Showing papers by "Robert J. Lefkowitz published in 1983"

Catecholamine-induced desensitization of turkey erythrocyte adenylate cyclase is associated with phosphorylation of the beta-adrenergic receptor

Abstract: Preincubation of turkey erythrocytes with catecholamines desensitizes the beta-adrenergic receptor-adenylate cyclase complex in the plasma membranes of these cells. Photoaffinity labeling of the beta-adrenergic receptors with 125I-labeled p-azidobenzylcarazolol (125I-pABC) and subsequent analysis by NaDodSO4/polyacrylamide gel electrophoresis demonstrates an altered mobility of receptor peptides from desensitized cells compared to controls [Stadel, J.M., Nambi, P., Lavin, T.N., Heald, S.L., Caron, M.G. & Lefkowitz, R.J. (1982) J. Biol. Chem. 257, 9242-9245]. The time course of alteration in beta-adrenergic receptor mobility correlates with that for desensitization of isoproterenol-stimulated adenylate cyclase activity. The altered mobility of the receptor peptides from desensitized cells is also observed if the receptors are first purified and then photoaffinity labeled with 125I-pABC. The cyclic nucleotide analog 8-bromoadenosine 3',5'-cyclic monophosphate partially mimics catecholamines in promoting desensitization of the adenylate cyclase and modification of the receptor. Phosphorylation of the beta-adrenergic receptor in intact turkey erythrocytes was assessed by preincubating the cells with [32P]orthophosphate, desensitizing them with catecholamine, purifying the receptors, and then subjecting them to NaDodSO4/polyacrylamide gel electrophoresis. Desensitization is associated with a 2- to 3-fold increase in 32P incorporation into the receptor, which also demonstrates the characteristic alterations in mobility. These effects are blocked by the beta-adrenergic antagonist propranolol. Purified turkey erythrocyte beta-adrenergic receptors could be phosphorylated by incubation with [gamma-32P]ATP and the catalytic subunit of cAMP-dependent protein kinase. The mobility of the phosphorylated receptor peptides on NaDodSO4/polyacrylamide gel electrophoresis appears to correspond to that of the desensitized receptors. These data show that catecholamine-induced desensitization of adenylate cyclase in turkey erythrocytes correlates with a stable modification of the beta-adrenergic receptor and is associated with agonist-promoted phosphorylation of beta-receptor peptides.

Guanine nucleotides modulate the binding affinity of the oligopeptide chemoattractant receptor on human polymorphonuclear leukocytes.

Abstract: The oligopeptide chemoattractant receptor on human polymorphonuclear leukocyte (PMN) membranes exists in two affinity states. Since guanine nucleotides regulate the binding affinity and transductional activity of several other types of receptors, we examined the effect of nucleotides on the binding of N-formyl-methionyl peptides to their receptors on human PMN membranes. The addition of guanylylimidodiphosphate (0.1 mM), a nonhydrolyzable derivative of guanosine triphosphate (GTP), to PMN membrane preparations reduced the fraction of high-affinity receptors detected in equilibrium binding studies from 21.3 +/- 0.13 to 11.8 +/- 0.05% (P less than 0.03), without altering the binding affinities. Since the total number of receptors remained unchanged, the effect of guanylylimidodiphosphate was to convert a portion of the receptors from the high-affinity state to the low-affinity state. At the maximal concentration of guanine nucleotide tested, approximately 50% of the high-affinity sites were converted to low-affinity sites. The findings obtained by equilibrium binding were supported by kinetic studies since the dissociation of the radiolabeled oligopeptide chemoattractant N-formyl-methionyl-leucyl-[3H]phenylalanine from PMN membranes was accelerated in the presence of guanine nucleotide. The effect of guanine nucleotides was reversed upon washing, indicating that affinity conversion is bidirectional. The guanine nucleotide effects were greatest with nonhydrolyzable derivatives of GTP followed by GTP then guanosine diphosphate. Neither guanosine monophosphate nor any adenine nucleotide tested had an effect on receptor binding. These data suggest a role for guanine nucleotides in the regulation of stimulus-receptor coupling of chemoattractant receptors on human PMN.

Pure β -adrenergic receptor: the single polypeptide confers catecholamine responsiveness to adenylate cyclase

Abstract: The β-adrenergic receptor binding subunits from frog erythrocytes, hamster lung and guinea pig lung have been purified to apparent homogeneity and in all cases reside on a single polypeptide. Insertion of the pure receptors into phospholipid vesicles and subsequent fusion of these vesicles with a receptor-deficient cell conveys β-adrenergic responsiveness to the adenylate cyclase system of the acceptor cell. Such responsiveness is linearly dependent on the amount of receptor used in the fusion experiments and is independent of the receptor source. Moreover, this responsiveness displays appropriate β-adrenergic specificity. These results indicate that the β-adrenergic receptor polypeptide contains both the ligand binding site and the site responsible for mediating stimulation of adenylate cyclase activity, presumably via interaction with the guanine nucleotide regulatory protein.

In vitro desensitization of beta adrenergic receptors in human neutrophils. Attenuation by corticosteroids.

Abstract: The receptor alterations involved in catecholamine-induced desensitization of adenylate cyclase in human neutrophils have been investigated as has the ability of hydrocortisone to modify such alterations. Incubation of human neutrophils with isoproterenol for 3 h in vitro resulted in an 86% reduction in the ability of isoproterenol to stimulate cyclic AMP accumulation in the cells. Two types of receptor alterations were documented. There was a 40% reduction in the number of beta adrenergic receptors (42 vs. 25 fmol/mg protein, P < 0.005) present after desensitization as assessed by [3H]dihydroalprenolol ([3H]DHA) binding. In addition the receptors appeared to be relatively uncoupled from adenylate cyclase. This uncoupling was assessed by examining the ability of the agonist isoproterenol to stabilize a high-affinity form of the receptor, detected by computer modelling of competition curves for [3H]DHA binding. Desensitized receptors were characterized by rightward-shifted agonist competition curves. When hydrocortisone was added to the desensitizing incubations (combined treatment) there was a statistically significant attenuation in the desensitization process as assessed by the ability of isoproterenol to increase cyclic AMP levels in the cells. Although combined treatment did not prevent the decline in receptor number, it did attenuate the uncoupling of the receptors. Combined treatment resulted in competition curves intermediate between the control and the rightward-shifted desensitization curves. Prednisolone was similar to hydrocortisone in attenuating isoproterenol-induced uncoupling. Thus, steroids appeared to attenuate agonist-induced desensitization of the beta adrenergic receptor-adenylate cyclase system by dampening the ability of agonists to uncouple receptors without modifying their ability to promote down-regulation of beta adrenergic receptors.

Antibodies to the beta-adrenergic receptor: attenuation of catecholamine-sensitive adenylate cyclase and demonstration of postsynaptic receptor localization in brain.

Abstract: Antibodies to the beta 2-adrenergic receptor of frog erythrocytes have been raised in rabbits by immunization with purified receptor preparations. Binding of the antibodies to the receptors was demonstrated by immunoprecipitation and by the altered mobility of the antibody-bound receptors on steric-exclusion HPLC columns. As assessed by a radioimmunoassay developed with the antibody, beta 2-adrenergic receptors from several sources showed various degrees of immunological crossreactivity whereas several beta 1-adrenergic receptors did not crossreact. The antibody appeared to not bind at the ligand binding site of the receptor and did not perturb antagonist radioligand binding to the receptor. Nonetheless, the antibodies selectively attenuated catecholamine-stimulated adenylate cyclase. This suggests that the antibodies recognize and bind to domains of the receptor other than the binding site and that may be involved in coupling to other components of the adenylate cyclase system. Immunocytochemical techniques were used with the antibodies to delineate a postsynaptic localization of beta-adrenergic receptors in rat and frog brain. Thus, these anti-beta-adrenergic receptor antibodies provide a useful reagent for probing beta-adrenergic receptor structure, function, and localization.

Reconstitution of beta-adrenergic receptors in lipid vesicles: affinity chromatography-purified receptors confer catecholamine responsiveness on a heterologous adenylate cyclase system.

Abstract: The binding function of purified receptors can be assessed with radioligands, but the interaction of receptors with their biochemical effectors has not been amenable to direct study. Toward this end, procedures have been developed for directly demonstrating functionality of purified beta-adrenergic receptor preparations. Digitonin-solubilized beta-adrenergic receptors from frog erythrocytes or rat lung were purified approximately equal to 100- to 5,000-fold by affinity chromatography and inserted into a mixture of frog erythrocyte lipids and dimyristoyl phosphatidylcholine in the presence of octyl glucoside. Reconstitution of beta-adrenergic receptor binding was typically 25-50% and could also be effected with soybean phosphatidylcholine in the presence of octyl glucoside. The reconstituted beta-adrenergic receptors were then fused with Xenopus laevis erythrocytes, which contain prostaglandin E1-sensitive adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] but few beta-adrenergic receptors and little or no catecholamine-sensitive adenylate cyclase. Fusion of reconstituted receptor with Xenopus laevis erythrocytes establishes a substantial (2- to 10-fold) stimulation of the hybrid adenylate cyclase by the beta-agonist isoproterenol. The extent of stimulation depends on the amount of reconstituted beta-adrenergic receptor added, is blocked by propranolol, and is eliminated by boiling the beta-adrenergic receptor prior to reconstitution. The successful coupling of a purified receptor to a heterologous adenylate cyclase opens the way to the study of receptor structure---function relationships.

Plasma membrane receptors.

Abstract: Receptors are macromolecules in or on cells that mediate physiological responses upon binding specific li-gands. Over the past few years, important advances have been made in the understanding of the biology of receptors, both at a basic and at a clinical level. Receptors bind their ligands with remarkable selectiv-ity and with high affinity, permitting a given physiological response to be elicited with great specificity in the target tissue. The specific binding of agonists to receptors leads to the generation of signals that influence cell functions. The signal may be expressed as an altered rate of enzyme activity or ion transport, which then leads to the characteristic physiological responses within the cell. biological effects by virtue of their binding to cellular receptors. The more lipid soluble of these agents, such as steroid and thyroid hormones , are able to diffuse through the cell's plasma membrane and bind to intracellular receptors. Many of these agents, however, interact with receptors exposed on the external surface of the cell imbedded in the cellular plasma membrane. It is the purpose of this short essay to assess the current status of research on these membrane-bound receptors. It is only within the past fifteen years that the most proximal event in receptor function, that of ligand binding, has become amenable to direct experimental investigation. Such ligand-binding studies have facilitated rapid advances in the study of receptors. Several membrane receptors have been purified and an understanding of their function at a molecular level is now being realized. Ligand-binding studies have also shown that the numbers and properties of receptors are dynamically modulated by a variety of factors, including disease states and by chronic exposure to hormones and drugs (desensitization). This has provided an important approach to understanding the molecular basis for control of drug, neurotransmitter, and hormone sensitivity. Furthermore, the discovery of diverse receptors on circulating cells has provided a direct approach to the study of these receptors in disease states in man. Radioactive analogues of hormones and drugs may be used to label binding sites on cells and in cell-membrane preparations. In each instance it is necessary to demonstrate rigorously that the binding measured reflects association of the ligand with the relevant receptor. Many sites other than receptors may bind radioactive ligands saturably, with high affinity and with definable specificity. The most important hallmark of a receptor binding site identified in a radioligand binding assay is its …

Synthesis of iodine-125 labeled (+/-)-15-(4-azidobenzyl)carazolol: a potent beta-adrenergic photoaffinity probe.

Abstract: (+/-)-15-(4-Azidobenzyl)carazolol (2), a potent beta-adrenergic photoaffinity ligand developed in our laboratories, has been radioiodinated to theoretical specific activity (2175 Ci/mmol) and shown to label covalently beta-adrenergic receptor peptides in avian and amphibian erythrocyte membrane preparations. The radioiodinated analogues of the desired compound (2) were optimally prepared by two synthetic steps from (+/-)-15-(4-aminobenzyl)carazolol (8). The latter was iodinated with carrier-free Na125I and chloramine T to yield two major isotopomers (the monoiodinated derivatives 9 and 10), which were separated by thin-layer chromatography and converted via diazonium salt formation to their respective 4-azides, 12 and 6. These azides can be used interchangeably in ligand binding or photoaffinity labeling experiments. Compound 8 was obtained by catalytic reduction of the nitro derivative (7), which was arrived at by direct reaction of 1,1-dimethyl-2-(4-nitrophenyl)ethylamine (3) with 4-(2,3-epoxypropoxy)carbazole (5). Of the desired isomers, (+/-)-15-(4-azido-3-iodobenzyl)carazolol (6) could be synthesized from 1,1-dimethyl-2-(4-azido-3-iodophenyl)ethylamine (4) by direct reaction with 5. This and the preceding sequence of reactions were carried out by using nonradioactive materials, and separation and purification of products were accomplished by high-performance liquid chromatography. The compounds described have been shown to be potent beta-adrenergic antagonists by virtue of their ability to inhibit beta-adrenergic stimulation of adenylate cyclase or to compete for the binding of another beta-adrenergic ligand, [125I]cyanopindolol, to the beta-adrenergic receptors of frog erythrocytes. The photoactive azide derivatives of these compounds (6 and 12) have been shown to covalently incorporate into the beta-adrenergic receptor binding subunit of frog and turkey erythrocyte membrane preparations. Incorporation of the ligands into these polypeptides can be blocked specifically by both beta-adrenergic agonists and antagonists.

The beta-adrenergic receptor in heart failure.

Abstract: Although the role of the autonomic nervous system in the pathophysiology of heart failure has been studied for decades, only within the past few years have adrenergic receptors and their alterations occupied center stage. There is now considerable evidence linking such receptors to many of the phenomena of heart failure; recent work appears to have significant therapeutic implications.

The β-Adrenergic Receptor: Ligand Binding Studies Illuminate the Mechanism of Receptor-Adenylate Cyclase Coupling

Abstract: Publisher Summary This chapter relates the study of adrenergic receptors to the regulation of adenylate cyclase activity. The ubiquitous nature of the adrenergic responses has made these systems prototypes or models for the study of receptor-effector coupling in general. Progress is being made in the elucidation of the molecular mechanisms of transmembrane signaling via adrenergic receptors. The focus is primarily on studies of the β-adrenergic receptor-adenylate cyclase complex. Smooth muscle relaxation, inotropic and chronotropic regulation in the heart, and metabolic effects such as lipolysis are mediated through β-adrenergic receptors. β- Adrenergic responses are inhibited by a different set of drugs, which has little affinity for the α-receptors, such as propranolol, alprenolol, and pindolol. The characteristics of high potency and biological specificity make antagonist compounds particularly useful in the classification of adrenergic responses and in the direct study of adrenergic receptors. β-Adrenergic responses are directly linked to the activation of adenylate cyclase in the plasma membranes of target cells, suggesting that cyclic AMP (CAMP) mediates the regulatory effects of β-adrenergic agonists. The chapter discusses how understanding of receptor-cyclase coupling distilled from the investigations of the stimulatory β-adrenergic receptor-adenylate cyclase system may be applicable in understanding inhibition of adenylate cyclase activity, as mediated, for example, by α2- adrenergic receptors.