Figure 5.

Haem oxygenase (HO)‐1 induction contributed to cobalt protoporphyrin (CoPP)‐induced cell death of human colorectal carcinoma cells. (A), CoPP exhibited the most potent cytotoxicity against human colorectal carcinoma cells. Three metal protoporphyrins including CoPP, ferric protoporphyrin (FePP) and tin protoporphyrin (SnPP) were used. Cells were treated with different concentrations (4, 8 and 16 µmol/L) of the indicated chemicals for 12 h, and the viability of indicated cells was examined by an MTT assay. (B), CoPP, but not FePP or SnPP, induced HO‐1 protein expression in LOVO, HCT‐15 and COLO205 cells. As described in (A), the level of the HO‐1 protein was examined by Western blotting. (C), Knockdown of HO‐1 protein expression reversed the cytotoxicity elicited by CoPP in human colorectal carcinoma cells. Cells were transfected with scrambled or HO‐1 siRNA for 24 h followed by CoPP (8 µmol/L) stimulation. The viability of indicated cells was examined by an MTT assay (upper panel), and decreased expression of the HO‐1 protein in HO‐1 siRNA‐treated cells was observed (lower panel). The intensity of HO‐1 protein was quantitated with normalization to α‐TUB by a densitometric analysis (ImageJ), and expressed as folds of control (C). Data from three independent experiments were obtained, and results are shown as the mean ± SD. **P < 0.01 denotes a significant difference from the control (CON) group (A) or between indicated groups (C)