title: A Significant Role of the Truncated Ghrelin Receptor GHS-R1b in Ghrelin-induced Signaling in Neurons.
abstract: The truncated non-signaling ghrelin receptor growth hormone secretagogue R1b (GHS-R1b) has been suggested to simply exert a dominant negative role in the trafficking and signaling of the full and functional ghrelin receptor GHS-R1a. Here we reveal a more complex modulatory role of GHS-R1b. Differential co-expression of GHS-R1a and GHS-R1b, both in HEK-293T cells and in striatal and hippocampal neurons in culture, demonstrates that GHS-R1b acts as a dual modulator of GHS-R1a function: low relative GHS-R1b expression potentiates and high relative GHS-R1b expression inhibits GHS-R1a function by facilitating GHS-R1a trafficking to the plasma membrane and by exerting a negative allosteric effect on GHS-R1a signaling, respectively. We found a preferential Gi/o coupling of the GHS-R1a-GHS-R1b complex in HEK-293T cells and, unexpectedly, a preferential Gs/olf coupling in both striatal and hippocampal neurons in culture. A dopamine D1 receptor (D1R) antagonist blocked ghrelin-induced cAMP accumulation in striatal but not hippocampal neurons, indicating the involvement of D1R in the striatal GHS-R1a-Gs/olf coupling. Experiments in HEK-293T cells demonstrated that D1R co-expression promotes a switch in GHS-R1a-G protein coupling from Gi/o to Gs/olf, but only upon co-expression of GHS-R1b. Furthermore, resonance energy transfer experiments showed that D1R interacts with GHS-R1a, but only in the presence of GHS-R1b. Therefore, GHS-R1b not only determines the efficacy of ghrelin-induced GHS-R1a-mediated signaling but also determines the ability of GHS-R1a to form oligomeric complexes with other receptors, promoting profound qualitative changes in ghrelin-induced signaling.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain, dimartts@hotmail.com.
authors.forename: Gemma
authors.initials: G
authors.lastname: Navarro
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Aguinaga
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain.
authors.forename: Edgar
authors.initials: E
authors.lastname: Angelats
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain.
authors.forename: Mireia
authors.initials: M
authors.lastname: Medrano
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain.
authors.forename: Estefanía
authors.initials: E
authors.lastname: Moreno
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain.
authors.forename: Josefa
authors.initials: J
authors.lastname: Mallol
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Cortés
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain.
authors.forename: Enric I
authors.initials: EI
authors.lastname: Canela
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain.
authors.forename: Vicent
authors.initials: V
authors.lastname: Casadó
authors.affiliation: the School of Pharmacy, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom, and.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: McCormick
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Barcelona and Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas, 08028 Barcelona, Spain.
authors.forename: Carme
authors.initials: C
authors.lastname: Lluís
authors.affiliation: the Integrative Neurobiology Section, National Institute on Drug Abuse, Intramural Research Program, Baltimore, Maryland 21224 sferre@intra.nida.nih.gov.
authors.forename: Sergi
authors.initials: S
authors.lastname: Ferré
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D054439:Ghrelin / Q000502:physiology; D057809:HEK293 Cells; D006624:Hippocampus / Q000166:cytology; D006801:Humans; D009474:Neurons / Q000378:metabolism*; D055503:Protein Multimerization; D021122:Protein Subunits / Q000502:physiology; D021381:Protein Transport; D017207:Rats, Sprague-Dawley; D017447:Receptors, Dopamine D1 / Q000378:metabolism; D054440:Receptors, Ghrelin / Q000502:physiology*; D015398:Signal Transduction
chemical_list: D054439:Ghrelin; D021122:Protein Subunits; D017447:Receptors, Dopamine D1; D054440:Receptors, Ghrelin; D000262:Adenylyl Cyclases
keywords: HEK-293T cells; cAMP; dopamine receptor; ghrelin; ghrelin receptor; neuron; oligomerization; trafficking