title: The duplicated α7 subunits assemble and form functional nicotinic receptors with the full-length α7.
abstract: The α7 nicotinic acetylcholine receptor gene (CHRNA7) is linked to schizophrenia. A partial duplication of CHRNA7 (CHRFAM7A) is found in humans on 15q13-14. Exon 6 of CHRFAM7A harbors a 2-bp deletion polymorphism, CHRFAM7AΔ2bp, which is also associated with schizophrenia. To understand the effects of the duplicated subunits on α7 receptors, we fused α7, dupα7, and dupΔα7 subunits with various fluorescent proteins. The duplicated subunits co-localized with full-length α7 subunits in mouse neuroblastoma cells (Neuro2a) as well as rat hippocampal neurons. We investigated the interaction between the duplicated subunits and full-length α7 by measuring Förster resonance energy transfer using donor recovery after photobleaching and fluorescence lifetime imaging microscopy. The results revealed that the duplicated proteins co-assemble with α7. In electrophysiological studies, Leu at the 9'-position in the M2 membrane-spanning segment was replaced with Cys in dupα7 or dupΔα7, and constructs were co-transfected with full-length α7 in Neuro2a cells. Exposure to ethylammonium methanethiosulfonate inhibited acetylcholine-induced currents, showing that the assembled functional nicotinic acetylcholine receptors (nAChRs) included the duplicated subunit. Incorporation of dupα7 and dupΔα7 subunits modestly changes the sensitivity of receptors to choline and varenicline. Thus, the duplicated proteins are assembled and transported to the cell membrane together with full-length α7 subunits and alter the function of the nAChRs. The characterization of dupα7 and dupΔα7 as well as their influence on α7 nAChRs may help explain the pathophysiology of schizophrenia and may suggest therapeutic strategies.
authors: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125 and.
authors: Ying
authors: Y
authors: Wang
authors: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125 and.
authors: Cheng
authors: C
authors: Xiao
authors: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125 and.
authors: Tim
authors: T
authors: Indersmitten
authors: Department of Psychiatry, University of Colorado at Denver, Denver, Colorado 80045.
authors: Robert
authors: R
authors: Freedman
authors: Department of Psychiatry, University of Colorado at Denver, Denver, Colorado 80045.
authors: Sherry
authors: S
authors: Leonard
authors: Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125 and. Electronic address: lester@caltech.edu.
authors: Henry A
authors: HA
authors: Lester
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D045744:Cell Line, Tumor; D002794:Choline / Q000494:pharmacology; D020440:Gene Duplication; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D018722:Nicotinic Agonists / Q000494:pharmacology; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D012559:Schizophrenia / Q000235:genetics; D017384:Sequence Deletion; D000068580:Varenicline; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000235:genetics / Q000378:metabolism*
chemical_list: D001552:Benzazepines; D018722:Nicotinic Agonists; D021122:Protein Subunits; D011810:Quinoxalines; D064569:alpha7 Nicotinic Acetylcholine Receptor; D002794:Choline; D000109:Acetylcholine; D000068580:Varenicline
keywords: Choline; Electrophysiology; Fluorescence Recovery after Photobleaching (FRAP); Fluorescence Resonance Energy Transfer (FRET); Genomics; Ion Channel; Ligand-gated Channel; Nicotinic Acetylcholine Receptors (nAChR); Patch Clamp; Schizophrenia