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)

Insulin-like growth factor I (IGF-I)/somatomedin C is an important mediator of keratinocyte growth in vitro, and the expression of IGF-I receptors in the basal layer of normal epidermis suggests that this growth pathway may function in the regulation of keratinocyte growth in vivo as well. The pattern of IGF-I receptor expression in normal skin is distinct from that of the epidermal growth factor (EGF) receptor, suggesting that these receptors might be differentially regulated. The purpose of this study was to obtain a better understanding of IGF-I receptor function in the skin by examining IGF-I receptor expression in psoriatic epidermis and in cultured human keratinocytes. Our findings indicate that IGF-I receptor expression is increased in psoriasis as measured by protein tyrosine kinase assays of biopsy extracts and by immunohistochemical staining with an IGF-I receptor-specific monoclonal antibody. Unlike EGF receptor expression, which is also increased in psoriatic epidermis, the pattern of IGF-I receptor expression corresponds closely with the increased size of the keratinocyte proliferative compartment in psoriasis. Biochemical agents that diminish EGF receptor ligand binding (phorbol ester or calcium ionophore treatment) produce opposite effects on the IGF-I receptor. These results suggest that cellular expression and differential regulation of both growth factor receptor systems may control critical aspects of epidermal proliferation or function.
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PMID:The insulin-like growth factor I receptor is overexpressed in psoriatic epidermis, but is differentially regulated from the epidermal growth factor receptor. 131 74

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

The epidermal growth factor (EGF) receptor-associated protein tyrosine kinase activity has been suggested to play important roles in the EGF-enhanced, clathrin-coated pit-mediated receptor internalization (W. S. Chen, C. S. Lazar, M. Peonie, R. Y. Tsien, G. N. Gill, and M. G. Rosenfeld, 1987, Nature 328, 820-823) but the kinase substrate important for this process has not been identified. This study demonstrates that the EGF receptor, partially purified from A431 epidermoid carcinoma cells, catalyzes the phosphorylation of one of the two clathrin light chains, clathrin light chain a (LCa). The phosphorylation activity is stimulated by EGF and immunoprecipitated by an EGF receptor monoclonal antibody. The phosphorylation occurs exclusively on tyrosine residues. Amino acid composition of the major tryptic phosphopeptide of the EGF receptor-phosphorylated LCa corresponds closely to that of residues 1 to 97 of LCa. A stoichiometry of 0.2 mol phosphate/mol LCa was attained after 60 min at 30 degrees C and a Km value of 1.7 microM was determined for the reaction. LCa of either neuronal or non-neuronal origin could serve as a substrate. In addition to the EGF receptor tyrosine kinase, a particulate src-related protein tyrosine kinase purified from bovine spleen (C. M. E. Litwin, H.-C. Cheng, and J. H. Wang, 1991, J. Biol. Chem. 226, 2557-2566) was shown in this study to also phosphorylate the light chains. However, in contrast to the EGF receptor phosphorylation, both clathrin light chains a and b were phosphorylated by the spleen kinase, suggesting that the two tyrosine kinases have differential site specificities. Given the specificity of LCa phosphorylation by the EGF receptor, we propose that LCa phosphorylation on a tyrosine residue(s) may be important in EGF-induced receptor internalization.
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PMID:Differential in vitro phosphorylation of clathrin light chains by the epidermal growth factor receptor-associated protein tyrosine kinase and a pp60c-src-related spleen tyrosine kinase. 137 Jun 1

Many human tumors of epithelial origin contain cells overexpressing the epidermal growth factor (EGF) receptor, and there is convincing evidence that cancer cell growth is correlated with the loss of the normal regulation of the EGF receptor signal transduction pathway. Some cancers are clearly dependent on activation of the EGF receptor for their proliferation. Recently, a class of compounds, tyrphostins, which inhibit the protein tyrosine kinase activity of the growth factor receptor, have been described. In this report, we have examined the antiproliferative effects of potent new tyrphostins on a well-characterized human squamous cell carcinoma in vitro and in vivo. We found that two of these compounds (RG-13022 and RG-14620) suppressed not only EGF-stimulated cancer cell proliferation in vitro but also tumor growth in nude mice. RG-13022 also increased the life span of these tumor-bearing nude mice. When administered to tumor-bearing nude mice together with monoclonal antibodies to the EGF receptor at a suboptimal dose which had no effect alone, inhibition of tumor growth was markedly enhanced. These data suggest that tyrphostins have potential as anticancer agents.
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PMID:The antiproliferative effects of tyrosine kinase inhibitors tyrphostins on a human squamous cell carcinoma in vitro and in nude mice. 165 Nov 59

HER2 or c-erbB-2 is a putative growth factor receptor with sequence homology to the epidermal growth factor receptor. It is the human homologue of the rat protooncogene neu and may have an important role in human malignancies such as breast and ovarian cancers. Like other growth factor receptors, HER2 has intrinsic protein tyrosine kinase activity and undergoes autophosphorylation. Recently, we have demonstrated that, similar to the epidermal growth factor receptor, all autophosphorylation sites of HER2 are localized in the carboxyl terminus of this protein. In the present study, immunopurified HER2 was allowed to autophosphorylate, and tryptic phosphopeptides were generated. After purification of these phosphopeptides by high performance liquid chromatography, microsequencing was performed. Utilizing this approach, two autophosphorylation sites were unequivocally identified at Y1023 and Y1248. The sequences of two other tyrosine phosphorylated tryptic peptides were determined, but the exact site of autophosphorylation could not be determined because multiple tyrosines were located on each peptide. However, each of these peptides contains tyrosines that correspond to major autophosphorylation sites of the epidermal growth factor receptor, suggesting that, in addition to Y1023 and Y1248, Y1139 and Y1222 also serve as autophosphorylation sites of HER2.
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PMID:Identification of autophosphorylation sites of HER2/neu. 170 16

The CD45 antigen cluster identifies a family of transmembrane glycoprotein tyrosine phosphatases (PTPases) present on nearly all hemopoietic cells. Recent studies suggest that CD45 may play a role in the control of receptor mediated blood cell responses, and that expression of the CD45 gene varies during bone marrow cell maturation. However, relatively little is known of the mechanisms controlling CD45 expression and function. Here we show that the induction of granulocyte or monocyte differentiation of HL60 leukemia cells is accompanied by a rapid increase in CD45 antigen expression and CD45 PTPase activity. In contrast, other leukemia cell lines induced for monocyte/macrophage differentiation did not show increased CD45. Immunoprecipitation of radiolabelled CD45 glycoprotein from dimethyl sulphoxide (DMSO) treated HL60 cells indicated that the cells expressed 200 and 180 kD isoforms. Northern blots of steady-state RNA from HL60 cells showed a 4-11-fold increase in CD45 transcripts after DMSO treatment, but no alteration in the half-life of CD45 mRNA. Nuclear transcription assays showed that CD45 expression was controlled at the level of gene transcription. Namalwa Burkitt leukemia cells expressing the heterologous epidermal growth factor (EGF) receptor protein tyrosine kinase were used to assess the specificity of CD45 PTPase activity. Co-clustering of CD45 and the EGF receptor with specific monoclonal antibodies failed to alter the EGF stimulated tyrosine phosphorylation of the EGF receptor. These studies indicate that CD45 increases during myeloid maturation, and the expression of the CD45 gene is controlled at the level of gene transcription. Preliminary studies suggest that CD45 does not alter the protein tyrosine kinase activity of the EGF receptor in intact cells, suggesting substrate specificity in vivo.
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PMID:Regulation of CD45 expression in human leukemia cells. 185 Dec 41

The ligand-binding domain of the epidermal growth factor (EGF) receptor is separated from the cytoplasmic protein tyrosine kinase domain by a predicted single transmembrane segment. Antipeptide antibodies prepared against the outer portion of the predicted transmembrane segment confirmed this area was exposed only when cells were treated with permeabilizing agents. To investigate structural requirements for signal transduction by the transmembrane domain, three types of mutant EGF receptor were prepared. The first type was designed to shorten the transmembrane domain, the second to place proline substitutions within this domain, and the third to make amino acid substitutions analogous to those present in the transforming c-erbB2/neu oncoprotein. Mutant human receptors were expressed in null recipient mouse B82L and Chinese hamster ovary cells. All receptors bound EGF and exhibited EGF-stimulated protein tyrosine kinase activity in vivo as assayed using a 125I-labeled monoclonal anti-phosphotyrosine antibody. EGF stimulated growth of cells expressing each mutant receptor with similar dose-response characteristics. In contrast to other growth factor receptors, the transmembrane domain of the EGF receptor is tolerant to a variety of changes which neither mimic EGF action by constitutive activation nor interfere with ligand-induced signal transduction.
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PMID:Structural analysis of the transmembrane domain of the epidermal growth factor receptor. 200 11

Identification of a mutant epidermal growth factor (EGF) receptor that does not undergo downregulation has provided a genetic probe to investigate the role of internalization in ligand-induced mitogenesis. Contact-inhibited cells expressing this internalization-defective receptor exhibited a normal mitogenic response at significantly lower ligand concentrations than did cells expressing wild-type receptors. A transformed phenotype and anchorage-independent growth were observed at ligand concentrations that failed to elicit these responses in cells expressing wild-type receptors. These findings imply that activation of the protein tyrosine kinase activity at the cell membrane is sufficient for the growth-enhancing effects of EGF. Thus, downregulation can serve as an attenuation mechanism, without which transformation ensues.
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PMID:Ligand-induced transformation by a noninternalizing epidermal growth factor receptor. 230 63

Retroviral onc genes are derived from cellular proto-oncogenes that may function in normal cellular growth control. The epidermal growth factor (EGF) receptor is the proto-oncogene of erbB; both possess intrinsic protein tyrosine kinase activity, a property shared by several retroviral onc genes. The EGF receptor is a transmembrane glycoprotein with an external EGF binding domain and a cytoplasmic region that is homologous with other tyrosine kinases. erbB lacks the EGF binding and carboxyl terminal regions, which are thought to be important in regulation. The EGF receptor is regulated by several mechanisms: stimulation by ligand binding and self-phosphorylation, inhibition by heterologous phosphorylation and downregulation by ligand. EGF binding stimulates several early events, including phosphatidylinositol (PI) turnover in A431 cells. A PI kinase activity copurifies with the EGF receptor and some other tyrosine kinases, but this is a contaminant as it can be separated from the EGF receptor. Although the role of proto-onc genes in human malignancy is incompletely defined, increased numbers of EGF receptors are present in several types of human tumours. Overexpression of EGF receptors, as occurs in human epidermoid carcinoma A431 cells, can augment cell growth because of increased formation of active ligand:receptor complexes. Gene amplification is the mechanism underlying overexpression of EGF receptors in A431 cells and in some glioblastoma multiforme tumours.
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PMID:The EGF receptor: structure, regulation and potential role in malignancy. 282 44

This study investigated a possible role for the epidermal growth factor (EGF) receptor protein tyrosine kinase in phosphoinositide metabolism with plasma membrane vesicles from human epidermoid carcinoma (A431) cells. We found a novel chloroform-soluble product radiolabeled with [gamma-32P]ATP that did not migrate from the origin in the thin layer system designed to separate the phosphoinositides, appeared as a single band of Mr = 3500 on polyacrylamide gels in the presence of dodecyl sulfate, had an ultraviolet absorbance spectrum with a maximum at 275 nm and stained with Coomassie dye. Based on these properties this phosphorylation product is referred to as a proteolipid. The 32P label was not detected in phosphotyrosine [Tyr(P)], phosphoserine [Ser(P)] or phosphothreonine [Thr(P)] and was lost during acid or base hydrolysis. Phosphorylation of proteolipid was increased significantly by EGF, whereas phosphorylation of phosphatidic acid was decreased and labeling of phosphoinositides was unaffected. Thus, it appears that in A431 membranes the EGF receptor/kinase does not utilize phosphatidylinositol as a substrate, but does phosphorylate a membrane proteolipid.
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PMID:Phosphorylation of chloroform soluble compounds in plasma membranes of human epidermoid carcinoma A431 cells. 299 80


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