Decreased subunit stability as a novel mechanism for potassium current impairment by a KCNQ2 C terminus mutation causing benign familial neonatal convulsions.
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.
Soldovieri
Maria Virginia
MV
Division of Pharmacology, Department of Neuroscience, University of Naples Federico II, 80131 Naples.
Castaldo
Pasqualina
P
Iodice
Luisa
L
Miceli
Francesco
F
Barrese
Vincenzo
V
Bellini
Giulia
G
Miraglia del Giudice
Emanuele
E
Pascotto
Antonio
A
Bonatti
Stefano
S
Annunziato
Lucio
L
Taglialatela
Maurizio
M
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
D051658:KCNQ2 Potassium Channel; D051659:KCNQ3 Potassium Channel; D021122:Protein Subunits; D049452:Green Fluorescent Proteins