Chronic opioid receptor (OR) activation by morphine causes distinct cellular adaptations responsible for the development of tolerance. The present study examines the effect of chronic morphine exposure on the ability of high-efficacy agonists to mediate ␦-OR (DOR) and -OR (MOR) uncoupling and internalization, two regulatory mechanisms contributing to rapid desensitization of OR function. Chronic morphine treatment (1 M; 72 hr) of DOR carrying neuroblastoma x glioma (NG108-15) hybrid cells, a prototypical model system frequently used to study cellular aspects of opioid tolerance, completely blocked the capacity of [D-Ala 2 , D-Leu 5 ]enkephalin (DADLE) and etorphine to desensitize opioid-stimulated [ 35 S]GTP␥S binding and to mediate DOR internalization. Similar findings were obtained on stably DOR-and MOR-transfected human embryonic kidney (HEK) 293 cells. Chronic morphine treatment also heterologously impaired agonist regulation of non-opioid G-proteincoupled receptors, such as the m 4 -muscarinic acetylcholine receptor and the brain-type cannabinoid receptor. As a possible underlying mechanism, we found that chronic morphine treatment completely blocked agonist-induced redistribution of -arrestin1 in both NG108-15 and stably MOR-transfected HEK293 cells. Moreover, attenuation of -arrestin1 function appears to depend on persistent stimulation of MAP kinase activity during the course of chronic morphine treatment, because coincubation of the cells together with the MAP kinase blocker PD98059 fully restored -arrestin1 translocation and receptor internalization. These results demonstrate that chronic morphine treatment produces adaptational changes at the -arrestin1 level, which in turn attenuates agonist-mediated desensitization and internalization of G-protein-coupled receptors.
Inflammatory pain is counteracted by a number of physiological processes. For example, opioid receptors, which are present on peripheral terminals of sensory neurons, are activated by endogenous opioids, which are released from immune cells migrating to the inflamed tissue. Earlier data demonstrated that interleukin-6 contributes to such inflammation-induced analgesia. In this report, we demonstrated that interleukin-6 strongly induces -opioid receptor mRNA in the human neuroblastoma cell line SH SY5Y, whereas ␦-opioid receptor mRNA levels are not influenced. The mRNA increase in these cells is followed by an increase in -opioid receptor-specific binding. Using transcription factor decoy oligonucleotides, direct evidence was provided that the up-regulation of -opioid receptor mRNA in intact cells is dependent on the transcription factors signal transducers and activators of transcription 1 (STAT1) and STAT3, whereas other transcription factors, such as activator protein-1, nuclear factor (NF)-B, or NF-interleukin-6 are not involved. STAT1 and STAT3 bound to a site located at nucleotide Ϫ1583 on the promoter of the human -opioid receptor gene, as shown by transient transfection experiments, electrophoretic mobility shift assays, and transcription factor decoy oligonucleotides. A mutation analysis of the 5Ј-TTCATGGAA-3Ј
(IPTP, LMU). A secondary objective was to evaluate and compare the data in order to determine where efforts could be focused to optimise approaches for collection and use of information on animal poisonings. Materials and methods Poison centres Data on animal 9168 exposure calls to five German PCs were collected retrospectively for the time period January 1, 2012, to December 31, 2014. The date of inquiry, type of caller, animal details (species, age, sex) exposure reason (eg, accidental), type (eg, acute) and route (eg, oral) and main exposure agent were collected from all PCs; poisoning severity recorded at the time of inquiry was collected from one PC. Likelihood of exposure, causality and follow-up information were not collected.
Chemical probes that specifically modulate the activity of heterotrimeric G proteins provide excellent tools for investigating G protein-mediated cell signaling. Herein, we report a family of selective peptidyl Gαi/s modulators derived from peptide library screening and optimization. Conjugation to a cellpenetrating peptide rendered the peptides cell-permeable and biologically active in cell-based assays. The peptides exhibit potent guanine-nucleotide exchange modulator-like activity toward Gαi and Gαs. Molecular docking and dynamic simulations revealed the molecular basis of the protein−ligand interactions and their effects on GDP binding. This study demonstrates the feasibility of developing direct Gαi/s modulators and provides a novel chemical probe for investigating cell signaling through GPCRs/G proteins.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.