Transcriptional regulation of the rat glutamine synthetase gene by tumor necrosis factor‐α

Abstract

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 α (TNF‐α). This paper reports the regulation of GS expression in rat skeletal muscle which expresses high levels of GS. TNF‐α 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‐α treatment. To monitor transcriptional activation of GS by TNF‐α, and to identify a TNF‐α‐responsive element in the GS promoter, L6 cells were treated with TNF‐α 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‐α‐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‐α and identifies a TNF‐α‐responsive region at the 5′ flanking sequence of the GS gene.