An siRNA screen for NFAT activation identifies septins as coordinators of store-operated Ca2+ entry

摘要

The STIM1-ORAI1 pathway of store-operated Ca²⁺ entry is an essential component of cellular Ca²⁺ signaling. STIM1 senses depletion of intracellular Ca²⁺ stores in response to physiological stimuli, and relocalises within the endoplasmic reticulum (ER) to plasma membrane (PM)-apposed junctions, where it recruits and gates open plasma membrane ORAI1 Ca²⁺ channels. Here we used a genome-wide RNAi screen to identify filamentous septin proteins as critical regulators of store-operated Ca²⁺ entry. Septin filaments and phosphatidylinositol 4,5-bisphosphate (PIP2) rearrange locally at ER-PM junctions prior to and during formation of STIM1-ORAI1 clusters, facilitating STIM1 targeting to these junctions and promoting the stable recruitment of ORAI1. Septin rearrangement at junctions is required for PIP2 reorganisation and efficient STIM1-ORAI1 communication. Septins are known to demarcate specialized membrane regions such as dendritic spines, the yeast bud, and the primary cilium, and to serve as membrane diffusion barriers and/or signaling hubs in cellular processes including vesicle trafficking, cell polarity, and cytokinesis^–. Our data show that septins also organise the highly localised plasma membrane domains important in STIM1-ORAI1 signaling, and indicate that septins may organise membrane microdomains relevant to other signaling processes.