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

A genome-wide RNA interference analysis identifies the septin family of cytoskeletal filaments as important regulators of store-operated Ca 2+ entry into the cell; septins are shown to organize plasma membrane microdomains important in STIM1 and ORAI1 signalling, and may also be relevant in membrane microdomains underlying other signalling processes. Controlling store-operated Ca 2+ entry Cellular Ca 2+ signalling is regulated by STIM (stromal interaction molecule) proteins, which are Ca 2+ sensors in the endoplasmic reticulum that connect Ca 2+ store depletion to the opening of the Ca 2+ release-activated Ca 2+ (CRAC) channels in the plasma membrane. ORAI proteins are the pore subunits of the CRAC channel and control the opening of this channel. Here Sharma et al . present a genome-wide RNA interference analysis designed to identify essential regulators of store-operated Ca 2+ entry. They find that the septin family of cytoskeletal filaments are important regulators of this process, acting via the association between ORAI1 and STIM1. The STIM1–ORAI1 pathway of store-operated Ca 2+ entry is an essential component of cellular Ca 2+ signalling 1 . STIM1 senses depletion of intracellular Ca 2+ stores in response to physiological stimuli, and relocalizes within the endoplasmic reticulum to plasma-membrane-apposed junctions, where it recruits and gates open plasma membrane ORAI1 Ca 2+ channels. Here we use a genome-wide RNA interference screen in HeLa cells to identify filamentous septin proteins as crucial regulators of store-operated Ca 2+ entry. Septin filaments and phosphatidylinositol-4,5-bisphosphate (also known as PtdIns(4,5)P 2 ) rearrange locally at endoplasmic reticulum–plasma membrane junctions before 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 PtdIns(4,5)P 2 reorganization 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 signalling hubs in cellular processes such as vesicle trafficking, cell polarity and cytokinesis 2 , 3 , 4 . Our data show that septins also organize the highly localized plasma membrane domains that are important in STIM1–ORAI1 signalling, and indicate that septins may organize membrane microdomains relevant to other signal