title: Colocalization and regulated physical association of presynaptic serotonin transporters with A₃ adenosine receptors.
abstract: Activation of A₃ adenosine receptors (A₃ARs) rapidly enhances the activity of antidepressant-sensitive serotonin (5-HT) transporters (SERTs) in vitro, ex vivo, and in vivo. A₃AR agonist stimulation of SERT activity is lost in A₃AR knockout mice. A₃AR-stimulated SERT activity is mediated by protein kinase G1 (PKGI)- and p38 mitogen-activated protein kinase (MAPK)-linked pathways that support, respectively, enhanced SERT surface expression and catalytic activation. The mechanisms by which A₃ARs target SERTs among other potential effectors is unknown. Here we present evidence that A₃ARs are coexpressed with SERT in midbrain serotonergic neurons and form a physical complex in A₃AR/hSERT cotransfected cells. Treatment of A₃AR/SERT-cotransfected Chinese hamster ovary cells with the A₃AR agonist N⁶-(3-iodobenzyl)-N-methyl-5'-carbamoyladenosine (1 μM, 10 min), conditions previously reported to increase SERT surface expression and 5-HT uptake activity, enhanced the abundance of A₃AR/SERT complexes in a PKGI-dependent manner. Cotransfection of SERT with L90V-A₃AR, a hyperfunctional coding variant identified in subjects with autism spectrum disorder, resulted in a prolonged recovery of receptor/transporter complexes after A₃AR activation. Because PKGI and nitric-oxide synthetase are required for A₃AR stimulation of SERT activity, and proteins PKGI and NOS both form complexes with SERT, our findings suggest a mechanism by which signaling pathways coordinating A₃AR signaling to SERT can be spatially restricted and regulated, as well as compromised by neuropsychiatric disorders.
authors.affiliation: Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
authors.forename: Chong-Bin
authors.initials: CB
authors.lastname: Zhu
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Lindler
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Campbell
authors.forename: James S
authors.initials: JS
authors.lastname: Sutcliffe
authors.forename: William A
authors.initials: WA
authors.lastname: Hewlett
authors.forename: Randy D
authors.initials: RD
authors.lastname: Blakely
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D007150:Immunohistochemistry; D051379:Mice; D018345:Mice, Knockout; D011485:Protein Binding; D043684:Receptor, Adenosine A3 / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000378:metabolism*
chemical_list: D043684:Receptor, Adenosine A3; D050486:Serotonin Plasma Membrane Transport Proteins