Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:3.2.1.23 (beta-galactosidase)
14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tumor necrosis factor-alpha (TNF-alpha) has been shown to induce insulin resistance in cultured cells as well as in animal models. The aim of this study was to map the in vivo mechanism whereby TNF-alpha contributes to the pathogenesis of impaired insulin signaling, using obese and lean Zucker rats in which TNF-alpha activity was inhibited through adenovirus-mediated gene transfer. We employed a replication-incompetent adenovirus-5 (Ad5) vector to endogenously express a TNF inhibitor (TNFi) gene, which encodes a chimeric protein consisting of the extracellular domain of the human 55-kDa TNF receptor joined to a mouse IgG heavy chain. Control animals consisted of rats infected with the same titer of adenovirus carrying the lac-z complementary DNA, encoding for beta-galactosidase. There was a significant reduction in plasma insulin and free fatty acid levels in TNFi obese rats 2 days following Ad5 administration. The peripheral insulin sensitivity index was 50% greater, whereas hepatic glucose output was completely suppressed during hyperinsulinemic glucose clamps in TNFi obese animals, with no differences observed between the two lean groups. The improvement in peripheral and hepatic sensitivity to insulin seen in the obese animals was independent of insulin receptor (IR) number and insulin binding affinity for IR. However, TNF-alpha neutralization led to a 2.5-fold increase in tyrosine phosphorylation of IR in skeletal muscle, whereas this was unchanged in liver. There was also a 4-fold increase in particulate protein tyrosine phosphatase activity of skeletal muscle in TNFi obese animals vs. beta-galactosidase controls, whereas protein tyrosine phosphatase activity in liver was unchanged. These results suggest that TNF-alpha is a mediator of insulin resistance in obesity and may modulate IR signaling in skeletal muscle and liver through different pathways. TNF-alpha may affect insulin action in the liver either at sites distal to the IR or indirectly, possibly because of increased provision of gluconeogenic substrates or altered counterregulation. In addition, the Ad5-mediated gene delivery system employed here provides an in vivo model that is efficient and economical for exploring mechanisms involved in TNF-alpha-induced insulin resistance in various genetic models of obesity-linked diabetes.
...
PMID:An in vivo model for elucidation of the mechanism of tumor necrosis factor-alpha (TNF-alpha)-induced insulin resistance: evidence for differential regulation of insulin signaling by TNF-alpha. 983 30

Receptor protein tyrosine phosphatases (RPTPs) comprise a family of proteins that feature intracellular phosphatase domains and an ectodomain with putative ligand-binding motifs. Several RPTPs are expressed in the brain, including RPTP-kappa which participates in homophilic cell-cell interactions in vitro [Y.-P. Jiang, H. Wang, P. D'Eustachio, J.M. Musacchio, J. Schlessinger, J. Sap, Cloning and characterization of R-PTP-kappa, a new member of the receptor protein tyrosine phosphatase family with a proteolytically cleaved cellular adhesion molecule-like extracellular region, Mol. Cell. Biol. 13 (1993) 2942-2951; J. Sap, Y.-P. Jiang, D. Friedlander, M. Grumet, J. Schlessinger, Receptor tyrosine phosphatase R-PTP-kappa mediates homophilic binding, Mol. Cell. Biol. 14 (1994) 1-9]. The homology of RPTP-kappa's ectodomain to neural cell adhesion molecules indicates potential roles in developmental processes such as axonal growth and target recognition, as has been demonstrated for certain Drosophila RPTPs. The brain distribution of RPTP-kappa-expressing cells has not been determined, however. In a gene-trap mouse model with a beta-gal+neo (beta-geo) insertion in the endogenous RPTP-kappa gene, the consequent loss of RPTP-kappa's enzymatic activity does not produce any obvious phenotypic defects [W.C. Skarnes, J.E. Moss, S.M. Hurtley, R.S.P. Beddington, Capturing genes encoding membrane and secreted proteins important for mouse development, Proc. Natl. Acad. Sci. U.S.A. 92 (1995) 6592-6596]. Nevertheless, since the transgene's expression is driven by the endogenous RPTP-kappa promoter, distribution of the truncated RPTP-kappa/beta-geo fusion protein should reflect the regional and cellular expression of wild-type RPTP-kappa, and thus may identify sites where RPTP-kappa is important. Towards that goal, we have used this mouse model to map the distribution of the truncated RPTP-kappa/beta-geo fusion protein in the adult mouse brain using beta-galactosidase as a marker enzyme. Visualization of the beta-galactosidase activity revealed a non-random pattern of expression, and identified cells throughout the CNS that display RPTP-kappa promoter activity. Several neural systems highly expressed the transgene-most notably cortical, olfactory, hippocampal, hypothalamic, amygdaloid and visual structures. These well-characterized brain regions may provide a basis for future studies of RPTP-kappa function.
...
PMID:Expression of a truncated receptor protein tyrosine phosphatase kappa in the brain of an adult transgenic mouse. 1022 93

The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. Ubr1p, the recognition (E3) component of the Saccharomyces cerevisiae N-end rule pathway, contains at least two substrate-binding sites. The type 1 site is specific for N-terminal basic residues Arg, Lys, and His. The type 2 site is specific for N-terminal bulky hydrophobic residues Phe, Leu, Trp, Tyr, and Ile. Previous work has shown that dipeptides bearing either type 1 or type 2 N-terminal residues act as weak but specific inhibitors of the N-end rule pathway. We took advantage of the two-site architecture of Ubr1p to explore the feasibility of bivalent N-end rule inhibitors, whose expected higher efficacy would result from higher affinity of the cooperative (bivalent) binding to Ubr1p. The inhibitor comprised mixed tetramers of beta-galactosidase that bore both N-terminal Arg (type 1 residue) and N-terminal Leu (type 2 residue) but that were resistant to proteolysis in vivo. Expression of these constructs in S. cerevisiae inhibited the N-end rule pathway much more strongly than the expression of otherwise identical beta-galactosidase tetramers whose N-terminal residues were exclusively Arg or exclusively Leu. In addition to demonstrating spatial proximity between the type 1 and type 2 substrate-binding sites of Ubr1p, these results provide a route to high affinity inhibitors of the N-end rule pathway.
...
PMID:Bivalent inhibitor of the N-end rule pathway. 1036 69

By interaction cloning (yeast two-hybrid system) using the catalytic domain of protein kinase Czeta (PKCzeta) as bait, we cloned a human full-length cDNA with 62% nucleotide homology to the A6 protein recently cloned and characterized by Beeler et al. [Beeler, J.F., LaRochelle, W.J., Chedid, M., Tronick, S.R. & Aaronson, S. A. (1994) Mol. Cell. Biol. 14, 982-988]. The deduced amino acid sequence (349 amino acids) of the A6-related protein (A6rp) contained potential actin-binding sites and ATP-binding sites. We also cloned the murine homolog of A6rp. Human A6rp was expressed in an in-vitro transcriptional/translational system with an apparent molecular mass of 40 kDa and as a glutathione S-transferase (GST) fusion protein in bacteria. A polyclonal anti-(A6rp) was raised in rabbits and used for the identification of A6rp by immunoblotting. A6rp was found to be expressed at the mRNA and the protein levels in all cells and tissues investigated. GST-A6rp was phosphorylated by PKCzeta but not significantly by other PKC isoenzymes. Moreover, it was phosphorylated by casein kinase 2 and most effectively by the tyrosine kinase Src. In contrast to GST-A6rp, GST-A6 was also phosphorylated by PKC isoforms other than PKCzeta and strongly by CK2, but just weakly by Src. In contrast to the results of Beeler et al. on beta-galactosidase-A6, we were unable to demonstrate autokinase activity or tyrosine phosphorylation of either GST-A6 or GST-A6rp. In accordance with the potential ATP-binding sites, both proteins were able to bind ATP.
...
PMID:Cloning, expression and characterization of an A6-related protein. 1040 62

Human beta-glucuronidase (hGUSB) is a member of family 2 glycosylhydrolases that cleaves beta-D-glucuronic acid residues from the nonreducing termini of glycosaminoglycans. Amino acid sequence and structural homology of hGUSB and Escherichia coli beta-galactosidase active sites led us to propose that residues Glu(451), Glu(540), and Tyr(504) in hGUSB are involved in catalysis, Glu(451) being the acid-base residue and Glu(540) the nucleophile. To test this hypothesis, we introduced mutations in these residues and determined their effects on enzymes expressed in COS cells and GUSB-deficient fibroblasts. The extremely low activity in cells expressing Glu(451), Glu(540), and Tyr(504) hGUSBs supported their roles in catalysis. For kinetic analysis, wild type and mutant enzymes were produced in baculovirus and purified to homogeneity by affinity chromatography. The k(cat)/K(m) values (mM(-1).s(-1)) of the E540A, E451A, and Y504A enzymes were 34,000-, 9100-, and 830-fold lower than that of wild type hGUSB, respectively. High concentrations of azide stimulated the activity of the E451A mutant enzyme, supporting the role of Glu(451) as the acid-base catalyst. We conclude that, like their homologues in E. coli beta-galactosidase, Glu(540) is the nucleophilic residue, Glu(451) the acid-base catalyst, and Tyr(504) is also important for catalysis, although its role is unclear. All three residues are located in the active site cavity previously determined by structural analysis of hGUSB.
...
PMID:Active site residues of human beta-glucuronidase. Evidence for Glu(540) as the nucleophile and Glu(451) as the acid-base residue. 1043 23

Substitutions for Tyr-503 of beta-galactosidase caused large decreases of the activity. Both the galactosylation (k2) and degalactosylation (k3) rates were decreased. Substitutions by residues without transferable protons, caused k3 to decrease much more than k2 while substitutions with residues having transferable protons, caused approximately equal decreases of k2 and k3. Several lines of evidence showed this. The Km values of the substituted enzymes were much smaller than those for the wild type if the substituted amino acid residues did not have transferable protons; this was not the case when the substituted residues had transferable protons. Inhibition studies showed that the Km values were not small because of small Ks values but were small because of relatively small k3 values (compared with the k2 values). The conclusion that the k3 values are small relative to k2 upon substitution with residues without transferable protons is also based upon other studies: studies indicating that the reaction rates were similar with different substrates, studies in the presence of alcohol acceptors, studies showing that the rate of inactivation by 2,4-dinitrophenyl-2-deoxy-2-F-beta-D-galactopyranoside decreased much less than the rate of reactivation; studies on burst kinetics, and pH studies. The data suggest that Tyr-503 may be important for the degalactosylation reaction because of its ability to transfer protons and thereby facilitate cleavage of the transient covalent bond between galactose and Glu-537.
...
PMID:Tyr-503 of beta-galactosidase (Escherichia coli) plays an important role in degalactosylation. 1050 94

In response to extracellular stimuli, mitogen-activated protein kinase (MAPK, also known as ERK) translocates from the cytoplasm to the nucleus. MAP kinase kinase (MAPKK, also know as MEK), which possesses a nuclear export signal (NES), acts as a cytoplasmic anchor of MAPK. Here we show evidence that tyrosine (Tyr190 in Xenopus MPK1/ERK2) phosphorylation of MAPK by MAPKK is necessary and sufficient for the dissociation of the MAPKK-MAPK complex, and that the dissociation of the complex is required for the nuclear translocation of MAPK. We then show that nuclear entry of MAPK through a nuclear pore occurs via two distinct mechanisms. Nuclear import of wild-type MAPK (mol. wt 42 kDa) was induced by activation of the MAPK pathway even in the presence of wheat germ agglutinin or dominant-negative Ran, whereas nuclear import of beta-galactosidase (beta-gal)-fused MAPK (mol. wt 160 kDa), which occurred in response to stimuli, was completely blocked by these inhibitors. Moreover, while a dimerization-deficient mutant of MAPK was able to translocate to the nucleus upon stimulation, this mutant MAPK, when fused to beta-gal, became unable to enter the nucleus. These results suggest that monomeric and dimeric forms of MAPK enter the nucleus by passive diffusion and active transport mechanisms, respectively.
...
PMID:Two co-existing mechanisms for nuclear import of MAP kinase: passive diffusion of a monomer and active transport of a dimer. 1050 67

We have previously shown that CO(2) stimulation of the renal Na-HCO(3) cotransporter (NBC) activity is abrogated by general inhibitors of protein tyrosine kinases. The more selective inhibitor herbimycin also blocked this effect at concentrations known to preferentially inhibit Src family kinases (SFKs). We therefore examined a role for SFKs in CO(2)-stimulated NBC activity. To this end, we engineered OK cells to express the COOH-terminal Src kinase (Csk), a negative regulator of SFKs. CO(2) stimulated NBC activity normally in beta-galactosidase-expressing and untransfected control cells. In contrast, Csk-expressing cells had normal baseline NBC activity that was not stimulated by CO(2). CO(2) stimulation increased both total SFK activity and specific tyrosine phosphorylation of Src. The specific MEK1/2 inhibitor PD-98059 completely inhibited the CO(2) stimulation of NBC activity as well as the accompanying phosphorylation and activation of ERK1/2. Our data suggest the involvement of both SFKs, probably Src, and the "classic" MAPK pathway in mediating CO(2)-stimulated NBC activity in renal epithelial cells.
...
PMID:Regulation of the renal Na-HCO(3) cotransporter. XI. Signal transduction underlying CO(2) stimulation. 1051 83

The c-Fes protein-tyrosine kinase exhibits strong expression in myeloid hematopoietic cells. Previous studies have shown that Fes induces differentiation in the chronic myelogenous leukemia-derived cell line K-562, suggesting that the Fes signal for differentiation is dominant to the Bcr-Abl signal for transformation in these cells. In addition, Fes has been shown to associate with and phosphorylate Bcr on NH2-terminal sequences retained within Bcr-Abl. To determine whether Fes interacts directly with Bcr-Abl, kinase-inactive Bcr-Abl was coexpressed with Fes in 293T cells, and phosphorylation was assessed by anti-phosphotyrosine immunoblotting. Bcr-Abl was strongly phosphorylated by Fes under these conditions, suggestive of direct interaction. Similarly, tyrosine phosphorylation of kinase-inactive Fes was observed after coexpression with active Bcr-Abl. To test for the interaction of Fes with Bcr-Abl under physiological conditions, wild-type and kinase-defective Fes were stably expressed in the cytokine-dependent myeloid leukemia cell line, DAGM. Expression of either form of Fes alone did not affect the proliferation or interleukin 3 dependence of these cells. The DAGM/Fes cells were then infected with Bcr-Abl retroviruses, and their rates of cytokine-independent outgrowth were compared. Fes dramatically suppressed Bcr-Abl-induced DAGM cell outgrowth relative to a cell line expressing beta-galactosidase as a negative control. This effect required Fes tyrosine kinase activity, because the kinase-inactive form of Fes did not affect Bcr-Abl-induced cell outgrowth. The phosphotyrosine content of both wild-type and kinase-inactive Fes was strongly enhanced after coexpression with Bcr-Abl in DAGM cells, similar to the 293T result. Phosphorylation of wild-type Fes correlated with stimulation of Fes tyrosine kinase activity in the presence of Bcr-Abl. These results show that Fes and Bcr-Abl interact in myeloid cells, leading to Fes activation and suppression of Bcr-Abl-induced conversion to cytokine independence.
...
PMID:The c-Fes protein-tyrosine kinase suppresses cytokine-independent outgrowth of myeloid leukemia cells induced by Bcr-Abl. 1070 30

Studies in fibroblasts have shown that H2O2, as a model for oxidative damage, leads to a G1 growth arrest phenotypically similar to senescence. These observations as well as the observation that bladder cancer is associated with deletions of CDKN2, a gene important in normal senescence, led us to examine normal urothelial cell response to H2O2. We hypothesized that low dose H2O2 exposure would lead to p16 and/or p14arf mediated senescence. We show that H2O2 leads to endogenous beta-galactosidase expression similar to senescence, but instead of G1 arrest, it leads to G2/M growth arrest without induction of either p16 or p14arf. Lack of p21 induction and a similar G2/M growth arrest in E6 immortalized uroepithelial cells suggests that this response is independent of p53 as well. An increased level of cdc2 tyrosine-15 phosphorylation following H2O2 treatment suggests that the observed growth arrest is mediated by a G2 checkpoint mechanism.
...
PMID:A G2/M growth arrest response to low-dose intermittent H2O2 in normal uroepithelial cells. 1093 79


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---