Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The involvement of tyrosine phosphorylation in insulin action led us to hypothesize that increased activity of protein tyrosine phosphatases (PTPases) might contribute to insulin resistance in alloxan diabetes in the rat. Hepatic PTPase activity was measured using two artificial substrates phosphorylated on tyrosine: reduced, carboxyamidomethylated, and maleylated lysozyme (P-Tyr-RCML) and myelin basic protein (P-Tyr-MBP), as well as an autophosphorylated 48-kD insulin receptor tyrosine kinase domain (P-Tyr-IRKD). Rats that were made alloxan diabetic exhibited a significant increase in hepatic membrane (detergent-soluble) PTPase activity measured with P-Tyr-MBP, without a change in activity measured with P-Tyr-RCML or the P-Tyr-IRKD. The PTPase active with P-Tyr-MBP behaved as a high molecular weight peak during gel filtration chromatography. Characterization of this enzyme indicated it shared properties with CD45, the prototype for a class of transmembrane, receptor-like PTPases. Our results indicate that alloxan diabetes in the rat is associated with an increase in the activity of a large, membrane-associated PTPase which accounts for only a small proportion of insulin receptor tyrosine dephosphorylation. Nonetheless, increased activity of this PTPase may oppose tyrosine kinase-mediated insulin signal transmission, thus contributing to insulin resistance.
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PMID:Differential regulation of multiple hepatic protein tyrosine phosphatases in alloxan diabetic rats. 132 40

We examined the activities of particulate and cytosolic phosphotyrosine phosphatase (PTPase) and phosphoserine phosphatase (PSPase) in adipocytes and livers of diabetic rats. PTPase activity was assessed with [32P]tyrosine-phosphorylated insulin receptor (IR), whereas PSPase activity was assayed with [32P]serine-phosphorylated glycogen synthase. Diabetes increased adipocyte particulate PTPase activity and enhanced IR dephosphorylation by 75% on the 2nd, 93% on the 14th, and 108% on the 30th day. In contrast, cytosolic PTPase activity decreased by 78% on the 14th and 45% on the 30th day (no change on the 2nd day). Similar changes were observed with PSPase (increased activity in particulate and decreased in cytosolic). Insulin therapy for 14 or 30 days restored PTPase and PSPase activities in both fractions. Vanadate, despite rapid normalization of glycemia, restored these activities only after 30 days of therapy. Diabetes-related changes in liver PTPase activity were observed on the 14th day only. At this time, it was increased in both particulate and cytosolic fractions. There was spontaneous normalization of the liver PTPase activity at 30 days of diabetes. In contrast, liver cytosolic PSPase activity was significantly inhibited and not normalized by the 30th day of disease without therapy. In summary, diabetes appears to induce tissue-specific changes in PTPase and PSPase activities resulting in significant alterations in dephosphorylation of IR and glycogen synthase. Moreover, there appears to be a differential regulation of PTPase and PSPase activities in diabetes, particularly in the liver.
Diabetes 1991 Dec
PMID:Differential effects of diabetes on adipocyte and liver phosphotyrosine and phosphoserine phosphatase activities. 166 92

Vanadate ions, low-molecular-weight phosphate analogues, mimic most of the rapid actions of insulin in various cell types. When administered orally to diabetic hyperglycemic rats, vanadate reaches the circulation, mimics insulin stimulation of glucose uptake and metabolism, and leads to normoglycemic and partial anabolic states. In addition, vanadate restores tissue responsiveness to insulin and hepatic glycogen levels and activates new synthesis of key enzymes for carbohydrate metabolism. This suggests that correcting hyperglycemia is sufficient to correct the typical metabolic alterations found in streptozocin-induced diabetic rats. Several weeks of oral administration of vanadate to diabetic rats has not produced detectable liver or kidney toxicity. The mechanism by which vanadate mimics the actions of insulin is still obscure. Unlike insulin, vanadate does not seem to stimulate the autophosphorylation and endogenous tyrosine phosphorylation of insulin-receptor kinase or other intracellular proteins either directly or by virtue of its known inhibitory effect on protein phosphotyrosine phosphatase. Results from many studies support a model in which vanadate activates glucose metabolism by either utilizing an alternative (insulin-independent) cascade or bypassing the early events of the insulin-dependent cascade. Either of these possibilities is of clinical importance, because early insulin events may become defective, as a result of severe hyperinsulinemia, and may contribute to insulin resistance. Alternative pathways by which vanadate may stimulate glucose metabolism, e.g., by increasing intracellular Ca2+ levels and/or regulating intracellular and intravesicular pH, are discussed. From a clinical perspective, studies should be continued in evaluating the level of vanadate toxicity after prolonged treatment and searching for agents that potentiate its insulin mimetic actions in vitro and in vivo.
Diabetes 1990 Jan
PMID:Insulin-mimetic effects of vanadate. Possible implications for future treatment of diabetes. 221 51

To evaluate possible mechanisms by which insulin inhibits hepatic apolipoprotein B (apoB) secretion, we incubated primary cultures of rat hepatocytes with sodium orthovanadate, a phosphotyrosine phosphatase inhibitor and insulin-mimetic agent. Vanadate (10 microM) and insulin (10 nM) inhibited the medium accumulation of apoB (secretion) by 21 and 37%, respectively, without increasing intracellular apoB. The effects of insulin and vanadate together were not additive. Both insulin and vanadate enhanced intracellular glycogen accumulation by 82 and 37%, respectively. Unlike insulin, vanadate, at a concentration that inhibited apoB secretion (10 microM), had no effect on intracellular lipogenesis, inhibited the secretion of newly synthesized hepatic proteins, and had a delayed onset and termination of action on inhibition of apoB secretion. At higher concentrations (40 and 80 microM), vanadate stimulated intracellular lipogenesis. In conclusion, our data indicate that vanadate mimics insulin action in hepatocytes with regard to the inhibition of medium accumulation of apoB. These data are consistent with the hypothesis that inhibition of apoB secretion may be secondary to an increase in phosphotyrosine content at its site of synthesis. The kinases responsible for this effect have not been identified. Several effects of vanadate, however, are different from those of insulin, suggesting a differential sensitivity to vanadate, a divergence of the signal transfer by insulin and vanadate at the insulin-receptor or postreceptor level, or both.
Diabetes 1988 Sep
PMID:Insulin-mimetic effects of vanadate in primary cultures of rat hepatocytes. 304 89

Resistance to the biological action of insulin in its target tissues is a cardinal feature of non-insulin-dependent diabetes mellitus. Protein-tyrosine phosphatases (PTPases) have been postulated to play a key role in the regulation of the insulin action pathway, especially in skeletal muscle, the major site of insulin-mediated glucose disposal in vivo. To evaluate whether changes in the activity and/or abundance of candidate skeletal muscle PTPases is associated with severe resistance to insulin in an animal model, we measured PTPase enzyme activity and PTPase protein level by immunoblotting in subcellular fractions of skeletal muscle in lean (+/?), insulin-resistant obese (fa/fa), and diabetic (ZDF/Drt-fa/fa) Zucker rats. Using a phosphotyrosylmyelin basic protein substrate, the solubilized-particulate fraction PTPase activity was increased by 65% and 74% (P < .05) and in vitro dephosphorylation of a recombinant rat insulin receptor kinase domain was increased by 104% and 114% in obese and diabetic animals, respectively (P < .01). These changes in PTPase activity were associated with an increase in specific immunoreactivity of leukocyte common antigen-related PTPase ([LAR] by 42% and 50%), PTPase 1B (by 61% and 69%), and the SHZ domain containing PTPase (SH-PTP2) (by 44% and 48%) in the solubilized-particulate fraction of obese and diabetic animals, respectively (P < .05). In diabetic muscle, increased SH-PTP2 abundance was also associated with a shift of SH-PTP2 to a plasma membrane component, which may have important consequences for the activation of this enzyme in the insulin-resistant state. These results provide evidence that specific PTPases play a role in the insulin resistance of this genetic model of obesity and non-insulin-dependent diabetes.
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PMID:Increased abundance of specific skeletal muscle protein-tyrosine phosphatases in a genetic model of insulin-resistant obesity and diabetes mellitus. 766 92

To test whether protein tyrosine phosphatases (PTPases) may play a role in the insulin resistance of insulinopenic diabetes, we assessed PTPase activity as well as the protein and mRNA abundance of three major candidate PTPases in subcellular fractions of liver and skeletal muscle of streptozotocin-diabetic rats before and after insulin treatment. PTPase activity against the insulin receptor in liver and muscle cytosol increased to 120-125% of control in the diabetic animals and by an additional 5-10% after insulin treatment. In the particulate fraction, PTPase activity decreased to 65-70% of control in diabetic liver and muscle and increased to 115-120% of control after insulin treatment. Protein for the leukocyte common antigen-related PTPase paralleled the changes in the PTPase activity in the particulate fraction. SH-PTP2/syp and PTPase 1B were both significantly increased in diabetes. SH-PTP2/syp also exhibited an increased ratio of particulate to cytosol distribution in diabetic tissues (1.8-1.9) that was reversed after insulin treatment (0.79-0.95). Northern analysis suggested that the PTPases were regulated at a pretranslational level. These changes in the abundance and distribution of specific PTPases may be involved in the pathogenesis of insulin resistance in insulinopenic diabetes.
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PMID:Alterations in specific protein-tyrosine phosphatases accompany insulin resistance of streptozotocin diabetes. 776 48

Vanadate (sodium orthovanadate) is an insulin-mimetic agent and phosphotyrosine phosphatase inhibitor that has been proposed as a potential therapeutic agent for diabetes. We previously reported that vanadate decreased the number of cell-surface insulin receptors but inhibited receptor degradation in cultured lymphocytes (IM-9) (1). To determine whether vanadate affected receptors without intrinsic tyrosine kinase activity, its effects on LDL and transferrin receptors and their ligands were examined. Vanadate exposure resulted in a dose- and time-dependent decrease in LDL binding to cultured human fibroblasts associated with a decrease in cell surface receptor number while total solubilized cell LDL receptors increased. Vanadate also inhibited the LDL-mediated downregulation of total cellular LDL receptors in the absence and presence of cycloheximide consistent with an inhibition of LDL receptor degradation. In the case of the ligand, vanadate augmented the accumulation of intact 125I-LDL associated with an inhibition of up to 80% of the ability of LDL to decrease cholesterol synthesis. Since these actions were similar to the effects of lysosomotropic agents, we examined the effect of vanadate on intraendosomal pH using the fluorescent probe acridine orange. In contrast with chloroquine and NH4Cl, vanadate did not neutralize the pH of the acidic intracellular compartment. Furthermore, after a transient insulin-like effect, chronic exposure to vanadate diminished 125I-diferric transferrin binding to rat adipocytes. In contrast with the inhibitory action of NH4Cl, intracellular 59Fe uptake remained unaffected and was proportional to cell-surface binding capacity in the presence of vanadate. These data demonstrate a chronic effect of vanadate to promote the accumulation of intracellular receptors and to inhibit ligand and receptor degradation. The latter effect is not mediated by pH changes, appears to be localized to a late endosomal/lysosomal compartment, and suggests a possible role for tyrosine dephosphorylation in the regulation of receptor-ligand degradation.
Diabetes 1996 Aug
PMID:The insulin-mimetic agent vanadate promotes receptor endocytosis and inhibits intracellular ligand-receptor degradation by a mechanism distinct from the lysosomotropic agents. 869 Jan 56

When used alone, both vanadate and hydrogen peroxide (H2O2) are weakly insulin-mimetic, while in combination they are strongly synergistic due to the formation of aqueous peroxovanadium species pV(aq). Administration of these pV(aq) species leads to activation of the insulin receptor tyrosine kinase (IRK), autophosphorylation at tyrosine residues and inhibition of phosphotyrosine phosphatases (PTPs). We therefore undertook to synthesize a series of peroxovanadium (pV) compounds containing one or two peroxo anions, an oxo anion and an ancillary ligand in the inner co-ordination sphere of vanadium, whose properties and insulin-mimetic potencies could be assessed. These pV compounds were shown to be the most potent inhibitors of PTPs yet described. Their PTP inhibitory potency correlated with their capacity to stimulate IRK activity. Some pV compounds showed much greater potency as inhibitors of insulin receptor (IR) dephosphorylation than epidermal growth factor receptor (EGFR) dephosphorylation, implying relative specificity as PTP inhibitors. Replacement of vanadium with either molybdenum or tungsten resulted in equally potent inhibition of IR dephosphorylation. However IRK activation was reduced by greater than 80% suggesting that these compounds did not access intracellular PTPs. The insulin-like activity of these pV compounds were demonstrable in vivo. Intra venous (i.v.) administration of bpV(pic) and bpV(phen) resulted in the lowering of plasma glucose concentrations in normal rats in a dose dependent manner. The greater potency of bpV(pic) compared to bpV(phen) was explicable, in part, by the capacity of the former but not the latter to act on skeletal muscle as well as liver. Finally administration of bpV(phen) and insulin led to a synergism, where tyrosine phosphorylation of the IR beta-subunit increased by 20-fold and led to the appearance of four insulin-dependent in vivo substrates. The insulin-mimetic properties of the pV compounds raises the possibility for their use as insulin replacements in the management of diabetes mellitus.
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PMID:Peroxovanadium compounds: biological actions and mechanism of insulin-mimesis. 892 47

Vanadium and its compounds exhibit a wide variety of insulin-like effects. In this review, these effects are discussed with respect to the treatment of type I and type II diabetes in animal models, in vitro actions, antineoplastic role, treatment of IDDM and NIDDM patients, toxicity, and the possible mechanism(s) involved. Newly established CytPTK plays a major role in the bioresponses of vanadium. It has a molecular weight of approximately 53 kDa and is active in the presence of Co2+ rather than Mn2+. Among the protein-tyrosine kinase blockers, staurosporine is found to be a potent inhibitor of CytPTK but a poor inhibitor of InsRTK. Vanadium inhibits PTPase activity, and this in turn enhances the activity of protein tyrosine kinases. Our data show that inhibition of PTPase and protein tyrosine kinase activation has a major role in the therapeutic efficacy of vanadium in treating diabetes mellitus.
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PMID:Vanadium salts as insulin substitutes: mechanisms of action, a scientific and therapeutic tool in diabetes mellitus research. 899 1

Tumor necrosis factor-alpha (TNF-alpha) can modulate the signalling capacity of tyrosine kinase receptors; in particular, TNF-alpha has been shown to mediate the insulin resistance associated with animal models of obesity and noninsulin-dependent diabetes mellitus. In order to determine whether the effects of TNF-alpha might involve alterations in the expression of specific protein-tyrosine phosphatases (PTPases) that have been implicated in the regulation of growth factor receptor signalling, KRC-7 rat hepatoma cells were treated with TNF-alpha, and changes in overall tissue PTPase activity and the abundance of three major hepatic PTPases (LAR, PTP1B, and SH-PTP2) were measured in addition to effects of TNF-alpha on ligand-stimulated autophosphorylation of insulin and epidermal growth factor (EGF) receptors and insulin-stimulated insulin receptor substrate-1 (IRS-1) phosphorylation. TNF-alpha caused a dose-dependent decrease in insulin-stimulated IRS-1 phosphorylation and EGF-stimulated receptor autophosphorylation to 47-50% of control. Overall PTPase activity in the cytosol fraction did not change with TNF-alpha treatment, and PTPase activity in the particulate fraction was decreased by 55-66%, demonstrating that increases in total cellular PTPase activity did not account for the observed alterations in receptor signalling. However, immunoblot analysis showed that TNF-alpha treatment resulted in a 2.5-fold increase in the abundance of SH-PTP2, a 49% decrease in the transmembrane PTPase LAR, and no evident change in the expression of PTP1B. These data suggest that at least part of the TNF-alpha effect on pathways of reversible tyrosine phosphorylation may be exerted through the dynamic modulation of the expression of specific PTPases. Since SH-PTP2 has been shown to interact directly with both the EGF receptor and IRS-1, increased abundance of this PTPase, may mediate the TNF-alpha effect to inhibit signalling through these proteins. Furthermore, decreased abundance of the LAR PTPase, which has been implicated in the regulation of insulin receptor phosphorylation, may account for the less marked effect of TNF-alpha on the autophosphorylation state of the insulin receptor while postreceptor actions of insulin are inhibited.
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PMID:Effect of tumor necrosis factor-alpha on the phosphorylation of tyrosine kinase receptors is associated with dynamic alterations in specific protein-tyrosine phosphatases. 901 60


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