title: Saponarin activates AMPK in a calcium-dependent manner and suppresses gluconeogenesis and increases glucose uptake via phosphorylation of CRTC2 and HDAC5.
abstract: This study investigated the molecular mechanism of saponarin, a flavone glucoside, in the regulation of insulin sensitivity. Saponarin suppressed the rate of gluconeogenesis and increased cellular glucose uptake in HepG2 and TE671 cells by regulating AMPK. Using an in vitro kinase assay, we showed that saponarin did not directly interact with the AMPK protein. Instead, saponarin increased intracellular calcium levels and induced AMPK phosphorylation, which was diminished by co-stimulation with STO-609, an inhibitor of CAMKKβ. Transcription of hepatic gluconeogenesis genes was upregulated by nuclear translocation of CRTC2 and HDAC5, coactivators of CREB and FoxO1 transcription factors, respectively. This nuclear translocation was inhibited by increased phosphorylation of CRTC2 and HDAC5 by saponarin-induced AMPK in HepG2 cells and suppression of CREB and FoxO1 transactivation activities in cells stimulated by saponarin. The results from a chromatin immunoprecipitation assay confirmed the reduced binding of CRTC2 on the PEPCK and G6Pase promoters. In TE671 cells, AMPK phosphorylated HDAC5, which suppressed nuclear penetration and upregulated GLUT4 transcription, leading to enhanced glucose uptake. Collectively, these results suggest that saponarin activates AMPK in a calcium-dependent manner, thus regulating gluconeogenesis and glucose uptake.
authors.affiliation: Crop Foundation Division, National Institute of Crop Science, Rural Development Administration, Wanju-Gun, Jeollabuk-do 565-851, Republic of Korea.
authors.forename: Woo-Duck
authors.initials: WD
authors.lastname: Seo
authors.affiliation: Department of Biotechnology, College of Life Sciences & Biotechnology, Korea University, Seoul 136-713, Republic of Korea; Department of Food Bioscience and Technology, College of Life Sciences & Biotechnology, Korea University, Seoul 136-713, Republic of Korea.
authors.forename: Ji Hae
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Biotechnology, College of Life Sciences & Biotechnology, Korea University, Seoul 136-713, Republic of Korea; Department of Food Bioscience and Technology, College of Life Sciences & Biotechnology, Korea University, Seoul 136-713, Republic of Korea.
authors.forename: Yaoyao
authors.initials: Y
authors.lastname: Jia
authors.affiliation: Department of Biotechnology, College of Life Sciences & Biotechnology, Korea University, Seoul 136-713, Republic of Korea; Department of Food Bioscience and Technology, College of Life Sciences & Biotechnology, Korea University, Seoul 136-713, Republic of Korea.
authors.forename: Chunyan
authors.initials: C
authors.lastname: Wu
authors.affiliation: Department of Biotechnology, College of Life Sciences & Biotechnology, Korea University, Seoul 136-713, Republic of Korea; Department of Food Bioscience and Technology, College of Life Sciences & Biotechnology, Korea University, Seoul 136-713, Republic of Korea. Electronic address: junelee@korea.ac.kr.
authors.forename: Sung-Joon
authors.initials: SJ
authors.lastname: Lee
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D047310:Apigenin / Q000494:pharmacology*; D001562:Benzimidazoles / Q000494:pharmacology; D001713:Biphenyl Compounds; D002118:Calcium / Q000378:metabolism; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D020536:Enzyme Activators / Q000494:pharmacology*; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000378:metabolism; D005943:Gluconeogenesis; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4 / Q000378:metabolism; D005960:Glucosides / Q000494:pharmacology*; D056945:Hep G2 Cells; D006655:Histone Deacetylases / Q000378:metabolism; D006801:Humans; D007333:Insulin Resistance; D008687:Metformin / Q000494:pharmacology; D053644:Naphthalimides / Q000494:pharmacology; D010766:Phosphorylation; D011753:Pyrones / Q000494:pharmacology; D013876:Thiophenes / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D001562:Benzimidazoles; D001713:Biphenyl Compounds; C115163:CREB1 protein, human; C493245:CRTC2 protein, human; D017362:Cyclic AMP Response Element-Binding Protein; D020536:Enzyme Activators; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D051275:Glucose Transporter Type 4; D005960:Glucosides; D053644:Naphthalimides; D011753:Pyrones; C495692:SLC2A4 protein, human; C458525:STO 609; D013876:Thiophenes; D014157:Transcription Factors; C457771:saponarin; D047310:Apigenin; D008687:Metformin; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase; D055372:AMP-Activated Protein Kinases; C404500:HDAC5 protein, human; D006655:Histone Deacetylases; D005947:Glucose; C512408:4-hydroxy-3-(4-(2-hydroxyphenyl)phenyl)-6-oxo-7H-thieno(2,3-b)pyridine-5-carbonitrile; D002118:Calcium
keywords: AMPK; Gluconeogenesis; Glucose uptake; Saponarin