The Calcineurin B Subunit (CnB) Is a New Ligand of Integrin αM That Mediates CnB-Induced Apo2L/TRAIL Expression in Macrophages

Abstract

We showed previously that the calcineurin B subunit (CnB) plays an important role in activation of peritoneal macrophage, but the underlying mechanism remained unknown. To examine whether there is a CnB receptor on peritoneal macrophages, we performed the radioligand binding assay of receptors. The receptor saturation binding curve demonstrated high-affinity and specific binding; the maximum binding was 1090 fmol/105 cells, and the Kd was 70.59 pM. Then, we used a CnB affinity resin to trap potential receptors from highly purified peritoneal macrophage membranes. Mass spectrometry analysis showed that the binding protein was mouse integrin αM. We next performed a competition binding experiment to confirm the binding of CnB to integrin αM. This showed that FITC-CnB bound specifically to peritoneal macrophages and that binding was blocked by the addition of integrin αM Ab. We observed that CnB could induce TRAIL gene expression in peritoneal macrophages in vitro and in vivo. Integrin αM Ab blocking, RNA interference, and ligand competition experiments demonstrated that CnB-induced TRAIL expression is dependent on integrin αM. Furthermore, the tumoricidal activity of CnB-activated peritoneal macrophages is partially dependent on TRAIL. In addition, CnB treatment significantly prolongs the survival of mice bearing H22 ascites tumors, which has a positive correlation with the induction level of TRAIL. These results reveal a novel function of the CnB in innate immunity and cancer surveillance. They also point to a new signaling pathway leading to induction of TRAIL and suggest a possible application of CnB in cancer therapy.

Hypercalcaemia in a Patient with 2p13.2-p16.1 Duplication

“…Calcineurin is one of the most important proteins in the immune system. The calcineurin B subunit has been shown to activate macrophages and stimulate cytokine production by itself, regardless of the calcineurin A subunit [17,18,19,20]. This protein is thus a possible candidate for stimulation of extra-renal 1α-hydroxylation.…”

Surface antigen profiles of leukocytes and melanoma cells in lymph node metastases are associated with survival in AJCC stage III melanoma patients

“…CD11b is found primarily on innate immune cells of myeloid lineage, and plays important roles in cell adhesion, migration, chemotaxis, and phagocytosis [41]. Melanoma cell extravasation was decreased following a reduction in integrin α M β 2 levels on polymorphonuclear neutrophils by functional blocking of IL-8 binding [42], implicating CD11b in melanoma metastasis.…”

Combination of calcineurin B subunit (CnB) and 5‑fluorouracil reverses 5‑fluorouracil‑induced immunosuppressive effect and enhances the antitumor activity in hepatocellular carcinoma

“…The antitumor effect of CnB is closely related to its function in immune regulation because we also found that CnB can mature and activate dendritic cells and enhance antigen presentation and thus function as a novel adjuvant of cancer vaccines (22) and the Engerix-B ® HBV vaccine (23). Additionally, CnB can activate macrophages by binding to integrinαM, and then promotes the expression and secretion of TNF-related apoptosis-inducing ligand (TRAIL), a specific pro-apoptotic cytokine (24,25). Further, synergistic interaction between CnB and IFN-γ enhances macrophage antitumor activity by polarize tumor associated macrophages to M1-phenotype (26).…”