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)

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.
 ...
PMID:C-kinase phosphorylates the epidermal growth factor receptor and reduces its epidermal growth factor-stimulated tyrosine protein kinase activity. 632 73

The membranes from epidermoid carcinoma cells (A-431) that were surface iodinated while intact using catalysis by lactoperoxidase and 125I as iodide contain one major labeled protein of Mr = 180,000. This protein is clearly iodinated on the outside of the intact cell because it is not the major protein labeled when isolated membranes are iodinated. This major surface-iodinated protein is almost certainly the epidermal growth factor (EGF) receptor, since both have the same Mr and have identical sensitivity to proteases. Both are nearly quantitatively converted from an Mr = 180,000 form to an Mr = 160,000 form by an endogenous calcium-activated neutral protease when cells are broken in the presence of calcium. Both are degraded by trypsin only if trypsin has access to the inside of the cell. This latter finding implies that the surface-iodinated EGF receptor spans the plasma membrane. Since the EGF receptor is an autophosphorylating kinase whose activity is enhanced in the presence of EGF, the receptor was labeled and identified using [gamma-32P] ATP. While both iodination and EGF-enhanced phosphorylation occur on tyrosine residues, peptide mapping of the iodinated or phosphorylated Mr = 180,000 band showed that different peptides were being labeled. Since the EGF receptor-kinase spans the plasma membrane, the peptide iodinated on the surface of the intact cell must be different from the peptides that are probably autophosphorylated on the cytoplasmic side of the membrane.
 ...
PMID:Surface iodination of epidermal growth factor receptors in intact cells. 632 89

The stimulation of both phospholipase A2 (PLA2) enzymic activity and the production of prostaglandin E2 (PGE2) by transforming growth factor-alpha (TGF-alpha) and Ca2+ ionophore A23187 in TEA3A1 rat thymic epithelial cells were studied. TGF-alpha by itself at various concentrations (5-200 ng/ml) had no effect on the stimulation of PGE2 production. A23187 (1 microgram/ml) by itself stimulated PGE2 production on average by 18-fold over the control. When TGF-alpha (50 ng/ml) was added to the cells in the presence of A23187, a synergistic stimulation (on average 45-fold) of PGE2 production was observed. Synergistic stimulation was also observed at the level of arachidonic acid released from phospholipid pools, suggesting the activation of PLA2 enzymic activity. We have found that this synergistic activation of PLA2 enzymic activity and subsequent stimulation of PGE2 production required the activation of epidermal growth factor (EGF) receptor tyrosine kinase and Ca2+ influx. This was shown by the fact that genistein, an inhibitor of tyrosine kinase, blocks the synergistic stimulation by TGF-alpha and A23187 and by the fact that the stimulation of PGE2 production by TGF-alpha and A23187 is dependent on the culture-medium Ca2+ concentrations. The requirement for Ca2+ influx instead of intracellular mobilization of Ca2+ was shown by the fact that PGE2 production was not stimulated when cells were treated with TGF-alpha and thapsigargin. Moreover, the synergistic stimulation of PGE2 production by TGF-alpha and A23187 was not affected in protein kinase C down-modulated cells. In addition, the synergistic stimulation was not observed in cells treated with either phorbol 12-myristate 13-acetate (PMA) and TGF-alpha or PMA and A23187, and in cells treated with TGF-alpha and thapsigargin. The requirement for the activation of receptor tyrosine kinase seems to be specific to the EGF receptor, since a synergistic stimulation of PGE2 production was not observed when cells are treated with either insulin-like growth factor-I or fibroblast growth factor-I in the presence of A23187.
 ...
PMID:Activation of phospholipase A2 and stimulation of prostaglandin E2 production by transforming growth factor-alpha in rat thymic epithelial cells requires influx of calcium. 768 26

An expression cloning method which allows direct isolation of cDNAs encoding substrates for tyrosine kinases was applied to the study of the epidermal growth factor (EGF) receptor (EGFR) signaling pathway. A previously undescribed cDNA was isolated and designated eps15. The structural features of the predicted eps15 gene product allow its subdivision into three domains. Domain I contains signatures of a regulatory domain, including a candidate tyrosine phosphorylation site and EF-hand-type calcium-binding domains. Domain II presents the characteristic heptad repeats of coiled-coil rod-like proteins, and domain III displays a repeated aspartic acid-proline-phenylalanine motif similar to a consensus sequence of several methylases. Antibodies specific for the eps15 gene product recognize two proteins: a major species of 142 kDa and a minor component of 155 kDa, both of which are phosphorylated on tyrosine following EGFR activation by EGF in vivo. EGFR is also able to directly phosphorylate the eps15 product in vitro. In addition, phosphorylation of the eps15 gene product in vivo is relatively receptor specific, since the erbB-2 kinase phosphorylates it very inefficiently. Finally, overexpression of eps15 is sufficient to transform NIH 3T3 cells, thus suggesting that the eps15 gene product is involved in the regulation of mitogenic signals.
 ...
PMID:eps15, a novel tyrosine kinase substrate, exhibits transforming activity. 768 53

NIH 3T3 cells expressing high levels of the human epidermal growth factor (EGF) receptor were used to examine the effects of the lectin concanavalin A (Con A) on EGF-mediated signaling events. Proliferation of NIH 3T3 cells expressing high levels of the human EGF receptor was inhibited in a dose-dependent manner by Con A. At the same time, Con A also inhibited both dimerization and tyrosine phosphorylation of the EGF receptor. Tyrosine phosphorylation of the enzyme phospholipase C-gamma, a substrate of the phosphorylated EGF receptor kinase, was also inhibited. In contrast, EGF-stimulated changes in pH, calcium, and levels of inositol phosphates were unaffected by the presence of Con A. These results indicate that certain signals (changes in the levels of intracellular calcium, pH, and inositol phosphates) mediated by EGF binding to its receptor still occur when receptor dimerization and phosphorylation are dramatically decreased, suggesting that multiple independent signals are transmitted by the binding of EGF to its receptor.
 ...
PMID:EGF receptor-mediated signals are differentially modulated by concanavalin A. 781 52

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.
 ...
PMID:Staurosporine stimulates progesterone production by bovine placental cells. 791 70

We have examined the perturbation of epidermal growth factor (EGF) receptor-receptor interactions by a monoclonal antibody (13A9) that binds to the receptor extracellular domain. While 13A9 did not inhibit EGF binding, it inhibited energy transfer between fluorescent-labeled EGF molecules bound to receptors in membranes from human A431 cells by 70-100%. This antibody also inhibited EGF-stimulated receptor dimerization in membranes as assessed by chemical cross-linking and Fab fragments of the antibody strongly inhibited the EGF-stimulated dimerization of solubilized receptors when assessed by velocity sedimentation. However, under conditions where 13A9 inhibited receptor-receptor interactions within the plasma membranes, the antibody had no effect on EGF-stimulated receptor autophosphorylation or tyrosine kinase activity toward an exogenous substrate. Moreover, although the antibody significantly inhibited receptor dimerization in A431 cells, it had no effect on EGF-stimulated changes in cytosolic free [Ca2+] or 125I-EGF uptake in these cells, or on EGF-stimulated DNA synthesis in Swiss 3T3 cells. We conclude that the dimerization of the EGF receptors in a membrane environment is not required for full activation of tyrosine kinase activity and that inhibition of the dimerization of a large fraction of EGF receptors in cells does not necessarily inhibit several EGF-mediated cellular responses.
 ...
PMID:Inhibition of epidermal growth factor receptor aggregation by an antibody directed against the epidermal growth factor receptor extracellular domain. 822 25

In EGFR-T17 cells, which express high levels of the epidermal growth factor (EGF) receptor, addition of a saturating dose of EGF (10 nM) leads to an increase in Ins(1,4,5)P3/diacylglycerol and also to cytosolic calcium [Ca2+]i due to both intracellular redistribution and influx from extracellular medium. Pretreatment of cells with cis-unsaturated nonesterified fatty acids such as oleic acid (1 to 100 microM) inhibited EGF-stimulated Ins(1,4,5)P3 generation and Ca2+ release from intracellular stores. Furthermore, such a treatment completely suppress Ca2+ influx in a dose-dependent manner. At doses capable of suppressing such early signals, oleic acid did not alter the process of EGF-mediated internalization of the EGF/EGF-receptor complex, suggesting that [Ca2+]i rise did not mediate receptor internalization. EGF-induced cell proliferation assessed by either thymidine incorporation into DNA, direct cell counting, and microscopic observation was not altered by oleic acid, at doses able to block EGF-mediated early signals. In conclusion, suppression of Ins(1,4,5)P3 generation and [Ca2+]i rises by oleic acid did not alter EGF-receptor internalization nor EGF-induced cell mitosis. Such results suggest that [Ca2+]i rise is not instrumental for EGF-stimulated cell proliferation.
 ...
PMID:Oleic acid blocks epidermal growth factor-activated early intracellular signals without altering the ensuing mitogenic response. 848 41

Transforming growth factor alpha (TGF-alpha) is biosynthesized as a membrane-bound precursor protein, pro-TGF-alpha, that undergoes sequential endoproteolytic cleavages to release a soluble form of the factor. In the present study, we have analyzed the biosynthesis and regulation of TGF-alpha production in human tumor-derived cell lines that endogenously express pro-TGF-alpha and the epidermal growth factor (EGF) receptor. These cells biosynthesized membrane-anchored forms of the TGF-alpha that accumulated on the cell surface. Membrane-bound pro-TGF-alpha interacted with the EGF receptor, and complexes of receptor and pro-TGF-alpha contained tyrosine-phosphorylated receptor. Activation of the EGF receptor by soluble EGF or TGF-alpha had a dual effect on TGF-alpha production: an increase in pro-TGF-alpha mRNA levels and an increase in pro-TGF-alpha cleavage. These effects were largely prevented by preincubation with an anti-EGF receptor monoclonal antibody that blocked ligand binding. Growth factor autoinduction of cleavage could be stimulated by several second messenger pathways that are activated by the EGF receptor, including protein kinase C and intracellular calcium, and by other alternative mechanisms. EGF-stimulated cleavage of pro-TGF-alpha could be partially blocked by inhibition of these second messenger pathways. These results suggest that juxtacrine stimulation takes place in human tumor cells that coexpress both the EGF receptor and membrane-anchored TGF-alpha and that TGF-alpha is able to induce its own endoproteolytic cleavage by activating the EGF receptor.
 ...
PMID:Autocrine regulation of membrane transforming growth factor-alpha cleavage. 862 31

Transforming growth factor beta (TGF-beta) inhibits proliferation of keratinocytes cultured from normal anogenital epithelia; however, human papillomavirus (HPV)-immortalized cell lines often exhibit increased resistance. Present results demonstrate that TGF-beta 1 (1-10 pM) stimulates growth of multiple HPV-immortalized cell lines when cultures are maintained under conditions promoting squamous differentiation (MCDB153-LB medium with 1.0 mM calcium and without epidermal growth factor and bovine pituitary extract). Growth stimulation by TGF-beta 1 was not due to altered expression of type I or II receptors, but was increased after extended passage of cells in culture. Differentiation of immortal keratinocytes resulted in induction of RNAs encoding two markers of squamous differentiation, involucrin and keratin 1, and decreased expression of RNAs for the epidermal growth factor (EGF) receptor and two ligands, amphiregulin and TGF-alpha. Growth stimulation by TGF-beta 1 occurred indirectly via establishment of an autocrine loop. TGF-beta 1 increased expression of RNAs encoding the EGF-R and amphiregulin, and also increased numbers of cell-surface EGF-Rs without altering their affinity. In contrast, TGF-beta 1 inhibited autonomous growth and transcription of amphiregulin RNA in normal keratinocytes. Growth stimulation by TGF-beta 1 could be blocked by a monoclonal antibody that competes for binding to the EGF-R or by a mixture of monoclonal antibodies that neutralize amphiregulin activity, confirming the importance of this autocrine pathway. Thus, partial abrogation of the growth inhibitory response to TGF-beta 1 sensitizes HPV-immortalized keratinocytes to a growth stimulatory signal mediated by an EGF-R-dependent pathway involving autocrine stimulation by amphiregulin.
 ...
PMID:Transforming growth factor beta 1 supports autonomous growth of human papillomavirus-immortalized cervical keratinocytes under conditions promoting squamous differentiation. 878 Aug 94


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>