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)

Okadaic acid, a potent tumor promoter and inhibitor of phosphoserine/threonine protein phosphatases 1 and 2A, produces a large increase in epidermal growth factor (EGF) receptor phosphorylation in several cell types. The increases are limited to phosphoserine and phosphothreonine residues. 12-O-Tetradecanoylphorbol-13-acetate (TPA), a distinct tumor promoter and protein kinase C activator, also induces serine/threonine phosphorylation of the EGF receptor and is known to modulate receptor functions. Comparison of okadaic acid and TPA influences on the EGF receptor show significant differences. Okadaic acid did not promote phosphorylation of Thr-654, a major site of TPA-induced phosphorylation. However, other sites of phosphorylation were similar for the two tumor promoters. In vitro experiments with purified protein phosphatase 2A demonstrate the insensitivity of Thr-654 phosphorylation, which regulates EGF receptor function, to dephosphorylation by this okadaic acid-sensitive protein phosphatase. In contrast to TPA, okadaic acid did not attenuate the tyrosine kinase activity or ligand binding capacity of the EGF receptor. However, okadaic acid did produce a decrease in EGF-stimulated inositol phosphate formation in a manner distinct from that of TPA.
 ...
PMID:Okadaic acid-induced hyperphosphorylation of the epidermal growth factor receptor. Comparison with receptor phosphorylation and functions affected by another tumor promoter, 12-O-tetradecanoylphorbol-13-acetate. 165 56

The major site of phosphorylation of the epidermal growth factor (EGF) receptor after treatment of cells with EGF is threonine 669. Phosphorylation of this site is also associated with the transmodulation of the EGF receptor caused by platelet-derived growth factor and phorbol ester. A distinctive feature of the primary sequence surrounding threonine 669 is the proximity of 2 proline residues (-Pro-Leu-Thr669-Pro-). This site is not a substrate for phosphorylation by protein kinase C. To investigate the mechanism of the increased phosphorylation of the EGF receptor at threonine 669, in vitro assays were used to measure protein kinase and protein phosphatase activities present in homogenates prepared from cells treated with and without EGF. No evidence for the regulation of protein phosphatase activity was obtained in experiments using the [32P]phosphate-labeled EGF receptor as a substrate. A synthetic peptide corresponding to residues 663-681 of the EGF receptor was used as a substrate for protein kinase assays. Incubation of murine 3T3 L1 pre-adipocytes and human WI-38 fibroblasts with EGF caused a rapid increase (3-10-fold) in the level of threonine protein kinase activity detected in cell homogenates. Similar results were obtained after EGF treatment of Chinese hamster ovary cells expressing wild-type (Thr669) and mutated (Ala669) human EGF receptors. Activation of the threonine protein kinase activity was also observed in cells treated with platelet-derived growth factor, serum, and phorbol ester. Insulin-like growth factor-1 caused no significant change in protein kinase activity. Together these data indicate a role for the regulation of the activity of a threonine protein kinase in the control of the phosphorylation state of the EGF receptor at threonine 669. The significance of the identification of a growth factor-stimulated threonine protein kinase to the mechanism of signal transduction is discussed.
 ...
PMID:Mechanism of phosphorylation of the epidermal growth factor receptor at threonine 669. 254 83

The A431 human epidermoid carcinoma cell line exhibits a 30-100-fold overexpression of the epidermal growth factor (EGF) receptor. We have characterized a membrane-associated phosphotyrosyl-protein phosphatase (PTPase) in these cells since it seemed reasonable that overexpression of the EGF-receptor tyrosine kinase will be matched by high PTPase activity. Indeed, of 12 cell lines tested, the A431 cells had the highest specific PTPase activity. About 70% of the total cellular PTPase activity was found associated with membranes after cell fractionation. The membrane-associated PTPase was hydrophobic as judged by its behaviour in Triton X-114 phase partitioning. High-performance liquid chromatography (HPLC) on a DEAE column revealed a single, homogeneous species of membrane-associated PTPase with an apparent molecular mass of 43 kDa as determined by HPLC on a gel permeation column in the presence of Triton X-100. Comparison of this PTPase with the membrane-associated PTPase activities present in rat spleen and in the human chronic myelogenous leukemia cell line K562 revealed additional species resolvable by DEAE-HPLC. These findings suggest that cells may possess different PTPase activities depending on their growth and differentiation states.
 ...
PMID:Characterization of a membrane-associated phosphotyrosyl protein phosphatase from the A431 human epidermoid carcinoma cell line. 255 94

A simple and reproducible radioimmunoassay of the epidermal growth factor (EGF) receptor which uses 32P-labeled EGF receptor and anti-receptor monoclonal antibodies is reported. In vitro phosphorylation of A431 cell membranes with [gamma-32P]ATP in the presence of 20% dimethyl sulfoxide (which stimulates autophosphorylation of the EGF receptor) and 10 microM Na3VO4 (a potent inhibitor of phosphotyrosyl protein phosphatase) provides radiolabeled EGF receptor for radioimmunoassay without further purification. The most selective phosphorylation of the EGF receptor is achieved at ATP concentrations of 0.1-0.2 microM, which corresponds to the reported Km value for the autophosphorylation reaction of the EGF receptor (W. Weber, P.J. Bertics, and G.N. Gill, 1984, J. Biol. Chem. 259, 14631-14939). The incorporation of 32P into EGF receptors increases in proportion to the increase of ATP concentration up to 6 mol of labeled phosphate at 2.0 microM ATP. The label is entirely on tyrosine residues. The cell membranes can be stored at -70 degrees C for 3 months without loss of immunoreactivity and autophosphorylating activity. Standard curves for the radioimmunoassay were constructed employing either A431 cell membranes or whole cell homogenates containing a known amount of EGF receptor. The assay can detect 7 X 10(10) EGF receptor molecules or 20 ng of the receptor protein, and can quantitatively distinguish the difference in EGF receptor numbers between A431 cells and 29E2 and KB cells with 10-fold and 15-fold fewer receptors than A431 cells, respectively. 29E2 cells and KB cells express twofold more immunoreactive EGF receptors than EGF-binding sites. In contrast, A431 cells possess the same number of immunoreactive sites and receptor sites for EGF binding. To assess total EGF receptor expression, it is necessary to use a method which detects EGF receptors regardless of their intrinsic kinase activity, or capacity to bind EGF. This radioimmunoassay detects immunoreactive receptor molecules, even those which do not bind EGF.
 ...
PMID:A direct radioimmunoassay for human epidermal growth factor receptor using 32P-autophosphorylated receptor. 300 Feb 17

The regulation of protein phosphorylation by Zn2+ ions and by other divalent cations was studied in membrane vesicles from a normal mouse epithelial cell line, MMC-E (Mus musculus castaneous). Four major phosphoacceptor polypeptides were found in these membranes. Micromolar concentrations of Zn2+ ions inhibited the phosphorylation of the epidermal growth factor (EGF) receptor and of threonine residues in a 47,000-dalton polypeptide. In contrast, two polypeptides with molecular weights of 54,000 and 57,000 showed increased phosphorylation, mainly of serine residues, in the p.esence of Zn2+ ions. These results were not obtained using similar concentrations of other divalent cations and were apparently not due to an effect of Zn2+ ions on phosphoprotein phosphatases. Thus, the effects of Zn2+ ions on protein phosphorylation in membrane vesicles are complex and are not restricted to an inhibition of a single protein phosphatase or kinase.
 ...
PMID:Effects of Zn2+ ions on protein phosphorylation in epithelial cell membranes. 630 21

Gene amplification or HER-2/neu protein overexpression signals a poor outcome for bladder cancer patients. We investigated the anti-proliferative effect of IFN-gamma in HER-2/neu-transfected human bladder cancer cells (TCC-N5 and TCC-N10). The cells continued growing after IFN-gamma stimulation but did not activate the Janus kinase (Jak)/Stat pathway. We found Jak/Stat protein phosphatase in TCC-N5 and TCC-N10 cells with upregulated Src homology 2-containing protein tyrosine phosphatase-2 (SHP-2). After the cells had been treated with AG825, a HER-2/neu-specific inhibitor, SHP-2 expression declined, and Jak2/Stat1 reactivated. Similar results were reported in a mouse bladder cancer cell line, MBT2, with constitutive HER-2/neu overexpression. Further, AG825 pretreatment restored the anti-proliferation activity of IFN-gamma in TCC-N5 and TCC-N10 cells. Therefore, the suppression of IFN-gamma signaling in HER-2/neu-overexpressing bladder cancer cells might be due to SHP-2 upregulation. The regulation of SHP-2 by HER-2/neu provides a new target for blocking the HER-2/neu oncogenic pathway.
 ...
PMID:HER-2/neu raises SHP-2, stops IFN-gamma anti-proliferation in bladder cancer. 1734 77

Activation of HER-2/neu leads to multiple signalling cascades and plays a vital role in cell survival and growth. We used a signal transduction antibody array to characterize the tyrosine phosphorylation profiles in heregulin (HRG alpha1)-treated BT474 breast cancer cells, and identified a group of 80 molecules in which tyrosine phosphorylation was highly regulated by HRG-enhanced HER-2/neu signalling. These phosphoproteins included many known HER-2/neu-regulated molecules (e.g., SHC, Akt, Syk and Stat1) and proteins that had not been previously linked to HER-2/neu signalling, such as Fas-associated death domain protein (FADD), apoptosis repressor with CARD domain (ARC), and the tumour suppressor, protein phosphatase type 2A (PP2A). Pharmacological inhibition with HER-2 inhibitor AG825, PI3K inhibitor LY294002, MEK1/2 inhibitor PD98095, and p38MAPK inhibitor SB203580 confirmed that PP2A phosphorylation was modulated by the complicated, HER-2/neu-driven downstream signal network, with the PI3K and MEK1/2 positively, while the p38MAPK negatively regulating its tyrosine phosphorylation. In breast tumour specimens, expression of tyrosine-phosphorylated PP2A (pY307-PP2A) was highly increased in the HER-2/neu positive breast tumours, and significantly correlated to tumour progression, thus enhancing its potential prognostic value. Our data provide meaningful information in the elucidation of the HER-2-driven tyrosine phosphorylation network, and in the development of phosphopeptide-related targets as prognostication indicators.
 ...
PMID:Tyrosine phosphorylation of PP2A is regulated by HER-2 signalling and correlates with breast cancer progression. 1936 Mar 41