title: Direct interaction of GABAB receptors with M2 muscarinic receptors enhances muscarinic signaling.
abstract: Downregulation of G-protein-coupled receptors (GPCRs) provides an important mechanism for reducing neurotransmitter signaling during sustained stimulation. Chronic stimulation of M(2) muscarinic receptors (M(2)Rs) causes internalization of M(2)R and G-protein-activated inwardly rectifying potassium (GIRK) channels in neuronal PC12 cells, resulting in loss of function. Here, we show that coexpression of GABA(B) R2 receptors (GBR2s) rescues both surface expression and function of M(2)R, including M(2)R-induced activation of GIRKs and inhibition of cAMP production. GBR2 showed significant association with M(2)R at the plasma membrane but not other GPCRs (M(1)R, mu-opioid receptor), as detected by fluorescence resonance energy transfer measured with total internal reflection fluorescence microscopy. Unique regions of the proximal C-terminal domains of GBR2 and M(2)R mediate specific binding between M(2)R and GBR2. In the brain, GBR2, but not GBR1, biochemically coprecipitates with M(2)R and overlaps with M(2)R expression in cortical neurons. This novel heteromeric association between M(2)R and GBR2 provides a possible mechanism for altering muscarinic signaling in the brain and represents a previously unrecognized role for GBR2.
authors.affiliation: Peptide Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.
authors.forename: Stephanie B
authors.initials: SB
authors.lastname: Boyer
authors.forename: Sinead M
authors.initials: SM
authors.lastname: Clancy
authors.forename: Miho
authors.initials: M
authors.lastname: Terunuma
authors.forename: Raquel
authors.initials: R
authors.lastname: Revilla-Sanchez
authors.forename: Steven M
authors.initials: SM
authors.lastname: Thomas
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Moss
authors.forename: Paul A
authors.initials: PA
authors.lastname: Slesinger
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D016716:PC12 Cells; D011485:Protein Binding / Q000502:physiology; D051381:Rats; D043585:Receptor, Muscarinic M2 / Q000737:chemistry / Q000378:metabolism*; D018080:Receptors, GABA-B / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D043585:Receptor, Muscarinic M2; D018080:Receptors, GABA-B