BACKGROUND/AIMS: The expression of glutamine synthetase (GS) in the mammalian liver is confined to the hepatocytes surrounding the central vein and can be induced in cultures of periportal hepatocytes by co-cultivation with the rat-liver epithelial cell line RL-ET-14. We exploited these observations to identify the regulatory regions of the GS gene and the responsible signal-transduction pathway that mediates this effect. METHODS: Fetal hepatocytes of wild-type or GS-transgenic mice were co-cultured with RL-ET-14 cells to induce GS expression. Small-interfering RNA was employed to silence beta-catenin expression in the fetal hepatocytes prior to co-culture. RESULTS: Co-cultivation of RL-ET-14 cells with fetal mouse hepatocytes induced GS expression 4.2-fold. The expression of another pericentral enzyme, ornithine aminotransferase and a periportal enzyme, carbamoylphosphate synthetase, were not affected. Co-culture of RL-ET-14 cells with transgenic fetal mouse hepatocytes demonstrated that GS expression was induced via its upstream enhancer located at -2.5 kb and that the signal mediator required a functional beta-catenin pathway. CONCLUSIONS: The 'RL-ET-14' factor specifically induces GS expression, working via its upstream enhancer in a beta-catenin-dependent fashion.
de Kruithof Julio, M., Labruyere, W. T., Ruijter, J. M., Vermeulen, J. L., Stanulovic, V., Stallen, J. M., Baldysiak-Fiegel, A., Gebhardt, R., Lamers, W. H., & Hakvoort, T. B. M. (2005). The RL-ET-14 cell line mediates expression of glutamine synthetase through the upstream enhancer/promoter region. Journal of Hepatology, 43(1), 126-131. https://doi.org/10.1016/j.jhep.2005.01.036