Recombinant soluble human interleukin-5 (hIL-5) receptor molecules. Cross-linking and stoichiometry of binding to IL-5

Messing with βc: A unique receptor with many goals

Our understanding of the biological role of the βc family of cytokines has evolved enormously since their initial identification as bone marrow colony stimulating factors in the 1960's. It has become abundantly clear over the intervening decades that this family of cytokines has truly astonishing pleiotropic capacity, capable of regulating not only hematopoiesis but also many other normal and pathological processes such as development, inflammation, allergy and cancer. As noted in the current pandemic, βc cytokines contribute to the cytokine storm seen in acutely ill COVID-19 patients. Ongoing studies to discover how these cytokines activate their receptor are revealing insights into the fundamental mechanisms that give rise to cytokine pleiotropy and are providing tantalizing glimpses of how discrete signaling pathways may be dissected for activation with novel ligands for therapeutic benefit.

Differences in respiratory syncytial virus and influenza infection in a house-dust-mite-induced asthma mouse model: consequences for steroid sensitivity

A significant number of clinical asthma exacerbations are triggered by viral infection. We aimed to characterize the effect of virus infection in an HDM (house dust mite) mouse model of asthma and assess the effect of oral corticosteroids. HDM alone significantly increased eosinophils, lymphocytes, neutrophils, macrophages and a number of cytokines in BAL (bronchoalveolar lavage), all of which were sensitive to treatment with prednisolone (with the exception of neutrophils). Virus infection also induced cell infiltration and cytokines. RSV (respiratory syncytial virus) infection in HDM-treated animals further increased all cell types in BAL (except eosinophils, which declined), but induced no further increase in HDM-elicited cytokines. However, while HDM-elicited TNF-α (tumour necrosis factor-α), IFN-γ (interferon-γ), IL (interleukin)-2, IL-5 and IL-10 were sensitive to prednisolone treatment, concomitant infection with RSV blocked the sensitivity towards steroid. In contrast, influenza infection in HDM- challenged animals resulted in increased BAL lymphocytes, neutrophils, IFN-γ, IL-1β, IL-4, IL-5, IL-10 and IL-12, but all were attenuated by prednisolone treatment. HDM also increased eNO (exhaled NO), which was further increased by concomitant virus infection. This increase was only partially attenuated by prednisolone. RSV infection alone increased BAL mucin. However, BAL mucin was increased in HDM animals with virus infection. Chronic HDM challenge in mice elicits a broad inflammatory response that shares many characteristics with clinical asthma. Concomitant influenza or RSV infection elicits differing inflammatory profiles that differ in their sensitivity towards steroids. This model may be suitable for the assessment of novel pharmacological interventions for asthmatic exacerbation.

Structure analysis of the IL-5 ligand-receptor complex reveals a wrench-like architecture for IL-5Rα

Interleukin-5 (IL-5) is the key mediator for the function of eosinophil granulocytes, whose deregulation is characteristic of hypereosinophilic diseases and presumably contributes to allergic asthma. IL-5 signaling involves two transmembrane receptors, IL-5Rα and the common β chain, which upon formation of the ternary complex activate the JAK/STAT signaling cascade. To investigate the mechanism underlying ligand-receptor recognition, we determined the structure of IL-5 bound to the extracellular domain of IL-5Rα. IL-5 makes contact with all three fibronectin III-like domains of IL-5Rα, with the receptor architecture resembling a wrench. Mutagenesis data provide evidence that this wrench-like architecture is likely preformed. The structure demonstrates that for steric reasons, homodimeric IL-5 can bind only one receptor molecule, even though two equivalent receptor-binding sites exist. In regard to strong efforts being made to develop IL-5 antagonists for treating asthma and hypereosinophilic diseases, the advances in molecular understanding provided by this structure are of greatest value.

Defective eosinophil hematopoiesis ex vivo in inbred Rocky Mountain White (IRW) mice

We examine the proliferation and differentiation of bone marrow (BM) progenitors from inbred Rocky Mountain White (IRW) mice, a strain used primarily for retrovirus infection studies. In contrast to findings with BALB/c and C57BL/6 strains, IRW BM cells cannot proliferate or generate pure eosinophil cultures ex vivo in response to a defined cytokine regimen. Analysis of IRW BM at baseline was unremarkable, including 0.08 ± 0.03% Lin(-)Sca-1(+)c-kit(+) (LSK) hematopoietic stem cells and 5.2 ± 0.3% eosinophils; the percentage of eosinophil progenitors (EoPs; Lin(-)Sca-1(-)c-kit(+)CD34(+)IL-5Rα(+)) was similar in all three mouse strains. Transcripts encoding GM-CSFRα and the IL-3/IL-5/GM-CSF common β chain were detected at equivalent levels in IRW and BALB/c BM, whereas expression of transcripts encoding IL-5Rα, IL-3Rα, and GATA-2 was diminished in IRW BM compared with BALB/c. Expression of membrane-bound IL-5Rα and intracellular STAT5 proteins was also diminished in IRW BM cells. Diminished expression of transcripts encoding IL-5Rα and GATA-2 and immunoreactive STAT5 in IRW BM persisted after 4 days in culture, along with diminished expression of GATA-1. Western blot revealed that cells from IRW BM overexpress nonsignaling soluble IL-5Rα protein. Interestingly, OVA sensitization and challenge resulted in BM and airway eosinophilia in IRW mice; however, the responses were significantly blunted. These results suggest that IRW mice have diminished capacity to generate eosinophils in culture and in vivo, likely as a result of diminished signaling via IL-5Rα.

Biological implications of glycosaminoglycan interactions with haemopoietic cytokines

Heparan sulphate (HS) glycosaminoglycans (GAGs) are an integral part of the signalling complex of fibroblast derived growth factor (FGF) family members, HS being regarded as a coreceptor. FGFs are also retained in the tissues by binding to HS structures. Early studies on the contribution of the bone marrow stroma to haemopoiesis suggested that cytokines with a role in haemopoiesis were similarly retained in the stroma through interactions with HS. However, the functional outcomes of these cytokines binding HS were poorly understood. Here the GAG-binding properties of cytokines of the four alpha-helical bundle family and the biological consequences of such binding are reviewed. From this analysis it is apparent that although many of these cytokines do bind GAGs, GAG binding is not a consistent feature, nor is the site of GAG binding conserved among these cytokines. The biological outcome of GAG binding depends, in part, on the location of the GAG-binding site on the cytokine. In some cases GAG binding appears to block signalling, whereas in others signalling is likely to be facilitated by binding. It is postulated that the interactions of these cytokines with their receptor complexes evolved independently of GAG binding, with GAG binding being an additional feature for a subset of this cytokine family. Nevertheless, because GAG binding localizes cytokines to sites within tissues, these interactions are likely to be critically important for the biology of these cytokines.

Interleukin-5 receptor subunit oligomerization and rearrangement revealed by fluorescence resonance energy transfer imaging

Interleukin (IL)-5 exerts hematopoietic functions through binding to the IL-5 receptor subunits, alpha and betac. Specific assembly steps of full-length subunits as they occur in cell membranes, ultimately leading to receptor activation, are not well understood. We tracked the oligomerization of IL-5 receptor subunits using fluorescence resonance energy transfer (FRET) imaging. Full-length IL-5Ralpha and betac were expressed in Phoenix cells as chimeric proteins fused to enhanced cyan or yellow fluorescent protein (CFP or YFP, respectively). A time- and dose-dependent increase in FRET signal between IL-5Ralpha-CFP and betac-YFP was observed in response to IL-5, indicative of heteromeric receptor alpha-betac subunit interaction. This response was inhibited by AF17121, a peptide antagonist of IL-5Ralpha. Substantial FRET signals with betac-CFP and betac-YFP co-expressed in the absence of IL-5Ralpha demonstrated that betac subunits exist as preformed homo-oligomers. IL-5 had no effect on this betac-alone FRET signal. Interestingly, the addition of IL-5 to cells co-expressing betac-CFP, betac-YFP, and nontagged IL-5Ralpha led to further increase in FRET efficiency. Observation of preformed betac oligomers fits with the view that this form can lead to rapid cellular responses upon IL-5 stimulation. The IL-5-induced effects on betac assembly in the presence of nontagged IL-5Ralpha provide direct evidence that IL-5 can cause higher order rearrangements of betac homo-oligomers. These results suggest that IL-5 and perhaps other betac cytokines (IL-3 and granulocyte/macrophage colony-stimulating factor) trigger cellular responses by the sequential binding of cytokine ligand to the specificity receptor (subunit alpha), followed by binding of the ligand-subunit alpha complex to, and consequent rearrangement of, a ground state form of betac oligomers.

Interleukin-5 does not influence differential transcription of transmembrane and soluble isoforms of IL-5R alpha in vivo

Interleukin-5 (IL-5) promotes signal transduction and expansion of eosinophil colonies in bone marrow via interactions with its heterodimeric receptor (IL-5R). Two variants encoding soluble forms of the alpha subunit (sIL-5R alpha) have been described, although the signals promoting and/or limiting differential transcription remain to be clarified.

OBJECTIVES

Our intent was to explore the role of IL-5 in regulating differential transcription of these splice variants in vivo.

METHODS

We have designed a quantitative reverse transcriptase-polymerase chain reaction assay to detect transcripts encoding the transmembrane, soluble 1 and 2 forms of IL-5R alpha in two strains of wild-type (BALB/c and C57BL/6) and corresponding IL-5 gene-deleted mice. Wild-type mice respond to S. mansoni infection with a gradual increase in serum IL-5 and eosinophilia, which is not observed in IL-5 gene-deleted mice.

RESULTS AND CONCLUSIONS

We find that IL-5 is not necessary for differential splicing to occur in vivo, as all three forms of the IL-5R alpha are detected in both strains of IL-5 gene-deleted mice, with ratios of transcript expression (transmembrane : soluble 1 : soluble 2) that were indistinguishable from their wild-type counterparts. Differential splicing does vary markedly between strains, potentially because of local effects of strain-specific polymorphisms.

Cyclic peptide interleukin 5 antagonists mimic CD turn recognition epitope for receptor ?

The cyclic peptide AF17121 (Ac-VDECWRIIASHTWFCAEE) that inhibits interleukin 5 (IL-5) function and IL-5 receptor alpha-chain (IL-5Ralpha) binding has been derived from recombinant random peptide library screening and follow-up synthetic variation. To better understand the structural basis of its antagonist activity, AF17121 and a series of analogs of the parent peptide were prepared by solid phase peptide synthesis. Sequence variation was focused on the charged residues Asp(2), Glu(3), Arg(6), Glu(17), and Glu(18). Two of those residues, Glu(3) and Arg(6), form an EXXR motif that was found to be common among library-derived IL-5 antagonists. The E and R in the EXXR motif have a proximity similar to charged residues in a previously identified receptor alpha binding region, the beta-strand between the C- and D-helices of human IL-5. Optical biosensor interaction kinetics and cell proliferation assays were used to evaluate the antagonist activities of the purified synthetic peptides, by measuring competition with the highly active single chain IL-5. Analogs in which acidic residues (Asp(2), Glu(3), Glu(17), and Glu(18)) were replaced individually by Ala retained substantial competition activity, with multiple replacements in these residues leading to fractional loss of potency at most. In contrast, R6A analogs had strongly reduced competition activity. The results reveal that the arginine residue is crucial for the IL-5Ralpha binding of AF17121, while the acidic residues are not essential though likely complex-stabilizing particularly in the Asp(2)-Glu(3) region. By CD, AF17121 exhibited mostly disordered structure with evidence for a small beta-sheet content, and replacement of the arginine had no influence on the observed secondary structure of the peptides. The dominance of Arg(6) in AF17121 activity corresponds to previous findings of dominance of the positive charge balance in the antiparallel beta-sheet of IL-5 composed of (88)EERRR(92) in one strand of the CD turn region of IL-5 and with Arg(32) in the neighboring beta-strand. These results argue that AF17121 and related library-derived peptides function by mimicking the CD turn receptor alpha recognition epitope in IL-5 and open the way to small molecule antagonist design.

Kinetic interaction analysis of human interleukin 5 receptor alpha mutants reveals a unique binding topology and charge distribution for cytokine recognition

Human interleukin 5 receptor alpha (IL5Ralpha) comprises three fibronectin type III domains (D1, D2, and D3) in the extracellular region. Previous results have indicated that residues in the D1D2 domains are crucial for high affinity interaction with human interleukin 5 (IL5). Yet, it is the D2D3 domains that have sequence homology with the classic cytokine recognition motif that is generally assumed to be the minimum cytokine-recognizing unit. In the present study, we used kinetic interaction analysis of alanine-scanning mutational variants of IL5Ralpha to define the residues involved in IL5 recognition. Soluble forms of IL5Ralpha variants were expressed in S2 cells, selectively captured via their C-terminal V5 tag by anti-V5 tag antibody immobilized onto the sensor chip and examined for IL5 interaction by using a sandwich surface plasmon resonance biosensor method. Marked effects on the interaction kinetics were observed not only in D1 (Asp(55), Asp(56), and Glu(58)) and D2 (Lys(186) and Arg(188)) domains, but also in the D3 (Arg(297)) domain. Modeling of the tertiary structure of IL5Ralpha indicated that these binding residues fell into two clusters. The first cluster consists of D1 domain residues that form a negatively charged patch, whereas the second cluster consists of residues that form a positively charged patch at the interface of D2 and D3 domains. These results suggest that the IL5 x IL5Ralpha system adopts a unique binding topology, in which the cytokine is recognized by a D2D3 tandem domain combined with a D1 domain, to form an extended cytokine recognition interface.

Decreased expression of membrane IL-5 receptor alpha on human eosinophils: I. Loss of membrane IL-5 receptor alpha on airway eosinophils and increased soluble IL-5 receptor alpha in the airway after allergen challenge

IL-5 is a key cytokine for eosinophil maturation, recruitment, activation, and possibly the development of inflammation in asthma. High concentrations of IL-5 are present in the airway after Ag challenge, but the responsiveness of airway eosinophils to IL-5 is not well characterized. The objectives of this study were to establish, following airway Ag challenge: 1) the expression of membrane (m)IL-5Ralpha on bronchoalveolar lavage (BAL) eosinophils; 2) the responsiveness of these cells to exogenous IL-5; and 3) the presence of soluble (s)IL-5Ralpha in BAL fluid. To accomplish these goals, blood and BAL eosinophils were obtained from atopic subjects 48 h after segmental bronchoprovocation with Ag. There was a striking reduction in mIL-5Ralpha on airway eosinophils compared with circulating cells. Furthermore, sIL-5Ralpha concentrations were elevated in BAL fluid, but steady state levels of sIL-5Ralpha mRNA were not increased in BAL compared with blood eosinophils. Finally, BAL eosinophils were refractory to IL-5 for ex vivo degranulation, suggesting that the reduction in mIL-5Ralpha on BAL eosinophils may regulate IL-5-mediated eosinophil functions. Together, the loss of mIL-5Ralpha, the presence of sIL-5Ralpha, and the blunted functional response (degranulation) of eosinophils to IL-5 suggest that when eosinophils are recruited to the airway, regulation of their functions becomes IL-5 independent. These observations provide a potential explanation for the inability of anti-IL-5 therapy to suppress airway hyperresponsiveness to inhaled Ag, despite a reduction in eosinophil recruitment.

Decreased expression of membrane IL-5 receptor alpha on human eosinophils: II. IL-5 down-modulates its receptor via a proteinase-mediated process

In the accompanying study, we demonstrated that following Ag challenge, membrane (m)IL-5Ralpha expression is attenuated on bronchoalveolar lavage eosinophils, soluble (s)IL-5Ralpha is detectable in BAL fluid in the absence of increased steady state levels of sIL-5Ralpha mRNA, and BAL eosinophils become refractory to IL-5 for ex vivo degranulation. We hypothesized that IL-5 regulates its receptor through proteolytic release of mIL-5Ralpha, which in turn contributes to the presence of sIL-5Ralpha. Purified human peripheral blood eosinophils were incubated with IL-5 under various conditions and in the presence of different pharmacological agents. A dose-dependent decrease in mIL-5Ralpha was accompanied by an increase in sIL-5Ralpha in the supernatant. IL-5 had no ligand-specific effect on mIL-5Ralpha or sIL-5Ralpha mRNA levels. The matrix metalloproteinase-specific inhibitors BB-94 and GM6001 and tissue inhibitor of metalloproteinase-3 partially inhibited IL-5-mediated loss of mIL-5Ralpha, suggesting that sIL-5Ralpha may be produced by proteolytic cleavage of mIL-5Ralpha. IL-5 transiently reduced surface expression of beta-chain, but had no effect on the expression of GM-CSFRalpha. Pretreatment of eosinophils with a dose of IL-5 that down-modulated mIL-5Ralpha rendered these cells unable to degranulate in response to further IL-5 stimulation, but they were fully responsive to GM-CSF. These findings suggest that IL-5-activated eosinophils may lose mIL-5Ralpha and release sIL-5Ralpha in vivo, which may limit IL-5-dependent inflammatory events in diseases such as asthma.

Biosensor analysis of dynamics of interleukin 5 receptor subunit beta(c) interaction with IL5:IL5R(alpha) complexes

To gain insight into IL5 receptor subunit recruitment mechanism, and in particular the experimentally elusive pathway for assembly of signaling subunit beta(c), we constructed a soluble beta(c) ectodomain (s(beta)(c)) and developed an optical biosensor assay to measure its binding kinetics. Functionally active s(beta)(c) was anchored via a C-terminal His tag to immobilized anti-His monoclonal antibodies on the sensor surface. Using this surface, we quantitated for the first time direct binding of s(beta)(c) to IL5R(alpha) complexed to either wild-type or single-chain IL5. Binding was much weaker if at all with either R(alpha) or IL5 alone. Kinetic evaluation revealed a moderate affinity (0.2-1 microM) and relatively fast off rate for the s(beta)(c) interaction with IL5:R(alpha) complexes. The data support a model in which beta(c) recruitment occurs with preformed IL5:R(alpha) complex. Dissociation kinetics analysis suggests that the IL5-alpha-beta(c) complex is relatively short-lived. Overall, this study solidifies a model of sequential recruitment of receptor subunits by IL5, provides a novel biosensor binding assay of beta(c) recruitment dynamics, and sets the stage for more advanced characterization of the roles of structural elements within R(alpha), beta(c), and cytokines of the IL5/IL3/GM-CSF family in receptor recruitment and activation.

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

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

Down-regulated IL-5 receptor expression on peripheral blood eosinophils from budesonide-treated children with asthma

BACKGROUND

The expression and function of cytokine receptors on peripheral blood eosinophils (PBE) from healthy and asthmatic children are poorly characterized.

METHODS

The PBE count and expression of IL-5 receptor (R) and GM-CSFR positive PBE was analyzed in nonsteroid-treated asthmatic children (n = 13), budesonide-treated asthmatic children (n = 24) and healthy children (n = 16) by flow cytometry. Alterations in intracellular EG2-epitope expression were used to measure the in vitro responsiveness of PBE to recombinant IL-5 and GM-CSF.

RESULTS

The PBE count was increased (P < 0.05) in both asthmatic groups, independent of treatment, as compared to healthy children. The IL-5R expression on PBE, as well as the in vitro responsiveness of PBE to recombinant IL-5, was reduced (P < 0.05), in budesonide-treated asthmatic children compared to nonsteroid-treated asthmatic children and healthy children. The proportion of GM-CSFR positive PBE and in vitro responsiveness of PBE to recombinant GM-CSF were not different between the groups. In vitro treatment with budesonide did not down-regulate the proportion of IL-5R positive PBE.

CONCLUSIONS

Budesonide-treatment of asthmatic children induces a selectively reduced IL-5R expression on PBE, concomitant with a reduced in vitro responsiveness of PBE to IL-5. We suggest that this budesonide-related down-regulation of the IL-5R might be a mechanism by which steroid treatment inhibits the action of IL-5 on eosinophil accumulation and activation in vivo.

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.

Antisense inhibition of membrane-bound human interleukin-5 receptor-alpha chain does not affect soluble receptor expression and induces apoptosis in TF-1 cells

Binding of human interleukin-5 (HuIL-5) to its membrane-anchored receptor (IL-5R) triggers multiple signaling pathways, cellular proliferation, and maturational responses, as well as protection from apoptosis. In contrast, soluble forms of the HuIL-5R have been shown to inhibit IL-5 signaling and, therefore, may represent naturally occurring negative regulators of IL-5 function. Because of the central role of IL-5 in promoting eosinophilia and airway hyperresponsiveness in animal models of asthma, antisense oligonucleotides specific either for the membrane form alone or for sequences shared between both the membrane and soluble forms of the HuIL-5Ralpha ligand binding chain were designed. The activities of these oligonucleotides were characterized in IL-5R-expressing erythroleukemic TF-1 cells. Herein we report that an antisense oligonucleotide targeted to a sequence unique to the alternatively spliced membrane-bound form of the HuIL-5Ralpha chain has been developed that selectively inhibits membrane, but not soluble, mRNA isoform expression. Both this membrane-specific oligonucleotide and an antisense oligonucleotide targeted to sequence common to both membrane and soluble isoforms were found to potently suppress cell surface IL-5Ralpha levels and IL-5-mediated cell survival by inducing apoptosis similar to IL-5 withdrawal. Thus, these oligonucleotides represent unique genetic agents with therapeutic potential for diseases with an eosinophilic component.

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.

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.

Isolation of recombinant BMP receptor IA ectodomain and its 2:1 complex with BMP-2

Bone morphogenetic protein-2 (BMP-2) is a member of the transforming growth factor beta superfamily which induces bone formation and regeneration, and important steps during early embryonic development. BMP-2 signals via oligomerization of type I and type II serine/threonine kinase receptors. We report here expression of the extracellular domain of the human type IA receptor for BMP-2 (BMPR-IA) in Escherichia coli. This soluble form of BMPR-IA (sBMPR-IA) was purified employing a BMP-2 affinity column. Gel filtration experiments and analysis of gel filtration fractions by polyacrylamide electrophoresis and densitometry reveal that BMP-2 forms a defined 1:2 complex with sBMPR-IA that can be purified and hopefully used for crystallization studies.

Biology of IL-5 in health and disease

LEARNING OBJECTIVES

Reading this article will increase the readers' knowledge of the biology of interleukin-5 (IL-5), an important cytokine. The immune and inflammatory responses of any organism are the basis of the defense mechanism ensuring its survival. The role of IL-5 in these processes, as well as in the pathogenesis of various diseases has been discussed along with the effects of various pharmacologic agents on the production and function of IL-5.

DATA SOURCES

A detailed literature search was performed. Studies considered relevant and important, in all languages, which involved humans and animals were used.

STUDY SELECTION

Information was obtained only from peer reviewed journals.

RESULTS

Interleukin-5 is normally produced by T-cells, mast cells, and eosinophils while Reed Sternberg and Epstein Barr virus (EBV) transformed cells also produce IL-5. Monoclonal antibodies (mAb) to IL-5 are potent inhibitors of IL-5 mediated tissue damage, secondary to eosinophil infiltration. The majority of the studies on IL-5 are preliminary, often the information is obtained from animal studies or in vitro systems and occasionally from pathologic tissue analysis. This along with the absence of confirmatory studies is a limiting factor. Nonetheless, the role of IL-5 in allergic and immunologic disease and asthma may be central to their pathogenesis.

CONCLUSIONS

Interleukin-5 is an important molecule that is participant to many processes that maintain health and are involved directly or indirectly in the pathogenesis of disease. Some pharmacologic agents can modify IL-5 production in vivo. Development of selective inhibitors of IL-5 may have a potential use for specific therapy of certain autoimmune, inflammatory, and neoplastic diseases.

The cell surface expression level of the human interleukin-5 receptor alpha subunit determines the agonistic/antagonistic balance of the human interleukin-5 E13Q mutein

The human interleukin-5 (IL-5) receptor consists of an alpha-chain that specifically binds the ligand with intermediate affinity, and a beta c-chain, that associates with the IL-5/IL-5R alpha complex, leading to a high-affinity, signal transducing receptor complex. Structure-function studies showed that modification of the putative beta c-chain binding site in IL-5 (E13Q mutein) converted the molecule into an antagonist. However, analysis of the effect of this mutant IL-5 on COS-1 cells transfected with both receptor subunits, did not show reduced interaction with the beta c subunit [Tavernier, J., Tuypens, T., Verhee, A., Plaetinck, G., Devos, R., Van der Heyden, J., Guisez, Y. & Oefner, C. (1995) Proc. Natl Acad. Sci. USA 89, 7041-7045]. To gain more insight into the mechanism of IL-5 antagonism by E13Q, we tested its biological activity on two FDC-P1 subclones that express clearly different numbers of alpha-subunits yet an almost constant number of murine beta c-subunits. Here we show that E13Q has a biological activity comparable to wild-type IL-5 only when a high number of alpha-chains is present on the cells. Confirming the critical role of the IL5R alpha cell-surface expression level, treatment with suboptimal doses of a neutralising anti-IL-5R alpha antibody results in reduced activity of the mutant but not of wild-type IL-5.

Hydrolysis and amino acid composition of proteins

Amino acid composition analysis is a classical protein analysis method, which finds a wide application in medical and food science research and is indispensable for protein quantification. It is a complex technique, comprising two steps, hydrolysis of the substrate and chromatographic separation and detection of the residues. A properly performed hydrolysis is a prerequisite of a successful analysis. The most significant developments of the technology in the last decade consist in the (i) reduction of the hydrolysis time by the use of microwave radiation energy; (ii) improvement in the sensitivity of the residue detection, the quantification of the sensitive residues and separation of the enantiomeric forms of the amino acids; (iii) application of amino acid analysis in the large-scale protein identification by database search; and (iv) gradual replacement of the original ion exchange residue separation by reversed-phase high-performance liquid chromatography. Amino acid analysis is currently facing an enormous competition in the determination of the identity of proteins and amino acid homologs by the essentially faster mass spectrometry techniques. The amino acid analysis technology needs further simplification and automation of the hydrolysis, chromatography and detection steps to withstand the pressure exerted by the other technologies.

IL-5 and IL-5 receptor in asthma

Eosinophils, along with mast cells are key cells involved in the innate immune response against parasitic infection whereas the adaptive immune response is largely dependent on lymphocytes. In chronic parasitic disease and in chronic allergic disease, IL-5 is predominantly a T cell derived cytokine which is particularly important for the terminal differentiation, activation and survival of committed eosinophil precursors. The human IL-5 gene is located on chromosome 5 in a gene cluster that contains the evolutionary related IL-4 family of cytokine genes. The human IL-5 receptor complex is a heterodimer consisting of a unique alpha subunit (predominantly expressed on eosinophils) and a beta subunit which is shared between the receptors for IL-3 & GM-CSF (more widely expressed). The alpha subunit is required for ligand-specific binding whereas association with the beta subunit results in increased binding affinity. The alternative splicing of the alpha IL-5R gene which contains 14 exons can yield several alpha-IL-5R isoforms including a membrane-anchored isoform (alpha IL-5Rm) and a soluble isoform (alpha IL-5Rs). Cytokines such as IL-5 produce specific and non-specific cellular responses through specific cell membrane receptor mediated activation of intracellular signal transduction pathways which, to a large part, regulate gene expression. The major intracellular signal transduction mechanism is activation of non-receptor associated tyrosine kinases including JAK and MAP kinases which can then transduce signals via a novel family of transcriptional factors named signal transducers and activators of transcription (STATS). JAK2, STAT1, and STAT5 appear to be particularly important in IL-5 mediated eosinophil responses. Asthma is characterized by episodic airways obstruction, increased bronchial responsiveness, and airway inflammation. Several studies have shown an association between the number of activated T cells and eosinophils in the airways and abnormalities in FEV1, airway reactivity and clinical severity in asthma. It has now been well documented that IL-5 is highly expressed in the bronchial mucosa of atopic and intrinsic asthmatics and that the increased IL-5 mRNA present in airway tissues is predominantly T cell derived. Immunocytochemical staining of bronchial biopsy sections has confirmed that IL-5 mRNA transcripts are translated into protein in asthmatic subjects. Furthermore, the number of activated CD4 + T cells and IL-5 mRNA positive cells are increased in asthmatic airways following antigen challenge and studies that have examined IL-5 expression in asthmatic subjects before and after steroids have shown significantly decreased expression following oral corticosteroid treatment in steroid-sensitive asthma but not in steroid resistant and chronic severe steroid dependent asthma. The link between T cell derived IL-5 and eosinophil activation in asthmatic airways is further strengthened by the demonstration that there is an increased number of alpha IL-5R mRNA positive cells in the bronchial biopsies of atopic and non-atopic asthmatic subjects and that the eosinophil is the predominant site of this increased alpha IL-5R mRNA expression. We have also shown that the subset of activated eosinophils that expressed mRNA for membrane bound alpha IL-5r inversely correlated with FEV1, whereas the subset of activated eosinophils that expressed mRNA for soluble alpha IL-5r directly correlated with FEV1. Hence, not only does this data suggest that the presence of eosinophils expressing alpha IL-5R mRNA contribute towards the pathogenesis of bronchial asthma, but also that the eosinophil phenotype with respect to alpha IL-5R isoform expression is of central importance. Finally, there are several animal, and more recently in vitro lung explant, models of allergen induced eosinophilia, late airway responses (LARS), and bronchial hyperresponsiveness (BHR)--all of which support a link between IL-5 and airway eosinophilia and bronc

Selective Inhibition of IL-5 Receptor α-Chain Gene Transcription by IL-5, IL-3, and Granulocyte-Macrophage Colony-Stimulating Factor in Human Blood Eosinophils

High affinity receptor for IL-5 (IL-5R), a predominant eosinophil maturation factor, is composed of an IL-5-binding α-chain (IL-5Rα) and a signal-transducing β-chain that is shared by IL-3 and granulocyte-macrophage CSF (GM-CSF) receptors (IL-3R and GM-CSFR). By Northern blot analysis of mRNAs obtained from normal human blood eosinophils, we show in this report that the hematopoietic cytokines IL-5, IL-3, and GM-CSF down-regulate IL-5Rα mRNA while up-regulating α-chain mRNAs for both IL-3R and GM-CSFR as well as the β-chain mRNA. More detailed characterization reveals that the down-regulation of IL-5Rα mRNA is specific to IL-3, IL-5, and GM-CSF; occurs very rapidly (reaching maximum inhibition within 2 h); is cytokine dose dependent; and does not require protein synthesis. Nuclear run-on and mRNA stability experiments demonstrate that cytokine-induced inhibition of IL-5Rα mRNA accumulation occurs at the level of IL-5Rα gene transcription, whereas enhanced accumulation of mRNAs for IL-3Rα and the β-chain results from reduced mRNA degradation. We suggest from these experiments that in human blood eosinophils, IL-5Rα gene transcription and IL-5Rα mRNA metabolism can be regulated by mechanisms that are distinct from those used for IL-3Rα and GM-CSFRα.

JAK2 and JAK1 Constitutively Associate With an Interleukin-5 (IL-5) Receptor α and βc Subunit, Respectively, and Are Activated Upon IL-5 Stimulation

The human interleukin-5 receptor (hIL-5R) consists of a unique α subunit (hIL-5Rα) and a common β subunit (βc) that activate two Janus kinases (JAK1 and JAK2) and a signal transducer and activator of transcription (STAT5). The precise stoichiometry of the hIL-5R subunits and the role of JAK kinases used in IL-5 signaling were investigated. We analyzed the interaction between hIL-5Rα and βc by immunoprecipitation using anti–hIL-5Rα and anti-βc monoclonal antibodies. The binding of JAK1 and JAK2 to each hIL-5R subunit was also evaluated in the hIL-5–responsive cell line, TF-h5Rα. It was observed that IL-5 stimulation induced the recruitment of βc to hIL-5Rα, although in the absence of IL-5 the subunits remain independent. In the absence of IL-5, JAK2 and JAK1 were associated with hIL-5Rα and βc, respectively. IL-5 stimulation resulted in tyrosine phosphorylation of JAK2, JAK1, βc, and STAT5. Moreover, IL-5–induced dimerization of IL-5R subunits caused JAK2 activation and βc phosphorylation even in the absence of JAK1 activation. Furthermore, tyrosine phosphorylation of JAK1 was dependent on the activation of JAK2. Detailed study of the C-terminal truncated cytoplasmic domain of hIL-5Rα revealed that the cytoplasmic stretch at position 346-387, containing the proline-rich region, is necessary for JAK2 binding. These observations suggest that activation of hIL-5Rα–associated JAK2 is indispensable for the IL-5 signaling event.

JAK2 and JAK1 Constitutively Associate With an Interleukin-5 (IL-5) Receptor α and βc Subunit, Respectively, and Are Activated Upon IL-5 Stimulation

The human interleukin-5 receptor (hIL-5R) consists of a unique α subunit (hIL-5Rα) and a common β subunit (βc) that activate two Janus kinases (JAK1 and JAK2) and a signal transducer and activator of transcription (STAT5). The precise stoichiometry of the hIL-5R subunits and the role of JAK kinases used in IL-5 signaling were investigated. We analyzed the interaction between hIL-5Rα and βc by immunoprecipitation using anti–hIL-5Rα and anti-βc monoclonal antibodies. The binding of JAK1 and JAK2 to each hIL-5R subunit was also evaluated in the hIL-5–responsive cell line, TF-h5Rα. It was observed that IL-5 stimulation induced the recruitment of βc to hIL-5Rα, although in the absence of IL-5 the subunits remain independent. In the absence of IL-5, JAK2 and JAK1 were associated with hIL-5Rα and βc, respectively. IL-5 stimulation resulted in tyrosine phosphorylation of JAK2, JAK1, βc, and STAT5. Moreover, IL-5–induced dimerization of IL-5R subunits caused JAK2 activation and βc phosphorylation even in the absence of JAK1 activation. Furthermore, tyrosine phosphorylation of JAK1 was dependent on the activation of JAK2. Detailed study of the C-terminal truncated cytoplasmic domain of hIL-5Rα revealed that the cytoplasmic stretch at position 346-387, containing the proline-rich region, is necessary for JAK2 binding. These observations suggest that activation of hIL-5Rα–associated JAK2 is indispensable for the IL-5 signaling event.

Biological and molecular characteristics of interleukin-5 and its receptor

Interleukin-5 (IL5) is a T cell-derived cytokine involved in the pathogenesis of atopic diseases. It specifically controls the production, the activation and the localization of Eosinophils. The Eosinophils are the major cause of tissue damage resulting in the symptoms of asthma and related allergic disorders. T cells purified from bronchoalveolar lavage and peripheral blood of asthmatics secrete elevated amount of IL5. Therefore IL5 emerges to be an attractive target for the generation of new anti-allergic drugs. Agents which inhibit either the production or the activity of IL5 could be expected to ameliorate the pathological effects of the allergic response. A better understanding of the biology of IL5 and the regulation of its expression is, however, a prerequisite for the development of new therapeutic agents. This review covers the major biological, molecular and structural aspects of IL5 research since the identification of this cytokine ten years ago.

Analysis of three human interleukin 5 structures suggests a possible receptor binding mechanism

We compared three crystal structures of human interleukin 5 (hIL5) expressed in either E. coli (hIL5E.coli), Sf9 cells (hIL5sf9) or Drosophila cells (hIL5Drosophila). The dimeric hIL5 structures show subtle but significant conformational differences which are probably a consequence of the different crystallization conditions trapping this protein into one of two states. We refer to these two distinct conformations as the 'open' and 'tight' state, according to the packing around the cleft between the two subunits. We hypothesize that these two stable conformational states reflect the structure of the free or receptor bound hIL5.

Spatial orientation of the alpha and betac receptor chain binding sites on monomeric human interleukin-5 constructs

Interleukin-5 (IL-5), a disulfide-linked homodimer, can be induced to fold as a biological active monomer by extending the loop between its third and fourth helices (Dickason, R. R., and Huston, D. P. (1996) Nature 379, 652-655). We have designed eight monomeric IL-5 proteins to optimize biological activity and stability of the monomer. This was achieved by (i) inserting the joining loop at three different positions, (ii) by introducing an additional intramolecular disulfide bridge onto these backbones, and (iii) by creating circular permutations to fix the position of the carboxyl-terminal helix relative to the three other helices. The proteins dimerize with Kd values ranging from 20 to 200 microM and are therefore monomeric at the picomolar concentrations where they are biologically active. Introduction of a second disulfide confers increased stability, but this increased rigidity results in lower activity of the protein. Contrary to wild type IL-5, mutation of the betac contact residue on the first helix, Glu12, to Lys, into the circularly permutated constructs, did not abolish TF-1 proliferative and eosinophil activation activities. These results indicate that activation of the IL-5 receptor complex is not mediated solely by Glu12 on the first helix, and alternative mechanisms are discussed.

Ligand-independent dimerization of the extracellular domain of the leptin receptor and determination of the stoichiometry of leptin binding

The leptin receptor is a class I transmembrane protein with either a short or a long cytoplasmic domain. Using chemical cross-linking we have analyzed the binding of leptin to its receptor. Cross-linking of radiolabeled leptin to different isoforms of the leptin receptor expressed on COS-1 cells reveals leptin receptor monomer, homodimer, and oligomer complexes. Cotransfection of the long and short form of the leptin receptor did not provide any evidence for the formation of heterodimer complexes. Soluble forms consisting of either the entire extracellular domain or the two cytokine receptor homologous domains of the leptin receptor were purified to homogeneity from recombinant baculovirus-infected insect cells by leptin affinity chromatography. Gel filtration chromatography showed that these proteins exist in a dimeric form. Analysis of the complex formed between soluble leptin receptor and leptin by native polyacrylamide gel electrophoresis, and data obtained from the amino acid composition of the complex provide direct evidence that the extracellular domain of the leptin receptor binds leptin in a 1:1 ratio.

The cytokine interleukin-5 (IL-5) effects cotransport of its receptor subunits to the nucleus in vitro

Interleukin (IL)-5 is central in regulating eosinophilia in allergic disease and parasitic infections. We have recently shown that human (h) IL-5 both possesses a functional nuclear localization signal capable of targeting a heterologous protein to the nucleus and localises to the nucleus of intact receptor-expressing cells. In this study, the extracellular domains of the hIL-5 alpha- and beta-receptor subunits were expressed in baculovirus, fluorescently labelled and assayed for nuclear targeting in vitro in the absence and presence of IL-5. The beta-subunit, which lacks IL-5 binding activity, only accumulated in the nucleus in the presence of both the hIL-5 binding alpha-subunit and hIL-5. The IL-5-binding alpha-subunit showed similar results. IL-5 thus effected nuclear transport of its alpha- and beta-receptor subunits apparently through a 'piggy back' mechanism, raising the possibility that IL-5's nuclear signalling role may be to cotarget its receptor subunits to the nucleus. This is the first demonstration of nuclear protein piggy back transport in vitro.

Monomeric isomers of human interleukin 5 show that 1:1 receptor recruitment is sufficient for function

The normally dimeric human interleukin 5 (IL-5) was re-engineered into two monomeric isomer forms to investigate mechanistic features of receptor recognition. One form, denoted GM1-IL-5, is a CD-loop expanded form, in which an 8-residue linker designed for flexibility was inserted between residues 85 and 86. The second, denoted DABC-IL-5, is a circularly permuted form of human IL-5 in which a chain discontinuity was introduced in the CD loop and the two consequent chain fragments were joined at the normal N and C termini by a di-glycyl linker. Both IL-5 isomers folded into stable monomers in solution as shown by sedimentation equilibrium and CD and formed an intrachain disulfide bond predicted from the structure of wild type IL-5. From titration microcalorimetry and optical biosensor analyses, both monomers were shown to interact with the IL-5 receptor alpha chain with 1:1 stoichiometry and affinities 30- to 40-fold weaker than for the dimeric wild type protein. And both monomers stimulated cell proliferation of human IL-5 receptor positive cells with a concentration dependence close to that of wild type. The data show that both monomeric and dimeric forms of IL-5 function through similar 1:1 receptor alpha chain recruitment processes and that it is the helical packing of the monomeric four-helix bundle unit in IL-5, rather than the helical connectivity itself, that appears to play the major role in presenting structural epitopes to trigger functional receptor activation.

Characterization of potential antagonists of human interleukin 5 demonstrates their cross-reactivity with receptors for interleukin 3 and granulocyte-macrophage colony-stimulating factor

The ligand-binding alpha-chain of the human interleukin 5 (IL-5) receptor was expressed in its soluble form, lacking the transmembrane and cytoplasmic domains, from recombinant baculovirus. The soluble receptor was used in a scintillation proximity assay to identify two chemical compounds that inhibit binding of human IL-5 to the soluble receptor alpha chain with IC50 of 8 microM and 11 microM. These compounds also inhibited the interaction of human IL-5 with its membrane-bound receptor, composed of the ligand-binding alpha chain and signal-transducing beta chain, and prevented signaling through the receptor. Analysis by surface plasmon resonance and matrix-assisted laser-desorption/ionization mass spectrometry showed that the identified compounds bound irreversibly to the receptor at a 1:1 (mol/mol) ratio, suggesting a covalent interaction with the alpha chain of the human IL-5 receptor. Both compounds also inhibited the interaction of the receptors for interleukin 3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF), which are involved in hematopoietic differentiation and activation of immune cells, thus eliminating them as potential therapeutic agents. The inhibition of the structurally closely related receptors for IL-5, IL-3 and GM-CSF by both compounds, while binding of interleukin-4 to its receptor was not affected, suggests that a similar reactive site exists in the ligand-binding domains of the receptors for IL-5, IL-3 and GM-CSF.

A single STAT recruitment module in a chimeric cytokine receptor complex is sufficient for STAT activation

We established a system of receptor chimeras that enabled us to induce heterodimerization of different cytoplasmic tails. Fusion constructs were created that are composed of the extracellular parts of the interleukin-5 receptor alpha and beta chains, respectively, and the transmembrane and intracellular parts of gp130, the signal transducing chain of the interleukin-6 receptor complex. In COS-7 transfectants we observed a dose-dependent interleukin-5-inducible STAT1 activation for which the presence of both the alpha and the beta chain chimera was needed. No STAT activity was detected if one of the cytoplasmic tails of the receptor complex was deleted, indicating that STAT activity resulted from a receptor dimer rather than from higher receptor aggregates. We further investigated whether dimerization of STAT1 depends on the juxtaposition of two STAT recruitment modules in a receptor complex. We show that a receptor dimer with only a single STAT1 docking site was still able to lead to STAT1 activation. This indicates that the formation of a paired set of STAT binding sites in a receptor complex is not the prerequisite for STAT factor dimerization. Our findings are discussed in view of alternative STAT dimerization models.

Mutants of single chain interleukin 5 show asymmetric recruitment of receptor alpha and betac subunits

Dual asymmetric mutagenesis of single-chain interleukin 5 (scIL5) was used to obtain evidence that the normally homodimeric IL5 molecule, which contains two 4-helix bundle domains arranged symmetrically about a 2-fold axis, can recruit receptor alpha and betac subunits asymmetrically. Functionally active scIL5 was constructed using recombinant DNA methods by linking two IL5 monomers with a Gly-Gly linker. Mutants were constructed at residues Arg91, Glu110, and Trp111, previously shown to be involved in IL5 receptor alpha chain binding, and at residue Glu13, known to be involved in signal transduction presumably through interaction with the receptor betac chain. Mutants were examined for receptor alpha chain binding by an optical biosensor assay and for bioactivity using a cell proliferation assay. Substitution of the two binding site residues R91 and W111 in the same 4-helix bundle domain caused a 5-fold greater reduction in receptor binding affinity than when the two substitutions were distributed one in each domain. Substitution of E13 and R91 either in the same or in opposite domains gave comparable IL5Ralpha chain binding kinetics, essentially unchanged from those of scIL5. However, in contrast to the binding affinity pattern observed with R91A/W111A dual mutants, distributing the E13A/R91A mutations between the two 4-helix bundle domains caused a 5-6-fold greater loss of bioactivity than when the two changes were in the same domain, leaving the other domain unaltered. Taken with previous mutagenesis data, these results are consistent with a single shared-site model of IL5-IL5Ralpha chain recognition in which a single alpha chain can orientate in either of two modes, each one of which is stabilized preferentially by one of the two 4-helix bundles of IL5. Furthermore, the results suggest that a single betac molecule is activated for each IL5, through the Glu13 residue on the same helix bundle domain that dominates the IL5Ralpha interaction.

Identifying structure-function relationships in four-helix bundle cytokines: towards de novo mimetics design

Many cytokines (growth-factor proteins) are constructed from a common four-helix bundle structural framework. Rapid advances have been made in relating the structure and function of a growing number of four-helix bundle cytokines. This understanding opens the way to design de novo mimetics through such strategies as cytokine hybrids, structure-excerpted scaffolds and contact residue topology mimics. These may provide leads for agonists and antagonists of cell growth and differentiation.

Creation of a biologically active interleukin-5 monomer

Interleukin-5 (IL-5) specifically induces the differentiation of eosinophils, which are important in host defence and the pathogenesis of allergies and asthma. Structurally, IL-5 is a unique member of the short-chain helical-bundle subfamily of cytokines whose canonical motif contains four helices (A-D) arranged in an up-up-down-down topology. In contrast to other subfamily members, which fold unimolecularly into a single helical bundle, IL-5 forms a pair of helical bundles by the interdigitation of two identical monomers that contribute a D helix to the other's A-C helices. We predicted that the lack of bioactivity by an IL-5 monomer was due to a short loop between helices C and D which physically prevents unimolecular folding of helix D into a functionally obligate structural motif. Here we report that, by lengthening this loop, we have engineered an insertional mutant of IL-5 that was expressed as a monomer with biological activity similar to that of native IL-5. These studies demonstrate that all of the structural features necessary for IL-5 to function are contained within a single helical bundle.

Single chain human interleukin 5 and its asymmetric mutagenesis for mapping receptor binding sites

Wild type human (h) interleukin 5 (wt IL5) is composed of two identical peptide chains linked by disulfide bonds. A gene encoding a single chain form of hIL5 dimer was constructed by linking the two hIL5 chain coding regions with Gly-Gly linker. Expression of this gene in COS cells yielded a single chain IL5 protein (sc IL5) having biological activity similar to that of wt IL5, as judged by stimulation of human cell proliferation. Single chain and wt IL5 also had similar binding affinity for soluble IL5 receptor alpha chain, the specificity subunit of the IL5 receptor, as measured kinetically with an optical biosensor. The design of functionally active sc IL5 molecule. Such mutagenesis was exemplified by changes at residues Glu-13, Arg-91, Glu-110, and Trp-111. The receptor binding and bioactivity data obtained are consistent with a model in which residues from both IL5 monomers interact with the receptor alpha chain, while the interaction likely is asymmetric due to the intrinsic asymmetry of folded receptor. The results demonstrate a general route to the further mapping of receptor and other binding sites on the surface of human IL5.

Interleukin-5 receptor alpha subunit gene regulation in human eosinophil development: identification of a unique cis-element that acts lie an enhancer in regulating activity of the IL-5R alpha promoter

Further functional and biochemical characterization of the nuclear factor(s) which interacts with the EOS1 enhancer-like element in the IL-5R alpha promoter is currently in progress. Since different transcription factors recognize and interact with DNA in distinct fashions and with distinct structural motifs, we have modeled potential binding of the EOS1 factor to its cis-element based upon its methylation interference pattern (Fig. 2), using a cylindrical DNA helical projection (Fig. 6). Over a length of two helical turns, all nuclear protein contacts indicated by methylation interference map to one side of the DNA helix, suggesting that EOS1 binds in the major groove, across the minor groove, and on only one side of the helix. Further review of the model also reveals a potential diad symmetry for the binding site, suggestive of binding by a homodimer and consistent with the formation of the two DNA-protein complexes in our electrophoretic mobility shift experiments that could represent interactions with monomer versus dimer. Comparison of the EOS1 binding motif to similar models for the binding of other transcription factor families for which structural crystallographic and/or binding data is available suggests a similarity of the EOS1 complex to that of the bacterial helix-turn-helix phage lambda and 434 repressor-operator complexes, and the Cys4 zinc finger glucocorticoid response element (GRE) DNA-binding motifs, all of which show similar diad symmetry and binding in the major groove on one side of the DNA. The possibility that EOS1 functions as a GRE is being investigated, especially since there is a consensus AP-1 site at bp -440 to -432 of the IL-5R alpha promoter, immediately adjacent to the EOS1 binding site (see Fig. 5 in reference [36]) and AP-1/GRE interactions have been identified for composite response elements in the regulation of a number of different genes. The identification or cloning of EOS1, a potentially novel and eosinophil lineage-active transcription factor, should enhance our understanding of the processes involved in eosinophil development in particular and myeloid lineage commitment and differentiation in general.

Characterization of critical residues in the cytoplasmic domain of the human interleukin-5 receptor alpha chain required for growth signal transduction

Interleukin (IL)-5 binds to a cell surface receptor composed of two polypeptide chains, alpha and beta, both belonging to the hemopoietic cytokine receptor family. Mouse cells expressing common mouse beta chain (AIC2B) that were transfected with human IL-5 receptor (R)alpha cDNA proliferated in response to picomolar concentrations of human IL-5, indicating that a functional receptor was reconstituted. We show that in these cells, human (h)IL-5 as well as mouse (m)IL-3 induce tyrosine phosphorylation of beta chain and JAK 2 kinase. Phosphorylated beta receptor was co-precipitated with anti-JAK 2 antibodies, suggesting that both molecules were physically associated. IL-5 and IL-3 also induce cytosolic DNA binding activity as measured by an electrophoretic mobility shift assay using the interferon-gamma responsive region of human Fc gamma 1 gene DNA element. A deletion mutant of hIL-5R alpha lacking the cytoplasmic part could bind hIL-5 normally in association with the beta chain, but was unable to transmit a biological signal. The cytoplasmic domain was also indispensable for tyrosine phosphorylation and activation of DNA binding proteins. A membrane-proximal proline-rich element of the hIL-5R alpha cytoplasmic domain that is conserved among different members of the hemopoietic cytokine receptor family was essential for biological activity. Point mutations in this motif also knocked out IL-5-inducible JAK 2 phosphorylation.

Characterization of recombinant extracellular domain of human interleukin-10 receptor

The extracellular region of the human interleukin-10 (hIL-10) receptor was expressed using a myeloma cell line and was purified to homogeneity by ligand-affinity chromatography. SDS-polyacrylamide gel electrophoresis analysis indicated that the soluble receptor is glycosylated and has an apparent molecular mass of 35,000-45,000. Under native conditions, soluble hIL-10 receptor was determined by gel filtration to be a monomeric protein. Soluble hIL-10 receptor was able to inhibit the binding of 125I-hIL-10 to the full-length receptor and was able to antagonize the effect of human IL-10 in cell proliferation and cytokine synthesis inhibition. The apparent dissociation constant (Kd) of soluble hIL-10 receptor was determined to be 563 +/- 59 pM, approximately 2- to 10-fold higher than that found on intact cells (Tan, J. C., Indelicato, S. R., Narula, S. K., Zavodny, P. J., and Chou, C.-C. (1993) J. Biol. Chem. 268, 21053-21059; Liu, Y., Wei, S. H.-Y., Ho, A. S.-Y., de Waal Malefyt, R., and Moore, K. W. (1994) J. Immunol. 152, 1821-1829). When hIL-10 binds soluble hIL-10 receptor in solution, a single complex was detected by gel filtration, and the complex was found to consist of two hIL-10 dimers and four soluble receptor monomers, suggesting that hIL-10 may induce a novel mode of oligomerization of the receptor upon binding.

Binding interactions of human interleukin 5 with its receptor alpha subunit. Large scale production, structural, and functional studies of Drosophila-expressed recombinant proteins

Human interleukin 5 (hIL5) and soluble forms of its receptor alpha subunit were expressed in Drosophila cells and purified to homogeneity, allowing a detailed structural and functional analysis. B cell proliferation confirmed that the hIL5 was biologically active. Deglycosylated hIL5 remained active, while similarly deglycosylated receptor alpha subunit lost activity. The crystal structure of the deglycosylated hIL5 was determined to 2.6-A resolution and found to be similar to that of the protein produced in Escherichia coli. Human IL5 was shown by analytical ultracentrifugation to form a 1:1 complex with the soluble domain of the hIL5 receptor alpha subunit (shIL5R alpha). Additionally, the relative abundance of ligand and receptor in the hIL5.shIL5R alpha complex was determined to be 1:1 by both titration calorimetry and SDS-polyacrylamide gel electrophoresis analysis of dissolved cocrystals of the complex. Titration microcalorimetry yielded equilibrium dissociation constants of 3.1 and 2.0 nM, respectively, for the binding of hIL5 to shIL5R alpha and to a chimeric form of the receptor containing shIL5R alpha fused to the immunoglobulin Fc domain (shIL5R alpha-Fc). Analysis of the binding thermodynamics of IL5 and its soluble receptor indicates that conformational changes are coupled to the binding reaction. Kinetic analysis using surface plasmon resonance yielded data consistent with the Kd values from calorimetry and also with the possibility of conformational isomerization in the interaction of hIL5 with the receptor alpha subunit. Using a radioligand binding assay, the affinity of hIL5 with full-length hIL5R alpha in Drosophila membranes was found to be 6 nM, in accord with the affinities measured for the soluble receptor forms. Hence, most of the binding energy of the alpha receptor is supplied by the soluble domain. Taken with other aspects of hIL5 structure and biological activity, the data obtained allow a prediction for how 1:1 stoichiometry and conformational change can lead to the formation of hIL5.receptor alpha beta complex and signal transduction.

Identification and characterization of a functional promoter region in the human eosinophil IL-5 receptor alpha subunit gene

The molecular basis for the commitment of multipotential myeloid progenitors to the eosinophil lineage, and the transcriptional mechanisms by which eosinophil-specific genes are subsequently expressed and regulated during eosinophil development are currently unknown. Interleukin-5 (IL-5) is a T cell and mast cell-derived cytokine with actions restricted to the eosinophil and closely related basophil lineages in humans. The high affinity receptor for IL-5 (IL-5R) is composed of an alpha subunit (IL-5R alpha) expressed by the eosinophil lineage, that associates with a beta c subunit shared with the receptors for IL-3 and granulocyte-macrophage colony stimulating factor (GM-CSF). As a prerequisite to studies of the transcriptional regulation of the IL-5R alpha subunit gene, we used three different methods, including primer extension, RNase protection, and 5'-RACE to precisely map the transcriptional start site to a position 15 base pairs (bp) upstream of the 5' end of the published sequence of IL-5R alpha exon 1. To initially identify the IL-5R alpha promoter, 3.5 kilobases (kb) and 561 bp of the 5' sequence flanking the transcriptional start site were subcloned into the promoterless pXP2-luciferase vector. Transient transfection of these constructs into an eosinophil-committed HL-60 subline, clone HL-60-C15, induced the expression of approximately 240-fold greater luciferase activity than the promoterless vector, identifying a strong functionally active promoter region within the 561 bp of sequence proximal to the transcriptional start site and with activity equivalent to pXP2 constructs containing the entire 3.5 kb of upstream sequence. To more precisely localize the cis-acting regulatory elements in this region important for promoter activity, a series of 5' deletion mutants of the 561-bp region were generated in the pXP2-luciferase vector. Deletion of the region between bp -432 and -398 reduced promoter activity by more than 80% in the HL-60-C15 cell line. Further analyses of the activity of the IL-5R alpha promoter constructs in various other eosinophil, myeloid, and non-myeloid cell lines indicated that the promoter was relatively myeloid and eosinophil lineage-specific in its expression. Consensus sequences for known transcription factor binding sites were not present in the 34-bp region of the promoter required for maximal activity, suggesting unique myeloid- and possibly eosinophil-specific regulatory elements.(ABSTRACT TRUNCATED AT 400 WORDS)