Remodeling of the Cytoskeleton and Regulation of Store-Operated Calcium Entry

Store-operated calcium entry (SOCE) is a critical Ca2+ entry and is activated by ER-Ca2+ store depletion while refilling the stores leads inactivation of the process. STIM1 is the main Ca2+ sensor protein in the ER that responds to store depletion, aggregates and translocates to ER-PM junctional domains, where it interacts with, and activates, the channels mediating SOCE, such as Orai1. However, little is known about other proteins that interact with STIM1 to facilitate the regulation of SOCE. In this study, we identified 155 specific STIM1 binding partners using a shotgun proteomic approach on STIM1 immunoprecipitated complex from HSG cell lysates. In order to determine quantitative changes in the STIM1 proteome during stimulation status, mixtures of lysates from control cells and stimulated cells with Tg were analyzed using a SILAC (Stable Isotope Labeling by Amino acids in Cell culture) approach. Our analysis reveal several interesting changes in the STIM1 proteome upon stimulation. As a result of the SILAC findings, we found that cytoskeletal interacting/remodeling proteins such as CDC42, ARP2, N-WASP, and zyxin interact with STIM1 and Orai1. In addition to inducing changes in cell morphology and actin cytoskeleton, some of these also significantly impact SOCE. Together, our data suggest that cytoskeletal remodeling has an important role in the assembly of the Orai1-STIM1 complex and regulation of SOCE.