title: Restricted collision coupling of the A2A receptor revisited: evidence for physical separation of two signaling cascades.
abstract: The A(2A)-adenosine receptor is a prototypical G(s) protein-coupled receptor but stimulates MAPK/ERK in a G(s)-independent way. The A(2A) receptor has long been known to undergo restricted collision coupling with G(s); the mechanistic basis for this mode of coupling has remained elusive. Here we visualized agonist-induced changes in mobility of the yellow fluorescent protein-tagged receptor by fluorescence recovery after photobleaching microscopy. Stimulation with a specific A(2A) receptor agonist did not affect receptor mobility. In contrast, stimulation with dopamine decreased the mobility of the D(2) receptor. When coexpressed in the same cell, the A(2A) receptor precluded the agonist-induced change in D(2) receptor mobility. Thus, the A(2A) receptor did not only undergo restricted collision coupling, but it also restricted the mobility of the D(2) receptor. Restricted mobility was not due to tethering to the actin cytoskeleton but was, in part, related to the cholesterol content of the membrane. Depletion of cholesterol increased receptor mobility but blunted activation of adenylyl cyclase, which was accounted for by impaired formation of the ternary complex of agonist, receptor, and G protein. These observations support the conclusion that the A(2A) receptor engages G(s) and thus signals to adenylyl cyclase in cholesterol-rich domains of the membrane. In contrast, stimulation of MAPK by the A(2A) receptor was not impaired. These findings are consistent with a model where the recruitment of these two pathways occurs in physically segregated membrane microdomains. Thus, the A(2A) receptor is the first example of a G protein-coupled receptor documented to select signaling pathways in a manner dependent on the lipid microenvironment of the membrane.
authors.affiliation: Institute of Pharmacology, Center of Biomolecular Medicine and Pharmacology, Medical University of Vienna, Währinger Strasse 13a, Vienna, Austria.
authors.forename: Christoforos
authors.initials: C
authors.lastname: Charalambous
authors.forename: Ingrid
authors.initials: I
authors.lastname: Gsandtner
authors.forename: Simon
authors.initials: S
authors.lastname: Keuerleber
authors.forename: Laura
authors.initials: L
authors.lastname: Milan-Lobo
authors.forename: Oliver
authors.initials: O
authors.lastname: Kudlacek
authors.forename: Michael
authors.initials: M
authors.lastname: Freissmuth
authors.forename: Jürgen
authors.initials: J
authors.lastname: Zezula
mesh_terms: D058908:Adenosine A2 Receptor Agonists; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D016716:PC12 Cells; D038761:Photobleaching; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D043705:Receptor, Adenosine A2A / Q000378:metabolism*; D017448:Receptors, Dopamine D2 / Q000378:metabolism
chemical_list: D058908:Adenosine A2 Receptor Agonists; D043705:Receptor, Adenosine A2A; D017448:Receptors, Dopamine D2; D002784:Cholesterol; D020929:Mitogen-Activated Protein Kinase Kinases; D019205:GTP-Binding Protein alpha Subunits, Gs; D000262:Adenylyl Cyclases