Dynamic regulation of ER‐PM junctions facilitates PI(4,5)P2 replenishment during receptor‐induced Ca2+ signaling (599.3)

Abstract

ER‐PM junctions are membrane interfaces between the endoplasmic reticulum (ER) and the plasma membrane (PM), permitting direct molecular interactions and exchange of signals between the two subcellular compartments. ER‐PM junctions have been implicated as important subcellular loci for lipid metabolism and calcium signaling. However, the molecular mechanisms underlying the regulation and functions of ER‐PM junctions are not well understood. Using a genetically‐encoded marker and live‐cell imaging, we found that ER‐PM junctions are dynamically regulated during calcium signaling. Elevation of cytosolic calcium induces the translocation of the ER membrane protein extended synaptotagmin‐1 (E‐Syt1) to ER‐PM junctions and enhances ER‐to‐PM connection. E‐Syt1‐mediated enhanced ER‐to‐PM connection facilitates the recruitment of Nir2, a phosphatidylinositol (PI) transfer protein, to ER‐PM junctions during receptor‐induced calcium signaling. Nir2 promotes replenishment of PM PI(4,5)P2 following receptor‐induced hydrolysis. Disruption of the enhanced ER‐to‐PM connection or Nir2 expression resulted in reduced PM PI(4,5)P2 replenishment and defective calcium signaling. These results demonstrate that calcium‐mediated dynamic regulation of ER‐PM junctions is crucial for maintaining PI(4,5)P2 levels at the PM and sustaining calcium signaling.