sto-609 and saponarin

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.

Topics: AMP-Activated Protein Kinases; Apigenin; Benzimidazoles; Biphenyl Compounds; Calcium; Calcium-Calmodulin-Dependent Protein Kinase Kinase; Cyclic AMP Response Element-Binding Protein; Enzyme Activators; Forkhead Box Protein O1; Forkhead Transcription Factors; Gluconeogenesis; Glucose; Glucose Transporter Type 4; Glucosides; Hep G2 Cells; Histone Deacetylases; Humans; Insulin Resistance; Metformin; Naphthalimides; Phosphorylation; Pyrones; Thiophenes; Transcription Factors