at 37°C at which point the fluorogenic peptide substrate (100 μM final concentration) for the chymotrypsin-like activity of the proteasome (i.e., Suc-LLVY-AMC) was added to extracts. The fluorescence assays (excitation/emission 380/440 nm) were conducted at 37°C for 750 sec, and n = 3. The pretreated extracts in B were not further incubated in the presence of the inhibitors and were directly assayed for the proteasome activity. ■, lactacystin; ○, pro-drug; ●, lovastatin; □, pravastatin.