UNIPROT:P04626 - FACTA Search

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

These studies describe the effect of protein kinase C (PKC) activation on the activity of voltage-sensitive L-type Ca2+ channels of GH3 pituitary cells. The rate of 45Ca2+ uptake was stimulated greater than 25-fold by depolarization in the presence of BAY K 8644; the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) reduced this response by 70% in a concentration-dependent fashion. Phorbol 12,13-dibutyrate (PDBu) inhibited depolarization-induced 45Ca2+ uptake within 1 min and caused a nearly maximal reduction after 1 h; its effects were rapidly reversible. TPA decreased the high K(+)-stimulated increase in intracellular free calcium ion concentration ([Ca2+]i) from 8.5- to 3.2-fold by 5 min and to 2.0-fold after 18 h without altering the peak [Ca2+]i response to the peptide hormone TRH. Ca2+ channel current, measured directly using the whole cell configuration of the patch-clamp technique, declined an average of 6.4% over 5 min for control cells and 28.9% when TPA was added to the bathing medium for 5 min. Treatment with 100 nM TPA for 24 h dramatically reduced peak current without shifting the peak of the current-voltage relationship. The mean peak Ca2+ channel current was reduced from 423 to 128 pA, although a few cells seemed completely resistant. To determine whether the effects of phorbol esters were due to the activation of PKC we tested the potency of several drugs to inhibit L-channel activity and to shift the affinity of the epidermal growth factor (EGF) receptor, an established PKC response.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Activation of protein kinase C reduces L-type calcium channel activity of GH3 pituitary cells. 131 2

We have previously shown that basic fibroblast growth factor (bFGF) inhibits the FSH-induced differentiation of cultured rat granulosa cells, as manifested by prominent reduction of the LH receptor expression. We now investigate the possible sites and mechanism of action of bFGF. Whereas bFGF decreased the cAMP formation induced by FSH, it enhanced the cAMP production caused by cholera toxin and forskolin, suggesting that bFGF exerted its inhibitory action on cell differentiation at a step to cAMP production. Photoaffinity labeling with 8-azido-[32P]cAMP revealed that bFGF markedly reduced the FSH-induced increase in the level of regulatory subunit RII beta of the cAMP-dependent protein kinase (PKA) type II. In contrast to its striking effect on RII beta expression (70-80% inhibition), bFGF decreased PKA enzymatic activity by only 30%. On the other hand, transforming growth factor-beta (TGF beta) slightly amplified the stimulatory action of FSH and antagonized the bFGF inhibitory effect on both LH receptor expression and RII beta synthesis. We report that the protein kinase C (PKC) activator 12-O-tetradecanoylphorbol-13-acetate (TPA), which impaired granulosa cell differentiation, also abolished the RII beta synthesis induced by FSH. The activation of PKC by bFGF in granulosa cells was supported by the following findings: (i) bFGF markedly enhanced the production of diacylglycerol (2.3-fold stimulation at 5 min), the intracellular activator of PKC; (ii) bFGF promoted tight association of PKC to cellular membranes, a process that is believed to correlate with the enzyme activation; (iii) bFGF induced the phosphorylation of an endogenous M(r) 78,000/pI 4.7 protein that appears as a specific PKC substrate; (iv) bFGF mimicked the TPA-induced transmodulation of the epidermal growth factor (EGF) receptor, reducing by 36% the 125I-EGF binding on granulosa cells. We conclude that bFGF may exert its repressive action on RII beta synthesis, PKA activity, and granulosa cell differentiation by primarily targeting PKC activation.
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PMID:Regulation of cyclic adenosine 3',5'-monophosphate-dependent protein kinase activity and regulatory subunit RII beta content by basic fibroblast growth factor (bFGF) during granulosa cell differentiation: possible implication of protein kinase C in bFGF action. 132 4

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

In the present study we have analyzed the effect of a synthetic protein kinase C (PKC) activator 3-(N-acetylamino)-5-(N-decyl-N-methylamino)-benzyl alcohol (ADMB) and the natural PKC-activating tumor-promoting agents 12-O-tetradecanoylphorbol 13-acetate (TPA) and mezerein on the antigenic phenotype of T47D human breast carcinoma cells. All three agents increased the surface expression of the tumor-associated antigen BCA 225 and various cellular antigens, including HLA class II antigens, intercellular adhesion molecule 1 (ICAM-1) and c-erbB-2. Expression of the same antigens was also upregulated to various extents in T47D cells by recombinant fibroblast (IFN beta) and immune (IFN gamma) interferon. Shedding of BCA 225 from T47D cells was induced by TPA, mezerein, IFN beta and IFN gamma, whereas ADMB did not display this activity. The ability of ADMB, TPA and mezerein to modulate the antigenic phenotype of T47D cells appears to involve a PKC-mediated pathway, since the PKC inhibitor, H-7, eliminates antigenic modulation. In contrast, the ability of IFN beta and IFN gamma to enhance the synthesis, expression and shedding of BCA 225, as well as to enhance HLA class II antigens, c-erbB-2 and ICAM-1 expression, was either unchanged or modestly reduced by simultaneous exposure to H-7. Analysis of steady-state mRNA levels for HLA class I antigens, HLA class II-DR beta antigen, ICAM-1 and c-erbB-2 indicated that the ability of H-7 to inhibit expression of these antigens in TPA-, mezerein- and ADMB-treated cells was not a consequence of a reduction in the steady-state levels of mRNAs for these antigens. The results of the present investigation indicate that the biochemical pathways mediating enhanced antigenic expression in T47D cells induced by TPA, mezerein and the synthetic PKC activator ADMB are different from those induced by recombinant interferons. Furthermore, up-regulation of antigenic expression in T47D cells can occur by a PKC-dependent or a PKC-independent pathway.
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PMID:Modulation of the antigenic phenotype of human breast carcinoma cells by modifiers of protein kinase C activity and recombinant human interferons. 135 26

The earliest responses to activation of the epidermal growth factor (EGF) receptor include a transient increase in calcium influx and a transient membrane hyperpolarization. The underlying mechanisms are, however, not well understood as yet. In the present study, we have applied patch clamp recording in the cell-attached and the outside-out mode, and fluorimetric cytosolic Ca2+ determinations, to identify the nature of the ion channels involved, to characterize their properties at the level of single channels, and to unravel their mechanism of activation. We provide evidence that activation of the EGF receptor results initially in the activation of voltage-independent Ca2+ channels that can be defined as direct receptor-operated channels. This in turn causes the activation of Ca(2+)-dependent K+ channels, which results in a (delayed) membrane hyperpolarization and then leads to the activation of a second class of Ca2+ channels that are sensitive to hyperpolarization. An autocatalytic generation of further hyperpolarization and Ca2+ influx is the predicted outcome of this ionic cascade. Based on the observed inhibitory effects of protein kinase C activation on the activity of Ca(2+)-dependent K+ channels, we propose that protein kinase C is involved in the negative regulation of this cascade, which explains the transient nature of these responses.
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PMID:Epidermal growth factor-activated calcium and potassium channels. 165 7

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.
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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

P185 is a receptor-like protein encoded by the neu/erbB-2 proto-oncogene. A point mutation in the transmembrane domain renders this protein oncogenic. We report here that incubation of cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) stimulates the phosphorylation of the normal neu protein (p185) and the oncogenic neu protein (p185*). The increased phosphorylation occurs mainly on serine and threonine residues. Phosphate labeling experiments showed that TPA causes a reduction of basal phosphotyrosine in p185 but not p185*. Immunoblotting with antiphosphotyrosine antibody yielded similar results. TPA also inhibited tyrosine phosphorylation of p185* in an in vitro immune complex kinase assay. These data suggest that protein kinase C, the receptor for TPA, regulates p185 function through serine or threonine phosphorylation.
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PMID:TPA inhibits the tyrosine kinase activity of the neu protein in vivo and in vitro. 167 82

The mutant c-erbB-2 gene encoding a protein with Glu instead of Val-659 in the transmembrane domain is able to transform NIH3T3 cells, while the wild type c-erbB-2 unless overexpressed does not. The mutant c-erbB-2 protein shows enhanced tyrosine kinase activity in vitro. Transient expression of this active c-erbB-2 stimulated the 12-O-tetradecanoylphorbol-13-acetate (TPA) response element, serum response element, and cyclic AMP response element. Particularly, stimulation of the TPA response element by active c-erbB-2 was prominent. In contrast, transient expression of wild type c-erbB-2 stimulated none of these elements. Transactivation of the TPA response element was also observed in a cell line that stably expresses active c-erbB-2. The active c-erbB-2-induced transactivation of the TPA response element was partially prevented either by down-regulation of protein kinase C or by the protein kinase C inhibitor H7. These results indicate that protein kinase C is partly involved in oncogenic signalling of the active c-erbB-2 protein that leads to Jun/Fos-mediated transcriptional activation in nuclei.
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PMID:Transactivation of the TPA-responsive element by the oncogenic C-erbB-2 protein is partly mediated by protein kinase C. 167 66

Staurosporine is a potent microbial inhibitor of a number of protein kinases, including protein kinase C, cyclic AMP-dependent kinase, and the tyrosine kinase pp60src. We have used staurosporine to investigate the role of phosphorylation in the regulation of the epidermal growth factor (EGF) receptor in both human epidermal carcinoma A431 cells and mouse Swiss 3T3 fibroblasts. We report here that staurosporine treatment causes enhancement in high affinity EGF binding and a decrease in the phosphorylation state of the unstimulated receptor at a number of residues, including threonine 669. Staurosporine also antagonizes the inhibition of high affinity EGF binding and the increase in phosphorylation state of the unstimulated EGF receptor by phorbol esters and the calcium ionophore A23187. Staurosporine is an effective inhibitor of the EGF-stimulated receptor tyrosine kinase in vitro and thus does not enhance EGF stimulation of EGF receptor autophosphorylation in vivo. These results suggest that phosphorylation plays a major role in the regulation of the high affinity binding state of the EGF receptor in both unstimulated and mitogenically activated cells.
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PMID:Regulation of the epidermal growth factor receptor by growth-modulating agents: effects of staurosporine, a protein kinase inhibitor. 168 32

To study the activity of the epidermal growth factor (EGF) receptor during EGF-directed internalization, liver epithelial cells were exposed to EGF at 37 degrees C for various periods of time, washed, and homogenized at 0 degrees C. EGF receptor autophosphorylation was assessed in homogenates using [gamma-32P]ATP. Autophosphorylation was stimulated 3- to 6-fold in homogenates of cells incubated with EGF (100 ng/ml) for 15 min but was at or below basal levels in homogenates of cells treated with EGF for 2.5-5 min. This was surprising because immunoblotting revealed that EGF receptor phosphotyrosine (P-Tyr) content in intact cells was near maximal from 30 s to 5 min after EGF treatment. Excess EGF (1 microgram/ml), added after homogenization but prior to the assay, increased autophosphorylation in homogenates of cells that had not been treated with EGF, but failed to increase activity in homogenates of cells treated with EGF in culture for 2.5-5 min. Suppression of tyrosine phosphorylation of an exogenous kinase substrate was also observed at times paralleling the suppression of EGF receptor autophosphorylation. The transient suppression of receptor autophosphorylation in the cell-free assay was not explained by persistent occupation of autophosphorylation sites by phosphate added in the intact cells. The sites were greater than 80% dephosphorylated during the homogenization. Additionally phosphatase inhibition that prevented the normal loss of EGF receptor P-Tyr in intact cells at 15 min did not affect the pattern of early (2.5-5 min) suppression and later (15 min) stimulation of autophosphorylation measured in the cell-free assay. The suppression was not explained by activation of protein kinase C in that depletion of greater than 95% of cellular protein kinase C activity by an 18-h incubation of cells with 10 microM 12-O-tetradecanoylphorbol 13-acetate (TPA) did not affect the early suppression of autophosphorylation in EGF-treated cells. Moreover, under the conditions tested, activation of protein kinase C by short-term treatment (0.5-10 min) with TPA or angiotensin II did not appreciably alter subsequent autophosphorylation in the cell-free assay. In contrast, a 30 degrees C preincubation of homogenates from cells with suppressed EGF receptor autophosphorylation led to the recovery of the ability of EGF to stimulate EGF receptor autophosphorylation. These results suggest that a rapid reversible protein kinase C-independent process prevents detection of EGF receptor kinase activity during an early phase of EGF-dependent receptor internalization.
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PMID:Transient epidermal growth factor (EGF)-dependent suppression of EGF receptor autophosphorylation during internalization. 169 15

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