The hepatic interleukin-6 receptor. Studies on its structure and regulation by phorbol 12-myristate 13-acetate-dexamethasone

Quantification of membrane-bound cytokine receptors by calibrated flow cytometry

We present a protocol for quantifying the expression of the receptor gp130 using a calibrated flow cytometric approach. We describe pitfalls for receptor quantification such as titration of primary antibodies and standardizing cell culture. Receptors are stained with primary antibodies and fluorophore-coupled secondary antibodies. Beads covered with defined numbers of immunoglobulin G stained with fluorophore-coupled secondary antibodies serve as calibrators. In this way, the fluorescence intensity of cells is converted to the number of receptors on the cell surface. For complete details on the use and execution of this protocol, please refer to Reeh et al. (2019).1.

Therapeutic Targeting of IL-11 for Chronic Lung Disease

Interleukin (IL)-11 was originally recognized as an immunomodulatory and hematopoiesis-inducing cytokine. However, although IL-11 is typically not found in healthy individuals, it is now becoming evident that IL-11 may play a role in diverse pulmonary conditions, including IPF, asthma, and lung cancer. Additionally, experimental strategies targeting IL-11, such as humanized antibodies, have recently been developed, revealing the therapeutic potential of IL-11. Thus, further insight into the underlying mechanisms of IL-11 in lung disease may lead to the ability to interfere with pathological conditions that have a clear need for disease-modifying treatments, such as IPF. In this review, we outline the effects, expression, signaling, and crosstalk of IL-11 and focus on its role in lung disease and its potential as a therapeutic target.

Different roles of interleukin 6 and interleukin 11 in the liver: implications for therapy

The interleukin 6 (IL6) family of proteins regulate important cellular processes and act through a variety of signaling pathways via a shared gp130 receptor. In the liver, there is a large body of evidence showing a protective and pro-regenerative role for IL6 cis and trans signaling. While a few studies suggest a pathological role for IL6 trans-signaling in the liver. IL11 is often thought of as similar to IL6 and redundancy has been inferred. However, recent studies reveal that IL6R and IL11RA are expressed on dissimilar cell types and these cytokines actually have very different roles in biology and pathology. In the liver, IL6R is mostly expressed on immune cells, whereas IL11RA is highly expressed on hepatocytes and hepatic stellate cells, both of which exhibit autocrine IL11 activity. In contrast to the beneficial effects of IL6 in the liver, IL11 causes liver disease and its expression in stromal and parenchymal cells leads to fibrosis, inflammation, steatosis and hepatic failure. In this review, we address IL6 and IL11 in the context of liver function. We end by discussing the possibility of IL6 gain-of-function versus IL11 inhibition as therapeutic approaches to treat liver disease. 1,2.

Interleukin-6 signaling requires only few IL-6 molecules: Relation to physiological concentrations of extracellular IL-6

Introduction

The aim of this study was to give quantitative insight into the number of cytokine molecules needed to activate a target cell and relate this to the physiological consequences of the amounts of cytokines typically detectable in humans. As a model system blood interleukin‐6 (IL‐6) was chosen since this cytokine is one of the most studied and clinically monitored cytokines, and because of the tools for the present investigations such as fully bioactive iodinated recombinant IL‐6, cellular cytokine binding assays, and bioassays have been thoroughly validated.

Methods

The key intermediates of the basic equilibrium principles that govern cytokine binding and exchange were deduced and applied on concrete estimations of cellular and extracellular IL‐6 binding in the bloodstream based on experimental binding data and data from the literature. In parallel, in vitro cellular IL‐6 binding data was substantiated by paired measurements of IL‐6 bioactivity on IL‐6 sensitive B9 hybridoma cells.

Results

Blood leucocytes and B9 cells expressed 50 to 300, 10 to 20 picomolar affinity, IL‐6 binding sites per cell and at physiological concentrations of IL‐6 less than 10 IL‐6 molecules seemed to be bound to blood cells. Nonetheless, binding off as few as four IL‐6 molecules per cell seemed to result in statistically significant bioactivity, whereas binding of 16 IL‐6 molecules triggered extensive cellular responses.

Conclusion

Together, the estimations and the measurements support the notion that target cells with more than 100 bioactive cytokine receptors per cell, such as T cells and hepatocytes, are likely to be under steady and substantial cytokine‐induced endocrine activation.

Response to IL-6 trans- and IL-6 classic signalling is determined by the ratio of the IL-6 receptor α to gp130 expression: fusing experimental insights and dynamic modelling

BACKGROUND

Interleukin-6 is a pleiotropic cytokine with high clinical relevance and an important mediator of cellular communication, orchestrating both pro- and anti-inflammatory processes. Interleukin-6-induced signalling is initiated by binding of IL-6 to the IL-6 receptor α and subsequent binding to the signal transducing receptor subunit gp130. This active receptor complex initiates signalling through the Janus kinase/signal transducer and activator of transcription pathway. Of note, IL-6 receptor α exists in a soluble and a transmembrane form. Binding of IL-6 to membrane-bound IL-6 receptor α induces anti-inflammatory classic signalling, whereas binding of IL-6 to soluble IL-6 receptor α induces pro-inflammatory trans-signalling. Trans-signalling has been described to be markedly stronger than classic signalling. Understanding the molecular mechanisms that drive differences between trans- and classic signalling is important for the design of trans-signalling-specific therapies. These differences will be addressed here using a combination of dynamic mathematical modelling and molecular biology.

METHODS

We apply an iterative systems biology approach using set-based modelling and validation approaches combined with quantitative biochemical and cell biological analyses.

RESULTS

The combination of experimental analyses and dynamic modelling allows to relate the observed differences between IL-6-induced trans- and classic signalling to cell-type specific differences in the expression and ratios of the individual subunits of the IL-6 receptor complex. Canonical intracellular Jak/STAT signalling is indifferent in IL-6-induced trans- and classic signalling.

CONCLUSION

This study contributes to the understanding of molecular mechanisms of IL-6 signal transduction and underlines the power of combined dynamical modelling, model-based validation and biological experiments. The opposing pro- and anti-inflammatory responses initiated by IL-6 trans- and classic signalling depend solely on the expression ratios of the subunits of the entire receptor complex. By pointing out the importance of the receptor expression ratio for the strength of IL-6 signalling this study lays a foundation for future precision medicine approaches that aim to selectively block pro-inflammatory trans-signalling. Furthermore, the derived models can be used for future therapy design.

Multiplicity of Glucocorticoid Action in Inhibiting Allograft Rejection

Glucocorticoids (GCs) are used as immunosuppressive and antiinflammatory agents in organ transplantation and in treating autoimmune diseases and inflammatory disorders. GCs were shown to exert their antiproliferative effects directly through blockade of certain elements of an early membrane-associated signal transduction pathway, modulation of the expression of select adhesion molecules, and by suppression of cytokine synthesis and action. GCs may act indirectly by inducing lipocortin synthesis, which in turn, inhibits arachidonic acid release from membrane-bound stores, and also by inducing transforming growth factor (TGF)-β expression that subsequently blocks cytokine synthesis and T cell activation. Furthermore, by preferentially inhibiting the production of Th1 cytokines, GCs may enhance Th2 cell activity and, hence, precipitate a long-lasting state of tolerance through a preferential promotion of a Th2 cytokine-secreting profile. In exerting their antiproliferative effects, GCs influence both transcriptional and posttranscriptional events by binding their cytosolic receptor (GR), which subsequently binds the promoter region of cytokine genes on select DNA sites compatible with the GCs responsible elements (GRE) motif. In addition to direct DNA binding, GCs may also directly bind to, and hence antagonize, nuclear factors required for efficient gene expression, thereby markedly reducing transcriptional rate. The pleiotrophy of the GCs action, coupled with the diverse experimental conditions employed in assessing the GCs effects, indicate that GCs may utilize more than one mechanism in inhibiting T cell activation, and warrant careful scrutiny in assigning a mechanism by which GCs exert their antiproliferative effects. © 1998 Elsevier Science Inc.

Peripheral blood mononuclear cell proliferation and cytokine production in sheep as affected by cortisol level and duration of stress

A large number of studies recognize glucocorticoids (Gc) as suppressors of inflammation; Gc exert an important role in coordinating the magnitude and duration of host immune responses. In the present in vitro investigation, we tested incremental levels of cortisol to verify the immunosuppressive or immunopermissive role of cortisol in sheep peripheral blood mononuclear cells (PBMC) after acute and chronic stress. Phytohemagglutinin (PHA)-stimulated PBMC were cultured for 24h and 96h at 37°C with 5% of CO₂ and varying cortisol levels: 10 ng/mL (baseline), 100 ng/mL (physiological poststressor), and 1,000 ng/mL [hyperactivated hypothalamic-pituitary-adrenal (HPA) axis]. The cell-free supernatants were collected for determination of IL-6, IL-1β, and IL-10 by ELISA, and the bromodeoxyuridine assay was performed on cells. Physiological cortisol concentration negatively affected the levels of IL-6 secreted by PBMC, resulting in increased cell proliferation after acute stress (24h of incubation). However, physiological cortisol concentration exhibited a reduction in cell proliferation induced by increased levels of IL-6 secreted by PBMC during chronic stress (96h of incubation). The cortisol concentration representing a hyperactivated HPA axis led to a reduction in cell proliferation after acute stress, which was probably induced by the elevated IL-10 production. Our results demonstrate that in sheep the effect of Gc on the immune system was related to the magnitude and the duration of stress. In particular, cortisol levels higher than physiological concentrations suppressed cell proliferation soon after acute stress. Instead, the physiological poststressor concentration of cortisol affected the immune responses in a bidirectional manner depending on the duration of the stressor.

Systems biology of IL-6, IL-12 family cytokines

Interleukin-6-type cytokines play important roles in the communication between cells of multicellular organisms. They are involved in the regulation of complex cellular processes such as proliferation and differentiation and act as key player during inflammation and immune response. A major challenge is to understand how these complex non-linear processes are connected and regulated. Systems biology approaches are used to tackle this challenge in an iterative process of quantitative experimental and mathematical analyses. Here we review quantitative experimental studies and systems biology approaches dealing with the function of Interleukin-6-type cytokines in physiological and pathophysiological conditions. These approaches cover the analyses of signal transduction on a cellular level up to pharmacokinetic and pharmacodynamic studies on a whole organism level.

Targeted antisense modulation of inflammatory cytokine receptors

Antisense technology is potentially a powerful means by which to selectively control gene expression. We have used antisense oligonucleotides to modulate the response of the hepatoma cell line, HepG2, to the inflammatory cytokine, IL-6, by inhibiting the expression of its multifunctional signal transducer, gp130. HepG2 cells respond to IL-6 by upregulating acute phase proteins, such as haptoglobin, by five- to tenfold. Gp130 is central to this response, as the upregulation of haptoglobin is almost completely blocked by the addition of high concentrations ( approximately 100 microg/ml) of a monoclonal antibody to gp 130. Antisense oligodeoxynucleotides complementary to the mRNA encoding gp 130 inhibited the upregulation of haptoglobin by IL-6-stimulated HepG2 cells by about 50%. However, a nonsense sequence also inhibited haptoglobin secretion by about 20%. To improve the specificity and efficiency of action, we targeted the antisense oligonucleotides to HepG2 cells using a conjugate of asialoglycoprotein-poly-L-lysine. The targeted antisense reduced the binding of IL-6 to HepG2 cells, virtually eliminating high affinity binding. In addition, it inhibited haptoglobin upregulation by over 70%. Furthermore, the dose of targeted antisense required for biological effect was reduced by about an order of magnitude as compared with unconjugated antisense. These results demonstrate the potential of antisense oligonucleotides as a means to control the acute phase response as well as the need for a greater understanding of the mechanism and dynamics of antisense molecules as they are developed toward therapeutic application.

Pretreatment with stress cortisol enhances the human systemic inflammatory response to bacterial endotoxin

OBJECTIVE

There is continuing controversy regarding the effect of glucocorticoids on a systemic inflammatory process. Based ona model of glucocorticoid action that includes both pro- and anti-inflammatory effects, we used the human experimental endotoxemia model to test the hypothesis that a transient elevation of plasma cortisol to stress-associated levels would enhance a subsequent (delayed) systemic inflammatory response to bacterial endotoxin.

DESIGN

Prospective, randomized, double-blind, placebo-controlled clinical investigation.

SETTING

Academic medical center.

SUBJECTS

Thirty-six healthy human volunteers.

INTERVENTIONS

Participants were randomized to receive a 6-hr intravenous infusion of saline (control), an intermediate dose of cortisol (Cort80; 6.3 mg/hr/70 kg), or a high dose of cortisol (Cort160; 12.6 mg/hr/70 kg) on day 1. On day 2, participants received an intravenous injection of 2 ng/kg Escherichia coli endotoxin followed by serial measurements of plasma cytokine concentrations.

MEASUREMENTS AND MAIN RESULTS

Baseline participant characteristics and cortisol and cytokine concentrations were similar in all three groups. The plasma cortisol response to endotoxemia on day 2 was similar in all three groups. The interleukin-6 response to endotoxemia was significantly increased in the Cort80 Group compared with the control Group (p = .004), whereas the interleukin-10 response was significantly suppressed (p = .034). Corresponding results for the Cort160 Group were not significantly different from control Group values.

CONCLUSIONS

In this study, transient elevation of in vivo cortisol concentrations to levels that are observed during major systemic stress enhanced a subsequent, delayed in vivo inflammatory response to endotoxin. This appeared to be a dose-dependent effect that was more prominent at intermediate concentrations of cortisol than at higher concentrations of cortisol.

Glucocorticoid regulation of the inflammatory response to injury

During the first half of the 20th century, physiologists were interested in the adrenal glands primarily because adrenalectomized animals failed to survive even mild degrees of systemic stress. It eventually became clear that hormones secreted by the adrenal cortex were critical for survival and, in this context, adrenal cortical hormones were widely considered to support or stimulate important responses to stress or injury. With the purification and manufacture of adrenal cortical hormones in the 1930s and 1940s, clinicians suddenly discovered the potent anti-inflammatory actions of glucocorticoids (GCs). This dramatic, and unexpected, discovery has dominated clinical and laboratory research into GC actions throughout the second half of the 20th century. More recent research is again reporting GC-induced stimulatory effects on a variety of inflammatory response components. These effects are usually observed at low GC concentrations, close to concentrations that are observed in vivo during basal, unstimulated states. For example, GC-mediated stimulation has been reported for the hepatic acute-phase response, for cytokine secretion, expression of cytokine/chemokine receptors, and for the pro-inflammatory mediator, macrophage migration inhibition factor. It seems clear that the long-held clinical view that GCs act solely as anti-inflammatory agents needs to be re-assessed. Varying doses of GCs do not lead simply to varying degrees of inflammation suppression, but rather GCs can exert a full range of effects from permissive to stimulatory to suppressive.

Synergistic induction of the nicotinamide adenine dinucleotide-linked 15-hydroxyprostaglandin dehydrogenase by an androgen and interleukin-6 or forskolin in human prostate cancer cells

The nicotinamide adenine dinucleotide-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH) catalyzes the oxidation of 15 (S)-hydroxyl group of prostaglandins and lipoxins and participates along with cyclooxygenases and lipoxygenases in controlling the cellular levels of prostaglandins and lipoxins. 15-PGDH could be induced by IL-6 and forskolin in addition to androgens in a time- and dose-dependent manner but not by other cytokines and growth factors in LNCaP cells. Concurrent addition of IL-6 and forskolin showed additive effect in the induction of 15-PGDH activity. However, combined addition of dihydrotestosterone (DHT) and IL-6 or DHT plus forskolin exhibited synergistic induction of 15-PGDH activity. The increase in enzyme activity was correlated with the expression of the enzyme protein as shown by Western blot analysis. The induction by DHT or IL-6 or forskolin or their combinations was inhibited by antiandrogen, casodex, in a dose-dependent manner, indicating that a functional androgen receptor was required for the action of any of these three agents. The induction by forskolin plus DHT or by either agent or by IL-6 alone was greatly inhibited by H-89, indicating the involvement of protein kinase A in the actions of forskolin, DHT, and IL-6. The induction of 15-PGDH by IL-6 was also blocked by some other protein kinase inhibitors, indicating the participation of MAPK, MAPK/ERK kinase, and STAT3 in the signaling pathway of IL-6. These results indicate that the induction of 15-PGDH by DHT, IL-6, and forskolin in LNCaP cells may involve a functional androgen receptor and phosphorylation-dependent multiple signaling pathways.

Protein kinase C delta associates with the interleukin-6 receptor subunit glycoprotein (gp) 130 via Stat3 and enhances Stat3-gp130 interaction

The transcriptional regulation of Stat proteins is controlled through their C-terminal domains, which harbor both a tyrosine phosphorylation site, required for dimerization and subsequent nuclear translocation, and a serine phosphorylation site, required for maximum transcriptional activity. Previously, we reported that protein kinase Cdelta (PKCdelta) phosphorylates and interacts with Stat3 in an interleukin (IL)-6-dependent manner. In this study, we further characterized this interaction, and investigated the potential role of such an interaction. We show here that the catalytic domain of PKCdelta interacts with the Src homology 2 domain and part of the adjacent C-terminal transactivation domain of Stat3. This interaction, which does not seem to involve a classical phosphotyrosine SH2-mediated binding, however, significantly enhances the interaction of Stat3 and the IL-6 receptor subunit glycoprotein (gp) 130, which is the initial step for Stat3 activation by IL-6. Expression of a dominant negative PKCdelta or depletion of the endogenous PKCdelta by phorbol 12-myristate 3-acetate treatment abrogates the association of Stat3 with gp130. At the same time, PKCdelta is recruited to gp130 via association with Stat3, which may facilitate its phosphorylation on the gp130 receptor. Finally, we identified Thr-890, a putative PKC phosphorylation site on gp130, to be critical for the effect of PKCdelta. Our data indicate that PKCdelta plays important regulatory roles in IL-6 signaling.

Molecular mechanisms of immunomodulatory activity of glucocorticoids

The development and function of cells in the immune system are regulated by many intrinsic and extrinsic factors. One class of molecule that affects immune cells belongs to the neuroendocrine system and the best-studied mediators in this category are glucocorticoids. These are small lypophilic molecules that participate in a wide number of normal and pathologic processes. This paper concentrates on their physiologic and pharmacologic effects on the immune response.

Topical glucocorticoids application induced an augmentation in the expression of IL-1alpha while inhibiting the expression of IL-10 in the epidermis in murine contact hypersensitivity

The repeated application of glucocorticoids (GC) on the skin augmented the inflammatory response of both allergic and irritant contact dermatitis in our studies. In order to further clarify the mechanism of such an augmentation of contact hypersensitivity (CHS), we investigated the modulatory effects of cytokines in the epidermis after the administration of GC at challenged sites in CHS. Diflucortolone valerate was applied to BALB/c mice on alternate days for a total of nine times. On day 12, they were contact sensitized with dinitrofluorobenzene (DNFB). Next, on day 17, one day after the last application of GC, they were challenged with DNFB on the ear. The whole challenged ear lobes were removed after a hapten challenge and then were analysed by the RT-PCR method or underwent an immunohistochemical analysis. To clarify the modulatory effects of cytokines in vivo, DNFB sensitized mice pre-treated with GC were injected with rIL-10, IL-1 receptor antagonist (ra) and anti-IL-1alpha monoclonal antibody (mAb) and thereafter were challenged with DNFB. A RT-PCR analysis has demonstrated IL-10 mRNA to be detected in the challenged skin of non-GC-pretreated mice but not in that of GC-pre-treated mice after challenge. On the other hand, the expression of IL-1alpha mRNA in the challenged skin of mice pretreated with GC was more strongly detected that that in mice without GC-pretreatment. Furthermore, an immuno-histochemical analysis in the challenge showed the expression of IL-10 in the skin showed the expression of IL-10 in the challenged epidermis of the non-GC-pretreated mice but not in the GC-pretreated mice and IL-1alpha was also strongly expressed in the epidermis of the GC-pretreated mice. A subcutaneous injection of anti-IL-1alpha mAb or IL-1 ra inhibited the augmented CHS reaction in the GC-pretreated mice. A subcutaneous injection of rIL-10 also inhibited the augmentation of the CHS reaction in the GC-pretreated mice; however, no such inhibition was observed in the non-GC-pretreated mice. These results indicated that both an up-regulation of IL-1alpha production and the inhibition of the IL-10 production in the epidermis at the challenged skin sites in the GC-pretreated mice appear to play a critical role in the GC-induced augmentation of murine CHS.

Levels of HBV-DNA and HBsAg after acute liver allograft rejection treatment by corticoids and OKT3

The aim of this work was to analyze whether the treatment of acute rejection of orthotopic liver transplants (OLT), either with corticoids or OKT3, has any effect on the levels of hepatitis B virus (HBV)-DNA and HBsAg in individuals which were originally affected by cirrhosis or fulminant hepatic failure as a result of B virus. We have found that HBV-DNA is present in macrophages, B cells and both CD4+ and CD8+ T cells after OLT in all cases studied. Interestingly, the levels of HBV-DNA and HBsAg in the serum analyzed were increased extremely rapidly in the patients treated with OKT3 in an acute rejection episode. However, the serum levels of HBV-DNA and HBsAg found were lower when the patients were treated with steroids, and were not found in non-treated patients. As the serum levels of HBV-DNA increase, the process of liver reinfection could be accelerated; therefore, these results may help to understand how OKT3 and corticoids immunosuppressive therapy may accelerate the reinfection of OLT by HBV. In conclusion, our results suggest that special care must be taken in the use of OKT3 in the treatment of acute liver rejection episodes in chronic or fulminant HBV transplanted patients.

Pretreatment with glucocorticoids enhances T-cell effector function: possible implication for immune rebound accompanying glucocorticoid withdrawal

Glucocorticoids (GCs) exert their immunosuppressive/antiproliferative effects largely through inhibition of cytokine expression, and paradoxically upregulate the expression of (proinflammatory) cytokine receptors on select nonlymphoid cells. Clinically, withdrawal of GCs was frequently associated with worsening of the outcome of heightened immunity disorders, thereby implicating enhanced cytokine and cytokine receptor expression as a possible consequence of acute/short-term GCs withdrawal. In view of the significance of this complication of GC therapy, we addressed the effect of GC withdrawal on cytokine receptor expression and subsequent T-cell effector function, using the proliferation of human T cells as biological readout. To mimic GC withdrawal, T cells were treated with GCs or controls, stimulated, and incubated for 16-20 h at 37 degrees C, washed, and reactivated for a further 4-48 h. Surface marker expression was assessed by FACS analysis, and proliferation was determined by measuring the cellular uptake of tritiated thymidine. Dexamethasone (DEX) and prednisolone (PRED), in a concentration-dependent manner, inhibited T-cell proliferation induced by anti-CD28 Ab + PMA. However, pretreatment of T cells activated with mitogens, cross-linking antibodies, or PMA + ionomycin ("CD3-bypass" stimulation regimen), but not resting T cells, with DEX or PRED resulted in a marked increase in IL-IR, IL-2R alpha, and IL-6R expression, which was accompanied by a significant enhancement in T-cell proliferation. This effect of GCs was neither stimulus specific nor did it result from alteration in cell viability, and was paralleled by augmentation in cytokine (rIL-2) effects on DEX-pretreated and preactivated T cells. Taken together, our results underline the dual effects of GCs in regulating T-cell activation and cytokine expression. In essence, GCs directly inhibited T-cell proliferation by suppressing cytokine production, and, by enhancing cytokine receptor expression, pretreatment with GCs augmented T-cell proliferation.

Induction of cytokine receptors by glucocorticoids: functional and pathological significance

Current concepts on the role of glucocorticoid hormones in the regulation of inflammatory and immune responses depict this role as being inhibitory. Over the past decade, however, a large variety of studies have shown that glucocorticoids also exert stimulatory effects on immune function, suggesting that the present concept of the role of glucocorticoids in the immune system in not sufficient and needs to be extended. Here, Jan Wiegers and Hans Reul ask how these apparently paradoxical effects fit together and what their functional and pathological significance might be.

STAT3 acts as a co-activator of glucocorticoid receptor signaling

Interleukin-6 (IL-6) and glucocorticoids are important mediators of inflammatory and immunological responses. Glucocorticoids are known to synergistically enhance IL-6-mediated cellular responses. We now show that IL-6 also has a synergistic effect upon glucocorticoid signaling. In particular, IL-6-activated STAT3 associates with ligand-bound glucocorticoid receptor to form a transactivating/signaling complex, which can function through either an IL-6-responsive element or a glucocorticoid-responsive element. These findings reveal a new level of interaction between these two crucial signaling cascades and indicate that activated STAT3 can also act as a transcriptional co-activator without direct association with its DNA binding motif.

Use of immobilized synthetic peptides for the identification of contact sites between human interleukin-6 and its receptor

Synthetic peptides immobilized on cellulose membranes proved to be a powerful tool for the identification of sites in the cytokine IL-6 involved in receptor binding. Similarly, a region in the extracellular part of the IL-6 receptor which is important for interaction with its ligand was identified.

Site-directed mutagenesis of human CNTF: functional analysis of recombinant variants

Ciliary neurotrophic factor (CNTF), interleukin-6 (IL-6), leukemia inhibitory factor (LIF), and oncostatin M (OSM) share functional properties, a predicted common helical framework, and partially identical receptor components. CNTF is a survival promoting factor for various types of neurons in vitro and in vivo. In the present study, structural features essential for the biological function of human CNTF were investigated. Several recombinant CNTF variants were constructed by PCR and expressed in E. coli. Their survival promoting activities were determined using cultures of embryonic chick and newborn rat dorsal root ganglion cells. Deletion of 14 N-terminal and 18 C-terminal amino acids significantly increased bioactivity compared to wild-type (wt) CNTF. Further truncation of the CNTF molecule at the N- or C-terminus resulted in a significant reduction or complete loss of activity. Substitution of two amino acids (Lys154Glu and Trp157Pro) abolished the survival promoting effect. Recently described analogous substitutions in IL-6 had resulted in a partial IL-6 receptor antagonist. However, the double substitution variant had no significant inhibitory effect on wtCNTF activity in assays with both wt and mutant factor. The CNTF variants constructed had almost identical effects on both chick and rat neurons indicating a close similarity of the avian and the mammalian CNTF receptor complex. The present results also demonstrate that a core segment of the CNTF molecule is indispensable for biological function. Analogous segments important for activity have already been identified in the related molecules IL-6, LIF, and OSM. Thus, our data confirm the close structural relationship of CNTF to these "neuropoietic" cytokines. In addition, they demonstrate that site-directed mutagenesis of recombinant human CNTF can yield molecules which show increased survival promoting activity on mammalian neurons.

Induction of metallothionein and stomatin by interleukin-6 and glucocorticoids in a human amniotic cell line

Interleukin 6 (IL-6) is an important mediator of various kinds of inflammatory and immune responses. The human amniotic cell line UAC has an increased number of IL-6 receptors after treatment by glucocorticoids. To find a possible activity of IL-6 on these cells, a cDNA library of IL-6- and dexamethasone-treated cells was screened with cDNA probes from both induced and non-induced cells. Two cDNAs showed a differential hybridization signal. The first one corresponds to metallothionein, a group of small cysteine-rich proteins thought to participate in the metabolism and storage of zinc and to protect cells against oxidative damage. A second cDNA corresponds to the recently cloned cDNA of band 7 integral membrane protein also called stomatin. In hereditary stomatocytosis, absence of this protein in erythrocyte membranes is associated with high Na+ and low K+ intracellular concentrations [Stewart, G. W., Hepworth-Jones, B. E., Keen, J. N., Dash, B. C. J., Argent, A. C. & Casimir, C. M. (1992) Blood 79, 1593-1601]. In UAC cells both metallothionein and stomatin are induced by dexamethasone and IL-6 in a more than additive manner. Western blot analysis shows that stomatin protein is induced in a similar way as its mRNA. IL-6 and dexamethasone induce a state of resistance against hydrogen peroxide toxicity in UAC cells. Metallothionein induction might be partly responsible for this cytoprotection against oxidative stress.

Biosynthesis and half-life of the interleukin-6 receptor and its signal transducer gp130

Interleukin-6 (IL-6) exerts its action via a receptor complex composed of a ligand-binding subunit (gp80) and a signal transducer (gp130) which both belong to the hematopoietic receptor super-family. Very little is known about the biosynthesis and the biological half-lives of proteins of this superfamily. Therefore, we studied the biosynthesis and maturation of the interleukin-6 receptor and its signaling subunit gp130 by pulse chase experiments in stably transfected Madin-Darby canine kidney cells. We found that both proteins are synthesized as precursors with apparent molecular masses of 67 kDa and 130 kDa, respectively. These receptor forms are processed within 45-60 min into mature proteins of 82 kDa and 150 kDa containing complex-type oligosaccharides. The signal transducer gp130 shows a similar maturation in human hepatoma cells HepG2. The IL-6 receptor appears at the cell surface 45 min after completion of its synthesis in the endoplasmic reticulum. In both cell types studied, gp80 and gp130 are rapidly turned over with half-lives of 2-3 h. These half-lives were unaffected by the presence of the ligand IL-6.

Regulation of interleukin-6 receptor expression by interleukin-6 in human monocytes--a re-examination

We have studied the expression and regulation of the interleukin-6 receptor (gp80) and its signal transducer gp130 in primary human blood monocytes. Here, we show that freshly isolated human monocytes express mRNAs for gp80 and gp130. In contrast to a previous report [(1989) FEBS Lett. 249, 27-30] we find that neither lipopolysaccharide nor interleukin-6 (IL-6) lead to a down-regulation of IL-6 receptor mRNA in monocytes. Also in the human monocytic cell line Mono Mac 6 no effect of IL-6 on receptor mRNA levels was observed. For signal transducer gp130 mRNA in monocytes a small and transient up-regulation by IL-6 was found.

The acute phase response

Adult mammals respond to tissue damage by implementing the acute phase response, which comprises a series of specific physiological reactions. This review outlines the principal cellular and molecular mechanisms that control initiation of the tissue response at the site of injury, the recruitment of the systemic defense mechanisms, the acute phase response of the liver and the resolution of the acute phase response.

Recombinant soluble human interleukin-6 receptor. Expression in Escherichia coli, renaturation and purification

The recombinant soluble human interleukin-6 receptor (srhIL-6R) was expressed in Escherichia coli as a non-glycosylated protein comprising the first 339 amino acids after the signal peptide. The protein accumulated within the cells as insoluble protein aggregates (inclusion bodies). After solubilization, 10% of the denatured srhIL-6R could be renaturated by an in vitro folding procedure using L-arginine and the glutathione-redox system. The native receptors were purified to near homogeneity by affinity chromatography on an IL-6-Sepharose column. The functional features of the recombinant soluble receptor were further analysed. A part of the extracellular domain (amino acids 145-345) of the human interleukin-6 receptor (IL-6R) was expressed in E. coli and the purified protein was used to raise antibodies in rabbits. Characterization of the antiserum obtained indicated that an epitope of 13 amino acids close to the transmembrane region is needed for recognition by the antibodies. Since the antiserum obtained did not interfere with IL-6 binding, it could be used to establish a cell-free IL-6-binding assay, In this assay, the srhIL-6R bound IL-6 with an affinity of Kd = 1.5 nM as measured by Scatchard-plot analysis. When 125I-IL-6 was chemically cross-linked to the purified srhIL-6R and analyzed by SDS/PAGE, several 125I-IL-6-containing bands were detected, indicating the possible existence of a multimeric structure of the natural IL-6/IL-6R complex. The srhIL-6R was shown to exhibit biological activity, i.e. it stimulated acute-phase protein synthesis in the recently established human hepatoma cell line HepG2-IL-6 which does not express the IL-6-binding subunit of the IL-6R complex on the cell surface.