Mast cells and basophils are main drivers of allergic reactions and anaphylaxis, for which prevalence is rapidly increasing. Activation of these cells leads to a tightly controlled release of inflammatory mediators stored in secretory granules. The release of these granules is dependent on intracellular calcium (Ca2+) signals. Ca2+ release from endolysosomal compartments is mediated via intracellular cation channels, such as two-pore channel (TPC) proteins. Here, we uncover a mechanism for how TPC1 regulates Ca2+ homeostasis and exocytosis in mast cells in vivo and ex vivo. Notably, in vivo TPC1 deficiency in mice leads to enhanced passive systemic anaphylaxis, reflected by increased drop in body temperature, most likely due to accelerated histamine-induced vasodilation. Ex vivo, mast cell-mediated histamine release and degranulation was augmented upon TPC1 inhibition, although mast cell numbers and size were diminished. Our results indicate an essential role of TPC1 in endolysosomal Ca2+ uptake and filling of endoplasmic reticulum Ca2+ stores, thereby regulating exocytosis in mast cells. Thus, pharmacological modulation of TPC1 might blaze a trail to develop new drugs against mast cell-related diseases, including allergic hypersensitivity.

During inflammation, neutrophils are one of the first responding cells of innate immunity, contributing to a fast clearance of infection and return to homeostasis. However, excessive neutrophil infiltration accelerates unsolicited disproportionate inflammation for instance in autoimmune diseases such as rheumatoid arthritis. The transient-receptor-potential channel-kinase TRPM7 is an essential regulator of immune system homeostasis. Naïve murine T cells with genetic inactivation of the TRPM7 enzyme, due to a point mutation at the active site, are unable to differentiate into pro-inflammatory T cells, whereas regulatory T cells develop normally. Moreover, TRPM7 is vital for lipopolysaccharides (LPS)-induced activation of murine macrophages. Within this study, we show that the channel-kinase TRPM7 is functionally expressed in neutrophils and has an important impact on neutrophil recruitment during inflammation. We find that human neutrophils cannot transmigrate along a CXCL8 chemokine gradient or produce reactive oxygen species in response to gram-negative bacterial lipopolysaccharide LPS, if TRPM7 channel or kinase activity are blocked. Using a recently identified TRPM7 kinase inhibitor, TG100-115, as well as murine neutrophils with genetic ablation of the kinase activity, we confirm the importance of both TRPM7 channel and kinase function in murine neutrophil transmigration and unravel that TRPM7 kinase affects Akt1/mTOR signaling thereby regulating neutrophil transmigration and effector function. Hence, TRPM7 represents an interesting potential target to treat unwanted excessive neutrophil invasion.

Cyclooxygenase-2 (COX-2) is a key regulator of inflammation. High constitutive COX-2 expression enhances survival and proliferation of tumor cells, whereas it adversely impacts anti-tumor immunity. We recently identified the melastatin-like transient-receptor-potential-7 (TRPM7) protein as modulator of immune homeostasis. TRPM7 is essential for leukocyte proliferation and differentiation, and upregulated in several cancer tissues. It combines a cation channel with an α-kinase, which is linked to inflammatory cell responses, and associated with hallmarks of tumor progression. A role in leukemia is not established. Here, we show that inhibiting TRPM7 in CML patient cells results in reduced constitutive COX-2 expression and cell proliferation. Using the CML-derived cell line HAP1 harboring CRISPR/Cas9-mediated TRPM7 knockout or a point mutation inactivating TRPM7 kinase, we could link this defect to reduced AKT activation. Pharmacologic blockade of TRPM7 in wildtype HAP1 cells confirmed the effect on COX-2 via altered AKT signaling. Addition of an AKT activator on TRPM7 kinase-dead cells reconstituted the phenotype. Inhibition of TRPM7 resulted in reduced COX-2 expression in peripheral blood mononuclear cells derived from CML patients, and diminished patient-derived CD34+ cell proliferation. We highlight a role of TRPM7 kinase in AKT-driven COX-2 expression, and suggest a beneficial potential of TRPM7 blockade in COX-2-directed chemotherapy.