Objective      To determine the effect of cucurbitacin E (CuE) on the apoptosis in human colonic cancer Caco-2 cells and investigate the underlying molecular mechanism.       Methods      The Caco-2 cells were treated with CuE at 0.001

0.01

0.1

1 and 10 μmol/L for 24

48 or 72 h respectively. The morphological changes of the nuclei were observed after Hoechst 33258 staining. The changes of cell apoptosis were detected by TUNEL assay and flow cytometry coupled with Annexin V-FITC/PI staining respectively. Western blot assay was used to detect the protein expression of Caspase-3

cleaved Caspase-3

PARP

cleaved PARP and Bcl-2.       Results      The results of both Hoechst 33258 staining and TUNEL assay showed that CuE obviously induced the apoptosis of Caco-2 cells in a dose- and time-dependent manner (P0.05). The results of flow cytometry coupled with Annexin V-FITC/PI staining revealed that with the increase of CuE dose

the proportion of apoptotic cells to total cells was increased significantly (P0.05). Western blot analysis showed that after treating Caco-2 cells with CuE for 24 h

the protein expression of Caspase-3 and PARP was obviously decreased

whereas that of cleaved Caspase-3 and cleaved PARP was significantly increased. Meanwhile

the expression of Bcl-2 protein was significantly decreased (P0.05).       Conclusion      CuE induces the apoptosis in human colonic cancer Caco-2 cells

which might be due to its inhibiting Bcl-2 expression

activating Caspase-3

and then triggering PARP cleavage.