title: Role of the third intracellular loop in the subtype-specific internalization and recycling of muscarinic M2 and M4 receptors.
abstract: Muscarinic M2, M4, and M2-M4 chimera receptors were transiently expressed in HEK-293 tsA201 cells, and agonist-dependent internalization of these receptors and recycling of internalized receptors were examined by measuring the amount of cell-surface receptors as [3H]N-methylscopolamine (NMS) binding activity. Coexpression of a dominant negative form of dynamin (DN-dynamin,dynamin K44A) greatly reduced the agonist-dependent internalization of M4 receptors but not of M2 receptors, as was reported by Vögler et al. (J Biol Chem 273, 12155-12160, 1998).The agonist-dependent internalization of M2/M4-i3/M2 chimera receptors (M2 receptors with the i3 loop replaced by that of M4 receptors) was greatly reduced by co-expression of DN-dynamin as was the case for M4 receptors, whereas the agonist-dependent internalization of M4/M2-i3/M4 chimera receptors was hardly affected by co-expression of DN-dynamin as was the case for M2 receptors.Internalized M2/M4-i3/M2 receptors as well as internalized M4 receptors were shown to be recycled back to the cell surface after removal of agonists, whereas no recycling was observed for M4/M2-i3/M4 receptors as well as M2 receptors. These results indicate that the i3 loops of M2 and M4 receptors take a major role in their agonist-dependent internalization and recycling.
authors.affiliation: Institute for Biomolecular Science, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588, Japan.
authors.forename: Norihiro
authors.initials: N
authors.lastname: Yoshida
authors.forename: Eri
authors.initials: E
authors.lastname: Jojima
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Saito
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Haga
mesh_terms: D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D034281:Dynamins / Q000235:genetics / Q000378:metabolism; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D007700:Kinetics; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs / Q000235:genetics; D043585:Receptor, Muscarinic M2 / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D043588:Receptor, Muscarinic M4 / Q000819:agonists / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
chemical_list: D043585:Receptor, Muscarinic M2; D043588:Receptor, Muscarinic M4; D002217:Carbachol; D054769:G-Protein-Coupled Receptor Kinase 2; D034281:Dynamins