title: Novel G423S mutation of human alpha7 nicotinic receptor promotes agonist-induced desensitization by a protein kinase C-dependent mechanism.
abstract: The alpha7 nicotinic acetylcholine receptor subunit (CHRNA7) gene harbors a high degree of polymorphism. In this study, we found a novel variant (1267 G to A) in exon 10 of the CHRNA7 gene in a Japanese population. This variant results in glycine-to-serine substitution at position 423 (G423S) located in the large cytoplasmic loop of the protein. To clarify the possibility that the G423S mutation alters the pharmacological properties of alpha7 receptors, acetylcholine (ACh)-elicited current through alpha7-G423S mutant receptors expressed in Xenopus laevis oocytes was measured using the two-electrode voltage-clamp technique. We found that the current elicited by ACh (1 mM, 5 s) through alpha7-G423S receptors, but not through alpha7 receptors, was significantly decreased by treatment with a protein kinase C activator, phorbol-12-myristate-13-acetate (PMA, 10-30 nM). In addition, PMA (10 nM) selectively promoted a progressive decrease in alpha7-G423S current induced by repetitive application of ACh pulses (1 mM, 0.1 s, 0.17-0.33 Hz) compared with alpha7 current. PMA also enhanced the inactivation of alpha7-G423S mutant receptors induced by a prolonged application of choline (30 microM) without affecting alpha7 receptor responses. Western blot analysis showed that the treatment with PMA (30 nM) increased the serine phosphorylation level of the alpha7-G423S mutant receptors but not that of the wild-type receptors. These findings demonstrate that the G423S mutation promotes receptor desensitization by a protein kinase C-dependent mechanism. Thus, we provide the first evidence that a variant in the human CHRNA7 gene alters the function of alpha7 nicotinic receptors.
authors.affiliation: Department of Clinical Pharmacology, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan. htsuneki@pha.u-toyama.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tsuneki
authors.forename: Soushi
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Kazue
authors.initials: K
authors.lastname: Takagi
authors.forename: Syota
authors.initials: S
authors.lastname: Kagawa
authors.forename: Masahiko
authors.initials: M
authors.lastname: Tsunoda
authors.forename: Masahiko
authors.initials: M
authors.lastname: Murata
authors.forename: Tadasu
authors.initials: T
authors.lastname: Matsuoka
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Wada
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Kurachi
authors.forename: Ikuko
authors.initials: I
authors.lastname: Kimura
authors.forename: Toshiyasu
authors.initials: T
authors.lastname: Sasaoka
mesh_terms: D000328:Adult; D000818:Animals; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009154:Mutation; D018722:Nicotinic Agonists / Q000494:pharmacology*; D010766:Phosphorylation; D020641:Polymorphism, Single Nucleotide; D011493:Protein Kinase C / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D013329:Structure-Activity Relationship; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014982:Xenopus laevis; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: C579167:Chrna7 protein, human; D018722:Nicotinic Agonists; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate