title: Regulation of serotonin transport in human platelets by tyrosine kinase Syk.
abstract: Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter involved in the regulation of numerous neuro-physiological processes. The circulating level of 5-HT is regulated by the membrane transporter SERT present both in the presynaptic nerve terminals and blood platelets. 5-HT transport is a process tightly regulated by a variety of factors including protein phosphorylation. Aim of this study was to ascertain if also the SERT Tyr-phosphorylation mediated by Syk-kinase concurs to the regulation of SERT activity. Indeed we found that 5-HT uptake decreased upon platelet exposure to piceatannol or Syk-inhibitor II, two structurally unrelated inhibitors of the tyrosine-kinase Syk. Tyr-phosphorylation of anti-SERT-immuno-stained proteins in membrane extracts and in anti-SERT-immuno-precipitates, decreased upon platelet treatment with piceatannol, in parallel with a reduction of Syk-activity. Syk was immuno-revealed in the anti-SERT immuno-precipitates, which displayed a piceatannol-sensitive kinase activity towards SERT itself and the Syk-substrate α-sinuclein. Syk inhibitors also caused a decrease of the monensin-induced 5-HT-efflux from platelets and of imipramine binding to them. It is concluded that, in addition to the phosphorylation of SERT mediated by various other kinases, also that catalyzed by Syk might play an important role in the 5-HT transport, likely favoring the transporter conformation exposing the neurotransmitter binding sites.
authors.affiliation: Department of Biological Chemistry, Viale G. Colombo 3, University of Padova, Padova, Italy.
authors.forename: Martina
authors.initials: M
authors.lastname: Pavanetto
authors.forename: Alessandro
authors.initials: A
authors.lastname: Zarpellon
authors.forename: Christian
authors.initials: C
authors.lastname: Borgo
authors.forename: Arianna
authors.initials: A
authors.lastname: Donella-Deana
authors.forename: Renzo
authors.initials: R
authors.lastname: Deana
mesh_terms: D000929:Antidepressive Agents, Tricyclic / Q000737:chemistry / Q000494:pharmacology; D001792:Blood Platelets / Q000201:enzymology*; D006801:Humans; D007099:Imipramine / Q000737:chemistry / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000378:metabolism; D013267:Stilbenes / Q000494:pharmacology; D000072377:Syk Kinase
chemical_list: D000929:Antidepressive Agents, Tricyclic; D047908:Intracellular Signaling Peptides and Proteins; D050486:Serotonin Plasma Membrane Transport Proteins; D013267:Stilbenes; D012701:Serotonin; C041525:3,3',4,5'-tetrahydroxystilbene; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D007099:Imipramine