AMP-activated protein kinase modulates the gene expression of aquaporin 9 via forkhead box a2.

Aquaporin 9 (AQP9) is permeable to glycerol, which is a source material in lipogenesis and gluconeogenesis in the liver. We investigated the transcriptional regulation of the AQP9 gene by AMP-activated protein kinase (AMPK), known as an energy sensor in cells since AMPK contributes to the metabolism of carbohydrate, lipid, and protein by regulating the expression of many enzymes and transcription factors in metabolic pathways. An AMPK activator, 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside (AICAR), was observed to suppress the expression of the AQP9 gene in HepG2 cells by promoting the phosphorylation of AMPK and AKT/PKB. Forkhead box a2 (Foxa2) was speculated to be one of the transcriptional regulators of AQP9 gene expression repressed by AICAR from the results of a reporter gene assay with a plasmid containing the promoter region of the AQP9 gene and knock-down of the Foxa2 gene by a specific siRNA. AICAR was determined to induce the phosphorylation and nuclear exclusion of Foxa2. Leptomycin B, inhibiting the binding of the nuclear exclusion signal sequence and chromosome region maintenance 1, prevented nuclear export of Foxa2 triggered by AICAR. These results suggest that the activated AMPK by AICAR causes suppression of the gene expression of AQP9 through transcriptional regulation by Foxa2.