The extracellular and transmembrane domains of the γC and interleukin (IL)-13 receptor α1 chains, not their cytoplasmic domains, dictate the nature of signaling responses to IL-4 and IL-13

Previously, we demonstrated that the γC subunit of type I IL-4 receptor was required for robust tyrosine phosphorylation of the downstream adapter protein, IRS-2, correlating with the expression of genes (ArgI, Retnla, and Chi3l3) characteristic of alternatively activated macrophages. We located an I4R-like motif (IRS-2 docking sequence) in the γC cytoplasmic domain but not in the IL-13Rα1. Thus, we predicted that the γC tail directed enhanced IRS-2 phosphorylation. To test this, IL-4 signaling responses were examined in a mutant of the key I4R motif tyrosine residue (Y325F) and different γC truncation mutants (γ285, γ308, γ318, γ323, and γFULL LENGTH (FL)) co-expressed in L-cells or CHO cells with wild-type (WT) IL-4Rα. Surprisingly, IRS-1 phosphorylation was not diminished in Y325F L-cell mutants suggesting Tyr-325 was not required for the robust insulin receptor substrate response. IRS-2, STAT6, and JAK3 phosphorylation was observed in CHO cells expressing γ323 and γFL but not in γ318 and γ285 mutants. In addition, when CHO cells expressed γ318, γ323, or γFL with IL-2Rβ, IL-2 induced phospho-STAT5 only in the γ323 and γFL clones. Our data suggest that a smaller (5 amino acid) interval than previously determined is necessary for JAK3 activation/γC-mediated signaling in response to IL-4 and IL-2. Chimeric receptor chains of the γC tail fused to the IL-13Rα1 extracellular and transmembrane domain did not elicit robust IRS-2 phosphorylation in response to IL-13 suggesting that the extracellular/transmembrane domains of the IL-4/IL-13 receptor, not the cytoplasmic domains, control signaling efficiency. Understanding this pathway fully will lead to rational drug design for allergic disease.

Regulation of inflammation by interleukin-4: a review of "alternatives"

Studies of IL-4 have revealed a wealth of information on the diverse roles of this cytokine in homeostatic regulation and disease pathogenesis. Recent data suggest that instead of simple linear regulatory pathways, IL-4 drives regulation that is full of alternatives. In addition to the well-known dichotomous regulation of Th cell differentiation by IL-4, this cytokine is engaged in several other alternative pathways. Its own production involves alternative mRNA splicing, yielding at least two functional isoforms: full-length IL-4, encoded by the IL-4 gene exons 1-4, and IL-4δ2, encoded by exons 1, 3, and 4. The functional effects of these two isoforms are in some ways similar but in other ways quite distinct. When binding to the surface of target cells, IL-4 may differentially engage two different types of receptors. By acting on macrophages, a cell type critically involved in inflammation, IL-4 induces the so-called alternative macrophage activation. In this review, recent advances in understanding these three IL-4-related branch points--alternative splicing of IL-4, differential receptor engagement by IL-4, and differential regulation of macrophage activation by IL-4--are summarized in light of their contributions to inflammation.

IL-4 engagement of the type I IL-4 receptor complex enhances mouse eosinophil migration to eotaxin-1 in vitro

Background

Previous work from our laboratory demonstrated that IL-4Rα expression on a myeloid cell type was responsible for enhancement of Th2-driven eosinophilic inflammation in a mouse model of allergic lung inflammation. Subsequently, we have shown that IL-4 signaling through type I IL-4 receptors on monocytes/macrophages strongly induced activation of the IRS-2 pathway and a subset of genes characteristic of alternatively activated macrophages. The direct effect(s) of IL-4 and IL-13 on mouse eosinophils are not clear. The goal of this study was determine the effect of IL-4 and IL-13 on mouse eosinophil function.

Methods

Standard Transwell chemotaxis assay was used to assay migration of mouse eosinophils and signal transduction was assessed by Western blotting.

Results

Here we determined that (i) mouse eosinophils express both type I and type II IL-4 receptors, (ii) in contrast to human eosinophils, mouse eosinophils do not chemotax to IL-4 or IL-13 although (iii) pre-treatment with IL-4 but not IL-13 enhanced migration to eotaxin-1. This IL-4-mediated enhancement was dependent on type I IL-4 receptor expression: γC-deficient eosinophils did not show enhancement of migratory capacity when pre-treated with IL-4. In addition, mouse eosinophils responded to IL-4 with the robust tyrosine phosphorylation of STAT6 and IRS-2, while IL-13-induced responses were considerably weaker.

Conclusions

The presence of IL-4 in combination with eotaxin-1 in the allergic inflammatory milieu could potentiate infiltration of eosinophils into the lungs. Therapies that block IL-4 and chemokine receptors on eosinophils might be more effective clinically in reducing eosinophilic lung inflammation.

Contribution of alternatively activated macrophages to allergic lung inflammation: a tale of mice and men

The concept that macrophages play an active role in inflammatory responses began its development in the late 1800s with the now iconic studies by Elie Metchnikoff using starfish larvae and Daphnia [reviewed in Kaufmann SHE: Nat Immunol 2008;9:705-712 and Cavaillon JM: J Leukoc Biol 2011;90:413-424]. Based on his observation of the phagocyte response to a foreign body (rose thorn) and yeast, he proposed that phagocytes acted in host defense and were active participants in the inflammatory process. Flash forward more than 100 years and we find that these basic tenets hold true. However, it is now appreciated that macrophages come in many different flavors and can adopt a variety of nuanced phenotypes depending on the tissue environment in which the macrophage is found. In this brief review, we discuss the role of one type of macrophage termed the alternatively activated macrophage (AAM), also known as the M2 type of macrophage, in regulating allergic lung inflammation and asthma. Recent studies using mouse models of allergic lung inflammation and samples from human asthma patients contribute to the emerging concept that AAMs are not just bystanders of the interleukin (IL)-4- and IL-13-rich environment found in allergic asthma but are also active players in orchestrating allergic lung disease.

Adoptive transfer of IL-4Rα+ macrophages is sufficient to enhance eosinophilic inflammation in a mouse model of allergic lung inflammation

BACKGROUND

The IL-4 receptor α (IL-4Rα) chain has a broad expression pattern and participates in IL-4 and IL-13 signaling, allowing it to influence several pathological components of allergic lung inflammation. We previously reported that IL-4Rα expression on both bone marrow-derived and non-bone marrow-derived cells contributed to the severity of allergic lung inflammation. There was a correlation between the number of macrophages expressing the IL-4Rα, CD11b, and IA(d), and the degree of eosinophilia in ovalbumin challenged mice. The engagement of the IL-4Rα by IL-4 or IL-13 is able to stimulate the alternative activation of macrophages (AAM). The presence of AAM has been correlated with inflammatory responses to parasites and allergens. Therefore, we hypothesized that IL-4Rα⁺ AAM play an active role in allergic lung inflammation. To directly determine the role of AAM in allergic lung inflammation, M-CSF-dependent macrophages (BMM) were prepared from the bone-marrow of IL-4Rα positive and negative mice and transferred to IL-4RαxRAG2(-/-) mice. Wild type TH2 cells were provided exogenously.

RESULTS

Mice receiving IL-4Rα(+/+) BMM showed a marked increase in the recruitment of eosinophils to the lung after challenge with ovalbumin as compared to mice receiving IL-4Rα(-/-) BMM. As expected, the eosinophilic inflammation was dependent on the presence of TH2 cells. Furthermore, we observed an increase in cells expressing F4/80 and Mac3, and the AAM marker YM1/2 in the lungs of mice receiving IL-4Rα(+/+) BMM. The BAL fluid from these mice contained elevated levels of eotaxin-1, RANTES, and CCL2.

CONCLUSIONS

These results demonstrate that transfer of IL-4Rα + macrophages is sufficient to enhance TH2-driven, allergic inflammation. They further show that stimulation of macrophages through IL-4Rα leads to their alternative activation and positive contribution to the TH2-driven allergic inflammatory response in the lung. Since an increase in AAM and their products has been observed in patients with asthma exacerbations, these results suggest that AAM may be targeted to alleviate exacerbations.

Transfer of in vivo primed transgenic T cells supports allergic lung inflammation and FIZZ1 and Ym1 production in an IL-4Rα and STAT6 dependent manner

Background

CD4+ T helper type 2 (T_H2) cells, their cytokines IL-4, IL-5 and IL-13 and the transcription factor STAT6 are known to regulate various features of asthma including lung inflammation, mucus production and airway hyperreactivity and also drive alternative activation of macrophages (AAM). However, the precise roles played by the IL-4/IL-13 receptors and STAT6 in inducing AAM protein expression and modulating specific features of airway inflammation are still unclear. Since T_H2 differentiation and activation plays a pivotal role in this disease, we explored the possibility of developing an asthma model in mice using T cells that were differentiated in vivo.

Results

In this study, we monitored the activation and proliferation status of adoptively transferred allergen-specific naïve or in vivo primed CD4+ T cells. We found that both the naïve and in vivo primed T cells expressed similar levels of CD44 and IL-4. However, in vivo primed T cells underwent reduced proliferation in a lymphopenic environment when compared to naïve T cells. We then used these in vivo generated effector T cells in an asthma model. Although there was reduced inflammation in mice lacking IL-4Rα or STAT6, significant amounts of eosinophils were still present in the BAL and lung tissue. Moreover, specific AAM proteins YM1 and FIZZ1 were expressed by epithelial cells, while macrophages expressed only YM1 in RAG2^-/- mice. We further show that FIZZ1 and YM1 protein expression in the lung was completely dependent on signaling through the IL-4Rα and STAT6. Consistent with the enhanced inflammation and AAM protein expression, there was a significant increase in collagen deposition and smooth muscle thickening in RAG2^-/- mice compared to mice deficient in IL-4Rα or STAT6.

Conclusions

These results establish that transfer of in vivo primed CD4+ T cells can induce allergic lung inflammation. Furthermore, while IL-4/IL-13 signaling through IL-4Rα and STAT6 is essential for AAM protein expression, lung inflammation and eosinophilia are only partially dependent on this pathway. Further studies are required to identify other proteins and signaling pathways involved in airway inflammation.

A potential new target for asthma therapy: a disintegrin and metalloprotease 10 (ADAM10) involvement in murine experimental asthma

BACKGROUND

Elevated levels of CD23, a natural regulator of IgE production, have been shown to decrease the signs of lung inflammation in mice. The aim of this study was to study the involvement of ADAM10, the primary CD23 sheddase, in experimental asthma.

METHODS

ADAM10 was blocked either by using mice with a B-cell-specific deletion of the protease or pharmacologically by intranasal administration of selective ADAM10 inhibitors. Airway hypersensitivity (AHR) and bronchoaveolar lavage fluid (BALF) eosinophilia and select BALF cytokine/chemokine levels were then determined.

RESULTS

Using an IgE and mast cell-dependent mouse model, B-cell-specific ADAM10(-/-) mice (C57B/6 background) exhibited decreased eosinophilia and AHR when compared with littermate (LM) controls. Treatment of C57B/6 mice with selective inhibitors of ADAM10 resulted in an even further decrease in BALF eosinophilia, as compared with the ADAM10(-/-) animals. Even in the Th2 selective strain, Balb/c, BALF eosinophilia was reduced from 60% to 23% respectively. In contrast, when an IgE/mast cell-independent model of lung inflammation was used, the B-cell ADAM10(-/-) animals and ADAM10 inhibitor treated animals had lung inflammation levels that were similar to the controls.

CONCLUSIONS

These results thus show that ADAM10 is important in the progression of IgE-dependent lung inflammation. The use of the inhibitor further suggested that ADAM10 was important for maintaining Th2 levels in the lung. These results thus suggest that decreasing ADAM10 activity could be beneficial in controlling asthma and possibly other IgE-dependent diseases.

NF-κB signaling participates in both RANKL- and IL-4-induced macrophage fusion: receptor cross-talk leads to alterations in NF-κB pathways

NF-κB activation is essential for receptor activator for NF-κB ligand (RANKL)-induced osteoclast formation. IL-4 is known to inhibit the RANKL-induced osteoclast differentiation while at the same time promoting macrophage fusion to form multinucleated giant cells (MNG). Several groups have proposed that IL-4 inhibition of osteoclastogenesis is mediated by suppressing the RANKL-induced activation of NF-κB. However, we found that IL-4 did not block proximal, canonical NF-κB signaling. Instead, we found that IL-4 inhibited alternative NF-κB signaling and induced p105/50 expression. Interestingly, in nfκb1(-/-) bone marrow-derived macrophages (BMM), the formation of both multinucleated osteoclast and MNG induced by RANKL or IL-4, respectively, was impaired. This suggests that NF-κB signaling also plays an important role in IL-4-induced macrophage fusion. Indeed, we found that the RANKL-induced and IL-4-induced macrophage fusion were both inhibited by the NF-κB inhibitors IκB kinase 2 inhibitor and NF-κB essential modulator inhibitory peptide. Furthermore, overexpression of p50, p65, p52, and RelB individually in nfκb1(-/-) or nfκb1(+/+) BMM enhanced both giant osteoclast and MNG formation. Interestingly, knockdown of nfκb2 in wild-type BMM dramatically enhanced both osteoclast and MNG formation. In addition, both RANKL- and IL-4-induced macrophage fusion were impaired in NF-κB-inducing kinase(-/-) BMM. These results suggest IL-4 influences NF-κB pathways by increasing p105/p50 and suppressing RANKL-induced p52 translocation and that NF-κB pathways participate in both RANKL- and IL-4-induced giant cell formation.

TLR2 signaling and Th2 responses drive Tannerella forsythia-induced periodontal bone loss

Periodontal disease (PD) is a chronic inflammation of the tooth-supporting soft tissue and alveolar bone due to infection by a select group of gram-negative microbes, which leads to tooth loss if untreated. Because mice deficient in CD4(+) cells are resistant to infection-induced alveolar bone loss, Th cells have been implicated in bone-destructive processes during PD. However, the extent to which different Th cell subtypes play roles in pathogenesis or host protection remains to be defined and is likely to vary depending on the dominant microorganism involved. By far, Porphyromonas gingivalis is the best-studied periodontal microbe in PD. Although the gram-negative anaerobe Tannerella forsythia is also a vital contributor to periodontal bone loss, almost nothing is known about immune responses to this organism. Previous studies from our laboratory revealed that T. forsythia induces periodontal bone loss in mice and that this bone loss depends on the bacterially expressed BspA protein. In this study, we showed that T. forsythia activates murine APCs primarily through TLR2-dependent signaling via BspA. Furthermore, T. forsythia infection causes a pronounced Th2 bias, evidenced by T cell expression of IL-5, but not IFN-γ or IL-17, in draining lymph nodes. Consistently, deficiencies in TLR2 or STAT6 result in resistance to T. forsythia-induced alveolar bone loss. Thus, TLR2 signaling and Th2 cells play pathogenic roles in T. forsythia-induced alveolar bone destruction.

Transcriptional control of rapid recall by memory CD4 T cells

Memory T cells are distinguished from naive T cells by their rapid production of effector cytokines, although mechanisms for this recall response remain undefined. In this study, we investigated transcriptional mechanisms for rapid IFN-γ production by Ag-specific memory CD4 T cells. In naive CD4 T cells, IFN-γ production only occurred after sustained Ag activation and was associated with high expression of the T-bet transcription factor required for Th1 differentiation and with T-bet binding to the IFN-γ promoter as assessed by chromatin immunoprecipitation analysis. By contrast, immediate IFN-γ production by Ag-stimulated memory CD4 T cells occurred in the absence of significant nuclear T-bet expression or T-bet engagement on the IFN-γ promoter. We identified rapid induction of NF-κB transcriptional activity and increased engagement of NF-κB on the IFN-γ promoter at rapid times after TCR stimulation of memory compared with naive CD4 T cells. Moreover, pharmacologic inhibition of NF-κB activity or peptide-mediated inhibition of NF-κB p50 translocation abrogated early memory T cell signaling and TCR-mediated effector function. Our results reveal a molecular mechanism for memory T cell recall through enhanced NF-κB p50 activation and promoter engagement, with important implications for memory T cell modulation in vaccines, autoimmunity, and transplantation.

Expression of neuroimmune semaphorins 4A and 4D and their receptors in the lung is enhanced by allergen and vascular endothelial growth factor

Background

Semaphorins were originally identified as molecules regulating a functional activity of axons in the nervous system. Sema4A and Sema4D were the first semaphorins found to be expressed on immune cells and were termed "immune semaphorins". It is known that Sema4A and Sema4D bind Tim-2 and CD72 expressed on leukocytes and PlexinD1 and B1 present on non-immune cells. These neuroimmune semaphorins and their receptors have been shown to play critical roles in many physiological and pathological processes including neuronal development, immune response regulation, cancer, autoimmune, cardiovascular, renal, and infectious diseases. However, the expression and regulation of Sema4A, Sema4D, and their receptors in normal and allergic lungs is undefined.

Results

Allergen treatment and lung-specific vascular endothelial growth factor (VEGF) expression induced asthma-like pathologies in the murine lungs. These experimental models of allergic airway inflammation were used for the expression analysis of immune semaphorins and their receptors employing immunohistochemistry and flow cytometry techniques. We found that besides accessory-like cells, Sema4A was also detected on bronchial epithelial and smooth muscle cells, whereas Sema4D expression was high on immune cells such as T and B lymphocytes. Surprisingly, under inflammation various cell types including macrophages, lymphocytes, and granulocytes in the lung expressed Tim-2, a previously defined marker for Th2 cells. CD72 was found on lung immune, inflammatory, and epithelial cells. Bronchial epithelial cells were positive for both plexins, whereas some endothelial cells selectively expressed Plexin D1. Plexin B1 expression was also detected on lung DC. Both allergen and VEGF upregulated the expression of neuroimmune semaphorins and their receptors in the lung tissue. However, the lung tissue Sema4A-Tim2 expression was rather weak, whereas Sema4D-CD72 ligand-receptor pair was vastly upregulated by allergen. Soluble Sema4D protein was present in the lung lysates and a whole Sema4A protein plus its dimer were readily detected in the bronchoalveolar (BAL) fluids under inflammation.

Conclusions

This study clearly shows that neuroimmune semaphorins Sema4A and Sema4D and their receptors might serve as potential markers for the allergic airway inflammatory diseases. Our current findings pave the way for further investigations of the role of immune semaphorins in inflammation and their use as potential therapeutic targets for the inflammatory lung conditions.

Alternatively spliced variants of interleukin-4 promote inflammation differentially

IL-4δ2 is a natural splice variant of IL-4 that lacks the region encoded by the second exon. Numerous reports have suggested that the expression levels of IL-4δ2 change in various diseases, especially those with pulmonary involvement, but the in vivo effects of this splice variant have never been studied. Replication-deficient, AdV-mediated gene delivery of mIL-4δ2 to mouse lungs in vivo was used, and the effects compared with similar adenoviral delivery of mIL-4 or with infection with a noncoding NULL viral construct. Overexpression of IL-4δ2 or IL-4 caused pulmonary infiltration by T and B lymphocytes, whereas in contrast to IL-4, IL-4δ2 did not induce eosinophilia or goblet cell hyperplasia. Microarray analysis of global gene expression revealed that IL-4δ2 and IL-4 had differential effects on gene expression. These splice variants also differentially regulated pulmonary levels of the cytokines TNF-α, eotaxin, IL-1α, IFN-γ, and MCP-1, whereas both tended to increase total lung collagen modestly. Pulmonary infiltration by lymphocytes in response to overexpression of IL-4δ2 was attenuated but not abrogated completely by germline deficiency of IL-4Rα or STAT6, whereas deficiency of endogenous IL-4 had no effect. Thus, IL-4δ2 promotes lymphocytic inflammation in vivo (although differentially from IL-4, in part), and the effects of IL-4δ2 are not mediated by endogenous IL-4. Differential targeting of IL-4δ2 and IL-4 may therefore be considered in developing future therapeutic agents.

STAT6 expression in multiple cell types mediates the cooperative development of allergic airway disease

Th2 cells induce asthma through the secretion of cytokines. Two such cytokines, IL-4 and IL-13, are critical mediators of many features of this disease. They both share a common receptor subunit, IL-4Rα, and signal through the STAT6 pathway. STAT6(-/-) mice have impaired Th2 differentiation and reduced airway response to allergen. Transferred Th2 cells were not able to elicit eosinophilia in response to OVA in STAT6(-/-) mice. To clarify the role of STAT6 in allergic airway inflammation, we generated mouse bone marrow (BM) chimeras. We observed little to no eosinophilia in OVA-treated STAT6(-/-) mice even when STAT6(+/+) BM or Th2 cells were provided. However, when Th2 cells were transferred to STAT6×Rag2(-/-) mice, we observed an eosinophilic response to OVA. Nevertheless, the expression of STAT6 on either BM-derived cells or lung resident cells enhanced the severity of OVA-induced eosinophilia. Moreover, when both the BM donor and recipient lacked lymphocytes, transferred Th2 cells were sufficient to induce the level of eosinophilia comparable with that of wild-type (WT) mice. The expression of STAT6 in BM-derived cells was more critical for the enhanced eosinophilic response. Furthermore, we found a significantly higher number of CD4(+)CD25(+)Foxp3(+) T cells (regulatory T cells [Tregs]) in PBS- and OVA-treated STAT6(-/-) mouse lungs compared with that in WT animals suggesting that STAT6 limits both naturally occurring and Ag-induced Tregs. Tregs obtained from either WT or STAT6(-/-) mice were equally efficient in suppressing CD4(+) T cell proliferation in vitro. Taken together, our studies demonstrate multiple STAT6-dependent and -independent features of allergic inflammation, which may impact treatments targeting STAT6.

Splice isoforms of human interleukin-4 are functionally active in mice in vivo

Interleukin-4 (IL-4) acts on cultured cells in a species-specific fashion, although several reports have suggested that human (h) IL-4 may be functionally active in rodents in vivo. The latter finding, if true, would not only offer possibilities for pre-clinical testing of novel hIL-4-targeting therapies in animals, but also suggests new opportunities for mechanistic studies of IL-4 and its receptors. Conventional IL-4 is encoded by four exons, whereas its poorly studied alternatively spliced isoform is encoded by exons 1, 3 and 4 (IL-4δ2). Replication-deficient adenovirus-mediated gene delivery of hIL-4 isoforms (hIL-4 or hIL-4δ2) to mouse lungs caused similar pulmonary infiltration of T and B lymphocytes, but not eosinophils. There were significant differences in the changes of pulmonary cytokine milieu induced by hIL-4 compared with hIL-4δ2, with hIL-4δ2 inducing higher levels of pro-inflammatory (tumour necrosis factor-α, IL-1, and monocyte chemotactic protein-1) and T helper type 1 (IL-12 and interferon-γ) cytokines. There was no elevation in endogenous mouse (m) IL-4 or mIL-4δ2 mRNAs, and germ-line deficiency of mIL-4 did not affect the degree of pulmonary infiltration. When combined with an ovalbumin model of asthma, hIL-4δ2 stimulated a greater accumulation of lymphocytes than did hIL-4. Pulmonary infiltration of lymphocytes induced by expression of hIL-4 or hIL-4δ2 was attenuated, but not completely abrogated, by germ-line deficiency of mIL-4Rα or murine signal transducer and activator of transcription 6, suggesting that these signalling molecules mediate the in vivo effects of hIL-4 isoforms in mice. These findings suggest that splice isoforms of human IL-4 are functionally active in vivo in mice, and partially share the effects of the corresponding species-specific isoforms.

Control of RSV-induced lung injury by alternatively activated macrophages is IL-4R alpha-, TLR4-, and IFN-beta-dependent

Severe respiratory syncytial virus (RSV)-induced bronchiolitis has been associated with a mixed "Th1" and "Th2" cytokine storm. We hypothesized that differentiation of "alternatively activated" macrophages (AA-M phi) would mediate the resolution of RSV-induced lung injury. RSV induced interleukin (IL)-4 and IL-13 by murine lung and peritoneal macrophages, IL-4R alpha/STAT6-dependent AA-M phi differentiation, and significantly enhanced inflammation in the lungs of IL-4R alpha(-/-) mice. Adoptive transfer of wildtype macrophages to IL-4R alpha(-/-) mice restored RSV-inducible AA-M phi phenotype and diminished lung pathology. RSV-infected Toll-like receptor (TLR)4(-/-) and interferon (IFN)-beta(-/-) macrophages and mice also failed to express AA-M phi markers, but exhibited sustained proinflammatory cytokine production (e.g., IL-12) in vitro and in vivo and epithelial damage in vivo. TLR4 signaling is required for peroxisome proliferator-activated receptor gamma expression, a DNA-binding protein that induces AA-M phi genes, whereas IFN-beta regulates IL-4, IL-13, IL-4R alpha, and IL-10 expression in response to RSV. RSV-infected cotton rats treated with a cyclooxygenase-2 inhibitor increased expression of lung AA-M phi. These data suggest new treatment strategies for RSV that promote AA-M phi differentiation.

Abstract 4014: Differential expression and activation of IRS1 and IRS2 in breast cancer cell lines

Numerous studies have shown that IL-4 can protect various types of tumor cells from chemotherapeutic agents including breast cancer cells. There are two main signaling pathways activated by IL-4; the STAT6, signal transducers and activators of transcription pathway, that results in expression of IL-4-responsive genes and the IRS1/2 signaling pathway that influences cellular proliferation and survival. IL-4 can act directly on many tumor cell types to prevent apoptosis. The IL-4-induced activation of STAT6 has been shown to up-regulate anti-apoptotic proteins, cFlip and BcLxL, in cancer. IRS1/2 molecules link the IL-4R and IGF-1R to signaling pathways that regulate cellular proliferation and survival, and are therefore implicated in cancer progression. Recent studies showed that IRS2 regulates mammary tumor metastasis in a mouse model of breast cancer and that knocking out IRS2 rendered the tumor cells less invasive and more susceptible to apoptosis in response to growth factor withdrawal. IRS1 was not required for metastasis and was actually suggested to be a suppressor of metastasis in breast cancer and an enhancer of proliferation. IRS2 suppressed the function of IRS1 by strongly activating the Akt/mTOR signaling pathway and inducing the serine phosphorylation of IRS1. We have found that expression of IRS1, in contrast to IRS2, leads to enhanced sensitivity to chemotherapy-induced cell death in 32D cells. Furthermore, it has been shown that MCF7 cells are more sensitive to docetaxel-induced death as compared to MDA-MB-231 cells. We propose that sensitivity of breast cancer cells to chemotherapy is in part regulated by the relative abundance of IRS1 and IRS2 and their phosphorylation status. To begin to test this hypothesis, we cultured breast cancer cells lines in the presence or absence of IL-4 and evaluated the IRS pathways. We found that MCF7 cells highly expressed IRS1 with little IRS2 while MDA-MB-231 cells expressed relatively equal amounts of IRS1 and IRS2. In MCF7 cells IL-4 induced the potent tyrosine phosphorylation of IRS1 with very little tyrosine phosphorylation of IRS2. However, in MDA-MB-231 cells, IL-4 induced the tyrosine phosphorylation of both IRS1 and IRS2 equally. However, the level of IRS1 phosphorylation in MDA-MD-231 cells was less than that observed in MCF7 cells. Taken together with previous publications, these results suggest that the differential activation status of IRS1 and IRS2 in breast cancer can lead to differential metastatic and chemosensitivity phenotypes.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4014.

Regulation of the T helper cell type 2 (Th2)/T regulatory cell (Treg) balance by IL-4 and STAT6

During the development of immune responses to pathogens, self-antigens, or environmental allergens, naive CD4(+) T cells differentiate into subsets of effector cells including Th1, Th2, and Th17 cells. The differentiation into these subsets is controlled by specific transcription factors. The activity of these effector cells is limited by nTregs and iTregs, whose differentiation and maintenance are dependent on the transcription factor Foxp3. The regulation of autoimmune diseases mediated by Th1 and Th17 cells by Tregs has been studied and reviewed extensively. However, much less has been presented about the interplay between Tregs and Th2 cells and their contribution to allergic disease. In this perspective, we discuss the regulation of Th2 cells by Tregs and vice versa, focusing on the interplay between the IL-4-activated STAT6/GATA3 pathway and Foxp3.

Complex regulation of tartrate-resistant acid phosphatase (TRAP) expression by interleukin 4 (IL-4): IL-4 indirectly suppresses receptor activator of NF-kappaB ligand (RANKL)-mediated TRAP expression but modestly induces its expression directly

Interleukin 4 (IL-4) inhibits receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast formation and functional activity in a STAT6-dependent manner. IL-4 down-regulates expression of tartrate-resistant acid phosphatase (TRAP) in mature osteoclasts. To determine whether IL-4 regulates TRAP promoter activity, RAW264.7 cells were transfected with a TRAP promoter-luciferase reporter. Treatment with IL-4 alone modestly enhanced TRAP luciferase activity. However, IL-4 suppressed the ability of RANKL to up-regulate TRAP-luciferase activity, suggesting that IL-4 has multiple effects on TRAP transcription. IL-4 also reduced the RANKL-induced association of RNA polymerase II with the TRAP gene in osteoclasts. The TRAP promoter contains a STAT6-binding motif, and STAT6 bound to the endogenous TRAP promoter after IL-4 treatment. To determine the impact of STAT6 binding, we transfected cells with STAT6VT, a constitutively active STAT6 mutant. STAT6VT alone up-regulated TRAP-luciferase activity; this effect was abrogated by mutating the STAT6 binding site in the minimal TRAP promoter. STAT6VT did not inhibit the potent up-regulation of TRAP promoter activity caused by overexpression of NFATc1, PU.1, and microphthalmia transcription factor, downstream targets of macrophage colony-stimulating factor and RANKL. IL-4 down-regulated the expression of c-Fos and NFATc1 in mature osteoclasts. Knockdown of NFATc1 by short interfering RNA caused TRAP expression to be down-regulated, and ectopic expression of NFATc1 abrogated the IL-4-induced down-regulation of TRAP. These results suggest that STAT6 plays two distinct roles in TRAP expression. The IL-4-induced activation of STAT6 mediates suppression of the RANKL-induced TRAP promoter activity indirectly by inhibiting NFATc1 expression. However, in the absence of RANKL and osteoclast differentiation, STAT6 binds the TRAP promoter after IL-4 treatment and directly enhances TRAP expression.

An atopy-associated polymorphism in the ectodomain of the IL-4R(alpha) chain (V50) regulates the persistence of STAT6 phosphorylation

Several commonly occurring polymorphisms in the IL-4R(alpha) have been associated with atopy in humans; the Q576R and the S503P polymorphisms reside in the cytoplasmic domain, whereas the I50 to V50 polymorphism resides in the extracellular domain of the IL-4R(alpha). The effects of these polymorphisms on signaling remain controversial. To determine the effect of the polymorphisms on IL-4 signaling in human cells, we stably transfected the human monocytic cell line U937 with murine IL-4R(alpha) cDNA bearing the I or V at position 50 and the P503/R576 double mutant. Each form of the murine IL-4R(alpha) mediated tyrosine phosphorylation of STAT6 in response to murine IL-4 treatment similar to the induction of tyrosine phosphorylation by human IL-4 signaling through the endogenous human IL-4R(alpha). After IL-4 removal, tyrosine-phosphorylated STAT6 rapidly decayed in cells expressing I50 or P503R576 murine IL-4Ralpha. In contrast, STAT6 remained significantly phosphorylated for several hours after murine IL-4 withdrawal in cells expressing the V50 polymorphism. This persistence in tyrosine-phosphorylated STAT6 was associated with persistence in CIS mRNA expression. Blocking IL-4 signaling during the decay phase using the JAK inhibitor AG490 or the anti-IL-4R(alpha) Ab M1 abrogated the persistence of phosphorylated STAT6 observed in the V50-IL-4R(alpha)-expressing cells. These results indicate that the V50 polymorphism promotes sustained STAT6 phosphorylation and that this process is mediated by continued engagement of IL-4R(alpha), suggesting enhanced responses of V50 IL-4R when IL-4 is limiting.

IRS-2 phosphorylation and association with p85 and Grb2 after engagement of type I IL-4 receptor (IL-4R). (38.2)

We previously showed that IL-4 elicited stronger tyrosine phosphorylation of insulin receptor substrate (IRS)-2 than IL-13. This IRS-2 phosphorylation difference was observed even at high concentrations of IL-13 and was due to the exclusive ability of IL-4 to bind to type I IL-4 Rs (IL-4Rα + γC). Furthermore, IL-4 but not IL-13, significantly augmented expression of a subset of alternatively-activated macrophage (AAM) genes, arginase I, found in inflammatory zone (FIZZ)1, and Ym1 in WT bone marrow-derived macrophages (BMM). In this study, we further analyzed signaling differences between IL-4 and IL-13 downstream of the IRS-2 pathway. IL-4 stimulation resulted in enhanced association of the p85 subunit of PI-3' kinase with IRS-2 as compared to IL-13, while only IL-4 induced the association of Grb2 with IRS-2 in WT BMM. Since IRS-2 activation leads to PI-3' K activation, we investigated the effect of wortmannin on induction of the AAM genes. IL-4-induced expression of FIZZ1 was suppressed by wortmannin to the levels induced by IL-13. Arginase I and Ym1 expression was unaffected by wortmannin. These data suggest that the type I IL-4R can direct site-specific phosphorylation of IRS-2, resulting in enhanced recruitment of adaptor molecules and augmented expression of a subset of AAM genes. In addition, they suggest these genes are differentially affected by the IRS-2/PI-3' K pathway. (PHS AI38985)

Alternatively activated macrophages participate in the recruitment of eosinophils to the lung in a murine model of allergic lung inflammation (79.2)

The IL-4 receptor α (IL-4Rα) chain has a broad expression pattern and is involved in IL-4 and IL-13 signaling, allowing it to influence various pathological components of allergic lung inflammation. We've previously reported that IL-4Rα expression on both bone marrow derived and non-bone marrow derived cells contributes to the severity of allergic lung inflammation. We found a correlation between the expansion of cells expressing the IL-4Rα, CD11b, and IAd and the degree of eosinophilia in ovalbumin challenged mice, suggesting a possible role for monocytes in the development of disease. To determine the role of CD11b+ cells in allergic lung inflammation, CD11b cells were developed in vitro from IL-4Rα positive and negative mice and transferred to IL-4RαxRAG2 knockout mice; TH2 cells were provided exogenously. Mice receiving IL-4Rα+, CD11b+ cells showed a marked increase in the recruitment of eosinophils to the lung after challenge with ovalbumin as compared to mice receiving IL-4Rα-, CD11b+ cells. Furthermore, an increase in cells expressing the macrophage marker F4/80 and the alternatively activated macrophage marker Ym-1 were recruited to the lungs of mice receiving IL-4Rα+, CD11b+ cells. These results suggest that stimulation of macrophages through IL-4Rα leads to their alternative activation and participation in the recruitment of eosinophils to the lung. (PHS AI38985)

Type I IL-4Rs selectively activate IRS-2 to induce target gene expression in macrophages

Although interleukin-4 (IL-4) and IL-13 participate in allergic inflammation and share a receptor subunit (IL-4Ralpha), they have different functions. We compared cells expressing type I and II IL-4Rs with cells expressing only type II receptors for their responsiveness to these cytokines. IL-4 induced highly efficient, gammaC-dependent tyrosine phosphorylation of insulin receptor substrate 2 (IRS-2), whereas IL-13 was less effective, even when phosphorylation of signal transducer and activator of transcription 6 (STAT6) was maximal. Only type I receptor, gammaC-dependent signaling induced efficient association of IRS-2 with the p85 subunit of phosphoinositide 3-kinase or the adaptor protein growth factor receptor-bound protein 2. In addition, IL-4 signaling through type I IL-4Rs induced more robust expression of a subset of genes associated with alternatively activated macrophages than did IL-13. Thus, IL-4 activates signaling pathways through type I IL-4Rs qualitatively differently from IL-13, which cooperate to induce optimal gene expression.

Francisella tularensis live vaccine strain induces macrophage alternative activation as a survival mechanism

Francisella tularensis (Ft), the causative agent of tularemia, elicits a potent inflammatory response early in infection, yet persists within host macrophages and can be lethal if left unchecked. We report in this study that Ft live vaccine strain (LVS) infection of murine macrophages induced TLR2-dependent expression of alternative activation markers that followed the appearance of classically activated markers. Intraperitoneal infection with Ft LVS also resulted in induction of alternatively activated macrophages (AA-Mphi). Induction of AA-Mphi by treatment of cells with rIL-4 or by infection with Ft LVS promoted replication of intracellular Ftn, in contrast to classically activated (IFN-gamma plus LPS) macrophages that promoted intracellular killing of Ft LVS. Ft LVS failed to induce alternative activation in IL-4Ralpha(-/-) or STAT6(-/-) macrophages and prolonged the classical inflammatory response in these cells, resulting in intracellular killing of Ft. Treatment of macrophages with anti-IL-4 and anti-IL-13 Ab blunted Ft-induced AA-Mphi differentiation and resulted in increased expression of IL-12 p70 and decreased bacterial replication. In vivo, Ft-infected IL-4Ralpha(-/-) mice exhibited increased survival compared with wild-type mice. Thus, redirection of macrophage differentiation by Ft LVS from a classical to an alternative activation state enables the organism to survive at the expense of the host.