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 role of epidermal growth factor (EGF) receptor autophosphorylation sites in the regulation of receptor functions has been studied using cells transfected with mutant EGF receptors. Simultaneous point mutation of 4 tyrosines (Y1068, Y1086, Y1148, Y1173) to phenylalanine, as well as removal of these sites by truncation of the carboxyl-terminal 123 amino acid residues, resulted in reduced receptor phosphorylation of an in vivo specific substrate phospholipase C-gamma 1 to less than 50% compared to the wild-type receptor. The internalization rate constant Ke was also significantly lower in these mutants (0.15/min) compared to cells transfected with wild-type receptor (0.27/min). Additional mutation of tyrosine 992 to phenylalanine in the truncated receptor mutant (Dc-123F) further decreased the receptor internalization rate to a minimal level (ke = 0.07-0.10/min), equivalent to the ke measured for cells expressing kinase-negative receptor (A721). Moreover, tyrosine kinase activity of the Dc-123F receptor toward phospholipase C-gamma 1, compared to wild-type receptor, was reduced by 90%. Taken together, these results show that EGF receptor lacking five autophosphorylation sites functions similar to a kinase-negative receptor. Mutation of tyrosine residue Y992 alone in the context of full length EGF receptor, however, did not affect receptor internalization or kinase activity toward phospholipase C-gamma 1. These data indicate that tyrosine 992 is critical for substrate phosphorylation and internalization only in the context of the truncated receptor, and that minor autophosphorylation sites, such as Y992, may act as compensatory regulatory sties in the absence of the major EGF receptor autophosphorylation sites.
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PMID:Multiple autophosphorylation sites of the epidermal growth factor receptor are essential for receptor kinase activity and internalization. Contrasting significance of tyrosine 992 in the native and truncated receptors. 131 35

The inhibition mechanisms of the epidermal growth factor (EGF) receptor tyrosine kinase and the cAMP-dependent kinase activities by erbstatin and its analogue, RG 14921, were studied by kinetic analysis. Both compounds were slow-binding inhibitors of the EGF receptor kinase. Erbstatin inhibited the EGF receptor kinase as a partial competitive inhibitor with respect to both ATP and the peptide substrate, suggesting that it binds at a site distinct from the ATP and peptide binding sites of the enzyme, and thus lowers the binding affinities of the enzyme for both substrates. In contrast, the analogue RG 14921 inhibited EGF receptor kinase activity as a non-competitive inhibitor with respect to both ATP and the peptide substrate. The distinct modes of inhibition by structurally related compounds suggest a dynamic and possibly extended structure of the catalytic center of the kinase domain of the receptor. Erbstatin and RG 14921 exerted similar effects on cAMP-dependent protein kinase activity. In this system, both compounds displayed potent inhibition and acted by a mode of competitive inhibition with respect to ATP and non-competitive with the peptide substrate.
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PMID:Inhibition kinetics and selectivity of the tyrosine kinase inhibitor erbstatin and a pyridone-based analogue. 131 62

In order to evaluate the possible contribution of phospholipase D (PLD) stimulation to the mitogenic response, a screening of a variety of different compounds, some of which are known to be potent mitogens, was performed using the well characterized Chinese hamster lung fibroblast (CCL39) cell line. In wild type CCL39 cells, or derivatives expressing high levels of either the human M1 muscarinic receptor (Hm1) or the human epidermal growth factor (EGF) receptor (39M1-81 and 39ER22 clones, respectively), thrombin, a potent mitogen for all three cell types, elicited the rapid activation of PLD (t1/2 activation, 30 s). Carbachol-mediated activation of the Hm1 receptor in the 39M1-81 clone, which is not a mitogenic signal, produced a similarly rapid although greater activation of PLD. Addition of EGF to the 39ER22 clone was able to provoke both a mitogenic response and stimulate PLD, albeit a comparatively small effect. In each case, the stimulation of PLD correlated closely with the ability to stimulate inositol phospholipid breakdown and was entirely dependent on the activation of protein kinase C. Moreover, the ability of both thrombin and carbachol to stimulate PLD was found to be rapidly desensitized, with a similar time course of desensitization (t1/2 desensitization, 90 s). It has recently been reported that an increase in phospholipase C (PLC)-mediated phosphocholine (PC) hydrolysis by either addition of agonist or by extracellular addition of PC-specific PLC enzyme constitutes a mitogenic signal. In this regard, in addition to stimulation of PLD, thrombin and carbachol were both able to stimulate the activity of a phosphocholine-specific phospholipase C (PC-PLC), which did not appear to desensitize within the time course employed. By contrast, EGF was unable to elicit the stimulation of PC-PLC. Ligands such as fibroblast growth factor (FGF) and platelet-derived growth factor (PDGF), which bind to and activate receptors with intrinsic tyrosine kinase activity, are potent mitogens for CCL39 cells but were unable to stimulate either PLD or PC-PLC activity. Furthermore, exogenous addition of purified PC-PLC enzyme, although able to induce a strong and lasting hydrolysis of PC, was unable to produce a mitogenic signal on its own. On the basis of these results, we conclude that the activation of both PLD and PC-PLC is neither sufficient nor required to produce a mitogenic response.
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PMID:Stimulation of phosphatidylcholine breakdown by thrombin and carbachol but not by tyrosine kinase receptor ligands in cells transfected with M1 muscarinic receptors. Rapid desensitization of phosphocholine-specific (PC) phospholipase D but sustained activity of PC-phospholipase C. 133 Oct 66

Selective inhibitors of tyrosine kinases, tyrphostin 23 and genistein, produced concentration-dependent inhibition of voltage-operated calcium channel currents in vascular smooth muscle cells isolated from rabbit ear artery. The potency of these two structurally dissimilar inhibitors was similar to that reported for their action as inhibitors of tyrosine kinases. Daidzein, an inactive analogue of genistein, had little inhibitory effect on calcium channel currents at concentrations below 300 microM consistent with an action of these agents at a tyrosine kinase. However, tyrphostin 1, a reportedly less active tyrphostin derivative, also inhibited calcium channel currents with a potency similar to tyrphostin 23. These findings suggest that voltage-operated calcium channels in vascular smooth muscle may be modulated by endogenous tyrosine kinase(s) which display different sensitivities to inhibitors compared with the epidermal growth factor (EGF) receptor. Alternatively the possibility of direct blocking actions of these inhibitors at voltage-operated calcium channels cannot be excluded.
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PMID:Tyrosine kinase inhibitors block calcium channel currents in vascular smooth muscle cells. 133 77

Ligand-induced dimerization of growth factor receptors is crucial for stimulation of their intrinsic protein tyrosine kinase activity promoting receptor autophosphorylation by an intermolecular mechanism. Moreover, the suppressive and negative dominant action of defective epidermal growth factor receptor (EGFR) was shown to be caused by formation of inactive heterodimers with normal EGFR leading to diminished biological signaling. In this report we explore the structural requirements and functional significance of heterodimerization between EGFR and HER2. HER2 (also called c-erbB-2 or neu) is a member of the EGFR family whose natural ligand is still unknown. We show that in response to EGF, wild type EGFR and various EGFR mutants were able to undergo heterodimerization with HER2. Addition of EGF to transfected cells co-expressing HER2 with a kinase negative point mutant of EGFR (K721A) stimulated heterodimer formation, tyrosine phosphorylation of K721A and HER2, and tyrosine phosphorylation of one of their known substrates, phospholipase C gamma. However, the binding of EGF to transfected cells co-expressing HER2 together with another EGFR mutant CD533 (a deletion mutant lacking most of the cytoplasmic domain of EGFR) caused heterodimerization and inhibition of tyrosine kinase activity. It appears therefore that EGF-induced heterodimerization of EGFR and HER2 can promote either stimulatory or inhibitory influences on kinase activity. We propose that the nature of receptor interactions on the cell surface can either activate or inhibit the initiation of growth factor-controlled cellular signaling.
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PMID:Heterodimerization of c-erbB2 with different epidermal growth factor receptor mutants elicits stimulatory or inhibitory responses. 134 15

Amplification and/or overexpression of the erbB-2 gene have been demonstrated in 20-30% of adenocarcinomas of the breast, ovary, lung, and stomach and are associated with aggressive clinical course and poor prognosis. Interference with erbB-2 function by the use of monoclonal antibodies is a promising approach to the treatment of these diseases. In this study we demonstrate that a combination of two anti-erbB-2-specific antibodies inhibited the growth of human gastric tumor cells in vitro. This combination antibody therapy also inhibited the growth of human tumor cell lines growing as xenografts in nude mice and was able to dramatically reduce established tumors. This is the first reported observation of tumor regression induced by anti-erbB-2 monoclonal antibodies. Treatment was not curative in that tumors regrew after 6 weeks. Treatment with either single antibody alone did not inhibit cell growth or tumor formation. Pulse chase and tyrosine kinase activity experiments were used to investigate the activity of the erbB-2 gene product (gp185erbB-2). The formation of complexes by two antibodies was found to interfere with receptor function and mimic some properties of a typical receptor ligand. Selective interference of the erbB-2 receptor by combination antibody therapy may be advantageous for the treatment of human cancers.
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PMID:Therapy of an animal model of human gastric cancer using a combination of anti-erbB-2 monoclonal antibodies. 134 49

The c-erbB-2/neu gene encodes a transmembrane protein of 185 kDa (p185) with tyrosine kinase activity and extensive sequence homology to epidermal growth factor receptor. Amplification and overexpression of the c-erbB-2/neu gene has been shown in certain human tumors and is postulated to be important in human carcinogenesis. High levels of expression of the c-erbB-2/neu gene have been reported in non-small-cell lung cancer (NSCLC) cell lines and primary tumors from the United States. Since geographical and cultural factors may contribute to the development of certain types of cancer, we examined p185 examined p185 expression in 120 tumors from Chinese patients with lung cancers of different cell types and used immunohistochemical staining to determine the extent and general significance of p185 expression in human primary lung cancer. Our results demonstrate that 58.8% of the NSCLCs expressed p185 and that expression of p185 was observed only in NSCLC and not in small-cell lung cancers. Thirty-three of 41 adenocarcinomas and 24 of 55 squamous cell carcinomas among the NSCLCs examined were found to express p185 at levels different from those of normal lung. For the squamous cell carcinomas, p185 expression was correlated with lymph node metastasis (P less than 0.01), but for the adenocarcinomas, it was not (P greater than 0.05). In addition, expression of p185 in NSCLC was significantly more frequent in patients in advanced clinical stages. Our findings indicate that p185 expression is a frequent event and a general phenomenon in NSCLC and is correlated with poor clinical prognostic indicators, suggesting that expression of p185 may be of potential prognostic importance in NSCLC.
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PMID:Overexpression of the c-erbB-2/neu-encoded p185 protein in primary lung cancer. 135 Jan 98

The proto-oncogene designated erbB2 or HER2 encodes a 185-kilodalton transmembrane tyrosine kinase (p185erbB2), whose overexpression has been correlated with a poor prognosis in several human malignancies. A 45-kilodalton protein heregulin-alpha (HRG-alpha) that specifically induced phosphorylation of p185erbB2 was purified from the conditioned medium of a human breast tumor cell line. Several complementary DNA clones encoding related HRGs were identified, all of which are similar to proteins in the epidermal growth factor family. Scatchard analysis of the binding of recombinant HRG to a breast tumor cell line expressing p185erbB2 showed a single high affinity binding site [dissociation constant (Kd) = 105 +/- 15 picomolar]. Heregulin transcripts were identified in several normal tissues and cancer cell lines. The HRGs may represent the natural ligands for p185erbB2.
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PMID:Identification of heregulin, a specific activator of p185erbB2. 135 Mar 81

In this work, we have used Xenopus oocyte maturation as a read-out for examining the ability of the neu tyrosine kinase (p185neu) to participate with the epidermal growth factor (EGF) receptor in a common signal transduction pathway. We find that unlike the case for the EGF receptor, which elicits EGF-dependent maturation of these oocytes as reflected by their germinal vesicle breakdown (GVBD), neither the normal neu tyrosine kinase (p185val664) nor the oncogenic form of neu (p185glu664) are able to effectively trigger this maturation event. However, expression of p185glu664 causes a specific and significant promotion of the progesterone-induced GVBD, reducing the half-time for this maturation even from approximately 9 h to approximately 5 h. Stimulation of the progesterone-induced GVBD did not occur following the expression of a kinase-deficient p185neu protein (in which a lysine residue at position 758 was changed to alanine). Essentially identical results were obtained when the mRNAs coding for fusion proteins comprised of the extracellular domain of the receptor for immunoglobulin E (IgE), and the membrane-spanning and tyrosine kinase domains of normal or oncogenic p185neu (designated IgER/p185val664 and IgER/p185glu664, respectively), were injected into oocytes. Antigen-induced crosslinking of IgER/p185val164 proteins expressed in oocytes caused a reduction in the half-time for the progesterone-stimulated GVBD from approximately 9 h to approximately 7 h. Thus, the aggregation of the membrane-spanning and/or tyrosine kinase domains of p185val664 partially mimics the effects of the oncogenic forms of p185neu. Overall, the results of these studies suggest that the activation of the p185neu tyrosine kinase by a point mutation within its membrane-spanning helix, or an aggregation event, can result in the facilitation of oocyte maturation events that are elicited by other factors (e.g. progesterone). However, the activated p185neu tyrosine kinases are not able to mimic the EGF-stimulated EGF receptor tyrosine kinase in triggering oocyte maturation, which suggests that the EGF receptor and the p185neu tyrosine kinase do not input into identical signal transduction pathways in these cells.
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PMID:The effects of the normal and oncogenic forms of the neu tyrosine kinase, and the corresponding forms of an immunoglobulin E receptor/neu tyrosine kinase fusion protein, on Xenopus oocyte maturation. 135 69

The rat neu oncogene product is a member of the epidermal growth factor (EGF) receptor subgroup of the superfamily of growth factor receptor tyrosine kinases. The oncogenic activation of the neu protein occurs by a point mutation within its transmembrane region which results in an increase in its tyrosine kinase activity. Using three different forms of neu expressed in insect cells via baculovirus infection, we have examined the biochemical differences between the normal and transforming forms of neu and investigated the role of the transmembrane domain in its tyrosine kinase activity. One form of neu which was expressed in insect cells consisted of the complete tyrosine kinase domain but lacked the extracellular and transmembrane regions (designated NTK). The other two forms consisted of the tyrosine kinase domain, the transmembrane domain, and 40 amino acids of the extracellular domain. One of these transmembrane forms of neu contained the normal valine residue at position 664 within the transmembrane region (MS-N), while the other contained the oncogenic glutamic acid residue at this position (MS-T). Direct comparisons of NTK, MS-N, and MS-T have shown that the NTK protein is capable of the highest extents of both autophosphorylation activity and the tyrosine phosphorylation of exogenous substrate, suggesting that the presence of the transmembrane region of neu suppresses the tyrosine kinase activity of this receptor. In addition, we have found that the oncogenic point mutation within the transmembrane region stimulates the tyrosine kinase activity of the neu protein by allowing it to more effectively utilize Mg2+. Overall, the results of these studies suggest that the valine to glutamic acid substitution at position 664 may at least partially relieve a negative constraint imparted by the membrane-spanning domain on the tyrosine kinase activity of neu and enables a more effective use of Mg2+ in the catalysis of tyrosine phosphorylation of exogenous substrates.
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PMID:Biochemical comparisons of the normal and oncogenic forms of insect cell-expressed neu tyrosine kinases. 135 72


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