Calreticulin (CRT) is a multifunctional Ca2+-binding molecular chaperone in the endoplasmic reticulum. In mammals, the expression level of CRT differs markedly in a variety of organs and tissues, suggesting that CRT plays a specific role in each cell type. In the present study, we focused on CRT functions in the kidney, where overall expression of CRT is quite low, and established CRT-overexpressing kidney epithelial cell-derived Madin-Darby canine kidney cells by gene transfection. We demonstrated that, in CRT-overexpressing cells, the morphology was apparently changed, and the original polarized epithelial cell phenotype was destroyed. Furthermore, CRT-overexpressing cells showed enhanced migration through Matrigel®-coated Boyden chamber wells, compared with controls. E-cadherin expression was significantly suppressed at the protein and transcriptional levels in CRT-overexpressing cells compared with controls. On the other hand, the expression of mesenchymal protein markers, such as N-cadherin and fibronectin, was up-regulated. We also found that the expression of Slug, a repressor of the E-cadherin promoter, was up-regulated by overexpression of CRT through altered Ca2+ homeostasis, and this led to enhanced binding of Slug to the E-box element in the E-cadherin promoter. Thus, we conclude that CRT regulates the epithelial-mesenchymal transition-like change of cellular phenotype by modulating the Slug/E-cadherin pathway through altered Ca2+ homeostasis in cells, suggesting a novel function of CRT in cell-cell interaction of epithelial cells.
Epithelial to Mesenchymal Transition in Madin-Darby Canine Kidney Cells Is Accompanied by Down-regulation of Smad3 Expression, Leading to Resistance to Transforming Growth Factor-β-induced Growth Arrest
