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)

In previous studies, combinations of immunotoxins reactive with different cell-surface antigens have exerted additive cytotoxicity against tumor cells in culture. In this report we describe a combination of 2 immunotoxins that produce synergistic cytotoxic activity. Recombinantly derived ricin A chain (RTA) was conjugated with murine monoclonal antibodies (MAbs) 317G5, 260F9, 454A12 and 741F8 that bound to cell-surface determinants of 42, 55, 180 (transferrin receptor) and 185 kDa (HER-2/neu) expressed by the SKBr3 human breast-cancer cell line. When inhibition of clonogenic growth was measured in a limiting dilution assay, the combination of 260F9-RTA and 454A12-RTA produced synergistic cytotoxic activity against SKBr3 and 2 other breast-cancer cell lines. All other combinations produced only additive inhibition of clonogenic growth. Simultaneous binding of 260F9 and 454A12 was not supra-additive, but sub-populations of cells which lacked one or the other antigen could be detected. Kinetic studies of internalization, using antibodies conjugated with gold particles, indicated that 454A12 remained within peripheral endosomes for a longer interval in the presence of 260F9. This change in the traffic of the transferrin receptor may contribute to synergy between 260F9-RTA and 454A12-RTA.
 ...
PMID:A combination of two immunotoxins exerts synergistic cytotoxic activity against human breast-cancer cell lines. 135 85

A murine monoclonal antibody, TA1, is directed against an epitope on the extracellular domain of the HER-2/neu (c-erbB-2) gene product. Requirements for TA1-induced internalization of c-erbB-2 have been studied using the SKBr3 human breast cancer cell line and several rat fibroblast cell lines that express either wild-type or mutant human c-erbB-2. Internalization of TA1 was monitored by assaying protease-resistant uptake of 125I-labeled TA1, by electron microscopy of gold-labeled TA1, and by inhibition of clonogenic growth of cells incubated with TA1 that had been conjugated with blocked ricin. Similar rates of internalization of TA1 were observed in SKBr3 and in rat fibroblasts that expressed human c-erbB-2. The route of endocytosis was the same as that observed with antibodies against other membrane receptors. Anti-c-erbB-2 and anti-transferrin receptor cointernalized through clathrin-coated pits, coated vesicles, endosomes, and multivesicular bodies. Products of mutant c-erbB-2 that lacked a portion of the tyrosine kinase domain or that lacked most of the cytoplasmic domain were endocytosed in the presence of TA1 as promptly as the wild-type c-erbB-2 product. Slightly more rapid internalization of TA1 was observed in rat cells that expressed c-erbB-2 with a single point mutation in the transmembrane domain. Taken together, our data suggest that neither the intracytoplasmic domain nor receptor phosphorylation is required for antibody-mediated endocytosis of c-erbB-2.
 ...
PMID:Requirements for the internalization of a murine monoclonal antibody directed against the HER-2/neu gene product c-erbB-2. 168 May 47

We have developed a quantitative method to evaluate the interaction between cell surface receptors and the endocytic apparatus. This method exploits occupancy-dependent changes in internalization rates that occur in cells expressing high numbers of receptors. We found that constitutive internalization of the transferrin receptor behaves as a simple, first order process that is unaltered by ligand. Internalization of the epidermal growth factor (EGF) receptor, however, behaves as a saturable, second order process that is induced by receptor occupancy. Internalization of EGF receptors occurs through at least two distinct pathways: a low capacity pathway that has a relatively high affinity for occupied receptors, and a low affinity pathway that has a much higher capacity. The high affinity pathway was observed in all cells having receptors with intrinsic tyrosine kinase activity. Mutant EGF receptors lacking kinase activity could not utilize the high affinity pathway and were internalized only through the low affinity one. Mutated receptors with decreased affinity for kinase substrates were also internalized at decreased rates through the high affinity, inducible pathway. In the case of vitellogenin receptors in Xenopus oocytes, occupied receptors competed more efficiently for internalization than empty ones. Insulin increased the endocytic capacity of oocytes for vitellogenin receptors. Similarly, serum increased the capacity of the inducible pathway for EGF receptors in mammalian cells. These data are consistent with a model of internalization in which occupied receptors bind to specific cellular components that mediate rapid internalization. Ligand-induced internalization results from an increase in the affinity of occupied receptors for the endocytic apparatus. Hormones can also indirectly regulate endocytosis by increasing the number of coated pits or their rate of internalization. The ability to dissect receptor-specific effects from cell-specific ones should be very useful in investigating the molecular mechanisms of receptor mediated endocytosis.
 ...
PMID:Quantitative analysis of the endocytic system involved in hormone-induced receptor internalization. 197 91

To assess the functional significance of phosphorylation of the epidermal growth factor (EGF) receptor at Thr654, we compared the effects of 12-O-tetradecanoyl-13-acetate (TPA) on ligand-induced internalization and down-regulation between wild-type and mutant receptors that contain an alanine substitution at position 654. Activation of protein kinase C with TPA blocked EGF-induced internalization and down-regulation of Thr654 receptors and inhibited in vivo tyrosine kinase activity by 80%. TPA did not inhibit transferrin receptor internalization or constitutive EGF receptor internalization, suggesting that protein kinase C activation inhibits only the ligand-induced process. Inhibition by TPA of induced internalization, down-regulation, and kinase activity required threonine at position 654 since full-length Ala654 EGF receptors were significantly resistant to TPA inhibition of these ligand-induced activities. However, C'-terminal truncation further enhanced this resistance to TPA inhibition. The EGF-dependent internalization of kinase-inactive receptors truncated at residue 1022 was also impaired by TPA in Thr654 receptors, but not in Ala654 receptors, indicating that phosphorylation at Thr654 also interferes with tyrosine kinase-independent receptor activities. We conclude that the dominant regulatory effect of protein kinase C on the EGF receptor is mediated through phosphorylation at Thr654 which effectively inactivates the receptor. The submembrane region of the EGF receptor appears to regulate transmission of conformational information from the extracellular ligand-binding site to the cytoplasmic kinase and regulatory domains.
 ...
PMID:Phosphorylation of the epidermal growth factor receptor at threonine 654 inhibits ligand-induced internalization and down-regulation. 217 10

Expression of the product of the c-erbB-2 gene, a proto-oncogene related to, but distinct from c-erbB-1 encoding the epidermal growth factor receptor (EGF-R), was investigated in human urinary bladder carcinomas. In addition, levels of EGF-R and transferrin receptor were also analyzed using an immunohistochemical approach, and the results compared with histological pattern and grading, and tumor staging. Increased expression of c-erb B-2 product was found in 32% of cases (7/22), a positive reaction being observed in 60% of transitional cell carcinoma (TCC) Grade 3 lesions (3/5), 20% of Grade 2 TCCs (2/10) and 100% of adenocarcinomas (AC) (2/2), but in none of the cases of squamous cell carcinoma (SCC). Although no statistical correlation with staging was evident, TCCs or SCCs of high grade and stage often showed EGF-R-positive staining, whereas other well differentiated lesions and normal bladder epithelium were generally negative. Most cases of urinary bladder carcinoma were positive for the transferrin receptor, which was not detected in normal bladder. The results thus suggested that a positive reaction for c-erbB-2 product is correlated with TCC histological grading or AC morphology. A high intensity of EGF-R staining in human bladder carcinomas may be associated with poor differentiation and invasion, whereas transferrin receptor expression might reflect tumor growth.
 ...
PMID:Immunohistochemical analysis of c-erbB-2 oncogene product and epidermal growth factor receptor expression in human urinary bladder carcinomas. 220 26

Individual gold particles with a diameter of approximately 10 to 40 nm can be visualized using video-enhanced contrast microscopy (Nanovid) (De Brabander et al., Cell Motil. Cytoskel. 6, 105-113 (1986)). This technique allows a study of the dynamic properties of receptors and ligands in living cells at high resolution. We have studied epidermal growth factor (EGF) receptor internalization in human epidermoid carcinoma A431 cells, using a monoclonal anti-EGF-receptor antibody conjugated to 20-nm gold particles, referred to as 2E9-gold. Exposure of A431 cells to 2E9-gold at 37 degrees C resulted in binding of the complex at the cell surface. Most of the gold particles exhibit a Brownian type of movement, while a minority appeared immobile. Binding of the 2E9-gold complex is followed by internalization, as judged from Nanovid light microscopy studies in combination with electron microscopic observations. The internalized gold particles clearly cluster into large aggregates, most likely multivesicular bodies. Individual gold particles as well as aggregates are characterized by a saltatory movement, by which the gold particles eventually move from the cell periphery towards the cell center. Addition of EGF results in an increased rate of internalization of 2E9-gold, while Na-azide and nocodazole completely immobilize the intracellular gold particles, as has been demonstrated previously for the transferrin receptor.
 ...
PMID:Dynamics of epidermal growth factor receptor internalization studied by Nanovid light microscopy and electron microscopy in combination with immunogold labeling. 278 46

The regulation of protein phosphorylation by sphingosine in A431 human epidermoid carcinoma cells was examined. Sphingosine is a competitive inhibitor of phorbol ester binding to protein kinase C (Ca2+/phospholipid-dependent enzyme) and potently inhibits phosphotransferase activity in vitro. Addition of sphingosine to intact A431 cells caused an inhibition of the phorbol ester-stimulated phosphorylation of two protein kinase C substrates, epidermal growth factor (EGF) receptor threonine 654 and transferrin receptor serine 24. We conclude that sphingosine inhibits the activity of protein kinase C in intact A431 cells. However, further experiments demonstrated that sphingosine-treatment of A431 cells resulted in the regulation of the EGF receptor by a mechanism that was independent of protein kinase C. First, sphingosine caused an increase in the threonine phosphorylation of the EGF receptor on a unique tryptic peptide. Second, sphingosine caused an increase in the affinity of the EGF receptor in A431 and in Chinese hamster ovary cells expressing wild-type (Thr654) and mutated (Ala654) EGF receptors. Sphingosine was also observed to cause an increase in the number of EGF-binding sites expressed at the surface of A431 cells. Examination of the time course of sphingosine action demonstrated that the effects on EGF binding were rapid (maximal at 2 mins) and were observed prior to the stimulation of receptor phosphorylation (maximal at 20 mins). We conclude that sphingosine is a potently bioactive molecule that modulates cellular functions by: 1) inhibiting protein kinase C; 2) stimulating a protein kinase C-independent pathway of protein phosphorylation; and 3) increasing the affinity and number of cell surface EGF receptors.
 ...
PMID:Regulation of the epidermal growth factor receptor phosphorylation state by sphingosine in A431 human epidermoid carcinoma cells. 316 30

The epidermal growth factor (EGF) receptor is a substrate for phosphorylation by the calcium- and phospholipid-dependent protein kinase (protein kinase C) at Thr654. The hypothesis that this phosphorylation is causally related to the regulation of the functional properties of the EGF receptor was tested by substitution of Thr654 with an alanine residue. Activation of protein kinase C using phorbol ester caused a decrease in the high affinity binding of EGF to Chinese hamster ovary cells expressing wild-type [Thr654]EGF receptors. Similar results were obtained with cells expressing mutated [Ala654]EGF receptors. The regulation of the protein kinase activity of the EGF receptor by protein kinase C was examined using a synthetic peptide substrate for tyrosine phosphorylation. Protein kinase C caused a Ca2+-dependent decrease in the tyrosine-protein kinase activity of the wild-type [Thr654]EGF receptor. In contrast, no inhibition of the tyrosine-protein kinase activity of the mutated [Ala654]EGF receptor caused by protein kinase C was detected. In further experiments, the desensitization of EGF action caused by the activation of protein kinase C was examined by investigating the regulation of the transferrin receptor by EGF. Phorbol ester was observed to cause the desensitization of signaling by the wild-type [Thr654] and mutated [Ala654]EGF receptors. These data are consistent with a role for the phosphorylation of EGF receptor Thr654 in the regulation of the receptor tyrosine-protein kinase activity. However, the inhibition of the high affinity binding of EGF to cell-surface receptors caused by protein kinase C does not require Thr654. It is concluded that independent mechanisms account for the regulation by protein kinase C of the EGF receptor affinity and tyrosine-protein kinase activity.
 ...
PMID:Independent mechanisms account for the regulation by protein kinase C of the epidermal growth factor receptor affinity and tyrosine-protein kinase activity. 337 75

The effect of herbimycin A on the biosynthesis of epidermal growth factor (EGF) receptor was examined in human epidermoid carcinoma A431 cells. Cells were pulse-labelled with [35S]methionine, and EGF receptor biosynthesis was quantified by immunoprecipitation using a monoclonal anti-(EGF receptor) antibody. In the presence of herbimycin A, an immature 160 kDa EGF receptor precursor accumulated in 1 h and disappeared completely in 4 h. Pulse-labelled 160 kDa receptor precursor in the absence of herbimycin A, however, was converted normally into a 170 kDa one by chase with herbimycin A. Herbimycin A affected neither the synthesis of the secreted form of EGF receptor devoid of cytoplasmic domain, nor that of the transferrin receptor in A431 cells. The herbimycin A-induced degradation of 160 kDa EGF receptor precursor was not inhibited by an inhibitor of lysosomal enzymes, NH4Cl. Endoglycosidase H digestion of the 160 kDa precursor converted it into the deglycosylated 130 kDa precursor peptide. These results suggested that herbimycin A selectively acted on the EGF receptor precursor during the synthesis of the 160 kDa form, probably on the cytoplasmic domain, to form an aberrant molecule which was subjected to rapid degradation in the endoplasmic reticulum.
 ...
PMID:Accelerated degradation of 160 kDa epidermal growth factor (EGF) receptor precursor by the tyrosine kinase inhibitor herbimycin A in the endoplasmic reticulum of A431 human epidermoid carcinoma cells. 803 92

Bispecific antibodies of a new category, termed "antigen forks", were constructed by crosslinking antibodies that recognized pairs of distinct tumor cell surface antigens. At concentrations of 1-100 nM, several such forks inhibited the growth of human tumor cell lines bearing both relevant antigens. The same cells were not inhibited by unconjugated component antibodies, and the active conjugates did not inhibit the growth of human cell lines that expressed lower levels of relevant antigens. The three most active antigen forks all contained monoclonal antibody 454A12, which recognizes human transferrin receptor. This antibody was conjugated respectively to antibodies 113F1 (against a tumor-associated glycoprotein complex), 317G5 (against a 42-kDa tumor-associated glycoprotein), or 520C9 (against the c-erbB-2 protooncogene product). The 317G5-454A12 fork strongly inhibited the HT-29 and SW948 human colorectal cancer cell lines, while the 113F1-454A12 and 520C9-454A12 forks strongly inhibited the SK-BR-3 human breast cancer cell line and the 113F1-454A12 fork was also effective against SW948. By designing forks against antigens of incompatible function that are co-expressed at high levels on tumor cells but not on normal tissues, it may be possible to generate reagents that inhibit tumor growth with enhanced selectivity.
 ...
PMID:Antigen forks: bispecific reagents that inhibit cell growth by binding selected pairs of tumor antigens. 804 25


1 2 3 Next >>