Receptor最新文献

Studies from space flights over the past two decades have demonstrated that there are basic physiological changes in humans during space flight. These changes include cephalad fluid shifts, loss of fluid and electrolytes, loss of muscle mass, space motion sickness, anemia, reduced immune response, and loss of calcium and mineralized bone. The cause of most of these manifestations is not known but the general approach has been to investigate systemic and hormonal changes. However, data from the 1973-1974 Skylabs, Spacelab 3 (SL-3), Spacelab D-I (SL-DI), and now the new SLS-1 missions support a more basic biological response to microgravity that may occur at the tissue, cellular, and molecular level. This report summarizes ground-based and SLS-1 experiments that examined the mechanism of loss of red blood cell mass in humans, the loss of bone mass and lowered osteoblast growth under space flight conditions, and loss of immune function in microgravity.

DNA-protein interactions around the regulatory region of the pS2 gene were studied to gain insight into the mechanisms that operate in the estrogen receptor regulated expression of this gene in the MCF-7 human breast cancer cell. Using a revised photocrosslinking technology in combination with gel retardation assays, two distinct multiprotein DNA complexes were shown to assemble in an estrogen receptor-dependent process. Immunological analysis demonstrated the participation of both the estrogen receptor and a c-fos related protein in the formation of these complexes. The results support a model of estrogen receptor function in which the receptor facilitates the formation of multiprotein complexes at DNA sites that can regulate the transcription of a hormone responsive gene by RNA polymerase II and any additional general transcription machinery. These receptor-containing complexes are referred to as "receptorsomes."

Activins are multifunctional proteins with effects on a broad spectrum of cells and tissues. They are structurally related to a large family of growth and differentiation factors that includes the inhibins, the transforming growth factors b (TGFb), the bone morphogenetic proteins (BMP), Mullerian inhibitory substance, and a number of gene products that control the development of Drosophila and Xenopus. Although the cellular signaling mechanisms of these factors remain unclear, cDNAs encoding cell surface receptors for activin have been cloned. Those receptors are transmembrane serine kinases, suggesting a novel form of signaling. Overexpression of activin receptors in Xenopus embryos indicates that these molecules are functionally involved in the transmission of the activin signal.

The receptor for parathyroid hormone (PTH) and PTH-related protein (PTHrP) is a member of a subfamily of G-protein-coupled receptors. This subfamily includes receptors for calcitonin, secretin, vasoactive intestinal polypeptide, glucagon, and related peptides, growth hormone-releasing hormone, and pituitary adenylate cyclase activating peptide. These receptors couple agonist occupancy to activation of adenylate cyclase and, in some cases, to increases in Cai2+, but the molecular basis of signalling is unclear Mutagenesis studies of recombinant PTH/PTHrP receptors indicates that large portions of the third intracellular loop and C-terminal tail can be deleted and/or mutated without major loss of receptor-G-protein interaction, as evidenced by high affinity ligand binding and signal transduction. However, specific determinants in these domains appear to modulate the efficiency of effector activation. Further studies are needed to define the contact sites for PTH/PTHrP receptor-G-protein interaction.

Hepatocyte nuclear factor 4 (HNF-4), found in liver, kidney, and intestine, is a potent transcriptional activator that controls the expression of a wide variety of genes, including those involved in fatty acid and cholesterol metabolism, glucose metabolism, urea biosynthesis, blood coagulation, hepatitis B infections, and liver differentiation. HNF-4 is also a member of the steroid hormone receptor superfamily and has been highly conserved throughout evolution, suggesting that it might respond to an as yet unidentified ligand. In this presentation, some of the current findings regarding the role of HNF-4 in liver-specific gene expression are reviewed.

Models of the lectin-homology domains of the human and murine low-affinity receptors for IgE (Fc epsilon RII/CD23) were built on the basis of sequence similarity with rat mannose-binding protein, the structure of which is known. The sites on Fc epsilon RII/CD23 that are possibly involved in the interaction with IgE and with another ligand, CD21/CR2, are proposed. The models may assist the design of protein engineering experiments for the study of the reactivity of these molecules.

Addition of 5-HT or SK&F 103829 (2,3,4,5 tetrahydro-8[methyl-sulfonyl]-1 H-3-benzazepin-7-ol hydrobromide) contracts isolated strips of canine lower esophageal sphincter (LES) circular smooth muscle. 5-HT acts directly on the smooth muscle, since pretreatment with the neurotoxin TTX does not inhibit this contraction. Depletion of extracellular calcium or pretreatment with nifedipine inhibited the contraction to both 5-HT and SK&F 103829. Therefore, in this smooth muscle, the contraction produced by both 5-HT and SK&F 103829 requires extracellular calcium and is sensitive to inhibition by a voltage-dependent Ca2+ channel antagonist. In addition, with respect to 5-HT, SK&F 103829 appeared to act as a partial agonist. Receptor alkylation studies using phenoxybenzamine demonstrated no receptor reserve for the contractile response to 5-HT. Nonsurmountable antagonism of the contraction induced by 5-HT and SK&F 103289 was observed with several 5-HT2 antagonists, i.e., methysergide, ketanserin, cyproheptadine, and LY 53857. Using a method established for pseudoirreversible antagonism, the Ki values for these 5-HT2 receptor antagonists were estimated. Results suggested that both 5-HT and SK&F 103829 contract the canine LES by interacting at the same receptor site and that this receptor site has characteristics of the 5-HT2 receptor. Finally, neither bulbocapnine, domperidone, nor prazosin significantly alters the response to 5-HT or SK&F 103829. Thus, isolated strips of canine LES contain a contractile 5-HT2 receptor, and SK&F 103829 behaves as a partial agonist at this site.

Radioligand-receptor binding techniques identified two angiotensin II (ANG II) receptor subtypes in rat renal glomerular membranes. This characterization was made possible by employing two highly-specific nonpeptide ANG II antagonists: Losartan (DuP 753), which is specific to the AT1 subtype, and PD 123319, which is specific to the AT2 subtype. The majority of ANG II receptors in glomerular membranes corresponded to the AT1 subtype.

The extracellular portion of the alpha-subunit of human high-affinity receptor for immunoglobulin-E (IgE), which contains two immunoglobulin (Ig) domains, was modeled on the basis of sequence similarity with antibody domains of known three-dimensional structure. Each receptor domain contains 86 amino acid residues, and both domains were modeled as bilayer structures. In both domains, one layer is made up of three anti-parallel beta-strands and the other of four strands, with the two layers linked by a disulfide bridge. The two domains show significant sequence similarity with each other (22 identities) and with the homologous domains of the murine and rat high-affinity receptors for IgE and the Fc gamma receptors from various species. Two plausible modes of association of the domains were considered: In the first, the two domains were positioned end-to-end, with essentially only longitudinal interactions between them; in the second, the molecule is more bent, with more lateral interactions between the two domains. The models will be useful in the design of protein engineering studies of this and homologous receptors to delineate the site of interaction with ligand. Furthermore, they may lend themselves as possible probes in crystallographic analyses by molecular replacement techniques.

The full-length human estrogen receptor (hER) as well as two overlapping peptides of hER were overproduced in Escherichia coli JM109 cells, using the inducible pIC vector system. The N-terminal receptor peptide contains the DNA-binding domain as well as the hinge region, whereas the C-terminal peptide contains the same hinge region and the hormone-binding domain. Typically, 1-6 mg of estrogen receptor (ER) peptides can be recovered from 1 L E. coli cell cultures. The majority of the overexpressed proteins are found in inclusion bodies, which allow the isolation of ER peptides in high yields and of 50-80% purity. Induction for short time periods at 10 microM inducer yielded up to 50% of the ER peptides in soluble form with full biological activity. Both the intact receptor and the C-terminal fragment specifically bound estrogens and antiestrogens, whereas ER peptides that contained the DNA-binding domain were retained on a DNA-agarose resin.