Fig. 1

Expression analysis and sensitivity testing of human colon carcinoma cell lines. Colon cancer cell line HT-29, SW480, SW620, HCT116 and CaCo-2 and human melanoma cell line Sk-Mel5 were characterized. a Quantitative real-time RT-PCR and western blot for claudin-3 (left) and claudin-4 expression (right), revealing high claudin-3 and -4 expression in HT-29 and HCT116, mediate claudin-3 expression in SW480 and SW620 and a strong claudin-3 expression in CaCo-2 and no claudin-3 or -4 expression in Sk-Mel5 cells. Columns: mean of triplicates, bars: SD. b Cell sensitivity toward recombinant CPE protein. Tumor cells were treated at indicated concentrations for 72 h. The cytotoxicity was determined by MTT assay and compared to untreated control. Strong cytotoxic effects were seen in all colon cancer cells. Claudin-negative cell line Sk-Mel5 was unaffected and used as negative control. All assays were performed in three independent experiments and expressed as mean percent of untreated control. Bars: SD. Level of significance was calculated by Student’s t-test; * P < 0.05, **; P < 0.001, *** P < 0.0001