Tumour necrosis factor α decreases glucose-6-phosphatase gene expression by activation of nuclear factor κB

The key insulin-regulated gluconeogenic enzyme G6Pase (glucose-6-phosphatase) has an important function in the control of hepatic glucose production. Here we examined the inhibition of G6Pase gene transcription by TNF (tumour necrosis factor) in H4IIE hepatoma cells. TNF decreased dexamethasone/dibtuyryl cAMP-induced G6Pase mRNA levels. TNFα, but not insulin, led to rapid activation of NFκB (nuclear factor κB). The adenoviral overexpression of a dominant negative mutant of IκBα (inhibitor of NFκB α) prevented the suppression of G6Pase expression by TNFα, but did not affect that by insulin. The regulation of G6Pase by TNF was not mediated by activation of the phosphoinositide 3-kinase/protein kinase B pathway, extracellular-signal-regulated protein kinase or p38 mitogen-activated protein kinase. Reporter gene assays demonstrated a concentration-dependent down-regulation of G6Pase promoter activity by the transient overexpression of NFκB. Although two binding sites for NFκB were identified within the G6Pase promoter, neither of these sites, nor the insulin response unit or binding sites for Sp proteins, was necessary for the regulation of G6Pase promoter activity by TNFα. In conclusion, the data indicate that the activation of NFκB is sufficient to suppress G6Pase gene expression, and is required for the regulation by TNFα, but not by insulin. We propose that NFκB does not act by binding directly to the G6Pase promoter.