Goldman P S, Schlador M L, Shapiro R A, Nathanson N M
Department of Pharmacology, University of Washington, Seattle, Washington 98195-7750, USA.
J Biol Chem. 1996 Feb 23;271(8):4215-22. doi: 10.1074/jbc.271.8.4215.
When the m1 and m2 muscarinic acetylcholine receptors are transiently expressed in JEG-3 cells, the m2, but not the m1, receptor undergoes agonist-induced sequestration. Both receptors exhibit internalization when expressed in Y1 cells. These results suggest that the m1 and m2 receptors use distinct cellular mechanisms or pathways for agonist-induced internalization and that JEG-3 cells are deficient in the mechanism or pathway used by the m1 receptor. Transfection experiments with chimeric receptors indicate that the specificity for agonist-induced internalization for the m2 receptor lies in the carboxyl-terminal fifth of the receptor. The intracellular carboxyl-terminal tail of the m2 receptor is neither sufficient nor required for the m2-specific sequestration. Site-directed mutagenesis demonstrates that two amino acids in the carboxyl-terminal end of the third cytoplasmic loop of the m2 receptor are required for sequestration in JEG-3 cells. In addition, the sixth transmembrane domain, which is adjacent to this cytoplasmic domain, is also required. Thus, m2-specific agonist-induced sequestration requires sequences both in the carboxyl-terminal end of the third cytoplasmic loop and the adjacent transmembrane domain.
