FOXO1 and HNF-4 are involved in regulation of hepatic glucokinase gene expression by Resveratrol

Abstract

Resveratrol, a polyphenol derived from grapes, exerts important effects on glucose and lipid metabolism, yet detailed mechanisms mediating these effects remain unknown. The liver plays a central role in energy homeostasis, and glucokinase (GK) is a key enzyme involved in glucose utilization. Resveratrol activates SIRT1 (sirtuin 1), which promotes deacetylation of the forkhead transcription factor FoxO1. Previously, we reported that FoxO1 can suppress and that HNF-4 can stimulate GK expression in the liver. Here, we examined the role of FoxO1 and HNF-4 in mediating resveratrol effects on liver GK expression. Resveratrol suppressed hepatic GK expression in vivo and in isolated hepatocytes, and knocking down FoxO1 with shRNAs disrupted this effect. Reporter gene, gel shift, supershift assay, and chromatin immunoprecipitation studies show that FoxO1 binds to the GK promoter and that the interplay between FoxO1 and HNF-4 within the GK promoter is essential for mediating the effects of resveratrol. Resveratrol promotes deacetylation of FoxO1 and enhances its recruitment to the FoxO-binding element. Conversely, resveratrol suppresses recruitment of HNF-4 to its binding site, and knockdown of FoxO1 blocks this effect of resveratrol. Coprecipitation and chromatin immunoprecipitation studies show that resveratrol enhances interaction between FoxO1 and HNF-4, reduces binding of HNF-4 to its own site, and promotes its recruitment to the FoxO site in a FoxO1-dependent manner. These results provide the first evidence that resveratrol represses GK expression via FoxO1 and that the interaction between FoxO1 and HNF-4 contributes to these effects of resveratrol.The liver is a key organ in energy homeostasis, and glucokinase (GK) 3 plays a major role in promoting hepatic glucose utilization and maintenance of blood glucose homeostasis.Compared with other hexokinases, GK has a smaller molecular mass (100 versus 52 kDa, respectively) and a lower affinity for glucose, with an S 0.5 for glucose in the range of about 7-8 mmol/liter. Although GK binds to a regulatory protein (GKRP) and exists as a monomer, it displays sigmoidal kinetics with a Hill coefficient of about 1.5-1.7, indicating cooperativity with its substrate, glucose (1-3). These characteristics allow GK to react with glucose across the range of physiological glucose concentrations reached in vivo. Although GK is expressed predominantly in hepatocytes and pancreatic ␤-cells, it also is expressed in some neuroendocrine cells of the gastrointestinal tract and the brain, where it also may contribute to glucose sensing (4).In the liver, GK is expressed predominantly in the less aerobic perivenous zone (5), and its expression is stimulated by insulin (6). Previous studies indicate that several transcription factors, including USF-1 and -2 (upstream stimulatory factor-1 and -2) (7, 8), HIF-1 (hypoxia-inducible factor-1) (9), PPAR␥ (peroxisome proliferator-activated receptor-␥) (10), sterol regulatory element binding protein-1c (11,12), and hepatocyte nuclear factor-4␣ (HNF-4␣) (...