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: Maria Virginia Soldovieri, Pasqualina Castaldo, Luisa Iodice, Francesco Miceli, Vincenzo Barrese, Giulia Bellini, Emanuele Miraglia del Giudice, Antonio Pascotto, Stefano Bonatti, Lucio Annunziato, Maurizio Taglialatela
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 281 Issue 1 Pg. 418-28 (Jan 06 2006) ISSN: 0021-9258 [Print] United States
• PMID: 16260777 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• KCNQ2 Potassium Channel
• KCNQ3 Potassium Channel
• Protein Subunits
• Green Fluorescent Proteins

Topics

• Animals
• CHO Cells
• Carcinoma, Hepatocellular
• Cell Line, Tumor
• Cell Membrane (physiology)
• Cricetinae
• Epilepsy, Benign Neonatal (genetics, physiopathology)
• Frameshift Mutation
• Green Fluorescent Proteins (genetics)
• Humans
• Infant, Newborn
• KCNQ2 Potassium Channel (chemistry, genetics, physiology)
• KCNQ3 Potassium Channel (chemistry, genetics, physiology)
• Liver Neoplasms
• Mutagenesis
• Patch-Clamp Techniques
• Protein Subunits (chemistry, physiology)
• Transfection