Caffeic acid phenethyl ester down-regulates claudin-2 expression at the transcriptional and post-translational levels and enhances chemosensitivity to doxorubicin in lung adenocarcinoma A549 cells

Claudin-2 is highly expressed in human lung adenocarcinoma cells and involved in the promotion of proliferation. Here, we searched for a compound, which can decrease claudin-2 expression using lung adenocarcinoma A549 cells. In the screening using compounds included in royal jelly and propolis, the protein level of claudin-2 was dose-dependently decreased by caffeic acid phenethyl ester (CAPE), whereas the mRNA level and promoter activity were only decreased by 50 mu M CAPE. These results suggest that CAPE down-regulates claudin-2 expression mediated by two different mechanisms. CAPE (50 mu M) decreased the level of p-NF-kappa B, whereas it increased that of I kappa B. The CAPE-induced decrease in promoter activity of claudin-2 was blocked by the mutation in an NF-kappa B-binding site. The inhibition of NF-kappa B may be involved in the decrease in mRNA level of claudin-2. The CAPE (10 mu M)-induced decrease in claudin-2 expression was inhibited by chloroquine, a lysosomal inhibitor. CAPE increased the expression and activity of protein phosphatase (PP) 1 and 2A The CAPE-induced decrease in claudin-2 expression was blocked by cantharidin, a potent PPs inhibitor. The cell proliferation was suppressed by CAPE, which was partially rescued by ectopic expression of claudin-2. In addition, the toxicity and accumulation of doxorubicin in 3D spheroid cells were enhanced by CAPE, which was inhibited by ectopic expression of claudin-2. Taken together, CAPE downregulates claudin-2 expression at the transcriptional and post-translational levels, and enhances sensitivity of cells to doxorubicin in 3D culture conditions. CAPE may be a useful adjunctive compound in the treatment of lung adenocarcinoma. (C) 2018 Elsevier Inc. All rights reserved.