Identification of tumor necrosis factor as a transcriptional regulator of the phosphoenolpyruvate carboxykinase gene following endotoxin treatment of mice

Abstract

The decreased synthesis of hepatic phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting enzyme of gluconeogenesis, that occurs during endotoxemia was shown previously in rats to occur at the transcriptional level. In the current study, the exogenous administration of human recombinant tumor necrosis factor (TNF), a proximal mediator of endotoxic shock, reduced the PEPCK transcription rate, mRNAPEPCK levels, and PEPCK enzyme activity in a time- and dose-dependent manner in CD-1 mice. Comparable amounts of circulating TNF were measured in mice 2 h after injection of human recombinant TNF (10(5) U) or a 50% lethal dose of Escherichia coli endotoxin (20 mg/kg). Direct action of TNF to decrease the PEPCK transcription rate was confirmed in vitro with H-4-II-E Reuber hepatoma cells, in which a dose-dependent inhibition of PEPCK transcription was observed with 1 to 100 U of TNF per ml. A role for TNF-elicited changes in PEPCK gene expression during endotoxemia was confirmed by the protective effect of rabbit polyclonal antibodies to recombinant murine TNF. C57BL/6 mice passively immunized with anti-TNF 4 h prior to endotoxin challenge exhibited normal PEPCK enzyme activity. Neutralization of circulating TNF with anti-TNF failed, however, to prevent the hypoglycemia commonly observed during endotoxemia, suggesting the participation of other mediators. Anti-TNF treatment reduced circulating interleukins 1 and 6 at 3 and 6 h after endotoxin treatment, respectively. These results suggest that during endotoxemia, the development of hypoglycemia is multifaceted and that several cytokines are most likely involved. The findings from the Reuber hepatoma cell model afford an opportunity in future work to map putative cytokine response elements in the PEPCK promoter responsible for perturbed hormonal regulation of the gene during endotoxemia.