A novel KCNQ4 pore-region mutation (p.G296S) causes deafness by impairing cell-surface channel expression

Abstract

Mutations in the potassium channel gene KCNQ4 underlie DFNA2, a subtype of autosomal dominant progressive, high-frequency hearing loss. Based on a phenotype-guided mutational screening we have identified a novel mutation c.886G>A, leading to the p.G296S substitution in the pore region of KCNQ4 channel. The possible impact of this mutation on total KCNQ4 protein expression, relative surface expression and channel function was investigated. When the G296S mutant was expressed in Xenopus oocytes, electrophysiological recordings did not show voltage-activated K(+) currents. The p.G296S mutation impaired KCNQ4 channel activity in two manners. It greatly reduced surface expression and, secondarily, abolished channel function. The deficient expression at the cell surface membrane was further confirmed in non-permeabilized NIH-3T3 cells transfected with the mutant KCNQ4 tagged with the hemagglutinin epitope in the extracellular S1-S2 linker. Co-expression of mutant and wild type KCNQ4 in oocytes was performed to mimic the heterozygous condition of the p.G296S mutation in the patients. The results showed that the G296S mutant exerts a strong dominant-negative effect on potassium currents by reducing the wild type KCNQ4 channel expression at the cell surface. This is the first study to identify a trafficking-dependent dominant mechanism for the loss of KCNQ4 channel function in DFNA2.

Cellular and Molecular Mechanisms of Autosomal Dominant Form of Progressive Hearing Loss, DFNA2

“…In this report, we have confirmed impaired cell surface expression of the pore segment mutation G296S of hKv7.4 (18) and have demonstrated that all known pore region mutations of the channel that have been reported to cause progressive hearing loss in humans (L274H, W276S, L281S, and G285C) exhibit similar expression phenotype. Functionally, none of the pore segment mutants yielded measurable current.…”

“…The remaining two missense mutations are located at S3 and the C-terminal domains. Only two mutant forms, G285S and G296S, have been evaluated at the cellular level to determine the functional implications in heterologous expression system (2,18).…”

Vestibular Role of KCNQ4 and KCNQ5 K+ Channels Revealed by Mouse Models

“…1, A and G). Similar mutations in KCNQ4 are known to interfere with plasma membrane expression (7,33,34). Indeed, neuronal somata in the vestibular ganglion of Kcnq4 dn/dn mice (5), which express the trafficking-deficient G286S mutant (7), showed intense cytoplasmic KCNQ4 labeling (Fig.…”

Identification of a novel in-frame deletion in KCNQ4 (DFNA2A) and evidence of multiple phenocopies of unknown origin in a family with ADSNHL

“…KCNQ4 is a known deafness gene that encodes a potassium channel expressed in the inner and outer ear, and the P-loop is involved in the formation of the tetrameric structure and function of KCNQ4 channels (Figures 2a and c). 11 The c.806_808delCCT mutation predicts the in-frame deletion of serine at position 269 (p.S269del) within the conserved N-terminal region of the P-loop of KCNQ4. Twelve other deaf relatives were also heterozygous for the p.S269del variant, which was absent in all unaffected relatives ( Figure 1).…”