title: Constitutive endocytic cycle of the CB1 cannabinoid receptor.
abstract: The CB1 cannabinoid receptor (CB1R) displays a significant level of ligand-independent (i.e. constitutive) activity, either when heterologously expressed in nonneuronal cells or in neurons where CB1Rs are endogenous. The present study investigates the consequences of constitutive activity on the intracellular trafficking of CB1R. When transfected in HEK-293 cells, CB1R is present at the plasma membrane, but a substantial proportion ( approximately 85%) of receptors is localized in intracellular vesicles. Detailed analysis of CB1-EGFP expressed in HEK-293 cells shows that the intracellular CB1R population is mostly of endocytic origin and that treatment with inverse agonist AM281 traps CB1R at the plasma membrane through a monensin-sensitive recycling pathway. Co-transfection with dominant positive or dominant negative mutants of the small GTPases Rab5 and Rab4, but not Rab11, profoundly modifies the steady-state and ligand-induced intracellular distribution of CB1R, indicating that constitutive endocytosis is Rab5-dependent, whereas constitutive recycling is mediated by Rab4. In conclusion, our results indicate that, due to its natural constitutive activity, CB1R permanently and constitutively cycles between plasma membrane and endosomes, leading to a predominantly intracellular localization at steady state.
authors.affiliation: ESPCI-CNRS UMR 7637, Laboratoire Neurobiologie et Diversité Cellulaire, Ecole Supérieure de Physique et de Chimie Industrielles, 10 Rue Vauquelin, 75231 Paris Cedex 05, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Leterrier
authors.forename: Damien
authors.initials: D
authors.lastname: Bonnard
authors.forename: Damien
authors.initials: D
authors.lastname: Carrel
authors.forename: Jean
authors.initials: J
authors.lastname: Rossier
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Lenkei
mesh_terms: D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D011992:Endosomes / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D021381:Protein Transport; D043884:Receptor, Cannabinoid, CB1 / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D043884:Receptor, Cannabinoid, CB1; D011993:Recombinant Fusion Proteins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins