ABSTRACT
Glycogen synthase kinase-3beta (GSK-3beta) is a key target and effector of downstream insulin signalling. Using comparative protein kinase assays and molecular docking studies we characterize the emodin-derivative 4-[N-2-(aminoethyl)-amino]-emodin (L4) as a sensitive and potent inhibitor of GSK-3beta with peculiar features. Compound L4 shows a low cytotoxic potential compared to other GSK-3beta inhibitors determined by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay and cellular ATP levels. Physiologically, L4 acts as an insulin-sensitizing agent that is able to enhance hepatocellular glycogen and fatty acid biosynthesis. These functions are particularly stimulated in the presence of elevated concentrations of glucose and in synergy with the hormone action at moderate but not high insulin levels. In contrast to other low molecular weight GSK-3beta inhibitors (SB216763 and LiCl) or Wnt-3alpha-conditioned medium, however, L4 does not induce reporter and target genes of activated beta-catenin such as TOPflash, Axin2 and glutamine synthetase. Moreover, when present together with SB216763 or LiCl, L4 counteracts expression of TOPflash or induction of glutamine synthetase by these inhibitors. Because L4 slightly activates beta-catenin on its own, these results suggest that a downstream molecular step essential for activation of gene transcription by beta-catenin is also inhibited by L4. It is concluded that L4 represents a potent insulin-sensitizing agent favouring physiological effects of insulin mediated by GSK-3beta inhibition but avoiding hazardous effects such as activation of beta-catenin-dependent gene expression which may lead to aberrant induction of cell proliferation and cancer.
Subject(s)
Emodin/pharmacology , Glycogen Synthase Kinase 3/antagonists & inhibitors , Insulin/pharmacology , Protein Kinase Inhibitors/pharmacology , beta Catenin/metabolism , Animals , Axin Protein , Casein Kinase II/antagonists & inhibitors , Casein Kinase II/metabolism , Cell Death/drug effects , Cell Survival/drug effects , Cells, Cultured , Cytoskeletal Proteins/genetics , Cytoskeletal Proteins/metabolism , Emodin/analogs & derivatives , Emodin/chemistry , Fatty Acids/biosynthesis , Glycogen/metabolism , Glycogen Synthase Kinase 3/metabolism , Glycogen Synthase Kinase 3 beta , Hepatocytes/drug effects , Hepatocytes/enzymology , Humans , Inhibitory Concentration 50 , Mice , Models, Biological , Models, Molecular , Protein Stability/drug effects , Rats , TCF Transcription Factors/metabolism , Transcription, Genetic/drug effectsABSTRACT
Matrix metalloproteinases (MMPs) play an important role in physiological and pathological matrix remodeling. Here, we report that the natural anthraquinones, emodin, emodic acid, chrysazin, physcion, and rhein differentially inhibit several members of this enzyme family, the gelatinases MMP-2 and -9, and the collagenase MMP-13. The IC50 values determined by measuring the activities of human recombinant catalytic domains of these enzymes varied in the micromolar range. Emodin and emodic acid most potently inhibited MMP-9 with IC50 values of 15 and 10 microM, respectively. With MMP-13, emodic acid was 3-times less potent than emodin which showed a similar IC50 value (13 microM) as chrysazin. These results are of interest in view of the widespread medicinal use of anthraquinones and their derivatives.
