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

The potential for genetically altered microglia to influence glioma treatment

Diffuse and unstoppable infiltration of brain and spinal cord tissue by neoplastic glial cells is the single most important therapeutic problem posed by the common glioma group of tumors: astrocytoma, oligoastrocytoma, oligodendroglioma, their malignant variants and glioblastoma. These neoplasms account for more than two thirds of all malignant central nervous system tumors. However, most glioma research focuses on an examination of the tumor cells rather than on host-specific, tumor micro-environmental cells and factors. This can explain why existing diffuse glioma therapies fail and why these tumors have remained incurable. Thus, there is a great need for innovation. We describe a novel strategy for the development of a more effective treatment of diffuse glioma. Our approach centers on gaining control over the behavior of the microglia, the defense cells of the CNS, which are manipulated by malignant glioma and support its growth. Armoring microglia against the influences from glioma is one of our research goals. We further discuss how microglia precursors may be genetically enhanced to track down infiltrating glioma cells.

IL-13 R110Q, a Naturally Occurring IL-13 Polymorphism, Confers Enhanced Functional Activity in Cultured Human Bronchial Smooth Muscle Cells

Purpose

Interleukin (IL)-13, a Th2-type cytokine, plays a pivotal role in the pathogenesis of asthma through its direct effects on airway smooth muscles. A naturally occurring IL-13 polymorphism, R110Q, is strongly associated with increased total serum IgE levels and asthma. In the present study, we aimed to determine whether the IL-13 R110Q variant would display different biochemical properties or altered functions in comparison with wild-type (WT) IL-13 in cultured human bronchial smooth muscle cells (hBSMCs).

Methods

Culture supernatants and cell proteins were collected from cultured hBSMCs that were treated with 50 ng/mL IL-13 or IL-13 R110Q for 24 hours. Eotaxin released into hBSMC culture medium was determined by ELISA. The expression levels of the high-affinity IgE receptor (FcεRI) α-chain, smooth muscle-specific actin alpha chain (α-SMA), smooth muscle myosin heavy chain (SmMHC), and calreticulin in the cells were measured on Western blots.

Results

Compared with WT IL-13, treatment with the IL-13 R110Q variant resulted in a significant increase in eotaxin release as well as significant, although modest, increases in the expression levels of α-SMA, SmMHC, calreticulin, and FcεRI α-chain.

Conclusions

The results of the present study suggenst that the IL-13 R110Q variant may enhance enhanced functional activities in hBSMCs.

Specific targeting of human interleukin (IL)-13 receptor α2-positive cells with lentiviral vectors displaying IL-13

The ability to selectively and efficiently target transgene delivery to specific cell types in vitro and in vivo remains one of the formidable challenges in gene therapy. Lentiviral vectors have several advantages that make them attractive as gene delivery vehicles and their tropism can be altered through pseudotyping, allowing transgene delivery to specific populations of cells. The human interleukin-13 receptor α2 (IL-13Rα2) is uniquely overexpressed in many different human tumors, making it an attractive target for cancer therapy. In this study, we examined whether IL-13Rα2-positive tumor cells can be specifically targeted with lentiviral vector pseudotypes containing a truncated fusion (F) protein derived from measles virus (MV) and a tail-truncated and receptor-blind MV hemagglutinin (H) protein bearing IL-13 at the C terminus. The retargeted lentiviral vector efficiently transduced cells that express high levels of IL-13Rα2, but not cells expressing low levels of IL-13Rα2 in vitro. In vivo, it specifically targeted IL-13Rα2-positive glioma cell xenografts in immunodeficient mice in the context of subcutaneous and intracranial glioma models. Similar lentiviral vectors may be developed for targeting other tumors expressing specific cell surface receptors.

Immunotherapy targets in pediatric cancer

Immunotherapy for cancer has shown increasing success and there is ample evidence to expect that progress gleaned in immune targeting of adult cancers can be translated to pediatric oncology. This manuscript reviews principles that guide selection of targets for immunotherapy of cancer, emphasizing the similarities and distinctions between oncogene-inhibition targets and immune targets. It follows with a detailed review of molecules expressed by pediatric tumors that are already under study as immune targets or are good candidates for future studies of immune targeting. Distinctions are made between cell surface antigens that can be targeted in an MHC independent manner using antibodies, antibody derivatives, or chimeric antigen receptors versus intracellular antigens which must be targeted with MHC restricted T cell therapies. Among the most advanced immune targets for childhood cancer are CD19 and CD22 on hematologic malignancies, GD2 on solid tumors, and NY-ESO-1 expressed by a majority of synovial sarcomas, but several other molecules reviewed here also have properties which suggest that they too could serve as effective targets for immunotherapy of childhood cancer.

Design of a novel interleukin-13 antagonist from analysis of informational structure

Interleukin-13 (IL-13) is one of the cytokines involved in the development of Th2-type immune response. It plays an important role in the pathogenesis of asthma and other allergic diseases. Two deletion forms of IL-13 were constructed on a basis of informational structure analysis and expressed in E. coli cells. They were found to differ in ability to stimulate proliferation of TF-1 cell line. Deletion variant 146 (DV146) completely lacks such activity, whereas DV148 provides about 50% of the proliferation stimulation. The simultaneous addition of DV146 with full-length IL-13 suppresses proliferation depending on the concentration of the deletion form. Thus, the designed protein acts as an antagonist of IL-13.

Human adrenomedullin up-regulates interleukin-13 receptor alpha2 chain in prostate cancer in vitro and in vivo: a novel approach to sensitize prostate cancer to anticancer therapy

Interleukin-13 (IL-13) receptor alpha2 (IL-13Ralpha2), a high-affinity IL-13 binding subunit and a tumor antigen, is amplified in a variety of human tumor cell lines and tumors in vivo. By cDNA microarray, we have shown that gene transfer of human and rat adrenomedullin (AM) up-regulates IL-13Ralpha2 in a human prostate tumor cell line. Here, we show that IL-13Ralpha2 mRNA and protein are also up-regulated in PC-3 prostate tumor cells by recombinant AM (rAM) and human synthetic AM peptide in a dose-dependent manner in vitro and in vivo in mouse prostate tumor model. The 8- to 10-fold up-regulation of IL-13Ralpha2 by rAM or AM peptide in prostate tumor cells in vitro and in vivo increased their sensitivity to IL-13PE cytotoxin consisting of IL-13 and a truncated form of Pseudomonas exotoxin. Immunodeficient mice with established prostate tumors transfected with AM or treated with AM peptide showed reduction in tumor size by intratumoral administration of IL-13PE in a dose-dependent manner. At the highest dose (three 100 mug/kg/d every alternate day), >70% reduction of tumor size was observed compared with controls (P Collapse

Key Words Collapse

MESH Headings

• ADP Ribose Transferases/therapeutic use
• Adrenomedullin/analysis
• Adrenomedullin/genetics
• Adrenomedullin/physiology
• Animals
• Bacterial Toxins/therapeutic use
• Cell Line, Tumor
• Exotoxins/therapeutic use
• Gene Expression Regulation, Neoplastic
• Humans
• Immunotoxins/therapeutic use
• Interleukin-13/metabolism
• Interleukin-13/therapeutic use
• Interleukin-13 Receptor alpha2 Subunit/genetics
• Male
• Mice
• Prostatic Neoplasms/drug therapy
• Prostatic Neoplasms/metabolism
• Prostatic Neoplasms/pathology
• RNA, Messenger/analysis
• Up-Regulation
• Virulence Factors/therapeutic use
• Pseudomonas aeruginosa Exotoxin A

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Grants

• Z01 BC005740 Intramural NIH HHS

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Affiliation(s)

Bharat H Joshi Tumor Vaccines and Biotechnology Branch, Division of Cellular and Gene Therapies, Center for Biologics Evaluation and Research, Food and Drug Administration, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA
Pamela Leland
Alfonso Calvo
Jeffrey E Green
Raj K Puri

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Effect of IL-13 receptor alpha2 levels on the biological activity of IL-13 variant R110Q

BACKGROUND

IL-13 is a key cytokine associated with the asthmatic phenotype. IL-13 signals via its cognate receptor, a complex of IL-13 receptor (IL-13R) alpha 1 chain with IL-4 receptor alpha; however, a second protein, IL-13Ralpha2, also binds IL-13. Recently a polymorphic variant of IL-13 (R110Q) has been shown to be associated with atopy.

OBJECTIVE

To investigate the binding properties of this IL-13 variant to its cognate receptors.

METHODS

We used surface plasmon resonance to measure the binding kinetics of R110Q to its receptors. Primary human fibroblasts were grown from endobronchial biopsies obtained from volunteers. Receptor levels were measured by fluorescence-activated cell sorting.

RESULTS

There was no significant difference in the binding of R110Q with soluble human IL-13Ralpha1 compared with IL-13 (32 +/- 5 nmol/L and 36 +/- 7 nmol/L, respectively; P = .625). However, a small but significant difference was observed in the binding of R110Q to soluble human IL-13Ralpha2 compared with IL-13 (840 +/- 87 pmol/L and 1.1 +/- .05 nmol/L, respectively; P = .04). We observed that primary human lung fibroblasts expressed different levels of IL-13Ralpha2. Eotaxin release from fibroblasts expressing low IL-13Ralpha2 levels was significantly higher in response to R110Q compared with IL-13. This was not evident in cells that had high baseline IL-13Ralpha2 levels.

CONCLUSION

These results suggest that relatively small changes in functional properties of a ligand combined with variation in receptor levels in vivo can result in significant differences in responsiveness.

CLINICAL IMPLICATIONS

Expression of R110Q and low IL-13Ralpha2 levels can result in important biological differences that may have clinical relevance in an atopic environment.

A modular interface of IL-4 allows for scalable affinity without affecting specificity for the IL-4 receptor

BACKGROUND

Interleukin 4 (IL-4) is a key regulator of the immune system and an important factor in the development of allergic hypersensitivity. Together with interleukin 13 (IL-13), IL-4 plays an important role in exacerbating allergic and asthmatic symptoms. For signal transduction, both cytokines can utilise the same receptor, consisting of the IL-4Ralpha and the IL-13Ralpha1 chain, offering an explanation for their overlapping biological functions. Since both cytokine ligands share only moderate similarity on the amino acid sequence level, molecular recognition of the ligands by both receptor subunits is of great interest. IL-4 and IL-13 are interesting targets for allergy and asthma therapies. Knowledge of the binding mechanism will be important for the generation of either IL-4 or IL-13 specific drugs.

RESULTS

We present a structure/function analysis of the IL-4 ligand-receptor interaction. Structural determination of a number of IL-4 variants together with in vitro binding studies show that IL-4 and its high-affinity receptor subunit IL-4Ralpha interact via a modular protein-protein interface consisting of three independently-acting interaction clusters. For high-affinity binding of wild-type IL-4 to its receptor IL-4Ralpha, only two of these clusters (i.e. cluster 1 centered around Glu9 and cluster 2 around Arg88) contribute significantly to the free binding energy. Mutating residues Thr13 or Phe82 located in cluster 3 to aspartate results in super-agonistic IL-4 variants. All three clusters are fully engaged in these variants, generating a three-fold higher binding affinity for IL-4Ralpha. Mutagenesis studies reveal that IL-13 utilizes the same main binding determinants, i.e. Glu11 (cluster 1) and Arg64 (cluster 2), suggesting that IL-13 also uses this modular protein interface architecture.

CONCLUSION

The modular architecture of the IL-4-IL-4Ralpha interface suggests a possible mechanism by which proteins might be able to generate binding affinity and specificity independently. So far, affinity and specificity are often considered to co-vary, i.e. high specificity requires high affinity and vice versa. Although the binding affinities of IL-4 and IL-13 to IL-4Ralpha differ by a factor of more than 1000, the specificity remains high because the receptor subunit IL-4Ralpha binds exclusively to IL-4 and IL-13. An interface formed by several interaction clusters/binding hot-spots allows for a broad range of affinities by selecting how many of these interaction clusters will contribute to the overall binding free energy. Understanding how proteins generate affinity and specificity is essential as more and more growth factor receptor families show promiscuous binding to their respective ligands. This limited specificity is, however, not accompanied by low binding affinities.

IL-13 R130Q, a common variant associated with allergy and asthma, enhances effector mechanisms essential for human allergic inflammation

Genetic factors are known to strongly influence susceptibility to allergic inflammation. The Th2 cytokine IL-13 is a central mediator of allergy and asthma, and common single-nucleotide polymorphisms in IL13 are associated with allergic phenotypes in several ethnically diverse populations. In particular, IL13+2044GA is expected to result in the nonconservative replacement of arginine 130 (R130) with glutamine (Q). We examined the impact of IL13+2044GA on the functional properties of IL-13 by directly comparing the activity of WT IL-13 and IL-13 R130Q on primary human cells involved in the effector mechanisms of allergic inflammation. Our results show that IL-13 R130Q was significantly more active than WT IL-13 in inducing STAT6 phosphorylation and CD23 expression in monocytes and hydrocortisone-dependent IgE switching in B cells. Notably, IL-13 R130Q was neutralized less effectively than WT IL-13 by an IL-13R2 decoy. Decreased neutralization of the minor variant could contribute to its enhanced in vivo activity. Neither IL-13 variant was able to engage T cells, which suggests that increased allergic inflammation in carriers of IL13+2044A depends on enhanced IL-13-mediated Th2 effector functions rather than increased Th2 differentiation. Collectively, our data indicate that natural variation in the coding region of IL13 may be an important genetic determinant of susceptibility to allergy.

Potent receptor-mediated cytotoxicity of granulocyte colony-stimulating factor-Pseudomonas exotoxin, a fusion protein against myeloid leukemia cells

A chimeric toxin in which the cell-surface binding domain of Pseudomonas exotoxin A was replaced with mature human granulocyte colony-stimulating factor (G-CSF) was produced in Escherichia coli, purified and tested for its biological activity on the human G-CSF-responsive myeloid leukemia cell line, UT7/GR. This fusion protein, termed G-CSF-PE40, showed potent cytotoxicity in the cell line in a dose-dependent manner. G-CSF-PE40 displaced binding of biotinylated G-CSF to its receptor, and the cytotoxicity of G-CSF-PE40 was neutralized by an excess of wild-type G-CSF, indicating the receptor-mediated effects of this chimeric toxin. When G-CSF-PE40 was injected into normal mice, they showed transient neutropenia but no significant changes in the numbers of red blood cells or platelets. Furthermore, G-CSF-PE40 prolonged the survival of mice transplanted with syngeneic myeloid leukemia cells. These observations suggest that G-CSF-PE40 may be useful in targeted therapy of myeloid leukemia cells expressing G-CSF receptors.

Function of a conserved residue in the amino terminal alpha-helix of four helical bundle cytokines

The Glu residue in the helix A is conserved among many cytokines. Mutation in this residue converts some cytokines to an antagonist. Such an artificial cytokine with an antagonist activity may be useful in a clinical area. In this study we generated a mutant granulocyte colony-stimulating factor (G-CSF) termed G-CSF.E20K in which this residue is substituted to Lys. It is known that G-CSF binds to a homodimeric receptor, while other cytokines which can be converted to antagonists bind to heterodimeric receptors. We showed that G-CSF.E20K does not bind to the receptor at all, and that it fails to stimulate proliferation. Thus, the mutant did not act as an antagonist. We propose that the nature of the receptor, namely whether it is a homodimer or heterodimer, determines the antagonist activity of the mutant.

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.

Genetics of IL-13 and functional relevance of IL-13 variants

Studies in both humans and mice clearly show that interleukin (IL)-13 is a central regulator of allergic inflammation. Numerous single nucleotide polymorphisms have been recently identified in the IL-13 gene and have been found to be associated with allergic and/or asthmatic phenotypes in different populations throughout the world. Furthermore, functional genomics studies are highlighting mechanistic pathways that may link genetic variation in IL-13 and disease. IL-13 is therefore an ideal model to study the impact of genetic variation on the regulation of gene expression and function in complex diseases.

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.

Interleukin-13 gene therapy reduces inflammation, vascularization, and bony destruction in rat adjuvant-induced arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease characterized by synovial pannus formation, leukocyte infiltration, and angiogenesis. Adenoviral production of interleukin-13 (IL-13) reduces levels of proinflammatory mediators in an explant model of RA synovial tissue in vitro. To assess this approach in an animal model of arthritis, we compared intra-articular injections of an adenovirus producing rat IL-13 (AxCArIL-13), a control virus, and rat ankles receiving phosphate-buffered saline (PBS) in rat adjuvant-induced arthritis (AIA). We demonstrate that IL-13 levels are normally low in ankles throughout the course of rat AIA. We show that administration of AxCArIL-13 before arthritis onset significantly reduces ankle circumference, paw volume, bony destruction, the number of polymorphonuclear cells (PMNs), the quantity of blood vessels, and levels of monocyte chemoattractant protein (MCP)-1 in ankles. When administered as a treatment to inflamed ankles, AxCArIL-13 decreases articular index scores, paw volumes, bony destruction, vascularization, tumor necrosis factor-alpha (TNF-alpha) levels, and the quantity of monocytes, lymphocytes, and PMNs. Thus, increasing IL-13 levels significantly ameliorates the course of rat AIA, suggesting that similar strategies for the treatment of human RA are worthy of further study.

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.

Structural model of human IL-13 defines the spatial interactions with the IL-13Ralpha/IL-4Ralpha receptor

Interleukin-13 (IL-13) plays a key role in immune responses and inflammation. A structural model of human IL-13 (HuIL-13) based on the nuclear magnetic resonance and X-ray structure of IL-4 is put forward. Unlike previous models, this model is based on new sequence alignments that take into account the formation of the two disulfide linkages that have been determined experimentally. The proposed structure of human IL-13 is similar to IL-4, consisting of a four helix bundle with hydrophobic residues lining the core of the molecule and surface polar residues showing a high degree of solvent accessibility. Regions of HuIL-13 that are critical for the interaction with its receptors are explored and discussed in relation to existing mutagenic studies. From these studies we predict that helices A and C of HuIL-13 interact with the IL-4 receptor alpha (IL-4Ralpha) region and helix D is responsible for the interaction with the IL-13 receptor alpha 1 (IL-13Ralpha1) receptor.

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.

Solution structure of human IL-13 and implication for receptor binding

Interleukin-13 has been implicated as a key factor in asthma, allergy, atopy and inflammatory response, establishing the protein as a valuable therapeutic target. The high-resolution solution structure of human IL-13 has been determined by multidimensional NMR. The resulting structure is consistent with previous short-chain left-handed four-helix bundles, where a significant similarity in the folding topology between IL-13 and IL-4 was observed. IL-13 shares a significant overlap in biological function with IL-4, a result of the common alpha chain component (IL-4Ralpha) in their respective receptors. Based on the available structural and mutational data, an IL-13/IL-4Ralpha model and a sequential mechanism for forming the signaling heterodimer is proposed for IL-13.

Solution structure of interleukin-13 and insights into receptor engagement

The complex and interrelated function of the interleukin cytokines relies on a range of pro-inflammatory and anti-inflammatory immune responses mediated by an array of receptors, and there is considerable cross-reactivity for related cytokines. Recent findings continue to elucidate the expression patterns of interleukin receptors associated with a range of diseases, including cancer. We report here the first experimentally determined high-resolution structure of human interleukin-13 (IL-13). The experimental structure is significantly different from an earlier homology model, which could have led to improper estimation of receptor interaction surfaces and design of mutational experiments. Similarities between the presented IL-13 structure and the homologous interleukin-4 (IL-4) are discussed. Additionally, mutation data for IL-4 and IL-13 are analyzed and combined with a detailed structural analysis of the IL-4/IL4Ralpha interface that leads us to postulate interactions at the IL-13/receptor interface. The structural comparison is used to interpret the different affinities for various receptors and establishes the basis for further mutational experiments and antagonist design.

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.

Regulation of allergic airways inflammation by cytokines and glucocorticoids

Cytokines mediate the allergic inflammatory response of the airways, and glucocorticosteroids ameliorate allergy symptoms by regulating cytokine expression. Recent studies provide insight into the manner by which cytokines work together to mediate allergic airway disease. Real progress has also been gained in our understanding of subcellular mechanisms of allergic inflammation, particularly the role of transcription factors in regulating the expression of specific cytokine profiles and the differentiation of the TH2 subset. This article provides an update of recently reported findings in this field and highlights emerging concepts of allergic inflammation.

Invited lecture: activation of the epithelial mesenchymal trophic unit in the pathogenesis of asthma

BACKGROUND

A recent NIH Workshop and an ERS Task Force concluded that more work was needed to understand mechanisms of severe and chronic asthma. This report describes a series of studies that identify aberrant epithelial mesenchymal signalling in the airways as an important event in maintaining inflammation and driving remodelling in response to environmental injury.

METHODS

Immunohistochemistry, genotyping and functional studies conducted on cultured asthmatic cells and mucosal biopsies were used to identify biochemical pathways involved in epithelial injury and repair in asthma and their relationship to disease severity.

RESULTS

Our findings suggest that the asthmatic state results from an interaction between a susceptible epithelium and Th-2-mediated inflammation to alter the communication between the epithelium and the underlying mesenchyme - the epithelial mesenchymal trophic unit - leading to disease persistence, airway remodelling and refractoriness to corticosteroid treatment.

CONCLUSIONS

Asthma is more than an inflammatory disorder, but requires engagement of important signalling pathways involved in epithelial repair and tissue remodelling. These pathways involving EGFRs and TGF-betaRs provide targets against which to develop novel therapies for chronic asthma.

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.