Store-operated calcium entry (SOCE) is triggered by assembly of Orai1 with STIM proteins in ER-PM junctions. Plasma membrane PIP₂ as well as PIP₂-binding protein, SEPT4, significantly impact Orai1-STIM1 interaction. While septins and PIP₂ can organize the actin cytoskeleton, it is unclear whether the status of actin within the junctions contributes to SOCE. We report herein that actin remodeling modulates STIM1 clustering. Our findings show that a PIP₂- and SEPT4-dependent mechanism involving CDC42, WASP/WAVE, and ARP2 regulates actin remodeling into a ring-like structure around STIM1 puncta. CDC42 localization in the ER-plasma membrane region is enhanced following ER-Ca²⁺ store depletion. PIP₂ depletion or knockdown of SEPT4 attenuate the recruitment of CDC42 to the ER-PM region. Importantly, knockdown of SEPT4, or CDC42+ARP2, disrupts the organization of actin as well as STIM1 clustering. Consequently, Orai1 recruitment to STIM1 puncta, SOCE, and NFAT translocation to the nucleus are all attenuated. Ca²⁺ influx induced by STIM1-C terminus is not affected by CDC42 knockdown. In aggregate, our findings reveal that PIP₂ and SEPT4 affect Orai1/STIM1 clustering by coordinating actin remodeling within ER-PM junctions. This dynamic reorganization of actin has an important role in regulation of SOCE and downstream Ca²⁺-dependent effector functions.

储存操作的钙进入 (SOCE) 是由 Orai1 与 ER-PM 连接处的 STIM 蛋白组装触发的。质膜 PIP ₂以及 PIP ₂结合蛋白 SEPT4 显着影响 Orai1-STIM1 相互作用。虽然 septins 和 PIP ₂可以组织肌动蛋白细胞骨架，但尚不清楚连接内肌动蛋白的状态是否有助于 SOCE。我们在此报告肌动蛋白重塑调节 STIM1 聚类。我们的研究结果表明，涉及 CDC42、WASP/WAVE 和 ARP2 的 PIP ₂和 SEPT4 依赖机制调节肌动蛋白重塑为 STIM1 斑点周围的环状结构。^{ER-Ca 2+}储存耗尽后，CDC42 在 ER 质膜区域的定位增强。画中画₂SEPT4 的消耗或敲低会减弱 CDC42 向 ER-PM 区域的募集。重要的是，敲除 SEPT4 或 CDC42+ARP2 会破坏肌动蛋白的组织以及 STIM1 聚类。因此，向 STIM1 puncta、SOCE 和 NFAT 易位到细胞核的 Orai1 募集都减弱了。由 STIM1-C 末端诱导的Ca ²⁺流入不受 CDC42 敲低的影响。总之，我们的研究结果表明，PIP ₂和 SEPT4 通过协调 ER-PM 连接内的肌动蛋白重塑来影响 Orai1/STIM1 聚类。^{肌动蛋白的这种动态重组在调节 SOCE 和下游 Ca 2+}依赖性效应器功能中具有重要作用。