High-frequency HTR3B variant associated with major depression dramatically augments the signaling of the human 5-HT _3AB receptor

Abstract

The 5-hydroxytryptamine-3 (5-HT3) receptor mediates the fast excitatory neurotransmission of serotonin and is known to mediate the nausea/emesis induced by radio/chemotherapy and anesthetics. A polymorphism encoding the variation Y129S in the 5-HT3B subunit exists in high frequency in the general population and has been shown to be inversely correlated to the incidence of major depression in women. We show that 5-HT3AB(Y129S) receptors exhibit a substantially increased maximal response to serotonin compared with WT receptors in two fluorescence-based cellular assays. In electrophysiological recordings, the deactivation and desensitization kinetics of the 5-HT3AB ( 5-HT3 ͉ ligand-gated ion channel ͉ polymorphism ͉ serotonin ͉ receptor kinetics S erotonin [5-hydroxytryptamine (5-HT)] is a major neurotransmitter in both the CNS and the peripheral nervous system (PNS), where it plays a key role in basic functions such as mood, sleep, appetite regulation, and libido (1). Serotonergic signaling is mediated via a plethora of G protein-coupled receptors, whereas only one serotonin-gated ion channel has been identified: the 5-HT 3 receptor (2).5-HT 3 receptors are expressed in both the CNS and the PNS. Presynaptic 5-HT 3 receptors are known to modulate the synaptic release of various neurotransmitters (3-5), whereas postsynaptic 5-HT 3 receptors are responsible for the fast excitatory response to serotonin (6). The role of the 5-HT 3 receptor in general physiology and pathophysiology is not well established. However, the 5-HT 3 receptor is known to mediate the nausea and emesis caused by radio/chemotherapy and anesthetics (7). Furthermore, 5-HT 3 antagonists have proven effective in the treatment of irritable bowel disease (7). Finally, the 5-HT 3 receptor has been suggested to be involved in anxiety, depression, pain, alcohol dependence, and eating disorders (7,8).The 5-HT 3 receptor is a nonselective cation channel belonging to the superfamily of Cys-loop ligand-gated ion channels that includes receptors for the neurotransmitters ACh, ␥-aminobutyric acid, and glycine. These receptors are pentameric assemblies, where the five subunits form a central ion channel path (9). To date, five 5-HT 3 subunits have been cloned: 5-HT 3A -5-HT 3E (10-12). Transcripts of 5-HT 3A , 5-HT 3B , and 5-HT 3C subunits have been demonstrated in both the CNS and the PNS (11-13), whereas 5-HT 3D and 5-HT 3E transcripts have been detected only in peripheral tissues (12). By using 5-HT 3B -specific antibodies, the existence of the 5-HT 3B subunit in the human hippocampus (14) as well as in the CNS in rodents (15) has been confirmed. Whereas homomeric 5-HT 3A receptors are functional, the other subunits only form functional receptors when coexpressed with 5-HT 3A (11,16). The homomeric 5-HT 3A and the heteromeric 5-HT 3AB receptors are the best characterized 5-HT 3 receptors, whereas the physiological relevance of subunits 5-HT 3c -5-HT 3E has just started to be unraveled. In heterologous expression systems, the 5-HT 3A :5-HT 3B stoichiometry an...

Discovery of a Novel Allosteric Modulator of 5-HT3 Receptors

“…In agreement with previous studies (26,39), 5-HT elicited currents through the 5-HT 3 A receptor with an EC 50 Fig. 2A).…”

“…Molecular Biology-The generation of 5-HT3A-pCIneo and 5-HT3B-pCIneo plasmids has been described previously (26,27). Human 5-HT3C and 5-HT3E cDNAs were cloned by PCR from I.M.A.G.E.…”

Elucidation of Molecular Impediments in the α6 Subunit for in Vitro Expression of Functional α6β4* Nicotinic Acetylcholine Receptors

“…Insertion of the myc tag into ␣3 and C1 was found not to alter the functional properties of the ␣3␤4 and C1␤4 nAChRs (data not shown). Furthermore, the validity of the ELISA was verified in control experiments performed in parallel, where transfection of tsA201 cells with HA-tagged 5-HT3B was found not to result in significant cell surface expression, whereas co-expression of HA-5-HT3B with WT 5-HT3A gave rise to significant levels of cell surface expression of the HA-tagged subunit (54). As can be seen from Fig.…”

“…Enzyme-linked Immunosorbent Assay (ELISA)-The ELISA was performed essentially as described previously (54). The tsA201 cells transfected with ␣3, myc-␣3, myc-␣6, myc-C1, myc-C2, myc-C6, or myc-␣6 F223L cDNAs together with ␤4 cDNA were seeded into poly-D-lysine-coated 24-well plates (3 ϫ 10 5 cells/well).…”

Serotonin Type 3 Receptor Genes: HTR3A, B, C, D, E

“…Furthermore, two missense mutations in HTR3A (c.1031G>A and c.1172C>G) were detected in schizophrenic patients and may be involved in the etiology of schizophrenia [17,[22][23][24][25]. The deletion c.-_100_102delAAG within the 5Ú TR of HTR3B seems to contribute to the etiology of BPAD [26] and the SNP c.386A>C in HTR3B was found to be associated with major depression [18], both of which have been shown to be functional and presumably predispose to the susceptibility of the respective condition [27,28].…”