Elevation of sensitivity to anticancer agents of human lung adenocarcinoma A549 cells by knockdown of claudin-2 expression in monolayer and spheroid culture models.

Claudins, tight junctional proteins, regulate the paracellular permeability of ions and small molecules. Claudin-2 is highly expressed in human lung adenocarcinoma cells and is involved in the up-regulation of cell proliferation. However, the effect of claudin-2 on cellular sensitivity to anticancer agents has not been clarified. The cytotoxicity of anticancer agents such as cisplatin, gefitinib and doxorubicin (DXR) was increased by claudin-2 knockdown in A549 cells. Claudin-2 knockdown also significantly decreased the expression level of multidrug resistance-associated protein/ABCC2. The expression levels of other drug efflux transporters were unchanged. The intracellular accumulation of 5-chloromethylfluorescein diacetate (CMFDA) and DXR, substrates of ABCC2, was increased by claudin-2 knockdown, whereas the efflux was decreased. MK-571, an inhibitor of ABCC2, enhanced the cytotoxicity of anticancer agents. Claudin-2 knockdown decreased the levels of p-c-Jun and nuclear Sp1. SP600125, an inhibitor of c-Jun, and mithramycin, an inhibitor of Sp1, decreased the level of ABCC2. The promoter activity of ABCC2 was decreased by claudin-2 knockdown, SP600125 and mithramycin treatments, suggesting that claudin-2 is involved in the up-regulation of ABCC2 expression at the transcriptional level. Claudin-2 knockdown increased the paracellular permeability of DXR in a 2D monolayer culture model. In addition, the accumulation of DXR into spheroids was enhanced by claudin-2 knockdown, resulting in a reduction in cell viability. We suggest that claudin-2 may be a novel therapeutic target in lung adenocarcinoma, because claudin-2 knockdown increased the accumulation of anticancer agents in cancer cells and spheroids.

MicroRNA-488 inhibits progression of colorectal cancer via inhibition of the mitogen-activated protein kinase pathway by targeting claudin-2.

Colorectal cancer (CRC) affects people globally, and lymph node metastasis (LNM) is an important indicator of poor clinical outcome in CRC. The current study aims to evaluate the role of microRNA-448 (miR-488) and claudin-2 (CLDN2) in epithelial-mesenchymal transition (EMT) and LNM of CRC through the MAPK signaling pathway. First, microarray analysis indicated that miR-488 was poorly expressed in CRC, whereas CLDN2 was highly expressed. Additionally, the bioinformatics website MicroRNA.org and the dual luciferase reporter gene assay found that CLDN2 was a target gene of miR-488. Next, the results for the correlations between expression of miR-488 and clinicopathological characteristics of CRC indicated that the expression of miR-488 was closely associated with differentiation degree, LNM, and Dukes stages in CRC patients. Moreover, overexpression of miR-488 inhibited the activation of the MAPK signal transduction pathway. Notably, loss- and gain-of-function experiments demonstrated that upregulation of miR-488 suppressed SW480 cell viability, invasion, and migration and promoted apoptosis in SW480 cells. Finally, overexpression of miR-488 inhibited LNM, microlymphatic vessel density, and tumor growth in nude mice. We conclude that overexpression of miR-488 could suppress the cell proliferation, EMT, and LNM of CRC cells via inhibition of the CLDN2-mediated MAPK signaling pathway, which could be a new molecular therapy target for CRC.

STAT6 deficiency ameliorates severity of oxazolone colitis by decreasing expression of claudin-2 and Th2-inducing cytokines.

Patients suffering from ulcerative colitis (UC) exhibit chronic colonic inflammation caused by a dysregulated mucosal immune response and epithelial barrier disruption. Th2 cytokines, including IL-13, have been implicated in the pathogenesis of UC. IL-13 induces phosphorylation of STAT6, and we previously demonstrated increased epithelial p-STAT6 in children with UC. In this study, we investigated the role of STAT6 in oxazolone colitis, a murine model of UC, by inducing colitis in STAT6-deficient (STAT6(-/-)) and wild type (WT) mice. We observed increased epithelial cell, T cell, macrophage, and NKT cell STAT6 phosphorylation, as well as increased p-STAT6(+) IL-13-producing NKT cells, in colitic WT mice. Colitis was attenuated in STAT6(-/-) mice, with improvements in weight, colon length, and histopathology. There was decreased induction of the pore-forming tight junction protein claudin-2 in STAT6(-/-) mice. Similarly, short hairpin RNA STAT6 knockdown reduced claudin-2 induction and transepithelial resistance decrease in IL-13-treated human T84 cells. Tissue expression of IL-13, IFN-γ, IL-17, and IL-10 mRNA was similarly induced in WT and STAT6(-/-) colitic mice; however, we observed increased mRNA expression for the Th2-inducing cytokines IL-33 and thymic stromal lymphopoietin in WT mice with colitis, which was abrogated in STAT6(-/-) mice. Mesenteric lymph node cells from STAT6(-/-) mice with colitis exhibited reduced secretion of IL-4, IL-5, IL-13, and IFN-γ. IL-33 augmented mesenteric lymph node cell secretion of IL-5, IL-13, IL-6, and IFN-γ. These data implicate STAT6 in the pathogenesis of colitis in vivo with important roles in altering epithelial barrier function and regulating Th2-inducing cytokine production.