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Glutamine synthetase (GS) is expressed at high levels in subsets of cells in some tissues and at low levels in all cells of other tissues, suggesting that the GS gene is surrounded by multiple regulatory elements.We searched for such elements in the 2.5-kbupstreamregionand in the 2.6-kbfirst intronof theGSgene, usingFTO-2Bhepatoma andC2/7muscle cells as representatives of both cell types and transient transfec-tion assays as our tools. | Eur. J. Biochem. 270 206-212 2003 FEBS 2003 doi 10.1046 j.1432-1033.2003.03424.x Upstream and intronic regulatory sequences interact in the activation of the glutamine synthetase promoter Rocio M. Garcia de Veas Lovillo Jan M. Ruijter Wil T. Labruyere Theodorus B. M. Hakvoort and Wouter H. Lamers AMC Liver Center Academic Medical Center University of Amsterdam Amsterdam the Netherlands Glutamine synthetase GS is expressed at high levels in subsets of cells in some tissues and at low levels in all cells of other tissues suggesting that the GS gene is surrounded by multiple regulatory elements. We searched for such elements in the 2.5-kb upstream region and in the 2.6-kb first intron of the GS gene using FTO-2B hepatoma and C2 7 muscle cells as representatives of both cell types and transient transfection assays as our tools. In addition to the entire upstream region and entire intron an upstream enhancer module at -2.5 kb and 5 middle and 3 modules of the first intron were tested. The main effects of the respective modules and their combinatorial interactions were quantified using the analysis of variance anova technique. The upstream enhancer was strongly stimulatory the middle intron module strongly inhibitory and the 3 -intron module weakly stimulatory in both hepatoma and muscle cells. The 5 -intron module was strongly stimulatory in muscle cells only. The major new finding was that in both cell types the upstream enhancer and 5 -intron module needed to be present simultaneously to fully realize their transactivational potencies. This interaction was responsible for a pronounced inhibitory effect of the 5 -intron module in the absence of the upstream enhancer in hepatoma cells and for a strong synergistic effect of these two modules when present simultaneously in muscle cells. The main difference between hepatoma and muscle cells therefore appeared to reside in tissue-specific differences in activity of the respective regulatory elements due to interactions .
