Mast cells counteract regulatory T-cell suppression through interleukin-6 and OX40/OX40L axis toward Th17-cell differentiation

The development of inflammatory diseases implies inactivation of regulatory T (Treg) cells through mechanisms that still are largely unknown. Here we showed that mast cells (MCs), an early source of inflammatory mediators, are able to counteract Treg inhibition over effector T cells. To gain insight into the molecules involved in their interplay, we set up an in vitro system in which all 3 cellular components were put in contact. Reversal of Treg suppression required T cell-derived interleukin-6 (IL-6) and the OX40/OX40L axis. In the presence of activated MCs, concomitant abundance of IL-6 and paucity of Th1/Th2 cytokines skewed Tregs and effector T cells into IL-17-producing T cells (Th17). In vivo analysis of lymph nodes hosting T-cell priming in experimental autoimmune encephalomyelitis revealed activated MCs, Tregs, and Th17 cells displaying tight spatial interactions, further supporting the occurrence of an MC-mediated inhibition of Treg suppression in the establishment of Th17-mediated inflammatory responses. © 2009 by The American Society of Hematology

Reciprocal influence of B cells and tumor macro and microenvironments in the ApcMin/+model of colorectal cancer

One of the most fascinating aspects of the immune system is its dynamism, meant as the ability to change and readapt according to the organism needs. Following an insult, we assist to the spontaneous organization of different immune cells which cooperate, locally and at distance, to build up an appropriate response. Throughout tumor progression, adaptations within the systemic tumor environment, or macroenvironment, result in the promotion of tumor growth, tumor invasion and metastasis to distal organs, but also to dramatic changes in the activity and composition of the immune system. In this work, we show the changes of the B-cell arm of the immune system following tumor progression in the ApcMin/+model of colorectal cancer. Tumor macroenvironment leads to an increased proportion of total and IL-10-competent B cells in draining LNs while activates a differentiation route that leads to the expansion of IgA+lymphocytes in the spleen and peritoneum. Importantly, serum IgA levels were significantly higher in ApcMin/+than Wt mice. The peculiar involvement of IgA response in the adenomatous transformation had correlates in the gut-mucosal compartment where IgA-positive elements increased from normal mucosa to areas of low grade dysplasia while decreasing upon overt carcinomatous transformation. Altogether, our findings provide a snapshot of the tumor education of B lymphocytes in the ApcMin/+model of colorectal cancer. Understanding how tumor macroenvironment affects the differentiation, function and distribution of B lymphocytes is pivotal to the generation of specific therapies, targeted to switching B cells to an anti-, rather than pro-, tumoral phenotype

Repurposing of the Antiepileptic Drug Levetiracetam to Restrain Neuroendocrine Prostate Cancer and Inhibit Mast Cell Support to Adenocarcinoma

A relevant fraction of castration-resistant prostate cancers (CRPC) evolve into fatal neuroendocrine (NEPC) tumors in resistance to androgen deprivation and/or inhibitors of androgen receptor pathway. Therefore, effective drugs against both CRPC and NEPC are needed. We have previously described a dual role of mast cells (MCs) in prostate cancer, being capable to promote adenocarcinoma but also to restrain NEPC. This finding suggests that a molecule targeting both MCs and NEPC cells could be effective against prostate cancer. Using an in silico drug repurposing approach, here we identify the antiepileptic drug levetiracetam as a potential candidate for this purpose. We found that the protein target of levetiracetam, SV2A, is highly expressed by both NEPC cells and MCs infiltrating prostate adenocarcinoma, while it is low or negligible in adenocarcinoma cells. In vitro, levetiracetam inhibited the proliferation of NEPC cells and the degranulation of MCs. In mice bearing subcutaneous tumors levetiracetam was partially active on both NEPC and adenocarcinoma, the latter effect due to the inhibition of MMP9 release by MCs. Notably, in TRansgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mice subjected to surgical castration to mimic androgen deprivation therapy, levetiracetam reduced onset and frequency of both high grade prostatic intraepithelial neoplasia, adenocarcinoma and NEPC, thus increasing the number of cured mice showing only signs of tumor regression. Our results demonstrate that levetiracetam can directly restrain NEPC development after androgen deprivation, and that it can also block adenocarcinoma progression through the inhibition of some MCs functions. These findings open the possibility of further testing levetiracetam for the therapy of prostate cancer or of MC-mediated diseases

Mast Cells and Th17 Cells Contribute to the Lymphoma-Associated Pro-Inflammatory Microenvironment of Angioimmunoblastic T-Cell Lymphoma

Reports focusing on the immunological microenvironment of peripheral T-cell lymphomas (PTCL) are rare. Here we studied the reciprocal contribution of regulatory (Treg) and interleukin-17-producing (Th17) T-cells to the composition of the lymphoma-associated microenvironment of angioimmunoblastic T-cell lymphoma (AITL) and PTCL not otherwise specified on tissue microarrays from 30 PTCLs not otherwise specified and 37 AITLs. We found that Th17 but not Treg cells were differently represented in the two lymphomas and correlated with the amount of mast cells (MCs) and granulocytes, which preferentially occurred in the cellular milieu of AITL cases. We observed that MCs directly synthesized interleukin-6 and thus contribute to the establishment of a proinflammatory, Th17 permissive environment in AITL. We further hypothesized that the AITL clone itself could be responsible for the preferential accumulation of MCs at sites of infiltration through the synthesis of CXCL-13 and its interaction with the CXCR3 and CXCR5 receptors expressed on MCs. Consistent with this hypothesis, we observed MCs efficiently migrating in response to CXCL-13. On these bases, we conclude that MCs have a role in molding the immunological microenvironment of AITL toward the maintenance of pro-inflammatory conditions prone to Th17 generation and autoimmunity. Copyright \ua9 American Society for Investigative Pathology

Regulation of base excision repair: Ntg1 nuclear and mitochondrial dynamic localization in response to genotoxic stress

Numerous human pathologies result from unrepaired oxidative DNA damage. Base excision repair (BER) is responsible for the repair of oxidative DNA damage that occurs in both nuclei and mitochondria. Despite the importance of BER in maintaining genomic stability, knowledge concerning the regulation of this evolutionarily conserved repair pathway is almost nonexistent. The Saccharomyces cerevisiae BER protein, Ntg1, relocalizes to organelles containing elevated oxidative DNA damage, indicating a novel mechanism of regulation for BER. We propose that dynamic localization of BER proteins is modulated by constituents of stress response pathways. In an effort to mechanistically define these regulatory components, the elements necessary for nuclear and mitochondrial localization of Ntg1 were identified, including a bipartite classical nuclear localization signal, a mitochondrial matrix targeting sequence and the classical nuclear protein import machinery. Our results define a major regulatory system for BER which when compromised, confers a mutator phenotype and sensitizes cells to the cytotoxic effects of DNA damage

Functional regulation of FEN1 nuclease and its link to cancer

Flap endonuclease-1 (FEN1) is a member of the Rad2 structure-specific nuclease family. FEN1 possesses FEN, 5′-exonuclease and gap-endonuclease activities. The multiple nuclease activities of FEN1 allow it to participate in numerous DNA metabolic pathways, including Okazaki fragment maturation, stalled replication fork rescue, telomere maintenance, long-patch base excision repair and apoptotic DNA fragmentation. Here, we summarize the distinct roles of the different nuclease activities of FEN1 in these pathways. Recent biochemical and genetic studies indicate that FEN1 interacts with more than 30 proteins and undergoes post-translational modifications. We discuss how FEN1 is regulated via these mechanisms. Moreover, FEN1 interacts with five distinct groups of DNA metabolic proteins, allowing the nuclease to be recruited to a specific DNA metabolic complex, such as the DNA replication machinery for RNA primer removal or the DNA degradosome for apoptotic DNA fragmentation. Some FEN1 interaction partners also stimulate FEN1 nuclease activities to further ensure efficient action in processing of different DNA structures. Post-translational modifications, on the other hand, may be critical to regulate protein–protein interactions and cellular localizations of FEN1. Lastly, we also review the biological significance of FEN1 as a tumor suppressor, with an emphasis on studies of human mutations and mouse models

Mast cell within the microenvironment: Cellular and matrix cross-talk in physiopathological conditions

Mast cells are triggered to release histamine and other mediators of inflammation when immunoglobulin E (IgE) receptors on the cell membrane are brought into close proximity, i.e. aggregated. This is usually accomplished in model systems by crosslinking IgE-loaded receptors with multivalent ligands, but can also be achieved by monovalent ligands bound to a fluid lipid bilayer, which may be patterned or homogeneous. With homogeneous membranes, the receptors on the mast cell develop a spatial pattern that bears some similarity to the T cell synapse. Ligand presentation on membranes may be a good model for the interactions of mast cells with various parasites; thus, the development of spatial patterns of receptors and the consequence for mast cell signaling is likely to be important for this most basic mast cell role. In this chapter, we review the role of the spatial organization of signaling components and IgE receptors in mast cell signaling. \ua9 2013 Nova Science Publishers, Inc. All rights reserved

Selective activation of Fyn/PI3K and p38 MAPK regulates IL-4 production in BMMC under nontoxic stress condition

Mast cells have the ability to react to multiple stimuli, implicating these cells in many immune responses. Specific signals from the microenvironment in which mast cells reside can activate different molecular events that govern distinct mast cells responses. We previously demonstrated that hydrogen peroxide (H(2)O(2)) promotes IL-4 and IL-6 mRNA production and potentates FcepsilonRI-induced cytokine release in rat basophilic leukemia RBL-2H3 cells. To further evaluate the effect of an oxidative microenvironment (which is physiologically present in an inflammatory site) on mast cell function and the molecular events responsible for mast cell cytokine production in this environment, we analyzed the effect of H(2)O(2) treatment on IL-4 production in bone marrow-derived, cultured mast cells. Our findings show that nanomolar concentrations of H(2)O(2) induce cytokine secretion and enhance IL-4 production upon FcepsilonRI triggering. Oxidative stimulation activates a distinct signal transduction pathway that induces Fyn/PI3K/Akt activation and the selective phosphorylation of p38 MAP kinase. Moreover, H(2)O(2) induces AP-1 and NFAT complexes that recognize the IL-4 promoter. The absence of Fyn and PI3K or the inhibition of p38 MAPK activity demonstrated that they are essential for H(2)O(2)-driven IL-4 production. These findings show that mast cells can respond to an oxidative microenvironment by initiating specific signals capable of eliciting a selective response. The findings also demonstrate the dominance of the Fyn/p38 MAPK pathway in driving IL-4 production

The mast cell: an antenna of the microenvironment that directs the immune response

Mast cells (MCs) have long been considered as critical effector cells during immunoglobulin (Ig)E-mediated allergic disease and immune response to parasites. Recent studies, however, suggest that this understanding of MC function is incomplete and does not consider the complex roles that MCs play in adaptive and innate immunity. The added function gives an innovative vision of regulation of immune responses and the development of autoimmune diseases. It had been assumed that the aggregation of Fc epsilon receptor I with IgE and specific antigen is the main stimulus able to induce the MC activation, degranulation, release, and generation of mediators of the allergic reaction. However, MCs exhibit an array of molecules involved in cell-cell and cell-extracellular matrix adhesion, mediating delivery of costimulatory signals that empower those cells with an ability to react to multiple nonspecific and specific stimuli. Their tissue distribution and their capability to release many cytokines after stimulation indicate MCs as potential regulatory linkers between innate and acquired immunity. In this review, we will summarize some findings on the roles of MCs in innate and acquired immunity, on the molecular mechanism and signaling pathways, and on selective signals that induce discrete MC response and its ability to polarize adaptive-immune response