Tumor necrosis factor α induces γ-glutamyltransferase expression via nuclear factor-κB in cooperation with Sp1

γ-Glutamyltransferase (GGT) cleaves the γ-glutamyl moiety of glutathione (GSH), an endogenous antioxidant, and is involved in mercapturic acid metabolism and in cancer drug resistance when overexpressed. Moreover, GGT converts leukotriene (LT) C4 into LTD4 implicated in various inflammatory pathologies. So far the effect of inflammatory stimuli on regulation of GGT expression and activity remained to be addressed. We found that the proinflammatory cytokine tumor necrosis factor alpha (TNFα) induced GGT promoter transactivation, mRNA and protein synthesis, as well as enzymatic activity. Remicade, a clinically used anti-TNFα antibody, small interfering RNA (siRNA) against p50 and p65 nuclear factor-kappaB (NF-κB) isoforms, curcumin, a well characterized natural NF-κB inhibitor, as well as a dominant negative inhibitor of kappaB alpha (IκBα), prevented GGT activation at various levels, illustrating the involvement of this signaling pathway in TNFα-induced stimulation. Over-expression of receptor of TNFα-1 (TNFR1), TNFR-associated factor-2 (TRAF2), TNFR-1 associated death domain (TRADD), dominant negative (DN) IκBα or NF-κB p65 further confirmed GGT promoter activation via NF-κB. Linker insertion mutagenesis of 536 bp of the proximal GGT promoter revealed NF-κB and Sp1 binding sites at -110 and -78 relative to the transcription start site, responsible for basal GGT transcription. Mutation of the NF-κB site located at -110 additionally inhibited TNFα-induced promoter induction. Chromatin immunoprecipitation (ChIP) assays confirmed mutagenesis results and further demonstrated that TNFα treatment induced in vivo binding of both NF-κB and Sp1, explaining increased GGT expression, and led to RNA polymerase II recruitment under inflammatory conditions.