Involvement of G protein-coupled receptor kinase-6 in desensitization of CGRP receptors. 2000

N Aiyar, and J Disa, and K Dang, and A N Pronin, and J L Benovic, and P Nambi
Department of Cardiovascular Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, PA 19406-0939, USA. nambi_aiyar-1@sbphrd.com

This investigation was undertaken to study the mechanisms of calcitonin gene-related peptide (CGRP)-mediated desensitization using recombinant porcine CGRP receptors stably expressed in human embryonic kidney (HEK-293) cells. Pretreatment of these cells with human alphaCGRP resulted in an approximately 60% decrease in CGRP-stimulated adenylyl cyclase activity and an approximately 10-fold rightward shift in the dose-response curve of CGRP. This effect was rapid (t(1/2) approximately 5 min) and was accompanied by a significant decrease in [125I]CGRP binding to membrane preparations from CGRP-pretreated cells. In contrast, CGRP pretreatment had no effect on isoproterenol- or forskolin-stimulated adenylyl cyclase activity in these cells. The potential involvement of protein kinase A or protein kinase C in CGRP-mediated desensitization was studied using selective inhibitors or activators of these kinases. Pretreatment of the cells with forskolin (adenylyl cyclase activator) or phorbol dibutyrate (protein kinase C activator) had no effect on CGRP-mediated adenylyl cyclase activity and did not influence CGRP-mediated desensitization. However, pretreatment of the cells with 2-(8-[(dimethylamino)methyl]-6,7,8, 9-tetrahydropyrido[1,2-a]indol-3-yl]-3-(1-methylindol-3-yl)m aleimide hydrochloride (Ro 32-0432) (a potent inhibitor of protein kinase C) resulted in significant attenuation of CGRP-mediated desensitization with an IC(50) approximately 3 microM. To establish whether this effect might be due to inhibition of other protein kinases by Ro 32-0432, its effect was tested against several G protein-coupled receptor kinases (GRKs). Ro 32-0432 was found to inhibit GRK2, GRK5, and GRK6 with IC(50) values of 29, 3.6, and 16 microM, respectively, suggesting that its effect on CGRP-mediated desensitization might be a result of GRK inhibition. To further test this hypothesis, as well as the potential GRK specificity, the cells were treated with antisense oligonucleotides to GRK2, GRK5, and GRK6. While GRK2 and GRK5 antisense nucleotides had no effect on CGRP-mediated desensitization, the GRK6 antisense nucleotide treatment significantly reversed CGRP-mediated desensitization. These results suggest the involvement of GRK6 in CGRP-mediated desensitization in HEK-293 cells.

UI MeSH Term Description Entries
D007211 Indoles Benzopyrroles with the nitrogen at the number one carbon adjacent to the benzyl portion, in contrast to ISOINDOLES which have the nitrogen away from the six-membered ring.
D007457 Iodine Radioisotopes Unstable isotopes of iodine that decay or disintegrate emitting radiation. I atoms with atomic weights 117-139, except I 127, are radioactive iodine isotopes. Radioisotopes, Iodine
D008566 Membranes Thin layers of tissue which cover parts of the body, separate adjacent cavities, or connect adjacent structures. Membrane Tissue,Membrane,Membrane Tissues,Tissue, Membrane,Tissues, Membrane
D010446 Peptide Fragments Partial proteins formed by partial hydrolysis of complete proteins or generated through PROTEIN ENGINEERING techniques. Peptide Fragment,Fragment, Peptide,Fragments, Peptide
D011758 Pyrroles Azoles of one NITROGEN and two double bonds that have aromatic chemical properties. Pyrrole
D011869 Radioligand Assay Quantitative determination of receptor (binding) proteins in body fluids or tissue using radioactively labeled binding reagents (e.g., antibodies, intracellular receptors, plasma binders). Protein-Binding Radioassay,Radioreceptor Assay,Assay, Radioligand,Assay, Radioreceptor,Assays, Radioligand,Assays, Radioreceptor,Protein Binding Radioassay,Protein-Binding Radioassays,Radioassay, Protein-Binding,Radioassays, Protein-Binding,Radioligand Assays,Radioreceptor Assays
D002460 Cell Line Established cell cultures that have the potential to propagate indefinitely. Cell Lines,Line, Cell,Lines, Cell
D004305 Dose-Response Relationship, Drug The relationship between the dose of an administered drug and the response of the organism to the drug. Dose Response Relationship, Drug,Dose-Response Relationships, Drug,Drug Dose-Response Relationship,Drug Dose-Response Relationships,Relationship, Drug Dose-Response,Relationships, Drug Dose-Response
D004789 Enzyme Activation Conversion of an inactive form of an enzyme to one possessing metabolic activity. It includes 1, activation by ions (activators); 2, activation by cofactors (coenzymes); and 3, conversion of an enzyme precursor (proenzyme or zymogen) to an active enzyme. Activation, Enzyme,Activations, Enzyme,Enzyme Activations
D004791 Enzyme Inhibitors Compounds or agents that combine with an enzyme in such a manner as to prevent the normal substrate-enzyme combination and the catalytic reaction. Enzyme Inhibitor,Inhibitor, Enzyme,Inhibitors, Enzyme

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