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

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Query: UNIPROT:O95477 (membrane-bound)
29,236 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Insulin caused a transient increase in H2O2 accumulation in human fat cell suspensions that was observed only in the presence of an inhibitor of catalase and heme-containing peroxidases, such as azide, and reached peak levels of 30 microM within 5 min. The cells contained a plasma membrane-bound NADPH oxidase, producing 1 mol H2O2/mol of NADPH oxidation, that was activated on exposure of intact cells to insulin at contrations that are physiologically relevant (0.1-10 nM). The hormone effect was rapid and was due to a selective increase in substrate affinity. The enzyme was magnesium dependent, required a flavine nucleotide for optimal activity, and was most active at pH 5.0-6.5. In contrast to all other hormone- or cytokine-sensitive NADPH oxidases that have been characterized in sufficient detail, the human fat cell oxidase retained its hormone responsiveness after cell disruption, and only Mn2+, but no ATP, was required for a ligand-induced activation in crude plasma membranes. The results demonstrate that insulin utilizes tyrosine kinase-independent pathways for receptor signaling and strongly support the view that H2O2 contributes to the intracellular propagation of the insulin signal.
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PMID:Human fat cells possess a plasma membrane-bound H2O2-generating system that is activated by insulin via a mechanism bypassing the receptor kinase. 131 14

1. The effect of a sunflower oil-enriched diet on plasma membrane-bound protein kinase C, protein kinase A, casein and tyrosine kinase activities was studied. 2. The diet induced an increase in the content of linoleic acid and a decrease in the content of palmitic acid. The anisotropy parameter (rs) of the fluorescence probe DPH and SDPH decreased strongly in the experimental group. 3. Protein kinase C was stimulated more than two times. Tyrosine kinase, protein kinase A and casein kinase activities were increased by 65, 57 and 40%, respectively. 4. We suggest that a more fluid lipid environment favours higher plasma membrane-bound protein kinase activities.
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PMID:Effect of a sunflower oil-supplemented diet on protein kinase activities of rat liver plasma membranes. 147 8

Recent studies on the structure of the B cell antigen receptor demonstrate that the membrane-bound and antigen-binding immunoglobulin molecules are noncovalently associated with a heterodimer of two novel transmembrane proteins. The B cell antigen receptor is thus a multicomponent receptor complex whose structural features are similar to those of the T cell antigen receptor complex. Cross-linking of the B cell antigen receptor results in rapid tyrosine phosphorylation of substrate proteins. This suggests that the B cell receptor belongs to a subgroup of the tyrosine kinase receptor family with a noncovalently associated src-like tyrosine kinase.
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PMID:Antigen receptors on B lymphocytes. 159 Oct 6

Tyrosine kinase activity was determined in neonatal and adult human brain, oligodendrogliomas, and astrocytomas. The astrocytomas were divided into low- (grade I and grade II) and high-grade (grade III and grade IV) tumors. We measured the tyrosine kinase activity in the cytosolic and membrane fraction using poly(glutamic acid:tyrosine, 4:1) as an artificial substrate. The cytosolic activity in oligodendrogliomas (n = 7), low-grade astrocytomas (n = 7), and neonatal brain (n = 1) was increased, on average, two- to fourfold compared with that in normal adult brain (n = 14). The cytosolic activities of high-grade astrocytomas (n = 11) were in approximately the same range as found in normal adult brain. The absence of an increase in cytosolic activity in high-grade astrocytomas compared with adult brain is likely due to the occurrence of necrosis in these tumors. In contrast to the cytosolic activity, no differences were found in the membrane-bound activity. By fast protein liquid chromatography, at least three forms of cytosolic protein tyrosine kinase could be separated, which eluted at 0, 115, and 210 mM NaCl. In most cases the highest amount of activity eluted at 210 mM NaCl. However, in oligodendrogliomas, high-grade astrocytomas, and neonatal brain, more activity eluted at 115 mM NaCl than in normal adult brain (p = 0.043). Nevertheless, protein tyrosine kinases from all three peaks contributed to the elevated levels of total cytosolic activity of oligodendrogliomas and low-grade astrocytomas.
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PMID:Protein tyrosine kinases in human brain and gliomas. 172 1

The effect of tyrosine kinase inhibitor, erbstatin, on cell growth and mRNA expression of growth-factor/receptor system was examined in 6 human gastric-carcinoma cell lines. Erbstatin inhibited both EGF-induced and serum-stimulated cell growth of all 6 cell lines (TMK-1, MKN-1, -7, -28, -45, -74) in a dose-dependent manner. 3H-thymidine incorporation by TMK-1 cells was also suppressed by erbstatin. Erbstatin inhibited protein kinase activity of EGF receptor, p185ERBB2 and pp60c-src in TMK-1 cells. The expression of mRNA of EGF receptor gene and ERBB-2 by TMK-1 cells was not changed by erbstatin treatment, whereas that of c-src was slightly decreased. Interestingly, erbstatin decreased membrane-bound TGF-alpha precursor as measured by anti-TGF-alpha antibody-binding assay, although mRNA expression for TGF-alpha was not altered by erbstatin. Our findings suggest that erbstatin may act as a growth inhibitor for human gastric-carcinoma cells and may not only inhibit tyrosine kinase activities but also negatively modulate the post-transcriptional step of TGF-alpha expression.
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PMID:Effects of tyrosine kinase inhibitor, erbstatin, on cell growth and growth-factor/receptor gene expression in human gastric carcinoma cells. 184 25

Transforming growth factor alpha (TGF alpha) is a 6 kDa polypeptide mitogen that interacts with the epidermal growth factor receptor and activates its intrinsic tyrosine kinase. The mature 50 amino acid TGF alpha is released from a 159 or 160 amino acid integral membrane glycoprotein precursor, denoted proTGF alpha, via cleavage at both termini by an unknown protease with elastase-like specificity. Rat proTGF alpha is encoded by a 4.5 kb mRNA that is transcribed from a gene containing 6 exons and spanning 85 kb of DNA. Expression of TGF alpha is most prevalent and abundant in transformed cells and tumors, but also detectable at modest levels in a limited number of normal cells and tissues. In many neoplastic cells, proteolytic processing of proTGF alpha is incomplete and/or inefficient, resulting in the preponderance of soluble and/or membrane-bound forms larger than the mature TGF alpha. To characterize the biological activities of the transmembrane TGF alpha precursor in the absence of processing, amino acid substitutions were introduced at the cleavage sites by site-directed mutagenesis of the rat TGF alpha cDNA. Fibroblasts expressing the mutant proTGF alpha constructs did not secrete TGF alpha, but did accumulate proTGF alpha at the cell surface. Coincubation of these cells with A431 cells resulted in binding and autophosphorylation of EGF receptors, and mobilization of intracellular calcium in A431 cells, demonstrating that the transmembrane proTGF alpha can activate EGF receptors on adjacent cells, leading to signal transduction. In addition, rat fibroblasts constitutively expressing the wild-type or mutant proTGF alpha became morphologically transformed in culture, and induced tumors in nude mice. Thus, the interaction between membrane-anchored ligand and receptor triggers mitogenesis that can culminate in neoplastic transformation. To characterize the physiological and pathological effects of TGF alpha in vivo, particularly with respect to epithelial cells, transgenic mice were developed which overexpress the growth factor in multiple or specific tissues. Widespread overexpression of TGF alpha driven by the metallothionein promoter induced epithelial hyperplasia in several organs, including liver and intestine, without disrupting normal tissue architecture. In contrast, the pancreas displayed increased proliferation of both acinar cells and fibroblasts, and focal alteration of acinar cell differentiation. This pancreatic hyperplasia, fibroplasia, and metaplasia were reproduced when TGF alpha expression was placed under control of the elastase promoter, and thus locally restricted to acinar cells, suggesting autocrine and/or paracrine mode of action. Finally, overexpression of TGF alpha promoted neoplastic transformation of certain epithelia. In coagulation gland, there was dramatic hyperplasia and dysplasia with focal evidence of carcinoma in situ.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Transforming growth factor alpha: expression, regulation and biological action of its integral membrane precursor. 210 1

We identified the earliest events in autophosphorylation of the insulin receptor after insulin addition. Insulin-stimulated autophosphorylation at specific sites in the tyrosine kinase domain of the receptor's beta-subunit is correlated kinetically with activation of kinase-catalyzed phosphorylation of a model substrate (reduced and carboxyamidomethylated lysozyme; RCAM-lysozyme). To identify these sites, the deduced amino acid sequence of the 3T3-L1 adipocyte insulin receptor of the mouse was determined. Insulin-induced activation of substrate phosphorylation was shown to require autophosphorylation of three neighboring tyrosines (Tyr1148, Tyr1152, and Tyr1153) in the mouse receptor. A search for cellular substrates of the receptor kinase revealed that insulin causes accumulation of a 15,000-Mr phosphorylated (on tyrosine) cytosolic protein (pp15) in 3T3-L1 adipocytes treated with oxophenylarsine (PAO). PAO blocks turnover of the phosphoryl group of pp15, causing its accumulation, and thereby appears to interrupt signal transmission from the receptor to the glucose-transport system. Two membrane-bound protein phosphotyrosine phosphatases that are inhibited by PAO and are apparently responsible for the turnover of the pp15 phosphoryl group have been purified from 3T3-L1 adipocytes and characterized. These and other results support the hypothesis that turnover of the phosphoryl group of pp15, a product of insulin-receptor tyrosine kinase action, couples signal transmission to the glucose-transport system. [32P]pp15 was purified to homogeneity from 3T3-L1 adipocytes. Amino acid and radiochemical sequence analysis of the purified tryptic [32P]phosphopeptide revealed that pp15 is the phosphorylation product of 422(aP2) protein, a 15,000-Mr adipocyte protein whose cDNA we previously cloned and sequenced. 422(aP2) protein was found to bind fatty acids. When exposed to a free fatty acid, notably oleic acid, 422(aP2) protein becomes an excellent substrate of the isolated insulin-receptor tyrosine kinase. Compelling evidence indicates that on binding fatty acid, 422(aP2) protein undergoes a conformational change whereby Tyr19 becomes accessible to the receptor tyrosine kinase and undergoes O-phosphorylation. Adipose tissue and skeletal and heart muscle, which exhibit insulin-stimulated glucose uptake, express a specific insulin-responsive glucose transporter. A cDNA (GT2) that encodes this protein was isolated from a mouse 3T3-L1 adipocyte library and sequenced. We also isolated and characterized the corresponding mouse gene GLUT4. DNase I footprinting with nuclear extracts from 3T3-L1 cells revealed that a differentiation-specific nuclear factor binds to the GLUT4 promoter. The purified transcription factor C/EBP binds at the same position.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Insulin-receptor tyrosine kinase and glucose transport. 216 54

The platelet-derived growth factor (PDGF) receptor is a single membrane-spanning polypeptide of 180,000 daltons with a ligand-stimulatable tyrosine kinase site. We have investigated changes in the structure and association state of the receptor that are induced by ligand binding, but which precede autophosphorylation. Chemical cross-linking of PDGF-bound 32P-labeled receptor and 125I-PDGF-labeled receptor resulted in the generation of a radiolabeled cross-linked complex of 370-390 kDa. This band, as well as the 180-190-kDa PDGF receptor band, were recognized by a PDGF receptor-specific antipeptide antibody. The appearance of the 370-390-kDa band was PDGF-dependent and was seen irrespective of whether the receptor was membrane-bound, solubilized, or highly (approximately 90%) purified. Sedimentation analysis of the 125I-PDGF cross-linked receptor showed that both 180-190- and 370-390-kDa labeled species sedimented as a single peak at about 11.5 S, a position expected of a receptor dimer, demonstrating that the liganded receptor exists essentially as a dimer. In contrast, unliganded receptors sedimented as a single species at 7 S, a position consistent with a monomeric structure. The monomer-dimer interconversion was absolutely ligand-dependent and occurred independent of autophosphorylation. These results demonstrate and intimate correlation between PDGF binding and inter-receptor bond formation, and raise the possibility that the phenomenon may be causally linked to the process of kinase activation.
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PMID:Ligand-induced dimerization of the platelet-derived growth factor receptor. Monomer-dimer interconversion occurs independent of receptor phosphorylation. 254 80

We have located the distal boundary of the tyrosine kinase domain of the EGF receptor and have identified a distinct sequence in the C' terminus required for EGF-dependent receptor internalization, leading to receptor down-regulation and degradation. Within this receptor domain, an 18 amino acid highly negatively charged region of predicted helical structure is required both for endocytosis via a high-affinity, saturable pathway and for ligand-stimulated increases in cytosolic calcium. In contrast to kinase-inactive, internalization-competent receptors, kinase-active, internalization-defective receptors effectively signaled gene transcription, morphological transformation, and growth. These observations support the hypothesis that mitogenic responses to EGF are mediated by activation of the intrinsic protein tyrosine kinase activity of the membrane-bound receptor, with ligand-induced internalization serving to terminate the signal.
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PMID:Functional independence of the epidermal growth factor receptor from a domain required for ligand-induced internalization and calcium regulation. 279 Sep 60

An endogenous membrane-bound substrate of the insulin receptor beta-subunit tyrosine kinase in liver, pp120, has been identified as HA4, a 110-kDa membrane glycoprotein localized primarily to the bile canalicular domain of the hepatocyte. HA4 has been implicated in bile salt transport and cell adhesion. Monoclonal antibodies to HA4 were used to identify it as a substrate of the insulin receptor kinase. Anti-pp120 and anti-HA4 were found to cross-react, and phosphopeptide maps for each of the corresponding antigens were identical. The identification of pp120 as HA4 serves to link insulin action through the receptor tyrosine kinase activity to bile metabolism and raises questions pertaining to the intracellular site(s) of action of the insulin receptor.
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PMID:Identification of pp120, an endogenous substrate for the hepatocyte insulin receptor tyrosine kinase, as an integral membrane glycoprotein of the bile canalicular domain. 284 3


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