Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.26 (GSK)
 6,788 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several polycations were tested for their abilities to inhibit the activity of glycogen synthase kinase 3 (GSK-3). L-Polylysine was the most powerful inhibitor of GSK-3 with half-maximal inhibition of glycogen synthase phosphorylation occurring at approx. 100 nM. D-Polylysine and histone H1 were also inhibitory, but the concentration dependence was complex, and DL-polylysine was the least effective inhibitor. Spermine caused about 50% inhibition of GSK-3 at 0.7 mM and 70% inhibition at 4 mM. Inhibition of GSK-3 by L-polylysine could be blocked or reversed by heparin. A heat-stable polycation antagonist isolated from swine kidney cortex also blocked the inhibitory effect of L-polylysine on GSK-3 and blocked histone H1 stimulation of protein phosphatase 2A activity. Under the conditions tested, L-polylysine also inhibited GSK-3 catalyzed phosphorylation of type II regulatory subunit of cAMP-dependent protein kinase and a 63 kDa brain protein, but only slightly inhibited phosphorylation of inhibitor 2 or proteolytic fragments of glycogen synthase that contain site 3 (a + b + c). L-Polylysine at a concentration (200 nM) that caused nearly complete inhibition of GSK-3 stimulated casein kinase I and casein kinase II, but had virtually no effect on the catalytic subunit of cAMP-dependent protein kinase. These results suggest that polycations can be useful in controlling GSK-3 activity. Polycations have the potential to decrease the phosphorylation state of glycogen synthase at site 3, both by inhibiting GKS-3 as shown in this study and by stimulating the phosphatase reaction as shown previously (Pelech, S. and Cohen, P. (1985) Eur. J. Biochem. 148, 245-251).
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PMID:Inhibitory effect of polycations on phosphorylation of glycogen synthase by glycogen synthase kinase 3. 254 Aug 33

Immotile bovine caput epididymal sperm contain levels of protein phosphatase activity twofold higher than do mature motile caudal sperm. Comparison of the inhibition profiles of endogenous phosphatase activities detected by okadaic acid (OA) and calyculin A (CA) revealed a pattern consistent with the predominance of a type 1 protein phosphatase (PP1). Immunoblot analysis identified PP1 gamma 2 (the testis-specific isoform of PP1) as the only PP1 isoform in sperm and showed little protein phosphatase 2A (PP2A). In addition, of the known PP1 inhibitors, i.e., DARPP-32, inhibitor 1 (I1), and inhibitor 2 (I2), only I2-like activity was detected in sperm. Inhibition of PP1 by the heat-stable I2-like activity purified from sperm could be reversed with purified glycogen synthase kinase-3 (GSK-3). Furthermore, sperm extracts contain an inactive complex of PP1 and I2 (termed PP1I) that could also be activated by purified GSK-3. The presence of GSK-3 in sperm was demonstrated by activation of purified PP1I, and quantitation revealed that immotile caput sperm contained sixfold higher GSK-3 activity than motile caudal sperm. Immunoblot analysis confirmed the expression of GSK-3 in sperm and revealed the occurrence of both the alpha and beta isoforms. Our findings suggest that the higher PP1 activity measured in immotile sperm, presumably due to higher GSK-3 activity, is responsible for holding motility in check. This conclusion was supported by the observation that the phosphatase inhibitors OA and CA, at micromolar and nanomolar levels, respectively, were able to induce motility in completely immotile bovine caput epididymal sperm and to stimulate the kinetic activity of mature caudal sperm. The intrasperm levels of cAMP, pH, and calcium were unaltered by treatment with these inhibitors. The results suggest a biochemical basis for the development and regulation of sperm motility and a possible physiological role for the PP1/I2/GSK-3 system.
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PMID:Sperm motility development in the epididymis is associated with decreased glycogen synthase kinase-3 and protein phosphatase 1 activity. 883 95

Axin is a negative regulator of embryonic axis formation in vertebrates, which acts through a Wnt signal transduction pathway involving the serine/threonine kinase GSK-3 and beta-catenin. Axin has been shown to have distinct binding sites for GSK-3 and beta-catenin and to promote the phosphorylation of beta-catenin and its consequent degradation. This provides an explanation for the ability of Axin to inhibit signaling through beta-catenin. In addition, a more N-terminal region of Axin binds to adenomatous polyposis coli (APC), a tumor suppressor protein that also regulates levels of beta-catenin. Here, we report the results of a yeast two-hybrid screen for proteins that interact with the C-terminal third of Axin, a region in which no binding sites for other proteins have previously been identified. We found that Axin can bind to the catalytic subunit of the serine/threonine protein phosphatase 2A through a domain between amino acids 632 and 836. This interaction was confirmed by in vitro binding studies as well as by co-immunoprecipitation of epitope-tagged proteins expressed in cultured cells. Our results suggest that protein phosphatase 2A might interact with the Axin.APC.GSK-3.beta-catenin complex, where it could modulate the effect of GSK-3 on beta-catenin or other proteins in the complex. We also identified a region of Axin that may allow it to form dimers or multimers. Through two-hybrid and co-immunoprecipitation studies, we demonstrated that the C-terminal 100 amino acids of Axin could bind to the same region as other Axin molecules.
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PMID:Identification of a domain of Axin that binds to the serine/threonine protein phosphatase 2A and a self-binding domain. 992 Aug 88

Hyperphosphorylated tau, which is the major protein of the neurofibrillary tangles in Alzheimer's disease brain, is most probably the result of an imbalance of tau kinase and phosphatase activities in the affected neurons. By using metabolically competent rat brain slices as a model, we found that selective inhibition of protein phosphatase 2A by okadaic acid induced an Alzheimer-like hyperphosphorylation and accumulation of tau. The hyperphosphorylated tau had a reduced ability to bind to microtubules and to promote microtubule assembly in vitro. Immunocytochemical staining revealed hyperphosphorylated tau accumulation in pyramidal neurons in cornu ammonis and in neocortical neurons. The topography of these changes recalls the distribution of neurofibrillary tangles in Alzheimer's disease brain. Selective inhibition of protein phosphatase 2B with cyclosporin A did not have any significant effect on tau phosphorylation, accumulation, or function. These studies suggest that protein phosphatase 2A participates in regulation of tau phosphorylation, processing, and function in vivo. A down-regulation of protein phosphatase 2A activity can lead to Alzheimer-like abnormal hyperphosphorylation of tau.
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PMID:Phosphorylation of microtubule-associated protein tau is regulated by protein phosphatase 2A in mammalian brain. Implications for neurofibrillary degeneration in Alzheimer's disease. 1068 33

Axin forms a complex with adenomatous polyposis coli gene product (APC), glycogen synthase kinase-3beta (GSK-3beta), and beta-catenin through different binding sites and downregulates beta-catenin. GSK-3beta-dependent phosphorylation of APC-(1211-2075) which has the Axin-binding site was facilitated by Axin, but that of APC-(959-1338) which lacks the Axin-binding site was not. Axin-(298-506) or Axin-(298-832), which has the GSK-3beta- and beta-catenin- but not APC-binding sites, did not enhance GSK-3beta-dependent phosphorylation of either APC-(1211-2075) or APC-(959-1338). Furthermore, beta-catenin stimulated the phosphorylation of APC-(959-1338) and APC-(1211-2075) by GSK-3beta in the presence of Axin. Consistent with these in vitro observations, expression of beta-catenin or Axin in COS cells promoted an SDS gel band shift of APC. These results indicate that APC complexed with Axin is effectively phosphorylated by GSK-3beta and that beta-catenin may modulate this phosphorylation. In addition, the heterodimeric form of protein phosphatase 2A (PP2A) directly bound to Axin, and PP2A complexed with Axin dephosphorylated APC phosphorylated by GSK-3beta. Taken together, these results suggest that GSK-3beta-dependent phosphorylation of APC can be modulated by beta-catenin and PP2A complexed with Axin.
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PMID:GSK-3beta-dependent phosphorylation of adenomatous polyposis coli gene product can be modulated by beta-catenin and protein phosphatase 2A complexed with Axin. 1069 23

In the Wnt/Wingless pathway, accumulation of beta-catenin/Armadillo protein is a key regulatory step. Vertebrate Axin is a negative regulator of Wnt signaling, promoting glycogen synthase kinase-3beta-mediated phosphorylation of beta-catenin and thereby destabilizing beta-catenin. Using Drosophila cell culture systems, we demonstrated that a Drosophila homolog of Axin (Daxin) inhibits Wingless-induced Armadillo accumulation and Drosophila T-cell factor-dependent transcription induced by Wingless, Dishevelled, and Armadillo. The carboxy-terminal portion of Daxin is not essential for the inhibitory activity, but a mutant only consisting of this portion behaves as a dominant-negative protein. Moreover, interactions between Daxin and Zeste-white 3, Armadillo, Dishevelled, protein phosphatase 2A and Daxin itself were shown, providing direct evidence that Daxin is a scaffold protein in the Wingless pathway.
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PMID:Biochemical characterization of the Drosophila axin protein. 1083 83

Axin forms a complex with adenomatous polyposis coli gene product, glycogen synthase kinase-3beta (GSK-3beta), beta-catenin, Dvl, and protein phosphatase 2A and functions as a scaffold protein in the Wnt signaling pathway. In the Axin complex, GSK-3beta efficiently phosphorylates beta-catenin, which is then ubiquitinated and degraded by proteasome. We isolated a novel protein that binds to Axin and named it Axam (for Axin associating molecule). Axam formed a complex with Axin in intact cells and bound directly to Axin. Axam inhibited the complex formation of Dvl with Axin and the activity of Dvl to suppress GSK-3beta-dependent phosphorylation of Axin. Furthermore, Axam induced the degradation of beta-catenin in SW480 cells and inhibited Wnt-dependent axis duplication in Xenopus embryos. These results suggest that Axam regulates the Wnt signaling pathway negatively by inhibiting the binding of Dvl to Axin.
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PMID:Inhibition of Wnt signaling pathway by a novel axin-binding protein. 1094 33

Protein kinase C-zeta (PKC-zeta) is a serine/threonine kinase downstream from phosphatidylinositol 3-kinase in insulin signaling pathways. However, specific substrates for PKC-zeta that participate in the biological actions of insulin have not been reported. In the present study, we identified insulin receptor substrate-1 (IRS-1) as a novel substrate for PKC-zeta. Under in vitro conditions, wild-type PKC-zeta (but not kinase-deficient mutant PKC-zeta) significantly phosphorylated IRS-1. This phosphorylation was reversed by treatment with the serine-specific phosphatase, protein phosphatase 2A. In addition, the overexpression of PKC-zeta in NIH-3T3(IR) cells caused significant phosphorylation of cotransfected IRS-1 as demonstrated by [(32)P]orthophosphate labeling experiments. In rat adipose cells, endogenous IRS-1 coimmunoprecipitated with endogenous PKC-zeta, and this association was increased 2-fold upon insulin stimulation. Furthermore, the overexpression of PKC-zeta in NIH-3T3(IR) cells significantly impaired insulin-stimulated tyrosine phosphorylation of cotransfected IRS-1. Importantly, this was accompanied by impaired IRS-1-associated phosphatidylinositol 3-kinase activity. Taken together, our results raise the possibility that IRS-1 is a novel physiological substrate for PKC-zeta. Because PKC-zeta is located downstream from IRS-1 and phosphatidylinositol 3-kinase in established insulin signaling pathways, PKC-zeta may participate in negative feedback pathways to IRS-1 similar to those described previously for Akt and GSK-3.
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PMID:Protein kinase C-zeta phosphorylates insulin receptor substrate-1 and impairs its ability to activate phosphatidylinositol 3-kinase in response to insulin. 1106 44

Axin, a negative regulator of the Wnt signaling pathway, forms a complex with glycogen synthase kinase-3beta (GSK-3beta), beta-catenin, adenomatous polyposis coli (APC) gene product, and Dvl, and it regulates GSK-3beta-dependent phosphorylation in the complex and the stability of beta-catenin. Using yeast two-hybrid screening, we found that regulatory subunits of protein phosphatase 2A, PR61beta and -gamma, interact with Axin. PR61beta or -gamma formed a complex with Axin in intact cells, and their interaction was direct. The binding site of PR61beta on Axin was different from those of GSK-3beta, beta-catenin, APC, and Dvl. Although PR61beta did not affect the stability of beta-catenin, it inhibited Dvl- and beta-catenin-dependent T cell factor activation in mammalian cells. Moreover, it suppressed beta-catenin-induced axis formation and expression of siamois, a Wnt target gene, in Xenopus embryos, suggesting that PR61beta acts either at the level of beta-catenin or downstream of it. Taken together with the previous observations that PR61 interacts with APC and functions upstream of beta-catenin, these results demonstrate that PR61 regulates the Wnt signaling pathway at various steps.
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PMID:Inhibition of the Wnt signaling pathway by the PR61 subunit of protein phosphatase 2A. 1129 46

Neurofibrillary tangles (NFTs) are classic lesions of Alzheimer's disease. NFTs are bundles of abnormally phosphorylated tau, the paired helical filaments. The initiating mechanisms of NFTs and their role in neuronal loss are still unknown. Accumulating evidence supports a role for the activation of proteolytic enzymes, caspases, in neuronal death observed in brains of patients with Alzheimer's disease. Alterations in tau phosphorylation and tau cleavage by caspases have been previously reported in neuronal apoptosis. However, the links between the alterations in tau phosphorylation and its proteolytic cleavage have not yet been documented. Here, we show that, during staurosporine-induced neuronal apoptosis, tau first undergoes transient hyperphosphorylation, which is followed by dephosphorylation and cleavage. This cleavage generated a 10-kDa fragment in addition to the 17- and 50-kDa tau fragments previously reported. Prior tau dephosphorylation by a glycogen synthase kinase-3beta inhibitor, lithium, enhanced tau cleavage and sensitized neurons to staurosporine-induced apoptosis. Caspase inhibition prevented tau cleavage without reversing changes in tau phosphorylation linked to apoptosis. Furthermore, the microtubule depolymerizing agent, colchicine, induced tau dephosphorylation and caspase-independent tau cleavage and degradation. Both phenomena were blocked by inhibiting protein phosphatase 2A (PP2A) by okadaic acid. These experiments indicate that tau dephosphorylation precedes and is required for its cleavage and degradation. We propose that the absence of cleavage and degradation of hyperphosphorylated tau (due to PP2A inhibition) may lead to its accumulation in degenerating neurons. This mechanism may contribute to the aggregation of hyperphosphorylated tau into paired helical filaments in Alzheimer's disease where reduced PP2A activity has been reported.
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PMID:Linking alterations in tau phosphorylation and cleavage during neuronal apoptosis. 1547 65


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