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:P04626 (erbB-2)
5,251 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The epidermal growth factor (EGF) receptor is a tyrosine-specific protein kinase with autophosphorylating activity. A 300 amino acid-long region of the receptor's cytoplasmic domain matches (35-90% homology) sequences of transforming proteins from the src family and includes a putative nucleotide binding site. Several of the src transforming proteins have tyrosine kinase activity, but v-erb-B, which appears to be a truncated EGF receptor, is virtually identical to the receptor over this region and yet lacks detectable kinase activity. To locate possible acceptor sites in the v-erb-B protein, we have mapped these sites in the human EGF receptor. We report here that three tyrosine sites near the C-terminus are phosphorylated in vitro. In intact cells, we find that EGF stimulates phosphorylation of several sites, the tyrosine 14 residues from the C-terminus being modified the most extensively. The equivalent site is absent in the v-erb-B protein of avian erythroblastosis virus (AEV) and may influence tyrosine kinase activity.
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PMID:Autophosphorylation sites on the epidermal growth factor receptor. 609 Sep 45

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.
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PMID:The kinetics of tyrosine phosphorylation by the purified epidermal growth factor receptor kinase of A-431 cells. 610 Dec 63

Monoclonal anti-epidermal growth factor (EGF) receptor antibodies were used as a diagnostic tool for the investigation of the role of the receptor molecule in the transduction of the biological effects mediated by EGF. The specificity of the antibodies was established by immunoprecipitation of the receptor from biosynthetically labeled cells. The previously described (Schreiber, A. B., Lax, I., Yarden, Y., Eshhar, Z., and Schlessinger, J. (1981) Proc. Natl. Acad. Sci U. S. A. 78, 7535-7539) 2F2-IgM antibody binds to or close to the binding site of the growth factor on the receptor molecule; it induces receptor clustering and internalization and triggers early and delayed effects of EGF. A monovalent Fab fragment of the 2G2-IgM antibody stimulates the EGF-receptor sensitive protein kinase, but does not induce receptor clustering and DNA synthesis. When cell-bound 2G2-Fab fragments are cross-linked with anti-mouse Ig antibodies, both receptor clustering and mitogenic activity are restored. A second monoclonal antibody against EGF-receptor denoted TL5-IgG does not interfere with the binding of EGF to the receptor, fails to induce receptor clustering, and does not possess any intrinsic bioactivity. The cross-linking of cell-bound TL5-IgG with anti-mouse Ig antibodies leads to the stimulation of DNA synthesis. It is concluded that the EGF-receptor, when properly triggered, contains all the biochemical attributes necessary for the initiation of biological effects. Receptor clustering, even when mediated via domains distinct from the hormone binding site on the receptor molecule, appears as a necessary and sufficient signal for the induction of DNA synthesis.
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PMID:Biological role of epidermal growth factor-receptor clustering. Investigation with monoclonal anti-receptor antibodies. 629 87

The Ca2+- and phospholipid-dependent protein kinase (C-kinase) binds tightly in the presence of Ca2+ to purified membranes of A431 human epidermoid carcinoma cells. The major membrane substrate for C-kinase is the epidermal growth factor (EGF) receptor. Phosphorylation of the EGF receptor is Ca2+-dependent and occurs at threonine and serine residues. After tryptic digestion of the receptor, three major phosphothreonine-containing peptides were identified. These are identical with three new phosphopeptides present in the EGF receptor isolated from A431 cells treated with either of the tumor promoters 12-O-tetradecanoylphorbol 13-acetate or teleocidin. C-kinase catalyzes phosphorylation at these same sites in purified EGF receptor protein. These results indicate that, in A431 cells exposed to tumor promoters, C-kinase catalyzes phosphorylation of a significant population of EGF receptor molecules. This phosphorylation of EGF receptors results in decreased self-phosphorylation of the EGF receptor at tyrosine residues both in vivo and in vitro and in decreased EGF-stimulated tyrosine kinase activity in vivo.
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PMID:C-kinase phosphorylates the epidermal growth factor receptor and reduces its epidermal growth factor-stimulated tyrosine protein kinase activity. 632 73

The 170 000 dalton hepatic epidermal growth factor (EGF) receptor is phosphorylated on serine and tyrosine residues. The evidence indicates that distinct protein kinases are involved. Since EGF and agents that elevate cAMP are believed to participate in the regulation of liver regeneration, we tested whether or not the catalytic subunit of cAMP-dependent protein kinase (catalytic subunit), a known serine kinase, would utilize the EGF receptor as a substrate. The catalytic subunit increased phosphorylation of the EGF receptor in purified rat liver plasma membranes. The serine specificity of the catalytic subunit was established by phosphoamino acid analysis of electrophoretically purified EGF receptor. The result was confirmed by catalytic subunit phosphorylation of affinity purified preparations of the EGF receptor. The rates of dephosphorylation of the membrane-associated EGF receptor phosphorylated on different residues were compared. Dephosphorylation of serine residues (after catalytic subunit phosphorylation) was considerably slower (t1/2 greater than 120 sec) than the removal of phosphotyrosine after stimulation with EGF (t1/2 less than 30 sec).
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PMID:Phosphorylation of the hepatic EGF receptor with cAMP-dependent protein kinase. 632 68

This paper demonstrates spontaneous transfer of epidermal growth factor (EGF) receptor mitogenicity from human A431 carcinoma cells to receptor negative mouse cells. The fact of transfer was documented by the demonstration in the recipient cell of normal EGF-binding affinity, covalent labeling of transferred receptor by 125I-EGF, and reactivity with specific anti-human receptor antibody. Phosphorylation experiments suggest that in the transferred receptor the protein kinase site tends to face the inside of the cell. The transferred receptor imposed upon the normally unresponsive cells a mitogenic responsiveness to EGF in the nM concentration range, as measured by stimulation of DNA replication. EGF-dependent mitogenesis in the recipient cells was abolished by both anti-EGF antibody and anti-human receptor antibody, indicating that the transferred mitogenicity is both EGF and receptor specific. For NR-6 cells without transplanted receptor, the same antibody had no effect on non-EGF-dependent mitogenesis. Interestingly, although the transferred receptor displayed normal behavior in several respects, it did not mediate rapid internalization and degradation of bound EGF.
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PMID:Mitogenic activity of the epidermal growth factor receptor after transfer from A431 carcinoma cells to receptor-negative fibroblastic cells. 633 51

We have purified the epidermal growth factor (EGF) receptor/protein kinase from the livers of normal mice by affinity chromatography. The biochemical properties of the liver receptor are very similar to those of the EGF receptor previously prepared from the human tumor cell line A-431 [Cohen, S., Ushiro, H., Stoscheck, C. & Chinkers, M. (1982) J. Biol. Chem. 257, 1523-1531]. The liver receptor for EGF is a glycoprotein of Mr 170,000. It binds 125I-labeled EGF and possesses an EGF-stimulable protein kinase activity specific for tyrosine residues. Both autophosphorylation and kinase activity toward exogenous substrates are demonstrable. The EGF receptor purified from normal mouse liver is antigenically related to the receptor purified from human A-431 cells.
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PMID:Purification and characterization of epidermal growth factor receptor/protein kinase from normal mouse liver. 698 68

Activation of several protein kinases is mediated, at least in part, by phosphorylation of conserved Thr or Tyr residues located in a variable loop region, near the active site. In certain kinases, this activation loop also controls access of peptide substrates to the active site. In the corresponding region of the epidermal growth factor (EGF) receptor, a potential phosphorylation site, Tyr-845, does not appear to have a major regulatory role. In order to find out whether this variable loop can modulate the peptide phosphorylation and self-phosphorylation activities of the EGF receptor kinase, we investigated the role of residues around Tyr-845, using site-directed mutagenesis. Multiple sequence alignment showed that residues Glu-842, Glu-844 and His-846 are conserved or nearly conserved in eight members of the EGF receptor family. Mutants Glu-842-->Ser, Glu-844-->Gln and His-846-->Ala were expressed in the baculovirus/insect cell system, purified to near-homogeneity and characterized with respect to their peptide phosphorylation and self-phosphorylation activities. All three mutants were active, and these changes did not affect ATP binding directly. However, all mutations increased the Km(app.) for peptide substrates and MnATP in peptide phosphorylation reactions. The Vmax. for the phosphorylation of peptide RREELQDDYEDD was unaltered, but the Vmax. for self-phosphorylation (with variable [MnATP]) decreased 4-, 2- and 7-fold for mutants Glu-842-->Ser, Glu-844-->Gln and His-846-->Ala respectively, compared with the wild-type. These results suggest that binding of this peptide restored an optimal conformation at the active site that might be impaired by the mutations. A study of the dependence of initial rates of self-phosphorylation on cytoplasmic domain concentration showed that the order of reaction increased with the progress of self-phosphorylation. Both pre-phosphorylation and high concentrations of ammonium sulphate restored maximal or near-maximal levels of self-phosphorylation in the mutants, possibly through compensating conformational changes. A plausible homology model, based on the cyclic AMP-dependent protein kinase catalytic subunit, accommodated the sequence Glu-841-Glu-Lys-Glu as an insertion in the peptide binding loop at the edge of the active site cleft. The model suggests that Glu-844 and His-846 may participate in H-bonding interactions, thus stabilizing the active site region, while Glu-842 does not appear to interact with regions of the catalytic core.
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PMID:An investigation of the role of Glu-842, Glu-844 and His-846 in the function of the cytoplasmic domain of the epidermal growth factor receptor. 775 68

Transforming growth factor beta (TGF beta) acts on epithelial thyroid cells, negatively controlling their proliferation and functions. The effects of TGF beta on epithelial rat thyroid cells (FRTL-5) and on two TGF beta-resistant rat thyroid cell clones (FRTL-5H2 and FRTL-R) were investigated. FRTL-5H2 represents a rat thyroid cell clone overexpressing active erbB-2 oncogene, recently obtained after FRTL-5 cell infection with a retrovirus vector carrying the erbB-2 human oncogene (G. Mincione et al., Cancer Res., 53: 5548-5553, 1993). FRTL-R is a FRTL-5 subclone spontaneously isolated after long term in culture. FRTL-5H2 and FRTL-R cell clones were stimulated by TGF beta at the same concentration of 5 ng/ml that induced 70% inhibition of [3H]thymidine incorporation in control FRTL-5 thyroid cells. Nuclear events regulated by TGF beta, such as cyclin and cyclin-dependent kinase gene expression, were then analyzed. In FRTL-5 cells, TGF beta was found to reduce the expression of cdk2 and cyclin A genes; the same treatment did not modify nuclear gene expression in the resistant cell clones. TGF beta is known to reduce iodide uptake in thyroid cells; in both FRTL-5H2 and FRTL-R cells, TGF beta was found to inhibit the thyrotropin-induced iodide uptake. Thus, thyroid cell clones, resistant to the growth-inhibitory activity of TGF beta, were sensitive to TGF beta inhibition of iodide incorporation, suggesting that TGF beta activates divergent signaling pathways in these cells, separately controlling cell proliferation and differentiation parameters. Studies on TGF beta receptors showed similar amounts of TGF beta-binding species on FRTL-5 cells and TGF beta-resistant clones, while 125I-labeled TGF beta cross-linking experiments revealed differences; thus, the TGF beta-resistant cells showed a 40% decrease in the amount of labeled type II TGF beta receptor on the cell surface. However, this different pattern of TGF beta receptors cannot totally account for the shown TGF beta resistance to growth inhibition that might also be due to perturbation in signaling pathways.
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PMID:Epithelial rat thyroid cell clones, escaping from transforming growth factor beta negative growth control, are still inhibited by this factor in the ability to trap iodide. 779 96

Progesterone (P4) production by the bovine placenta differs from that of other steroidogenic tissue in two important respects: 1) it is calcium-dependent but cyclic nucleotide-independent and 2) it is suppressed by an endogenous inhibitor for most of the life span of the placenta. This natural refractory state of the placenta can be overcome in in vitro incubations of fetal cotyledon cells by agents that increase intracellular calcium (3-isobutylmethylxanthine [MIX], calcium ionophore (A23187), addition of substrate (pregnenolone, hydroxycholesterol), and stimulators of protein kinase C (PKC) such as phorbol ester (TPA). We therefore tested, in cultures of cotyledonary cells, two compounds that have been reported to inhibit protein kinases: 1) staurosporine (STA), an inhibitor of PKC, cAMP-dependent kinase, tyrosine kinase (TK), and the epidermal growth factor (EGF) receptor TK, and 2) genistein, an inhibitor of TK. It was found that STA stimulated steroidogenesis in a dose-dependent manner in both the absence and presence of added calcium. STA (10(-9) M) stimulated at least a twofold increase in P4 production by cultured fetal cotyledon cells throughout the first half of gestation (50-130 days). EGF was also found to cause a twofold stimulation of P4 production, and the effect was additive to that of STA. Both basal and EGF- or STA-stimulated production were inhibited by genistein. In contrast, two inhibitors of PKC and PKA (H-7, H-8) had no effect on P4 production. We conclude that STA-induced steroidogenesis in the bovine placenta is not related to its reported ability to inhibit PKC, TK, or EGF receptor TK.
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PMID:Staurosporine stimulates progesterone production by bovine placental cells. 791 70


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