Cadmium, Vectorial Active Transport, and MT-3–Dependent Regulation of Cadherin Expression in Human Proximal Tubular Cells

Previous studies from this laboratory have implicated the expression of the third isoform of metallothionein (MT-3) in the maintenance of proximal tubular vectorial active ion transport. It was shown that HK-2 cells have no expression of MT-3 and do not form domes in culture; whereas, the human proximal tubular (HPT) cells and HK-2 cells stably transfected with MT-3 [HK-2(MT-3)] form these structures. In the present study, this association was further explored by determining the effect of MT-3 expression on the expression of the E -, P -, N -, K -, and Ksp-cadherins. It was demonstrated that the HPT cells and HK-2(MT-3) cells had significant elevations in the expression of messenger RNA and protein for the E -, P -, and Ksp-cadherins compared with that of the HK-2 cells transfected with the blank vector [HK-2(blank vector)]. In contrast, the HK-2(blank vector) cells had significantly elevated expression of N- and K-cadherin compared with both the HPT and HK-2(MT-3) cell lines. These patterns of cadherin expression provide strong evidence that MT-3 might be involved in epithelial to mesenchymal transition that is postulated to occur during several disease states and in the mesenchymal to epithelial transition that occurs during normal kidney morphogenesis. A final goal of the study was to determine if Cd(+2) exposure influenced vectorial active transport of the proximal tubular cells and if this might occur through alterations in the expression of MT-3. It was shown that exposure to Cd(+2) eliminated vectorial active transport by the proximal tubular cell lines, but that Cd(+2) exposure did not reduce the expression of the MT-3 protein. The study shows that the level of MT-3 expression in HPT cells influences transepithelial resistance and cadherin expression but does not influence the Cd(+2)-induced loss of vectorial active transport.