title: Naturally occurring variations in the human 5-HT3A gene profoundly impact 5-HT3 receptor function and expression.
abstract: BACKGROUND
  The serotonin [5-hydroxytryptamine (5-HT)]-gated ion channel 5-HT3 is involved in the mediation of postoperative and radiotherapy/chemotherapy-induced nausea/emesis and in irritable bowel syndrome. It has also been suggested to play a role in various psychiatric diseases. Five naturally occurring single nucleotide polymorphisms leading to amino acid changes have been identified in the human 5-HT3A gene.
  
  
  RESULTS
  We investigated the functional effects of these polymorphisms on the 5-HT3A receptor using fluorescence-based cellular assays. Notably, variants A33T, S253N, and M257I displayed 5-HT-induced maximal responses of 3-64% of the wild-type response, whereas R344H and P391R exhibited wild-type-like function. All variants displayed wild-type-like potencies of 5-HT and three 5-HT3 antagonists. Furthermore, all variants displayed Kd values similar to that of the wild-type receptor in a [H]GR65630-binding assay. The surface expression of A33T, M257I, and R344H was reduced 2-4-fold compared with the wild-type, despite similar total expression levels. Finally, coexpression of wild-type 5-HT3A or 5-HT3B subunits with 5-HT3A variants A33T, S253N, or M257I resulted in mixed or heteromeric receptors, characterized by significantly reduced maximal responses to 5-HT compared with the wild-type receptors.
  
  
  CONCLUSIONS
  Three polymorphisms of the 5-HT3A gene gave rise to functionally impaired receptors whose function could not be rescued by either wild-type 5-HT3A or 5-HT3B. Three of the variant receptors were surface-expressed at reduced levels in spite of total expression levels similar to wild-type, indicating that these variants affect receptor biogenesis and/or trafficking. These severe single nucleotide polymorphism effects hold promise for identification of new 5-HT3A gene-disease causalities.
authors.affiliation: Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Karen
authors.initials: K
authors.lastname: Krzywkowski
authors.forename: Anders A
authors.initials: AA
authors.lastname: Jensen
authors.forename: Christopher N
authors.initials: CN
authors.lastname: Connolly
authors.forename: Hans
authors.initials: H
authors.lastname: Bräuner-Osborne
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D015870:Gene Expression; D014644:Genetic Variation; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D010597:Pharmacogenetics; D020641:Polymorphism, Single Nucleotide; D021122:Protein Subunits; D044406:Receptors, Serotonin, 5-HT3 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014162:Transfection
chemical_list: D021122:Protein Subunits; D044406:Receptors, Serotonin, 5-HT3; D011994:Recombinant Proteins