Figure 2

Apigenin-induced proteasomal inhibition and apoptosis in MDA-MB-231 breast cancer cells. (a) Inhibition of proteasomal chymotrypsin (CT)-like activity by apigenin in MDA-MB-231 cells. Cells were treated with various concentrations of apigenin for 24 hours, were harvested and were analyzed for the proteasomal chymotrypsin-like activity in cell extracts. (b) Western blot analysis for accumulation of ubiquitinated proteins (Ub-Prs), Bax, IκBα and poly(ADP-ribose) polymerase cleavage (PARP) in the above prepared cell extracts after 72 hours of treatment. Arrow, ubiquitinated IκBα (p56). Three independent experiments were performed and each individual experiment was tested in triplicate. Similar results were found with all experiments and the data shown represent one experiment; bars, standard deviation. DMSO, dimethylsulfoxide. *P < 0.05, **P < 0.01. The number under each band of the western blot indicates a quantitative analysis by densitometry. Quantitative number for IκBα included both bands of intact IκBα (p37) and ubiquitinated IκBα (p56).