The RL-ET-14 cell line mediates expression of glutamine synthetase through the upstream enhancer/promoter region.

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 β-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 −2.5kb and that the signal mediator required a functional β-catenin pathway. Conclusions The ‘RL-ET-14' factor specifically induces GS expression, working via its upstream enhancer in a β-catenin-dependent fashion.