Wang_2014_J.Biol.Chem_289_26451

The alpha7 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, CHRFAM7ADelta2bp, which is also associated with schizophrenia. To understand the effects of the duplicated subunits on alpha7 receptors, we fused alpha7, dupalpha7, and dupDeltaalpha7 subunits with various fluorescent proteins. The duplicated subunits co-localized with full-length alpha7 subunits in mouse neuroblastoma cells (Neuro2a) as well as rat hippocampal neurons. We investigated the interaction between the duplicated subunits and full-length alpha7 by measuring Forster resonance energy transfer using donor recovery after photobleaching and fluorescence lifetime imaging microscopy. The results revealed that the duplicated proteins co-assemble with alpha7. In electrophysiological studies, Leu at the 9'-position in the M2 membrane-spanning segment was replaced with Cys in dupalpha7 or dupDeltaalpha7, and constructs were co-transfected with full-length alpha7 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 dupalpha7 and dupDeltaalpha7 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 alpha7 subunits and alter the function of the nAChRs. The characterization of dupalpha7 and dupDeltaalpha7 as well as their influence on alpha7 nAChRs may help explain the pathophysiology of schizophrenia and may suggest therapeutic strategies.