Downregulation of chemoresistance by claudin-14 silencing in human colorectal cancer cells

An exceptional expression of claudins (CLDNs), tight junction (TJ) proteins, is observed in various solid cancer tissues. However, the pathophysiological roles of CLDNs have not been clarified in detail. CLDN14 is highly expressed in human colorectal cancer (CRC) tissues and cultured cancer epithelial cells. We found CLDN14 silencing decreased cell viability without affecting spheroid size in the three-dimensional (3D) spheroid model of DLD-1 cells derived from human CRC. Mitochondria activity and oxidative stress level were reduced by CLDN14 silencing. Furthermore, CLDN14 silencing decreased the expression levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and its target antioxidative genes. CLDN14 was colocalized with ZO-1, a scaffolding protein in the TJ. CLDN14 silencing induced the disruption of TJ barrier such as the reduction of transepithelial electrical resistance and elevation of fluxes of small molecules including glucose in two-dimensional (2D) cultured model,. The depletion of glucose induced the elevation of ROS generation, mitochondria activity, and Nrf2 expression. These results suggest that CLDN14 increases Nrf2 expression in spheroids mediated via the formation of paracellular barrier to glucose. The cytotoxicities of doxorubicin, an anthracycline anticancer drug, and oxaliplatin, a platinum-based agent, were augmented by an Nrf2 activator in 2D cultured cells. The anticancer drug-induced toxicity was enhanced by CLDN14 silencing in 3D spheroids. We suggest that CLDN14 may potentiate chemoresistance mediated by the suppression of paracellular glucose permeability and activation of the Nrf2 signaling pathway in CRC cells.