Development of a human interleukin-6 receptor antagonist

The role of the interleukin (IL)-6/IL-6 receptor axis in cancer

Interleukin-6 (IL-6) is a pleiotropic cytokine that activates a classic signalling pathway upon binding to its membrane-bound receptor (IL-6R). Alternatively, IL-6 may 'trans-signal' in a manner that is facilitated by its binding to a soluble derivative of the IL-6 receptor (sIL-6R). Resultant signal transduction is, respectively, driven by the association of IL-6/IL-6R or IL-6/sIL-6R complex with the membrane-associated signal transducer, gp130 (Glycoprotein 130). Distinct JAK (Janus tyrosine kinase)/STAT (signal transducers and activators of transcription) and other signalling pathways are activated as a consequence. Of translational relevance, overexpression of IL-6 has been documented in several neoplastic disorders, including but not limited to colorectal, ovarian and breast cancer and several haematological malignancies. This review attempts to summarise our current understanding of the role of IL-6 in cancer development. In short, these studies have shown important roles for IL-6 signalling in tumour cell growth and survival, angiogenesis, immunomodulation of the tumour microenvironment, stromal cell activation, and ultimate disease progression. Given this background, we also consider the potential for therapeutic targeting of this system in cancer.

Crystal structure of interleukin-6 in complex with a modified nucleic acid ligand

IL-6 is a secreted cytokine that functions through binding two cell surface receptors, IL-6Rα and gp130. Because of its involvement in the progression of several chronic inflammatory diseases, IL-6 is a target of pharmacologic interest. We have recently identified a novel class of ligands called SOMAmers (S low Off-rate Modified Aptamers) that bind IL-6 and inhibit its biologic activity. SOMAmers exploit the chemical diversity of protein-like side chains assembled on flexible nucleic acid scaffolds, resulting in an expanded repertoire of intra- and intermolecular interactions not achievable with conventional aptamers. Here, we report the co-crystal structure of a high affinity SOMAmer (K_d = 0.20 nm) modified at the 5-position of deoxyuridine in a complex with IL-6. The SOMAmer, comprised of a G-quartet domain and a stem-loop domain, engages IL-6 in a clamp-like manner over an extended surface exhibiting close shape complementarity with the protein. The interface is characterized by substantial hydrophobic interactions overlapping the binding surfaces of the IL-6Rα and gp130 receptors. The G-quartet domain retains considerable binding activity as a disconnected autonomous fragment (K_d = 270 nm). A single substitution from our diversely modified nucleotide library leads to a 37-fold enhancement in binding affinity of the G-quartet fragment (K_d = 7.4 nm). The ability to probe ligand surfaces in this manner is a powerful tool in the development of new therapeutic reagents with improved pharmacologic properties. The SOMAmer·IL-6 structure also expands our understanding of the diverse structural motifs achievable with modified nucleic acid libraries and elucidates the nature with which these unique ligands interact with their protein targets.

Molecular interactions within the IL-6/IL-12 cytokine/receptor superfamily

Production of cytokines by immune cells in response to stimuli and the binding of cytokines to specific receptors on target cells is a central feature of the immune response. The IL-12 cytokine family is particularly influential in determining the fate of T cells and is characterized by the sharing of cytokine and receptor subunits. A thorough understanding of the molecular interactions within this family will be a key to the development of therapeutic inhibitors or enhancers of IL-12 family function. While the current structural and molecular data for IL-12 family members is limited, there is ample information on the structurally related IL-6 cytokine family. This review will summarize the current structural and mutagenesis data within the IL-12 family and will attempt to utilize similarities between the IL-6 and IL-12 families to understand molecular interactions between IL-12 family subunits and with receptor components.

Interleukin-6 in sepsis and capillary leakage syndrome

Bacterial sepsis is one of the most frequent and dreaded causes of death in intensive care units. According to the current understanding of sepsis, bacterial components activate innate immune responses via pattern-recognition receptors that stimulate signaling pathways, thereby leading to activation of NF-κB and the release of cytokines, alarming the organism and coordinating appropriate defense mechanisms. The resulting "cytokine storm" not only restricts bacterial invasion; it also harms the host by triggering a hemodynamic collapse with a drop in blood pressure, which could lead to death. One of the cytokines released during sepsis is interleukin-6 (IL-6). Originally described as a B-cell-stimulating factor, this cytokine has since been shown to have multiple additional functions. Interestingly, there is emerging evidence of IL-6 trans-signaling in the pathogenesis of sepsis. We review recent findings and discuss whether therapeutic interference with IL-6 trans-signaling may be beneficial in this important clinical scenario.

Opposing roles of RAGE and Myd88 signaling in extensive liver resection

In extensive liver resection secondary to primary or metastatic liver tumors, or in living donor liver transplantation, strategies to quell deleterious inflammatory responses and facilitate regeneration are essential. The receptor for advanced glycation endproducts (RAGE) and myeloid differentiating factor 88 (Myd88) are implicated in the inflammatory response. To establish the contributions of RAGE vs. Myd88 signaling in extensive liver resection, we probed the effect of RAGE and/or Myd88, the latter primarily a key transducer of major toll-like receptors and also implicated in interleukin-1 (Il1) signaling, in a murine model of extensive (85%) hepatectomy. We report that, although Myd88 is thoroughly essential for survival via regulation of NF-κB and TNF-α, deletion of RAGE significantly improved survival compared to wild-type, Myd88-null, or RAGE-null/Myd88-null mice. RAGE opposes Myd88 signaling at multiple levels: by suppression of p65 levels, thereby reducing activation of NF-κB and consequent production of cyclin D1, and by suppression of Il6-mediated phosphorylation of Stat3, thereby down-regulating Pim1 and suppressing the hyperplastic response. Further, RAGE-dependent suppression of glyoxalase1, a detoxification pathway for pre-AGEs, enhances AGE levels and suppresses Il6 action. We conclude that blockade of RAGE may rescue liver remnants from the multiple signals that preclude adaptive proliferation triggered primarily by Myd88 signaling pathways.

Interleukin-6 subfamily cytokines and rheumatoid arthritis: role of antagonists

Many cytokines have been implicated in the inflammatory pathways that characterize rheumatoid arthritis (RA) and related inflammatory diseases of the joints. These include members of the interleukin-6 (IL-6) family of cytokines, several of which have been detected in excess in the synovial fluid from RA patients. What makes the IL-6 group of cytokines a family is their common use of the glycoprotein 130 (gp130) receptor subunit, to which they bind with different affinities. Several strategies have been developed to block the pro-inflammatory activities of IL-6 subfamily cytokines. These include the application of monoclonal antibodies, the creation of mutant form(s) of the cytokine with enhanced binding affinity to gp130 receptor and the generation of antagonists by selective mutagenesis of the specific cytokine/gp130 receptor-binding site(s). The rationale for the use of anti-cytokine therapy in inflammatory joint diseases is based on evidence from studies in vitro and in vivo, which implicate major cytokines such as interleukin-1 (IL-1), tumour necrosis factor (TNF)-alpha and IL-6 in RA pathogenesis. In particular, IL-6 subfamily antagonists have a wide range of potential therapeutic and research applications. This review focuses on the role of some of the IL-6 subfamily cytokines in the pathogenesis of the inflammatory diseases of the joints (IJDs), such as RA. In addition, an overview of the recently developed antagonists will be discussed.

Oncogene-induced senescence relayed by an interleukin-dependent inflammatory network

Oncogene-induced cellular senescence (OIS) is emerging as a potent cancer-protective response to oncogenic events, serving to eliminate early neoplastic cells from the proliferative pool. Using combined genetic and bioinformatic analysis, we find that OIS is linked specifically to the activation of an inflammatory transcriptome. Induced genes included the pleiotropic cytokine interleukin-6 (IL-6), which upon secretion by senescent cells acted mitogenically in a paracrine fashion. Unexpectedly, IL-6 was also required for the execution of OIS, but in a cell-autonomous mode. Its depletion caused the inflammatory network to collapse and abolished senescence entry and maintenance. Furthermore, we demonstrate that the transcription factor C/EBPbeta cooperates with IL-6 to amplify the activation of the inflammatory network, including IL-8. In human colon adenomas, IL-8 specifically colocalized with arrested, p16(INK4A)-positive epithelium. We propose a model in which the context-dependent cytostatic and promitogenic functions of specific interleukins contribute to connect senescence with an inflammatory phenotype and cancer.

Alternative splicing of mRNA of mouse interleukin-4 and interleukin-6

Interleukin-4 and interleukin-6 are multifunctional regulatory proteins, which participate both in haemopoiesis and in immunopoiesis. The alternative splicing of these interleukins in humans is known to proceed in a tissue-specific manner. Additionally, changes in splicing can also be dependent on tissue pathology. In this work, we report on the presence of alternatively spliced mRNA (IL-4delta2mRNA), lacking exon 2, in mouse bone marrow and spleen cells. We find that in unstimulated cells IL-4mRNA levels strongly dominate over IL-4delta2mRNA levels. Both increase in response to stimulation, with the concentration of the alternative variant rising earlier and faster than that of the full-length variant. In all other tissues studied dominance of IL-4delta2mRNA over the full-length variant was not observed. In addition, we find expression of three forms of IL-6 mRNA: the full-length IL-6 mRNA, IL-6Delta3 mRNA, and IL-6Delta5 mRNA in the second and third trimester placenta tissue and in the spleen of mice immunized with a high dose of sheep erythrocytes. It is anticipated that translation of these mRNA variants can generate proteins capable of binding to some subunits of the IL-6 receptor, thus possessing effector function. Alternative splicing is discussed as a source of cytokines with new regulatory properties.

New developments in IL-6 dependent biology and therapy: where do we stand and what are the options?

Interleukin-6 (IL-6) is a four-helical protein which, on target cells, binds to a specific IL-6-receptor and two molecules of the promiscuous signal transducing protein gp130. Structure-function analysis defined three molecular contact sites between IL-6 and its receptor subunits. Using this information, competitive antagonistic proteins as well as hyperagonistic proteins were developed. Possible therapeutic applications of IL-6 antagonists are in IL-6 dependent haematological disorders (Castleman's disease, POEMS syndrome, multiple myeloma) and bone diseases (Paget's disease, osteoporosis). Designer IL-6 antagonists could suppress inflammatory activity in rheumatic and autoimmune diseases and could prevent secondary amyloidosis. IL-6 antagonists could also prove advantageous in myocardial infarction and unstable angina pectoris. IL-6 antagonists might slow down development of (mesangioproliferative) glomerulonephritis. On the other hand, hyperagonistic variants of IL-6 have a potential in ex vivo expansion of bone marrow stem cells and as thrombopoietic agents. They might also be developed into drugs to support liver regeneration in vivo and to treat stress-induced cardiac insufficiency.

Woodchuck interleukin-6 gene: structure, characterization, and biologic activity

Woodchuck is an important animal model for studying human hepatitis B virus (HBV) infection. Within the cytokine network, interleukin-6 (IL-6) plays an important role in immune responses that may lead to viral clearance. To further understand woodchuck IL-6 biology, we cloned and characterized the IL-6 gene from white blood cells. The complete woodchuck IL-6 gene is about 7 kb and consists of five exons and four introns. The IL-6 gene organization of the woodchuck is similar to those of the human, rat, and mouse. Also several elements are highly conserved in the 300 bp promoter region of the IL-6 gene, including a nuclear factor kappa B (NF-kappaB) binding site. The woodchuck IL-6 gene encodes a polypeptide of 207 amino acids in a precursor form and 189 amino acids in the mature form. The expressed protein was 23 kDa according to SDS-PAGE. To demonstrate biologic activity, we expressed woodchuck IL-6 and showed that the purified recombinant protein induced terminal differentiation, as reflected by upregulation of Fcgamma receptor expression, and substantially inhibited proliferation of M1 cells, a murine myeloid leukemia cell line. The inhibitory effect of woodchuck IL-6 on M1 cells was blocked by an anti-gp130 monoclonal antibody, suggesting that woodchuck IL-6 activity is specifically mediated by signaling through the IL-6 receptor complex. Cloning of the woodchuck IL-6 gene and demonstrating biologic activity of the gene product will facilitate studies of human hepatitis B virus using the woodchuck model.

Mapping of the Leptin Binding Sites and Design of a Leptin Antagonist

The leptin/leptin receptor system shows strong similarities to the long-chain cytokine interleukin-6 (IL-6) and granulocyte colony-stimulating factor cytokine/receptor systems. The IL-6 family cytokines interact with their receptors through three different binding sites I-III. The leptin structure was superposed on the crystal structures of several long-chain cytokines, and a series of leptin mutants was generated focusing on binding sites I-III. The effect of the mutations on leptin receptor (LR) signaling and on binding to the membrane proximal cytokine receptor homology domain (CRH2) of the LR was determined. Mutations in binding site I at the C terminus of helix D show a modest effect on signaling and do not affect binding to CRH2. Binding site II is composed of residues at the surface of helices A and C. Mutations in this site impair binding to CRH2 but have only limited effect on signaling. Site III mutations around the N terminus of helix D impair receptor activation without affecting binding to CRH2. We identified an S120A/T121A mutant in binding site III, which lacks any signaling capacity, but which still binds to CRH2 with wild type affinity. This leptin mutant behaves as a potent leptin antagonist both in vitro and in vivo.

Affinity maturation of leukemia inhibitory factor and conversion to potent antagonists of signaling

Leukemia inhibitory factor (LIF)-induced cell signaling occurs following sequential binding to the LIF receptor alpha-chain (LIFR), then to the gp130 co-receptor used by all members of the interleukin-6 family of cytokines. By monovalently displaying human LIF on the surface of M13 phage and randomizing clusters of residues in regions predicted to be important for human LIFR binding, we have identified mutations, which lead to significant increases in affinity for binding to LIFR. Six libraries were constructed in which regions of 4-6 amino acids were randomized then panned against LIFR. Mutations identified in three distinct clusters, residues 53-57, 102-103, and 150-155, gave rise to proteins with significantly increased affinity for binding to both human and mouse LIFR. Combining the mutations for each of these regions further increased the affinity, such that the best mutants bound to human LIFR with >1000-fold higher affinity than wild-type human LIF. NMR analysis indicated that the mutations did not alter the overall structure of the molecule relative to the native protein, although some local changes occurred in the vicinity of the substituted residues. Despite increases in LIFR binding affinity, these mutants did not show any increase in activity as agonists of LIF-induced proliferation of Ba/F3 cells expressing human LIFR and gp130 compared with wild-type LIF. Incorporation of two additional mutations (Q29A and G124R), which were found to abrogate cell signaling, led to the generation of highly potent antagonists of both human and murine LIF-induced bioactivity.

Development of an IL-6 antagonist peptide that induces apoptosis in 7TD1 cells

Interleukin-6 (IL-6) is a pleiotropic cytokine involved in the regulation of proliferation and differentiation of hematopoietic cells and in the pathogenesis of many diseases, including multiple myeloma. This study pursues a way to interfere with IL-6 pathway in an attempt to modulate its biological activity. Here we describe the rational design and biological evaluation of peptides able to antagonize the murine IL-6 activity by interfering with IL-6 Receptor alpha in 7TD1 cells, a IL-6-dependent B-cell line. Of the peptide tested, only Guess 4a is capable of interfering with IL-6 transducing pathway, therefore inducing growth arrest and apoptosis of 7TD1 cells.

Analysis of the leukemia inhibitory factor receptor functional domains by chimeric receptors and cytokines

In contrast to other hematopoietic cytokine receptors, the leukemia inhibitory factor receptor (LIFR) possesses two cytokine binding modules (CBMs). Previous studies suggested that the NH(2)-terminal CBM and the Ig-like domain of the LIFR are most important for LIF binding and activity. Using the recently engineered designer cytokine IC7, which induces an active heterodimer of the LIFR and gp130 after binding to the IL-6R, and several receptor chimeras of the LIFR and the interleukin-6 receptor (IL-6R) carrying the CBM of the IL-6R in place of the COOH-terminal LIFR CBM, we could assign individual receptor subdomains to individual binding sites of the ligand. The NH(2)-terminal CBM and the Ig-like domain of the LIFR bind to ligand site III, whereas the COOH-terminal CBM contacts site I. Furthermore, we show that LIFR mutants carrying the IL-6R CBM instead of the COOH-terminal CBM can replace the IL-6R by acting as an alpha-receptor for IL-6. However, in situations where a signaling competent receptor is bound at IL-6 site I, ligand binding to site III is an absolute requirement for participation of the receptor in a signaling heterodimer with gp130; i.e., a functional receptor complex of IL-6 type cytokines cannot be assembled solely via site I and II as in the growth hormone receptor complex.

Interleukin-6 N-terminal peptides modulate the expression of junB protooncogene and the production of fibrinogen in HepG2 cells

Interleukin-6 (IL-6) is a helical cytokine exerting pleiotropic activities including the regulation of hematopoiesis, B cell activation and acute-phase reaction. The structure-function relationship of the molecule is the subject of intensive investigation using point and deletion mutants. Our objective was to analyse the role of the N-terminal 18-46 region in IL-6-mediated expression of junB protooncogene and fibrinogen production, reflecting the acute phase response, with synthetic overlapping peptides. mRNA expression of junB was monitored by competitive RT-PCR, while sandwich ELISA was used for the detection of fibrinogen in the supernatant of HepG2 human hepatoma cells. We found that even short synthetic octapeptides can be stimulatory (in the absence of IL-6) or inhibitory (in the presence of IL-6) in both assays. To establish the molecular mechanism by which synthetic peptides exert their biological effects electromobility shift assay was carried out using HepG2 nuclear extracts. Peptides inducing junB expression initiate gel shifts of STAT3/DNA complexes, which may indicate the involvement of this signal transduction pathway. Circular dicroism spectroscopy data suggest that 8-11-mer peptides representing different parts of the 18-46 region have a marked tendency to adopt ordered conformations in a water/trifluoroethanol (1:1 v/v) mixture. Competition studies with rhIL-6 and selected fluorophore-labelled peptides indicate the presence of more than one binding site on soluble IL-6 receptor. Considering the possible multiple etiologic role of IL-6 in the pathogenesis of various diseases, these peptides could be useful for dissection of IL-6 related biological effects.

A structural template for gp130-cytokine signaling assemblies

The gp130-cytokine system has been fertile ground for protein structure-function studies aimed at elucidating the basis of ligand recognition and receptor activation. A number of longstanding questions involve the mechanism of the stepwise assembly of the active signaling complexes, as well as the structure of the gp130-cytokine complexes. It has been clear from functional studies that the paradigm of gp130-cyokine recognition will differ substantially from the classical homo-dimeric systems, typified by human growth hormone (hGH) and its receptor. Recently, a crystal structure of a viral interleukin-6 (vIL-6), complexed with the D1D2D3 domains of the gp130 extracellular domain, has resolved many of these questions, and reconciled much of the functional and mutagenesis data which have existed for a variety of gp130-cytokines. In this review, we discuss the structure of the vIL-6/gp130 complex in some detail and suggest that the geometry of this complex will be a common structural template utilized by other gp130-cytokines, as well as cytokines from distinct signaling systems.

Detection of direct binding of human herpesvirus 8-encoded interleukin-6 (vIL-6) to both gp130 and IL-6 receptor (IL-6R) and identification of amino acid residues of vIL-6 important for IL-6R-dependent and -independent signaling

Human herpesvirus 8 (HHV-8) is associated with Kaposi's sarcoma, primary effusion lymphoma, and multicentric Castleman's disease; in all of these diseases, interleukin-6 (IL-6) has been implicated as a likely mitogenic and/or angiogenic factor. HHV-8 encodes a homologue of IL-6 (viral IL-6 [vIL-6]) that has been shown to be biologically active in several assays and whose activities mirror those of its mammalian counterparts. Like these proteins, vIL-6 mediates its effects through the gp130 signal transducer, but signaling is not dependent on the structurally related IL-6 receptor (IL-6R; gp80) subunit of the receptor-signal transducer complex. However, as we have shown previously, IL-6R can enhance vIL-6 signal transduction and can enable signaling through a gp130 variant (gp130.PM5) that is itself unable to support vIL-6 activity, indicating that IL-6R can form part of the signaling complex. Also, our analysis of a panel of vIL-6 mutants in transfection experiments in Hep3B cells (that express IL-6R and gp130) showed that most were able to function normally in this system. Here, we have used in vitro vIL-6-receptor binding assays to demonstrate direct binding of vIL-6 to both gp130 and IL-6R and vIL-6-induced gp130-IL-6R complex formation, and we have extended our functional analyses of the vIL-6 variants to identify residues important for IL-6R-independent and IL-6R-dependent signaling through native gp130 and gp130.PM5, respectively. These studies have identified residues in vIL-6 that are important for IL-6R-independent and IL-6R-mediated functional complex formation between vIL-6 and gp130 and that may be involved directly in binding to gp130 and IL-6R.

Structure of an extracellular gp130 cytokine receptor signaling complex

The activation of gp130, a shared signal-transducing receptor for a family of cytokines, is initiated by recognition of ligand followed by oligomerization into a higher order signaling complex. Kaposi's sarcoma-associated herpesvirus encodes a functional homolog of human interleukin-6 (IL-6) that activates human gp130. In the 2.4 angstrom crystal structure of the extracellular signaling assembly between viral IL-6 and human gp130, two complexes are cross-linked into a tetramer through direct interactions between the immunoglobulin domain of gp130 and site III of viral IL-6, which is necessary for receptor activation. Unlike human IL-6 (which uses many hydrophilic residues), the viral cytokine largely uses hydrophobic amino acids to contact gp130, which enhances the complementarity of the viral IL-6-gp130 binding interfaces. The cross-reactivity of gp130 is apparently due to a chemical plasticity evident in the amphipathic gp130 cytokine-binding sites.

Improving the refolding yield of interleukin-4 through the optimization of local interactions

Interleukin-4 (IL-4) is a multifunctional cytokine that plays an important role in the regulation of various immune responses. However, the development of IL-4 or IL-4 variants into potential therapeutic drugs is hindered by the low efficiency of the in vitro refolding process of this protein. In this work, we have investigated the improvement of the refolding yield of IL-4 using two different rational design approaches. The first one is based on the so-called inverse hydrophobic effect and involved the replacement of a solvent exposed, non-conserved, hydrophobic residue (W91) by serine. This led to an increase in stability of 1.4 kcal mol(-1) and shifted the midpoint transition temperature (Tm) from 62 to 70 degrees C. The second approach is based on the stabilization of alpha-helices through the introduction of favorable local interactions. This strategy resulted in the following helix sequence for helix C of IL-4, 68ASAAEANRHKQLIRFLKRLDRNLWGLAG95. The mutant protein was stabilized by 0.5 kcal mol(-1), the Tm shifted to 68 degrees C, and a two-fold increase in the refolding yield was consistently observed. Our results make the large-scale production of IL-4 derivatives economically more viable, suggest that a similar approach can be applied to other related proteins, and may represent a general strategy to improve in vitro refolding yields through the selective optimization of the stability of alpha-helices.

New perspectives on the design of cytokines and growth factors

A combination of molecular modelling, conventional epitope scanning and combinatorial techniques, such as phage display and DNA shuffling, has greatly improved our understanding of ligand-receptor interactions. It has therefore been possible to develop powerful cytokine-growth factor antagonists and new designer cytokines, with altered receptor specificities or with greatly enhanced biological activity. Recently, small circular peptides that mimic or block the effects of natural cytokines and growth factors have been developed; such small peptides are likely to open new avenues in therapeutics.

Kaposi's sarcoma-associated herpesvirus-encoded interleukin-6

Since the discovery of the virus in 1994, the rapid pace with which Karposi's sarcoma-associated herpesvirus (KSHV) research has progressed has quickly led to a broad understanding of the structure of the virus and its biology and pathology in humans. Molecular piracy of potentially useful cellular genes has emerged as a characteristic feature of this virus. The viral homolog of human IL-6, vIL-6 is an example in kind. Studies in vitro and in vivo have shown that vIL-6 can stimulate the growth of KSHV-infected primary infusion lymphoma (PEL) cells, can promote hematopoiesis, and act as an angiogenic factor through the induction of vascular endothelial growth factor (VEGF). It is not difficult to envision how vIL-6, through these properties and perhaps others yet to be identified, can contribute to KSHV survival and spread in the human population.

The primary sequence of rhesus monkey rhadinovirus isolate 26-95: sequence similarities to Kaposi's sarcoma-associated herpesvirus and rhesus monkey rhadinovirus isolate 17577

The primary sequence of the long unique region L-DNA (L for low GC) of rhesus monkey rhadinovirus (RRV) isolate 26-95 was determined. The L-DNA consists of 130,733 bp that contain 84 open reading frames (ORFs). The overall organization of the RRV26-95 genome was found to be very similar to that of human Kaposi sarcoma-associated herpesvirus (KSHV). BLAST search analysis revealed that in almost all cases RRV26-95 coding sequences have a greater degree of similarity to corresponding KSHV sequences than to other herpesviruses. All of the ORFs present in KSHV have at least one homologue in RRV26-95 except K3 and K5 (bovine herpesvirus-4 immediate-early protein homologues), K7 (nut-1), and K12 (Kaposin). RRV26-95 contains one MIP-1 and eight interferon regulatory factor (vIRF) homologues compared to three MIP-1 and four vIRF homologues in KSHV. All homologues are correspondingly located in KSHV and RRV with the exception of dihydrofolate reductase (DHFR). DHFR is correspondingly located near the left end of the genome in RRV26-95 and herpesvirus saimiri (HVS), but in KSHV the DHFR gene is displaced 16,069 nucleotides in a rightward direction in the genome. DHFR is also unusual in that the RRV26-95 DHFR more closely resembles HVS DHFR (74% similarity) than KSHV DHFR (55% similarity). Of the 84 ORFs in RRV26-95, 83 contain sequences similar to the recently determined sequences of the independent RRV isolate 17577. RRV26-95 and RRV17577 sequences differ in that ORF 67.5 sequences contained in RRV26-95 were not found in RRV17577. In addition, ORF 4 is significantly shorter in RRV26-95 than was reported for RRV17577 (395 versus 645 amino acids). Only four of the corresponding ORFs between RRV26-95 and RRV17577 exhibited less than 95% sequence identity: glycoproteins H and L, uracil DNA glucosidase, and a tegument protein (ORF 67). Both RRV26-95 and RRV17577 have unique ORFs between positions 21444 to 21752 and 110910 to 114899 in a rightward direction and from positions 116524 to 111082 in a leftward direction that are not found in KSHV. Our analysis indicates that RRV26-95 and RRV17577 are clearly independent isolates of the same virus species and that both are closely related in structural organization and overall sequence to KSHV. The availability of detailed sequence information, the ability to grow RRV lytically in cell culture, and the ability to infect monkeys experimentally with RRV will facilitate the construction of mutant strains of virus for evaluating the contribution of individual genes to biological properties.

Expression of interleukin-6 in human dorsal root ganglion cells

The expression of Interleukin-6 (IL-6) was studied in normal dorsal root ganglia (DRG) of juvenile and foetal humans, using immunohistochemistry and in situ hybridization techniques. There was an expression of IL-6-like immunoreactivity in more than 75% out of neuronal cells in the juvenile ganglia with a peripheral localization, and also an expression in the foetal ganglion cells. There was a co-localization of IL-6 with substance P (SP) and calcitonin gene-related peptide (CGRP) in more than 60% of the DRG cells, respectively. By in situ hybridization 0.9% of the cells in the juvenile ganglia and 1.1% of the cells in the foetal ganglia showed a positive signal for IL-6. In addition, expression of IL-6 was found in juvenile medulla spinalis, preferentially in the white matter.

Human herpesvirus 8 interleukin-6 (vIL-6) signals through gp130 but has structural and receptor-binding properties distinct from those of human IL-6

Human herpesvirus 8 (HHV-8) has been associated with classical, endemic (African), and AIDS-related Kaposi's sarcoma (KS), body cavity-based primary effusion lymphomas, and multicentric Castleman's disease (MCD). HHV-8 encodes a functional homologue of interleukin-6 (IL-6), a cytokine that promotes the growth of KS and myeloma cells and is found at elevated levels in MCD lesions and patient sera. We have previously reported that the viral IL-6 (vIL-6) gene product can support the growth of the IL-6-dependent murine hybridoma cell line, B9, and that the gp80 (IL-6 receptor [IL-6R]) component of the IL-6 receptor-signal transducer (gp180) complex plays a role in mediating this activity. However, it has been shown by others that vIL-6 can function in human cells independently of IL-6R. Here we have extended our functional studies of vIL-6 by identifying transcription factors and pathways used in human Hep3B cells, investigating the utilization of gp130 and IL-6R by vIL-6, and undertaking mutational analyses of vIL-6 and gp130. The data presented here establish that vIL-6, in common with its endogenous counterparts, can mediate signal transduction through gp130 and activate multiple transcription factors, map residues within the vIL-6 protein that are and are not important for vIL-6 signalling, and identify a gp130 mutant that is nonfunctional with respect to vIL-6 signalling in the absence of IL-6R but that retains the ability to mediate vIL-6 and human IL-6 (hIL-6) signal transduction when IL-6R is coexpressed. The data presented demonstrate functional and mechanistic similarities between vIL-6 and endogenous IL-6 proteins but also highlight differences in the structural and receptor-binding properties of vIL-6 relative to its human counterpart.

A rhesus macaque rhadinovirus related to Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8 encodes a functional homologue of interleukin-6

The rhesus rhadinovirus strain 17577 (RRV strain 17577) genome is essentially colinear with human herpesvirus 8 (HHV8)/Kaposi's sarcoma-associated herpesvirus (KSHV) and encodes several analogous open reading frames (ORFs), including the homologue of cellular interleukin-6 (IL-6). To determine if the RRV IL-6-like ORF (RvIL-6) is biologically functional, it was expressed either transiently in COS-1 cells or purified from bacteria as a glutathione S-transferase (GST)-RvIL-6 fusion and analyzed by IL-6 bioassays. Utilizing the IL-6-dependent B9 cell line, we found that both forms of RvIL-6 supported cell proliferation in a dose-dependent manner. Moreover, antibodies specific to the IL-6 receptor (IL-6R) or the gp130 subunit were capable of blocking the stimulatory effects of RvIL-6. Reciprocal titrations of GST-RvIL-6 against human recombinant IL-6 produced a more-than-additive stimulatory effect, suggesting that RvIL-6 does not inhibit but may instead potentiate normal cellular IL-6 signaling to B cells. These results demonstrate that RRV encodes an accessory protein with IL-6-like activity.

Interaction of granulocyte colony-stimulating factor (G-CSF) with its receptor. Evidence that Glu19 of G-CSF interacts with Arg288 of the receptor

Granulocyte colony-stimulating factor (G-CSF) forms a tetrameric complex with its receptor, comprising two G-CSF and two receptor molecules. The structure of the complex is unknown, and it is unclear whether there are one or two binding sites on G-CSF and the receptor. The immunoglobulin-like domain and the cytokine receptor homologous module of the receptor are involved in G-CSF binding, and Arg288 in the cytokine receptor homologous module is particularly important. To identify residues in G-CSF that interact with Arg288, selected charged residues in G-CSF were mutated to Ala. To clarify whether there are two binding sites, a chimeric receptor was created in which the Ig domain was replaced with that of the related receptor gp130. This chimera bound G-CSF but could not transduce a signal, consistent with failure of dimerization and loss of one binding site. The G-CSF mutants had reduced mitogenic activity on cells expressing wild-type receptor. When tested with the chimeric receptor, all G-CSF mutants except one (E46A) showed reduced binding, suggesting that Glu46 is important for interaction with the Ig domain. On cells expressing R288A receptor, all the G-CSF mutants except E19A showed reduced mitogenic activity, indicating that Glu19 of G-CSF interacts with Arg288 of the receptor.

Leukemia inhibitory factor, Interleukin 6, and other cytokines using the GP130 transducing receptor: roles in inflammation and injury

Inflammation refers to a complex set of mechanisms by which tissues respond to injury and infection. Among the many soluble mediators associated with this process, cytokines are known to be crucial in regulating a variety of cellular and molecular events. Leukemia inhibitory factor (LIF), interleukin 6 (IL-6), IL-11, and possibly other members of this cytokine family are key mediators in various inflammatory processes such as the acute-phase reaction, tissue damage, and infection. These cytokines can act in both pro-inflammatory and anti-inflammatory ways, depending on a number of variables. We emphasize here recent work utilizing knockout mice, which has highlighted the roles of LIF and IL-6, particularly in interactions between the immune and nervous systems.

The human cationic antimicrobial protein (hCAP18), a peptide antibiotic, is widely expressed in human squamous epithelia and colocalizes with interleukin-6

Peptide antibiotics are widespread in nature and, by providing a rapid first line of defense, may be key players in the innate immune system. Although epithelia are the main barriers shielding the internal environment from microorganisms, the role for peptide antibiotics in epithelial protection is unclear. We recently reported that the human cationic antimicrobial protein hCAP18, the precursor of the antimicrobial peptide called LL-37, is not expressed by normal human keratinocytes but is induced in various inflammatory skin disorders. In the present study we demonstrate that hCAP18 is consistently expressed at both mRNA and protein levels in squamous epithelia of the mouth, tongue, esophagus, cervix, and vagina in humans. The gene for hCAP18 contains promoter elements that are potentially regulated by interleukin-6, and our data further show a colocalization between interleukin-6 and hCAP18 expression in these tissues. Our finding that hCAP18 is widely produced in squamous epithelia suggests a role for this peptide in epithelial antimicrobial defense. Furthermore, colocalization with interleukin-6 indicates a potential local mechanism for the upregulation of hCAP18 at the epithelial surfaces.

Increase of interleukin-6 mRNA in the spinal cord following peripheral nerve injury in the rat: potential role of IL-6 in neuropathic pain

Interleukin-6 (IL-6) is a multifunctional cytokine whose actions include modulation of proliferation, differentiation, and maturation of hemapoietic progenitors and other cell lineages; growth regulation of certain carcinoma cell lines; and control of cellular metabolic activities. Initially described in terms of its activities in the immune system and inflammation, accumulating evidence supports an essential role of IL-6 in the development, differentiation, regeneration and degeneration of neurons in the peripheral and central nervous system. We have previously demonstrated that immunoreactive-like IL-6 protein is significantly elevated in the spinal cord in response to peripheral nerve injury that results in neuropathic pain behaviors in the rat. In the current study, our objective was to determine if the source of IL-6 protein was endogenous to the central nervous system by measuring any detectable increases in spinal IL-6 mRNA expression following established mononeuropathy procedures associated with neuropathic pain: spinal nerve cryoneurolysis (SPCN) or spinal nerve tight ligation (SPTL). Using in situ hybridization and a digoxigenin-labeled oligonucleotide, IL-6 mRNA in neurons was significantly elevated at 3 and 7 days post SPCN and 7 days post SPTL in both dorsal and ventral horns. The cellular localization of the IL-6 mRNA expression was predominately neuronal as confirmed by NeuN serial staining. For example, in the SPCN 7 day group, IL-6 mRNA cell profiles in the ipsilateral dorsal horn were significantly different from the normal group (38.7+/-12.8 vs. 4.89+/-1.6, p<0.001). These data demonstrate the central, spinal production of a proinflammatory cytokine in response to a peripheral nerve injury. In addition, these results add to the growing body of literature implicating these immune products, cytokines, as potential neuromodulators/neurotransmitters and provides further evidence for their role in the nociceptive processing which leads to chronic pain.

S-phase induction by interleukin-6 followed by chemotherapy in patients with refractory multiple myeloma

The plasma cell labeling index (PCLI) in patients with multiple myeloma (MM) is relatively low and this has been associated with the low rate of remission following chemotherapy. Interleukin-6 (IL-6) has been demonstrated to be a major growth factor of myeloma cells. In order to increase the S-phase proportion of myeloma cells, which might increase the sensitivity to chemotherapy, we gave rhIL-6 followed by chemotherapy to 15 myeloma patients with refractory disease. A total of 25 treatment cycles were administered since ten patients had two cycles. The rhIL-6 dose was 2.5 (n = 3), 5.0 (n = 6) and 10.0 microg/kg (n = 6) by subcutaneous injection once daily for 5 days and chemotherapy was administered on the last day of rhIL-6 injection. The effect of rhIL-6 treatment on labeling index (LI) was heterogeneous, but no statistically significant change was noted for this particular group as a whole. In two patients an increase (mean 7.7%) in LI of mononuclear bone marrow cells during the rhIL-6 treatment was demonstrated and in one patient a decrease of 2.8% was seen. Assessment of PCLI demonstrated an increase of 2.9% in one out of six patients and a decrease of 1.9% in one out of six patients. None of the 15 patients achieved remission according to standard criteria. During the rhIL-6 treatment, 14 of the 15 patients developed mild constitutional adverse events (AE) well known in patients treated with IL-6, and none of the AE in the subsequent chemotherapy phase were related to IL-6. In conclusion, our study demonstrated that rhIL-6 can be administered safely to patients with refractory MM, but the cell cycle recruitment approach was not sufficiently effective to be of clinical value.

A new type of cytokine receptor antagonist directly targeting gp130

The interleukin-6-type family of cytokines bind to receptor complexes that share gp130 as a common signal-transducing subunit. So far, receptor antagonists for interleukin-6-type cytokines have been constructed that still bind to the specific ligand binding subunit of the receptor complex, but have lost the ability to stimulate gp130. Such receptor antagonists compete for a specific receptor of a member of the cytokine family. Interleukin-6 only binds to gp130 when complexed with the interleukin-6 receptor that exists as a membrane bound and soluble molecule. Here we have constructed fusion proteins that consist of the soluble form of the human interleukin-6 receptor covalently linked to interleukin-6 receptor antagonists. These fusion proteins directly bind to gp130. Moreover, at concentrations of 10-50 nM they completely neutralize not only the biological activity of interleukin-6 but also of other cytokines of the interleukin-6-type family that act via gp130 homodimers or gp130/LIF-R heterodimers. Therefore, these gp130 targeting cytokine antagonists might be useful therapeutic tools in disease states that are related to cytokines of the interleukin-6 family.

Specific targeting of cytokine-secreting cells: a bispecific diabody recognizing human interleukin-6 and CD3 induces T cell-mediated killing

Cytokines have been implicated in the pathophysiology of many diseases. Although there have been many attempts to neutralize the activity of cytokines in vivo and in vitro, no strategies have been developed to specifically eliminate cells that overexpress cytokines. Considering the fact that cytokines in part remain cell associated on secretion, we have constructed a bispecific diabody consisting of a nonneutralizing scFv antibody recognizing human interleukin-6 (IL-6) and an scFv corresponding to the monoclonal antibody (mAb) OKT3, which recognizes and activates the human T cell receptor. Here we show that the diabody recognized both human IL-6 and human CD3. In the presence of human T cells, the diabody induced killing of human hepatoma cells that had been transfected with a human IL-6 cDNA. The extent of killing was dependent on the ratio of effector/target cells and increased with increasing concentrations of the diabody. Untransfected control cells or human hepatoma cells that secrete the IL-6-related cytokine leukemia inhibitory factor (LIF) remained unaffected. We conclude that diabodies recognizing cytokines can be used to specifically target cytokine-secreting cells.

The immunoglobulin-like module of gp130 is required for signaling by interleukin-6, but not by leukemia inhibitory factor

The transmembrane protein gp130 is a shared component of the receptor complexes for the interleukin-6 (IL-6)-type cytokines, which include IL-6, leukemia inhibitory factor (LIF) and oncostatin M (OSM). In addition to its role in the generation of high affinity receptors, gp130 is required for signal transduction by these cytokines. In the present study we have examined the role of the N-terminal located, extracellular immunoglobulin (Ig)-like module of gp130 in signal transduction by IL-6 and LIF. We have expressed wild-type human gp130 or three mutants in murine myeloid M1-UR21 cells that lack functional endogenous gp130 but express the IL-6 receptor (IL-6R) and the LIF receptor (LIFR). By measuring cellular responses, such as morphological changes upon differentiation, soft agar colony formation, and induction of tyrosine phosphorylation of the signal transducer and activator of transcription, STAT3, we show that signaling by IL-6, but not LIF, is significantly reduced by mutations in the Ig-like module of gp130. However, the binding of 125I-labeled IL-6 or LIF is not affected by these mutations. We also present evidence that the Ig-like module forms part of the epitope of an anti-gp130 monoclonal antibody that neutralizes the bioactivity of IL-6, but not of LIF or OSM. The data suggest that gp130-activation by IL-6 and LIF requires different regions of gp130, that the Ig-like module of gp130 may be required for IL-6-induced gp130 dimerization, and that the stoichiometry of the high affinity IL-6 receptor-complex differs from those of the receptor-complexes for LIF and OSM.

Recombinant human single chain Fv antibodies recognizing human interleukin-6. Specific targeting of cytokine-secreting cells

A human antibody library was displayed on the surface of filamentous bacteriophage and screened for binding to human interleukin-6 (IL-6). Two antibody-bearing phages were selected that bound IL-6. The complementary-determining region 3 loops of the variable heavy chains of these two antibodies differed in length and sequence and recognized two distinct epitopes. One of the single chain Fv fragments isolated (H1) was found to bind human (but not murine) IL-6 with an affinity comparable to that of the human IL-6 receptor. H1 also recognized newly synthesized human IL-6 intracellularly, as shown by indirect immunofluorescence. H1 did not neutralize human IL-6, and the H1 epitope was mapped to a region of IL-6 not involved in interactions with IL-6, IL-6 receptor, or the signal-transducing protein gp130. To target IL-6-secreting cells, we then constructed a bispecific antibody fragment (a diabody) comprising H1 and the antigen binding site of the T-cell activating monoclonal antibody OKT3. The diabody led to T-cell-mediated killing of cells secreting IL-6.

Analysis of the mechanism of action of anti-human interleukin-6 and anti-human interleukin-6 receptor-neutralising monoclonal antibodies

Anti-human interleukin-6 (human IL-6) and anti-human IL-6 receptor (IL-6R)-neutralising monoclonal antibodies (mAbs) are among the most promising human IL-6-specific inhibitors and have been shown to exert short-term beneficial effects in clinical trials. Simultaneous treatment with different anti-human IL-6 or anti-human IL-6R mAbs was recently suggested to be a potent way to inhibit the action of the cytokine in vivo. Although some of these mAbs are already used, their mechanisms of action and the location of their epitopes on the surface of human IL-6 and human IL-6R are still unknown. Here, we analysed the capacity of several anti-human IL-6 and anti-human IL-6R mAbs to inhibit the interaction between human IL-6, human IL-6R, and human glycoprotein 130 (gp130). We mapped the epitopes of several of these mAbs by studying their binding to human IL-6 and human IL-6R mutant proteins. Our results show that several anti-human IL-6 and anti-human IL-6R-neutralising mAbs block the binding between human IL-6 and human IL-6R, whereas others block the binding to gp130. We provide evidence that some of the latter mAbs inhibit interaction with gp130beta1, whereas others interfere with the binding to gp130beta2. Our results suggest that residues included in the C'D' loop of human IL-6R interact with gp130beta2.

Induction of interleukin-6 (IL-6) autoantibodies through vaccination with an engineered IL-6 receptor antagonist

Neutralization of cytokine activity by monoclonal antibodies or receptor antagonists is beneficial in the treatment of immune and neoplastic diseases, but the necessity for continuous parenteral delivery of these anticytokine agents poses considerable practical limitations. A viable alternative is to induce a neutralizing antibody response. Using transgenic mice with high circulating levels of human interleukin-6 (hIL-6), we show that injection of the hIL-6 receptor antagonist Sant1 (an IL-6 variant with seven amino-acid substitutions) induces a strong anti-hIL-6 antibody response. The elicited antibodies bind circulating hIL-6 with very high affinity, totally masking it, and neutralize hIL-6 bioactivity both in vitro and in vivo.

Molecular modeling-guided mutagenesis of the extracellular part of gp130 leads to the identification of contact sites in the interleukin-6 (IL-6).IL-6 receptor.gp130 complex

The transmembrane protein gp130 is involved in many cytokine-mediated cellular responses and acts therein as the signal-transducing subunit. In the case of interleukin-6 (IL-6), the signal-transducing complex is composed of the ligand IL-6, the IL-6 receptor (IL-6R, gp80, CD126), and at least two gp130 (CD130) molecules. The extracellular part of the signal transducer gp130 consists of six fibronectin type III-like domains. It has recently been shown that the three membrane distal domains bind to the IL-6. IL-6R complex. A structural model of the IL-6.IL-6R.gp130 complex enabled us to propose amino acid residues in these domains of gp130 interacting with IL-6 bound to its receptor. The proposed amino acid residues located in the B'C' loop (Val252) and in the F'G' loop (Gly306, Lys307) of domain 3 and in the hinge region (Tyr218) connecting domains 2 and 3 of gp130 were mutated to disturb ternary complex formation. Binding of wild type and mutants of the extracellular region of gp130 was studied by use of a co-precipitation assay and Scatchard analysis. All mutants showed decreased binding to the IL-6.IL-6R complex. Biological function of the membrane-bound gp130 mutants was studied by STAT (signal transducer and activator of transcription) activation in COS-7 cells and by proliferation of stably transfected Ba/F3 cells. Reduced binding of the mutants was accompanied by decreased biological activity. The combined approach of molecular modeling and site-directed mutagenesis has led to the identification of amino acid residues in gp130 required for complex formation with IL-6 and its receptor.

Interleukin-6 (IL-6)--a molecule with both beneficial and destructive potentials

Interleukin-6 (IL-6), a member of the neuropoietic cytokine family, initially was described in terms of its activities in the immune system and during inflammation. Accumulating evidence supports an essential role of IL-6 in the development, differentiation, regeneration and degeneration of neurons in the peripheral and central nervous system. Major sites of IL-6 synthesis are neurons and glial cells. Interleukin-6 functions are mediated by a specific receptor system composed of a binding site and a signal transducer. This receptor system can be modulated by a complex of IL-6 and soluble IL-6 receptor acting as agonist. The IL-6 can exert completely opposite actions on neurons, triggering either neuronal survival after injury or causing neuronal degeneration and cell death in disorders such as Alzheimer's disease. Development of selective IL-6 agonists and antagonists, as well as the usage of soluble IL-6 receptors, offers new possibilities for the treatment of neurodegenerative disorders. Furthermore, optimized genetic mouse models, including transgenic and knockout animals, should help to define the physiological and pathophysiological role of IL-6 in the nervous system.

Solution structure of recombinant human interleukin-6

Interleukin-6 (IL-6) is a 185 amino acid cytokine which exerts multiple biological effects in vivo and whose dysregulation underlies several disease processes. The solution structure of recombinant human interleukin-6 has now been determined using heteronuclear three and four-dimensional NMR spectroscopy. The structure of the molecule was determined using 3044 distance and torsion restraints derived by NMR spectroscopy to generate an ensemble of 32 structures using a combined distance geometry/simulated annealing protocol. The protein contains five alpha-helices interspersed with variable-length loops; four of these helices constitute a classical four-helix bundle with the fifth helix located in the CD loop. There were no distance violations greater than 0.3 A in any of the final 32 structures and the ensemble has an average-to-the-mean backbone root-mean-square deviation of 0.50 A for the core four-helix bundle. Although the amino-terminal 19 amino acids are disordered in solution, the remainder of the molecule has a well defined structure that shares many features displayed by other long-chain four-helix bundle cytokines. The high-resolution NMR structure of hIL-6 is used to rationalize available mutagenesis data in terms of a heteromeric receptor complex.

Interleukin-6: structure-function relationships

Interleukin-6 (IL-6) is a multifunctional cytokine that plays a central role in host defense due to its wide range of immune and hematopoietic activities and its potent ability to induce the acute phase response. Overexpression of IL-6 has been implicated in the pathology of a number of diseases including multiple myeloma, rheumatoid arthritis, Castleman's disease, psoriasis, and post-menopausal osteoporosis. Hence, selective antagonists of IL-6 action may offer therapeutic benefits. IL-6 is a member of the family of cytokines that includes interleukin-11, leukemia inhibitory factor, oncostatin M, cardiotrophin-1, and ciliary neurotrophic factor. Like the other members of this family, IL-6 induces growth or differentiation via a receptor-system that involves a specific receptor and the use of a shared signaling subunit, gp130. Identification of the regions of IL-6 that are involved in the interactions with the IL-6 receptor, and gp130 is an important first step in the rational manipulation of the effects of this cytokine for therapeutic benefit. In this review, we focus on the sites on IL-6 which interact with its low-affinity specific receptor, the IL-6 receptor, and the high-affinity converter gp130. A tentative model for the IL-6 hexameric receptor ligand complex is presented and discussed with respect to the mechanism of action of the other members of the IL-6 family of cytokines.

Analysis of the Human Interleukin-6/Human Interleukin-6 Receptor Binding Interface at the Amino Acid Level: Proposed Mechanism of Interaction

The interaction between interleukin-6 (IL-6) and IL-6 receptor (IL-6R) is the initial and most specific step in the IL-6 signaling pathway. Understanding its mechanism at the amino acid level is the basis for developing small IL-6–inhibiting molecules. We studied the human IL-6 (hIL-6)/hIL-6R binding interface by a combination of molecular modelling and site-directed mutagenesis. Our model suggests that the center of the interface between the two molecules consists of hydrophobic contacts predicted to account for most of the binding-free energy. These contacts can be regarded as a hydrophobic core shielded by hydrophilic residues that are also needed for recognition. Following this hypothesis, we altered in hIL-6 and hIL-6R residues predicted to reside in the contact region and to interact with each other. We studied the capacity of these mutants to form an IL-6/IL-6R complex and their ability to transduce the signal. This combined approach has led to the identification of certain residue-clusters in the binding interface and to a rational explanation of their specific interactions, suggesting therein a likely mechanism of complex formation. The results confirm the predictive model and strongly support our hypothesis. Comparison with other cytokines and their α-subunit receptors suggests that the structural location of certain binding sites are conserved.

Identification of residues in the putative 5th helical region of human interleukin-6, important for activation of the IL-6 signal transducer, gp130

We have previously shown that L58 in the putative 5th helical region of human interleukin-6 (IL-6) is important for activation of the IL-6 signal transducer gp130 [de Hon et al. (1995) FEBS Lett. 369, 187-191]. To further explore the importance of individual residues in this region for gp130 activation we have now combined Ala substitutions of residues E52, S53, S54, K55, E56, L58 and E60 with other substitutions in IL-6, known to affect gp130 activation (Q160E and T163P). The combination mutant protein with L58A completely lost the capacity to induce the proliferation of XG-1 myeloma cells, and could effectively antagonize wild type IL-6 activity on these cells. Moreover, the data suggest that besides L58, S54 particularly, but also E52, S53, K55 and E56 contribute to gp130 activation.