Abstract:
Calcium signaling pathways play important roles in regulation of cellular processes in eukaryotes ranging from yeast to human. Because of the high degree in gene conservation from yeast to human, the small molecule inhibitors effectively function in yeast might exert their function in human as well. Our previous studies using a ∆zds1 yeast-based assay could identified a flavonoid 5-hydroxy-3,7-dimethoxyflavone (5-OH-3,7-DMF) from Kaempferia parviflora Wall. Ex. Baker showed inhibitory activity against the Ca2+-signals in the mutant yeast YNS17 strain (Δ zds1). This study aimed to investigate biological activity of 5-OH-3,7-DMF related to calcium signaling pathways. Genetic analyses in several mutant yeast strains showed that Mck1, a protein kinase in the calcium signaling pathway, was the molecular target of the 5-OH-3,7-DMF. Yeast MCK1 is an ortholog GSK-3β gene coding for glycogen synthase kinase-3β in human. There were many reportes on the relationship between high expression level of GSK-3β and several pathogenesis including type 2 Diabetes and Alzheimer’s disease. 5-OH-3,7-DMF showed in vitro inhibitory activity against GSK-3β with an IC50 values of 9.72 ± 0.15 µM with 85.6 ± 7.41 % of inhibition. Interestingly, 5-OH-3,7-DMF showed ATP non-competitive binding mode to GSK-3β by Dixon plot (Ki = 13.04 μM) and substrate competitive binding mode to GSK-3β by Dixon plot (Ki = 53.92 μM). The treatment of insulin-resistant HepG2 cells model with crude extracted of K. parviflora (CE) or 5-OH-3,7-DMF caused a decrease in G6Pase gene expression and only 5-OH-3,7-DMF could recover glycogen levels through decreasing phosphorylation of glycogen synthase (GS) protein. Moreover, when the cells grown in high glucose-high insulin (HGHI) medium treated with 5-OH-37-DMF, phosphorylation of GSK-3 was abolished as comparable values to those of controls (LiCl and GSK-3β inhibitor I). These findings indicated that 5-OH-3,7-DMF might be a potential GSK-3 inhibitor that modulates the glucose homeostasis and might be potential for type II diabetes drug development.
