TRPM7 is an essential regulator for volume-sensitive outwardly rectifying anion channel

Tomohiro Numata,Kaori Sato-Numata,Yasuo Mori,Meredith C Hermosura,Yasunobu Okada

doi:10.1038/s42003-021-02127-9

Abstract

Animal cells can regulate their volume after swelling by the regulatory volume decrease (RVD) mechanism. In epithelial cells, RVD is attained through KCl release mediated via volume-sensitive outwardly rectifying Cl− channels (VSOR) and Ca2+-activated K+ channels. Swelling-induced activation of TRPM7 cation channels leads to Ca2+ influx, thereby stimulating the K+ channels. Here, we examined whether TRPM7 plays any role in VSOR activation. When TRPM7 was knocked down in human HeLa cells or knocked out in chicken DT40 cells, not only TRPM7 activity and RVD efficacy but also VSOR activity were suppressed. Heterologous expression of TRPM7 in TRPM7-deficient DT40 cells rescued both VSOR activity and RVD, accompanied by an increase in the expression of LRRC8A, a core molecule of VSOR. TRPM7 exerts the facilitating action on VSOR activity first by enhancing molecular expression of LRRC8A mRNA through the mediation of steady-state Ca2+ influx and second by stabilizing the plasmalemmal expression of LRRC8A protein through the interaction between LRRC8A and the C-terminal domain of TRPM7. Therefore, TRPM7 functions as an essential regulator of VSOR activity and LRRC8A expression.

Highlights

Animal cells can regulate their volume after swelling by the regulatory volume decrease (RVD) mechanism
We found that expression of hLRRC8A mRNA was reduced to 59.4 ± 3.3% (n = 5) in HeLa cells treated with TRPM7siRNA (Fig. 1c and Supplementary Fig. 3a)
These results indicate that both LRRC8A expression and volume-sensitive outwardly rectifying Cl− channels (VSOR) activity are closely correlated with TRPM7 expression

Summary

Introduction

Animal cells can regulate their volume after swelling by the regulatory volume decrease (RVD) mechanism. RVD is attained through KCl release mediated via volume-sensitive outwardly rectifying Cl− channels (VSOR) and Ca2+-activated K+ channels. Volume-regulatory KCl release was shown to primarily result from parallel activation of the volume-sensitive Cl− channels and Ca2+-activated K+ channels[3,4,5], the latter identified later as IK16. Activation of these volume-regulatory channels is preceded by activation of a type of nonselective cation channels[7,8,9], which was recently identified as TRPM7 in human epithelial cells and shown to be induced by membrane stretch associated with osmotic cell swelling[10]. We demonstrate that TRPM7 expression is essential for LRRC8A expression and VSOR activity and, thereby playing a crucial prerequisite role in the RVD process

Methods

Results

Conclusion