Anoctamin 8 tethers endoplasmic reticulum and plasma membrane for assembly of Ca²⁺ signaling complexes at the ER/PM...

Communication and material transfer between membranes and organelles take place at membrane contact sites (MCSs). MCSs between the ER and PM, the ER/PM junctions, are the sites where the ER Ca²⁺ sensor STIM1 and the PM Ca²⁺ influx channel Orai1 cluster. MCSs are formed by tether proteins that bridge the opposing membranes, but the identity and role of these tethers in receptor-evoked Ca²⁺ signaling is not well understood. Here, we identified Anoctamin 8 (ANO8) as a key tether in the formation of the ER/PM junctions that is essential for STIM1-STIM1 interaction and STIM1-Orai1 interaction and channel activation at a ER/PM PI(4,5)P₂-rich compartment. Moreover, ANO8 assembles all core Ca²⁺ signaling proteins: Orai1, PMCA, STIM1, IP₃ receptors, and SERCA2 at the ER/PM junctions to mediate a novel form of Orai1 channel inactivation by markedly facilitating SERCA2-mediated Ca²⁺ influx into the ER. This controls the efficiency of receptor-stimulated Ca²⁺ signaling, Ca²⁺ oscillations, and duration of Orai1 activity to prevent Ca²⁺ toxicity. These findings reveal the central role of MCSs in determining efficiency and fidelity of cell signaling.