ABSTRACT: TMEM16/
anoctamin (ANO)
proteins form Ca2+ -activated
ion channels or
phospholipid scramblases. We found that both TMEM16A/ANO1 and TMEM16F/ANO6 produced Cl- currents when activated by intracellular Ca2+ , but only TMEM16F was able to expose
phosphatidylserine to the outer leaflet of the plasma membrane. Mutations within TMEM16F or TMEM16A/F chimeras similarly changed Cl- currents and
phospholipid scrambling, suggesting the same intramolecular pathway for Cl- and
phospholipids. When overexpressed, TMEM16A and TMEM16F produced spontaneous Cl- currents at 37°C even at resting intracellular Ca2+ levels, which was abolished by inhibition of
phospholipase A2 (PLA2 ). Connversely, activation of PLA2 or application of active PLA2 , as well as lipid peroxidation induced by
reactive oxygen species (ROS) using
staurosporine or
tert-butyl hydroperoxide, enhanced ion currents by TMEM16A/F and in addition activated
phospholipid scrambling by TMEM16F. Thus,
TMEM16 proteins are activated by an increase in intracellular Ca2+ , or independent of intracellular Ca2+ , by modifications occurring in plasma and intracellular membrane
phospholipids. These results may help to explain why regions distant to the TMEM16 pore and the Ca2+ binding sites control Cl- currents and
phospholipid scrambling. Regulation of
TMEM16 proteins through modification of membrane
phospholipids occurs during regulated cell death such as apoptosis and ferroptosis. It contributes to inflammatory and nerve injury-induced
hypersensitivity and generation of
pain and therefore provides a regulatory mechanism that is particularly relevant during disease.