title: Ubiquitination-independent trafficking of G protein-coupled receptors to lysosomes.
abstract: Ubiquitination of cytoplasmic lysine residues can target G protein-coupled receptors (GPCRs) to proteasomes and has recently been shown to also be required for sorting of certain GPCRs to lysosomes following ligand-induced endocytosis. We addressed the generality of this mechanism by examining regulated proteolysis of the murine delta opioid receptor (DOR) expressed in human embryonic kidney 293 cells, a well characterized model system in which receptors are sorted to lysosomes. Incubation of cells in the presence of the highly specific proteasome inhibitor lactacystin did not detectably affect ligand-induced proteolysis of DOR but significantly delayed ligand-induced proteolysis of epidermal growth factor receptors. Mutation of all cytoplasmic lysine residues in DOR, creating a mutant opioid receptor that is unable to be ubiquitinated, did not detectably inhibit either ligand-induced endocytosis or proteolytic degradation of endocytosed receptors. Furthermore, the lysine-mutated DOR, like its wild type counterpart, colocalized extensively with lysosomes after ligand-induced endocytosis. These results demonstrate that ubiquitination of DOR is not required either for its ligand-induced endocytosis or for postendocytic trafficking to lysosomes.
authors.affiliation: Department of Psychiatry, University of California, San Francisco, California 94143-0984, USA. mbt2m@itsa.ucsf.edu
authors.forename: Michael
authors.initials: M
authors.lastname: Tanowitz
authors.forename: Mark
authors.initials: M
authors.lastname: Von Zastrow
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001120:Arginine; D002460:Cell Line; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008239:Lysine; D008247:Lysosomes / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D021381:Protein Transport; D017465:Receptors, Opioid, delta / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D017465:Receptors, Opioid, delta; D011994:Recombinant Proteins; D025801:Ubiquitin; D001120:Arginine; D019204:GTP-Binding Proteins; D008239:Lysine