Transcriptional regulation of the rat glutamine synthetase gene by tumor necrosis factor-alpha

The expression of glutamine synthetase (GS) is induced in rat skeletal muscle cells (L-6) in response to treatment with the inflammatory cytokine tumor necrosis factor alpha (TNF-alpha). This paper reports the regulation of GS expression in rat skeletal muscle which expresses high levels of GS. TNF-alpha treatment leads to a 3-4-fold increase in GS activity in a dose-dependent and time-dependent manner. Northern-blot analysis of GS mRNA revealed an increased mRNA concentration, reaching a peak at 12 h in response to TNF-alpha treatment. To monitor transcriptional activation of GS by TNF-alpha, and to identify a TNF-alpha-responsive element in the GS promoter, L6 cells were treated with TNF-alpha following transfection of GS-chloramphenicol-acetyltransferase (CAT) constructs. The first 251-bp fragment at the GS upstream sequence showed basal promoter activity, but failed to show any TNF-alpha-inducible activity. However, a 2.5-3-fold induction was noted in constructs extending up to 1.1 kb. This data demonstrates that the rat GS gene is transcriptionally regulated by TNF-alpha and identifies a TNF-alpha-responsive region at the 5' flanking sequence of the GS gene.