Human mast cells express intracellular TRAIL

Mast Cells and Skin and Breast Cancers: A Complicated and Microenvironment-Dependent Role

Mast cells are important sentinel cells in host defense against infection and major effector cells in allergic disease. The role of these cells in cancer settings has been widely debated. The diverse range of mast cell functions in both immunity and tissue remodeling events, such as angiogenesis, provides multiple opportunities for mast cells to modify the tumor microenvironment. In this review, we consider both skin and breast cancer settings to address the controversy surrounding the importance of mast cells in the host response to tumors. We specifically address the key mediators produced by mast cells which impact tumor development. The role of environmental challenges in modifying mast cell responses and opportunities to modify mast cell responses to enhance anti-tumor immunity are also considered. While the mast cell's role in many cancer contexts is complicated and poorly understood, the activities of these tissue resident and radioresistant cells can provide important opportunities to enhance anti-cancer responses and limit cancer development.

Activation of KIT modulates the function of tumor necrosis factor-related apoptosis-inducing ligand receptor (TRAIL-R) in mast cells

BACKGROUND

Mastocytosis is characterized by the accumulation of mast cells (MCs) associated with activating mutations of KIT. Tumor necrosis factor-related apoptosis-inducing ligand receptors (TRAIL-Rs) are preferentially expressed on neoplastic cells and induce the extrinsic apoptotic pathway. Recent studies reported on the expression of TRAIL-Rs and TRAIL-induced apoptosis in cultured human MCs, which depend on stem cell factor (SCF)-induced or constitutive KIT activation.

MATERIAL AND METHODS

We sought to further define the impact of TRAIL-Rs on MCs in vivo and in vitro. Using Cre/loxP recombination, we generated mice with MC-specific and ubiquitous knockout of TRAIL-R. In these mice, anaphylaxis and numbers of MCs were investigated. We also explored the expression and function of TRAIL-Rs in cultured murine and human MCs upon activation of KIT. By conducting immunofluorescence staining, we analyzed the expression of TRAIL-Rs in MCs infiltrating the bone marrow of patients with mastocytosis.

RESULTS

MC-specific deletion of TRAIL-R was associated with a slight, but significant increase in anaphylaxis. Numbers of MCs in MC-specific knockouts of TRAIL-R were comparable to controls. Whereas cultured IL-3-dependent murine MCs from wild-type mice were resistant to TRAIL-induced apoptosis, SCF-stimulated MCs underwent apoptosis in response to TRAIL. Interestingly, activating KIT mutations also promoted sensitivity to TRAIL-mediated apoptosis in human MCs. In line with these findings, MCs infiltrating the bone marrow of patients with mastocytosis expressed TRAIL-R1.

CONCLUSIONS

Activation of KIT regulates the function of TRAIL-Rs in MCs. TRAIL-R1 may represent an attractive diagnostic and therapeutic target in diseases associated with KIT mutations, such as mastocytosis.

Mast cells' integrated actions with eosinophils and fibroblasts in allergic inflammation: implications for therapy

Mast cells (MCs) and eosinophils (Eos) are the key players in the development of allergic inflammation (AI). Their cross-talk, named the Allergic Effector Unit (AEU), takes place through an array of soluble mediators and ligands/receptors interactions that enhance the functions of both the cells. One of the salient features of the AEU is the CD48/2B4 receptor/ligand binding complex. Furthermore, MCs and Eos have been demonstrated to play a role not only in AI but also in the modulation of its consequence, i.e., fibrosis/tissue remodeling, by directly influencing fibroblasts (FBs), the main target cells of these processes. In turn, FBs can regulate the survival, activity, and phenotype of both MCs and Eos. Therefore, a complex three players, MCs/Eos/FBs interaction, can take place in various stages of AI. The characterization of the soluble and physical mediated cross talk among these three cells might lead to the identification of both better and novel targets for the treatment of allergy and its tissue remodeling consequences.

Treatment strategies in mastocytosis

Treatment recommendations for mastocytosis are based mostly on expert opinion rather than evidence obtained from controlled clinical trials. In this article, treatment options for mastocytosis are presented, with a focus on the control of mediator-related symptoms in patients with indolent disease.

IL-36 Receptor Antagonist with Special Emphasis on IL-38

IL-36 is another family member of IL-1 and induces the production of proinflammatory cytokines and activates MAPK and NFκB pathways. IL-36 is a common mediator of innate and adaptive immune response and is inhibited by IL-36 receptor antagonist (RA). IL-36RA acts on IL-36 receptor ligand which exerts proinflammatory effect in vivo and in vitro. IL-38 binds to IL-36 receptor as does IL-36RA and has similar biological effects on immune cells. IL-38 is also a member of IL-1 cytokine and shares some characteristics of IL-1RA, binding the same IL-1 receptor type I. IL-38 plays a role in the pathogenesis of inflammatory diseases, exerting protective effect in some autoimmune diseases. Both IL-38 and IL-36RA have an anti-inflammatory biological effect, however in some cases have contrary effects.

Impact of IL-33 on PGD2 Generation by Activated Human Cord Blood-Derived Mast Cell: Lack of Effect on Tryptase Release

Mast cells are important not only in allergic reactions, but also in inflammation and are involved in a variety of responses including the immediate release of potent inflammatory mediators after activation by cross-linking of FcεRI molecules. Prostaglandin D2 (PGD2) is a major cyclooxygenase metabolite of arachidonic acid produced by mast cells and it is released following allergen challenge in allergic diseases. IL-33 is an iflammatory cytokine which is critically involved in the regulation of in vitro and in vivo cyclooxygenase production, providing a potential therapeutic target for inflammatory disorders. In this study, using human derived umbelical cord blood mast cells, we show that IL-33 (50 ng/ml), and calcium ionophore A 23187 (0.5 μg/ml), compound 48/80 (10−5 M) or anti-IgE (10 μg/ml), enhaced the production of PGD2 and this effect was inhibited by indomethacin. However, IL-33 was unable to induce tryptase release in these cells. These effects confirm the inflammatory property of IL-33 by stimulating PGD2 but not tryptase in human mast cells. The inhibitory effect of this new cytokine may have a potential therapeutic response in allergic and inflammatory diseases.

Calcium Ionophore A23187 and Compound 48/80 Induce PGD2 and Tryptase in Human Cord Blood-Derived Mast Cells: Lack of Effect of IL-18

Immunological and biochemical reactions associated with inflammation are elicited in response to a physical or immunological challenge. Early in inflammation there is mobilization and infiltration of neutrophils, mast cells and macrophages to the site of inflammation. These cells release pro-inflammatory compounds icluding cytokines, vasoactive peptides (eg., histamine), and eicosanoids. The release of prostaglandin D2 (PGD2) and tryptase induced by anti-IgE, A23187 and compound 48/80 were studied using in vitro a good and valid model of human cord blood-derived mast cells (HCBDMC). Tryptase is a mast cell product and enhances vasopermeability with anticoagulant activities. In this study we measure the release of PGD2 and tryptase on mast cells activate by anti-IgE, calcium ionophore A23187, polybasic compound 48/80 (an agent containing a cationic region adjacent to a hydrophobic moiety, which works by activating G proteins) and IL-18. The generation of PGD2 was measured by radioimmunoassay. Release of PGD2 was detectable (after 12 h) following challenge with anti-IgE, A23187 and compound 48/80. Our data show that mature HCBDMC produce proinflammatory PGD2 following triggering with anti-IgE and with IgE-independent agonists, such as calcium ionophore A23187 and polybasic compound 48/80, while IL-18 was unable to stimulate the release of PGD2 or tryptase on HCBDMC. Although a great deal has been learned about the mediators produced by mast cells, the ultimate biologic function(s) of mast cells remains a mystery.

Novel transcript variants of TRAIL show different activities in activation of NF-κB and apoptosis

AIMS

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has many transcript variants, but whether they possess distinct function is not completely known. In the present study, we compared the function of these TRAIL variants.

MAIN METHODS

A bioinformatics analysis was performed to examine potential TRAIL variants. For the functional study, over-expression of TRAIL isoforms was used to examine their NF-κB inducing and apoptotic activities in both cancer and normal cells. Moreover, soluble TRAIL E4 variant protein was expressed and purified in prokaryotic cells, and was used for apoptotic assay.

KEY FINDINGS

We cloned seven truncated TRAIL variants, designated as AK, E2, E3, E4, DA, BX424, and BX439. In comparison with the wild type TRAIL protein expressed from full-length RefSeq, over-expression of all these TRAIL variants activated NF-κB and its targeting genes in human cells at varying degrees. Some isoforms including BX424, DA and E4 even showed NF-κB, IL8, CCL4 and CCL20 promoter activating activity stronger than the wild type protein. All truncated variant proteins had no toxicity to normal human cells, similar to the wild type protein; however, they all failed to induce apoptosis in cancer cells that are sensitive to TRAIL. Recombinant soluble TRAIL E4 protein also failed to antagonize TRAIL-induced apoptosis in cancer cells.

SIGNIFICANCE

Truncated TRAIL variant proteins lost apoptotic activity but retained or even enhanced the NF-κB activating potentials, these results suggest that TRAIL variants may play roles in non-apoptotic cellular processes that are more important than we previously thought.