title: Differential role of the carboxyl-terminal tyrosine in down-regulation and sequestration of the m2 muscarinic acetylcholine receptor.
abstract: Muscarinic acetylcholine receptor (mAChR) number can be altered in response to sustained agonist exposure. Short term agonist exposure (seconds to minutes) causes a rapid removal of mAChR from the cell surface (sequestration) while agonist exposure for longer periods of time (hours) causes a decrease in total receptor number (down-regulation). Tyrosine residues located in the cytoplasmic tails of a number of membrane receptors have been demonstrated to be important in the regulation by either sequestration, as is the case with the mannose 6-phosphate receptor and other receptors endocytosed via clathrin coated vesicles, or down-regulation, as is the case with the beta 2-adrenergic receptor. Mutation of the lone cytoplasmic tail tyrosine residue (Tyr-459) of the mammalian m2 mAChR to Phe, Trp, or Ala did not affect agonist-induced sequestration, although it significantly attenuated agonist-induced down-regulation. Conversion of m2 Tyr-459 to Ile did not affect the rate or extent of agonist-induced sequestration or down-regulation, but the sensitivity of this mutant receptor to agonist-induced down-regulation was slightly decreased. Agonist and antagonist binding as well as functional coupling to the inhibition of cAMP accumulation was unaffected by any of the mutations to Tyr-459. These results are the first to identify a site in a mAChR involved in the down-regulation of receptor in response to agonist.
authors.affiliation: Department of Pharmacology, University of Washington, Seattle 98195.
authors.forename: P S
authors.initials: PS
authors.lastname: Goldman
authors.forename: N M
authors.initials: NM
authors.lastname: Nathanson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002822:Choriocarcinoma; D000242:Cyclic AMP / Q000378:metabolism*; D015536:Down-Regulation; D005260:Female; D006801:Humans; D007700:Kinetics; D008156:Luciferases / Q000096:biosynthesis / Q000378:metabolism; D008322:Mammals; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019832:N-Methylscopolamine; D011247:Pregnancy; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000096:biosynthesis / Q000378:metabolism*; D012602:Scopolamine Derivatives / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D014407:Tumor Cells, Cultured; D014443:Tyrosine; D014594:Uterine Neoplasms; D001616:beta-Galactosidase / Q000096:biosynthesis / Q000378:metabolism
chemical_list: D018343:Receptors, Adrenergic, beta-2; D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; D014443:Tyrosine; D011813:Quinuclidinyl Benzilate; D002217:Carbachol; D000242:Cyclic AMP; D008156:Luciferases; D001616:beta-Galactosidase; D019832:N-Methylscopolamine