title: Identification of two serine residues essential for agonist-induced 5-HT2A receptor desensitization.
abstract: 5-HT(2A) serotonin receptors represent the principal molecular targets for LSD-like hallucinogens and atypical antipsychotic drugs. It has been proposed that a dysregulation of 5-HT(2A) receptor-mediated signaling may contribute to the pathogenesis of schizophrenia and related diseases. A major mechanism for the attenuation of GPCR signaling following agonist activation typically involves the phosphorylation of serine and/or threonine residues by various kinases. Ser/Thr phosphorylation leads to the binding of accessory proteins and the uncoupling of the G proteins, thereby preventing further signaling. The molecular mechanisms by which 5-HT(2A) receptors are desensitized are unknown, and to date, no residues essential for agonist-mediated desensitization have been identified. Thus, we mutated, individually or in groups, all of the 37 serines and threonines in the cytoplasmic domains of the 5-HT(2A) receptor and assessed the effects of these mutations on agonist-mediated desensitization. We discovered that mutation of two residues, S421 in the C-terminal tail and S188 in the second intracellular loop, to alanine resulted in a significant block of agonist-induced desensitization. Intriguingly, a single-nucleotide polymorphism, of unreported frequency, at the S421 locus has been reported (S421F); the S421F mutation, like the S421A mutation, significantly attenuated agonist-mediated desensitization. Taken together, these findings indicate that the process of agonist-mediated desensitization of 5-HT(2A) receptors requires the presence of two nonconserved serine residues located in distinct intracellular loops.
authors.affiliation: Department of Biochemistry, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Gray
authors.forename: Beth A
authors.initials: BA
authors.lastname: Compton-Toth
authors.forename: Bryan L
authors.initials: BL
authors.lastname: Roth
mesh_terms: D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008969:Molecular Sequence Data; D010703:Phorbol Esters / Q000737:chemistry / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000737:chemistry / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D011814:Quipazine / Q000494:pharmacology; D051381:Rats; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000235:genetics / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D013912:Threonine / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D004791:Enzyme Inhibitors; D010703:Phorbol Esters; D010716:Phosphatidylinositols; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin; D011994:Recombinant Proteins; D017366:Serotonin Receptor Agonists; D013912:Threonine; D012701:Serotonin; D012694:Serine; D011814:Quipazine; D011493:Protein Kinase C