OBJECTIVE: To explore the effect of sodium tungstate on glucose metabolism in adipocytes and its mechanism. METHODS: After 3T3-L1 preadipocytes were differentiated into adipocytes, these adipocytes were incubated with sodium tungstate (0, 150, 300, 500, and 700 micromol/L) for 48 h, and then glucose consumption of the adipocytes was detected by glucose-oxidase assay. Glucose transport was determined by the uptake of 2-deoxy-[3H]-D-glucose, and the expression of glucose transport-4 (GLUT-4) mRNA was identified by semi-quantitative RT-PCR. RESULTS: Sodium tungstate (150 approximately 700 micromol/L) could significantly increase the glucose consumption and glucose transport with a concentration dependent-effect. Sodium tungstate could increase GLUT-4 mRNA expression. CONCLUSION Sodium tungstate can enhance the glucose metabolism of adipocytes by up-regulating the expression of GLUT-4 mRNA.
3T3-L1 Cells ; Adipocytes ; metabolism ; Animals ; Glucose ; metabolism ; Glucose Transporter Type 4 ; biosynthesis ; genetics ; Hypoglycemic Agents ; pharmacology ; Mice ; RNA, Messenger ; biosynthesis ; genetics ; Tungsten Compounds ; pharmacology ; Up-Regulation

Protein-tyrosine phosphatases (PTPs) constitute a family of receptor-like, and cytoplasmic enzymes, which catalyze the dephosphorylation of phosphotyrosine residues in a variety of receptors and signaling molecules. Together with protein tyrosine kinases (PTKs), PTPs are critically involved in regulating many cellular signaling processes. In this study, diverse compounds were screened for PTP inhibition and selectively screened for inhibitors with the end product inhibition properties. Among phosphate analogues and their derivatives for PTP inhibition, Keggin compounds phosphomolybdate (PM) and phosphotungstate (PT) strongly inhibited both PTP-1B and SHP-1, with K(i) values of 0.06-1.2 micromM in the presence of EDTA. Unlike the vanadium compounds, inhibition potencies of PM and PT were not significantly affected by EDTA. PM and PT were potent, competitive inhibitors for PTPs, but relatively poor inhibitors of Ser/Thr phosphatase. Interestingly, PM and PT did not inhibit alkaline phosphatase at all. The crystal structure of PTP-1B in complex with PM, at 2.0 A resolution, reveals that MoO(3), derived from PM by hydrolysis, binds at the active site. The molybdenium atom of the inhibitor is coordinated with six ligands: three oxo-ligands, two apical water molecules and a S atom of the catalytic cysteine residue. In support of the crystallographic finding, we observed that molybdenium oxides (MoO(3), MoO(2), and MoO(2)Cl(2)) inhibited PTP-1B with IC(50) in the range 5-15 micromM.
Binding, Competitive ; Catalytic Domain ; Crystallography, X-Ray ; Dose-Response Relationship, Drug ; Drug Evaluation, Preclinical ; Edetic Acid/pharmacology ; Enzyme Inhibitors/*pharmacology ; Human ; Inhibitory Concentration 50 ; Kinetics ; Models, Molecular ; Molybdenum/*pharmacology ; Phosphoric Acids/*pharmacology ; Protein Structure, Tertiary ; Protein-Tyrosine-Phosphatase/*antagonists & inhibitors/*chemistry/isolation & purification ; Substrate Specificity ; Tungsten Compounds/*pharmacology