Association of serum IL-30 and soluble GP130 with the risk of psoriasis vulgaris.

Cytokines play a major role in the pathogenesis and progression of psoriasis. Interleukin (IL)-30 is a multifunctional cytokine. It binds to glycoprotein 130 (GP130) and inhibits the GP130 signaling pathways of psoriasis associated cytokines such as IL-6, IL-11, and IL-27. The study intended to assess associations of IL-30 and GP130 with the risk of psoriasis and Psoriasis Area Severity Index (PASI) score. Therefore, we measured the serum levels of IL-30 and GP130 in psoriasis patients and in a control group. An enzyme linked immunosorbent assay (ELISA) technique was used to measure IL-30 and GP130 levels in the serum of 43 patients and 43 normal controls. Statistical analysis of IL-30 and GP130 serum levels among patients and control groups and their correlation with PASI scores were performed. IL-30 serum levels showed a significant increase in patients with psoriasis compared with controls (p < 0.001) and a positive correlation with PASI scores. While serum levels of GP130 were not different in psoriatic patients and in the control group. Furthermore, the receiver operating characteristic (ROC) curve showed that IL-30 had diagnostic ability for prediction of psoriasis in comparison to controls, at cut of point of >14.34 showed a sensitivity of 97.7%, 100% specificity. In conclusion, IL-30 was elevated in psoriasis patients than controls, therefore, it can be considered a sensitive biomarker for diagnosis of psoriasis.

Molecular Design of Novel Inhibitor by Targeting IL-6Rα using Combined Pharmacophore and Experimentally Verified Plant Products with Scaffold-Hopping Techniques: A Dual Therapeutic Strategy for COVID-19 and Cancer.

The IL-6/IL-6R/gp130 complex serves as a significant indicator of cytokine release syndrome in COVID-19 and chronic inflammation, increasing the risk of cancer. Therefore, we identified IL-6Rα as a potential target to block gp130 interaction. Notably, there has been no reception of approval for an orally available drug to serve this purpose, to date. In this study, we targeted IL-6Rα to inhibit IL-6Rα/gp130 interaction. The selection of the lead candidate L821 involved the amalgamation of three drug discovery approaches. This library was screened employing tertiary structure-based pharmacophore models followed by molecular docking models, scaffold-hopping, MM/PBSA as well as MM/GBSA analysis, and assessments of pKi and ADMET properties. After evaluating the binding interactions with key amino acids, 15 potential ligands were chosen, with the top ligand undergoing further investigation by means of molecular dynamics simulations. Considering the stability of the complexes, the strong interactions observed between ligand and residues of IL-6Rα/gp130, and the favorable binding free energy calculations, L821 emerged as the prime candidate for inhibiting IL-6Rα. Notably, L821 exhibited a docking-based binding affinity of -9.5 kcal/mol. Our study presents L821 as a promising inhibitor for future in vitro analysis, potentially combatting SARS-CoV-2-related cytokine storms and serving as an oncogenic drug therapy.

Structural insights into the assembly and activation of the IL-27 signaling complex.

Interleukin 27 (IL-27) is a heterodimeric cytokine that elicits potent immunosuppressive responses. Comprised of EBI3 and p28 subunits, IL-27 binds GP130 and IL-27Rα receptor chains to activate the JAK/STAT signaling cascade. However, how these receptors recognize IL-27 and form a complex capable of phosphorylating JAK proteins remains unclear. Here, we used cryo electron microscopy (cryoEM) and AlphaFold modeling to solve the structure of the IL-27 receptor recognition complex. Our data show how IL-27 serves as a bridge connecting IL-27Rα (domains 1-2) with GP130 (domains 1-3) to initiate signaling. While both receptors contact the p28 component of the heterodimeric cytokine, EBI3 stabilizes the complex by binding a positively charged surface of IL-27Rα and Domain 1 of GP130. We find that assembly of the IL-27 receptor recognition complex is distinct from both IL-12 and IL-6 cytokine families and provides a mechanistic blueprint for tuning IL-27 pleiotropic actions.

Structure of the IL-27 quaternary receptor signaling complex.

Interleukin 27 (IL-27) is a heterodimeric cytokine that functions to constrain T cell-mediated inflammation and plays an important role in immune homeostasis. Binding of IL-27 to cell surface receptors, IL-27Rα and gp130, results in activation of receptor-associated Janus Kinases and nuclear translocation of Signal Transducer and Activator of Transcription 1 (STAT1) and STAT3 transcription factors. Despite the emerging therapeutic importance of this cytokine axis in cancer and autoimmunity, a molecular blueprint of the IL-27 receptor signaling complex, and its relation to other gp130/IL-12 family cytokines, is currently unclear. We used cryogenic-electron microscopy to determine the quaternary structure of IL-27, composed of p28 and Epstein-Barr Virus-Induced 3 (Ebi3) subunits, bound to receptors, IL-27Rα and gp130. The resulting 3.47 Å resolution structure revealed a three-site assembly mechanism nucleated by the central p28 subunit of the cytokine. The overall topology and molecular details of this binding are reminiscent of IL-6 but distinct from related heterodimeric cytokines IL-12 and IL-23. These results indicate distinct receptor assembly mechanisms used by heterodimeric cytokines with important consequences for targeted agonism and antagonism of IL-27 signaling.

Discovery and characterization of a monoclonal antibody targeting a conformational epitope of IL-6/IL-6Rα to inhibit IL-6/ IL-6Rα/gp130 hexameric signaling complex formation.

The functional interleukin 6 (IL-6) signaling complex is a hexameric structure composed of IL-6, IL-6Rα, and the signaling receptor gp130. There are three different modes of IL-6 signaling, classic signaling, trans-signaling, and trans-presentation, which are not functionally redundant and mediate pleiotropic effects on both physiological and pathophysiological states. Monoclonal antibodies against IL-6 or IL-6Rα have been successfully developed for clinical application. However, designing therapeutic interventions that block specific modes of IL-6 signaling in a pathologically relevant manner remains a great challenge. Here, we constructed a fusion protein Hyper-IL-6 (HyIL-6) composed of human IL-6 and IL-6Rα to develop specific blocking antibodies against the IL-6/IL-6Rα complex. We successfully screened the monoclonal antibody C14mab, which can bind to HyIL-6 with the binding constant 2.86 × 10-10 and significantly inhibit IL-6/IL-6Rα/gp130 complex formation. In vitro, C14mab effectively inhibited HyIL-6-stimulated signal transducer and activator of transcription 3 (STAT3) activation and related vascular endothelial growth factor (VEGF) induction. Moreover, C14mab efficaciously suppressed HyIL-6-induced acute phase response in vivo. Our data from hydrogen-deuterium exchange mass spectrometry demonstrate that C14mab mainly binds to site IIIa of IL-6 and blocks the final step in the interaction between gp130 and IL-6/IL-6Rα complex. Additionally, data from enzyme-linked immunosorbent assays and kinetics assays indicate that C14mab interacts simultaneously with IL-6 and IL-6Rα, while it does not interact with IL-6Rα alone. The unique features of C14mab may offer a novel alternative for IL-6 blockade and illuminate a better therapeutic intervention targeting IL-6.

A Hybrid Soluble gp130/Spike-Nanobody Fusion Protein Simultaneously Blocks Interleukin-6 trans-Signaling and Cellular Infection with SARS-CoV-2.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can induce mild to life-threatening symptoms. Especially individuals over 60 years of age or with underlying comorbidities, including heart or lung disease and diabetes, or immunocompromised patients are at a higher risk. Fatal multiorgan damage in coronavirus disease 2019 (COVID-19) patients can be attributed to an interleukin-6 (IL-6)-dominated cytokine storm. Consequently, IL-6 receptor (IL-6R) monoclonal antibody treatment for severe COVID-19 cases has been approved for therapy. High concentrations of soluble IL-6R (sIL-6R) were found in COVID-19 intensive care unit patients, suggesting the involvement of IL-6 trans-signaling in disease pathology. Here, in analogy to bispecific antibodies (bsAbs), we developed the first bispecific IL-6 trans-signaling inhibitor, c19s130Fc, which blocks viral infection and IL-6 trans-signaling. c19s130Fc is a designer protein of the IL-6 trans-signaling inhibitor cs130 fused to a single-domain nanobody directed against the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. c19s130Fc binds with high affinity to IL-6:sIL-6R complexes as well as the spike protein of SARS-CoV-2, as shown by surface plasmon resonance. Using cell-based assays, we demonstrate that c19s130Fc blocks IL-6 trans-signaling-induced proliferation and STAT3 phosphorylation in Ba/F3-gp130 cells as well as SARS-CoV-2 infection and STAT3 phosphorylation in Vero cells. Taken together, c19s130Fc represents a new class of bispecific inhibitors consisting of a soluble cytokine receptor fused to antiviral nanobodies and principally demonstrates the multifunctionalization of trans-signaling inhibitors. IMPORTANCE The availability of effective SARS-CoV-2 vaccines is a large step forward in managing the pandemic situation. In addition, therapeutic options, e.g., monoclonal antibodies to prevent viral cell entry and anti-inflammatory therapies, including glucocorticoid treatment, are currently developed or in clinical use to treat already infected patients. Here, we report a novel dual-specificity inhibitor to simultaneously target SARS-CoV-2 infection and virus-induced hyperinflammation. This was achieved by fusing an inhibitor of viral cell entry with a molecule blocking IL-6, a key mediator of SARS-CoV-2-induced hyperinflammation. Through this dual action, this molecule may have the potential to efficiently ameliorate symptoms of COVID-19 in infected individuals.

Functional and structural analysis of cytokine-selective IL6ST defects that cause recessive hyper-IgE syndrome.

BACKGROUND: Biallelic variants in IL6ST, encoding GP130, cause a recessive form of hyper-IgE syndrome (HIES) characterized by high IgE level, eosinophilia, defective acute phase response, susceptibility to bacterial infections, and skeletal abnormalities due to cytokine-selective loss of function in GP130, with defective IL-6 and IL-11 and variable oncostatin M (OSM) and IL-27 levels but sparing leukemia inhibitory factor (LIF) signaling. OBJECTIVE: Our aim was to understand the functional and structural impact of recessive HIES-associated IL6ST variants. METHODS: We investigated a patient with HIES by using exome, genome, and RNA sequencing. Functional assays assessed IL-6, IL-11, IL-27, OSM, LIF, CT-1, CLC, and CNTF signaling. Molecular dynamics simulations and structural modeling of GP130 cytokine receptor complexes were performed. RESULTS: We identified a patient with compound heterozygous novel missense variants in IL6ST (p.Ala517Pro and the exon-skipping null variant p.Gly484_Pro518delinsArg). The p.Ala517Pro variant resulted in a more profound IL-6- and IL-11-dominated signaling defect than did the previously identified recessive HIES IL6ST variants p.Asn404Tyr and p.Pro498Leu. Molecular dynamics simulations suggested that the p.Ala517Pro and p.Asn404Tyr variants result in increased flexibility of the extracellular membrane-proximal domains of GP130. We propose a structural model that explains the cytokine selectivity of pathogenic IL6ST variants that result in recessive HIES. The variants destabilized the conformation of the hexameric cytokine receptor complexes, whereas the trimeric LIF-GP130-LIFR complex remained stable through an additional membrane-proximal interaction. Deletion of this membrane-proximal interaction site in GP130 consequently caused additional defective LIF signaling and Stüve-Wiedemann syndrome. CONCLUSION: Our data provide a structural basis to understand clinical phenotypes in patients with IL6ST variants.

Potent antitumor effects of cell-penetrating peptides targeting STAT3 axis.

To date, there are no inhibitors that directly and specifically target activated STAT3 and c-Myc in the clinic. Although peptide-based inhibitors can selectively block activated targets, their clinical usage is limited because of low cell penetration and/or serum stability. Here, we generated cell-penetrating acetylated (acet.) STAT3, c-Myc, and Gp130 targeting peptides by attaching phosphorothioated (PS) polymer backbone to peptides. The cell-penetrating peptides efficiently penetrated cells and inhibited activation of the intended targets and their downstream genes. Locally or systemically treating tumor-bearing mice with PS-acet.-STAT3 peptide at low concentrations effectively blocked STAT3 in vivo, resulting in significant antitumor effects in 2 human xenograft models. Moreover, PS-acet.-STAT3 peptide penetrated and activated splenic CD8+ T cells in vitro. Treating immune-competent mice bearing mouse melanoma with PS-acet.-STAT3 peptide inhibited STAT3 in tumor-infiltrating T cells, downregulating tumor-infiltrating CD4+ T regulatory cells while activating CD8+ T effector cells. Similarly, systemic injections of the cell-penetrating c-Myc and Gp130 peptides prevented pancreatic tumor growth and induced antitumor immune responses. Taken together, we have developed therapeutic peptides that effectively and specifically block challenging cancer targets, resulting in antitumor effects through both direct tumor cell killing and indirectly through antitumor immune responses.

Kinetics of cytokine receptor trafficking determine signaling and functional selectivity.

Cytokines activate signaling via assembly of cell surface receptors, but it is unclear whether modulation of cytokine-receptor binding parameters can modify biological outcomes. We have engineered IL-6 variants with different affinities to gp130 to investigate how cytokine receptor binding dwell-times influence functional selectivity. Engineered IL-6 variants showed a range of signaling amplitudes and induced biased signaling, with changes in receptor binding dwell-times affecting more profoundly STAT1 than STAT3 phosphorylation. We show that this differential signaling arises from defective translocation of ligand-gp130 complexes to the endosomal compartment and competitive STAT1/STAT3 binding to phospho-tyrosines in gp130, and results in unique patterns of STAT3 binding to chromatin. This leads to a graded gene expression response and differences in ex vivo differentiation of Th17, Th1 and Treg cells. These results provide a molecular understanding of signaling biased by cytokine receptors, and demonstrate that manipulation of signaling thresholds is a useful strategy to decouple cytokine functional pleiotropy.

The multi-site docking protein Grb2-associated binder 1 (Gab1) enhances interleukin-6-induced MAPK-pathway activation in an SHP2-, Grb2-, and time-dependent manner.

BACKGROUND: Cytokine-dependent activation of signalling pathways is tightly orchestrated. The spatiotemporal activation of signalling pathways dictates the specific physiological responses to cytokines. Dysregulated signalling accounts for neoplastic, developmental, and inflammatory diseases. Grb2-associated binder (Gab) family proteins are multi-site docking proteins, which expand cytokine-induced signal transduction in a spatial- and time-dependent manner by coordinating the recruitment of proteins involved in mitogen activated protein kinase (MAPK)/extracellular-signal regulated kinase (ERK) and phosphatidyl-inositol-3-kinase (PI3K) signalling. Interaction of Gab family proteins with these signalling proteins determines strength, duration and localization of active signalling cascades. However, the underlying molecular mechanisms of signal orchestration by Gab family proteins in IL-6-induced signalling are only scarcely understood. METHODS: We performed kinetic analyses of interleukin-6 (IL-6)-induced MAPK activation and analysed downstream responses. We compared signalling in wild-type cells, Gab1 knock-out cells, those reconstituted to express Gab1 mutants, and cells expressing gp130 receptors or receptor mutants. RESULTS: Interleukin-6-induced MAPK pathway activation can be sub-divided into an early Gab1-independent and a subsequent Gab1-dependent phase. Early Gab1-independent MAPK activation is critical for the subsequent initiation of Gab1-dependent amplification of MAPK pathway activation and requires binding of SH2 domain-containing phosphatase 2 (SHP2) to the interleukin-6 receptor complex. Subsequent and coordinated recruitment of Grb2 and SHP2 to Gab1 is essential for Gab1-dependent amplification of IL-6-induced late MAPK pathway activation and subsequent gene expression. CONCLUSIONS: Overall, we elaborated the molecular requirements for Gab1-dependent, spatiotemporal orchestration of interleukin-6-dependent MAPK signalling. We discriminated IL-6-induced Gab1-independent, early activation of MAPK signalling and Gab1-dependent, sustained activation of MAPK signalling.

Physical proximity and functional cooperation of glycoprotein 130 and glycoprotein VI in platelet membrane lipid rafts.

OBJECTIVE: Clinical and laboratory studies have demonstrated that platelets become hyperactive and prothrombotic in conditions of inflammation. We have previously shown that the proinflammatory cytokine interleukin (IL)-6 forms a complex with soluble IL-6 receptor α (sIL-6Rα) to prime platelets for activation by subthreshold concentrations of collagen. Upon being stimulated with collagen, the transcription factor signal transducer and activator of transcription (STAT) 3 in platelets is phosphorylated and dimerized to act as a protein scaffold to facilitate the catalytic action between the kinase Syk and the substrate phospholipase Cγ2 (PLCγ2) in collagen-induced signaling. However, it remains unknown how collagen induces phosphorylation and dimerization of STAT3. METHODS AND RESULTS: We conducted complementary in vitro experiments to show that the IL-6 receptor subunit glycoprotein 130 (GP130) was in physical proximity to the collagen receptor glycoprotein VI (GPVI in membrane lipid rafts of platelets. This proximity allows collagen to induce STAT3 activation and dimerization, and the IL-6-sIL-6Rα complex to activate the kinase Syk and the substrate PLCγ2 in the GPVI signal pathway, resulting in an enhanced platelet response to collagen. Disrupting lipid rafts or blocking GP130-Janus tyrosine kinase (JAK)-STAT3 signaling abolished the cross-activation and reduced platelet reactivity to collagen. CONCLUSION: These results demonstrate cross-talk between collagen and IL-6 signal pathways. This cross-talk could potentially provide a novel mechanism for inflammation-induced platelet hyperactivity, so the IL-6-GP130-JAK-STAT3 pathway has been identified as a potential target to block this hyperactivity.

Repurposing the selective estrogen receptor modulator bazedoxifene to suppress gastrointestinal cancer growth.

Excessive signaling through gp130, the shared receptor for the interleukin (IL)6 family of cytokines, is a common hallmark in solid malignancies and promotes their progression. Here, we established the in vivo utility of bazedoxifene, a steroid analog clinically approved for the treatment of osteoporosis, to suppress gp130-dependent tumor growth of the gastrointestinal epithelium. Bazedoxifene administration reduced gastric tumor burden in gp130Y757F mice, where tumors arise exclusively through excessive gp130/STAT3 signaling in response to the IL6 family cytokine IL11. Likewise, in mouse models of sporadic colon and intestinal cancers, which arise from oncogenic mutations in the tumor suppressor gene Apc and the associated ß-catenin/canonical WNT pathway, bazedoxifene treatment reduces tumor burden. Consistent with the proposed orthogonal tumor-promoting activity of IL11-dependent gp130/STAT3 signaling, tumors of bazedoxifene-treated Apc-mutant mice retain excessive nuclear accumulation of ß-catenin and aberrant WNT pathway activation. Likewise, bazedoxifene treatment of human colon cancer cells harboring mutant APC did not reduce aberrant canonical WNT signaling, but suppressed IL11-dependent STAT3 signaling. Our findings provide compelling proof of concept to support the repurposing of bazedoxifene for the treatment of gastrointestinal cancers in which IL11 plays a tumor-promoting role.

Selective loss of function variants in IL6ST cause Hyper-IgE syndrome with distinct impairments of T-cell phenotype and function.

Hyper-IgE syndromes comprise a group of inborn errors of immunity. STAT3-deficient hyper-IgE syndrome is characterized by elevated serum IgE levels, recurrent infections and eczema, and characteristic skeletal anomalies. A loss-of-function biallelic mutation in IL6ST encoding the GP130 receptor subunit (p.N404Y) has very recently been identified in a singleton patient (herein referred to as PN404Y) as a novel etiology of hyper-IgE syndrome. Here, we studied a patient with hyper-IgE syndrome caused by a novel homozygous mutation in IL6ST (p.P498L; patient herein referred to as PP498L) leading to abrogated GP130 signaling after stimulation with IL-6 and IL-27 in peripheral blood mononuclear cells as well as IL-6 and IL-11 in fibroblasts. Extending the initial identification of selective GP130 deficiency, we aimed to dissect the effects of aberrant cytokine signaling on T-helper cell differentiation in both patients. Our results reveal the importance of IL-6 signaling for the development of CCR6-expressing memory CD4+ T cells (including T-helper 17-enriched subsets) and non-conventional CD8+T cells which were reduced in both patients. Downstream functional analysis of the GP130 mutants (p.N404Y and p.P498L) have shown differences in response to IL-27, with the p.P498L mutation having a more severe effect that is reflected by reduced T-helper 1 cells in this patient (PP498L) only. Collectively, our data suggest that characteristic features of GP130-deficient hyper-IgE syndrome phenotype are IL-6 and IL-11 dominated, and indicate selective roles of aberrant IL-6 and IL-27 signaling on the differentiation of T-cell subsets.

The SNP rs4252548 (R112H) which is associated with reduced human height compromises the stability of IL-11.

Height is a complex human phenotype that is influenced by variations in a high number of genes. Recently, a single nucleotide polymorphism (SNP) within IL11 (rs4252548) has been described to be associated with height in adults of European ancestry. This coding SNP leads to the exchange of Arg-112 to His-112 within the cytokine Interleukin-11 (IL-11), which has a well-established role in osteoclast development and bone turnover. The functional consequences of the R112H mutation are unknown so far. In this study, we show by molecular replacement that Arg-112 does not participate in binding of IL-11 to its receptors IL-11R and glycoprotein 130 (gp130). Recombinant IL-11 R112H expressed in E. coli displays a correct four-helix-bundle folding topology, and binds with similar affinity to IL-11R and the IL-11/IL-11R/gp130 complex. IL-11 R112H induces cell proliferation and phosphorylation of the downstream transcription factor STAT3 indistinguishable from IL-11. However, IL-11 R112H fails to support the survival of osteoclast progenitor cells and is less thermally stable, which is caused by the loss of the positive charge on the protein surface since protonation of the histidine side chain recovers stability.

Bazedoxifene as a Novel GP130 Inhibitor for Pancreatic Cancer Therapy.

The IL6/GP130/STAT3 pathway is crucial for tumorigenesis in multiple cancer types, including pancreatic cancer, and presents as a viable target for cancer therapy. We reported Bazedoxifene, which is approved as a selective estrogen modulator by FDA, as a novel inhibitor of IL6/GP130 protein-protein interactions using multiple ligand simultaneous docking and drug repositioning approaches. STAT3 is one of the major downstream effectors of IL6/GP130. Here, we observed Bazedoxifene inhibited STAT3 phosphorylation and STAT3 DNA binding, induced apoptosis, and suppressed tumor growth in pancreatic cancer cells with persistent IL6/GP130/STAT3 signaling in vitro and in vivo In addition, IL6, but not INFγ, rescued Bazedoxifene-mediated reduction of cell viability. Bazedoxifene also inhibited STAT3 phosphorylation induced by IL6 and IL11, but not by OSM or STAT1 phosphorylation induced by INFγ in pancreatic cancer cells, suggesting that Bazedoxifene inhibits the GP130/STAT3 pathway mediated by IL6 and IL11. Furthermore, Bazedoxifene combined with paclitaxel or gemcitabine synergistically inhibited cell viability and cell migration in pancreatic cancer cells. These results indicate that Bazedoxifene is a potential agent and can generate synergism when combined with conventional chemotherapy in human pancreatic cancer cells and tumor xenograft in mice. Therefore, our results support that Bazedoxifene as a novel inhibitor of GP130 signaling and may be a potential and safe therapeutic agent for human pancreatic cancer therapy. Mol Cancer Ther; 15(11); 2609-19. ©2016 AACR.

Study of Fibronectin Type III-Like Domains Role in Activation of gp130 Receptor.

Chimeric gp130 receptors were produced to study the role of three fibronectin type III-like domains in activation of gp130 receptor machinery. The ligand-induced dimerization of gp130 was sufficient to trigger STAT3 signaling pathway. These findings can be used as the basis in designing novel therapeutic gp130 inhibitors.

Interleukin-11: A Multifunctional Cytokine with Intrinsically Disordered Regions.

Cytokine interleukin-11 (IL-11) is a multifunctional protein with diverse roles in the normal cell signaling and in various pathologies. The structure of IL-11 is characterized by a four-helix bundle motif comprising two pairs of antiparallel α-helices arranged in an up-up-down-down configuration. Evaluation of the intrinsic disorder predisposition of human IL-11 by several computational tools clearly shows that this protein is predicted to have functional disordered regions potentially involved in interaction with natural binding partners. Signaling by IL-11 proceeds via an interaction of the protein with its membrane-specific receptor IL-11Rα and a subsequent interaction of the complex with the transmembrane signal-transducing receptor GP130. Cytoplasmic domain of IL-11Rα is predicted to be very disordered, and noticeable amount of disorder is present even in the large extracellular domain of the protein. GP130 is also predicted to have long disordered region that is located at the C-terminal of the protein and is expected to have several disorder-based binding sites. It shows that intrinsic disorder might play an important role in functioning of this signaling machine. A specific subset of the calcium sensor proteins (calmodulin, S100P, S100B, NCS-1, GCAP-1/2) exhibits metal-dependent binding of IL-11 with dissociation constants in a range of 1-19 µM, and the structural features of their hinge regions likely ensure selectivity and calcium sensitivity of IL-11 binding to the EF-hand proteins studied. IL-11 exhibits multiple effects on hematopoietic and non-hematopoietic systems. It plays a major role in orchestrating complex processes of tumor development and progression.

A soluble form of the interleukin-6 family signal transducer gp130 is dimerized via a C-terminal disulfide bridge resulting from alternative mRNA splicing.

Interleukin-6 (IL-6) signaling can be divided into classic signaling (via the membrane-bound IL-6 receptor, IL-6R) and trans-signaling (via the soluble IL-6R, sIL-6R), and both modes of signaling activate cells via a homodimer of the ubiquitously expressed ß-receptor glycoprotein 130 (gp130). IL-6 trans-signaling is responsible for most of the pro-inflammatory activities of IL-6 and plays a role in many inflammatory diseases including inflammation-driven cancers. IL-6 trans-signaling can be selectively inhibited by soluble forms of gp130. To date, three forms of sgp130 (full-length sgp130, sgp130-RAPS and sgp130-E10) with different molecular weight have been described, which originate from alternative splicing or alternative polyadenylation of the gp130 mRNA. All these proteins are capable of blocking signaling of the IL-6/sIL-6R complex, albeit with different efficacy. The full length form of sgp130 comprises the domains D1 to D6 and a short unique C-terminus which arises from alternative splicing. In the present study, we analyze the role of a unique cysteine residue (Cys-628) within this C-terminus, which is contained neither in the membrane-bound gp130 nor in the two other sgp130 forms. Full-length sgp130 can form a disulfide-linked dimer via this cysteine residue. These natural sgp130 dimers are absent under reducing conditions or in a sgp130 C628A mutant. Although the disulfide-dimerized sgp130 represents only a small fraction of the total amount of sgp130 and, thus, may appear to be dispensable for the global inhibitory activities of sgp130 in the circulation, it may represent a further possibility to modulate gradients of sgp130 with different properties depending on the local redox potential in a cell- or tissue-dependent manner.

Modular organization of Interleukin-6 and Interleukin-11 α-receptors.

Interleukin (IL)-6 and IL-11 are the only canonical members of the IL-6 family of cytokines that induce signaling through a homodimer of the common ß-receptor glycoprotein (gp)130. A pre-requisite for signal transduction is the initial binding of the cytokines to their unique α-receptors, IL-6R and IL-11R. The cell-type specific expression of the two receptors determines the target cells of IL-6 and IL-11, because gp130 is ubiquitously expressed. However, ciliary neurotrophic factor (CNTF) and IL-27p28/IL-30 have been described as additional ligands for the IL-6R, underlining a remarkable plasticity among the cytokines of the IL-6 family and their receptors. In this study, we show that neither IL-6 nor IL-11 can bind to and signal through the α-receptor of the respective other cytokine. We further create eight chimeric IL-6/IL-11 receptors, which are all biologically active. We find that the domains D1 to D3, which contain the cytokine binding module (CBM), determine which cytokine can activate the chimeric receptor, whereas the stalk region, the transmembrane region, or the intracellular region do not participate in the ligand selectivity of the receptor and are therefore interchangeable between IL-6R and IL-11R. These results suggest a modular organization of the IL-6R and IL-11R, and a similar signal transduction complex of the two cytokines.

Novel Insights into Interleukin 6 (IL-6) Cis- and Trans-signaling Pathways by Differentially Manipulating the Assembly of the IL-6 Signaling Complex.

The IL-6 signaling complex is described as a hexamer, formed by the association of two IL-6·IL-6 receptor (IL-6R)·gp130 trimers, with gp130 being the signal transducer inducing cis- and trans-mediated signaling via a membrane-bound or soluble form of the IL-6R, respectively. 25F10 is an anti-mouse IL-6R mAb that binds to both membrane-bound IL-6R and soluble IL-6R with the unique property of specifically inhibiting trans-mediated signaling events. In this study, epitope mapping revealed that 25F10 interacts at site IIb of IL-6R but allows the binding of IL-6 to the IL-6R and the recruitment of gp130, forming a trimer complex. Binding of 25F10 to IL-6R prevented the formation of the hexameric complex obligate for trans-mediated signaling, suggesting that the cis- and trans-modes of IL-6 signaling adopt different mechanisms for receptor complex assembly. To study this phenomenon also in the human system, we developed NI-1201, a mAb that targets, in the human IL-6R sequence, the epitope recognized by 25F10 for mice. Interestingly, NI-1201, however, did not selectively inhibit human IL-6 trans-signaling, although both mAbs produced beneficial outcomes in conditions of exacerbated IL-6 as compared with a site I-directed mAb. These findings shed light on the complexity of IL-6 signaling. First, triggering cis- versus trans-mediated IL-6 signaling occurs via distinctive mechanisms for receptor complex assembly in mice. Second, the formation of the receptor complex leading to cis- and trans-signaling biology in mice and humans is different, and this should be taken into account when developing strategies to inhibit IL-6 clinically.