The critical role of STIM1-dependent Ca2+ signalling during T-cell development and activation

The miR-641-STIM1 and SATB1 axes play important roles in the regulation of the Th17/Treg balance in ITP

Immune thrombocytopenia (ITP) is an autoimmune disease caused by T-cell dysfunction. Recently, several studies have shown that a disturbed Th17/Treg balance contributes to the development of ITP. MicroRNAs (miRNAs) are small noncoding RNA moleculesthat posttranscriptionally regulate gene expression. Emerging evidences have demonstrated that miRNAs play an important role in regulating the Th17/Treg balance. In the present study, we found that miR-641 was upregulated in ITP patients. In primary T cells, overexpression of miR-641 could cause downregulation of its target genes STIM1 and SATB1, thus inducing a Th17 (upregulated)/Treg (downregulated) imbalance. Inhibition of miR-641 by a miR-641 sponge in primary T cells of ITP patients or by antagomiR-641 in an ITP murine model could cause upregulation of STIM1 and SATB1, thus restoring Th17/Treg homeostasis. These results suggested that the miR-641-STIM/SATB1 axis plays an important role in regulating the Th17/Treg balance in ITP.

Rapamycin Controls Lymphoproliferation and Reverses T-Cell Responses in a Patient with a Novel STIM1 Loss-of-Function Deletion

PURPOSE

Deficiency of stromal interaction molecule 1 (STIM1) results in combined immunodeficiency accompanied by extra-immunological findings like enamel defects and myopathy. We here studied a patient with a STIM1 loss-of-function mutation who presented with severe lymphoproliferation. We sought to explore the efficacy of the mTOR inhibitor rapamycin in controlling disease manifestations and reversing aberrant T-cell subsets and functions, which has never been used previously in this disorder.

METHODS

Clinical findings of the patient were collected over time. We performed immunological evaluations before and after initiation of rapamycin treatment, including detailed lymphocyte subset analyses, alterations in frequencies of circulating T follicular helper (cTFH) and regulatory T (Treg) cells and their subtypes as well as T cell activation and proliferation capacities.

RESULTS

A novel homozygous exon 2 deletion in STIM1 was detected in a 3-year-old girl with severe lymphoproliferation, recurrent infections, myopathy, iris hypoplasia, and enamel hypoplasia. Lymphoproliferation was associated with severe T-cell infiltrates. The deletion resulted in a complete loss of protein expression, associated with a lack of store-operated calcium entry response, defective T-cell activation, proliferation, and cytokine production. Interestingly, patient blood contained fewer cTFH and increased circulating follicular regulatory (cTFR) cells. Abnormal skewing towards TH2-like responses in certain T-cell subpopulations like cTFH, non-cTFH memory T-helper, and Treg cells was associated with increased eosinophil numbers and serum IgE levels. Treatment with rapamycin controlled lymphoproliferation, improved T-cell activation and proliferation capacities, reversed T-cell responses, and repressed high IgE levels and eosinophilia.

CONCLUSIONS

This study enhances our understanding of STIM1 deficiency by uncovering additional abnormal T-cell responses, and reveals for the first time the potential therapeutic utility of rapamycin for this disorder.

Trogocytosis of cancer-associated fibroblasts promotes pancreatic cancer growth and immune suppression via phospholipid scramblase anoctamin 6 (ANO6)

In pancreatic ductal adenocarcinoma (PDAC), the fibroblastic stroma constitutes most of the tumor mass and is remarkably devoid of functional blood vessels. This raises an unresolved question of how PDAC cells obtain essential metabolites and water-insoluble lipids. We have found a critical role for cancer-associated fibroblasts (CAFs) in obtaining and transferring lipids from blood-borne particles to PDAC cells via trogocytosis of CAF plasma membranes. We have also determined that CAF-expressed phospholipid scramblase anoctamin 6 (ANO6) is an essential CAF trogocytosis regulator required to promote PDAC cell survival. During trogocytosis, cancer cells and CAFs form synapse-like plasma membranes contacts that induce cytosolic calcium influx in CAFs via Orai channels. This influx activates ANO6 and results in phosphatidylserine exposure on CAF plasma membrane initiating trogocytosis and transfer of membrane lipids, including cholesterol, to PDAC cells. Importantly, ANO6-dependent trogocytosis also supports the immunosuppressive function of pancreatic CAFs towards cytotoxic T cells by promoting transfer of excessive amounts of cholesterol. Further, blockade of ANO6 antagonizes tumor growth via disruption of delivery of exogenous cholesterol to cancer cells and reverses immune suppression suggesting a potential new strategy for PDAC therapy.

Inhibition of Calcium Signaling Prevents Exhaustion and Enhances Anti-Leukemia Efficacy of CAR-T Cells via SOCE-Calcineurin-NFAT and Glycolysis Pathways

Chimeric antigen receptor (CAR) T cells are potent agents for recognizing and eliminating tumors, and have achieved remarkable success in the treatment of patients with refractory leukemia and lymphoma. However, dysfunction of T cells, including exhaustion, is an inevitable obstacle for persistent curative effects. Here, the authors initially found that calcium signaling is hyperactivated via sustained tonic signaling in CAR-T cells. Next, it is revealed that the store-operated calcium entry (SOCE) inhibitor BTP-2, but not the calcium chelator BAPTA-AM, markedly diminishes CAR-T cell exhaustion and terminal differentiation of CAR-T cells in both tonic signaling and tumor antigen exposure models. Furthermore, BTP-2 pretreated CAR-T cells show improved antitumor potency and prolonged survival in vivo. Mechanistically, transcriptome and metabolite analyses reveal that treatment with BTP-2 significantly downregulate SOCE-calcineurin-nuclear factor of activated T-cells (NFAT) and glycolysis pathways. Together, the results indicate that modulating the SOCE-calcineurin-NFAT pathway in CAR-T cells renders them resistant to exhaustion, thereby yielding CAR products with enhanced antitumor potency.

New Insights on the Role of TRP Channels in Calcium Signalling and Immunomodulation: Review of Pathways and Implications for Clinical Practice

Calcium is the most abundant mineral in the human body and is central to many physiological processes, including immune system activation and maintenance. Studies continue to reveal the intricacies of calcium signalling within the immune system. Perhaps the most well-understood mechanism of calcium influx into cells is store-operated calcium entry (SOCE), which occurs via calcium release-activated channels (CRACs). SOCE is central to the activation of immune system cells; however, more recent studies have demonstrated the crucial role of other calcium channels, including transient receptor potential (TRP) channels. In this review, we describe the expression and function of TRP channels within the immune system and outline associations with murine models of disease and human conditions. Therefore, highlighting the importance of TRP channels in disease and reviewing potential. The TRP channel family is significant, and its members have a continually growing number of cellular processes. Within the immune system, TRP channels are involved in a diverse range of functions including T and B cell receptor signalling and activation, antigen presentation by dendritic cells, neutrophil and macrophage bactericidal activity, and mast cell degranulation. Not surprisingly, these channels have been linked to many pathological conditions such as inflammatory bowel disease, chronic fatigue syndrome and myalgic encephalomyelitis, atherosclerosis, hypertension and atopy.

Stimulation of ORAI1 expression, store-operated Ca2+ entry, and osteogenic signaling by high glucose exposure of human aortic smooth muscle cells

Diabetes and chronic kidney disease (CKD) both trigger vascular osteogenic signaling and calcification leading to early death by cardiovascular events. Osteogenic signaling involves upregulation of the transcription factors CBFA1, MSX2, and SOX9, as well as alkaline phosphatase (ALP), an enzyme fostering calcification by degrading the calcification inhibitor pyrophosphate. In CKD, osteogenic signaling is triggered by hyperphosphatemia, which upregulates the serum and glucocorticoid-inducible kinase SGK1, a strong stimulator of the Ca²⁺-channel ORAI1. The channel is activated by STIM1 and accomplishes store-operated Ca²⁺-entry (SOCE). The present study explored whether exposure of human aortic smooth muscle cells (HAoSMCs) to high extracellular glucose concentrations similarly upregulates ORAI1 and/or STIM1 expression, SOCE, and osteogenic signaling. To this end, HAoSMCs were exposed to high extracellular glucose concentrations (15 mM, 24 h) without or with additional exposure to the phosphate donor ß-glycerophosphate. Transcript levels were estimated using qRT-PCR, protein abundance using Western blotting, ALP activity using a colorimetric assay kit, calcium deposits utilizing Alizarin red staining, cytosolic Ca²⁺-concentration ([Ca²⁺]_i) by Fura-2-fluorescence, and SOCE from increase of [Ca²⁺]_i following re-addition of extracellular Ca²⁺ after store depletion with thapsigargin (1 μM). As a result, glucose enhanced the transcript levels of SGK1 and ORAI1, ORAI2, and STIM2, protein abundance of ORAI1, SOCE, the transcript levels of CBFA1, MSX2, SOX9, and ALPL, as well as calcium deposits. Moreover, glucose significantly augmented the stimulating effect of ß-glycerophosphate on transcript levels of SGK1 and ORAI1, SOCE, the transcript levels of osteogenic markers, as well as calcium deposits. ORAI1 inhibitor MRS1845 (10 μM) significantly blunted the glucose-induced upregulation of the CBFA1 and MSX2 transcript levels. In conclusion, the hyperglycemia of diabetes stimulates expression of SGK1 and ORAI1, thus, augmenting store-operated Ca²⁺-entry and osteogenic signaling in HAoSMCs.

Role of the Ca2+-Calcineurin-Nuclear Factor of Activated T cell Pathway in Mitofusin-2-Mediated Immune Function of Jurkat Cells

Background:

Mitofusin-2 (MFN2), a well-known mitochondrial fusion protein, has been shown to participate in innate immunity, but its role in mediating adaptive immunity remains poorly characterized. In this study, we explored the potential role of MFN2 in mediating the immune function of T lymphocytes.

Methods:

We manipulated MFN2 gene expression in Jurkat cells via lentiviral transduction of MFN2 small interfering RNA (siRNA) or full-length MFN2. After transduction, the immune response and its underlying mechanism were determined in Jurkat cells. One-way analysis of variance and Student's t-test were performed to determine the statistical significance between the groups.

Results:

Overexpression of MFN2 enhanced the immune response of T lymphocytes by upregulating Ca²⁺ (359.280 ± 10.130 vs. 266.940 ± 10.170, P = 0.000), calcineurin (0.513 ± 0.014 vs. 0.403 ± 0.020 nmol/L, P = 0.024), and nuclear factor of activated T cells (NFATs) activation (1.040 ± 0.086 vs. 0.700 ± 0.115, P = 0.005), whereas depletion of MFN2 impaired the immune function of T lymphocytes by downregulating Ca²⁺ (141.140 ± 14.670 vs. 267.060 ± 9.230, P = 0.000), calcineurin (0.054 ± 0.030 nmol/L vs. 0.404 ± 0.063 nmol/L, P = 0.000), and NFAT activation (0.500 ± 0.025 vs. 0.720 ± 0.061, P = 0.012). Furthermore, upregulated calcineurin partially reversed the negative effects of MFN2 siRNA on T cell-mediated immunity evidenced by elevations in T cell proliferation (1.120 ± 0.048 vs. 0.580 ± 0.078, P = 0.040), interleukin-2 (IL-2) production (473.300 ± 24.100 vs. 175.330 ± 12.900 pg/ml, P = 0.000), and the interferon-γ/IL-4 ratio (3.080 ± 0.156 vs. 0.953 ± 0.093, P = 0.000). Meanwhile, calcineurin activity inhibitor depleted the positive effects of overexpressed MFN2 on T cells function.

Conclusions:

Our findings suggest that MFN2 may regulate T cell immune functions primarily through the Ca²⁺-calcineurin-NFAT pathway. MFN2 may represent a potential therapeutic target for T cell immune dysfunction-related diseases.

Correlation of clinical features and genetic profiles of stromal interaction molecule 1 (STIM1) in colorectal cancers

STIM1 overexpression has been observed in a portion of colorectal cancer (CRC) patients and associated with cancer cell invasion and migration. To characterize the distinctive expression profiles associated with stromal interaction molecule 1 (STIM1) overexpression/low-expression between CRC subtypes, and further assess the divergence transcription regulation impact of STIM1 between colon (COADs) and rectum (READs) adenocarcinomas in order to depict the role of SOCE pathway in CRCs, we have conducted a comprehensive phenome-transcriptome-interactome analysis to clarify underlying molecular differences of COADs/READs contributed by STIM1. Results demonstrated that a number of novel STIM1-associated signatures have been identified in COADs but not READs. Specifically, the presence of STIM1 overexpression in COADs, which represented a disturbance of the SOCE pathway, was associated with cell migration and cell motility properties. We identified 11 prognostic mRNA/miRNA predictors associated with the overall survival of COAD patients, suggesting the correlation of STIM1-associated features to clinicopathological outcomes. These findings enhance our understanding on differences between CRC subtypes in panoramic view, and suggested STIM1 as a promising therapeutic biomarker in COADs.