Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P04626 (erbB-2)
 5,251 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tyrosine kinase activity of the epidermal growth factor (EGF) receptor can be regulated by its state of association. Studies done with the purified receptor solubilized in Triton X-100 indicate that dimer formation results in negative regulation of kinase, whereas successive binding of EGF and ATP shift the association equilibrium toward the catalytically active monomeric form. The promotion of the monomeric state by ATP can be mimicked by various nonphosphorylating analogs indicating that nucleotide binding rather than autophosphorylation is responsible for stabilizing the monomeric receptor form. Truncated receptor forms, lacking either the external EGF-binding domain or the internal kinase (ATP-binding) domain, are unable to form stable dimers. These results suggest that both intra- and extracellular domains of the receptor act to stabilize the kinase-regulatory dimer.
 ...
PMID:Regulation of kinase and intermolecular bonding in intact and truncated epidermal growth factor receptor. 301 92

Tyrosine-specific protein kinase activity of the epidermal growth factor (EGF) receptor, pp60v-src and pp110gag-fes was inhibited in vitro by an isoflavone genistein. The inhibition was competitive with respect to ATP and noncompetitive to a phosphate acceptor, histone H2B. By contrast, genistein scarcely inhibited the enzyme activities of serine- and threonine-specific protein kinases such as cAMP-dependent protein kinase, phosphorylase kinase, and the Ca2+/phospholipid-dependent enzyme protein kinase C. When the effect of genistein on the phosphorylation of the EGF receptor was examined in cultured A431 cells, EGF-stimulated serine, threonine, and tyrosine phosphorylation was decreased. Phosphoamino acid analysis of total cell proteins revealed that genistein inhibited the EGF-stimulated increase in phosphotyrosine level in A431 cells.
 ...
PMID:Genistein, a specific inhibitor of tyrosine-specific protein kinases. 310 39

The specific tyrosine phosphorylation of glucose-6-phosphate dehydrogenase (G6PDH) by the epidermal growth factor (EGF) receptor in vitro is demonstrated. The Km values of the substrate G6PDH and of ATP for the receptor tyrosine kinase were ca. 1 and 10 microM, respectively. The rate of phosphorylation was EGF dependent, with a four-fold increase in Vmax in the presence of EGF. The phosphorylation was stimulated maximally by 0.2 microM or greater EGF, with an ED50 of ca. 20 nM which is consistent with the affinity of the solubilized receptor for EGF. Using conditions of 5 microM G6PDH, 100 microM ATP, 5 mM Mg2+, and 1 mM Mn2+, up to 0.3 mol phosphate was incorporated into 1 mol of the 55-kDa subunit of Baker's yeast G6PDH. Tryptic peptide mapping revealed several unique phosphopeptides for both Baker's yeast and bovine adrenal G6PDH. The patterns of phosphopeptides for a given enzyme were identical for basal and EGF-stimulated phosphorylation.
 ...
PMID:Epidermal growth factor receptor tyrosine kinase phosphorylation of glucose-6-phosphate dehydrogenase in vitro. 312 60

The epidermal growth factor (EGF) receptor, which exhibits intrinsic protein tyrosine kinase activity, undergoes a rapid, intramolecular self-phosphorylation reaction following EGF activation. The primary sites of tyrosine self-phosphorylation in vivo are located in the extreme carboxyl-terminal region of the molecule, principally Tyr-1173. To test the biological and biochemical consequences of this EGF receptor self-phosphorylation, we made the mutation Tyr----Phe-1173. Membranes containing the mutated receptor exhibited an ED50 for EGF activation of tyrosine kinase activity equivalent to control receptor at both high and low substrate levels, but exhibited reduced basal and EGF-stimulated tyrosine kinase activity at low, non-saturating substrate levels. The Tyr----Phe-1173 mutant possessed high affinity EGF binding and could still self-phosphorylate other tyrosine sites in an intramolecular fashion with a low Km for ATP (200 nM), suggesting that this alteration did not grossly change receptor structure. When EGF-dependent growth of Chinese hamster ovary cells expressing comparable levels of control or mutant EGF receptor was measured, the ability of the mutant receptor to mediate cell growth in response to EGF was reduced by approximately 50%, yet both receptors exhibited a similar affinity and ED50 for EGF. These results support the concept that this self-phosphorylation site can act as a competitive/alternate substrate for the EGF receptor, and that this region of the molecule is important in modulating its maximal biological activity.
 ...
PMID:Alteration of epidermal growth factor receptor activity by mutation of its primary carboxyl-terminal site of tyrosine self-phosphorylation. 334 10

It was previously demonstrated that the epidermal growth factor (EGF) receptor in human A431 cells undergoes a slow post-translational modification by which it acquires EGF binding capacity (Slieker, L.J., and Lane, M.D. (1985) J. Biol. Chem. 260, 687-690). In this report, the role of glycosylation in the acquisition of ligand binding activity and in the intracellular translocation of the receptor precursor is characterized. Human A431 cells were incubated with [35S]methionine, and 35S-labeled EGF receptors were purified either by immunoprecipitation (total receptor) or by adsorption to an EGF affinity matrix (high affinity, or active receptor). The half-time for receptor activation is approximately 30 min and precedes its acquisition of resistance to endo-beta-N-acetylglucosaminidase H (t 1/2 = 75 min), a medial Golgi event. Activation is blocked by tunicamycin and is markedly slowed (t 1/2 = 120 min) by 1-deoxynojirimycin, an inhibitor of glucosidase I. In the latter case, the oligosaccharide chains are not further processed to complex forms. Treatment of the active high mannose receptor with endo-beta-N-acetylglucosaminidase H generates a fully active aglycoreceptor polypeptide, indicating that core oligosaccharide addition is a prerequisite for activation but that oligosaccharide chains are not intrinsically required for EGF binding. Subcellular fractionation studies showed that the EGF receptor is activated in the endoplasmic reticulum and that translocation from that organelle is extremely slow (t 1/2 = 75 min). Since the latter translocation rate approximates that for the acquisition of the resistance to endoglycosidase H, transit from the endoplasmic reticulum appears to be rate-limiting for the maturation of the receptor. Both tunicamycin and 1-deoxynojirimycin inhibit exit from the endoplasmic reticulum in parallel with their effects on the acquisition of binding activity. Immunoprecipitation of 35S-labeled EGF receptor with antiphosphotyrosine antibody in the presence of ATP suggested that the autophosphorylation activity of the receptor is also acquired post-translationally. The possible correlation of this to EGF binding activity is discussed.
 ...
PMID:Synthesis of epidermal growth factor receptor in human A431 cells. Glycosylation-dependent acquisition of ligand binding activity occurs post-translationally in the endoplasmic reticulum. 349 Apr 80

The epidermal growth factor (EGF) receptor is a transmembrane glycoprotein of relative molecular mass 170,000 with intrinsic ligand-dependent protein tyrosine kinase activity. Binding of EGF to its receptor activates a number of immediate biochemical processes, such as alterations of intracellular free calcium, pH, and increased transcription of several responsive genes, which usually culminate many hours later in DNA replication and cell division. Abolishing the tyrosine kinase activity of three related oncogenes, v-src, v-mos, and v-fps, eliminates their capacity to transform cell. Several reports have suggested that specific aspects of EGF receptor function are independent of the intrinsic tyrosine kinase activity; however, these studies used an antibody against EGF receptor which failed to activate phosphorylation of exogenous substrates and an insertional mutation in the EGF receptor tyrosine kinase domain which had not been shown to abolish protein kinase activity in cells. Because many transmembrane receptors interact with intrinsic membrane proteins to activate second messenger systems, it is important to resolve experimentally whether mechanisms, in addition to activation of the intrinsic tyrosine kinase activity, mediate some EGF actions. From functional analyses of an EGF receptor containing a single amino-acid mutation at a site required for phosphate transfer from ATP, we conclude that the tyrosine kinase activity of the EGF receptor is essential for the diverse biochemical effects of EGF, including rapid alterations in intracellular calcium, activation of gene transcription, receptor down-regulation and the ultimate stimulatory effects on cell proliferation.
 ...
PMID:Requirement for intrinsic protein tyrosine kinase in the immediate and late actions of the EGF receptor. 349 22

Partial cleavage with trypsin has been used to study the structure of the epidermal growth factor (EGF) receptor purified from human carcinoma cells. Following affinity labeling of the receptor with 125I-EGF or the ATP analogue 5'-p-fluorosulfonyl benzoyl[14C]adenosine, metabolic labeling with [35S]methionine, [3H]glucosamine, or [32P]orthophosphate, or in vitro autophosphorylation with [gamma-32P]ATP, tryptic cleavage defines the following three regions of the 180-kDa receptor protein: 1) a 125-kDa trypsin-resistant domain which contains sites of glycosylation, EGF binding, and an EGF-specific threonine phosphorylation site; 2) an adjacent 40-kDa fragment which contains serine and threonine phosphorylation sites and is further cleaved to a 30-kDa trypsin-resistant domain; and 3) a terminal 15-kDa portion of the receptor that contains the sites of tyrosine phosphorylation and is degraded to small fragments in the presence of trypsin. Both the 125- and 40-kDa regions of the EGF receptor appear to be required for receptor-associated protein kinase activity since separation of these regions by tryptic cleavage abolishes this activity, and both regions are specifically labeled with an ATP affinity analogue, suggesting that both are involved in ATP binding. Additional 63- and 48-kDa phosphorylated fragments are generated upon trypsin treatment of EGF receptor from EGF-treated cells. The potential usefulness of partial tryptic cleavage in studying the EGF receptor and the possible biological function of the 30-kDa trypsin-resistant fragment of the receptor are discussed.
 ...
PMID:Characterization of structural domains of the human epidermal growth factor receptor obtained by partial proteolysis. 608 49

The epidermal growth factor (EGF) receptor and other growth factor receptors have been shown to possess tyrosine-specific protein kinase activity. Before the demonstration of kinase activity in growth factor receptors, tyrosine kinases of molecular weight (MW) 60,000 (60K) were found to be encoded by the src oncogene and other oncogenes related to src. Our earlier work on intracellular processing of the EGF receptor, a 170,000-MW polypeptide, provided evidence for proteolytic separation of well defined structural domains, and suggested to us the possibility of separating functional domains by limited proteolysis. The isolation of such kinase domains should facilitate comparison of the receptor/kinase with other well characterized kinases including those of oncogene origin. We report here the identification of a catalytically functional 42K kinase derived proteolytically from the isolated human EGF receptor. This fragment, comparable in size to pp60src, carries the kinase ATP-binding site, and functions catalytically even after detachment from the EGF-binding site and the major autophosphorylation region.
 ...
PMID:42,000-molecular weight EGF receptor has protein kinase activity. 609 Sep 43

The protein kinase associated with the purified epidermal growth factor (EGF) receptor from membrane (Mr = 150,000) or vesicle (Mr = 170,000) preparations of A-431 cells was shown to catalyze the phosphorylation of the peptide Leu-Glu-Asp-Ala-Glu-Tyr-Ala-Ala-Arg-Arg-Arg-Gly at the tyrosine residue. EGF enhanced peptide phosphorylation by 3-5-fold. The steady state kinetic analysis of the purified kinase from membranes showed that the reaction mechanism was of the sequential type in either the presence of absence of EGF. Thus, the peptide and ATP must bind to the enzyme before any product is released. Both neurotensin 8-13 and kyotorphin were inhibitors but not substrates of the protein kinase. Kyotorphin was a linear noncompetitive inhibitor with ATP as the variable substrate and a linear competitive inhibitor with peptide as the variable substrate. ADP, a product of the kinase reaction, was a linear noncompetitive inhibitor with respect to ATP and a linear competitive inhibitor with respect to peptide. Based on these data, it can be suggested that the tyrosine protein kinase from A-431 cells catalyzes a Ordered Bi Bi reaction where peptide is the first substrate to bind and ADP is the last product to be released.
 ...
PMID:The kinetics of tyrosine phosphorylation by the purified epidermal growth factor receptor kinase of A-431 cells. 610 Dec 63

The membranes from epidermoid carcinoma cells (A-431) that were surface iodinated while intact using catalysis by lactoperoxidase and 125I as iodide contain one major labeled protein of Mr = 180,000. This protein is clearly iodinated on the outside of the intact cell because it is not the major protein labeled when isolated membranes are iodinated. This major surface-iodinated protein is almost certainly the epidermal growth factor (EGF) receptor, since both have the same Mr and have identical sensitivity to proteases. Both are nearly quantitatively converted from an Mr = 180,000 form to an Mr = 160,000 form by an endogenous calcium-activated neutral protease when cells are broken in the presence of calcium. Both are degraded by trypsin only if trypsin has access to the inside of the cell. This latter finding implies that the surface-iodinated EGF receptor spans the plasma membrane. Since the EGF receptor is an autophosphorylating kinase whose activity is enhanced in the presence of EGF, the receptor was labeled and identified using [gamma-32P] ATP. While both iodination and EGF-enhanced phosphorylation occur on tyrosine residues, peptide mapping of the iodinated or phosphorylated Mr = 180,000 band showed that different peptides were being labeled. Since the EGF receptor-kinase spans the plasma membrane, the peptide iodinated on the surface of the intact cell must be different from the peptides that are probably autophosphorylated on the cytoplasmic side of the membrane.
 ...
PMID:Surface iodination of epidermal growth factor receptors in intact cells. 632 89


<< Previous 1 2 3 4 5 6 7 Next >>