Rev-erbα activation down-regulates hepatic Pck1 enzyme to lower plasma glucose in mice

REV-ERB alpha (NR1D1) is a nuclear heme receptor that controls many cellular processes including cell differentiation, lipid metabolism, and inflammatory responses. Although REV-ERB alpha has been also implicated in regulation of glucose homeostasis, the mechanism for this regulation remains unclear. Here we investigate a potential role of REV-ERB alpha in regulation of PCK1 (phosphoenolpyruvate carboxykinase 1), a rate-limiting enzyme in gluconeogenesis. Hepatoma cells (Hepa-1c1c7 and HepG2 cells), wild-type mice and streptozotocin-induced diabetic mice were treated with SR9009, a specific REV-ERB alpha agonist. The relative mRNA and protein levels of enzymes in the cells or mouse livers were determined by qPCR and Western blotting, respectively. The fasting plasma glucose test was performed to determine the effects of Rev-erb alpha on glucose homeostasis. Transcriptional regulation of Pck1 by Rev-erb alpha was investigated using a combination of luciferase reporter, mobility shift, and chromatin immunoprecipitation (ChIP) assays. SR9009 treatment significantly decreased the mRNA level of Pck1 in mouse hepatoma Hepa-1c1c7 cells, whereas other major enzymes involved in gluconeogenesis (pyruvate carboxylase, glucose-6-phosphatase, fructose bisphosphatase and Pck2) and in glycolysis (phosphofructokinase and hexokinase-1) were unaffected. Consistent with the mRNA change, the protein level of Pck1 was down-regulated. Similarly, a repressive action of REV-ERB alpha on PCK1 expression was observed in human HepG2 hepatoma cells. SR9009 administration to wild-type or diabetic mice significantly reduced the level of fasting plasma glucose. This coincided with decreased mRNA and protein levels of Pck1 in the liver. In addition, the diabetic mice showed an improvement in glucose tolerability after SR9009 treatment. Promoter analysis, mobility shift, and ChIP assays revealed that Rev-erb alpha trans-repressed Pck1 through direct binding to -325 to -320 bp region (a RevRE site) in the gene promoter. In conclusion, Rev-erb alpha activation down-regulates hepatic Pck1 to lower plasma glucose.