Molecular underpinning of intracellular pH regulation on TMEM16F

TMEM16F, a dual functional phospholipid scramblase and ion channel, is important in blood coagulation, skeleton development, HIV infection and cell fusion. Despite the advances in understanding its structure and activation mechanism, how TMEM16F is regulated by intracellular factors remains largely elusive. Here we report that TMEM16F lipid scrambling and ion channel activities are strongly influenced by intracellular pH (pHi). We find that low pHi attenuates whereas high pHi potentiates TMEM16F activation. Our biophysical characterizations pinpoint that the pHi regulatory effects on TMEM16F stem from protonation and deprotonation of the Ca2+ binding sites, which in turn reduces and enhances Ca2+ binding affinity, respectively. We further demonstrate that intracellular alkalization of 0.5 pHi can significantly promote TMEM16F activities in a choriocarcinoma cell line. Our findings thus uncover a regulatory mechanism of TMEM16F by pHi and shine light on understanding the pathophysiological roles of TMEM16F in diseases with dysregulated pHi including cancer.