Characterization of TMEM43 as a novel ion channel

Abstract

TMEM43 is a transmembrane protein with four transmembrane (TM) domains. The TMEM43 gene has been reported to play supportive but critical roles in many human diseases, such as cancer, arrhythmogenic right ventricular cardiomyopathy (ARVC), and auditory neuropathy spectrum disorder (ANSD). However, the direct characterization of the TMEM43 protein is missing. In this study, we examined the function of TMEM43 in vitro. Heterologous expression of TMEM43 demonstrated that TMEM43 is permeable to Na⁺, K⁺, and Cs⁺ ions, indicating that TMEM43 is a nonselective cation channel. The TMEM43-mediated current decreased gradually with lowering external solution pH, further characterizing TMEM43 as an external-pH sensing channel. Utilizing the endogenous cysteine residue at TM3, we could predict that the pore-forming residue of TMEM43 lies near TM3 and Loop2 domain. Importantly, stochastic channel openings from the lipid bilayer-reconstituted purified TMEM43 protein were observed, strengthening the proposal of TMEM43 as an ion channel. Lastly, the heterologous expression of TMEM43-p.(Arg372Ter) resulted in a loss of channel activity in a dominant-negative fashion, as in the hearing loss phenotype in humans. These results together disclose the molecular and functional properties of TMEM43 and identify TMEM43 as a novel ion channel. The physiological identity of TMEM43 provided in this study will promote future research on TMEM43-related diseases.