P388 cells were treated with 2 μmol/L of shikonin for different hours, followed by measurement of the protesomal CT-like activity (A) and Western blotting analysis using specific antibodies against ubiquitinated proteins (Ub-prs), PARP, GAPDH (loading control, B) and annexin-PI binding assay (C). Columns, means of independent triplicate experiments; bars, SD. Cell death rate (%) was shown.