STIM1

cGAS–STING通路是一种进化上保守的免疫信号通路，对微生物防御至关重要（STING：天然免疫新核心，免疫治疗新靶点）。与其他主要依赖于固定信号事件的先天免疫途径不同，STING在细胞中具有高度的流动性，流动性异常与神经退行性疾病等相关。STINGSTING是一种跨膜蛋白，以二聚体的形式存在于内质网上，其CDN结合结构域面对细胞质。在配体结合之前，每个STING单体的连接区域被交叉，配体结合结构域位于各自的跨膜结构域的另一侧。cGAMP的结合诱导了连接体区域的结构重排，其中配体结合结构域被旋转到与跨膜结构域平行。这种旋转被认为是STING激活和内质网通过COPII囊泡离开的关键。然后STING易位到内质网中间室（ERGIC）和高尔基体，在那里它招募激酶TBK1，它磷酸化STING本身和转录因子IRF3。磷酸化的IRF3易位到细胞核，启动IFN-I基因和ISGs的转录。此外，在这一过程中，STING激活了其他IFN非依赖的信号通路，分子细节未知。STING囊泡然后退出反式高尔基网络（TGN），继续前往核内体和溶酶体，在那里，STING囊泡最终被降解以终止信号传导。STING转运三步1. STING在内质网上STING不包含将其引导到内质网的信号序列，但为什么STING定位于内质网，并保持在内质网?帮助内质网保持STING的过程包括Ca2+传感器基质相互作用分子1（STIM1）和逆行COPII囊泡运输。STIM1通过钙通道控制Ca2+进入内质网，这在淋巴细胞的激活和增殖中至关重要。STIM1也通过直接绑定STING的ER保留因子。使用2,3-cGAMP的刺激会破坏这种相互作用，从而允许STING内质网退出。STIM1的缺失从内质网释放出STING，导致tonic IFN-I信号。所以STIM1缺陷的患者同时出现淋巴细胞减少（由于淋巴细胞中的钙通量缺陷）和自身免疫病。高尔基体-内质网逆行穿梭也起着重要作用。STING不是简单地固定在静息状态下的内质网上；相反，它通过分泌途径不断移动。内质网保留因素和逆行穿梭的结合可能建立了STING内质网定位的“表象”。此外，还有其他的辅助因子负责调节内质网上的STING蛋白水平，包括toll相互作用蛋白（TOLLIP）、E3泛素连接酶三部分基序蛋白30α（TRIM30α）和PTPN1/ 2，它们分别调节稳态下STING的溶酶体和蛋白酶体降解。2. 从内质网转移至高尔基体配体结合后，STING开始从内质网易位到高尔基体，这个过程需要COPII囊泡的组装。Sar1、Sec13、和Sec31的丢失阻止了STING配体结合时离开内质网，并减弱了STING信号。除了经典的COPII囊泡装置外，内质网上的其他一些蛋白质和复合物对STING从内质网到高尔基体的运输也很重要。在没有转位子复合物成分TRAPβ的情况下，配体诱导的STING运输被阻止。内质网蛋白iRhom2促进TRAPβ和STING的相互作用。与TRAPβ缺陷类似，iRhom2的丢失也会阻止STING从ER离开。由于TRAPβ和iRhom2不影响COPII装置的蛋白质运输，它们可能调节内质网的横向移动，以到达ER出口位点。一旦STING到达高尔基体，就会引发一系列的生化事件：(1)通过CTT招募TBK1；(2) TBK1磷酸化STING（丝氨酸366）和自身；(3)STING使IRF3聚合并招募到ILxIS基序，TBK1磷酸化IRF3；(4) p-IRF3二聚并易位到细胞核以开启免疫基因表达。除了磷酸化，其他翻译后修饰对高尔基体上的刺信号至关重要。例如，STING在半胱氨酸88和91处被顺式高尔基体定位的酰基转移酶DHC3/7/15棕榈酰化。用硝基呋喃衍生物C-178、C-179和H-151阻断刺棕榈酰化，可以防止STING寡聚和信号体组装。多种蛋白（AMFR、INSIG1、ZDHHC1、RNF26、TRIM32和TRIM56）对STING的泛素化对高尔基体的信号转导也很重要。此外，一些蛋白质辅助因子直接或间接地促进高尔基体上刺信号体的形成。S6K和SREBP裂解激活蛋白（SCAP）促进IRF3招募到STING-TBK1。而核心自噬蛋白ATG9a在膜扩张中负调控STING-TBK1复合物的形式和下游IFN信号传导，蛋白磷酸酶Mg2+/Mn2+依赖的1a和蛋白磷酸酶6催化亚基通过去磷酸化抑制信号传导。IFN-高尔基体易位也是抑制独立活性所必需的。例如，STING介导的NF-κB信号通路需要TBK1与高尔基体上的刺c端结合，但不需要STING磷酸化。STING介导的自噬需要STING从内质网转移到ER-GIC，这是自噬膜的一个已知来源。STING介导的UPR和细胞死亡需要STING从内质网退出。有趣的是，STING介导的UPR和自噬活性都被定位到相同的基序上（一个包含氨基酸322-343的α-螺旋），这表明这两种活性可能依赖于一个尚未确定的共同过程。STING内质网单独退出（在到达ERGIC或高尔基体之前）是否诱导任何细胞信号也不清楚。3. 后高尔基体穿梭和溶酶体降解虽然有许多已知的STING辅助因子在内质网到高尔基体阶段起作用，但已知的高尔基体后STING转运的辅助因子要少得多。后高尔基体的STING运输减弱了IFN信号。因此，这些辅助因子的功能缺失将延长STING信号。一旦STING在高尔基体上被磷酸化，STING降解的过程就开始了。适配器蛋白复合物1（AP-1）结合一个双亮氨酸基序以及在STING CTT结构域磷酸化的S366残基。然后，AP-1将磷酸化的STING分类到clathrin蛋白包被的囊泡中，运输到内溶酶体。AP-1的抑制增强了STING信号。STING高尔基体出口也需要反式高尔基GRIP和包含蛋白2的螺旋-螺旋结构域2（GCC2/ GCC185）。GCC2属于TGN上的Golgin蛋白家族，通过APs将囊泡转移到RAB GTPases。TGN是一个主要的分拣枢纽，在这里各类物质被分类到各种运输工具，以贩运到细胞的不同区室)。一旦STING到达核内体，它再次被UBE2N泛素化。HGS、VPS37A、UBAP1、Tsg101和Vps4是STING辅助因子。C9ORF72和UNC93B1也能促进STING溶酶体降解，尽管分子细节仍有待确定。STING还驱动非经典的自噬，这可能有助于其自身被自噬小体降解。目前还不清楚STING囊泡是与溶酶体融合还是被溶酶体吞噬，以及膜拓扑结构在每种情况下是如何工作的。参考资料Chu, T.-T., X. Tu, K. Yang, J. Wu, J.J. Repa, and N. Yan. 2021. Tonic primeboost of STING signalling mediates Niemann-Pick disease type C. Nature. 596:570–57Decout, A., J.D. Katz, S. Venkatraman, and A. Ablasser. 2021. The cGAS-STING pathway as a therapeutic target in inflammatory diseases. Nat. Rev. Immunol. 21:548–569

Study provides further validation of the potentially broad utility for CRAC channel inhibitors in inflammatory diseases Data show that inhibiting store-operated Ca2+ entry (SOCE) with a selective CRAC channel inhibitor reduced IBD severity in murine models LA JOLLA, Calif., Aug. 9, 2022 /PRNewswire/ -- CalciMedica Inc. ("CalciMedica" or the "Company), the CRAC (calcium release-activated calcium) channel company, today announced the publication of preclinical data in EMBO Molecular Medicine that describes the potential utility for CRAC channel inhibitors in inflammatory bowel disease (IBD). The paper, titled "Store-operated calcium entry controls innate and adaptive immune cell function in inflammatory bowel disease," was conducted by CalciMedica's scientific co-founder, Stefan Feske, M.D., and his team at NYU Grossman School of Medicine in collaboration with senior researchers at the Charité – Universitätsmedizin Berlin, Germany, Britta Siegmund, M.D. and Carl Weidinger, M.D., and co-authored by CalciMedica's co-founder and Chief Scientific Officer, Ken Stauderman, Ph.D. "The data gathered in this study indicate that inhibiting store-operated calcium entry (SOCE) may represent a potential new treatment approach for IBD," said Dr. Stauderman. "By investigating immune cell composition in the lamina propria of patients with ulcerative colitis and Crohn's disease, this study demonstrates not only that SOCE regulates the function of immune cells that drive IBD pathology, but also that inhibiting SOCE with a CRAC channel inhibitor slows the production of pro-inflammatory cytokines. Similar results were observed in a murine adoptive T cell transfer model of IBD. This work is important as it confirms the potential utility of using CRAC channel inhibitors as a treatment for IBD." IBD is characterized by dysregulated intestinal immune responses and manifests primarily as ulcerative colitis (UC) and Crohn's disease (CD). The study authors used mass cytometry to analyze the immune cell composition in the lamina propria in patients with UC and CD. They observed an enrichment of CD4+ effector T cells producing IL-17A and TNF, IFNγ+ CD8+ T cells, T regulatory (Treg) cells, and innate lymphoid cells. The function of these immune cells is regulated by store-operated Ca2+ entry (SOCE), which results from the opening of Ca2+ release-activated Ca2+ (CRAC) channels formed primarily by ORAI1 and STIM1 proteins. By inhibiting SOCE in cultured cells with a CRAC channel inhibitor, the authors observed a reduction in the production of pathogenic cytokines while having no effect on the viability, differentiation, and function of intestinal epithelial cells. Additionally, in a mouse model of IBD, T cell-specific deletion of CRAC channel genes showed that Stim2, Orai1, and Stim1- deficient T cells have quantitatively increasing defects in SOCE, which correlate with gradually more pronounced impairment of cytokine production by Th1 and Th17 cells and decreases in intestinal inflammation. Moreover, inhibiting SOCE with CM4620 (zegocractin, the active agent in Auxora), CalciMedica's selective ORAI1 CRAC channel inhibitor, resulted in reduced intestinal inflammation, colitogenic T cell function and weight loss, suggesting that inhibition of ORAI1 CRAC channels could be a viable treatment for IBD in humans. Dr. Feske has a financial interest in CalciMedica with the relationship managed according to the policies of NYU Langone Health. About CM4620 (Zegocractin) CM4620 (zegocractin) is the active ingredient in CalciMedica's lead product candidate Auxora, an intravenous (IV) formulation that in animal models and clinical trials has prevented acute epithelial and/or endothelial cell injury and inflammation in organs, such as the pancreas, lungs and kidneys. Auxora is currently being evaluated in multiple ongoing clinical trials: a blinded, placebo-controlled Phase 2b trial in patients with acute pancreatitis with accompanying systemic inflammatory response syndrome (SIRS), a Phase 2 dose-escalation trial in patients with COVID-19 pneumonia and acute respiratory distress syndrome (ARDS) requiring invasive mechanical ventilation, and an investigator-initiated Phase 1/2 trial in pediatric asparaginase-associated pancreatitis (AAP), which develops in approximately 10% of lymphocytic leukemia (ALL) patients who receive asparaginase as part of their chemotherapy regimen. Auxora has been evaluated in CARDEA, a 284-patient randomized, placebo-controlled trial in hospitalized COVID-19 pneumonia patients that was Part Two of a Phase 2 trial. The results were published in the peer reviewed journal Critical Care in April 2022. The results of Part One of the trial, a randomized open label trial in 30 critical and severe COVID-19 pneumonia patients, were also published Critical Care in August 2020. Results of a randomized open label Phase 2a trial in 21 acute pancreatitis patients with SIRS were published in the peer reviewed journal, Pancreas, in June 2021. About CalciMedica, Inc. CalciMedica is a clinical-stage biopharmaceutical company advancing a new class of medicines designed to act upon calcium release-activated calcium (CRAC) channels, a group of ion channel targets not addressed by any approved drugs. CalciMedica is developing CRAC channel inhibitors for unmet needs in acute critical illness and looks to expand the potential uses of CRAC channel inhibitors to certain chronic diseases that have the common thread of inflammation in their pathogenesis. The Company has a portfolio of potent and selective small molecule CRAC channel inhibitors including Auxora, its lead product candidate, which is formulated as a proprietary IV nanoemulsion specifically designed for acute critical illnesses. CalciMedica is headquartered in La Jolla, CA. For more information, please visit the company website at . SOURCE CalciMedica