Mast cell production and response to IL-4 and IL-13

IL-4 was identified as the first cytokine to be produced by mast cells and is responsible for promoting mast cell IL-13 production. IL-4 and IL-13 play a prominent role in stimulating and maintaining the allergic response. As closely related genes, IL-4 and IL-13 share a common receptor subunit, IL-4Rα, necessary for signaling. Here we summarize the literature on mast cell activation associated with IL-4 and IL-13 production, including downstream signaling. We also describe the positive and negative roles each cytokine plays in mast cell immunity and detail the differences that exist between mouse and human mast cell responses to IL-4 and IL-13.

Mast cell homeostasis and the JAK-STAT pathway

The Janus kinase/signal transducer and activator of transcription (JAK-STAT) pathway mediates important responses in immune cells. Activation of any of the four JAK family members leads to phosphorylation of one or more of seven STAT family members. Phosphorylation of STAT family members leads to their dimerization and translocation into the nucleus, in which they bind specific DNA sequences to activate gene transcription. Regulation of JAKs and STATs therefore has a significant effect on signal transduction and subsequent cellular responses. Mast cells are important mediators of allergic disease and asthma. These cells have the ability to cause profound inflammation and vasodilation upon the release of preformed mediators, as well as subsequent synthesis of new inflammatory mediators. The regulation of mast cells is therefore of intense interest for the treatment of allergic disease. An important regulator of mast cells, STAT5, is activated downstream of the receptors for immunoglobulin E, interleukin-3 and stem cell factor. STAT5 contributes to mast cell homeostasis, by mediating proliferation, survival, and mediator release. Regulators of the JAK-STAT pathway, such as the suppressors of cytokine signaling (SOCS) and protein inhibitor of activated STAT (PIAS) proteins, are required to fine tune the immune response and maintain homeostasis. A better understanding of the role and regulation of JAKs and STATs in mast cells is vital for the development of new therapeutics.

Characterization of cis-regulatory elements conferring mercury-induced interleukin-4 gene expression in rat mast cells: a role for signal transducer and activator of transcription 6 and TATA box binding sites

We have previously shown that oxidative stress is involved in the pathogenesis of a mercuric chloride (HgCl(2))-induced, T helper type 2 (Th2)-driven autoimmune syndrome in Brown Norway (BN) rats. In the context of the syndrome, the oxidative stress-induced mast cell response seems to determine the development of the early phase of vasculitis, while oxidative stress-mediated interleukin (IL)-4 production may contribute to the subsequent Th2-driven autoimmune response. However, the molecular basis of IL-4 gene transcription induced by HgCl(2) in mast cells remains unknown. In the present study, we dissect the critical regulatory mechanisms in the IL-4 gene promoter in the rat mast cell line RBL-2H3. Immunoprecipitation provided evidence that treatment with HgCl(2) increased phosphorylation of signal transducer and activator of transcription 6 (STAT6). Transient transfection reporter analyses with a series of 5' end deletions of the IL-4 promoter produced evidence that STAT6 and TATA box binding sites are important in HgCl(2)-induced IL-4 gene expression. Subsequent elimination of one or both sites by site-directed mutagenesis significantly inhibited IL-4 promoter activity. Our results provide evidence that STAT6 and TATA box regulatory elements play an important role in HgCl(2)-induced IL-4 transcription in rat mast cells.

STAT5 isoforms: controversies and clarifications

STAT (signal transducer and activator of transcription) family transcription factors are critical regulators of the development and differentiation of many cell types. STAT isoforms are generated by alternative splicing, but have also been suggested to be generated post-transcriptionally. In this issue of the Biochemical Journal, Schuster and colleagues have identified cathepsin G as the protease that cleaves full-length STAT5 (STAT5alpha) to generate a C-terminally truncated form in immature myeloid cells. However, the authors argue that this proteolytically generated isoform does not occur naturally in vivo; rather, it is artificially generated by cathepsin G during the preparation of cell extracts. This new evidence calls into question the physiological significance of this putative isoform and forces the general re-examination of proteolytically generated STAT isoforms.

Signal transducer and activator of transcription signals in allergic disease

Signal transducer and activator of transcription (STAT) proteins are a group of transcription factors that transmit signals from the extracellular milieu of cells to the nucleus. They are crucial for the signaling of many cytokines that are mediators of allergic inflammation and impact various cell types critical to allergy including epithelial cells, mast cells, lymphocytes, dendritic cells, and eosinophils. Dysregulation of STAT signaling has been implicated in allergic disease, highlighting the importance of these ubiquitous molecules in allergic inflammation and the potential of these pathways as a target for therapeutic intervention. This review will summarize the current understanding of the roles of STAT signaling in allergic disease and the potential of targeting STATs for the treatment of allergic disorders, emphasizing recent observations.

Costimulation with interleukin-4 and interleukin-10 induces mast cell apoptosis and cell-cycle arrest: the role of p53 and the mitochondrion

OBJECTIVE

The aim of this study was to determine the mechanism by which interleukin (IL)-4 + IL-10 costimulation regulates mast cell numbers to maintain immune homeostasis.

MATERIALS AND METHODS

We employed mouse bone marrow-derived mast cells (BMMC) to measure the effects of IL-4 + IL-10 on survival and cell-cycle progression. p53-Deficient, bax-deficient, and bcl-2 transgenic BMMC were compared to wild-type cells to determine the role of these proteins in apoptosis. The molecular regulation of apoptosis and cell-cycle progression was investigated using flow cytometric analysis, RNase protection, and Western blotting.

RESULTS

IL-4 + IL-10 induced BMMC apoptosis and arrest. Apoptosis was p53-dependent. Cell death was accompanied by loss of mitochondrial membrane potential, the importance of which was demonstrated by resistance to IL-4 + IL-10-mediated cell death when Bax was deleted or Bcl-2 was overexpressed. Those cells not killed by apoptosis demonstrated a p53-independent G1 cell-cycle arrest. Apoptosis and arrest may be explained by reduced IL-3 receptor signaling.

CONCLUSION

Costimulation with IL-4 + IL-10 partly controls mast cell homeostasis through a delayed apoptosis and arrest program that is induced by a blockade of IL-3 receptor signaling. The delay in these negative effects would allow the protective effects of mast cell activation to occur for several days.

Stat6-protease but not Stat5-protease is inhibited by an elastase inhibitor ONO-5046

A short isoform of Stat6 (65-kDa Stat6), a product of proteolytic processing by an undefined protease (Stat6-protease) in the nucleus, downregulates Stat6-mediated signaling in mast cells. Similarly, Stat5-mediated signaling is downregulated by Stat5-protease in myeloid progenitors. These proteases share a number of characteristics, including their nuclear localization and susceptibility to protease inhibitors. Here, we further investigated these Stat proteases. Interestingly, the activity of Stat6-protease but not of Stat5-protease was inhibited by ONO-5046, an elastase inhibitor that inhibits the activity of neutrophil elastase (NE) and NE-related protease proteinase 3 (PR3). Although both NE and PR3 were able to cleave Stat6 in vitro, the cleavage sites of Stat6 by NE or PR3 differed from that by Stat6-protease in mast cells. In addition, both NE and PR3 could also cleave Stat5, but they differed from Stat5-protease in myeloid progenitors. These results suggest that Stat6-protease may belong to the elastase family but differs from NE or PR3.

Interleukin-4 and interleukin-13 signaling connections maps

Cytokines are inflammatory mediators important in responding to pathogens and other foreign challenges. Interleukin-4 (IL-4) and IL-13 are two cytokines produced by T helper type 2 cells, mast cells, and basophils. In addition to their physiological roles, these cytokines are also implicated in pathological conditions such as asthma and allergy. IL-4 can stimulate two receptors, type I and type II, whereas IL-13 signaling is mediated only by the type II receptor (see the STKE Connections Maps). These cytokines activate the Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling cascades, which may contribute to allergic responses. In addition, stimulation of the phosphatidylinositol 3-kinase (PI3K) pathway through recruitment of members of the insulin receptor substrate family may contribute to survival and proliferation.