ER membrane protein complex 1 interacts with STIM1 and regulates store-operated Ca²⁺entry

Store-operated calcium entry (SOCE) is the process by which the emptying of endoplasmic reticulum (ER) Ca2+ stores causes an influx of Ca2+ across the plasma membrane (PM). It is the major Ca2+ influx pathway in nonexcitable cells and has a wide array of physiological functions. Upon store depletion, stromal interaction molecule 1 (STIM1), an ER calcium sensor relocates into discrete puncta at the ER-PM junction region, which results in the coupling of Ca2+ channels to initiate SOCE. However, the mechanism regulating STIM1 activity remains poorly understood. Here, we performed affinity purification of STIM1 and uncovered ER membrane protein complex 1 (EMC1) as an STIM1 binding partner. We showed that this interaction occurred in the ER through the intraluminal region of STIM1. After store depletion, EMC1 does not cluster adjacent to the PM, which suggests that it is distributed differently from STIM1. EMC1 knockdown with small interfering RNA resulted in a marked decrease in SOCE. Thus, these findings suggest that EMC1 functions as a positive regulator of SOCE.