Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Receptor Aggregation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20Linked to original sources
PubMed1981

Subunit structure of cell surface proteins: disulfide bonding in antigen receptors, Ly-2/3 antigens, and transferrin receptors of murine T and B lymphocytes.

The surface proteins of lymphocytes from spleen and thymus and several cultured lymphoid tumor lines were radioiodinated in situ, solubilized with Triton X-100, and examined for the presence of disulfide-bonded subunits by two-dimensional (intact, reduced) NaDodSO4/polyacrylamide gel electrophoresis. [Hynes, R. O. & Destree, A. (1977) Proc. Natl. Acad. Sci. USA 74, 2855-2859]. Few lymphocyte surface proteins were found to consist of disulfide-bonded subunits, and the most prominent of these could be identified. In normal B lymphocytes and B-lymphoma cells, IgD or IgM (or both) were the major disulfide-bonded proteins, and these were easily detectable, even without immunoprecipitation. In contrast, analysis of thymocytes and T-lymphoma cells did not reveal any protein resembling immunoglobulin in its chain structure. The major labeled thymocyte membrane protein consisting of disulfide-bonded subunits was identified as the Ly-2/3 antigen. It appeared to contain disulfide-bonded homodimers of Mr 35,000 (alpha 2) noncovalently associated with a second pair of homodimers of Mr 30,000 (beta 2). Peptide mapping showed these polypeptides to be homologous. A third disulfide-bonded homodimer, which was heterogeneous in apparent Mr, appeared to be part of the Ly-2/3 complex. All cultured T- and B-lymphoma lines examined were found to possess a major surface protein that appeared to be a disulfide-bonded homodimer of a polypeptide of Mr 95,000. This protein was identified as the receptor for transferrin. It is suggested that the presence of two or more subunits in cell surface receptors renders their ligand functionally bivalent, making ligand-induced receptor aggregation possible.

Animals↗
PubMed1994

The CD45 tyrosine phosphatase regulates specific pools of antigen receptor-associated p59fyn and CD4-associated p56lck tyrosine in human T-cells.

A newly isolated T-cell line (CB1) derived from a T-acute lymphoblastic leukaemia (T-ALL) patient contained cells (40% of total) which did not express the CD45 phosphotyrosine phosphatase. The cells were sorted into CD45- and CD45+ populations and shown to be clonal in origin. T-cell receptor (TCR) cross-linking or coligation of the TCR with its CD4/CD8 co-receptors induced tyrosine phosphorylation and calcium signals in CD45+ but not in CD45- cells. Unexpectedly, whole cell p56lck and p59fyn tyrosine kinase activities were not reduced in CD45- compared to CD45+ cells. A novel technique was therefore developed to isolated specific pools of aggregated receptors expressed at the cell surface, together with their associated tyrosine kinases. Using this technique it was shown that cell surface CD4-p56lck kinase activity was 78% lower in CD45- than in CD45+ cells. Phosphorylation of TCR zeta- and gamma-chains occurred in TCR immunocomplexes from CD45+ but not CD45- cells, despite comparable levels of p59fyn and TCR proteins. Furthermore, TCR-associated tyrosine kinase activity towards an exogenous substrate was 84% lower in CD45- than in CD45+ cells. Addition of recombinant p59fyn to TCR immunocomplexes isolated from CD45-cells restored the phosphorylation of the TCR zeta- and gamma-chains. Our results demonstrate that CD45 selectively regulates the pools of p59fyn and p56lck kinases which are associated with the TCR and CD4 at the cell surface. Activation by CD45 of these receptor-associated kinase pools correlates with the ability of the TCR and its coreceptors to couple to intracellular signalling pathways.

CD4 Antigens↗
PubMed1998

Modelling human sperm-egg interactions in vitro: signal transduction pathways regulating the acrosome reaction.

Recent advances in characterizing sperm surface receptors and ion channels, when combined with the rapidly expanding knowledge of interactions among second messenger systems in somatic cells, permit formulation of a tentative molecular mechanism for the regulation of the human sperm acrosome reaction. As spermatozoa pass through the cumulus mass, progesterone binds to its sperm surface receptor, alkalinizes the sperm head cytosol and potentiates changes in intracellular ionized calcium. Primary binding of spermatozoa to egg involves receptors for mannosyl, N-acetylglucosaminyl and, possibly, fucosyl residues of the glycosylated zona protein, ZP3. These receptors aggregate on multivalent ligand binding, migrate to the equatorial region along an actin filament network formed between the plasma and acrosomal membranes during capacitation, and activate a G protein/protein kinase A/protein kinase C second messenger system and a secondary proteolysis signal. Binding of a receptor tyrosine kinase to ZP3 amino acid residues simultaneous with the sugar recognition event triggers tyrosine phosphorylation signalling. All signals combine to open a voltage-dependent calcium channel. The resulting elevated calcium signal depolymerizes the inter-membrane actin network and activates phospholipases, leading to an acrosome reaction.

Acrosome↗
PubMed1984

Characteristics of histamine release from isolated rat mast cells: differences when various ligands are used to induce secretion.

Differences are reported in the response of rat peritoneal mast cells to three releasing agents: ovalbumin, to which the rats were actively sensitized, anti-IgE, an immunoglobulin directed against the rat IgE molecule, and IgE chemically dimerized with suberimidate. Both the rate of histamine release and the rate of desensitization were measured for each of the three ligands. The calculated doubling times for the rates of histamine release due to ovalbumin, anti-IgE and dimer were 19.6 sec, 168 sec and 37.7 sec respectively. The calculated half-lives for the rate of desensitization due to ovalbumin, anti-IgE and dimer were 348 sec, 5900 sec and 3450 sec respectively. The three ligands are all believed to act by crosslinking Fc receptors on the cell surface but the pattern of responses obtained varied with the ligand used. It is proposed that some component of the transduction mechanism linking the stimulus to the cell to the subsequent response can distinguish between the various sizes or conformations of Fc receptor aggregates formed on the cell surface.

Animals↗
PubMed1989

Influence of the red blood cell Ca2+-ion concentration on the erythrocyte aggregation in stasis.

Ca2+ ions were transported into the cell by incubation of the erythrocyte suspension with ionophore A23187, a lipophil electric neutral ion complexing substance. Erythrocyte aggregation could be increased twice, when doubling the intracellular Ca2+-ion concentration. Our measurements lead to the suggestion that an increase of the cytoplasmatic Ca2+ ion changes the physical and/or biochemical properties of the aggregation receptors on the membrane surface, i.e., cell-protein interactions are regulated by alteration of the intracellular Ca2+-ion concentration.

Adolescent↗
PubMed1990

Two-step purification of full-length nerve growth factor receptor and maintenance of receptor-specific binding activity.

A method for the purification of full-length nerve growth factor receptor (NGFRc) using membranes from three different cell lines was developed. We emphasized recovery of NGFRc that retained specific binding activity. Lipids were required to preserve binding activity during solubilization and throughout the purification procedure. Phosphatidylcholine was used for this purpose. Lectin affinity chromatography followed by high-resolution anion-exchange chromatography was used, and a 3000-fold increase in specific binding activity was obtained for NGFRc from human melanoma A875 membranes. Seven percent of the original binding activity was recovered as pure NGFRc. NGFRc binding activity eluted at 0.35 M NaCl in anion-exchange chromatography of solubilized A875, rat pheochromocytoma PC12, and human neuroblastoma MC-IXC membranes. Eight and three percent of the original binding activity were recovered as highly enriched NGFRc from membranes prepared from PC12 and MC-IXC cells, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of highly enriched, 125I-labeled NGFRc revealed several protein species. After chromatography, identification of proteins as NGFRc was verified both by immunoprecipitation using receptor-specific monoclonal antibodies and by covalent cross-linking to 125I-NGF using N-hydroxysuccinimidyl-4-azidobenzoate. Predominantly, NGFRc was recovered as a mixture of species of 80 and 160-180 kDa. Small amounts of larger species as well as smaller species were observed, consistent with minor amounts of receptor aggregation and proteolysis occurring during purification.

Animals↗
PubMed1998

Hemopoietic growth factor receptor abnormalities in leukemia.

Growth factor and cytokine control of hemopoiesis, the process of blood cell development, is mediated by specific interactions with cell-surface receptors. Hemopoietic growth factor receptors belong to two major families, the transmembrane protein tyrosine kinases and the hemopoietin receptors. Ligand binding stimulates receptor aggregation and activation resulting in transduction of signals that induce diverse cellular responses including proliferation, maturation, prevention of apoptosis and/or functional activation. Deregulation of hemopoiesis can result in leukemia, the malignant transformation of blood cells, or the development of other hemoproliferative disorders. As hemopoietic growth factor receptors are integral to blood cell regulation, it is feasible that receptor abnormalities may contribute to leukemia by circumventing normal growth factor control or altering the balance of proliferation and differentiation. Although considerable experimental evidence has clearly established the leukemogenic potential of mutated growth factor receptors, studies to date suggest that such abnormalities contribute only rarely to human disease.

Humans↗
PubMed1995

Crystals of soluble interleukin-1 receptor complexed with its natural antagonist reveal a 1:1 receptor-ligand complex.

Interleukin-1 is a cytokine involved in the acute phase response against infection and injury. We obtained crystals of a complex of soluble, recombinant human interleukin-1 receptor and recombinant human interleukin-1 receptor antagonist, a naturally occurring antagonist. The crystals are suitable for X-ray analysis and diffract to 2.7 A resolution. Solvent content calculations indicate that the crystals contain one receptor and one antagonist molecule per asymmetric unit. Other receptor to antagonist ratios are highly unlikely. These results suggest that the interleukin-1 antagonist binds a single receptor molecule and does not cause receptor aggregation.

Base Sequence↗
PubMed1979

Localization of LH receptors on luteal cells with a ferritin--LH conjugate.

In order to study the distribution of LH (HCG) receptors on luteal cells ferritin was coupled to ovine LH with glutaraldehyde and purified by gel chromatography. The conjugate (FELH) competed with 125I-hCG for binding to isolated luteal membranes and stimulated a dose-dependent release of progesterone (P) from isolated luteal cells which was inhibited by PGF2 alpha. FELH was distributed as single molecules or in small clusters at intervals on the surfaces of luteal cells labeled at 37 degrees C, 4 degrees C or with formaldehyde prefixation. Capping or preferential labeling at one site was not observed. The general distribution of LH (hCG) binding sites at 37 degrees C was confirmed by light-microscopic autoradiography. The distribution at 4 degrees C or with prefixation was more diffuse than at 37 degrees C suggesting that FELH binding induces small changes in receptor aggregation. Binding of FELH was specific since excess hCG reduced FELH binding to luteal cells. In cells labeled at 4 degrees C, rinsed and warmed to 37 degrees C FELH was observed along cell surfaces and within some coated vesicles and a few lysosomes within minutes suggesting that receptor internalization is a rapid and possibly continual process.

Animals↗
PubMed1987

Insulin-like and insulin-inhibitory effects of monoclonal antibodies for different epitopes on the human insulin receptor.

Monoclonal antibodies previously shown to react with five distinct epitopes on the human insulin receptor were tested for their metabolic effects on isolated human adipocytes. Two antibodies which reacted with receptor alpha-subunit and completely inhibited 125I-insulin binding mimicked the actions of insulin to stimulate lipogenesis from [14C]glucose and to inhibit catecholamine-induced lipolysis. On a molar basis, these antibodies were comparable in potency with insulin itself. Two other antibodies which decreased insulin binding only slightly or not at all also mimicked these metabolic effects of insulin. One of these antibodies reacted with receptor beta-subunit. In contrast, a further antibody which reacted with alpha-subunit and inhibited insulin binding did not affect basal lipogenesis or catecholamine-induced lipolysis, but was able to antagonize the effects of insulin on these processes. The same antibody antagonized the insulin-like effect of another antibody with which it competed in binding to insulin receptor, but not the effect of an antibody which bound independently to the receptor. It is concluded that binding of ligand at or close to the insulin-binding site is neither necessary nor sufficient to trigger insulin-like metabolic effects, which may rather depend on some general property of antibodies, such as their ability to cross-link and aggregate receptor molecules.

Adipose Tissue↗
PubMed1988

An antibody to the low-density lipoprotein (LDL) receptor that partially inhibits the binding of LDL to cultured human fibroblasts.

A monoclonal antibody, raised initially against pure bovine low-density lipoprotein (LDL) receptor, was found to bind saturably to LDL receptors on the surface of cultured human fibroblasts. It was apparently internalized by the cells but rapidly returned to the surface and was not significantly degraded. LDL did not affect the binding of antibody. However, the antibody reduced both the apparent affinity of the receptor for LDL and the amount of LDL bound. In the presence of antibody, the concentration of LDL required for one-half maximum binding increased from 14.5 nM to 22.3 nM at 37 degrees C and from 2.8 nM to 11.5 nM at 4 degrees C. Maximum heparin-releasable binding of LDL was reduced by 56% at 37 degrees C and by 36% at 4 degrees C. Fab fragments halved the affinity at both temperatures without affecting the maximum amount of LDL bound. At 4 degrees C, maximum heparin-releasable LDL binding was the same as that of antibody and of Fab fragments. At 37 degrees C, heparin-releasable binding of LDL and binding of Fab fragments were double that at 4 degrees C, whereas binding of antibody remained unchanged. The results suggest that the antibody bound to a site on the receptor remote from the LDL binding region and that intact antibody recycled with the receptor. It halved LDL binding and degradation at 37 degrees C and reduced binding at 4 degrees C, probably through a different mechanism. The possibility that both cooling and antibody led to receptor aggregation is discussed.

Antibodies, Monoclonal↗
PubMed1999

Thrombin receptor occupancy modulates aggregation efficiency and platelet surface expression of vWF and thrombospondin at low thrombin concentrations.

Previous studies evaluating requirements for occupancy of thrombin receptors in normal platelet secretion and aggregation, using the thrombin antagonists hirudin and PPACK (D-Phe-Pro-Arg-chloromethylketone), have suggested that at low thrombin activating concentrations (0.025-0.13 U/ml), occupancy was required only in the first 45-60 s following activation. In our study, we differentiate between thrombin receptor occupancy requirements for surface expression of secreted adhesive proteins, for activation of GPIIb-IIIa receptors, and for aggregation of washed platelets (WP) in laminar shear flow. Platelets activated with 0.05 U/ml thrombin for 10 min to allow maximal secretion (hereafter referred to as "pre-activated platelets"), then sheared, showed a 50-70% decrease in platelet counts after 60 s of shear. Treatment of pre-activated platelets with hirudin or PPACK produced a 65% reduction of capture efficiencies, alphaG (reflecting experimental/theoretical initial rates of aggregation), as well as a 30-40% decrease in the surface expression of von Willebrand factor (vWF) and thrombospondin (TSP). However, alpha-granule membrane P-selectin expression and numbers of activated GPIIb-IIIa receptors were comparable for treated and non-treated platelets. No significant difference in any of the parameters tested was observed when platelets were similarly pre-activated with 0.2 U/ml thrombin, due to treatment with thrombin antagonists. Binding of soluble FITC-vWF (GRGDSP-sensitive) to pre-activated, thrombin antagonist treated platelets, was greatly reduced (> or =80%). Soluble Fg was shown to bind to antagonist-treated pre-activated platelets, but could not significantly enhance platelet aggregation. Although occupancy of thrombin receptors by catalytically active thrombin is required transiently for secretion and activation of platelets, there is a further requirement for thrombin occupancy at low thrombin concentrations, for optimizing initial rates of platelet aggregation, surface expression of vWF and TSP, and activated GPIIb-IIIa ligand recognition.

Blood Platelets↗
PubMed1996

Requirements for mouse mammary tumour virus internalization in mouse mammary epithelial cells.

Methylamine, a lysosomotropic alkalinizing agent, blocked mouse mammary tumour virus (MMTV) infection in normal mouse mammary epithelium, suggesting that internalization and acidification are necessary for cell penetration. This mechanism was further supported by the fact that intact MMTV induced the translocation of its cellular binding protein from the plasmalemma to the microsomes; however, isolated gp52, the MMTV envelope protein that binds this receptor, did not redistribute the binding protein. These data suggest that either another viral component, in addition to gp52, is needed for cell entry or that internalization requires receptor aggregation, which only the multivalent viral envelope can induce.

Animals↗
PubMed2001

Immunohistochemical demonstration of the NK(1) tachykinin receptor on muscle and epithelia in guinea pig intestine.

BACKGROUND AND AIMS: Previous immunohistochemical studies failed to reveal neurokinin (NK)(1) tachykinin receptors on intestinal muscle, despite convincing pharmacologic data indicating their presence. This study aimed to apply optimal immunohistochemical methods to reveal the receptors. METHODS: NK(1)-receptor immunoreactivity was examined by confocal microscopy in tissue incubated with or without 10(-7) mol/L substance P (SP), 10(-7) mol/L SP plus 10(-6) mol/L NK(1) receptor antagonist (CP99994), or with fluorescent cyanine 3.18 (Cy3) SP. RESULTS: Without incubation, NK(1)-receptor immunoreactivity was strong on muscle of the rectum and distal colon and weak in proximal colon and small intestine. NK(1) receptor was located on the surface of muscle cells in all gut regions. Exposure to SP increased the intensity of immunoreactivity, and the receptor moved into the cytoplasm. Mobilization of the receptor by SP was blocked by the NK(1)-receptor antagonist CP99994. Cy3-SP was internalized by muscle cells and colocalized with the receptor. NK(1)-receptor immunoreactivity occurred on crypt epithelial cells in the small intestine and the base of glands in the proximal colon. CONCLUSIONS: The NK(1) receptor occurs on the external muscle throughout the small and large intestines. SP binds and triggers NK(1)-receptor aggregation and internalization in the muscle.

Animals↗
PubMed2006

EBV B lymphoma cell lines from patients with post-transplant lymphoproliferative disease are resistant to TRAIL-induced apoptosis.

Lymphomas associated with post-transplant lymphoproliferative disease (PTLD) represent a significant complication of immunosuppression in transplant recipients. In immunocompetent individuals, EBV-specific cytotoxic T lymphocytes (CTL) prevent the outgrowth of activated B lymphoblasts through apoptosis induction. Soluble versions of TNF-related apoptosis-inducing ligand/Apo2 ligand (TRAIL) can induce apoptosis in numerous tumor cell types. Given the therapeutic potential of TRAIL, we examined the sensitivity of EBV+ spontaneous lymphoblastoid cell lines (SLCL) derived from patients with PTLD to treatment with soluble TRAIL. Despite abundant expression of TRAIL receptors (TRAIL-R), resistance to TRAIL-induced apoptosis was observed in all SLCL examined. This resistance could not be overcome by concomitant treatment with several pharmacological agents. Unlike BJAB positive control cells, for each SLCL tested, cleavage and activation of caspase 8 was inhibited due to failed recruitment of FADD and caspase 8 to TRAIL receptors upon stimulation. Further indicative of a proximal defect, TRAIL receptor aggregation could not be detected on the cell surface of SLCL following ligand engagement. These results suggest that the use of TRAIL for eliminating PTLD-associated tumors may be of limited clinical utility, and illustrate another mechanism by which EBV+ B lymphoma cells can evade tumor surveillance at the level of death receptor signaling.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1984

Internalization and rapid recycling of macrophage Fc receptors tagged with monovalent antireceptor antibody: possible role of a prelysosomal compartment.

Binding and pinocytosis of polyvalent IgG-containing immune complexes by mouse macrophages leads to the selective removal of Fc receptors (FcR) from the cell surface and to the rapid delivery of receptor and ligand to lysosomes, where both are degraded (I. Mellman and H. Plutner, 1984, Journal of Cell Biology, 98:1170-1177). In this paper, we have studied the internalization of FcR tagged with a monovalent probe that, unlike IgG-complexes, cannot cross-link adjacent receptors. We have used an Fab fragment of high affinity anti-FcR monoclonal antibody whose binding was completely sensitive to low pH (4.0) at 4 degrees C. Thus, surface-bound (acid-releasable) and intracellular (acid-resistant) 125I-Fab could be readily distinguished. Incubation of J774 macrophages with 125I-Fab at 37 degrees C did not lead to the accumulation of large amounts of the antibody in the acid-resistant compartment. After 3 h, only 20% of the total cell-associated radiolabel was intracellular. The internalized 125I-Fab was also shown by Percoll gradient centrifugation to be associated primarily with low density endosomes, as opposed to lysosomes. Significantly, most of the labeled antibody returned rapidly to the plasma membrane, still bound to FcR. This recycling was complete within 10 min, was unaffected by NH4Cl, and was only slightly inhibited by the Na+-H+ ionophore monensin. These results indicate that monovalent Fab-FcR complexes are internalized, delivered to endosomes, and rapidly returned to the cell surface. Since the internalization of polyvalent IgG-complexes removed the FcR from this recycling pathway and caused its transport to lysosomes, we suggest that the state of receptor aggregation in the endosome membrane helps determine its intracellular fate.

Animals↗
PubMed1988

Does vector-free gravity simulate microgravity? Functional and morphologic attributes of clinorotated nerve and muscle grown in cell culture.

Cocultured Xenopus neurons and myocytes were subjected to non-vectorial gravity by clinostat rotation to determine if microgravity, during space flights, may affect cell development and communications. Clinorotated cells showed changes consistent with the hypothesis that cell differentiation, in microgravity, is altered by interference with cytoskeleton-related mechanisms. We found: increases in the myocyte and its nuclear area, "fragmentation" of nucleoli, appearance of neuritic "aneurysms", decreased growth in the presence of "trophic" factors, and decreased yolk utilization. The effects were most notable at 1-10 rpm and depended on the onset and duration of rotation. Some parameters returned to near control values within 48 hrs after cessation of rotation. Cells from cultures rotated at higher speeds (>50 rpm) appeared comparable to controls. Compensation by centrifugal forces may account for this finding. Our data are consistent, in principle, with effects on other, flighted cells and suggest that "vector-free" gravity may simulate certain aspects of microgravity. The distribution of acetylcholine receptor aggregates, on myocytes, was also altered. This indicates that brain development, in microgravity, may also be affected.

Animals↗
PubMed1993

A theoretical analysis for the effect of focal contact formation on cell-substrate attachment strength.

For many cell types, growth, differentiation, and motility are dependent on receptor-mediated adhesion to ligand-coated surfaces. Focal contacts are strong, specialized, adhesive connections between cell and substrate in which receptors aggregate and connect extracellular ligand to intracellular cytoskeletal molecules. In this paper, we present a mathematical model to examine how focal contact formation affects cellular adhesive strength. To calculate adhesive strength with and without focal contacts, we use a one-dimensional tape peeling analysis to determine the critical tension necessary to peel the membrane. Receptor-ligand bonds are modeled as adhesive springs. In the absence of focal contacts, we derive analytic expressions for the critical tension at low and high ligand densities and show how membrane morphology affects adhesion. Then, focal contacts are modeled as cytoplasmic nucleation centers which bind adhesion receptors. The extent of adhesive strengthening upon focal contact formation depends on the elastic rigidity of the cytoskeletal connections, which determines the structural integrity of the focal contact itself. We consider two limits to this elasticity, very weak and rigid. Rigid cytoskeletal connections give much greater attachment strengths. The dependence of attachment strength on measurable model parameters is quite different in these two limits, which suggests focal contact structure might be deduced from properly performed adhesion experiments. Finally, we compare our model to the adhesive strengthening response reported for glioma cell adhesion to fibronectin (Lotz et al., 1989. J. Cell Biol. 109:1795-1805). Our model successfully predicts the observed detachment forces at 4 degrees C and yields values for the number of fibronectin receptors per glioma cell and the density of cytoskeletal connection molecules (talin) involved in receptor clusters which are consistent with measurements for other cell types. Comparison of the model with data at 37 degrees C suggests that while cytoskeletal cross-linking and clustering of fibronectin receptors significantly increases adhesion strength, specific glioma cell-substratum attachment sites possess little mechanical rigidity and detach through a peeling mechanism, consistent with the view that these sites of < or = 15 nm cell-substrate separation are precursors to fully formed, elastically rigid focal contacts.

Animals↗