Development of a time-resolved fluorescence resonance energy transfer assay (cell TR-FRET) for protein detection on intact cells

An assay named Cell TR-FRET based on time-resolved fluorescence resonance energy transfer, here utilized for detection of receptor proteins on intact cells, is described. In this assay, intact membrane-biotinylated Sf9 cells expressing human interleukin-2Ralpha due to infection with a recombinant baculovirus were prelabeled with a streptavidin-europium (Eu(3+)) chelate, the donor. These prelabeled cells were used in a homogeneous assay by addition of a fluorochrome-labeled anti-hIL-2Ralpha-specific antibody, 7G7B6-Cy5, the acceptor. Binding of 7G7B6-Cy5 to hIL-2Ralpha expressed on the cell surface and europium-labeled streptavidin to surface biotin esters brings the donor and the acceptor in close proximity, allowing transfer of energy from the excited state donor to the acceptor. This energy transfer was specifically inhibited by unlabeled antibody and by free biotin. The described assay constitutes a general method since no specific component of the cell membrane is labeled, thereby allowing a number of binding studies on the cell membrane, including receptor density determinations, to be performed. In addition, due to the rapid fashion in which the Cell TR-FRET assay is accomplished, it can be a valuable method not only for identifying novel membrane-associated proteins, but also for drug screening of large samples in high-throughput format.

Purification, crystallization and preliminary X-ray diffraction of a complex between IL-10 and soluble IL-10R1

A complex between interleukin-10 and the extracellular domain of its high-affinity receptor (sIL-10R1) has been crystallized from polyethylene glycol solutions. Crystals suitable for diffraction analysis required the modification of the NXS/T glycosylation sites on sIL-10R1 by site-directed mutagenesis and inclusion of the detergent cyclohexyl-methyl-beta-D-maltopyranoside in the crystallization experiments. The crystals belong to space group P3(2)12 or its enantimorph P3(1)12, with unit-cell parameters a = b = 46.23, c = 307.78 A, alpha = beta = 90, gamma = 120 degrees, and diffract X-rays to approximately 2.9 A. The IL-10 dimer is positioned on a crystallographic twofold, resulting in one IL-10 chain and one sIL-10R1 chain in the asymmetric unit, which corresponds to a solvent content of approximately 44%.

Expression of a functional IL-13Ralpha1 by rat B cells

IL-13 mediates its effects through a complex receptor system including IL-4Ralpha and a functional IL-13Ralpha1. IL-13 has been reported to have no effects on mouse B cells due to a lack of receptor expression. However, on human B cells a functional IL-13Ralpha1 has been described. Here, we identified the rat IL-13Ralpha1 in order to analyze its expression and function in rat B cells. The expression of IL-13Ralpha1 has been shown by the presence of mRNA and the corresponding protein in purified rat B cells and in rat hybridoma B cell line. Rat B cells are able to bind IL-13 and to proliferate when cultured with CD40 ligand and IL-13. In vivo experiments showed that administration of IL-13 did enhance IgE production. These results suggest a direct interaction of rat B cells with IL-13 through a functional receptor with an increase of IgE production and provide a relevant model to further study the activity of IL-13 and to better understand its role in human diseases.

A novel, soluble homologue of the human IL-10 receptor with preferential expression in placenta

The cytokine receptor family type 2 (CRF2) comprises receptors for important immunomediators like interferons and interleukin-10 (IL-10). We identified a novel member of this family which represents the first exclusively soluble receptor in this group and was therefore designated as CRF2-soluble 1 (CRF2-s1). The CRF2-s1 gene covers about 28 kb and is located on chromosome 6 in close proximity to the CRF2 members interferon (IFN)-gamma receptor 1 and IL-20 receptor 1. It comprises seven exons and generates two different mRNA splice variants, CRF2-s1-long and CRF2-s1-short. CRF2-s1-long and CRF2-s1-short encode proteins of 263 and 231 amino acids, respectively. A comparison of predicted protein structures led to the postulation that each receptor variants binds a different ligand. Quantitative analysis of human mRNA expression revealed a very restricted pattern for both splice forms. CRF2-s1 turned out to be the first member of this receptor family which was expressed neither in resting nor in stimulated leucocyte populations. CRF2-s1-long was only expressed in placenta, whereas CRF2-s1-short was additionally expressed in human mammary gland and, at a lower level, in skin, spleen, thymus and stomach. The preferential expression of CRF2-s1 in placenta suggests a role for this receptor in establishing and maintaining successful pregnancy.

Cytokine-specific transcriptional regulation through an IL-5Ralpha interacting protein

Cytokine receptors consist of multiple subunits, which are often shared between different receptors, resulting in the functional redundancy sometimes observed between cytokines. The interleukin 5 (IL-5) receptor consists of an IL-5-specific alpha-subunit (IL-5Ralpha) and a signal-transducing beta-subunit (betac) shared with the IL-3 and granulocyte-macrophage colony-stimulating factor (GM-CSF) receptors. In this study, we sought to find a role for the cytoplasmic domain of IL-5Ralpha. We show that syntenin, a protein containing PSD-95/Discs large/zO-1 (PDZ) domains, associates with the cytoplasmic tail of the IL-5Ralpha. Syntenin was found to directly associate with the transcription factor Sox4. Association of syntenin with IL-5Ralpha was required for IL-5-mediated activation of Sox4. These studies identify a mechanism of transcriptional activation by cytokine-specific receptor subunits.

Interleukin-18 regulates both Th1 and Th2 responses

Although interleukin-18 is structurally homologous to IL-1 and its receptor belongs to the IL-1R/Toll-like receptor (TLR) superfamily, its function is quite different from that of IL-1. IL-18 is produced not only by types of immune cells but also by non-immune cells. In collaboration with IL-12, IL-18 stimulates Th1-mediated immune responses, which play a critical role in the host defense against infection with intracellular microbes through the induction of IFN-gamma. However, the overproduction of IL-12 and IL-18 induces severe inflammatory disorders, suggesting that IL-18 is a potent proinflammatory cytokine that has pathophysiological roles in several inflammatory conditions. IL-18 mRNA is expressed in a wide range of cells including Kupffer cells, macrophages, T cells, B cells, dendritic cells, osteoblasts, keratinocytes, astrocytes, and microglia. Thus, the pathophysiological role of IL-18 has been extensively tested in the organs that contain these cells. Somewhat surprisingly, IL-18 alone can stimulate Th2 cytokine production as well as allergic inflammation. Therefore, the functions of IL-18 in vivo are very heterogeneous and complicated. In principle, IL-18 enhances the IL-12-driven Th1 immune responses, but it can also stimulate Th2 immune responses in the absence of IL-12.

Studies of murine schistosomiasis reveal interleukin-13 blockade as a treatment for established and progressive liver fibrosis

In several allergic, autoimmune, and infectious diseases, fibrosis is a major cause of morbidity and mortality. Here, using a model of infection-induced liver fibrosis, we show that interleukin (IL)-13 is required at all stages of Schistosomiasis mansoni infection to induce fibrosis. IL-4 production was preserved in IL-13-deficient mice, yet failed to significantly contribute to the fibrotic response in either acute or chronic infection. Significant fibrosis develops in all infected mice, although the magnitude of the response varies widely in inbred mice. C3H/HeN, BALB/c, and C57BL/6 mice develop high, intermediate, and low levels of fibrosis, respectively. Despite these differences, IL-13 antagonism resulted in a marked amelioration of fibrosis in all strains. The fibrotic mechanism in the high- and low-responder strains was unrelated to their tissue eosinophil or mast cell responses, but did correlate with their patterns of IL-13, IL-10, and interferon gamma (IFN-gamma) mRNA expression. Indeed, severe fibrosis correlated with a high IL-13 and low IFN-gamma/IL-10 mRNA response. Because fibrotic diseases are typically progressive disorders, an important issue was to determine whether IL-13 inactivation might be used to treat an established and ongoing fibrotic disease. Here, IL-13 antagonism was highly efficacious, even after fibrosis and the Th2 cytokine response were firmly established. These studies demonstrate the central role played by IL-13 in fibrogenesis and suggest that therapeutic approaches aimed at disrupting the IL-13 pathway will be highly effective at preventing fibrotic disease caused by chronic Th2-mediated inflammatory reactions.

Regulation of interleukin (IL)-18 receptor alpha chain expression on CD4(+) T cells during T helper (Th)1/Th2 differentiation. Critical downregulatory role of IL-4

Interleukin (IL)-18 has been well characterized as a costimulatory factor for the induction of IL-12-mediated interferon (IFN)-gamma production by T helper (Th)1 cells, but also can induce IL-4 production and thus facilitate the differentiation of Th2 cells. To determine the mechanisms by which IL-18 might regulate these diametrically distinct immune responses, we have analyzed the role of cytokines in the regulation of IL-18 receptor alpha chain (IL-18Ralpha) expression. The majority of peripheral CD4(+) T cells constitutively expressed the IL-18Ralpha. Upon antigen stimulation in the presence of IL-12, marked enhancement of IL-18Ralpha expression was observed. IL-12-mediated upregulation of IL-18Ralpha required IFN-gamma. Activated CD4(+) T cells that expressed low levels of IL-18Ralpha could produce IFN-gamma when stimulated with the combination of IL-12 and IL-18, while CD4(+) cells which expressed high levels of IL-18Ralpha could respond to IL-18 alone. In contrast, T cell stimulation in the presence of IL-4 resulted in a downregulation of IL-18Ralpha expression. Both IL-4(-/)- and signal transducer and activator of transcription (Stat)6(-/)- T cells expressed higher levels of IL-18Ralpha after TCR stimulation. Furthermore, activated T cells from Stat6(-/)- mice produced more IFN-gamma in response to IL-18 than wild-type controls. Thus, positive/negative regulation of the IL-18Ralpha by the major inductive cytokines (IL-12 and IL-4) determines the capacity of IL-18 to polarize an immune response.

Crystal structure of the IL-10/IL-10R1 complex reveals a shared receptor binding site

Interleukin 10 (IL-10) is a dimeric cytokine that plays a central role in suppressing inflammatory responses. These activities are dependent on the interaction of IL-10 with its high-affinity receptor (IL-10R1). This intermediate complex must subsequently recruit the low-affinity IL-10R2 chain before cell signaling can occur. Here we report the 2.9 A crystal structure of IL-10 bound to a soluble form of IL-10R1 (sIL-10R1). The complex consists of two IL-10s and four sIL-10R1 molecules. Several residues in the IL-10/sIL-10R1 interface are conserved in all IL-10 homologs and their receptors. The data suggests that formation of the active IL-10 signaling complex occurs by a novel molecular recognition paradigm where IL-10R1 and IL-10R2 both recognize the same binding site on IL-10.

Peptide insertions in domain 4 of hbeta(c), the shared signalling receptor subunit for GM-CSF, IL3 and IL5, induce ligand-independent activation

A mutant form of the common beta-subunit of the GM-CSF, interleukin-3 (IL3) and IL5 receptors is activated by a 37 residue duplicated segment which includes the WSXWS motif and an adjacent, highly conserved, aliphatic/basic element. Haemopoietic expression of this mutant, hbeta(c)FIDelta, in mice leads to myeloproliferative disease. To examine the mechanism of activation of this mutant we targetted the two conserved motifs in each repeat for mutagenesis. Here we show that this mutant exhibits constitutive activity in BaF-B03 cells in the presence of mouse or human GM-CSF receptor alpha-subunit (GMRalpha) and this activity is disrupted by mutations of the conserved motifs in the first repeat. In the presence of these mutations the receptor reverts to an alternative conformation which retains responsiveness to human IL3 in a CTLL cell line co-expressing the human IL3 receptor alpha-subunit (hIL3Ralpha). Remarkably, the activated conformation is maintained in the presence of substitutions, deletions or replacement of the second repeat. This suggests that activation occurs due to insertion of extra sequence after the WSXWS motif and is not dependent on the length or specific sequence of the insertion. Thus hbeta(c) displays an ability to fold into functional receptor conformations given insertion of up to 37 residues in the membrane-proximal region. Constitutive activation most likely results from a specific conformational change which alters a dormant, inactive receptor complex, permitting functional association with GMRalpha and ligand-independent mitogenic signalling.

Cloning and characterization of IL-22 binding protein, a natural antagonist of IL-10-related T cell-derived inducible factor/IL-22

The class II cytokine receptor family includes the receptors for IFN-alphabeta, IFN-gamma, IL-10, and IL-10-related T cell-derived inducible factor/IL-22. By screening genomic DNA databases, we identified a gene encoding a protein of 231 aa, showing 33 and 34% amino acid identity with the extracellular domains of the IL-22 receptor and of the IL-20R/cytokine receptor family 2-8, respectively, but lacking the transmembrane and cytoplasmic domains. A lower but significant sequence identity was found with other members of this family such as the IL-10R (29%), cytokine receptor family 2-4/IL-10Rbeta (30%), tissue factor (26%), and the four IFN receptor chains (23-25%). This gene is located on chromosome 6q24, at 35 kb from the IFNGR1 gene, and is expressed in various tissues with maximal expression in breast, lungs, and colon. The recombinant protein was found to bind IL-10-related T cell-derived inducible factor/IL-22, and to inhibit the activity of this cytokine on hepatocytes and intestinal epithelial cells. We propose to name this natural cytokine antagonist IL-22BP for IL-22 binding protein.

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.

Neutralizing monoclonal antibodies can potentiate IL-5 signaling

IL-5 is a major determinant in the survival, differentiation and effector-functions of eosinophils. It mediates its effect upon binding and activation of a membrane bound receptor (R), composed of a ligand-specific alpha-chain and a beta-chain, shared with the receptors for IL-3 and granulocyte-macrophage colony-stimulating factor. We have generated and mapped the epitopes of three monoclonal antibodies (mAb) directed against this cytokine: the strong neutralizing mAb 5A5 and 1E1, and the very weak neutralizing mAb H30. We found that H30 as well as 5A5 can increase proliferation above the level induced by human (h)IL-5 alone, in a JAK-2-dependent manner, and at every sub-optimal hIL-5 concentration analyzed. This effect is dependent on mAb-mediated cross-linking of IL-5R complexes, and is only observed on cell lines expressing a hybrid human/mouse IL-5Ralpha-chain. We discuss these findings in view of the stoichiometric and topological requirements for an activated IL-5R. Since humanized anti-IL-5 mAb are currently in clinical testing, our findings imply that such mAb should be carefully evaluated for their potentiating effects.

Role of IL-9 in the pathophysiology of allergic diseases

Considerable evidence from both human and animal studies indicates that CD4(+) cells are the predominant cell type involved in the regulation of airway inflammation through the expression of T(H)2-type cytokines. The effects of T(H)2-type cytokines, particularly IL-4 and IL-5, on inflammatory and structural cells in airways have been studied in great detail. They were shown to be important for inflammatory cell maturation, activation and proliferation, IgE production, chemokine expression, mucus secretion, and bronchial hyperresponsiveness. Recent work has shown the potential importance of another T(H)2-type cytokine, IL-9. The development of transgenic mice overexpressing IL-9 has suggested a key role for this cytokine in the development of the asthmatic phenotype, including eosinophilic inflammation, bronchial hyperresponsiveness, elevated IgE levels, and increased mucus secretion. IL-9 has been shown to act on many cell types involved in asthma, including T cells, B cells, mast cells, eosinophils, neutrophils, and epithelial cells, and thus might be important in the pathophysiology of allergic asthma.

[Involvement of interleukin-4, and -13 in the pathogenesis of allergic diseases]

Allergic diseases are immunologic disorders in which various kinds of cells and many mediators are involved. Among them, the importance of interleukin(IL)-4 and IL-13 has recently emerged, based on the analyses of cytokine expression profiles in lesions, model mice, genetic factors, and responses to newly developed reagents. It is known that IL-4 and IL-13 are involved in the pathogenesis of allergic diseases, particularly bronchial asthma, by inducing class switching in B cells and expansion of Th2-type cells. However, IL-4 and IL-13 have a pivotal role in causing bronchial asthma by acting directly on bronchial tissues. Furthermore, it has been demonstrated that a single nucleotide polymorphism in the IL-13 gene is genetically correlated with bronchial asthma. These analyses provide new information for developing better methods of diagnosing and treating bronchial asthma.

Interleukin-18 enhances the production of interleukin-8 by eosinophils

Interleukin-18 (IL-18), a proinflammatory cytokine, leads to IFN-gamma production by NK or T cells, induces Th1 differentiation and suppresses IgE synthesis by B cells when acting on responding cells together with IL-12. IL-18 also exhibits biological activities related to allergic inflammation such as histamine or IL-4 release from basophils and accumulation of eosinophils in localized lesions in allergic model mice. In this study, Reverse transcription (RT)-PCR analysis revealed that IL-18 receptor alpha chain mRNA was expressed in both freshly prepared eosinophils and two eosinophilic cell lines (YY-1 and EoL-1 cells). Flow cytometry and RT-PCR analyses revealed that the treatment of YY-1 cells with n-butyric acid promoted cell maturation and caused an enhancement of IL-18 receptor alpha chain expression. IL-18 had little effect on the survival of peripheral eosinophils, but it dose-dependently augmented IL-8 synthesis by YY-1 cells. In addition, IL-18-mediated up-regulation of IL-8 expression in eosinophils from a patient suffering from hyper-eosinophilic syndrome was confirmed. Our findings using peripheral blood eosinophils and eosinophilic cell line suggest the functional importance of IL-18 in the induction of IL-8 and a potential proinflammatory role in allergy.

Structural and functional hot spots in cytokine receptors

The activation of cytokine receptors is a stepwise process that depends on their specific interaction with cognate cytokines, the formation of oligomeric receptor complexes, and the initiation of cytoplasmic phosphorylation events. The recent determination of the structure of extracellular domains of several cytokine receptors allows comparison of their cytokine-binding surfaces. This comparison reveals a common structural framework that supports considerable diversity and adaptability of the binding surfaces that determine both the specificity and the orientation of subunits in the active receptor complex. These regions of the cytokine receptors have been targeted for the development of specific agonists and antagonists. The physical coupling of signaling intermediates to the intracellular domains of their receptors plays a major role in determining biological responses to cytokines. In this review, we focus principally on the receptors for cytokines of the granulocyte-macrophage colony-stimulating factor (GM-CSF) family and, where appropriate, compare them with related cytokine receptors. Several paradigms are beginning to emerge that focus on the ability of the extracellular portion of the cytokine receptor to recognize the appropriate cytokine and on a phosphorylated motif in the intracellular region of the GM-CSF receptor that couples to a specific signaling pathway.

Interleukin-18 is a unique cytokine that stimulates both Th1 and Th2 responses depending on its cytokine milieu

IL-18 is a potent proinflammatory cytokine able to induce IFNgamma, GM-CSF, TNFalpha and IL-1 in immunocompetent cells, to activate killing by lymphocytes, and to up-regulate the expression of certain chemokine receptors. IL-18 is also essential to host defences against severe infections. In particular, the clearance of intracellular bacteria, fungi and protozoa requires the induction of host-derived IFNgamma, which evokes effector molecules such as nitric oxide. Also, IL-18 plays a part in the clearance of viruses, partly by the induction of cytotoxic T cells, and the expulsion of viruses is impaired in IL-18-deficient mice. IL-18 also enhances tumour rejection by its potent capacity to augment the cytotoxic activity of NK and T cells in vivo. In contrast, recent studies also demonstrate a convincing role for IL-18 in atopic responses, including atopic asthma. IL-18 induces naive T cells to develop into Th2 cells. Moreover, IL-18 also induces IL-13 and/or IL-4 production by NK cells, mast cells and basophils. Therefore, IL-18 should be seen as a unique cytokine that enhances innate immunity and both Th1- and Th2-driven immune responses.

Specificity in cytokine signal transduction: lessons learned from the IL-3/IL-5/GM-CSF receptor family

Cytokines mediate the transduction of proliferative, differentiation and survival signals in the hematopoietic system. Although the cytokine family is large and diverse, many different cytokines display broadly overlapping functions. This can be explained by the fact that cytokine receptors often share multiple subunits. Specificity in signal transduction can however be achieved through several mechanisms. This review focuses on how signal specificity can be achieved within the IL-3, IL-5 and GM-CSF receptor family. This is discussed in terms of receptor expression, recent advances in our understanding of intracellular signalling components, and analysis of null mutant knock-out mice.

Possible contribution of aminopeptidase N (APN/CD13) to invasive potential enhanced by interleukin-6 and soluble interleukin-6 receptor in human osteosarcoma cell lines

This study aimed at clarifying the role of Aminopeptidase N (APN), a Zn2+-dependent ectopeptidase localized on the cell surface of human osteosarcoma cell lines treated with proinflammatory cytokines. We investigated the proinflammatory cytokines interleukin-1 beta (IL-1beta), IL-6 and tumor necrosis factor alpha (TNF-alpha) as well as the anti-inflammatory cytokine transforming growth factor beta (TGF-beta) for their influence on APN regulation. Soluble IL-6 receptor (sIL-6R) was always used together with IL-6 to achieve a stable effect. In addition, the invasive potential of the osteosarcoma cell lines MG63 and HOS was examined. Competitive RT-PCR and Ala-pNA activity assays revealed that IL-6 and sIL-6R significantly increased the mRNA expression and activity of APN in both osteosarcoma cell lines. Although IL-1beta significantly stimulated APN mRNA expression in both cell lines, it influenced the enzyme activity only in MG63. TNF-alpha and TGF-beta, however, had an effect neither on mRNA expression nor on the enzyme activity of APN in both cell lines. In the Matrigel invasion assay, IL-6 and sIL-6R significantly up-regulated the transmigration of these cell lines, whereas other cytokines did not. The up-regulated invasion was inhibited by bestatin, a specific inhibitor of APN. Cellular migration correlated highly with APN activity (r = 0.79, P < 0.002). These findings suggest that APN contributes to the invasive potential of human osteosarcomas enhanced by IL-6 and SIL-6R.

Identification of the domain in the human interleukin-11 receptor that mediates ligand binding

The interleukin-11 receptor (IL-11R) belongs to the hematopoietic receptor superfamily. The functional receptor complex comprises IL-11, IL-11R and the signal-transducing subunit gp130. The extracellular part of the IL-11R consists of three domains: an N-terminal immunoglobulin-like domain, D1, and two fibronectin-type III-like (FNIII) domains and D2 and D3. The two FNIII domains comprise the cytokine receptor-homology region defined by a set of four conserved cysteine residues in the N-terminal domain (D2) and a WSXWS sequence motif in the C-terminal domain (D3). We investigated the structural and functional role of the third extracellular receptor domain of IL-11R. A molecular model of the human IL-11/IL-11R complex allowed the identification of amino acid residues in IL-11R to be involved in ligand binding. Most of them were located in the third extracellular domain, which therefore should be able to bind with high affinity to IL-11. To prove this prediction, domain D3 of the IL-11R was expressed in Escherichia coli, refolded and purified. For structural characterization, circular dichroism, fluorescence and NMR spectroscopy were used. By plasmon resonance experiments, we show that the ligand-binding capacity of this domain is as high as that one for the whole receptor. These results provide a basis for further structural investigations that could be used for the rational design of potential agonists and antagonists essential in human therapy.

Structure of the complete extracellular domain of the common beta subunit of the human GM-CSF, IL-3, and IL-5 receptors reveals a novel dimer configuration

The receptor systems for the hemopoietic cytokines GM-CSF, IL-3, and IL-5 consist of ligand-specific alpha receptor subunits that play an essential role in the activation of the shared betac subunit, the major signaling entity. Here, we report the structure of the complete betac extracellular domain. It has a structure unlike any class I cytokine receptor described thus far, forming a stable interlocking dimer in the absence of ligand in which the G strand of domain 1 hydrogen bonds into the corresponding beta sheet of domain 3 of the dimer-related molecule. The G strand of domain 3 similarly partners with the dimer-related domain 1. The structure provides new insights into receptor activation by the respective alpha receptor:ligand complexes.

IL-1H, an interleukin 1-related protein that binds IL-18 receptor/IL-1Rrp

IL-18, or IGIF (interferon-gamma inducing factor), is an IL-1-related, pro-inflammatory cytokine, which plays a pivotal role in systemic and local inflammation. We have identified and characterized IL-1H, a novel IL-1-related molecule. IL-1H appears to be expressed in most tissues with relatively high levels in testis, thymus and uterus. The IL-1H transcripts were stimulated by phorbol ester (PMA) in human cell lines (A431, THP-1 and KG-1) and peripheral blood mononuclear cells (HPBMC) and dendritic cells (NHDC). The protein sequence of IL-1H is mostly related to IL-1ra with a similarity of 36%. A short form of IL-1H was identified, and lacks a 40-amino acid segment in the amino-terminal region of the protein. When expressed in mammalian cells, two secreted polypeptides of IL-1H were identified: an uncleaved and a cleaved form starting with amino acid Val-46. Furthermore, IL-1H binds the IL-18 receptor, but not the IL-1 receptor. These findings suggest that IL-1H may be another ligand for the IL-18 receptor and a new player in the inflammatory and immune responses mediated by the IL-18/IL-18R axis.

Interleukin-5 receptor alpha chain expression and splicing during brain development in mice

We have studied the IL-5 production and responsiveness in the mouse brain. Both IL-5 and IL-5 receptor alpha chain (IL-5 Ralpha) were expressed in vitro in astrocytes, but not in neurons. IL-5 was expressed at constant levels during brain development, after birth, and in the adult brain of both normal mice and mice bearing infection or allergic reaction associated with high Th2 lymphocyte reactivity. Conversely, expression of IL-5 Ralpha was highly regulated both in quantitative terms and in the number of alternatively spliced isoforms. In embryos, we observed the classical transmembrane isoform and two new larger ones, in addition to three smaller soluble isoforms. At birth, a single soluble isoform was generated, and in the post-natal period, the major transmembrane and two or three soluble isoforms were detected. In adulthood, no expression of IL-5 Ralpha was detected in normal mice, but all the isoforms were produced in mice with inflammatory reactions. We propose that IL-5 has a specific autocrine and/or paracrine function in astrocytes, maintaining the homogeneity of the activation state in a given astrocyte population. The alternative splicing of IL-5 Ra modulates the brain tissue from the fully unresponsive to the highly sensitive state in regard to IL-5 stimulation. According to our results, IL-5 Ralpha splicing is controlled by an intrinsic program in the brain during the embryonic and postnatal periods, and an extrinsic systemic program reflecting the inflammatory reactions associated with high systemic IL-5 levels.

Structure and function of Toll-like receptor proteins

Beginning in 1997 with the identification of the first human homologue of the Drosophila protein Toll, a family of related molecules have been identified in both humans and other mammals. These Toll-like receptor (TLR) proteins appear to represent a conserved family of innate immune recognition receptors. TLR proteins share extended homology with receptors for the cytokines interleukin 1 (IL-1) and interleukin 18 (IL-18). These receptors are coupled to a signaling pathway that is conserved in mammals, insects, and plants, resulting in cellular activation, thereby stimulating innate immune defenses. A variety of bacterial and fungal products have been identified that serve as TLR ligands, and more recent studies have identified the first endogenous protein ligands for TLR proteins. While TLR signaling is likely to be a key feature of innate immune responses, these proteins may also regulate homeostasis via interaction with endogenous protein ligands.

Interleukin-11 signals through the formation of a hexameric receptor complex

Interleukin-11 (IL-11) is a member of the gp130 family of cytokines. These cytokines drive the assembly of multisubunit receptor complexes, all of which contain at least one molecule of the transmembrane signaling receptor gp130. IL-11 has been shown to induce gp130-dependent signaling through the formation of a high affinity complex with the IL-11 receptor (IL-11R) and gp130. Site-directed mutagenesis studies have identified three distinct receptor binding sites of IL-11, which enable it to form this high affinity receptor complex. Here we present data from immunoprecipitation experiments, using differentially tagged forms of ligand and soluble receptor components, which show that multiple copies of IL-11, IL-11R, and gp130 are present in the receptor complex. Furthermore, it is demonstrated that sites II and III of IL-11 are independent gp130 binding epitopes and that both are essential for gp130 dimerization. We also show that a stable high affinity complex of IL-11, IL-11R, and gp130 can be resolved by nondenaturing polyacrylamide gel electrophoresis, and its composition verified by second dimension denaturing polyacrylamide gel electrophoresis. Results indicate that the three receptor binding sites of IL-11 and the Ig-like domain of gp130 are all essential for this stable receptor complex to be formed. We therefore propose that IL-11 forms a hexameric receptor complex composed of two molecules each of IL-11, IL-11R, and gp130.

Impairment of STAT activation by IL-12 in a patient with atypical mycobacterial and staphylococcal infections

IL-12 plays a pivotal role in the stimulation of immune responses against intracellular infections. This role is manifested in the increased susceptibility to atypical mycobacterial and salmonella infections among individuals whose lymphocytes lack expression of IL-12Rbeta1. Here, we report on a patient with Mycobacterium avium infection, recurrent Staphylococcus aureus sinusitis, and multiple adverse drug reactions whose T cells were unable to produce IFN-gamma or proliferate in response to IL-12 despite the expression of wild-type IL-12Rbeta1 and IL-12Rbeta2. The defect in these functional responses to IL-12 was selective, as cytolytic activity induced by IL-12 was intact, and lymphocytes were responsive to stimulation by IL-2. An examination of cytokine signaling revealed that STAT4 and extracellular regulated kinase 1 (ERK1) activation by IL-12 was intact, whereas the activation of STAT1, -3, and -5 by IL-12 was lost. This impairment of STAT activation was specific for IL-12, as STAT activation by IL-2, IL-15, and IFN-gamma was unaffected. These findings demonstrate that the activation of STAT4 alone is not sufficient for IL-12-induced IFN-gamma production and proliferation and suggest that other STATs play a role in these responses to IL-12. While the etiology of the impaired IL-12 signaling in this patient has not yet been elucidated, the absence of mutations in IL-12Rbeta1 or IL-12Rbeta2 and the preservation of STAT4 activation raise the possibility that there may be a mutation in an as yet undiscovered component of the IL-12 signaling complex that is normally required for the recruitment and activation of STAT1, -3, and -5.

Differential inhibition of IL-6-type cytokine-induced STAT activation by PMA

Prior activation of mitogen-activated protein kinases by phorbol 13-myristate 12-acetate (PMA) results in an inhibition of interleukin (IL)-6-induced activation of the Janus kinase/signal transducer and activator of transcription (STAT) signaling pathway which is most likely mediated by the induction of suppressor of cytokine signaling-3 and requires the specific SHP2 binding site Y759 of the IL-6 signal transducer gp130. In this study, we demonstrate that PMA inhibits STAT activation by IL-6 and the related cytokine leukemia inhibitory factor (LIF) but not by oncostatin M (OSM). Since the LIF receptor also contains an SHP2 recruitment site whereas the OSM receptor lacks such a module, we propose that two SHP2 binding modules within a homo- or heterodimeric receptor are necessary to mediate the PMA inhibitory effect.

A novel cytokine receptor-ligand pair. Identification, molecular characterization, and in vivo immunomodulatory activity

As part of a large scale effort to discover novel secreted proteins, a cDNA encoding a novel cytokine was identified. Alignments of the sequence of the new protein, designated IL-17B, suggest it to be a homolog of the recently described T cell-derived cytokine, IL-17. By Northern analysis, EST distribution and real-time quantitative polymerase chain reaction analysis, mRNA was detected in many cell types. A novel type I transmembrane protein, identified in an EST data base by homology to IL-17R, was found to bind specifically IL-17B, as determined by surface plasmon resonance analysis, flow cytometry, and co-immunoprecipitation experiments. Readily detectable transcription of IL-17BR was restricted to human kidney, pancreas, liver, brain, and intestines and only a few of the many cell lines tested. By using a rodent ortholog of IL-17BR as a probe, IL-17BR message was found to be drastically up-regulated during intestinal inflammation elicited by indomethacin treatment in rats. In addition, intraperitoneal injection of IL-17B purified from Chinese hamster ovary cells caused marked neutrophil migration in normal mice, in a specific and dose-dependent manner. Together these results suggest that IL-17B may be a novel proinflammatory cytokine acting on a restricted set of target cell types. They also demonstrate the strength of genomic approaches in the unraveling of novel biological pathways.

A potent dimeric peptide antagonist of interleukin-5 that binds two interleukin-5 receptor alpha chains

Two series of peptides that specifically bind to the extracellular domain of the alpha chain of the human interleukin-5 receptor (IL-5Ralpha), but share no primary sequence homology to IL-5, were identified from libraries of random recombinant peptides. Affinity maturation procedures generated a 19-aa peptide that binds to the IL-5 receptor alpha/beta heterodimer complex with an affinity equal to that of IL-5 and is a potent and specific antagonist of IL-5 activity in a human eosinophil adhesion assay. The active form of the peptide is a disulfide-crosslinked dimer that forms spontaneously in solution. Gel filtration analysis, receptor-binding studies, and analytical ultracentrifugation reveal that the dimeric peptide binds simultaneously to two receptor alpha chains in solution. Furthermore, the dimer peptide, but not IL-5, can activate a chimeric receptor consisting of the IL-5Ralpha extracellular domain fused to the intracellular domain of the epidermal growth factor receptor, thus demonstrating that the peptide also promotes receptor dimerization in a cellular context. The functional antagonism produced by the bivalent interaction of the dimeric peptide with two IL-5R alpha chains represents a distinctive mechanism for the antagonism of cytokines that use heteromeric receptors.

Rescue of human T cells by interleukin-9 (IL-9) from IL-2 deprivation-induced apoptosis: correlation with alpha subunit expression of the IL-9 receptor

Interleukin-9 (IL-9) is a Th2-derived cytokine that uses the gamma-chain of the IL-2 receptor for signaling. Therefore, the responsiveness of human Th1 and Th2 cell clones to IL-9 was measured by examining the ability of this cytokine to prevent apoptosis induced by IL-2 deprivation. A time course study demonstrated that both subsets of T cell clones underwent apoptosis with similar kinetics when deprived of IL-2 and that viability could be maintained by the addition of either IL-4 or IL-7. Interestingly, IL-9 prevented apoptosis in only 2 (Th2) of 14 clones tested. Analysis of IL-9R alpha subunit expression on 18 T cell clones revealed that IL-9 responsiveness was directly proportional to the expression of the high-affinity receptor. IL-9 responsiveness was also dependent on long-term culturing because neither freshly isolated nor 3-day phytohemagglutinin (PHA)-stimulated peripheral blood lymphocytes (PBL) expressed IL-9R alpha. In summary, the data showed that IL-9 can rescue only a small subset of Th2 cells from apoptosis induced by growth factor withdrawal and that expression of IL-9R alpha is required for the antiapoptotic signals mediated by this cytokine.

Structure of the activation domain of the GM-CSF/IL-3/IL-5 receptor common beta-chain bound to an antagonist

Heterodimeric cytokine receptors generally consist of a major cytokine-binding subunit and a signaling subunit. The latter can transduce signals by more than 1 cytokine, as exemplified by the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-2 (IL-2), and IL-6 receptor systems. However, often the signaling subunits in isolation are unable to bind cytokines, a fact that has made it more difficult to obtain structural definition of their ligand-binding sites. This report details the crystal structure of the ligand-binding domain of the GM-CSF/IL-3/IL-5 receptor beta-chain (beta(c)) signaling subunit in complex with the Fab fragment of the antagonistic monoclonal antibody, BION-1. This is the first single antagonist of all 3 known eosinophil-producing cytokines, and it is therefore capable of regulating eosinophil-related diseases such as asthma. The structure reveals a fibronectin type III domain, and the antagonist-binding site involves major contributions from the loop between the B and C strands and overlaps the cytokine-binding site. Furthermore, tyrosine(421) (Tyr(421)), a key residue involved in receptor activation, lies in the neighboring loop between the F and G strands, although it is not immediately adjacent to the cytokine-binding residues in the B-C loop. Interestingly, functional experiments using receptors mutated across these loops demonstrate that they are cooperatively involved in full receptor activation. The experiments, however, reveal subtle differences between the B-C loop and Tyr(421), which is suggestive of distinct functional roles. The elucidation of the structure of the ligand-binding domain of beta(c) also suggests how different cytokines recognize a single receptor subunit, which may have implications for homologous receptor systems. (Blood. 2000;95:2491-2498)

The solution structure of the cytokine-binding domain of the common beta-chain of the receptors for granulocyte-macrophage colony-stimulating factor, interleukin-3 and interleukin-5

The haemopoietic cytokines, granulocyte-macrophage colony-stimulating factor, interleukin-3 and interleukin-5 bind to cell-surface receptors comprising ligand-specific alpha-chains and a shared beta-chain. The beta-chain is the critical signalling subunit of the receptor and its fourth domain not only plays a critical role in interactions with ligands, hence in receptor activation, but also contains residues whose mutation can lead to ligand-independent activation of the receptor. We have determined the NMR solution structure of the isolated human fourth domain of the beta-chain. The protein has a fibronectin type III fold with a well-defined hydrophobic core and is stabilised by an extensive network of pi-cation interactions involving Trp and Arg side-chains, including two Trp residues outside the highly conserved Trp-Ser-Xaa-Trp-Ser motif (where Xaa is any amino acid) that is found in many cytokine receptors. Most of the residues implicated in factor-independent mutants localise to the rigid core of the domain or the pi-cation stack. The loops between the B and C, and the F and G strands, that contain residues important for interactions with cytokines, lie adjacent at the membrane-distal end of the domain, consistent with their being involved cooperatively in binding cytokines. The elucidation of the structure of the cytokine-binding domain of the beta-chain provides insight into the cytokine-dependent and factor-independent activation of the receptor.

The costimulatory effect of IL-18 on the induction of antigen-specific IFN-gamma production by resting T cells is IL-12 dependent and is mediated by up-regulation of the IL-12 receptor beta2 subunit

IL-18 was originally described as a cytokine which induced IFN-gamma production by established Th1 cells in an IL-12-independent manner. However, subsequent studies demonstrated that exogenous IL-18 in the absence of IL-12 failed to drive Th1 differentiation of naive cells and induced IFN-gamma from established Th1 cells only in combination with IL-12. We have examined the role of endogenous IL-18 in controlling Th1 lineage commitment. When naive TCR-transgenic T cells were stimulated with antigen, anti-IL-18 antibodies resulted in partial inhibition of IFN-gamma production, but did not inhibit Th1 differentiation. To distinguish whether the inhibitory effect of anti-IL-18 antibodies was mediated directly by blocking IFN-gamma production or indirectly by blocking IL-12Rbeta2 up-regulation, naive T cells from IL-12 - / - mice were stimulated with anti-CD3 and IL-18. These cells failed to produce IFN-gamma, but markedly up-regulated IL-12Rbeta2 expression. We propose that the major effect of IL-18 on Th1 development is mediated by up-regulation of IL-12Rbeta2 expression, thereby enhancing IL-12-mediated signaling. The enhancement of IL-12Rbeta2 expression by IL-18 may be particularly important for the differentiation of foreign antigen- or autoantigen-specific Th1 cells when the stimulatory concentration of IL-12 in the microenvironment is just below the threshold required for Th1 development.

Epitope randomization redefines the functional role of glutamic acid 110 in interleukin-5 receptor activation

Sequence randomization through functional phage display of single chain human interleukin (IL)-5 was used to investigate the limits of replaceability of the Glu(110) residues that form a part of the receptor-binding epitope. Mutational analysis revealed unexpected affinity for IL-5 receptor alpha chain with variants containing E110W or E110Y. Escherichia coli-expressed Glu(110) variants containing E110W in the otherwise sequence-intact N-terminal half, including a variant with an E110A replacement in the sequence-disabled C-terminal half, were shown by their CD spectra to be folded into secondary structures similar to that of single chain human IL-5 (scIL-5). Biosensor kinetics analysis revealed that (E110W/A5)scIL-5 and (E110W/A6)scIL-5 had receptor alpha chain binding affinities similar to that of (wt/A5)scIL-5. However, (E110W/A6)scIL-5 had a significantly reduced bioactivity in TF-1 cell proliferation compared with both (wt/A5)scIL-5 and (E110W/A5)scIL-5, and this activity reduction was disproportionately greater than the much smaller effect of Glu(110) mutation on receptor binding affinity. The marked and disproportionate decrease in TF-1 proliferation observed with (E110W/A6)scIL-5 suggests a role for Glu(110) in the biological activity mediated by the signal transducing receptor betac subunit of the IL-5 receptor. This is also consistent with the lack of stimulation of JAK2 phosphorylation by the (E110W/A6)scIL-5 mutant in recombinant 293T cells, as compared with the concentration-dependent stimulation seen for scIL-5. The results reveal the dispensability of charge in the Glu(110) locus of IL-5 for receptor alpha chain binding and, in contrast, its heretofore underappreciated importance for receptor activation.

Receptor-binding conformation of the "ELR" motif of IL-8: X-ray structure of the L5C/H33C variant at 2.35 A resolution

The "ELR" (Glu-Leu-Arg) tripeptide sequence near the N-terminus of interleukin-8 (IL-8) contributes a large part of the receptor binding free energy. Prior X-ray and nuclear magnetic resonance (NMR) structures of IL-8 have shown this region of the molecule to be highly mobile. We reasoned that a hydrophobic interaction between the leucine and the neighboring beta-turn might exist in the receptor binding conformation of the N-terminus. To test this hypothesis, we mutated two residues to cysteine and connected the N-terminus to the beta-turn. The mutant retains receptor binding affinity reasonably close to wild type and allows the characterization of a high-affinity conformation that may be useful in the design of small IL-8 mimics. The L5C/H33C mutant is refined to R-values of R = 20.6% and Rfree = 27.7% at 2.35 A resolution. Other receptor binding determinants reside in the "N-loop" found after "ELR" and preceding the first beta-strand. All available structures of IL-8 have been found with one of two distinct N-loop conformations. One of these is relevant for receptor binding, based on NMR results with receptor peptides. The other conformation obscures the receptor-peptide binding surface and may have an undetermined but necessarily different function.

A model for assembly and activation of the GM-CSF, IL-3 and IL-5 receptors: insights from activated mutants of the common beta subunit

Granulocyte-macrophage colony stimulating factor (GM-CSF), Interleukin-3 (IL-3) and Interleukin-5 (IL-5) have overlapping, pleiotropic effects on hematopoietic cells, including neutrophils, eosinophils, monocytes and early progenitor cells. The high-affinity receptors for human GM-CSF, IL-3, and IL-5 share a common beta-subunit (hbeta(c)), which is essential for signalling and plays a major role in recruiting intracellular signalling molecules. While activation of the cytoplasmic tyrosine kinase JAK2 appears to be the initiating event for signalling, the immediate events that trigger this are still unclear. We have isolated a number of activated mutants of hbeta(c), which can be grouped into classes defined by their state of receptor phosphorylation, their requirement for alpha subunit as a cofactor, and their activities in primary cells and cell lines. We discuss these findings with regard to the stoichiometry, activation, and signalling of the normal GM-CSF/IL-3/IL-5 receptor complexes. Specifically, this work has implications for the role of the ligand-specific alpha-subunits in initiating the signalling through the beta-subunit, the role of beta subunit dimerization as a receptor trigger, and the function of receptor tyrosine phosphorylation in generating growth and survival signals. Based on the properties of the activated mutants and the recent structures of erythropoietin receptor (Epo-R) complexes, we propose a model in which (1) activation of hbeta(c) can occur via alternative states that differ with respect to stoichiometry and subunit assembly, but which all mediate proliferative responses, and (2) each of the different classes of activated mutants mimics one of these alternative states.

Interleukin 5 regulates the isoform expression of its own receptor alpha-subunit

The receptor for interleukin 5 (IL-5) consists of a cytokine-specific alpha chain (IL-5Ralpha) and a signaling beta chain, which is shared with interleukin 3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF). These 3 cytokines can act in eosinophil development and activation in vitro, but gene deletion or antibody blocking of IL-5 largely ablates eosinophilic responses in models of allergic disease or helminth infection. We investigated factors acting in differential IL-5Ralpha gene splicing to generate either the membrane-anchored isoform (TM-IL-5Ralpha) which associates with the common beta chain to allow IL-5 responsiveness, or a secreted, antagonist variant (SOL-IL-5Ralpha). In a murine myeloid cell line (FDC-P1), transfected with minigenes allowing expression of either IL-5Ralpha variant, IL-5 itself, but not IL-3 or GM-CSF, stimulated a reversible switch toward expression of TM-IL-5Ralpha. A switch from predominantly soluble isoform to TM-IL-5Ralpha messenger RNA (mRNA) expression was also seen during IL-5-driven eosinophil development from human umbilical cord blood-derived CD34(+) cells; this was accompanied by surface expression of IL-5Ralpha and acquisition of functional responses to IL-5. IL-3 and GM-CSF also supported eosinophil development and up-regulation of TM-IL-5Ralpha mRNA in this system, but this was preceded by expression of IL-5 mRNA and was inhibited by monoclonal antibody to IL-5. These data suggest IL-5-specific signaling, not shared by IL-3 and GM-CSF, leading to a switch toward up-regulation of functional IL-5Ralpha and, furthermore, that IL-3 and GM-CSF-driven eosinophil development is dependent on IL-5, providing an explanation for the selective requirement of IL-5 for expansion of the eosinophil lineage. (Blood. 2000;95:1600-1607)

Genomic organization of the human interleukin-12 receptor beta2-chain gene

The interleukin-12 receptor (IL-12R) is composed of two subunits, referred to as beta1 and beta2. Both chains are necessary for high-affinity IL-12 binding and signalling, although only the IL-12Rbeta2 chain contains the intracellular tyrosine residues responsible for STAT4 activation. This study presents the intron-exon organization of the human IL-12Rbeta2-chain gene. Polymerase chain reaction (PCR) primers designed across the cDNA (U46198) were used to trace introns, by comparing PCR product sizes obtained using cDNA and genomic DNA as templates. PCR products spanning introns were sequenced to determine the exact splice sites and flanking regions. The coding region of the gene was found to consist of 15 exons and 14 introns. All intron-exon boundaries are consistent with the consensus sequence for splice junctions (5' GT/AG 3'). Comparison of the intron-exon organization with the human GCSFR gene indicated a remarkably well conserved genomic organization between these two class I cytokine receptors. Interestingly, we identified an alternatively spliced mRNA, encoding a putative, truncated protein, lacking all signalling potential.

Interleukin-5, a therapeutic target in allergic inflammation

Images

[Mendelian predisposition to mycobacterial infections in humans]

Selective susceptibility to poorly pathogenic mycobacteria, such as bacille Calmette-Guérin (BCG) vaccine and environmental non-tuberculous mycobacteria (NTM), bas long been suspected to be a mendelian disorder but its molecular basis has remained elusive. Recently, recessive mutations in the interferon gamma receptor ligand-binding chain (IFN gamma R1), interferon gamma receptor signalling chain (IFN gamma R2), interleukin 12 p40 subunit (IL-12 p40), and interleukin 12 receptor beta 1 chain (IL-12R beta 1) genes have been identified in a number of patients with disseminated BCG or NTM infection. Although genetically distinct, these conditions are immunologically related and highlight the essential role of interferon gamma-mediated immunity in the control of mycobacteria in man.

Functional implications for signaling via the IL4R/IL13R complex on bovine cells

IL-4 and IL-13 share a wide range of activities on monocytes, epithelial cells and B cells and thus play an important role in host defense. Many of these activities are not conserved among species as human, but not murine, B cells are thought to be responsive to IL-13. We previously demonstrated that human IL-13 is highly conserved at the nucleic acid level with a candidate bovine IL-13 cDNA homologue. Moreover, recombinant human IL-13 stimulates Ig secretion by appropriately activated bovine B cells. These studies have been extended to examining Ig class switching at both the protein and mRNA levels in addition to examining other markers of cellular activation. Our results suggest that IL-13 influences B cell differentiation by enhancing IgM, IgG1, and IgE production. IL-13 stimulation alone increases MHC class II expression and progression through cell cycle, although at lower levels in comparison to rboIL-4. The biology of the receptors for IL-4 and IL-13 is complex and raises several key questions with regard to IL-4-dependent and -independent mechanisms of host immunomodulation. Recent studies suggest that at least four chains are involved. These include the p140 IL-4 binding chain (IL-4Ralpha), the common gamma chain (gammac chain), IL-13 receptor alpha- chain (IL-13Ralpha-1) and the IL-13 receptor alpha-2 chain (IL-13Ralpha-2). We have recently cloned cDNAs for the bovine homologues of the IL-13Ralpha-1 and IL-4Ralpha chains and evaluated mRNA expression for a variety of cell types following stimulation. The expression patterns and their implications for receptor chain utilization in signaling via these key TH2 signature cytokines will be discussed.

Exploring biomolecular recognition using optical biosensors

Understanding the basic forces that determine molecular recognition helps to elucidate mechanisms of biological processes and facilitates discovery of innovative biotechnological methods and materials for therapeutics, diagnostics, and separation science. The ability to measure interaction properties of biological macromolecules quantitatively across a wide range of affinity, size, and purity is a growing need of studies aimed at characterizing biomolecular interactions and the structural elements that drive them. Optical biosensors have provided an increasingly impactful technology for such biomolecular interaction analyses. These biosensors record the binding and dissociation of macromolecules in real time by transducing the accumulation of mass of an analyte molecule at the sensor surface coated with ligand molecule into an optical signal. Interactions of analytes and ligands can be analyzed at a microscale and without the need to label either interactant. Sensors enable the detection of bimolecular interaction as well as multimolecular assembly. Most notably, the method is quantitative and kinetic, enabling determination of both steady-state and dynamic parameters of interaction. This article describes the basic methodology of optical biosensors and presents several examples of its use to investigate such biomolecular systems as cytokine growth factor-receptor recognition, coagulation factor assembly, and virus-cell docking.

Tip60 interacts with human interleukin-9 receptor alpha-chain

Interleukin-9 (IL-9) exerts its pleiotropic effects through the IL-9 receptor (IL-9R) complex that consists of the ligand specific IL-9R alpha-chain, and the IL-2R gamma-chain. In this study, we used a modified yeast two-hybrid system to isolate cDNAs encoding proteins that interact with the intracellular domain of the human IL-9R alpha-chain (hIL-9Ralpha). We have identified Tip60, an HIV-1 Tat transcription cofactor, as an hIL-9Ralpha interacting protein. The interaction between hIL-9Ralpha and Tip60 was confirmed by coimmunoprecipitation and colocalization studies. This is the first demonstration that Tip60 associates with a membrane receptor. We also mapped amino acids 411-423 in hIL-9Ralpha and amino acids 100-147 in Tip60 to be important for interaction. Interestingly, the region in hIL-9alpha that binds Tip60 is adjacent to the site previously shown to interact with Stat3. Tip60 binds HIV-Tat and mediates Tat-dependent transactivation possibly through its histone acetyltransferase activity. Our results therefore suggest that Tip60 may act as a cofactor of Stat3 or as an adaptor protein for molecules that are important for IL-9 signaling.

Simultaneous antagonism of interleukin-5, granulocyte-macrophage colony-stimulating factor, and interleukin-3 stimulation of human eosinophils by targetting the common cytokine binding site of their receptors

Human interleukin-5 (IL-5), granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-3 are eosinophilopoietic cytokines implicated in allergy in general and in the inflammation of the airways specifically as seen in asthma. All 3 cytokines function through cell surface receptors that comprise a ligand-specific alpha chain and a shared subunit (beta(c)). Although binding of IL-5, GM-CSF, and IL-3 to their respective receptor alpha chains is the first step in receptor activation, it is the recruitment of beta(c) that allows high-affinity binding and signal transduction to proceed. Thus, beta(c) is a valid yet untested target for antiasthma drugs with the added advantage of potentially allowing antagonism of all 3 eosinophil-acting cytokines with a single compound. We show here the first development of such an agent in the form of a monoclonal antibody (MoAb), BION-1, raised against the isolated membrane proximal domain of beta(c). BION-1 blocked eosinophil production, survival, and activation stimulated by IL-5 as well as by GM-CSF and IL-3. Studies of the mechanism of this antagonism showed that BION-1 prevented the high-affinity binding of (125)I-IL-5, (125)I-GM-CSF, and (125)I-IL-3 to purified human eosinophils and that it bound to the major cytokine binding site of beta(c). Interestingly, epitope analysis using several beta(c) mutants showed that BION-1 interacted with residues different from those used by IL-5, GM-CSF, and IL-3. Furthermore, coimmunoprecipitation experiments showed that BION-1 prevented ligand-induced receptor dimerization and phosphorylation of beta(c), suggesting that ligand contact with beta(c) is a prerequisite for recruitment of beta(c), receptor dimerization, and consequent activation. These results demonstrate the feasibility of simultaneously inhibiting IL-5, GM-CSF, and IL-3 function with a single agent and that BION-1 represents a new tool and lead compound with which to identify and generate further agents for the treatment of eosinophil-dependent diseases such as asthma.

Identification of a 14-3-3 binding sequence in the common beta chain of the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 receptors that is serine-phosphorylated by GM-CSF

The common beta chain (beta(c)) of the granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 receptors is the major signaling subunit of these receptors coupling ligand binding to multiple biological activities. It is thought that these multiple functions arise as a consequence of the recruitment of specific signaling molecules to tyrosine-phosphorylated residues in the cytoplasmic domain of beta(c). However, the contribution of serine phosphorylation in beta(c) to the recruitment of signaling molecules is not known. We show here the identification of a phosphoserine motif in the cytoplasmic domain of beta(c) that interacts with the adaptor protein 14-3-3zeta. Coimmunoprecipitation and pull-down experiments with a glutathione S-transferase (GST):14-3-3zeta fusion protein showed that 14-3-3 directly associates with beta(c) but not the GM-CSF receptor alpha chain. C-terminal truncation mutants of beta(c) further showed that a region between amino acids 544 and 626 in beta(c) was required for its association with 14-3-3zeta. This region contains the sequence (582)HSRSLP(587), which closely resembles the RSXSXP (where S is phosphorylated) consensus 14-3-3 binding site identified in a number of signaling molecules, including Raf-1. Significantly, substitution of (582)HSRSLP(587) for EFAAAA completely abolished interaction of beta(c) with GST-14-3-3zeta. Furthermore, the interaction of beta(c) with GST-14-3-3 was greatly reduced in the presence of a peptide containing the 14-3-3 binding site, but only when (585)Ser was phosphorylated. Direct binding experiments showed that the peptide containing phosphorylated (585)Ser bound 14-3-3zeta with an affinity of 150 nmol/L. To study the regulation of (585)S phosphorylation in vivo, we raised antibodies that specifically recognized (585)Ser-phosphorylated beta(c). Using these antibodies, we showed that GM-CSF stimulation strongly upregulated (585)Ser phosphorylation in M1 myeloid leukemic cells. The proximity of the SHC-binding site ((577)Tyr) to the 14-3-3-binding site ((582)HSRSLP(587)) and their conservation between mouse, rat, and human beta(c) but not in other cytokine receptors suggest that they form a distinct motif that may subserve specialized functions associated with the GM-CSF, IL-3, and IL-5 receptors.

Role of IL-5 in the development of allergen-induced airway hyperresponsiveness

This review evaluates the role of IL-5 and IL-5-mediated eosinophil airway infiltration in the development of allergen-driven airway hyperresponsiveness. It discusses the structure and function of IL-5 and its receptor and the mechanisms of IL-5-triggered eosinophil accumulation and inflammation of the airways. New research data from murine models of airway inflammation and hyperresponsiveness utilizing different modes of sensitization to allergen and anti-IL-5 antibody or IL-5-deficient knock-out mice underscore the outstanding role of this cytokine in the pathogenesis of bronchial asthma. This review identifies possible directions for future treatment of airway hyperresponsiveness and concludes that targeting IL-5-driven inflammatory responses may be most beneficial for a novel therapy in bronchial asthma.

Direct interaction of STAT4 with the IL-12 receptor

Signal transduction by interleukin-12 (IL-12) requires phosphorylation and activation of STAT4. Direct interaction of the SH2 domain of STAT4 with a phosphotyrosine residue in the IL-12 receptor has been proposed to be required for the subsequent STAT4 phosphorylation. The IL-12 receptor beta2 subunit contains three tyrosine residues in its cytoplasmic domain. To test the hypothesis that one of these tyrosines is involved in binding STAT4, phosphopeptides were synthesized according to the amino acid sequences surrounding each of these tyrosine residues. Only the phosphopeptide containing pTyr800 strongly bound to STAT4 in a cell-free binding assay. When this phosphopeptide was introduced into TALL-104 cells, it blocked IL-12-induced STAT4 phosphorylation by competing with the IL-12 receptor for binding to STAT4. A series of alanine replacements was performed in this phosphopeptide to elucidate which amino acids surrounding the pTyr800 residue are critical for STAT4 binding. To summarize, the site on the IL-12 receptor which binds STAT4 can be described as -T-X-X-G-pY(800)-L-, where the core G-pY(800)-L motif is critical for the binding; the threonine at the pY-4 position has only a minor contribution and X represents amino acids not critical for the binding. These results demonstrate that only a small region of the IL-12 receptor is critically involved in binding STAT4 and suggest the feasibility that small molecule inhibitors could be identified which interfere with IL-12 signal transduction for treatment of autoimmune diseases.

Characterization of the cytoplasmic domain of interleukin-13 receptor-alpha

Interleukin (IL)-13 and IL-4 are pleiotropic immunoregulatory cytokines that share many overlapping biological properties reflecting the fact that both can utilize a receptor complex composed of the IL-4 receptor-alpha (IL-4Ralpha) chain and the IL-13Ralpha chain. The cytoplasmic domain of the IL-13Ralpha is 60 amino acids long and is essential for IL-13-dependent growth. It contains a Pro-rich domain in the membrane-proximal region and two Tyr residues. Here we show that a truncated IL-13Ralpha, lacking the 38 carboxyl-terminal residues but retaining the Pro-rich region, can support IL-13-dependent proliferation, although with reduced efficiency. A Y402F mutant of the cytoplasmic domain of IL-13Ralpha supported normal IL-13-induced growth. However, tyrosine phosphorylation of signal transducer and activator of transcription 3 (STAT3), which we show is induced by IL-13 and IL-4 in cells that express the IL-13Ralpha, was significantly reduced. The cytoplasmic domain of IL-13Ralpha was constitutively associated with STAT3, Tyk2, and Janus kinase 1 (JAK1). IL-13-induced tyrosine phosphorylation of IL-13Ralpha in vivo could not be detected using anti-Tyr(P) antibodies. A glutathione S-transferase fusion protein of the cytoplasmic domain of IL-13Ralpha was phosphorylated on tyrosine in vitro by JAK1, JAK3, and Tyk2, although the tyrosine phosphorylation events mediated by Tyk2 and JAK3 were not detectable using anti-phosphotyrosine antibodies. These data, together with the demonstration that IL-13Ralpha associates constitutively with Tyk2 and that Tyr-402 is involved in IL-13-induced phosphorylation of STAT3, suggest that the latter is mediated by Tyk2. Tyrosine phosphorylation of STAT3, which was not necessary for IL-13-induced proliferation, may account for some of the effects of IL-4 and IL-13 on the function of their targets.