title: Decreased subunit stability as a novel mechanism for potassium current impairment by a KCNQ2 C terminus mutation causing benign familial neonatal convulsions.
abstract: KCNQ2 and KCNQ3 K+ channel subunits underlie the muscarinic-regulated K+ current (I(KM)), a widespread regulator of neuronal excitability. Mutations in KCNQ2- or KCNQ3-encoding genes cause benign familiar neonatal convulsions (BFNCs), a rare autosomal-dominant idiopathic epilepsy of the newborn. In the present study, we have investigated, by means of electrophysiological, biochemical, and immunocytochemical techniques in transiently transfected cells, the consequences prompted by a BFNC-causing 1-bp deletion (2043deltaT) in the KCNQ2 gene; this frameshift mutation caused the substitution of the last 163 amino acids of the KCNQ2 C terminus and the extension of the subunit by additional 56 residues. The 2043deltaT mutation abolished voltage-gated K+ currents produced upon homomeric expression of KCNQ2 subunits, dramatically reduced the steady-state cellular levels of KCNQ2 subunits, and prevented their delivery to the plasma membrane. Metabolic labeling experiments revealed that mutant KCNQ2 subunits underwent faster degradation; 10-h treatment with the proteasomal inhibitor MG132 (20 microm) at least partially reversed such enhanced degradation. Co-expression with KCNQ3 subunits reduced the degradation rate of mutant KCNQ2 subunits and led to their expression on the plasma membrane. Finally, co-expression of KCNQ2 2043deltaT together with KCNQ3 subunits generated functional voltage-gated K+ currents having pharmacological and biophysical properties of heteromeric channels. Collectively, the present results suggest that mutation-induced reduced stability of KCNQ2 subunits may cause epilepsy in neonates.
authors.affiliation: Division of Pharmacology, Department of Neuroscience, University of Naples Federico II, 80131 Naples.
authors.forename: Maria Virginia
authors.initials: MV
authors.lastname: Soldovieri
authors.forename: Pasqualina
authors.initials: P
authors.lastname: Castaldo
authors.forename: Luisa
authors.initials: L
authors.lastname: Iodice
authors.forename: Francesco
authors.initials: F
authors.lastname: Miceli
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Barrese
authors.forename: Giulia
authors.initials: G
authors.lastname: Bellini
authors.forename: Emanuele
authors.initials: E
authors.lastname: Miraglia del Giudice
authors.forename: Antonio
authors.initials: A
authors.lastname: Pascotto
authors.forename: Stefano
authors.initials: S
authors.lastname: Bonatti
authors.forename: Lucio
authors.initials: L
authors.lastname: Annunziato
authors.forename: Maurizio
authors.initials: M
authors.lastname: Taglialatela
mesh_terms: D000818:Animals; D016466:CHO Cells; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000502:physiology; D006224:Cricetinae; D020936:Epilepsy, Benign Neonatal / Q000235:genetics* / Q000503:physiopathology; D016368:Frameshift Mutation; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D007231:Infant, Newborn; D051658:KCNQ2 Potassium Channel / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D051659:KCNQ3 Potassium Channel / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D008113:Liver Neoplasms; D016296:Mutagenesis; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000737:chemistry / Q000502:physiology*; D014162:Transfection
chemical_list: D051658:KCNQ2 Potassium Channel; D051659:KCNQ3 Potassium Channel; D021122:Protein Subunits; D049452:Green Fluorescent Proteins