Structure of the Human Serotonin 5‐HT₄ Receptor Gene and Cloning of a Novel 5‐HT₄ Splice Variant

Abstract

Several variants of the serotonin 5-HT 4 receptor are known to be produced by alternative splicing. To survey the existence and usage of exons in humans, we cloned the human 5-HT 4 gene. Based on sequence analysis seven C-terminal variants (a-g) and one internal splice variant (h) were found. We concentrated in this study on the functional characterization of the novel splice variant h, which leads to the insertion of 14 amino acids into the second extracellular loop of the receptor. The h variant was cloned as a splice combination with the C-terminal b variant; therefore, we call this receptor 5-HT 4(hb) . This novel receptor variant was expressed transiently in COS-7 cells, and its pharmacological profile was compared with those of the previously cloned 5-HT 4(a) and 5-HT 4(b) isoforms, with the latter being the primary reference for the h variant. In competition binding experiments using reference 5-HT 4 ligands, no significant differences were detected. However, the broadly used 5-HT 4 antagonist GR113808 discriminated functionally among the receptor variants investigated. As expected, it was an antagonist on the 5-HT 4(a) and 5-HT 4(b) variant but showed partial agonistic activity on the 5-HT 4(hb) variant. These data emphasize the importance of variations introduced by splicing for receptor pharmacology and may help in the understanding of conflicting results seen with 5-HT 4 ligands in different model systems. Key Words: Serotonin 5-HT 4 receptor-Serotonin 5-HT 4(hb) variantSplice variant-G protein-coupled receptor-Gene structure -Human-Serotonin.

Enhancement of the intrinsic defecation reflex by mosapride, a 5-HT4 agonist, in chronically lumbosacral denervated guinea pigs

“…The 5-HT4 receptor is a member of the seven transmembrane spanning G-protein-coupled family of receptors (Liu et al, 2005). The 5-HT4 receptor is thought to be coupled by Gs to the stimulation of adenylyl cyclase, increase in cAMP, and activation of PKA (Bender et al, 2000;Bockaert et al, 1990;Liu et al, 2005). The 5-HT4 receptor is pharmacologically defined by selective agonists such as SC 53116 and RS 67506, and selective antagonists such as GR 113808, SB 204070 and RS 39604 (Gale et al, 1994;Hegde et al, 1996).…”

Uncoupling and Endocytosis of 5-Hydroxytryptamine 4 Receptors

“…They are implicated in important physiological functions such as memory, cognition, feeding, respiratory control, and gastrointestinal motility (3)(4)(5)(6). Among the G protein-coupled receptor (GPCR) genes, the 5-HT 4 R gene is one of the largest (700 kb) (7,8). To date, nine variants have been cloned in human, four in mouse, and three in rat.…”

Constitutive dimerization of human serotonin 5‐HT4 receptors in living cells

“…The 5-HT 4 R is indeed one of the G-protein-coupled receptors (GPCRs) for which alternative mRNA splicing generates the most variants that differ in their C-terminal extremities [6]. In human, they are coded by a single and very complex gene which generates ten carboxy-terminal splice variants [7][8][9]. All 5-HT 4 R isoforms share the same ligand binding domain and are positively coupled to adenylyl cyclase.…”