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

Abstract

Despite advances in identifying deafness genes, determination of the underlying cellular and functional mechanisms for auditory diseases remains a challenge. Mutations of the human K ؉ channel hKv7.4 lead to post-lingual progressive hearing loss (DFNA2), which affects world-wide population with diverse racial backgrounds. Here, we have generated the spectrum of point mutations in the hKv7.4 that have been identified as diseased mutants. We report that expression of five point mutations in the pore region, namely L274H, W276S, L281S, G285C, and G296S, as well as the C-terminal mutant G321S in the heterologous expression system, yielded nonfunctional channels because of endoplasmic reticulum retention of the mutant channels. We mimicked the dominant diseased conditions by co-expressing the wild-type and mutant channels. As compared with expression of wild-type channel alone, the blend of wild-type and mutant channel subunits resulted in reduced currents. Moreover, the combinatorial ratios of wild type:mutant and the ensuing current magnitude could not be explained by the predictions of a tetrameric channel and a dominant negative effect of the mutant subunits. The results can be explained by the dependence of cell surface expression of the mutant on the wild-type subunit. Surprisingly, a transmembrane mutation F182L, which has been identified in a pre-lingual progressive hearing loss patient in Taiwan, yielded cell surface expression and functional features that were similar to that of the wild type, suggesting that this mutation may represent redundant polymorphism. Collectively, these findings provide traces of the cellular mechanisms for DFNA2.

Mechanisms of Calmodulin Regulation of Different Isoforms of Kv7.4 K+ Channels

“…These findings are in keeping with a previous report that determined that Kv7.4 G321S , when expressed alone, had impaired membrane trafficking. However, co-expression of the MT with the WT subunits facilitated membrane trafficking of the MT subunits (26). As shown in Fig.…”

“…Current traces were amplified, filtered (bandpass, 2-10 kHz), and digitized at 5-500 kHz using an analog-to-digital converter, Digidata 1322A (Molecular Devices), as described earlier (26). Fire-polished electrodes (3-5 M⍀) were pulled from borosilicate glass.…”

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.…”

Functional Significance of K+ Channel β-Subunit KCNE3 in Auditory Neurons

“…The bath solution was perfused (2-3 ml/min) constantly. The liquid junction potentials were measured and corrected as described (28,29). All recordings were carried out at room temperature (20 -21°C).…”

“…Ϫ/Ϫ SGNs from Pre-hearing to Post-hearing Era-KCNE3 has been shown to associate with and regulate the activity of several Kv ␣-subunits in heterologous expression systems (28,33). Although these previous reports have established, to a large extent, the unrestrained nature of the ␤-subunit KCNE3 interaction with multiple Kv channels, it remains to be demonstrated which of these associations produces a physiological impact in SGNs.…”