Figure 3.

Induction of apoptosis in human HCT-116 and SW480 colon cancer cells by curcumin. A, A cell-free caspase-3/-7 activity assay. HCT-116 and SW480 cells were treated with different curcumin concentrations (10, 20, and 30 µM) for 24 h, harvested and prepared whole cell extract was used for fluorescent detection of caspase-3/-7 activity (see Materials and Methods). Proteasome inhibitor MG132 was used as comparison with curcumin and the solvent, ethanol (E), was used as a control. Columns, mean of representative independent triplicate experiments; bars, SD. B, Western blot analysis. Cell extract from HCT-116 and SW480 cells treated with curcumin was analyzed by Western blot for PARP cleavage and Cyclin D1 detection (left and right panels). Proteasome inhibitor MG132 was used as comparison with curcumin (middle panel) and the solvent, ethanol (E), was used as a control. Actin was used as a loading control. Change in Cyclin D1 protein level was analyzed by densitometry and quantified using AlphaEase FC software. C, For TUNEL assay, HCT-116 and SW480 cells were treated for 24 h with 30 µM curcumin or ethanol (solvent) as a control. The TUNEL assay was performed by using an APO-DIRECT kit and the number of apoptotic (TdT positive) cells is indicated.