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 1,369 records · Page 76Linked to original sources
PubMed1995

Platelet glycoprotein IIb gene expression as a model of megakaryocyte-specific expression.

Glycoprotein (GP)IIb/IIIa is an integrin complex normally restricted in its expression to platelets and the megakaryocytes from which they are derived. This complex functions as a receptor for fibrinogen and other ligands and is involved in platelet aggregation. The receptor complex is expressed at high levels during final megakaryocyte differentiation. Further, while GPIIIa is expressed in other tissues as part of the vitronectin receptor, GPIIb is only expressed on maturing megakaryocytes and the platelets derived from them. Thus studies of the GPIIb gene may serve as a model of gene regulation during this process. Over the past several years, the genes for both GPIIb and IIIa have been cloned and analyzed. The GPIIb gene contains 30 exons over 18 kilobases (kb). The transcriptional start site has been determined and there does not appear to be a TATA-box immediately upstream of this site. Studies have been done to define regulatory elements upstream of the transcriptional start site. Most of these studies focused on the human promoter and on studies using megakaryocytic cell lines. These studies have defined several important tissue-specific promoter elements including a GATA454 site (454 basepairs upstream of the transcriptional start site that involves a GATA-binding consensus sequence), a GATA54 site and an Ets35 site (that involves an Ets-binding consensus sequence). Expression studies with megakaryocytic cell lines suggest that each of these sites effects expression approximately threefold. Further, an Ets510 site was also described that had a similar effect. While these studies were underway, we pursued studies of the rat 5'-flanking region using a rat primary marrow expression system. Qualitatively, our data support the human data; however, quantitatively, we found significant differences from the human studies done in cell lines. We found that the major tissue-specific promoter element was the GATA454 site. Mutations altering this site result in an approximately fiftyfold drop in expression. In comparison, eliminating the Ets510 site by truncation or point mutation had only a twofold effect on expression. Mutations at the Ets35 site did effect expression at a high level, decreasing expression approximately fifteenfold, while mutations at the GATA54 site effected expression by approximately ninefold. In addition, using 50 bp deletions, we have preliminarily defined two domains from -450 to -351 bp and -150 to -101 bp upstream of the transcriptional start site that effected expression. The former appears to contain a positive regulatory element, while the latter appears to be a silencer element.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Zinc potentiation of androgen receptor binding to nuclei in vitro.

Zn2+ potentiates binding of the 4.5S [3H]dihydrotestosterone-receptor complex to isolated rat prostate Dunning tumor nuclei in vitro when assayed in the presence of 300 microM ZnCl2, 3 mM MgCl2, 0.25 M sucrose, 5 mM mercaptoethanol, 0.15 M KCl, and 50 mM tris(hydroxymethyl)aminomethane, pH 7.5. In the presence of 5 mM mercaptoethanol, the concentration of 50 microM total Zn2+ required to promote half-maximal receptor binding to nuclei corresponds to a free Zn2+ concentration of 50 nM. The receptor-nuclear interaction appears to be selective for Zn2+; other divalent cations when added at a concentration of 1 mM to a buffer containing 5 mM mercaptoethanol are less effective (Ni2+) or have essentially no effect (Ca2+, Mg2+, Mn2+, Co2+, Cu2+, and Cd2+). Zn2+ does not alter the sedimentation rate of the 4.5S [3H]dihydrotestosterone receptor in the presence of mercaptoethanol; however, in the absence of mercaptoethanol, Zn2+ causes the receptor to aggregate. Zn2+-dependent nuclear binding of the 4.5S [3H]dihydrotestosterone receptor is saturable at 1.4 X 10(-13) mol of receptor sites/mg of DNA, corresponding to approximately 1150 sites/nucleus. In the presence of excess nuclei, up to 60% of added receptor is nuclear bound. An apparent binding constant for the receptor-nuclear interaction of 10(13) M-1 was approximated. Pyridoxal 5'-phosphate (less than or equal to 10 mM), but not 0.4 M KCl, inhibits Zn2+-dependent nuclear binding of the [3H]dihydrotestosterone receptor. Up to 66% of nuclear-bound receptor can be extracted in buffer containing 3 mM ethylenediaminetetraacetic acid plus either 0.4 M KCl or 10 mM pyridoxal 5'-phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

A cDNA presumptively coding for the alpha subunit of the receptor with high affinity for immunoglobulin E.

Rat mast cells and a neoplastic analogue such as rat basophilic leukemia (RBL) cells have receptors that have exceptionally high affinity for immunoglobulin E (IgE). When aggregated, these receptors induce cellular degranulation. The alpha chain of the receptor contains the binding site for IgE; the function(s) of the noncovalently associated beta and gamma chains is (are) still undefined. Using a cDNA library constructed from the mRNA of RBL cells, we have isolated a cDNA clone whose sequence predicts a putative 23-residue signal peptide, followed by a sequence that accurately predicts the amino acid composition, the peptide molecular weight, and six peptide sequences (encompassing 59 residues or 26% of the total number) determined for the alpha chain by direct analysis. These findings provide strong evidence that the cDNA codes for the alpha chain, even though expression has not been unambiguously achieved. The sequence suggests that the alpha chain contains a 180-residue extracellular portion with two homologous domains of approximately 35 residues, a 20-residue transmembrane segment containing an aspartic acid, and a 27-residue cytoplasmic portion containing 9 basic amino acids. The sequence shows no homology with the low-affinity receptor for IgE from lymphocytes but over 30% homology with an Fc gamma receptor.

Amino Acid Sequence↗
PubMed1969

Purification of an estrophilic protein from calf uterus.

A method has been devised for purifying the estrogen-binding protein ("uptake receptor") of uterine cytosol which circumvents the marked tendency of this receptor to aggregate during attempted isolation. Ammonium sulfate precipitation of the estradiol-receptor complex of calf uterine cytosol in the presence of calcium ions yields both an 8S complex and its 4S subunit which are stable during further purification by gel filtration and ion exchange chromatography. The major product is the 4S complex which does not revert to 8S in the absence of salt and which has been purified about 2500-fold. The approximate isoelectric points of these partially purified 8S and 4S complexes are 5.8 and 6.4, respectively.

Animals↗
PubMed1996

Pentameric subunit stoichiometry of a neuronal glutamate receptor.

Ionotropic glutamate receptors, neurotransmitter-activated ion channels that mediate excitatory synaptic transmission in the central nervous system, are oligomeric membrane proteins of unknown subunit stoichiometry. To determine the subunit stoichiometry we have used a functional assay based on the blockade of two alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate/kainate receptor subunit 1 (GluR1) mutant subunits selectively engineered to exhibit differential sensitivity to the open channel blockers phencyclidine and dizolcipine (MK-801). Coinjection into amphibian oocytes of weakly sensitive with highly sensitive subunit complementary RNAs produces functional heteromeric channels with mixed blocker sensitivities. Increasing the fraction of the highly sensitive subunit augmented the proportion of drug-sensitive receptors. Analysis of the data using a model based on random aggregation of receptor subunits allowed us to determine a pentameric stoichiometry for GluR1. This finding supports the view that a pentameric subunit organization underlies the structure of the neuronal ionotropic glutamate receptor gene family.

Animals↗
PubMed1999

39-kDa receptor-associated protein (RAP) facilitates secretion and ligand binding of extracellular region of very-low-density-lipoprotein receptor: implications for a distinct pathway from low-density-lipoprotein receptor.

We have expressed the extracellular regions of the low-density-lipoprotein (LDL) receptor and the very-low-density-lipoprotein (VLDL) receptor, along with the full-length forms of the receptors, in insect cells in a baculovirus system. The extracellular region of the LDL receptor has been secreted successfully into the culture medium, and it retained the capacities of binding 125I-labelled LDL and beta-VLDL. In contrast, the extracellular region of the VLDL receptor remained intracellular and it did not bind 125I-beta-VLDL. This difference in expression behaviour between the homologous regions of the two receptors suggests that the two receptor systems are different in receptor-protein maturation or protein targeting. Next we developed the co-expression system with 39-kDa receptor-associated protein (RAP). This co-expression facilitated the secretion of the extracellular region of the VLDL receptor into the culture medium and the secreted receptor bound 125I-beta-VLDL. The VLDL receptor remaining intracellular that was co-expressed with RAP also showed binding capacity to 125I-beta-VLDL, implying that the existence of RAP prevented receptor-protein aggregation or improved protein-folding status of the truncated VLDL receptor. On the other hand, expression of the extracellular region of the LDL receptor was not facilitated by RAP co-expression. Thus RAP plays an essential role in maintenance of the active conformation and secretion of the extracellular region of the VLDL receptor.

Animals↗
PubMed1980

Characterization of a specific, high affinity binding macromolecule for 1 alpha, 25-dihydroxyvitamin D3 in cultured chick kidney cells.

Cytosol prepared from vitamin D3-deficient kidney cells in culture contains a 3.7 S protein that specifically binds 1,25-dihydroxyvitamin D3 with high affinity and low capacity. Whole kidney homogenate cytosol preparations are shown to possess two 1,25-dihydroxyvitamin D3 binding macromolecules. One of the binding proteins sediments at 3.5 to 3.7 S while the second sediments at 6.0 S. The 6.0 S component has a greater affinity for 25-dihydroxyvitamin D3 than for 1,25-dihydroxyvitamin D3. Cultured cell cytosol was found to have little 6.0 S 25-hydroxyvitamin D3 binding protein. Scatchard analysis of the cultured cell cytosol reveals an equilibrium binding constant (KD) of 5.6 x 10 (-11) with 57 fmol of sites/mg of protein. The receptor-like protein has a Mr = 72,000 and as with other steroid receptors it aggregates in the presence of low potassium concentrations. Analog competition for receptor binding reveals the following potency order: 1,25-dihydroxyvitamin D3 > 25-hydroxyvitamin D3 > 1 alpha-hydroxyvitamin D3 > 24(R),25-dihydroxyvitamin D3; the receptor had no detectable affinity for vitamin D3. The kidney cells respond to 1,25-dihydroxyvitamin D3 by diminishing 25-hydroxyvitamin D3 1 alpha-hydroxylation and increasing 24R-hydroxylation. Cultured cells provide a preparation of cytosol which has allowed extensive characterization of the renal 1,25-dihydroxyvitamin D3 receptor and should facilitate investigations into the role this receptor plays in renal control of vitamin D3 metabolism.

Animals↗
PubMed1983

Down-regulation of opiate receptors in serum-free cultures of aggregating fetal brain cells.

Brain cells from rat embryos that were cultured in serum-free medium form aggregates which possess stereospecific binding of radioactive opiates. The specificity of these opiate receptors and their regulation by opiate alkaloids and enkephalin was studied. D-ala2, D-leu5-enkephalin (DADL) induced down-regulation of opiate receptors in aggregates prepared from the forebrain but had no effect on hindbrain aggregates, whereas the potent alkaloid etorphine induced down-regulation of the receptors in both tissues. Interestingly, morphine did not induce down-regulation in both tissues. The significance of these findings and their relationship to the control of different types of opiate receptors are discussed.

Animals↗
PubMed1983

Crosslinking of the receptors for immunoglobulin E depolarizes the plasma membrane of rat basophilic leukemia cells.

Aggregation of the receptor for IgE on mast cells, basophils, and a tumor analog, rat basophilic leukemia (RBL) cells, induces a calcium-dependent degranulation of the cells. We have measured the membrane potential (delta psi) of RBL cells during this reaction by using the tetraphenylphosphonium ion (Ph4P+) equilibration technique. We observed a 20-45% reduction in ionophore-sensitive Ph4P+ accumulation. The phenomenon persisted under conditions expected to collapse the mitochondrial membrane potential, consistent with the effect being due to a change in delta psi of the plasma membrane. We estimated that the change reflects a depolarization of 20 mV (from -90 to -70 mV, interior negative). Whereas degranulation fails to occur in the absence of external Ca2+, this was not true of the depolarization, indicating that the latter was not a consequence of secretion. When aggregation of the receptor is induced by reaction of the cell-bound IgE with a multivalent antigen, the secretory reaction can be halted by adding a univalent hapten. In this case, complete repolarization occurs. Equivalent depolarization was observed in the absence of Na+ but was diminished when both Ca2+ and Na+ were absent. Together, the data suggest that aggregation of the receptor opens ion channels and that the latter disappear promptly when the receptors are disaggregated. It is plausible that formation of these channels leads to the entry of Ca2+ and is an early and critical consequence of the aggregation of the receptors, thereby leading to degranulation.

Animals↗
PubMed1991

Polylysine increases the number of insulin binding sites in soluble insulin receptor preparations.

The effects of cationic polyamino acids on insulin binding to soluble insulin receptor preparations were studied. Incubation of partially or fully purified receptor preparations with polylysine (pLys) increased by several-fold the amount of [125I]insulin that remained associated with the receptor, as determined both by precipitation of receptor-insulin complexes by polyethylene glycol or by separation of the complexes from the free hormone by gel filtration. This elevation in the amount of bound insulin resulted from increased number of insulin binding sites, and could not be attributed to an increased affinity of the receptors to insulin. In fact, pLys reduced 2-3-fold the affinity of insulin binding to its receptor as determined by equilibrium binding studies, and by monitoring the rate of exchange of bound [125I]insulin with unlabeled hormone. pLys induced specific interactions between insulin and its native receptor since other basic compounds such as histone, spermidine, polymixin B, compound 48/80, lysine, and arginine failed to reproduce its effects. pLys did not interact with the free ligand, nor did it promote interactions between insulin and denatured receptor forms. Furthermore, pLys did not induce binding of insulin to other proteins present in the partially purified receptor preparations. The effects of pLys were time and dose-dependent and were proportional to the pLys chain length. The longer the chain, the greater was the effect. Enhanced insulin binding and receptor beta-subunit autophosphorylation (in the presence of insulin) exhibited a similar dependency on the chain length of pLys. pLys effects on insulin binding were associated with formation of large protein aggregates that remained trapped at the top of Sephacryl S-300 columns. These aggregates contained substantial amounts of receptor-insulin complexes. Our results suggest that pLys induces formation of receptor clusters that create de novo insulin binding sites among adjacent receptor tetramers. Alternatively, formation of receptor aggregates might facilitate insulin binding to a soluble receptor subfraction that otherwise fails to bind the hormone.

Animals↗
PubMed1992

Expression of early developmental genes in Dictyostelium discoideum is initiated during exponential growth by an autocrine-dependent mechanism.

Throughout growth, Dictyostelium cells continuously produce an autocrine factor, PSF, that accumulates in proportion to cell density. Production of PSF declines rapidly when cells are shifted to starvation conditions, and the properties of PSF are distinct from those of regulatory factors produced by starving cells. During late exponential growth, PSF induces expression of several early developmental genes, including those for proteins important in cAMP signaling and cell aggregation. Examples are the aggregation stage cAMP receptor (cAR1), the aggregation-specific form of cyclic nucleotide phosphodiesterase, and gp24 (contact sites B). Through PSF, growing cells detect environmental conditions (cell number high, food approaching depletion) that are appropriate for production of the gene products needed to initiate aggregation and development.

Animals↗
PubMed2005

ATP potentiates the formation of AChR aggregate in the co-culture of NG108-15 cells with C2C12 myotubes.

The role of adenosine 5'-triphosphate (ATP) and P2Y(1) nucleotide receptor in potentiating agrin-induced acetylcholine receptor (AChR) aggregation is being demonstrated in a co-culture system of NG108-15 cell, a mouse neuroblastoma X rat glioma hybrid cell line that resembles spinal motor neuron, with C2C12 myotube. In the co-cultures, antagonized P2Y(1) receptors showed a reduction in NG108-15 cell-induced AChR aggregation. Parallel to this observation, cultured NG108-15 cell secreted ATP into the conditioned medium in a time-dependent manner. Enhancement of ATP release from the cultured NG108-15 cells by overexpression of active mutants of small GTPases increased the aggregation of AChRs in co-culturing with C2C12 myotubes. In addition, ecto-nucleotidase was revealed in the co-culture, which rapidly degraded the applied ATP. These results support the notion that ATP has a role in directing the formation of post-synaptic apparatus in vertebrate neuromuscular junctions.

Adenosine Triphosphate↗
PubMed2003

Regulation of acetylcholine receptor clustering by the tumor suppressor APC.

At the developing neuromuscular junction, motor neuron-derived agrin triggers the differentiation of postsynaptic membrane into a highly specialized structure, where the nicotinic acetylcholine receptors (AChRs) are aggregated into high-density clusters. Agrin acts by activating the muscle-specific kinase MuSK and inducing coaggregation of the 43-kDa protein rapsyn with AChRs on muscle cell membrane. The signaling mechanism downstream of MuSK is poorly defined. We report here that the mouse tumor suppressor protein adenomatous polyposis coli (APC) has a role in AChR clustering and that the Wnt/beta-catenin pathway may crosstalk with agrin signaling cascade during synapse formation.

Adenomatous Polyposis Coli Protein↗
PubMed2001

Induction of multiple signaling loops by MuSK during neuromuscular synapse formation.

At the neuromuscular junction, two motor neuron-derived signals have been implicated in the regulation of synaptogenesis. Neuregulin-1 is thought to induce transcription of acetylcholine receptor (AChR) genes in subsynaptic muscle nuclei by activating ErbB receptors. Neural agrin aggregates AChRs by activating the receptor tyrosine kinase MuSK. Here, we show that these two signals act sequentially. Agrin, by activating MuSK, induces the synthesis and aggregation of both MuSK and ErbB receptors. ErbB acts downstream of MuSK in synapse formation. In this way, MuSK activation leads to the establishment of a neuregulin-1-dependent signaling complex that maintains MuSK, ErbB, and AChR expression at the synapse of electrically active muscle fibers.

Agrin↗
PubMed2001

Differential involvement of the P2Y1 and P2YT receptors in the morphological changes of platelet aggregation.

The relative contributions of the P2Y1 and P2YT receptors to the morphological changes induced in platelets by ADP or ADP-releasing agonists were assessed using two P2 antagonists, A2P5P and AR-C67085, selective for P2Y1 and P2YT, respectively. The P2Y1 receptor was found to be involved in i) the centralization of secretory granules elicited by ADP, ii) the formation of filopodia induced by released ADP in weakly activated platelets and iii) actin polymerization and the cytoskeletal translocation of cdc42, rac1 and rhoA, in an integrin alphaIIbbeta3 dependent manner, in ADP-stimulated platelets. In contrast, the P2YT receptor was shown i) to be essential for the formation of stable macroaggregates, ii) to enhance actin polymerization and the cytoskeletal translocation of small GTPases, probably through amplification of platelet aggregation, and iii) not to be involved in the early steps of platelet activation since its blockade did not affect the cytoskeletal translocation of rhoA.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1979

Aggregation-induced stability of dexamethasone receptors in rat kidney.

The stability of the dexamethasone-receptor complex of rat kidney cytosol was studied using homogenizing media of varying pH and composition. It was found that the complex is less stable with buffers usually employed for the study of steroid receptors such as Tris, EDTA etc., whereas the stability increases considerably with a solution composed of monothioglycerol 12 mmol/l and glycerol 5% in distilled water. Sepharose 4-B column chromatography revealed that the increased stability was associated with a larger form (probably an aggregate) of the receptor-steroid complex.

Animals↗