Structure of IL-13 receptor: analysis of subunit composition in cancer and immune cells

Interleukin-13 receptor-directed cytotoxin for malignant glioma therapy: from bench to bedside

Central nervous system malignant neoplasias, in particular, glioblastoma multiforme (GBM) have defied all current therapeutic modalities. New therapies involving tumor targeting approach are being explored. This approach relies on the identification of unique or over-expressed cell surface receptors or antigens on tumor cells. In that regard, we have identified receptor for an immune regulatory cytokine, interleukin-13 (IL-13), which is over-expressed on human malignant glioma cell lines and primary tumor cell cultures. To target IL-13 receptors (IL-13R) for cancer therapy, we have developed a recombinant fusion protein composed of IL-13 and a mutated form of Pseudomonas exotoxin (IL13-PE38QQR or IL-13 cytotoxin). The IL-13 cytotoxin was found to be highly selective and potent in killing human GBM cells in vitro while normal cells including immune cells, endothelial cells and normal brain cells were generally spared the cytotoxic effect of IL-13 cytotoxin. This is because these cells either expressed none or expressed low levels of IL-13R. Consistent with in vitro cytotoxic activity, IL-13 cytotoxin mediated remarkable anti-tumor activity to human glioma in animal xenograft models. The direct injection of IL-13 cytotoxin into subcutaneous human GBM tumors grown in nude mice produced complete and durable regression of established tumors. Intravenous and intraperitoneal administration of IL-13 cytotoxin also reduced tumor burden significantly with fewer complete responders. All animals tolerated therapy well with minimal toxicity to vital organs. Pre-clinical safety and toxicity studies were performed in mice, rats and monkeys. Systemic administration of IL-13 cytotoxin appeared to be well tolerated at high doses (up to 50 microg/kg). Intrabrain parenchyma administration of IL-13 cytotoxin at doses up to 100 microg/ml was very well tolerated without any evidence of gross or microscopic necrosis, whereas at 500 microg/ml dose, localized necrosis was observed in normal rat brain. Based on these encouraging pre-clinical studies, three Phase I/II clinical trials in adults with malignant glioma have been initiated. The first clinical trial involves convection-enhanced delivery (CED) of IL-13 cytotoxin into recurrent malignant glioma. This route of IL-13 cytotoxin administration appears to be fairly well tolerated with no neurotoxicity. The second clinical trial involves infusion of IL-13 cytotoxin by CED following tumor resection. The initial stage of the second study assessed histologic effect of drug administered prior to resection. In third one, IL-13 cytotoxin is infused by CED followed by tumor resection. All three clinical trials are currently ongoing.

Therapeutic attenuation of pulmonary fibrosis via targeting of IL-4- and IL-13-responsive cells

Severe forms of idiopathic interstitial pneumonia (IIP), such as usual interstitial pneumonia, can be impervious to modern steroid and immunosuppressive treatment regimens, thereby emphasizing the need for novel effective therapies. Consequently, research attention has been directed toward understanding the cytokine networks that may affect fibroblast activation and, hence, the progression of certain IIPs. This led us to investigate whether the specific targeting of resident lung cells responsive to IL-4 and IL-13 exerted a therapeutic effect in an experimental model of IIP, namely the bleomycin-induced model of pulmonary fibrosis. IL-4, IL-13, and their corresponding receptor subunits, IL-4Ralpha, IL-13Ralpha1, and IL-13Ralpha2, were maximally expressed at the mRNA and protein levels in whole lung samples on day 21 or 28 after an intratracheal bleomycin challenge. The intranasal administration of an IL-13 immunotoxin chimeric molecule (IL13-PE) from days 21-28, but not for 1-wk periods at earlier times, after bleomycin challenge had a significant therapeutic effect on histological and biochemical parameters of bleomycin-induced pulmonary fibrosis compared with the control group. The intranasal IL13-PE therapy significantly reduced the numbers of IL-4 and IL-13 receptor-positive mononuclear cells and macrophages and the levels of profibrotic cytokine and chemokine in the lungs of bleomycin-challenged mice on day 28. Thus, this study demonstrates that IL-4- and/or IL-13-binding cells are required for the maintenance of pulmonary fibrosis induced by bleomycin and highlights the importance of further investigation of antifibrotic therapeutics that target these cells during pulmonary fibrosis.

Potent antitumor activity of IL-13 cytotoxin in human pancreatic tumors engineered to express IL-13 receptor alpha2 chain in vivo

Interleukin-13 receptor (IL-13R) alpha2 chain plays a key role in ligand binding and internalization. We have recently demonstrated that this cytokine receptor chain has unique characteristics in tumor biology: it inhibits tumorigenicity of breast and pancreatic cancer in animal models. In this study, we have exploited IL-13Ralpha2 chain and established a novel approach for pancreatic cancer therapy. For this, a plasmid encoding the IL-13Ralpha2 chain gene was mixed with liposomes and injected into subcutaneously or orthotopically xenografted human pancreatic tumors in immunodeficient mice, followed by systemic or local therapy by a recombinant IL-13 cytotoxin. Only tumors forced to express IL-13Ralpha2 chain acquired extreme susceptibility to the antitumor effect of IL-13 cytotoxin. There was a dominant infiltration of cells including macrophages and natural killer cells in the regressing tumors. Since macrophages were found to produce nitric oxide, IL-13Ralpha2-targeted cancer therapy involved not only a direct tumor cell killing by IL-13 cytotoxin but also activation of innate immune response at the tumor site. Therefore, this approach may be a new powerful tool for pancreatic cancer or other localized cancer therapy.

Functional characterization of IL-13 receptor alpha2 gene promoter: a critical role of the transcription factor STAT6 for regulated expression

Interleukin (IL)-4 and IL-13 are two structurally and functionally related cytokines that have overlapping but also distinct biological activities. One of the components of the IL-13 receptor, the alpha2 chain (IL-13Ralpha2), has been reported to downregulate the cell responsiveness to IL-13, without affecting IL-4 signaling. Here, we report that TNFalpha synergizes with either IL-4 or IL-13 in inducing the IL-13Ralpha2 chain at both the mRNA and protein levels in the HaCaT human keratinocyte cell line. Further studies by 5'RACE identified as yet undescribed exonic sequences of the IL-13Ralpha2 5'UTR, provided evidence for the expression of alternatively spliced IL-13Ralpha2 transcripts and defined the transcription start of the IL-13Ralpha2 gene. A 1.5 kb region upstream of the first exon of the IL-13Ralpha2 gene displayed basal promoter activity when inserted in a reporter plasmid and transiently transfected in HaCaT cells. This promoter activity was further increased in response to IL-4 and IL-13. Furthermore, by electrophoretic mobility shift assay and site-directed mutagenesis, we showed that the IL-4/IL-13-induced promoter activity depended upon a positively acting STAT6 response element. Finally, TNFalpha was shown to potentiate IL-4/IL-13-induced IL-13Ralpha2 promoter activity when the same reporter construct was studied in stably but not in transiently transfected cells. These results suggest that the synergistic effect of TNFalpha on IL-4/IL-13-induced IL-13Ralpha2 expression is dependent upon chromatin re-modeling events.

Impact of interleukin-13 responsiveness on the synthetic and proliferative properties of Th1- and Th2-type pulmonary granuloma fibroblasts

Interleukin-13 (IL-13) has emerged as a major cytokine mediator of fibroblast activation and pulmonary fibrosis. Normal (from noninflamed lung), Th1-type (induced by the pulmonary embolization of purified peptide derivative-coated beads in mice sensitized to purified peptide derivative), and Th2-type (induced by the pulmonary embolization of Schistosoma mansoni egg antigen-coated beads in mice sensitized with S. mansoni eggs) primary fibroblast cell lines all exhibited constitutive gene expression of two receptor chains that bind and signal IL-13-mediated cellular events: IL-4Ralpha and IL-13Ralpha1. However, all three fibroblast cell lines exhibited divergent synthetic and proliferative responses to the exogenous addition of either recombinant IL-13 or a chimeric protein comprised of IL-13 and a truncated version of Pseudomonas exotoxin (IL13-PE), which targets and kills IL-13 receptor overexpressing cells. The exogenous addition of IL-13 to Th1-type and Th2-type fibroblast cultures significantly increased the cellular expression of IL-13Ralpha2, which may function as an IL-13 decoy receptor. After a 24-hour exposure to IL-13, the total collagen generation and cellular proliferation by Th2-type fibroblasts were significantly higher than that observed in similar numbers of normal and Th1-type fibroblasts. In addition IL13-PE, which binds with highest affinity to IL-13Ralpha2, exhibited down-regulatory effects on proliferation and matrix generation expression by Th1- and Th2-type, but not normal, fibroblasts. Thus, these data demonstrate that fibroblasts derived from murine pulmonary granulomas exhibit divergent expression of functional IL-13 receptor and this expression dictates the responsiveness and susceptibility to recombinant IL-13 and IL-13 immunotoxin, respectively.

Molecular cloning of the rat IL-13 alpha 2 receptor cDNA and its expression in rat tissues

The interleukin 13 alpha 2 receptor (IL-13Ralpha2) is highly expressed in human glioma cells. As a consequence this receptor has been proposed as a potential target for immunotherapeutic approaches for treating brain tumors. In developing animal models that may utilize the IL-13Ralpha2 receptor as an immunotherapeutic target, only the murine gene sequence has thus far been elucidated. The purpose of the present study, therefore, was to determine the gene sequence and tissue distribution of IL-13Ralpha2 in the rat. A search of the NCBI expressed sequence tag (EST) database with human and mouse IL-13Ralpha2 gene sequences identified a rat EST with high homology to the human and mouse IL-13Ralpha2 conserved region. Based on the sequence information, a 1917 bp rat IL-13Ralpha2 cDNA was cloned using the 5' and 3' RACE PCR technique. The cloned rat IL-13Ralpha2 cDNA contains a full-length 1158 bp open reading frame. The deduced protein is 91.2% and 54.2% homologous to mouse and human IL- 13Ralpha2, respectively, at the amino acid level. Analysis shows that the rat IL-13Ralpha2 is structurally conserved and similar to human and mouse. It has a very short cytoplasmic domain, an extracellular domain containing an N-terminal fibronectin type III domain, four putative N-glycosylation sites, and a growth factor and cytokine receptor family motif WSEWS. Using RT-PCR techniques, the mRNA of rat IL-13Ralpha2 was detected in rat brain, spleen, liver, thymus, stomach, testis, and three rat glioblastoma cell lines C6, A15A5 and 9L. The cloning of rat IL-13Ralpha2 may be helpful to establish a rat model for IL-13Ralpha2 related glioma therapies.

Convection enhanced delivery of IL13-PE38QQR for treatment of recurrent malignant glioma: presentation of interim findings from ongoing phase 1 studies

IL13PE38QQR is a recombinant toxin composed of the enzymatically-active portion of Pseudomonas Exotoxin A conjugated with human IL13. Binding of IL13-PE38 to the IL13 receptor (IL13R) permits internalization of the recombinant toxin resulting in selective and potent cytoxicity at nanomolar concentrations. Normal brain tissue expresses little or no IL13R, but malignant gliomas overexpress IL13R conferring the selective cytotoxicity to the agent. Convection-enhanced delivery (CED), a novel direct drug delivery method to tumor and peritumoral region uses positive pressure infusion to generate a pressure gradient that optimizes distribution of macromolecules within the brain. Three phase I studies have been initiated to investigate IL13-PE38QQR as an anti-tumor agent for the treatment of patients with recurrent malignant gliomas. As of January 2003 a total of 46 patients have been treated. The presentation at the March 2003 EANS Local Therapy of Glioma meeting reflects adverse event findings through January 2003 and survival data through March 2003. Intratumoral infusion with or without resection is fairly well-tolerated with corticosteroids prophylaxis particularly for patients with raised intracranial pressure. Post-resection infusion into the peritumoral brain parenchyma also appears to be very well tolerated. Histopathological tumor effect was seen at drug concentrations of 0.5-2.0 microg/mL. Although phase I studies do not focus on efficacy evaluation, prolonged survival times have been observed in this select population of patients. The preclinical data and details and preliminary results of the three clinical trials are reviewed.

IL-13 receptor-targeted cytotoxin cancer therapy leads to complete eradication of tumors with the aid of phagocytic cells in nude mice model of human cancer

Tumor-directed therapeutic approaches require unique or overexpressed specific Ag or receptor as a target to achieve selective tumor killing. However, heterogeneous expression of these targets on tumor cells limits the efficacy of this form of therapy. In this study, we forced abundant expression of IL-13Ralpha2 chain by plasmid-mediated gene transfer in head and neck, as well as prostate tumors to provide a potential target. This was followed by successfully treating xenograft tumor-bearing nude mice with IL-13R-directed cytotoxin (IL13-PE38QQR). Although we did not observe an indirect cytotoxic bystander effect conveyed to nontransduced tumor cells in vitro, our approach in vivo led to a complete regression of established tumors transfected with IL-13Ralpha2 chain in most animals. We found that the tumor eradication was achieved in part by infiltration of macrophages and NK cells, assessed by immunohistochemistry. Moreover, head and neck tumors xenografted in macrophage-depleted nude mice were less sensitive to the antitumor effect of IL-13 cytotoxin. Because we did not observe vector-related toxicity in any vital organs, our novel combination strategy of gene transfer of IL-13Ralpha2 chain and receptor-directed cytotoxin therapy may be a useful approach for the treatment of localized cancer.

Interleukin-13 receptor in psoriatic keratinocytes: overexpression of the mRNA and underexpression of the protein

Although several cytokines and their receptors have been involved in the development of psoriasis, the etiology is still unknown. In this study we looked for genes possibly involved in the disease by the reverse transcription-polymerase chain reaction differential display technique in lesional and nonlesional skin biopsies from psoriatic patients. We found the mRNA of the alpha1 chain of the interleukin-13 receptor expressed differentially in psoriatic biopsies. By reverse transcription-polymerase chain reaction, we confirmed an overexpression of the alpha1 chain of the IL-13 receptor and alpha chain of the interleukin-4 receptor mRNA in lesional skin psoriatic biopsies, when compared with skin biopsies from healthy subjects (p<0.01). The nonlesional skin obtained from a region close to a lesional zone in psoriatic patients presented also an overexpression of these mRNA in 50% of the samples. Interleukin-13 and interleukin-4 were not detected either as mRNA or as the proteins in any of the biopsies from psoriatic patients or healthy subjects. A monoclonal antibody to the alpha1 chain of the interleukin-13 receptor detected the receptor in the epidermal keratinocytes of psoriatic patients and of healthy subjects; however, the positive antibody reaction was stronger in skin tissue from healthy subjects than in psoriatic lesional skin tissue (p<0.01), although the mRNA was overexpressed. As interleukin-13 is a pleiotropic immunoregulatory cytokine with a variety of effects on different cell types, including monocytes, B lymphocytes, mast cells, and keratinocytes, we suggest, based on our results, that the interleukin-13 receptor possibly plays an important part in the early inflammatory process of psoriasis; however, its function is lost in the psoriatic keratinocytes.

Interleukin-13 fusion cytotoxin arrests Schistosoma mansoni egg-induced pulmonary granuloma formation in mice

Schistosoma mansoni egg-induced lung pathology requires the actions of interleukin (IL)-4 and IL-13. Because receptors for IL-4 and IL-13 share chains, we examined the effect of a fusion protein comprised of IL-13 and Pseudomonas exotoxin (IL13-PE) on the development of pulmonary granulomas in mice. At day 8 after an intravenous injection of live S. mansoni eggs, whole lung samples from IL13-PE-treated mice exhibited significantly lower IL-4 and IL-13 gene expression, smaller granulomas, decreased collagen levels, and increased IL-13 receptor alpha2 gene expression compared to controls. The therapeutic effects of IL13-PE were also observed at day 16 despite the termination of IL13-PE treatment at day 8. These studies demonstrate that targeting IL-4- and IL-13- responsive cells with IL13-PE effectively arrests S. mansoni egg granuloma formation.

Upregulation of IL-13 concentration in vivo by the IL13 variant associated with bronchial asthma

BACKGROUND

A substantial body of evidence exists to support the pivotal role of IL-13 in the pathogenesis of bronchial asthma. We recently found that a variant of the IL13 gene (Arg110Gln) is genetically associated with bronchial asthma, which is concordant with animal experiments using IL-13 in the development of asthma.

OBJECTIVE

To address whether the Gln110 variant of IL13 influences IL-13 function, contributing to the pathogenesis of bronchial asthma, we studied the functional properties of the variant.

METHODS

We generated 2 types of recombinant IL-13 proteins, the amino acids of which at 110 were arginine or glutamine, and analyzed the binding affinities with the IL-13 receptors, as well as the stability of the proteins. We further compared the relationship between the genotype and serum levels of IL-13.

RESULTS

The variant showed a lower affinity with the IL-13 receptor alpha2 chain, a decoy receptor, causing less clearance. The variant also demonstrated an enhanced stability in both human and mouse plasma. We further identified that asthmatic patients homozygous for the Gln110 variant have higher serum levels of IL-13 than those without the variant.

CONCLUSION

These results suggested that the variant might act as a functional genetic factor of bronchial asthma with a unique mechanism to upregulate local and systemic IL-13 concentration in vivo.

Interleukins-4, -5, and -13: emerging therapeutic targets in allergic disease

For the first time, allergic diseases have emerged as major public health concerns. Highly effective therapies for allergic disease now exist, but are plagued by serious side effects and the fact that a significant minority of patients remains unresponsive. Studies from many laboratories have established that T helper type 2 (T(H)2) cytokines contribute importantly to diseases such as asthma, and therapeutic strategies that target the key T(H)2 cytokines are of potential benefit in allergic disease. In this article, we will review the biology of the T(H)2 cytokines interleukin (IL)-4, IL-5, and IL-13 and their receptors, and will consider several novel strategies to neutralize these molecules in human and experimental asthma. While promising, newer therapies face a gauntlet of developmental challenges, but offer the hope of reducing allergic diseases once again to minor public health concerns.

Decreased allergic lung inflammatory cell egression and increased susceptibility to asphyxiation in MMP2-deficiency

Clearance of recruited immune cells is necessary to resolve inflammatory reactions. We show here that matrix metalloproteinase 2 (MMP2), as part of an interleukin 13 (IL-13)-dependent regulatory loop, dampens inflammation by promoting the egress of inflammatory cells into the airway lumen. MMP2-/- mice showed a robust asthma phenotype and increased susceptibility to asphyxiation induced by allergens. However, whereas the lack of MMP2 reduced the influx of cells into bronchoalveolar lavage (BAL), numerous inflammatory cells accumulated in the lung parenchyma. BAL of MMP2-/- mice lacked normal chemotactic activity, whereas lung inflammatory cells from the same mice showed appropriate chemotactic responses. Thus, MMP2 establishes the chemotactic gradient required for egression of lung inflammatory cells and prevention of lethal asphyxiation.

IL-4 receptors on human medulloblastoma tumours serve as a sensitive target for a circular permuted IL-4-Pseudomonas exotoxin fusion protein

Cytotoxins directed to interleukin-4 receptors have shown to mediate relatively selective cytotoxicity against a variety of human cancer cells in vitro and in vivo. In an ongoing Phase I clinical trial, a recombinant protein comprised of circularly permuted IL-4 fused to a mutated form of Pseudomonas exotoxin (the fusion protein termed IL-4(38-37)-PE38KDEL or cpIL4-PE) has shown antitumour activity against malignant glioma. Human medulloblastomas are neuroectodermal tumours that occur in children and have a poor prognosis. The goal of this study was to determine whether human medulloblastoma derived cell lines express interleukin-4 receptor and whether interleukin-4 receptor expression is accompanied by sensitivity to cpIL4-PE. Medulloblastoma cell lines express interleukin-4 receptor at the protein and mRNA levels as determined by binding, indirect immunofluorescence and RT--PCR studies. These cells expressed IL-4Ralpha (also known as IL-4Rbeta) and IL-13Ralpha1 (also known as IL-13Ralpha') chains, however common gamma(c), a component of the interleukin-4 receptor system in immune cells was not detected. Consistent with the expression of IL-4R, cpIL4-PE was found to be highly and specifically cytotoxic to four of five medulloblastoma cell lines. Susceptibility of medulloblastoma cell lines to cpIL4-PE seemed to correlate closely to the functional IL-4 binding sites in general as demonstrated by 125I-IL-4 binding, but did not seem to correlate with mRNA or cell surface immunoreactive receptor protein expression. The sensitivity of medulloblastoma cells to cpIL4-PE could be eliminated by concurrent incubation with IL-4 or IL-13, but not with IL-2. None of these cell lines showed any change in proliferation upon treatment with exogenous IL-4. These studies establish the interleukin-4 receptor as a medulloblastoma-associated target for possible tumour-directed cancer therapy. Further studies are warranted to investigate interleukin-4 receptor expression in primary medulloblastoma tumours and sensitivity to cpIL-4PE in vitro and in vivo.

In vivo overexpression of IL-13 receptor alpha2 chain inhibits tumorigenicity of human breast and pancreatic tumors in immunodeficient mice

Interleukin 13 receptor alpha2 (IL-13R(alpha)2) chain is highly expressed on some tumor cell lines and primary cell cultures. This receptor chain plays an important role in ligand binding and internalization. To determine the functional significance of overexpression of this chain, we stably transfected IL-13R(alpha)2 chain in human breast (MDA-MB-231) and pancreatic (PANC-1) cancer cell lines that naturally do not express this chain. There was no difference in growth between vector only transfected and IL-13R(alpha)2 chain transfected cells in vitro. However, surprisingly, in immunodeficient mice, tumorigenicity was profoundly inhibited in IL-13R(alpha)2 chain overexpressing tumors. Because breast tumors that grew later showed loss of IL-13R(alpha)2 gene expression, lack of tumorigenicity correlated positively with IL-13R(alpha)2 chain expression. Inflammatory cells including neutrophils and macrophages were identified in IL-13R(alpha)2 overexpressing regressing tumors and neutrophils were found to produce IL-13. IL-13 showed a modest antitumor activity to IL-13R(alpha)2 chain overexpressing tumors in vitro and in vivo. Furthermore, IL-13R(alpha)2 chain overexpressing tumors constitutively produced IL-8 that has been shown to have antitumor effect. These results establish a novel function of a cytokine receptor chain and further suggest that the presence of this chain on tumor cells by itself may play a key role in tumorigenicity.

Gene transfer of interleukin 13 receptor alpha2 chain dramatically enhances the antitumor effect of IL-13 receptor-targeted cytotoxin in human prostate cancer xenografts

IL-13Ralpha2 chain, the primary interleukin-13 (IL-13) binding protein, plays an important role in IL-13 binding and internalization. Based on these findings, in our previous study we transiently transfected four cancer cell lines that do not express IL-13Ralpha2 chain and demonstrated that these cells acquired increased sensitivity to IL-13 receptor-targeted recombinant cytotoxin, IL13-PE38QQR, which is composed of IL-13 and a mutated form of a Pseudomonas exotoxin. Although some prostate cancer cell lines express functional IL-13R, they are not highly sensitive to IL-13 cytotoxin. Here we investigated whether human prostate cancer and normal prostate epithelial cell lines express IL-13Ralpha2 chain and whether they can be sensitized to the cytotoxic effect of IL-13 cytotoxin after transient or stable gene transfer of IL-13Ralpha2 chain. Gene transfer of IL-13Ralpha2 chain improved binding activity of IL-13 and sensitivity to IL-13 cytotoxin in vitro. In vivo experiments demonstrated that gene transfer of IL-13Ralpha2 chain dramatically enhanced the antitumor activity of IL-13 cytotoxin in human prostate cancer xenograft models. These results suggest that IL-13R-targeted cytotoxin therapy of prostate cancer may be dramatically enhanced by gene transfer of IL-13Ralpha2 chain and this strategy, the combination of gene therapy and cytotoxin therapy, may be utilized in the treatment of localized prostate cancer.

Induction of the IL-13 receptor alpha2-chain by IL-4 and IL-13 in human keratinocytes: involvement of STAT6, ERK and p38 MAPK pathways

IL-4 and IL-13 are related cytokines which induce both pro- and anti-inflammatory effects depending on the cell type they act upon and the nature of the receptors expressed. The type I receptor complex is composed of the IL-4Ralpha and gammac and only binds IL-4, whereas, in the type II receptor, IL-4Ralpha dimerizes with IL-13Ralpha1 upon either IL-4 or IL-13 binding. Another ligand binding chain potentially implicated in the IL-4/IL-13 receptor has been described, the IL-13Ralpha2, but the regulation of its expression and its role in IL-4/IL-13 transduction is poorly understood. In this study we report that IL-4 and IL-13 upregulate IL-13Ralpha2 at both the mRNA and protein levels in the keratinocyte cell line HaCaT. In these cells, IL-4 or IL-13 were shown to activate the Janus Kinases JAK1 and JAK2, the transcription factor STAT6, and the ERK and p38 mitogen-activated protein kinases. We show that IL-4 or IL-13-induced IL-13Ralpha2 mRNA expression was inhibited by the ERK inhibitor U0126, the JAK inhibitor AG490 and, to a lesser extent, the p38 MAPK inhibitor SB203580. Moreover, expression of a constitutive active mutant of STAT6 alone did not modify IL-13Ralpha2 mRNA expression, but potentiated the effects of IL-4 or IL-13 on IL-13Ralpha2 expression. The constitutive active mutants of MEK1 or MKK6 increased the level of expression of IL-13Ralpha2 mRNA even in absence of stimulation. Our findings demonstrate, for the first time, that IL-4 and IL-13 can induce IL-13Ralpha2 expression in keratinocytes, and that the ERK and p38 MAPK together with JAK2 and STAT6 play a critical role in this process.

Expression of interleukin 13 receptor in glioma and renal cell carcinoma: IL13Ralpha2 as a decoy receptor for IL13

Glioma and renal cell carcinoma (RCC) cells express high affinity interleukin 13 (IL13) binding sites, but only RCC cell proliferation was inhibited by IL13. Both of these two cell types are IL2-receptor (gamma)c chain-negative. We thus used these cell models to investigate the patterns of expression of IL13Ralpha1, IL13Ralpha2, and IL4Ralpha chains and the role of IL13Ralpha2 in the response to IL13. Using new specific antibodies and flow cytometry, we observed a similar surface expression of IL4Ralpha and IL13Ralpha1 chains in most RCC and glioma cells, whereas IL13Ralpha2 was only present on five of six glioma cell lines. In all glioma cell lines, the amount of IL13Ralpha2 expression was 10 to 30 times higher than that of the two other chains. Although there was no surface or intracellular expression of IL13Ralpha2, its mRNA was detected in three of seven RCC cell lines. The expression on RCC cells of IL13Ralpha2 mRNA and/or that of high-affinity IL13 binding sites is not sufficient to predict IL13Ralpha2 protein expression. Blocking experiments showed that IL4 and IL13 strongly inhibited RCC cell proliferation through a unique receptor composed of IL4Ralpha and IL13Ralpha1 chains. Using RCC cells stably transfected with IL13Ralpha2 cDNA, we showed that the overexpression of IL13Ralpha2 decreased the response to IL13 but not that to IL4. Our results demonstrate that IL13Ralpha2 acts as a decoy receptor for IL13 and that it may exert a tight regulation of IL13 activity without impairing the IL4 response of the same cell target.

Suppression of an IL-13 autocrine growth loop in a human Hodgkin/Reed-Sternberg tumor cell line by a novel IL-13 antagonist

IL-13 has been proposed to be an autocrine growth factor for Hodgkin/Reed-Sternberg tumor cells (H/RS cells). Since we have recently identified and produced a novel IL-13 antagonist (IL-13E13K) that can suppress the biological activity of IL-13, here we examined whether IL-13E13K can inhibit growth of Hodgkin lymphoma (HL)-derived cell lines. IL-13E13K not only inhibited the growth of an unstimulated H/RS cell line (L1236) but also cells that were stimulated by exogenous IL-13 in a dose-dependent manner. Several HL-derived cell lines expressed IL-13 message and protein and message for various chains of IL-13R. H/RS cell lines expressed mRNA for the IL-13R alpha 1, IL-4R alpha, and IL-2R gamma chains. However, none of these cell lines expressed the IL-13R alpha 2 chain. An H/RS cell line (L1236) internalized the ligand-receptor complex after binding to a fusion protein composed of IL-13 and a mutated form of Pseudomonas exotoxin A (IL-13-PE38QQR, or IL-13 cytotoxin), as IL-13 cytotoxin was specifically cytotoxic to H/RS cells in vitro. These results indicate that IL-13E13K and IL-13 cytotoxin can effectively suppress growth of a L1236 H/RS cell line. Therefore, additional studies should be performed to determine the expression of IL-13 and IL-13R in primary clinical samples of Hodgkin's lymphoma and both agents should be further tested in vitro and in vivo as possible therapeutic agents for HL.

Identification of distinct roles for a dileucine and a tyrosine internalization motif in the interleukin (IL)-13 binding component IL-13 receptor alpha 2 chain

Interleukin (IL)-13 receptor alpha2 (IL-13Ralpha2) chain is an essential binding component for IL-13-mediated ligand binding. Recently, we have demonstrated that this receptor chain also plays an important role in the internalization of IL-13. To study the mechanism of IL-13 internalization, we generated mutated IL-13Ralpha2 chains that targeted trileucine residues (Leu(335), Leu(336), and Leu(337)) in the transmembrane domain and a tyrosine motif (Tyr(343)) in the intracellular domain and transfected these cDNAs in COS-7 cells. Cells that expressed a C-terminally truncated IL-13Ralpha2 chain (Delta335) did not bind IL-13, suggesting that the trileucine region modulates IL-13 binding. Truncation of IL-13Ralpha2 chain with a mutation in the trileucine region resulted in significantly decreased internalization compared with wild type IL-13Ralpha2 chain transfected cells. COS-7 cells transfected with tyrosine motif mutants exhibited a similar internalization level compared with wild type IL-13Ralpha2 chain transfected cells; however, dissociation of cell surface IL-13 was faster compared with wild type IL-13Ralpha2 transfectants. These results were further confirmed by determining the cytotoxicity of a chimeric protein composed of IL-13 and a mutated form of Pseudomonas exotoxin (IL13-PE38QQR) to cells that expressed IL-13Ralpha2 chain mutants. We further demonstrate that the IL-13Ralpha2 chain is not ubiquitinated and that internalization of IL-13Ralpha2 did not depend on ubiquitination. Together, our findings suggest that the dileucine motif in the trileucine region and tyrosine motif participate in IL-13Ralpha2 internalization in distinct manners.

Molecular cloning of canine IL-13 receptor alpha chain (alpha1 and alpha2) cDNAs and detection of corresponding mRNAs in canine tissues

This communication reports the cloning of cDNAs encoding two canine IL-13 receptor alpha chains (caIL-13Ralpha1 and caIL-13Ralpha2). As described for the members of type-I cytokine receptors, both caIL-13Ralpha1 and caIL-13Ralpha2 were found to contain the highly conserved motifs, such as cysteine and tryptophan residues in their N-terminal portion and the WSXWS at C-terminus. The isolated caIL-13Ralpha1 cDNA contains 1547 nucleotides with an open reading frame that encodes 405 amino acid residues. Canine IL-13Ralpha1 is 82.0 and 69.3% identical to human and mouse IL-13Ralpha1s, respectively, at the amino acid level. Canine IL-13Ralpha1 has an almost identical cytoplasmic domain to its human and mouse counterparts. The isolated caIL-13Ralpha2 cDNA contains 1454 nucleotides and encodes an open reading frame of 386 amino acid residues. Canine IL-13Ralpha2 is 62.6 and 47.5% identical to its human and mouse counterparts, respectively, at the amino acid level. Using RT-PCR with caIL-13Ralpha1 and caIL-13Ralpha2 specific primers, mRNAs of caIL-13Ralpha1 and caIL-13Ralpha2 were detected in most dog tissues. In addition, RT-PCR detected caIL-13Ralpha1 mRNA in one of two canine mastocytoma (C2 but not Br) cell lines and in a canine macrophage-derived cell line (DH82). CaIL-13Ralpha2 mRNA was detected in all three canine cell lines.

Characterization of a powerful high affinity antagonist that inhibits biological activities of human interleukin-13

Interleukin-13 (IL-13), a predominantly Th2-derived cytokine, appears to play a central pathological role in asthma, atopic dermatitis, allergic rhinitis, some parasitic infections, and cancer. We hypothesized that an IL-13 antagonist may have profound therapeutic utility in these conditions. We, therefore, mutagenized human IL-13 in which Glu at position 13 was substituted by a Lys residue. This highly purified recombinant IL-13 variant, IL-13E13K, bound with 4-fold higher affinity to the IL-13 receptor than wild-type IL-13 but retained no detectable proliferative activity on the TF-1 hematopoietic cell line. IL-13E13K competitively inhibited IL-13- and IL-4-dependent TF-1 proliferation. It also inhibited IL-13-induced STAT-6 (signal transduction and activator of transducer-6) activation in immune cells and cancer cells and reversed IL-13-induced inhibition of CD14 expression on human primary monocytes. These results demonstrate that high affinity binding and signal generation can be uncoupled efficiently in a ligand receptor interaction. These results also suggest that IL-13E13K may be a useful antagonist for the treatment of allergic, inflammatory, and parasitic diseases or even malignancies in which IL-13 plays a central role.

The interleukin-13 receptor alpha2 chain: an essential component for binding and internalization but not for interleukin-13-induced signal transduction through the STAT6 pathway

The interleukin-13 receptor (IL-13R) complex is composed of 2 different chains, IL-13Ralpha1 (also known as IL-13Ralpha') and IL-13Ralpha2 (also known as IL-13Ralpha). For a functional IL-13 receptor, the IL-13Ralpha1 chain forms a productive complex with the primary IL-4 binding protein (IL-4Ralpha also known as IL-4Rbeta). However, the function of the IL-13Ralpha2 chain is not clear even though this chain binds IL-13 with high affinity. This study demonstrates that IL-13Ralpha2 can undergo internalization after binding to ligand without causing activation of its signaling pathways. These conclusions were drawn on the basis of (1) internalization of (125)I-IL-13 in Chinese hamster ovarian (CHO-K1) and T98G glioblastoma cells transiently transfected with the IL-13Ralpha2 chain; (2) a recombinant chimeric fusion protein comprising IL-13 and a mutated form of Pseudomonas exotoxin (termed IL13-PE38QQR or IL-13 toxin) is specifically cytotoxic to IL-13Ralpha2-transfected CHO-K1 cells in a gene dose-dependent manner, whereas cells transfected with vector alone were not sensitive; and (3) IL-13 did not cause activation of signal transduction and activation of transcription 6 (STAT6) in IL-13Ralpha2-transfected cells. IL-13 efficiently caused activation of STAT6 protein in cells transfected with the IL-13Ralpha1 and IL-4Ralpha chains, and IL-13Ralpha2 inhibited this activation. Taken together, these observations indicate that internalization of IL-13Ralpha2 is signal independent and that this property of IL-13Ralpha2 can be exploited for receptor-directed cancer therapy.

Cloning and expression of a putative common cytokine receptor gamma chain (gammaC) gene in rainbow trout (Oncorhynchus mykiss)

A full length cDNA of a putative common cytokine receptor gamma chain (gammaC) gene of rainbow trout (Oncorhynchus mykiss) has been cloned and sequenced. The contiguous cDNA contained 2291 nucleotides, consisting of an ORF of 1029 bp, with a 72 bp 5' UTR and a 1190 bp 3' UTR. The coding region showed 44-46% identity to mammalian gammaC genes. The ORF translated into a 343 amino acid protein, with some 28-30% amino acid identity to the coding region of mammalian sequences. A predicted signal peptide and transmembrane domain were identified, giving a 206 amino acid extracellular domain and a 98 amino acid intracellular domain in the trout molecule. Five potential glycosylation sites were present in the extracellular domain, as were six conserved cysteine residues and the W-S-X-W-S motif typical of haemopoietin receptors. One of the most interesting differences between the trout and mammalian sequences was the lack of tyrosines in the trout intracellular domain. RT-PCR studies revealed a wide tissue distribution of gammaC expression, with detectable transcript in blood, spleen, gill, kidney, brain and liver. Low levels of gammaC transcript were detectable in unstimulated macrophage cultures and expression was increased by stimulation of the cells with recombinant trout interleukin-1beta (IL-1beta) or LPS. Similarly, in the RTG cell line which exhibited even lower level constitutive expression, stimulation with IL-1beta increased gammaC transcript levels but LPS had no effect.

Expression, purification, refolding, and characterization of recombinant human interleukin-13: utilization of intracellular processing

Interleukin-13 (IL-13) is a pleiotropic cytokine that elicits both proinflammatory and anti-inflammatory immune responses. Recent studies underscore its role in several diseases, including asthma and cancer. Solution studies of IL-13 and its soluble receptors may facilitate the design of antagonists/agonists which would require milligram quantities of specifically labeled protein. A synthetic gene encoding human IL-13 (hIL-13) was inserted into the pMAL-c2 vector with a cleavage site for the tobacco etch virus (TEV) protease. Coexpression of the fusion protein and TEV protease led to in vivo cleavage, resulting in high levels of hIL-13 production. hIL-13, localized to inclusion bodies, was purified and refolded to yield approximately 2 mg per liter of bacteria grown in minimal media. Subsequent biochemical and biophysical analysis of both the unlabeled and (15)N-labeled protein revealed a bioactive helical monomer. In addition, the two disulfide bonds were unambiguously demonstrated to be Cys29-Cys57 and Cys45-Cys71 by a combined proteolytic digestion and mass spectrometric analysis.

Sensitization of cancer cells to interleukin 13-pseudomonas exotoxin-induced cell death by gene transfer of interleukin 13 receptor alpha chain

We have demonstrated that primary interleukin 13 (IL-13) binding protein IL-13 receptor (IL-13R) alpha chain plays an important role in IL-13 binding and internalization in the IL-13R system. Although IL-13R alpha chain is expressed on many cancer cell lines, some cancer types do not express or express low levels of this receptor chain. Consequently, these cells show no or low sensitivity to the cytotoxic effect of a recombinant chimeric protein composed of IL-13 and a mutated form of a Pseudomonas exotoxin, IL13-PE38QQR. Here we demonstrate that pancreatic cancer, renal cell carcinoma, head and neck cancer, and glioblastoma cell lines that were genetically altered to express high levels of IL-13R alpha chain increase their binding affinity for IL-13, and increase their sensitivity to IL13-PE38QQR by at least 6-fold to 1000-fold compared with mock-transfected control cells. This observation was made by protein synthesis inhibition assay and confirmed by clonogenic assay. Our studies provide a proof of principle for a novel strategy for cancer therapy that combines gene transfer and targeted cytotoxin therapy.

Interleukin-13 fusion cytotoxin as a potent targeted agent for AIDS-Kaposi's sarcoma xenograft

Clinically advanced and rapidly progressive AIDS-associated Kaposi sarcoma (AIDS-KS) tumors require an aggressive tumor-directed therapy. We have observed that AIDS-KS cells express high levels of receptors for immune regulatory cytokine, interleukin-13 (IL-13). Two tumorigenic AIDS-KS cell lines, KS Y-1 and KS-imm, expressed 4560 and 9480 IL-13 binding sites per cell with an affinity (kd) of ∼0.9 and 3.7 nmol/L, respectively. IL-13 cytotoxin IL13-PE38QQR, consisting of human IL-13 and a derivative of Pseudomonas exotoxin, is specifically cytotoxic to KS tumor cells. Systemic and loco regional administration of IL13-PE38QQR in immunodeficient mice with established human KS tumors produced remarkable antitumor activity. Three intratumoral (IT) injections of IL-13 toxin (250 μg/kg per dose) on alternate days (qod) or 5 daily (qd) IT injections with lower doses (50 or 100 μg/kg per dose) resulted in a complete regression of established subcutaneous tumors in most animals. Daily IT treatment with 250 μg/kg of IL-13 toxin in another KS-derived cell line also produced complete responses. Twice daily intraperitoneal injections of IL13-PE38QQR (25 or 50 μg/kg per dose) for 10 days (total injections = 20) also completely eradicated KS Y-1 tumors. Intravenous administration of IL13-PE38QQR also suppressed tumor growth; however, complete responses were not observed. All animals tolerated the therapeutic doses of IL-13 toxin without any visible signs of toxicity. The efficacy of receptor-directed IL13-PE38QQR therapy in mice warrants further exploration of this drug for AIDS-KS treatment.

Interleukin-13 fusion cytotoxin as a potent targeted agent for AIDS-Kaposi's sarcoma xenograft

Clinically advanced and rapidly progressive AIDS-associated Kaposi sarcoma (AIDS-KS) tumors require an aggressive tumor-directed therapy. We have observed that AIDS-KS cells express high levels of receptors for immune regulatory cytokine, interleukin-13 (IL-13). Two tumorigenic AIDS-KS cell lines, KS Y-1 and KS-imm, expressed 4560 and 9480 IL-13 binding sites per cell with an affinity (kd) of ∼0.9 and 3.7 nmol/L, respectively. IL-13 cytotoxin IL13-PE38QQR, consisting of human IL-13 and a derivative of Pseudomonas exotoxin, is specifically cytotoxic to KS tumor cells. Systemic and loco regional administration of IL13-PE38QQR in immunodeficient mice with established human KS tumors produced remarkable antitumor activity. Three intratumoral (IT) injections of IL-13 toxin (250 μg/kg per dose) on alternate days (qod) or 5 daily (qd) IT injections with lower doses (50 or 100 μg/kg per dose) resulted in a complete regression of established subcutaneous tumors in most animals. Daily IT treatment with 250 μg/kg of IL-13 toxin in another KS-derived cell line also produced complete responses. Twice daily intraperitoneal injections of IL13-PE38QQR (25 or 50 μg/kg per dose) for 10 days (total injections = 20) also completely eradicated KS Y-1 tumors. Intravenous administration of IL13-PE38QQR also suppressed tumor growth; however, complete responses were not observed. All animals tolerated the therapeutic doses of IL-13 toxin without any visible signs of toxicity. The efficacy of receptor-directed IL13-PE38QQR therapy in mice warrants further exploration of this drug for AIDS-KS treatment.

Conversion of interleukin-13 into a high affinity agonist by a single amino acid substitution

We created a novel mutated form of human interleukin-13 (IL-13) in which a positively charged arginine (R) at position 112 was substituted to a negatively charged aspartic acid (D). This mutant, termed IL-13R112D, was expressed in Escherichia coli and purified to near homogeneity. IL-13R112D was found to be a potent IL-13 agonist with 5-10-fold improved binding affinity to IL-13 receptors compared with wild-type IL-13 (wtIL-13). The conclusion of IL-13 agonist activity was drawn on the basis of approximately 10-fold improved activity over wtIL-13 in several assays: (a) inhibition of CD14 expression in primary monocytes; (b) proliferation of TF-1 and B9 cell lines; and (c) activation of STAT6 in Epstein-Barr virus-immortalized B cells, primary monocytes, and THP-1 monocytic cell line. Furthermore, mutant IL-13R112D neutralized the cytotoxic activity of a chimeric fusion protein composed of wtIL-13 and a Pseudomonas exotoxin A (IL-13-PE38) approximately 10 times better than wtIL-13. Based on these results, it was concluded that IL-13R112D interacts with much stronger affinity than wtIL-13 on all cell types tested and that Arg-112 plays an important role in the interaction with its receptors (IL-13R). Thus, these results suggest that IL-13R112D may be a useful ligand for the study of IL-13 interaction with its receptors or, alternatively, in designing specific targeted agents for IL-13R-positive malignancies.

IL-4 regulation of IL-6 production involves Rac/Cdc42- and p38 MAPK-dependent pathways in keratinocytes

The stress-activated pathways leading to activation of p38 MAP kinase (p38 MAPK) and c-jun N-terminal kinases (JNK) have been shown to be activated by pro-inflammatory cytokines, physical and chemical stresses as well as a variety of hematopoietic growth factors. One exception is interleukin (IL)-4, which does not activate this pathway in hematopoietic cell. We report here that in A431, a keratinocytic cell line, IL-4 activates Rac and Cdc42 and their downstream effector p21-activated kinase (PAK). Rac and Cdc42 appear to regulate a protein kinase cascade initiated at the level of PAK and leading to activation of p38 MAPK, since IL-4 stimulates tyrosine phosphorylation of p38 MAPK and increases its catalytic activity. As A431 cells are able to produce IL-6 in response to IL-4 stimulation, we assessed the involvement of p38 MAPK in IL-6 gene expression. A pyrimidazole compound, SB203580, a specific inhibitor of p38 MAPK, inhibits production and gene expression of IL-6. SB203580 reduced significantly the stability of IL-6 mRNA. Here we provide evidence that p38 MAPK is activated in response to IL-4 and is involved in IL-6 synthesis by stabilizing IL-6 mRNA.

Binding of IL-4 to the IL-13Ralpha(1)/IL-4Ralpha receptor complex leads to STAT3 phosphorylation but not to its nuclear translocation

Interleukin-4 (IL-4) is a pleiotropic cytokine, which acts on both hematopoietic and non-hematopoietic cells, through different types of receptor complexes. In this study, we report that in human B cells, IL-4 caused rapid phosphorylation of Janus kinase (JAK) 1 and JAK3 tyrosine kinases. In keratinocytes, the hematopoietic-specific receptor common gamma(c) chain is not expressed and the IL-13 receptor alpha(1) (IL-13Ralpha(1)) participates in IL-4 signal transduction. In keratinocytes, IL-4 induced JAK1 and JAK2 phosphorylation but, unlike in immune cells, IL-4 did not involve JAK3 activation for its signaling. In both cell types, IL-4 induced phosphorylation and DNA binding activation of the signal transducer and activator of transcription (STAT) 6 protein. Furthermore, IL-4 stimulation of keratinocytes also induced tyrosine phosphorylation of STAT3 which was found to bind to the phosphorylated IL-13Ralpha(1). STAT3 however did not significantly translocate to the nucleus, nor did it bind with high affinity to target DNA sequences.

Kinetic analysis of high affinity forms of interleukin (IL)-13 receptors: suppression of IL-13 binding by IL-2 receptor gamma chain

Interleukin-13 (IL-13) is a pleiotropic cytokine that controls growth, differentiation, and apoptosis of immune and tumor cells. To understand the mechanisms of interaction between IL-13 and IL-13 receptors (IL-13R), and the role of the IL-2 receptor common gamma chain (gammac) in IL-13 binding and processing, we have examined IL-13 binding kinetics, dissociation/shedding, and internalization in renal cell carcinoma (RCC) cell lines. We observed a new phenomena in that the apparent rate of association, but not the dissociation, was strongly related to IL-13 concentration. We also observed cooperativity phenomena in IL-13 and IL-13R interaction in control RCC (MLneo) cells, but not in cells transfected with gammac chain (MLgammac). The number of IL-13 binding sites, the effective rate of ligand association, and the dissociation rate constants were reduced in gammac-transfected cells compared to control RCC cells. Two forms of IL-13R were detected in these cell lines, which differed in the kinetics of endocytosis and dissociation/exocytosis. Only a small fraction of bound receptors (14-24%) was rapidly internalized and the same fraction of the ligand-receptor complexes was shed and/or dissociated. The expression of gammac chain did not change any of these processes. A two independent high-affinity and moderate-affinity receptor model fit the kinetic observations in gammac-transfected cells. However, in control cells, the binding kinetics were more complicated. A mathematical model that fit a set of kinetic and steady state data in control cells was selected from a set of possible models. This best-fit model predicts that 1) two different IL-13R are expressed on the cell membrane, 2) a minor fraction of IL-13R exist as microclusters (homodimers and/or heterodimers) without exogenous IL-13, 3) high morphological complexity of the gammac-negative control cell membrane affects the cooperativity phenomena of IL-13 binding, and 4) a large number of co-receptor molecules is present, which helps keep the ligand on the cell surface for a long period of time after fast IL-13 binding and provides a negative control for ligand binding via production of the high affinity inhibitor bound to IL-13. Our data demonstrate that gammac exerts dramatic changes in the kinetic mechanisms of IL-13 binding.

Development of a recombinant interleukin-4-Pseudomonas exotoxin for therapy of glioblastoma

About 12,000 Americans are diagnosed with malignant astrocytoma each year. Despite surgery, radiotherapy, and chemotherapy, the prognosis of these patients remains poor. Targeted toxins based on the identification of novel antigens or receptors provide a promising new approach to treating cancer. We have identified one such cell surface protein in the form of interleukin (IL)-4 receptors (IL-4R) on human malignant astrocytoma. Normal brain tissues from frontal cortex and temporal lobe cortex do not express IL-4R. To target IL-4R, we generated a chimeric fusion protein composed of IL-4 and Pseudomonas exotoxin (IL4-PE). This toxin is highly cytotoxic to IL-4R-bearing human brain cancer cells. Preclinical toxicologic experiments were performed in mice, rats, and guinea pigs to determine an maximum tolerated dose. Intrathecal administration in cynomolgus monkeys produced high cerebrospinal fluid levels without any central nervous system or other abnormalities. When IL4-PE was injected into the right frontal cortex of rats, localized necrosis was observed at 1,000 but not < or =100 microg/ml doses. Intravenous administration of this biologic to monkeys produced reversible grade 3 or grade 4 elevations of hepatic enzymes in a dose-dependent manner. These results indicate that localized administration can produce nontoxic levels of IL4-PE that may have significant activity against astrocytoma. In vivo experiments with nude mice have demonstrated that IL4-PE has significant antitumor activity against human glioblastoma tumor model. Intratumor administration of IL4-PE has been initiated for the treatment of malignant astrocytoma in a phase I clinical trial.

Induction of 15-lipoxygenase expression by IL-13 requires tyrosine phosphorylation of Jak2 and Tyk2 in human monocytes

The enzyme 15-lipoxygenase (15-LO) participates in the dioxygenation of polyenoic fatty acids. This activity leads to the degradation of mitochondrial membranes during reticulocyte differentiation, the production of pro- and anti-inflammatory mediators by a variety of cell types, and the oxidation of lipids in atherosclerotic lesions. The cytokines, IL-4 and IL-13, are reported to induce the expression of 15-LO in human peripheral blood monocytes. In this report we explore the signaling mechanisms involved in the IL-13-mediated induction of 15-LO expression. First we demonstrate that the delayed induction of 15-LO requires continuous stimulation of monocytes for a minimum period of 12 h. We also found that tyrosine kinase inhibitors blocked the induction of 15-LO in a dose-dependent manner. By immunoprecipitation and antiphosphotyrosine blotting experiments, IL-13 was shown to induce tyrosine phosphorylation of Jak2 and Tyk2, but not Jak1 or Jak3, within 5 min of treatment in human monocytes. To investigate whether the early induction of tyrosine phosphorylation of both Jak2 and Tyk2 was ultimately involved in 15-LO expression, we generated antisense oligodeoxyribonucleotides (ODNs) against Tyk2 and Jak2. We employed a cationic lipid-mediated delivery technique to transfect the monocytes and found that both antisense ODNs inhibited expression of their target proteins by 75-85%. The treatments were specific and did not affect the expression of each other. Furthermore, the antisense ODNs to Jak2 and Tyk2 both inhibited the induction of expression of 15-LO in monocytes treated with IL-13. Parallel experiments with sense ODNs to Jak2 and Tyk2 did not affect their protein levels or the induction of 15-LO by IL-13, and down-regulation of Jak1 also did not affect expression of 15-LO. Our results suggest the novel finding that IL-13 can induce tyrosine phosphorylation of both Jak2 and Tyk2 in primary human monocytes. This occurs as an early and essential signal transduction event for the IL-13-mediated induction of 15-LO expression. These data represent the first characterization of upstream kinases involved in the induced expression of 15-LO.

An immune cell-selective interleukin 4 agonist

Interleukin 4 (IL-4) is a pleiotropic cytokine. Of the cell types responsive to IL-4, T cells express one IL-4 receptor (IL-4R) type, IL-4Ralpha/IL-2Rgamma (class I IL-4R), whereas endothelial cells express another type, IL-4Ralpha/IL-13Ralpha (class II IL-4R). It was hypothesized that IL-4 variants could be generated that would be selective for cell types expressing the different IL-4Rs. A series of IL-4 muteins were generated that were substituted in the region of IL-4 implicated in interactions with IL-2Rgamma. These muteins were evaluated in T cell and endothelial cell assays. One of these muteins, containing the mutation Arg-121 to Glu (IL-4/R121E), exhibited complete biological selectivity for T cells, B cells, and monocytes, but showed no activity on endothelial cells. Receptor binding studies indicated that IL-4/R121E retained physical interaction with IL-2Rgamma but not IL-13Ralpha; consistent with this observation, IL-4/R121E was an antagonist of IL-4-induced activity on endothelial cells. IL-4/R121E exhibits a spectrum of activities in vitro that suggest utility in the treatment of certain autoimmune diseases.

Interleukin-13 Receptor α′ But Not α Chain: A Functional Component of Interleukin-4 Receptors

In hematopoietic cells, interleukin-2 receptor (IL-2R) γ chain (termed γc) is shown to be a component of the IL-4R system, whereas in nonhematopoietic cells, γc is absent and it is not a component of the IL-4R system. Here, we show that the IL-13R α′ chain (termed IL-13Rα′) but not the IL-13R α chain (termed IL-13Rα) can substitute for γc and, thus, IL-13Rα′ forms a novel component of the IL-4R system. This conclusion was drawn on the basis of chemical cross-linking, immunoprecipitation, the ability of IL-13Rα′ but not IL-13Rα to augment IL-4 binding affinity, and the requirement of IL-13Rα′ for IL-4–induced STAT6 activation in Chinese hamster ovary (CHO) cells transfected with various receptor subunits. Cotransfection of IL-4 receptor p140 (termed IL-4Rβ) with γc or IL-13Rα′ increased IL-4 binding affinity and allowed for STAT6 activation in response to IL-4. However, cotransfection of all three chains did not further increase IL-4 binding or alter the extent of STAT6 activation suggesting that all three chains together do not seem to participate in IL-4 function. Instead, IL-4Rβ heterodimerizes with γc or IL-13Rα′ and mediates STAT6 activation. Cotransfection of IL-4Rβ with IL-13Rα neither increased IL-4 binding affinity nor allowed for STAT6 activation in response to IL-4 indicating that IL-13Rα does not convert binding affinity nor transmit signals for IL-4. Because IL-4 phosphorylates JAK1 and JAK2 tyrosine kinases in nonhematopoietic cells, we investigated whether JAK1 and JAK2 are required for IL-4–induced STAT6 activation in various transfectants. Cotransfection experiments with different chains of IL-4R and kinase-deficient JAK1 and JAK2 mutants in CHO cells showed that JAK1 and JAK2 are required for optimal activation of STAT6 in the α′β transfectant but only partially in the βγc transfectant. Taken together, our results show that IL-13Rα′ is a novel functional component of the IL-4R system and that JAK1 and JAK2 mediate IL-4–induced optimal activation of STAT6 in nonhematopoietic cells.

Interleukin-13 Receptor α′ But Not α Chain: A Functional Component of Interleukin-4 Receptors

In hematopoietic cells, interleukin-2 receptor (IL-2R) γ chain (termed γc) is shown to be a component of the IL-4R system, whereas in nonhematopoietic cells, γc is absent and it is not a component of the IL-4R system. Here, we show that the IL-13R α′ chain (termed IL-13Rα′) but not the IL-13R α chain (termed IL-13Rα) can substitute for γc and, thus, IL-13Rα′ forms a novel component of the IL-4R system. This conclusion was drawn on the basis of chemical cross-linking, immunoprecipitation, the ability of IL-13Rα′ but not IL-13Rα to augment IL-4 binding affinity, and the requirement of IL-13Rα′ for IL-4–induced STAT6 activation in Chinese hamster ovary (CHO) cells transfected with various receptor subunits. Cotransfection of IL-4 receptor p140 (termed IL-4Rβ) with γc or IL-13Rα′ increased IL-4 binding affinity and allowed for STAT6 activation in response to IL-4. However, cotransfection of all three chains did not further increase IL-4 binding or alter the extent of STAT6 activation suggesting that all three chains together do not seem to participate in IL-4 function. Instead, IL-4Rβ heterodimerizes with γc or IL-13Rα′ and mediates STAT6 activation. Cotransfection of IL-4Rβ with IL-13Rα neither increased IL-4 binding affinity nor allowed for STAT6 activation in response to IL-4 indicating that IL-13Rα does not convert binding affinity nor transmit signals for IL-4. Because IL-4 phosphorylates JAK1 and JAK2 tyrosine kinases in nonhematopoietic cells, we investigated whether JAK1 and JAK2 are required for IL-4–induced STAT6 activation in various transfectants. Cotransfection experiments with different chains of IL-4R and kinase-deficient JAK1 and JAK2 mutants in CHO cells showed that JAK1 and JAK2 are required for optimal activation of STAT6 in the α′β transfectant but only partially in the βγc transfectant. Taken together, our results show that IL-13Rα′ is a novel functional component of the IL-4R system and that JAK1 and JAK2 mediate IL-4–induced optimal activation of STAT6 in nonhematopoietic cells.

Novel anti-brain tumor cytotoxins specific for cancer cells

The vast majority of brain cancers (gliomas) express a receptor (R) for interleukin 13 (IL13). In order to achieve specific targeting of the IL13R in gliomas, we have mutagenized human (h) IL13. The mutation was made to alter IL13 interaction with the shared functional IL13/4 normal tissue receptor, but not with the glioma-associated receptor. We have thus produced hIL13.E13K (glutamic acid at position 13 changed to lysine) and fused it to derivatives of Pseudomonas exotoxin A. The hIL13.E13K-based cytotoxins are less active on normal cells and thus less toxic, and are better antitumor agents compared with the cytotoxins containing nonmutagenized hIL13.

Regulation of interleukin-13 receptor constituents on mature human B lymphocytes

Human B cells stimulated through both their immunoglobulin and CD40 receptors up-regulate 745 +/- 51 interleukin (IL)-13 ligand binding sites with an affinity of 0.91 +/- 0.08 nM within 24 h. IL-13 binds primarily to the IL-13Ralpha1 with subsequent sequestration of the IL-4Ralpha into the complex. IL-13Ralpha1 may also be found in those receptors capable of binding IL-4. gamma chain (gammac) participates in receptors capable of binding IL-4 but is not found in association with bound IL-13. Dimeric receptors composed of the IL-4Ralpha complexed with either the IL-13Ralpha1 or gammac occur simultaneously within defined B cell populations. mRNAs for all receptor constituents are increased subsequent to immunoglobulin stimulation alone, while maximal expression of IL-13Ralpha1 is more dependent upon co-stimulation of immunoglobulin and CD40 receptors. mRNA levels for IL-13Ralpha1 vary over a wider range subsequent to surface stimulation than other receptor components. Although gammac is not bound to IL-13 in B cells under the conditions evaluated, it may influence IL-13 binding by competing with IL-13Ralpha1 for association/sequestration with the IL-4Ralpha chain. IL-13Ralpha2 does not participate in the IL-13 receptor that is up-regulated upon activation of quiescent tonsillar B lymphocytes, although mRNA for the protein may be found in the centroblastic fraction of tonsillar cells.