Showing papers on "Receptor published in 1983"

Release of Ca2+ from a nonmitochondrial intracellular store in pancreatic acinar cells by inositol-1,4,5-trisphosphate.

Abstract: Activation of receptors for a wide variety of hormones and neurotransmitters leads to an increase in the intracellular level of calcium. Much of this calcium is released from intracellular stores but the link between surface receptors and this internal calcium reservoir is unknown. Hydrolysis of the phosphoinositides, which is another characteristic feature of these receptors, has been implicated in calcium mobilization. The primary lipid substrates for the receptor mechanism seem to be two polyphosphoinositides, phosphatidylinositol 4-phosphate (PtdIns4P) and phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2), which are rapidly hydrolysed following receptor activation in various cells and tissues. The action of phospholipase C on these polyphosphoinositides results in the rapid formation of the water-soluble products inositol 1,4-bisphosphate (Ins1,4P2) and inositol 1,4,5-trisphosphate (Ins1,4,5P3). In the insect salivary gland, where changes in Ins1,4P2 and Ins1,4,5P2 have been studied at early time periods, increases in these inositol phosphates are sufficiently rapid to suggest that they might mobilize internal calcium. We report here that micromolar concentrations of Ins1,4,5P3 release Ca2+ from a nonmitochondrial intracellular Ca2+ store in pancreatic acinar cells. Our results strongly suggest that this is the same Ca2+ store that is released by acetylcholine.

Phorbol diester receptor copurifies with protein kinase C

Abstract: The phorbol diester receptor present in the particulate fraction of rat brain was solubilized by divalent ion chelation in the absence of detergents. The soluble receptor was partially purified by (NH4)2SO4 precipitation, DEAE-cellulose, and gel filtration chromatography. The purified receptor required exogenous phospholipid for activity and displayed a Kd of 7 nM for [3H]phorbol 12, 13-dibutyrate. Biologically active phorbol analogs inhibited binding, whereas inactive analogs did not. The Ca2+-dependent, phospholipid-sensitive protein kinase C copurified with the phorbol receptor. Purified protein kinase C was activated directly by phorbol 12-myristate 13-acetate in the presence of phospholipid.

1,25-dihydroxyvitamin D3 receptors in human leukocytes

Abstract: A 1,25-dihydroxyvitamin D3 receptor macromolecule was detected in peripheral mononuclear leukocytes from normal humans. This macromolecule was found to be present in monocytes but absent from normal resting peripheral B and T lymphocytes. However, it was present in established lines of malignant B, T, and non-B, non-T human lymphocytes, as well as in T and B lymphocytes obtained from normal humans and activated in vitro.

Growth stimulation of A431 cells by epidermal growth factor: identification of high-affinity receptors for epidermal growth factor by an anti-receptor monoclonal antibody.

Abstract: Epidermal growth factor (EGF) at 3 nM maximally inhibits the proliferation of A431 epidermoid carcinoma cells. We show that at lower concentrations, in the range of 3-100 pM, EGF has a mitogenic effect on A431 cells. In the presence of 100 nM anti-EGF-receptor monoclonal IgG (designated 528), which inhibits A431 cell proliferation and blocks greater than 95% of EGF binding, EGF becomes mitogenic for A431 cells at concentrations up to 3 nM. These results suggest that a minor population of high-affinity EGF receptors may be involved in stimulation of A431 cell proliferation. Saturation binding assays with 125I-labeled EGF indicate that approximately equal to 0.1-0.2% of receptors for EGF are high-affinity receptors that bind EGF with an estimated Kd of 7 X 10(-11) M. This affinity is nearly 2 orders of magnitude higher than that of the remaining EGF receptors. Although A431 cell proliferation is maximally inhibited by nonsaturating amounts of EGF (3 nM), maximal inhibition by 528 IgG (approximately equal to 70% of maximal inhibition by EGF) requires saturating concentrations of antibody (approximately equal to 15 nM). Unlike EGF, rapid down-regulation is not observed with 528 IgG. These results indicate different mechanisms of growth inhibition of A431 cells by EGF and 528 IgG.

Pharmacology of opioids.

Abstract: The concept of multiple opioid receptors reconciles a large body of clinical and pharmacological data. Recent studies have shown that there are also multiple opioid binding sites. It would appear that there is considerable variability between species in both the specificity and selectivity of opioid receptors. This issue has not been explored systematically regarding opioid binding sites. Better characterization of the pharmacological profiles and receptor binding specificity for different species may help resolve some of the apparent disparities. The number of putative receptors now number nearly a dozen. Already subspecies of mu, kappa, and sigma receptors are being postulated. Both pharmacological and neurochemical methods may reveal even more. Some of the newer kappa agonists differ in their pharmacology from the prototypic kappa agonist ethylketazocine.

Imaging dopamine receptors in the human brain by positron tomography

Abstract: Neurotransmitter receptors may be involved in a number of neuropsychiatric disease states. The ligand 3-N-[11C]methylspiperone, which preferentially binds to dopamine receptors in vivo, was used to image the receptors by positron emission tomography scanning in baboons and in humans. This technique holds promise for noninvasive clinical studies of dopamine receptors in humans.

Identification of the C3bi receptor of human monocytes and macrophages by using monoclonal antibodies.

Abstract: We have obtained four monoclonal antibodies, IB4, OKM1, OKM9, and OKM10, all directed against the C3bi receptor of human monocytes and macrophages (M phi). Two criteria were used to determine the specificity of these antibodies. First, culture surfaces coated with the antireceptor antibodies caused specific down modulation of C3bi receptor activity on M phi adherent to these substrates. Second, receptor protein purified by using IB4 or OKM1 retained the ability to bind selectively to C3bi-coated erythrocytes. Each of the antibodies recognizes a distinct epitope on the C3bi receptor; they do not compete with one another for binding to monocytes. Further, when immobilized on a solid support, each of the antibodies binds a molecule from M phi lysates that can simultaneously bind one of the other monoclonal anti-C3bi receptor antibodies. OKM10 binds and masks the ligand-binding site of the C3bi receptor, while IB4, OKM1, and OKM9 bind to sites remote from the C3bi binding site. All four antibodies immunoprecipitated polypeptides of Mr 185,000 and 105,000 from 125I-surface-labeled M phi. IB4 also precipitates polypeptides of Mr 185,000, 153,000, and 105,000. We conclude that the C3bi receptor of human M phi is a complex composed of two polypeptides, Mr 185,000 and 105,000. We have identified monoclonal antibodies reacting with four distinct antigenic determinants of this complex. The determinant recognized by antibody OKM10 is at or near the ligand-binding site of the receptor. The determinant recognized by antibody IB4 is shared by at least two other leukocyte surface proteins.

Transient expression of interleukin 2 receptors. Consequences for T cell growth.

Abstract: T lymphocyte mitosis results from the interaction of interleukin 2 (IL-2) with specific receptors that appear only after appropriate immune stimulation. To assess the potential role of IL-2 receptor levels in determining the rate and magnitude of T cell proliferation, the expression of IL-2 receptors by lectin-stimulated human peripheral blood T cells was examined and correlated with T cell growth. Using biosynthetically radiolabeled IL-2 and anti-Tac, a monoclonal antibody that blocks IL-2 receptor binding, IL-2 receptors were found to accumulate slowly and asynchronously among lectin-stimulated T cells and to precede the onset of DNA synthesis. Moreover, a critical threshold of IL-2 receptor density appeared to be required before the commitment to cell cycle progression, as analyzed quantitatively by tritiated thymidine incorporation and flow cytometric analysis of cellular DNA content. Once maximal IL-2 receptor expression occurred, continued proliferation was IL-2 concentration dependent as assessed using homogenous immunoaffinity-purified IL-2. Upon removal of the activating lectin, IL-2 receptor levels progressively declined, and, in parallel, the rate of proliferation diminished. The decay of IL-2 receptors could not be attributed to IL-2-mediated down-regulation. Instead, renewed IL-2 receptor expression was dependent upon the reintroduction of the initial activating signal. Repetitive exposure to lectin resulted in a more rapid reexpression of maximal IL-2 receptor levels, which was then followed by an accelerated resumption of proliferation. Thus, the extent of T cell proliferation after immune stimulation depends upon the interplay of the IL-2 concentration available and the density of IL-2 receptors expressed, both of which are ultimately determined by antigen/lectin stimulation. The awareness of the transience and the antigen/lectin dependence of IL-2 receptor expression, together with the capacity to monitor T cell cultures for IL-2 receptor levels, should facilitate the initiation and maintenance of cloned, antigen-specific T cells in long-term culture. In addition, these findings suggest that, in vivo, the rapidity of acquisition of maximum IL-2 receptor levels by activated T cells and the duration of IL-2 receptor expression may well direct the magnitude of T cell clonal expansion and resultant immune responses.

Specific high-affinity receptors for 1,25-dihydroxyvitamin D3 in human peripheral blood mononuclear cells: presence in monocytes and induction in T lymphocytes following activation.

Abstract: Human peripheral blood monocytes have high affinity binding sites for 1,25-(OH)2D3 (Kd 0.14 nM, sedimentation coefficient 3.7S). Resting human peripheral blood T lymphocytes, however, do not have a demonstrable 1,25-(OH)2D3 receptor. After activation with phytohemagglutinin the T cells exhibit the receptor within 24 h, and this expression is blocked by cycloheximide. The receptor in activated T lymphocytes has a sedimentation coefficient of 3.7S and a high affinity (Kd 0.10 nM) for the ligand.

Characterization of a Human Ovarian Carcinoma Cell Line (NIH:OVCAR-3) with Androgen and Estrogen Receptors

Abstract: A cell line, NIH:OVCAR-3, has been established from the malignant ascites of a patient with progressive adenocarcinoma of the ovary after combination chemotherapy with cyclophosphamide, Adriamycin, and cisplatin. OVCAR-3 grows as a cobblestone-like monolayer with foci of multilayering, is tumorigenic in athymic mice, clones in agarose, and has an abnormal karyotype which includes a homogeneous staining region and a double minute chromosome. The cultured cells and xenografts contain cytoplasmic androgen- and estrogen-binding macromolecules with the specificity of the respective steroid hormone receptors. These components have sedimentation coefficients of 7 to 9S in low-salt sucrose-density gradients, have dissociation constants of 250 and 9.6 pM, and are present at concentrations of 30 and 28 fmol/mg cytosol protein characteristic of androgen and estrogen receptors, respectively. OVCAR-3 is resistant in vitro to clinically relevant concentrations of Adriamycin (5 X 10(-8) M), melphalan (5 X 10(-6) M), and cisplatin (5 X 10(-7) M) with survival compared to untreated controls of 43, 45, and 77%, respectively. Furthermore, there are multiple histological similarities between the patient's original tumor, the cell line, and the transplantable tumor. These data indicate that OVCAR-3 may be of use for investigations as to the significance of androgens and estrogens and the mechanisms of cytotoxic drug resistance in ovarian cancer.

Transferrin receptors in human tissues: their distribution and possible clinical relevance.

Abstract: The distribution of transferrin receptors (TR) has been studied in a range of normal and malignant tissues using four monoclonal antibodies, BK19.9, B3/25, T56/14 and T58/1. In normal tissues TR was found in a limited number of sites, notably basal epidermis, the endocrine pancreas, hepatocytes, Kupffer cells, testis and pituitary. This restricted pattern of distribution may be relevant to the characteristic pattern of iron deposition in primary haemachromatosis. In contrast to this limited pattern of expression in normal tissue, the receptor was widely distributed in carcinomas, sarcomas and in samples from cases of Hodgkin's disease. This malignancy-associated expression of the receptor may play a role in the anaemia of advanced malignancy by competing with the bone marrow for serum iron.

Anatomical distributions of four pharmacologically distinct 3H-L-glutamate binding sites

Abstract: Glutamate is thought to serve as a major excitatory neurotrans-mitter throughout the central nervous system (CNS)1,2; electrophysiological studies indicate that its action is mediated by multiple receptors. Four receptors have been characterized by their selective sensitivity to N-methyl-D-aspartate (NMDA), kainic acid (KA), quisqualic acid (QA) and 2-amino-4-phosphonobutyric acid (APB)1,3–5. Electrophysiological evidence indicates that these receptors are all present in the rat hippocampus and that the anatomically discrete synaptic fields within the hippocampus exhibit differential sensitivity to the selective excitatory amino acid agents3,6,7. Thus, we have used the hippocampus as a model system to investigate possible subpopulations of 3H-L-glutamate binding sites. By using quantitative autoradiography, the pharmacological specificity of 3H-L-glutamate binding in discrete terminal fields was determined. We report here that there are at least four distinct classes of 3H-L-glutamate binding sites which differ in their anatomical distribution, pharmacological profile and regulation by ions. Two of these sites seem to correspond to the KA and NMDA receptor classes, and a third site may represent the QA receptor. The fourth binding site does not conform to present receptor classifications. None of these binding sites corresponds to the major glutamate binding site observed in biochemical studies8–12.

Biological effects in vitro of monoclonal antibodies to human epidermal growth factor receptors.

Abstract: Four mouse hybridomas secreting monoclonal immunoglobulin G (IgG) antibodies to epidermal growth factor (EGF) receptors of A431 cells were obtained independently from four fusion experiments. Three of the antibodies, 528 IgG, 225 IgG, and 579 IgG, inhibited the binding of [125I]EGF to A431 cells by at least 95%, and they competed with each other for binding to A431 cells. These antibodies bound to A431 cells, HeLa-S cells and human foreskin fibroblasts with dissociation constants in the range of Kd = 0.6 X 10(-9) to 2.5 X 10(-9) M. The fourth monoclonal antibody, 455 IgG, bound to A431 cells with lower affinity (Kd = 2.0 X 10(-8) M), and it had no effect on the binding of either EGF or the other antibodies to A431 cells. All four antibodies immunoprecipitated EGF receptors from Triton X-100 extracts of A431 membranes, but they were unable to bind to three rodent cell lines. In biological assays, none of the antibodies was able to mimic EGF. The antibodies which inhibited the binding of EGF blocked EGF-enhanced phosphorylation of A431 membrane proteins and inhibited EGF induced human fibroblast proliferation. These three antagonistic antibodies also partially reversed the inhibition of A431 growth by EGF. In contrast, 455 IgG had no effect on the early or delayed cellular responses to EGF.

Receptors for C3b and C3bi promote phagocytosis but not the release of toxic oxygen from human phagocytes

Abstract: We have measured the release of H2O2 from granulocytes, monocytes, and macrophages during spreading on ligand-coated culture surfaces. While IgG-coated surfaces stimulate vigorous release of H2O2, neither C3b- nor C3bi-coated surfaces promoted appreciable release of H2O2 despite full ligation of C3b and C3bi receptors. We also measured release of H2O2 from cultured monocytes spreading on surfaces coated with both fibronectin and C3. Under such circumstances, the C3 receptors elicit a strong phagocytic response, but no H2O2 release was recorded. We conclude that the C3b and C3bi receptors of monocytes and granulocytes do not signal the generation of toxic oxygen intermediates from these cells.

Hormone-Induced Morphogenesis and Growth: Role of Mesenchymal–Epithelial Interactions

Abstract: Publisher Summary This chapter explains the role of mesenchymal–epithelial interactions in hormone induced morphogenesis and growth. The mechanism of steroid hormone action is thought to involve specific high-affinity receptor proteins. The hormone enters the cell, binds to the cytoplasmic receptor, which after activation translocates to the nucleus. The hormone–receptor complex in turn binds to nuclear acceptor sites on the chromatin. This activates a variety of metabolic processes, the most important being the stimulation of messenger RNA (mRNA) synthesis and the ultimate production of new proteins. The first indication that androgens can elicit their effects upon epithelial morphogenesis via the mediation of mesenchymal cells comes from studies in which urogenital epithelia from the embryonic seminal vesicle or urogenital sinus are grown in association with either urogenital mesenchyme or with non-target integumental mesenchyme. Urogenital mesenchyme induces specific epithelial morphogenesis, growth, and function within the genital tract and that the hormonal sensitivity of these morphogenetic processes resides in the mesenchyme that invariably contains nuclear hormone receptors. As morphogenetic processes are cyclic in adult genital tracts of many species, developmental properties are expressed in adulthood and, for this reason, appear to play a regulatory role in abnormal epithelial differentiation including carcinogenesis.

Transferrin receptor induction in mitogen-stimulated human T lymphocytes is required for DNA synthesis and cell division and is regulated by interleukin 2.

Abstract: Transferrin is required by many cells for growth. Mitogen-induced T lymphocyte proliferation is dependent on the presence of both interleukin 2 (IL-2; T-cell growth factor) and transferrin, even though resting lymphocytes do not have receptors for either. Exposure to mitogen (phytohemagglutinin) alone is sufficient to induce transient appearance of IL-2 receptors on lymphocytes. Using monoclonal antibodies to the IL-2 receptor and to the transferrin receptor, we examined those signals required for transferrin receptor induction during T lymphocyte proliferation. Our study has revealed that (i) monocytes, or a monocyte substitute such as the phorbol ester tetradecanoylphorbol 13-acetate, are required for transferrin receptor expression after mitogen exposure; (ii) the presence of IL-2 receptors is necessary for transferrin receptor induction; (iii) antibody to the IL-2 receptor inhibits thymidine incorporation (DNA synthesis) in lymphocytes, but only if administered before transferrin receptors have appeared; and (iv) antitransferrin receptor antibody inhibits DNA synthesis but has minimal effect on IL-2 receptor expression. Thus, IL-2 receptor induction leads to transferrin receptor induction and subsequent initiation of DNA synthesis. These data indicate that IL-2 stimulates T lymphocyte proliferation, at least in part, by induction of transferrin receptors on these cells.

Subclasses of adenosine receptors in the central nervous system: interaction with caffeine and related methylxanthines.

Abstract: 1. The potencies of caffeine and related methylxanthines as adenosine antagonists were assessed with respect to three apparent subtypes of adenosine receptors in rat brain preparations: (i) the A1-adenosine receptor which binds with a very high affinity the ligand [3H]cyclohexyladenosine (KD, 1 nM) in rat brain membranes; (ii) a ubiquitous low-affinity A2-adenosine receptor which activates cyclic AMP accumulation in rat brain slices—this A2-adenosine system exhibits an EC50 for 2-chloroadenosine of about 20µM; and (iii) a relatively high-affinity A2-adenosine receptor which activates adenylate cyclase in rat striatal membranes—this A2-adenosine system exhibits an EC50 for 2-chloroadenosine of about 0.5µM and is present in striatal but not in cerebral cortical membranes. 2. The rank order of potency for methylxanthines versus binding of 1 nM [3H]cyclohexyladenosine in membranes from eight rat brain regions is theophylline (IC50, 20–30µM) > paraxanthine (IC50, 40–65µM) > caffeine (IC50, 90–110µM) > theobromine (IC50, 210–280µM). There thus appears to be little difference in A1-receptors in different brain regions in terms of interaction with these methylxanthines. 1-Methylxanthine is more potent than caffeine in rat cerebral cortical membranes, while 3-methylxanthine and 7-methylxanthine are less potent than caffeine. 3. The rank order of potency for methylxanthines versus activation of cyclic AMP accumulation by 50µM 2-chloroadenosine in rat striatal slices is theophylline (IC50, 60µM) > paraxanthine (IC50, 90µM) > caffeine (IC50, 120µM) » theobromine (IC50, > 1000µM). Similar potencies pertain in cerebral cortical slices. 4. The rank order of potency of methylxanthines versus activation of adenylate cyclase by 1µM 2-chloroadenosine in rat striatal membranes is theophylline (IC50, 20µM) > paraxanthine (IC50, 40µM) > caffeine (IC50, 80µM) » theobromine (IC50, > 1000µM). 5. Caffeine and other methylxanthines, thus, antagonize effectively both A1- and A2-adenosine receptors in brain perparations. Theobromine appears less effective versus A2-receptors than versus A1-receptors. Caffeine exhibits aKi value of about 50µM at the very high-affinity A1-binding sites, aKi value of about 30µM at the low-affinity A2-adenosine site in brain slices, and aKi value of about 27µM at the high-affinity A2-adenosine site in striatal membranes. The functional significance of antagonism of such adenosine receptors by caffeinein situ will depend both on the local levels of adenosine and on the affinity for adenosine for the receptor, since antagonism by xanthines is competitive in nature. In addition, the functional significance of xanthine action will depend on the degree of inhibition of adenosine input which is required to alter the output signal. For a stimulatory input to adenylate cyclase via an A2-adenosine receptor, profound antagonism by methylxanthines is probably required to alter the cyclic AMP-mediated output signal, while for inhibitory input to adenylate cyclase via an A1-adenosine receptor, presumably a lesser degree of antagonism by methylxanthines may be required to alter the cyclic AMP-mediated output signal.

Recombinant immune interferon increases immunoglobulin G Fc receptors on cultured human mononuclear phagocytes.

Abstract: Although recent studies suggest that interferons can increase the number of IgG Fc receptor (FcR gamma) sites on mouse macrophages, direct assessment of similar effects on human mononuclear phagocytes is lacking. We therefore measured the specific binding of 125I- and fluorescein-labeled IgG1 to human monocytes and leukemic cell lines after culture in vitro with highly purified human interferons. We report that natural and recombinant human gamma-interferon causes a dramatic (nearly 10-fold) increase in the number of FcR gamma on normal human monocytes and on the human cell lines HL-60 and U-937. Alpha and beta-interferons cause a modest but significant increase in these receptors. This report demonstrates that gamma-interferon acts directly on human mononuclear phagocytes to increase FcR gamma sites, it identifies a qualitative difference in the physiologic actions of human type I and type II interferons, and it suggests that HL-60 and U-937 cells will be important models for further study of the molecular mechanisms of interferon action. The results reported here could also be the basis for a bioassay to assess the pharmacokinetics and variability of gamma-interferon action on monocytes of individual patients during treatment in vitro and in vivo.