title: Adenosine A2A receptor and dopamine D3 receptor interactions: evidence of functional A2A/D3 heteromeric complexes.
abstract: Adenosine A(2A) and dopamine D(2) receptors have been shown previously to form heteromeric complexes and interact at the level of agonist binding, G protein coupling, and trafficking. Because dopamine D(2) and D(3) receptors show a high degree of sequence homology, A(2A) and D(3) receptors may also interact in a similar manner. The present studies with confocal microscopy showed that A(2A)-yellow fluorescent protein (YFP) and D(3)-green fluorescent protein 2 (GFP2) receptors colocalize in the plasma membrane. Furthermore, fluorescence resonance energy transfer (FRET) analysis demonstrated that A(2A)-YFP and D(3)-GFP2 receptors give a positive FRET efficiency and are thereby likely to exist as heteromeric A(2A)/D(3) receptor complexes. Saturation experiments with [(3)H]dopamine demonstrated that the A(2A) receptor agonist 4-[2-[[6-amino-9(N-ethyl-beta-d-ribofuranuronaminoamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid (CGS-21680) reduced the affinity of the high-affinity agonist binding state of the D(3) receptor for [(3)H]dopamine. The A(2A) and D(2A) receptors seem to interact also at the level of G protein coupling, because the adenosine A(2A) receptor agonist CGS-21680 fully counteracted the D(3) receptor-mediated inhibition of a forskolin-mediated increase in cAMP levels. Taken together, when coexpressed in the same neuron, A(2A) and D(3) receptors seem to form A(2A)/D(3) heteromeric receptor complexes in which A(2A) receptors antagonistically modulate both the affinity and the signaling of the D(3) receptors. D(3) receptor is one of the therapeutic targets for treatment of schizophrenia, and therefore, the A(2A)/D(3) receptor interactions could provide an alternative antischizophrenic treatment.
authors.affiliation: Department of Neuroscience, Karolinska Institute, 17177 Stockholm, Sweden.
authors.forename: Maria
authors.initials: M
authors.lastname: Torvinen
authors.forename: Daniel
authors.initials: D
authors.lastname: Marcellino
authors.forename: Meritxell
authors.initials: M
authors.lastname: Canals
authors.forename: Luigi F
authors.initials: LF
authors.lastname: Agnati
authors.forename: Carmen
authors.initials: C
authors.lastname: Lluis
authors.forename: Rafael
authors.initials: R
authors.lastname: Franco
authors.forename: Kjell
authors.initials: K
authors.lastname: Fuxe
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000378:metabolism; D058908:Adenosine A2 Receptor Agonists; D004298:Dopamine / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal; D010627:Phenethylamines / Q000378:metabolism; D011869:Radioligand Assay; D043705:Receptor, Adenosine A2A / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D050637:Receptors, Dopamine D3
chemical_list: D058908:Adenosine A2 Receptor Agonists; C493593:DRD3 protein, human; D010627:Phenethylamines; D043705:Receptor, Adenosine A2A; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D000241:Adenosine; D004298:Dopamine