Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An assay for the estimation of phosphotyrosine phosphatase using the Folin-Ciocalteu phenol reaction to monitor enzyme activity is presented. The method is based on the property of the substrate phosphotyrosine not to react as a phenol until it is dephosphorylated. The method is sensitive, there is no interference from the use of detergents and it does not rely on special laboratory equipment to distinguish tyrosine from phosphotyrosine.
Biochem Mol Biol Int 1995 Aug
PMID:Measurement of phosphotyrosine phosphatase activity using the Folin-Ciocalteu phenol reaction. 758 Oct 10

A cDNA clone for the rat type 2 (AT2) angiotensin II receptor was stably transfected into human embryonic kidney 293 cells. Binding characteristics of CGP42112A (Kd = 0.18 nM, Bmax = 10.8 pmol/mg protein) and ligand specificity were indistinguishable from those obtained with the whole rat fetus and with transiently transfected COS-7 cells. Non-hydrolyzable guanine nucleotide analogs did not affect the ligand binding curve; interestingly, the guanine nucleotide analog's effect was observed in the presence of sulfhydryl reducing agent, suggesting that a certain redox condition may affect G protein coupling to this receptor. Using the established cell line, several second messenger systems were assessed. None of cAMP levels, cGMP levels, arachidonic acid release, or phosphotyrosine phosphatase activity was affected by angiotensin II stimulation of this receptor. Furthermore, the AT2 receptor did not undergo agonist-stimulated internalization. These results using the cloned receptor suggest that the transfected AT2 receptor fails to effectively couple to the major G protein-mediated signaling mechanisms and ligand-activated internalization in transfected 293 cells.
Mol Cell Endocrinol 1995 Jul
PMID:Characterization of a rat type 2 angiotensin II receptor stably expressed in 293 cells. 758 86

The beta receptor for platelet-derived growth factor (beta PDGFR) is activated by binding of PDGF and undergoes phosphorylation at multiple tyrosine residues. The tyrosine-phosphorylated receptor associates with numerous SH2-domain-containing proteins which include phospholipase C-gamma 1 (PLC gamma), the GTPase-activating protein of Ras (GAP), the p85 subunit of phosphatidylinositol 3 kinase (PI3K), the phosphotyrosine phosphatase Syp, and several other proteins. Our previous studies indicated that PI3K and PLC gamma were required for relay of the mitogenic signal of beta PDGFR, whereas GAP and Syp did not appear to be required for this response. In this study, we further investigated the role of GAP and Syp in mitogenic signaling by beta PDGFR. Focusing on the PLC gamma-dependent branch of beta PDGFR signaling, we constructed a series of mutant beta PDGFRs that contained the binding sites for pairs of the receptor-associated proteins: PLC gamma and PI3K, PLC gamma and GAP, or PLC gamma and Syp. Characterization of these mutants showed that while all receptors were catalytically active and bound similar amounts of PLC gamma, they differed dramatically in their ability to initiate DNA synthesis. This signaling deficiency related to an inability to efficiently tyrosine phosphorylate and activate PLC gamma. Surprisingly, the crippled receptor was the one that recruited PLC gamma and GAP. Thus, GAP functions to suppress signal relay by the beta PDGFR, and it does so by silencing PLC gamma. These findings demonstrate that the biological response to PDGF depends not only on the ability of the beta PDGFR to recruit signal relay enzymes but also on the blend of these receptor-associated proteins.
Mol Cell Biol 1995 Jun
PMID:The GTPase-activating protein of Ras suppresses platelet-derived growth factor beta receptor signaling by silencing phospholipase C-gamma 1. 776 Aug 2

Somatostatin receptors are abundantly expressed on a variety of human endocrine and epithelial tumors. The ability of these receptors to couple to effector pathways that inhibit the growth of these tumor cells has prompted the use of somatostatin agonists in the treatment of human neoplasms. It has been demonstrated that somatostatin stimulates a phosphotyrosine phosphatase in human tumor cells through a receptor-mediated process. This stimulation may counteract the growth-promoting properties of growth factors and the receptor tyrosine kinases that they activate. The recent cloning and characterization of distinct somatostatin receptor subtypes raise the possibility that different receptor subtypes mediate distinct effector pathways. To determine whether cloned somatostatin receptors could mediate coupling to phosphotyrosine phosphotyrosine phosphatase activity, we examined phosphatase activity after somatotostatin activation of the rat somatostatin receptors SSTR1 and SSTR2 after their stable expression in heterologous Chinese Hamster Ovary (CHO-K1) cells. We found that stimulation of SSTR1 cells was capable of increasing phosphotyrosine phosphatase activity, despite the coupling of both receptors to the inhibition of adenylyl cyclase in these cells. This activation was characterized by an EC50 of 70 nM and was sensitive to pertussis toxin. In addition, we demonstrate that activation of phosphotyrosine phosphatase activity in pituitary cell lines correlates with the endogenous expression of the SSTR1 gene within these cells.
Mol Endocrinol 1994 Oct
PMID:The somatostatin receptor SSTR1 is coupled to phosphotyrosine phosphatase activity in CHO-K1 cells. 785 46

The receptor like PTPase, PTP mu, displays structural similarity in its extracellular segment to members of the immunoglobulin superfamily of cell adhesion molecules. The full length form of PTP mu (200 kD) and a construct expressing only the intracellular PTPase domain-containing segment (80 kD) were expressed in the baculovirus/Sf9 cell system, purified and characterized. Full length PTP mu was membrane associated while the truncated form was recovered in the soluble fraction. PTP mu preferentially dephosphorylated a reduced carboxamidomethylated and maleylated derivative of lysozyme (RCML) over other tyrosine phosphorylated substrates such as myelin basic protein (MBP) or the synthetic peptide EDNDYINASL. The enzymatic properties of the soluble, truncated form of the enzyme were examined in detail. The pH optimum was 7.5. It dephosphorylated RCML with a Km of 400 nM and a Vmax of 725 nmol/min/mg. This form of the enzyme was 2 fold more active than full length PTP mu. Trypsinization of the full length form inhibited activity. Vanadate and molybdate, potent tyrosine phosphatase inhibitors, abolished activity of the enzyme. Zn++ and Mn++ ions, polylysine, poly-glu/tyr, and spermine were also inhibitory.
Mol Cell Biochem 1993 Nov
PMID:Purification and characterization of the human protein tyrosine phosphatase, PTP mu, from a baculovirus expression system. 793 45

We have cloned a developmentally regulated mitogen-activated protein kinase (extracellular signal-regulated kinase) from Dictyostelium discoideum designated ERK1. Using anti-pTyr antibodies, we show that ERK1 is phosphorylated on tyrosine in vivo and that it will phosphorylate myelin basic protein. The gene expresses two transcripts, one that is preferentially expressed during vegetative growth and early development and one that is induced during the multicellular stages. Developmental Western blots (immunoblots) using anti-ERK1 antibodies indicate that ERK1 is present throughout development. ERK1/lacZ reporter constructs suggest that, in the multicellular stages, the gene is preferentially expressed in a subpopulation of cells scattered throughout the organism, similar to the pattern seen with anterior-like cell markers. Antisense mutagenesis from a derepressible promoter indicates that ERK1 is essential for vegetative growth. Overexpression of ERK1 from either the Actin 15 promoter or the ERK1 promoter results in abnormal morphogenesis starting at the slug stage. Overexpression of ERK1 in null mutants of the phosphotyrosine phosphatase PTP2 results in the production of large aggregation streams and subsequent abnormal morphogenesis that indicate a genetic interaction between ERK1 and PTP2. These cells produce very large aggregation streams that break up into very small mounds that undergo abnormal morphogenesis. The genetic interaction between ERK1 and PTP2 appears to be specific since overexpression of ERK1 in a ptp1- null mutant does not produce the same phenotype. Our results indicate that ERK1 plays an essential role during the growth and differentiation of D. discoideum.
Mol Cell Biol 1994 Oct
PMID:Identification and functional analysis of a developmentally regulated extracellular signal-regulated kinase gene in Dictyostelium discoideum. 793 16

We have recently described the properties of delta Raf-1:ER, a fusion protein consisting of an oncogenic form of human Raf-1 and the hormone binding domain of the human estrogen receptor. In this study, we demonstrate that activation of delta Raf-1:ER in quiescent 3T3 cells (C2 cells), while sufficient to promote morphological oncogenic transformation, was insufficient to promote the entry of cells into DNA synthesis. Indeed, activation of delta Raf-1:ER potently inhibited the mitogenic response of cells to platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) treatment. Addition of beta-estradiol to quiescent C2 cells led to rapid, sustained activation of delta Raf-1:ER and MEK but only two- to threefold activation of p42 mitogen-activating protein (MAP) kinase activity. Addition of PDGF or EGF to quiescent C2 cells in which delta Raf-1:ER was inactive led to rapid activation of Raf-1, MEK, and p42 MAP kinase activities, and entry of the cells into DNA synthesis. In contrast, when delta Raf-1:ER was activated in quiescent C2 cells prior to factor addition, there was a significant inhibition of certain aspects of the signaling response to subsequent treatment with PDGF or EGF. The expression and activation of PDGF receptors and the phosphorylation of p70S6K in response to PDGF treatment were unaffected by prior activation of delta Raf-1:ER. In contrast, PDGF-mediated activation of Raf-1 and p42 MAP kinases was significantly inhibited compared with that of controls. Interestingly, the mitogenic and signaling responses of quiescent C2 cells to stimulation with fetal bovine serum or phorbol myristate acetate were unaffected by prior activation of delta Raf-1:ER. It seems likely that at least two mechanisms contribute to the effects of delta Raf-1:ER in these cells. First, activation of delta Raf-1:ER appeared to uncouple the activation of Raf-1 from the activation of the PDGF receptor at the cell surface. This may be due to the fact that mSOS1 is constitutively phosphorylated as a consequence of the activation of delta Raf-1:ER. Second, quiescent C2 cells expressing activated delta Raf-1:ER appear to contain an inhibitor of the MAP kinase pathway that, because of its apparent sensitivity to sodium orthovanadate, may be a phosphotyrosine phosphatase. It is likely that the inhibitory effects of delta Raf-1:ER observed in these cells are a manifestation of the activation of some of the feedback inhibition pathways that normally modulate a cell's response to growth factors. 3T3 cells expressing delta Raf-1:ER will be a useful tool in unraveling the role of Raf-1 kinase activity in the regulation of such pathways.
Mol Cell Biol 1994 Dec
PMID:Inhibition of platelet-derived growth factor- and epidermal growth factor-mediated mitogenesis and signaling in 3T3 cells expressing delta Raf-1:ER, an estradiol-regulated form of Raf-1. 796 25

Human platelets provide an attractive model for studying the regulation of tyrosine phosphorylations and cell-cell adhesion. Major non-receptor tyrosine-kinases are suggested to be responsible for an increase in protein tyrosine phosphorylation following platelet stimulation. Agonist-induced platelet activation triggers also the reorganization of the cytoskeleton with association of multiple signalling proteins. To understand if protein-tyrosine-phosphatases (PTPs) were involved in platelet aggregation, we have investigated the subcellular distribution of these enzymes in resting and thrombin-stimulated platelets. A high level of PTP activity in human resting cells is distributed for 65% and 35%, respectively, in cytosolic and particular fractions. About 10% of this activity are redistributed to the cytoskeletal network during platelet activation. This translocation is dependent on actin polymerization as proved by the disappearance of this phenomenon in cells pretreated by cytochalasin D. Moreover, immunoblotting using anti-PTP polyclonal antibodies indicates that two PTPs, SH-PTP1 and p58 related to HPTP beta, translocate from membranes to Triton X-100 insoluble fractions after platelet activation. This translocation is correlated with the redistribution of several signalling proteins suggesting the possible regulation between these molecules and PTPs.
Cell Mol Biol (Noisy-le-grand) 1994 Jul
PMID:Thrombin-induced redistribution of protein-tyrosine-phosphatases to the cytoskeletal complexes in human platelets. 798 21

Protein tyrosyl phosphorylation plays an essential role in regulating cellular events such as proliferation, differentiation and oncogenesis. The recent characterization of the family of protein tyrosine phosphatases (PTPases) suggests that dephosphorylation might be a crucial event in these phenomena. One of the functions of PTPases is to reverse the effect of protein tyrosine kinases (PTKases), many of which are oncogenes, suggesting that they may act as tumor suppressors as described for HPTP gamma. In order to investigate the implication in lung cancer of HPTP beta, a receptor PTPase, we have developed a semi-quantitative method derived from primer-directed reverse transcription (RT) and subsequent polymerase chain reaction (PCR) with 32P-labelled nucleotide. We have demonstrated that the expression of HPTP beta mRNA was dramatically decreased in lung adenocarcinomas and lung malpighian carcinomas as compared to normal lung tissue. In addition, HPTP beta was not expressed in the pulmonar adenocarcinoma cell line A427, which proliferates in a deregulated way. These results suggest that the loss of expression of HPTP beta might play a role in neoplasic transformation and thus this molecule could act as a tumor suppressor factor.
Cell Mol Biol (Noisy-le-grand) 1994 Jul
PMID:Implication of a protein-tyrosine-phosphatase in human lung cancer. 798 22

Using degenerate oligodeoxynucleotide primers we previously obtained cDNA fragments from ten different murine protein-tyrosine phosphatases (PTPases). Employing this same primer set, a method was developed to assess the expression levels of these PTPase family members in a fast and simple way. RT-PCR products of several cell types and tissue samples were used as probes on dot-blots containing the ten different PTPase fragments in equimolar amounts. Hybridization intensities at the various dots reflect the relative expression levels of the corresponding PTPases in the starting material. In this way expression of PTPases during mouse brain development could be monitored. Expression of PTP delta was found to be absent in embryonic stem cells but high in fetal and adult brain. PTP epsilon expression is shown to gradually increase in brain during maturation. Our method is generally applicable to gene families of which the transcripts can be detected with a single degenerate primer pair and is especially useful in situations where only limited amounts of RNA can be obtained.
Mol Biol Rep 1994 Mar
PMID:Rapid assessment of protein-tyrosine phosphatase expression levels by RT-PCR with degenerate primers. 807 90


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