title: Alternative splicing of the GABA(A) receptor alpha 4 subunit creates a severely truncated mRNA.
abstract: GABA(A) receptors, important sites of drug action, are chloride channels composed of 5 subunits chosen from among 19 or more. Alternative splicing for alpha 5, alpha 6, and rho 1 subunits results in truncated proteins which appear to lack function. We report a similar, relatively common (about 20%) form of alternative splicing of the alpha 4 subunit mRNA in mice and humans which, remarkably, creates a severely truncated message containing only the first two and last coding exons, with a frameshift in between. The only apparent translation product includes a short piece (39 amino acids) of the N-terminus right after the signal peptide. The splicing was developmentally and regionally regulated; the highest proportions of truncated alpha 4 mRNA, about 40%, were observed in embryonic day 18 whole brain and adult cerebellum. The truncated mRNA, when coexpresssed in human embryonic kidney (HEK) 293 cells with the complete alpha 4 subunit and beta1 and gamma 2 S subunits, reduced observed GABA currents without kinetic alterations. No such effect of truncated alpha 4 was observed with alpha1 subunit-containing receptors. Thus, the truncated alpha 4 N-terminus may play a post-translational regulatory role in intracellular folding/glycosylation/assembly of the alpha 4 subunit.
authors.affiliation: Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, MD 21201-1559, USA. dburt@umaryland.edu
authors.forename: Weitong
authors.initials: W
authors.lastname: Mu
authors.forename: Qing
authors.initials: Q
authors.lastname: Cheng
authors.forename: Jay
authors.initials: J
authors.lastname: Yang
authors.forename: David R
authors.initials: DR
authors.lastname: Burt
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000502:physiology; D002478:Cells, Cultured; D002531:Cerebellum / Q000502:physiology; D004594:Electrophysiology; D004622:Embryo, Mammalian / Q000502:physiology; D006801:Humans; D007668:Kidney / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics*; D011963:Receptors, GABA-A / Q000032:analysis / Q000096:biosynthesis / Q000235:genetics*; D017423:Sequence Analysis, RNA
chemical_list: D012333:RNA, Messenger; D011963:Receptors, GABA-A