Inhibition of Protein Tyrosine Phosphatase Activity

Chemical Inhibition of Protein Tyrosine Phosphatase Activity 

1 Protein Tyrosine Phosphatases (PTPs) and Their Catalytic Mechanism 

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Cuncic, C., S. Desmarais, N. Detich, A.S. Tracey, MJ. Gresser, and C. Ramachandran. 1999. Bis(N,N-dimethylhydroxamido)hydroxooxovanadate inhibition of protein tyrosine phosphatase activity in intact cells Comparison with vanadate. Biochem. Pharmacol. 58 1859-1867. 

Studies of the oxidation of organic sulfides with amino acid-derived ligands in acetonitrile revealed very little difference between the mechanism of their oxidation and that of halides, except for one major exception. Despite the fact that acid conditions are still required for the catalytic cycle, hydroxide or an equivalent is not produced in the catalytic cycle, so no proton is consumed [48], As a consequence, there is no requirement for maintenance of acid levels during a catalyzed reaction. Peroxo complexes of vanadium are well known to be potent insulin-mimetic compounds [49,50], Their efficacy arises, at least in part, from an oxidative mechanism that enhances insulin receptor activity, and possibly the activity of other protein tyrosine kinases activity [51]. With peroxovanadates, this is an irreversible function. Apparently, there is no direct effect on the function of the kinase, but rather there is inhibition of protein tyrosine phosphatase activity. The phosphatase regulates kinase activity by dephosphorylating the kinase. Oxidation of an active site thiol in the phosphatase prevents this down-regulation of kinase activity. Presumably, this sulfide oxidation proceeds by the process outlined above. 

Hydrogen peroxide (H202) exhibits insulin-like activity in isolated cells. Like that of vanadate, this effect is thought to be mediated by inhibition of protein-tyrosine phosphatases. 

GAO Y H and YAMAGUCHI M (2000) Suppressive effect of genistein on rat bone osteoclasts Involvement of protein kinase inhibition and protein tyrosine phosphatase activation. Int J Mol Med 5, 261-7. 

Receptor tyrosine kinases (RTKs) are activated (phosphorylated) by inhibition of a negatively regulating phosphatase upon treatment with UV (A, B, or C), hydrogen peroxide, or iodoacetamide. The phosphatase activity, (i.e., dephosphorylation and inactivation of RTKs) is restored upon the addition of thiol-regenerating agents, if not inhibited irreversibly by iodoacetamide [20]. H2O2 not only inactivates membrane-bound phosphatases but also diminishes cytosolic general protein tyrosine phosphatase activity in mouse fibroblasts [21]. Further, the activation of JNK by sodium arsenite, which is reactive towards thiols (especially vicinal dithiols), is by inactivation of a JNK phosphatase [22]. 

X0vanadates, which may result in irreversible inhibition of some protein tyrosine phosphatases, as opposed to the readily reversible phosphatase inhibition seen with vanadates. In addition, vanadate s substitution for phosphate within the enzyme structure may result in formation of a transition state analog of protein tyrosine phosphatase, thus changing the kinetics of tyrosine kinase activation, and effectively acting as a means of fine tuning the intracellular balance between phosphatase inhibition and kinase activation. ... 

Immunoblotting-based experiments using an anti-phosphotyrosine antibody showed that incubation of platelets with ajoene enhanced the phosphorylation of at least four proteins (estimated molecular weights 76, 80, 84 and 120 kDa), both in resting platelets and in platelets subsequently stimulated with thrombin (0.1 U/ml). This effect was both dose- and incubation-time-dependent. High concentrations of ajoene (50 pM) or long periods of incubation (10 min) led to nonselective hyperphosphorylation of numerous proteins. Also, protein tyrosine phosphatase activity was inhibited when platelets were incubated with ajoene before lysis, but not when ajoene was added to lysates of platelets which had not been pre-exposed to ajoene [99],... 

A different mode of interference of ascorbate with growth factor receptors was suggested by Monteiro et al. (1993). In HER 14 cells, physiological concentrations of ascorbate inhibited a protein tyrosine phosphatase acting on the EGF receptor. The effect could be prevented by EGF. Interestingly, the inhibitory effect of ascorbate on the phosphatase was more pronounced at low concentrations of ascorbate and low cell density, which was interpreted by the authors as indicating a prooxidant action of ascorbate. Activation of signal transduction pathways has been described for the insulin receptor tyrosine kinase (Koshio et al., 1988) and a protein tyrosine kinase in the rat liver plasma membrane (Chan et al., 1986). 

Perret D, Shields M, Saxon A, Kehry MR A mouse Fey Fee protein that inhibits mast cells through activation of FcyRIIB, SH2 domain-containing inositol SS phosphatase 1, and SH2 domain-containing protein tyrosine phosphatases. J Allergy Chn Immunol 2008 121 441-447. 

N-Nitrosamines have been shown to be inhibitors of cysteine-containing enzymes. For example, dephostatin and other N-methyl-N-nitrosoanilines (1) were found to be inhibitors of the protein tyrosin phosphatases, papain and caspase [90,91]. Inhibition results from the S-nitrosation of the critical cysteine residues in the active sites of the enzymes by the nitrosamines. Compounds 6 and 7 have been found to inhibit thrombus formation in arterioles and venules of rats [92], while N-nitrosamide 9 exhibited vasodilation and mutagenicity as a result of NO release [93]. 

Another AT2 pathway linked to apoptosis leads to a stimulation of a soluble protein tyrosine phosphatase, SHP-1, an enzyme that associates with insulin receptor substrate (IRS)-2 (Cui et al. 2002). Overexpression of a dominant negative form of SHP-1 in PC12W cells has been found to attenuate AT2 receptor-mediated inhibition of insulin signaling. Since insulin activates Akt, it is interesting that the mechanism of apoptosis in the angiotensin II-treated PC12W cell involves the dephosphorylation and inactivation of Akt. In NIE-115 neuroblastoma cells,... 

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