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Junctophilin-4, a component of the endoplasmic reticulum-plasma membrane junctions, regulates Ca2+ dynamics in T
Jin Seok Woo1, Sonal Srikanth1, Miyuki Nishi2
1Department of Physiology, David Geffen School of Medicine at the University of California, Los Angeles, Los Angeles, CA 90095;
Insights
Junctophilin-4 (JP4) regulates calcium signaling in T cells by interacting with STIM1 at ER-PM junctions. This interaction is crucial for maintaining calcium homeostasis and immune cell activation.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Store-operated Ca(2+) entry (SOCE) is vital for immune cell function, mediated by Orai1 and STIM1.
- The precise molecular architecture of ER-PM junctions in T cells, where STIM1 interacts with Orai1, is not fully understood.
Purpose of the Study:
- To investigate the role of junctophilin-4 (JP4) in T cell calcium signaling and SOCE.
- To elucidate the molecular mechanisms by which JP4 regulates ER-PM junctions and STIM1 localization.
Main Methods:
- Utilized genetic manipulation (silencing/expression) and biochemical assays to study JP4 function in T cells.
- Investigated JP4 localization at ER-PM junctions and its interaction with STIM1 and junctate.
- Assessed the impact of JP4 on ER Ca(2+) content, SOCE, NFAT/ERK signaling, and T cell activation markers.
Main Results:
- JP4 is expressed in T cells and localizes to ER-PM junctions, regulating Ca(2+) signaling.
- JP4 deficiency reduced ER Ca(2+) levels, impaired SOCE, and diminished T cell activation pathways (NFAT, ERK) and cytokine production.
- JP4 directly binds STIM1 and facilitates its junctional recruitment, while also forming a complex with junctate.
Conclusions:
- JP4 is a key regulator of SOCE in T cells by organizing ER-PM junctions.
- The junctate-JP4 complex cooperates with STIM1 to maintain ER Ca(2+) homeostasis and support T cell activation.
- JP4 represents a potential therapeutic target for modulating T cell-mediated immune responses.
Abstract:
Orai1 and stromal interaction molecule 1 (STIM1) mediate store-operated Ca(2+) entry (SOCE) in immune cells. STIM1, an endoplasmic reticulum (ER) Ca(2+) sensor, detects store depletion and interacts with plasma membrane (PM)-resident Orai1 channels at the ER-PM junctions. However, the molecular composition of these junctions in T cells remains poorly understood. Here, we show that junctophilin-4 (JP4), a member of junctional proteins in excitable cells, is expressed in T cells and localized at the ER-PM junctions to regulate Ca(2+) signaling. Silencing or genetic manipulation of JP4 decreased ER Ca(2+) content and SOCE in T cells, impaired activation of the nuclear factor of activated T cells (NFAT) and extracellular signaling-related kinase (ERK) signaling pathways, and diminished expression of activation markers and cytokines. Mechanistically, JP4 directly interacted with STIM1 via its cytoplasmic domain and facilitated its recruitment into the junctions. Accordingly, expression of this cytoplasmic fragment of JP4 inhibited SOCE. Furthermore, JP4 also formed a complex with junctate, a Ca(2+)-sensing ER-resident protein, previously shown to mediate STIM1 recruitment into the junctions. We propose that the junctate-JP4 complex located at the junctions cooperatively interacts with STIM1 to maintain ER Ca(2+) homeostasis and mediate SOCE in T cells.
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