Down-Regulation of Claudin-2 Expression by Cyanidin-3-Glucoside Enhances Sensitivity to Anticancer Drugs in the Spheroid of Human Lung Adenocarcinoma A549 Cells

Claudin-2 (CLDN2), an integral membrane protein located at tight junctions, is abnormally expressed in human lung adenocarcinoma tissues, and is linked to drug resistance in human lung adenocarcinoma A549 cells. CLDN2 may be a target for the prevention of lung adenocarcinoma, but there are few compounds which can reduce CLDN2 expression. We found that cyanidin-3-glucoside (C3G), the anthocyanin with two hydroxyl groups on the B-ring, and cyanidin significantly reduce the protein level of CLDN2 in A549 cells. In contrast, pelargonidin-3-glucoside (P3G), the anthocyanin with one hydroxyl group on the B-ring, had no effect. These results suggest that cyanidin and the hydroxyl group at the 3-position on the B-ring play an important role in the reduction of CLDN2 expression. The phosphorylation of Akt, an activator of CLDN2 expression at the transcriptional level, was inhibited by C3G, but not by P3G. The endocytosis and lysosomal degradation are suggested to be involved in the C3G-induced decrease in CLDN2 protein expression. C3G increased the phosphorylation of p38 and the p38 inhibitor SB203580 rescued the C3G-induced decrease in CLDN2 expression. In addition, SB203580 rescued the protein stability of CLDN2. C3G may reduce CLDN2 expression at the transcriptional and post-translational steps mediated by inhibiting Akt and activating p38, respectively. C3G enhanced the accumulation and cytotoxicity of doxorubicin (DXR) in the spheroid models. The percentages of apoptotic and necrotic cells induced by DXR were increased by C3G. Our data suggest that C3G-rich foods can prevent the chemoresistance of lung adenocarcinoma A549 cells through the reduction of CLDN2 expression.