KCNQ1 rescues TMC1 plasma membrane expression but not mechanosensitive channel activity

Abstract

Transmembrane channel‐like protein isoform 1 (TMC1) is essential for the generation of mechano‐electrical transducer currents in hair cells of the inner ear. TMC1 disruption causes hair cell degeneration and deafness in mice and humans. Although thought to be expressed at the cell surface in vivo, TMC1 remains in the endoplasmic reticulum when heterologously expressed in standard cell lines, precluding determination of its roles in mechanosensing and pore formation. Here, we report that the KCNQ1 Kv channel forms complexes with TMC1 and rescues its surface expression when coexpressed in Chinese Hamster Ovary cells. TMC1 rescue is specific for KCNQ1 within the KCNQ family, is prevented by a KCNQ1 trafficking‐deficient mutation, and is influenced by KCNE β subunits and inhibition of KCNQ1 endocytosis. TMC1 lowers KCNQ1 and KCNQ1‐KCNE1 K+ currents, and despite the surface expression, it does not detectably respond to mechanical stimulation or high salt. We conclude that TMC1 is not intrinsically mechano‐ or osmosensitive but has the capacity for cell surface expression, and requires partner protein(s) for surface expression and mechanosensitivity. We suggest that KCNQ1, expression of which is not thought to overlap with TMC1 in hair cells, is a proxy partner bearing structural elements or a sequence motif reminiscent of a true in vivo TMC1 hair cell partner. Discovery of the first reported strategy to rescue TMC1 surface expression should aid future studies of the TMC1 function and native partners.

A Tmc1 mutation reduces calcium permeability and expression of mechanoelectrical transduction channels in cochlear hair cells

“…Neither the configuration nor the role of TMC family members has been clear because of past inability to express the protein in a heterologous system and have it transported to the plasma membrane (19). However, a recent success was reported, but without production of mechanosensitivity (20). Some insight was derived from a possible evolutionary relationship between TMC1 and TMEM16 (ANO1), a Ca 2+ -activated chloride channel (21, 22).…”

A Mechanosensitive Channel, Mouse Transmembrane Channel-Like Protein 1 (mTMC1) Is Translated from a Splice Variant mTmc1ex1 but Not from the Other Variant mTmc1ex2

“…At least, when they were heterologously expressed, their localizations (i.e., retentions in cytosol) were not changed. However, it was recently reported that co-expression of KCNQ1, a K + channel, rescued hTMC1 plasma membrane targeting [9] although KCNQ1 is not thought to be an endogenous interacting protein of TMC1 in hair cells in the inner ear because of the lack of endogenous expression [9]. If the interaction with KCNQ1 is mediated by the N-terminus of TMC1, the difference between mTMC1ex1 and mTMC1ex2 may affect their interaction with KCNQ1.…”

“…If the interaction with KCNQ1 is mediated by the N-terminus of TMC1, the difference between mTMC1ex1 and mTMC1ex2 may affect their interaction with KCNQ1. Additionally, even when KCNQ1 was co-expressed, channel activities of hTMC1 were not detected, suggesting requirements of other components for the formation of a functional channel by TMC1 [9]. When the functional analyses of TMC1 in heterologous expression systems become possible, the functional differences between mTMC1ex1 and mTMC1ex2 might be revealed.…”

KCNQ and KCNE Isoform-Dependent Pharmacology Rationalizes Native American Dual Use of Specific Plants as Both Analgesics and Gastrointestinal Therapeutics

“…Patch-clamp electrophysiology experiments were performed as before ( Manville et al, 2018 ; Harkcom et al, 2019 ; Tedeschi et al, 2021 ) on CHO cells at room temperature (22–25°C). Using a whole-cell patch configuration under voltage-clamp conditions, data were obtained with an Axopatch Multiclamp 700A apparatus digitized and analyzed using pClamp 9.2 (Axon Instruments, Forster City, CA), together with Graphpad Prism 9 (Graphpad; La Jolla, CA, United States).…”

“…Patch-clamp electrophysiology experiments were performed as before Harkcom et al, 2019;Tedeschi et al, 2021) on CHO cells at room temperature (22-25 (Hampton, NH) or Sigma-Aldrich. Tannic acid was added to the extracellular bath solution at concentrations between 1 and 10 µM.…”