Molecular cloning, characterization and functional expression of the rat liver interleukin 6 receptor

The Roles of Neutrophils Linking Periodontitis and Atherosclerotic Cardiovascular Diseases

Inflammation plays a crucial role in the onset and development of atherosclerosis. Periodontitis is a common chronic disease linked to other chronic inflammatory diseases such as atherosclerotic cardiovascular disease (ASCVD). The mechanistic pathways underlying this association are yet to be fully understood. This critical review aims at discuss the role of neutrophils in mediating the relationship between periodontitis and ASCVD. Systemic inflammation triggered by periodontitis could lead to adaptations in hematopoietic stem and progenitor cells (HSPCs) resulting in trained granulopoiesis in the bone marrow, thereby increasing the production of neutrophils and driving the hyper-responsiveness of these abundant innate-immune cells. These alterations may contribute to the onset, progression, and complications of atherosclerosis. Despite the emerging evidence suggesting that the treatment of periodontitis improves surrogate markers of cardiovascular disease, the resolution of periodontitis may not necessarily reverse neutrophil hyper-responsiveness since the hyper-inflammatory re-programming of granulopoiesis can persist long after the inflammatory inducers are removed. Novel and targeted approaches to manipulate neutrophil numbers and functions are warranted within the context of the treatment of periodontitis and also to mitigate its potential impact on ASCVD.

Expression of cytokines and cytokine receptors in the rat brain after kainic acid-induced seizures

We have previously shown that IL-6 protein levels are increased in cerebrospinal fluid in humans after recent tonic-clonic seizures with unchanged levels of IL-1beta and TNFalpha. Here we studied the expression of cytokines IL-6, LIF, IL-1beta and TNFalpha and cytokine receptors IL-6R, LIFR and Gp130 in the rat brain after kainic acid-induced status epilepticus using Northern blot analysis and in situ hybridization histochemistry. After seizures, IL-6 mRNA was induced in the hippocampus, cortex, amygdala and meninges, and IL-6R was up-regulated in the hippocampus. LIF was up-regulated in the hippocampus, cortex and meninges after seizures, and LIFR mRNA was induced in the hippocampus and cortex. Gp130 was constitutively expressed in the brain. After seizures, Gp130 transcription was rapidly induced in the meninges. In thalamus, cortex, amygdala and hippocampus Gp130 mRNA was induced in a delayed fashion. IL-1beta transcription was induced in the temporal lobe cortex and thalamus, and TNFalpha in the hippocampus. In general, the cytokine and their receptor mRNA levels were low in intact rat brain, but were induced by seizures. Since IL-6 and LIF transcripts were induced in the meninges after seizures, the protein products of these transcripts may be more readily released in cerebrospinal fluid after seizures. In addition, the activity of IL-6 and LIF signaling pathways may be influenced by increased expression of their receptors after seizures.

Liver gene regulation in rats following both 70 or 90% hepatectomy and endotoxin treatment

BACKGROUND

The metabolic state effect of liver failure on liver gene regulation was evaluated in a rat model.

METHODS

Following 70 or 90% hepatectomy and lipopolysaccharide or vehicle treatment at intervals up to 24 h, the liver remnants were analyzed for mRNA levels for acute-phase, liver-specific and growth-related proteins.

RESULTS

After 70% hepatectomy mRNA for alpha 1-acid glycoprotein, alpha 2-macroglobulin, thiostatin and fibrinogen, haptoglobin increased three- to sevenfold (P < 0.05), and mRNA for cyclin D and histone 3 increased seven- and 15-fold (P < 0.05), respectively. After lipopolysaccharide injection and 70% hepatectomy were done, mRNA for acute-phase proteins raised significantly (P < 0.05), more to five to 20-fold, while mRNA for growth-related proteins raised significantly (P < 0.05) less to three- to fourfold. After 90% hepatectomy, acute-phase protein mRNA increased five- to ninefold (P < 0.05) more than after 70% hepatectomy, while mRNA for histone 3 and cyclin D did not increase within 24 h, which indicates a delayed growth after 90% hepatectomy. In 90% of hepatectomized rats treated with lipopolysaccharide, acute-phase protein mRNA raised three- to sixfold (P < 0.05) less than after vehicle treatment.

CONCLUSION

In endotoxemia from liver failure, the synthesis of acute-phase proteins is upregulated by gene regulation at the expense of that for regeneration, which may be an appropriate response for immediate survival. In severe liver failure, endotoxin may interfere with the appropriate gene regulation.

Interleukin 1β inhibits interleukin 6–mediated rat γ fibrinogen gene expression

Interleukin (IL)-1β and IL-6 are the 2 major inducers of a group of hepatic genes during acute inflammation; however, each cytokine uses different intracellular signaling molecules. In most instances, the 2 cytokines interact positively to enhance hepatic gene expression, but in one class of acute-phase reactants, which includes fibrinogen, IL-1β exerts a transient inhibitory effect over the IL-6 stimulatory signal. This study explored the effects of IL-1β/nuclear factor κB (NF-κB) and IL-6/signal transducer and activator of transcription 3 (STAT3) combinatory signaling on the transcriptional regulation of the rat γ fibrinogen gene. Northern blot and functional analyses employing luciferase reporter constructs driven by the rat γ fibrinogen promoter demonstrated that IL-1β inhibited the IL-6-mediated transcription of this gene. Exposing primary rat hepatocytes to IL-1β had no effect on IL-6-mediated STAT3 activation; instead, IL-1β-activated NF-κB associated with 2 IL-6 responsive elements (STAT3 binding site) on the rat γ fibrinogen promoter and blocked STAT3 binding to these regions. The competitive binding of NF-κB and STAT3 on the overlapping binding site provides a mechanism for the inhibition by IL-1β of the IL-6-mediated transactivation of rat γ fibrinogen.

Interleukin 1β inhibits interleukin 6–mediated rat γ fibrinogen gene expression

Interleukin (IL)-1β and IL-6 are the 2 major inducers of a group of hepatic genes during acute inflammation; however, each cytokine uses different intracellular signaling molecules. In most instances, the 2 cytokines interact positively to enhance hepatic gene expression, but in one class of acute-phase reactants, which includes fibrinogen, IL-1β exerts a transient inhibitory effect over the IL-6 stimulatory signal. This study explored the effects of IL-1β/nuclear factor κB (NF-κB) and IL-6/signal transducer and activator of transcription 3 (STAT3) combinatory signaling on the transcriptional regulation of the rat γ fibrinogen gene. Northern blot and functional analyses employing luciferase reporter constructs driven by the rat γ fibrinogen promoter demonstrated that IL-1β inhibited the IL-6-mediated transcription of this gene. Exposing primary rat hepatocytes to IL-1β had no effect on IL-6-mediated STAT3 activation; instead, IL-1β-activated NF-κB associated with 2 IL-6 responsive elements (STAT3 binding site) on the rat γ fibrinogen promoter and blocked STAT3 binding to these regions. The competitive binding of NF-κB and STAT3 on the overlapping binding site provides a mechanism for the inhibition by IL-1β of the IL-6-mediated transactivation of rat γ fibrinogen.

Reciprocal actions of interleukin-6 and brain-derived neurotrophic factor on rat and mouse primary sensory neurons

In low-density, serum-free cultures of neurons from embryonic rat dorsal root ganglia, interleukin-6 supports the survival of less than one third of the neurons yet virtually all of them bear interleukin-6 alpha-receptors. A finding that might explain this selectivity is that interleukin-6 acts on sensory neurons in culture through a mechanism requiring endogenous brain-derived neurotrophic factor. Antibodies or a trkB fusion protein that block the biological activity of brain-derived neurotrophic factor synthesized by dorsal root ganglion neurons also block the survival-promoting actions of interleukin-6 on these neurons. Two results indicate that interleukin-6 influences synthesis of brain-derived neurotrophic factor in adult dorsal root ganglion neurons. Intrathecal infusion of interleukin-6 in rats increases the concentration of brain-derived neurotrophic factor mRNA in rat lumbar dorsal root ganglia. The induction of brain-derived neurotrophic factor in dorsal root ganglion neurons that is seen after nerve injury in rats or wild-type mice is severely attenuated in mice with null mutation of the interleukin-6 gene. In brief, the ability of interleukin-6 to support the survival of embryonic sensory neurons in vitro depends upon the presence of endogenous brain-derived neurotrophic factor and the induction of brain-derived neurotrophic factor in injured adult sensory neurons depends upon the presence of endogenous interleukin-6.

The expression of interleukin-6 (IL-6), IL-6 receptor, and gp130-kilodalton glycoprotein in the rat decidua and a decidual cell line: regulation by 17beta-estradiol and prolactin

The cytokine interleukin 6 (IL-6), a major mediator of immune and acute phase responses of the liver, has been implicated in the termination of pregnancy once expressed in the uterus. This study was undertaken to investigate the expression and regulation of genes encoding IL-6 and IL-6 receptor (IL-6R) in rat decidual tissue. Total RNA obtained from rat decidual tissue on different days of pseudopregnancy was analyzed by RT-PCR using specific primers for IL-6, IL-6R, and 130-kDa glycoprotein (gp130). Ribosomal L19 primers served as an internal control. IL-6R and gp130 were found to be expressed in the decidua throughout development, while no messenger RNA (mRNA) for IL-6 was detected. Interestingly, within several hours of culture, decidual explants acquired the ability to express IL-6. The apparent ability of decidual cells to express IL-6 and its lack of expression in vivo led us to examine whether the IL-6 gene is actively inhibited. Primary decidual cells were cultured in the presence of estradiol, progesterone, or PRL. Progesterone showed no effect, whereas estradiol and PRL reduced the level of IL-6 mRNA expression. To examine the mechanism by which these hormones inhibit IL-6 expression, we used a simian virus 40-transformed decidual cell line (GG-AD), which expresses only estrogen receptor-beta (ERbeta). Like primary decidual cells in culture, GG-AD cells express IL-6, IL-6R, and gp130 mRNA. When cultured in the presence of estradiol (0-100 ng/ml), mRNA for IL-6 and its receptor components were down-regulated in a dose-dependent manner. Estradiol also caused a dose-dependent decrease in IL-6 protein secretion into the culture medium. The inhibitory effect of estradiol on IL-6 mRNA expression was reversed by the antiestrogen ICI-164,384. Similar inhibition of IL-6 and gp130 mRNA expression was observed with PRL treatment. However, PRL had no effect on IL-6R mRNA levels. PRL inhibition of IL-6 expression was totally reversed by tyrphostin AG490, a JAK2 inhibitor. In summary, the results of this investigation indicate that IL-6 expression, which is detrimental to the maintenance of pregnancy, is inhibited in the rat decidual tissue. This inhibition is induced by PRL and estradiol, which down-regulate not only IL-6 expression, but also the expression of IL-6 receptor and signaling proteins. The results also suggest that PRL signaling to the IL-6 gene is mediated through the long form of PRL receptor and involves JAK2 activation, whereas that of estradiol can be transduced by estrogen receptor-beta.

Disulfide bond structure and N-glycosylation sites of the extracellular domain of the human interleukin-6 receptor

The high affinity interleukin-6 (IL-6) receptor is a hexameric complex consisting of two molecules each of IL-6, IL-6 receptor (IL-6R), and the high affinity converter and signaling molecule, gp130. The extracellular "soluble" part of the IL-6R (sIL-6R) consists of three domains: an amino-terminal Ig-like domain and two fibronectin-type III (FN III) domains. The two FN III domains comprise the cytokine-binding domain defined by a set of 4 conserved cysteine residues and a WSXWS sequence motif. Here, we have determined the disulfide structure of the human sIL-6R by peptide mapping in the absence and presence of reducing agent. Mass spectrometric analysis of these peptides revealed four disulfide bonds and two free cysteines. The disulfides Cys102-Cys113 and Cys146-Cys157 are consistent with known cytokine-binding domain motifs, and Cys28-Cys77 with known Ig superfamily domains. An unusual cysteine connectivity between Cys6-Cys174, which links the Ig-like and NH2-terminal FN III domains causing them to fold back onto each other, has not previously been observed among cytokine receptors. The two free cysteines (Cys192 and Cys258) were detected as cysteinyl-cysteines, although a small proportion of Cys258 was reactive with the alkylating agent 4-vinylpyridine. Of the four potential N-glycosylation sites, carbohydrate moieties were identified on Asn36, Asn74, and Asn202, but not on Asn226.

The role of therapeutic apheresis in the treatment of cancer: a review

Immunosuppression is a hallmark of advanced malignancies in man. Over the past 40 years, many investigators have identified soluble immunosuppressive factors in blood, serum, ascitic fluid, and pleural fluid from cancers in man and other species. Suppressive factors have also been identified that are produced by tumors. The description of immunosuppressive factors in the blood of vertebrates who either have cancer or who are pregnant is significant, for only in pregnancy and cancer does a seemingly normal immune system tolerate immunogenic neoantigen. Tumor necrosis factors (TNFs) are known to be pleiotropic cytotoxic cytokines that are produced by macrophages and lymphocytes. These cells are thought to be suppressed in patients who have cancer or who are pregnant. Recently, elevated blood levels of soluble tumor necrosis factor receptors (sTNFRs) have been reported in the blood in a variety of cancers and pregnancy. In 1990, after our initial publication of the discovery of sTNFRs in the serum and low molecular weight ultrafiltrates of serum from a variety of cancer patients, others confirmed significant elevations of sTNFRs in cancer patients. This elevation was found to correlate with a poor prognosis. The biologic activity of proinflammatory cytokines as well as the suppressive role of their shed receptors is herein reviewed. Work with cancer patients using ultrapheresis to reduce these suppressive molecules by the authors and others is reviewed. Several recommendations are made for future directions.

Altered cytokine (receptor) mRNA expression as a tool in immunotoxicology

Molecular immunotoxicology is aimed at analysing exposure effects on the temporal expression of important immunoregulatory genes. Cytokines play key roles in the immune system and thus molecular immunotoxicology has focused on the analysis of cytokine (expression) levels. These targets offer important new avenues to explore both in terms of mechanistic understanding of immunotoxicity and in terms of developing new assays and tests for predicting the immunotoxic potential of novel compounds. Effects on cytokine levels can be analysed on two different levels, these being mRNA and protein. The choice essentially depends on the aim of the study. Proteins comprise the biological activity so they are a more direct measure than mRNA. mRNA on the other hand, measures at a specific point in time within a tissue or organ, whereas protein is measured in a body fluid, possibly as a spill-over from tissue, or in a supernatant as a summation over a culture period. mRNA levels are assayed using Northern or dot blotting that both comprise hybridisation and using reverse transcription-polymerase chain reaction (RT-PCR). Although the latter technique has both enormous sensitivity and relative ease of operation as important advantages, it requires much more effort in terms of quantitation. References to the nucleic acid sequences of human, murine, and rat cytokines and their receptors are presented (with accession numbers). Examples in which molecular techniques were successfully employed to assess immunotoxicity and (in some cases) understand mechanisms of action are also presented.

The expression of interleukin-6 in the pregnant rat corpus luteum and its regulation by progesterone and glucocorticoid

Interleukin (IL)-6, a multifunctional cytokine originally described as a T cell-derived factor, is also produced by different cell types, and it influences a wide variety of physiological and pathophysiological processes. Recent studies further suggest that IL-6 has a role in down-regulating hormone production by endocrine organs and can negatively affect the steroidogenic capacity of both ovaries and testes. Thus, the aims of this investigation were to examine whether IL-6 plays a role in luteolysis and, more specifically, to determine whether luteal cells express the IL-6 gene, whether this expression is developmentally and hormonally regulated in pregnancy, and whether the corpus luteum could be a target for IL-6 action. Using semiquantitative RT-PCR, messenger RNA (mRNA) encoding both components of the IL-6 receptor [the ligand-binding subunit (IL-6 R) and the IL-6 R-associated signal transducer (gp130)] were found to be highly expressed in corpora lutea throughout pregnancy. In contrast, IL-6 mRNA expression was barely detectable from day 4 through the end of pregnancy, whereas a sharp and abrupt expression of IL-6 mRNA occurred immediately after parturition. Although the corpus luteum does not express IL-6 mRNA during most of pregnancy, it could be induced to express this gene with an in vivo injection of the bacterial endotoxin, lipopolysaccharide. In addition, when corpora lutea from day-15 pregnant rats were isolated and maintained in culture, IL-6 mRNA that was undetectable at 0 h increased in a time-related manner and reached significant levels after 4 h of incubation, followed by a similar increase in IL-6 protein secreted in the culture media. Isolation of the small and large luteal cells by elutriation indicated that both cell populations can secrete IL-6 in culture. The apparent ability of luteal cells to spontaneously express IL-6 in vitro, together with the lack of IL-6 expression during most of pregnancy, led us to examine whether the IL-6 gene is silenced throughout pregnancy by luteotropic hormones. Corpora lutea from day-15 pregnant rats were cultured in the presence of different doses of progesterone; the synthetic glucocorticoid, dexamethasone; 17beta-estradiol; and PRL. Progesterone and dexamethasone markedly inhibited IL-6 mRNA expression, whereas 17beta-estradiol had a minimal inhibitory effect, and PRL did not affect IL-6 mRNA expression. In summary, results of this investigation have revealed that the rat corpus luteum expresses the IL-6 receptor system and that luteal cells are able to secrete IL-6. However, IL-6 gene expression is silenced during most of pregnancy, probably by the high levels of progesterone locally produced in the corpus luteum. The salient finding that progesterone and glucocorticoid strongly inhibit the expression of IL-6 in the corpus luteum suggests that one important luteotropic role of progesterone and glucocorticoids could be to prevent the expression of IL-6, which might have a deleterious effect on luteal function.

IL-6 functions in cynomolgus monkeys blocked by a humanized antibody to human IL-6 receptor

A humanized antibody to the human interleukin-6 receptor (IL-6R), hPM-1, blocked the interleukin-6 (IL-6) functions in normal cynomolgus monkey lymphocytes in vitro. The binding activity of hPM-1 to non-human primate IL-6R was examined in peripheral blood lymphocytes by flow cytometry. PM-1 recognized the IL-6R on T lymphocytes of cynomolgus and rhesus monkeys, but did not on those of marmosets. The homology between human IL-6R and its cynomolgus monkey counterpart was 97.3% in the extracellular domain of the amino acid sequence, as determined by DNA sequencing of the PCR product from peripheral blood mononuclear cells. PM-1 inhibited two functional parameters in vitro in cynomolgus monkeys: (1), T-cell proliferation stimulated by phytohemaglutinin and human IL-6; (2), Immunoglobulin G-production evoked by Staphylococcus aureus Cowan-1- and human IL-6-stimulated B lymphocytes. These data show that hPM-1 binds to and functionally blocks the cynomolgus monkey IL-6 receptors.

Antibodies to rat soluble IL-6 receptor stimulate B9 hybridoma cell proliferation

Interleukin-6 mediates its pleiotropic effects by interacting with its membrane bound receptor (gp80) or the soluble counterpart gp54, resulting in activation of a complex that includes the transducer protein gp130. We have generated a polyclonal antibody against the rat soluble IL-6 receptor (anti-rat sIL-6R) in rabbits. By Western blot analysis we show that purified anti-rat sIL-6R IgG antibody reacts specifically with recombinant rat sIL-6R generated from E. coli, baculovirus or adenovirus expression systems. Anti-rat sIL-6R inhibited IL-6-induced acute phase protein synthesis in rat (H35) but not human (HepG2) hepatoma cells, and did not affect stimulation of those cells by Oncostatin-M. Conversely, on the mouse hybridoma B9 cell line, IgG anti-rat sIL-6R showed a dose-dependent stimulation of proliferation. Fab fragments of this antibody did not stimulate, but abrogated IL-6-mediated hepatoma cell stimulation and B9 cell proliferation. Gel shift analysis of STAT nuclear factors showed activation of STAT DNA binding in nuclei of B9 cells treated with IgG anti-rat sIL-6R, whereas in H35, NIH-3T3 and M1 cells, only IL-6 could trigger a similar STAT activation. Our data suggest that mechanisms of IL-6 receptor activation and signalling in mouse B9 hybridoma cells show subtle but important differences from other IL-6-responsive cells.

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.

Harlequin granulocyte-colony stimulating factor interleukin 6 molecules with bifunctional and antagonistic activities

BACKGROUND

The granulocyte-colony stimulating factor (G-CSF) and the interleukin 6 (IL-6) are part of a large family of cytokines that regulate the production and the functional activity of hemopoietic cells. Recent studies have shown that IL-6 and G-CSF share structure homology and have partially overlapping functions.

OBJECTIVES

Our research gives some information for planning the production of new artificial cytokines in order to establish whether we could obtain molecules that had two functions or an inhibitory function.

STUDY DESIGN

Fourteen different chimeric molecules (called Harlequin molecules) of human IL-6 and G-CSF have been produced exchanging the sequence encoded by the 2nd to the 5th exon of the genes of the two cytokines.

RESULTS

In order to test their biological activity we performed different assays: proliferation of murine B9-cells and immunoglobulin production from human Epstein-Barr virus (EBV)-transformed B-cell lines for IL-6; induction of granulocytic differentiation of the murine 32DC13(G) cell line and normal bone marrow progenitor cells for G-CSF. Some chimeric molecules maintain the activity of either IL-6 and G-CSF and at least one (Harlequin 11) has both biological activities. One chimeric protein has no biological activity but competes, presumably at the receptor level, for the activity of the intact cytokine.

CONCLUSION

These studies can provide important information on the structure/function of the two cytokines. The bifunctional Harlequin molecule 11 could be a potential candidate as therapeutic agent.

Limulus factor D, a 43-kDa protein isolated from horseshoe crab hemocytes, is a serine protease homologue with antimicrobial activity

A glycoprotein (Mr = 43,000) from horseshoe crab hemocytes with antimicrobial activity against Gram-negative bacteria was purified. The internal peptide sequences coincided exactly with the deduced amino acid sequence of a cDNA clone, designated limulus factor D, which was isolated by screening a hemocyte cDNA library with an anti-human plasminogen antibody. The open reading frame codes for a precursor of factor D of 394 amino acid residues, including an NH2-terminal signal sequence. The COOH-terminal domain of factor D has significant sequence homology with the catalytic domain of mammalian serine proteases, in particular with human tissue plasminogen activator (32% identity), except for the substitution of Ser of the active site triad to Gly. Factor D has a unique NH2-terminal domain with weak sequence homology with part of the mammalian interleukin-6 receptor alpha-chain. Factor D is likely to have an important role in host defense mechanisms.

Characterization and biologic activities of recombinant rat soluble interleukin-6 receptor

The soluble interleukin-6 receptor (sIL-6R) consists of the extracellular domain of the membrane-bound IL-6 receptor (gp80) found on many types of cells. Contrary to most other soluble cytokine receptors, it possesses in vitro agonistic properties, yet its physiologic role remains unknown. We have generated a cDNA encoding the rat sIL-6R and have expressed and purified the protein using Escherichia coli and baculovirus systems. Analysis of purified protein by electrophoresis and silver staining showed a single band migrating at 35 kDa for E. coli (nonglycosylated) and at 47 kDa for baculovirus-derived material. The purified protein is biologically active, as determined by the ability to convert human hepatoma cells (HepG2) from nonresponsive to responsive to rat IL-6 and induce acute-phase protein synthesis. Most important, we show that rat sIL-6R directly induces proliferation of the IL-6-dependent murine hybridoma cell line (B9) in an IL-6-like manner, with 50% proliferation induced by 100 ng/ml of baculovirus-derived receptor protein. Physiologic concentrations of sIL-6R dramatically enhance the sensitivity of B9 cells to IL-6, indicating that the bioassay for IL-6 is susceptible to modulation by the presence of sIL-6R in rodent serum samples. This sIL-6R-dependent B9 cell proliferation is fully abrogated by antibodies directed against rodent IL-6 and indicates autocrine production of low amounts of IL-6 by the B9 cell line.

Insulin modulates STAT3 protein activation and gene transcription in hepatic cells

Treatment of rat hepatoma cells with insulin attenuated the interleukin 6 (IL-6) stimulation of acute phase plasma protein genes. To identify the potential mechanism of this action, the influence of insulin on IL-6 signal transduction was determined. An insulin dose-dependent reduction in signal transducer and activator of transcription 3 (STAT3) gene transcription, mRNA accumulation, protein concentration, and IL-6-inducible DNA binding activity was detected. A reduction in the IL-6-activated sis-inducible element binding of STAT3 was observed within 4 h of insulin treatment, whereas a maximal 3-4-fold lower STAT protein concentration was measured after 8-24 h of insulin treatment. Insulin mediated a similar magnitude reduction in the amount of mRNA encoding the IL-6 receptor alpha subunit and IL-6 binding activity. These effects of insulin appear to contribute to the strongly suppressed transcriptional induction of the IL-6-responsive acute phase plasma protein genes.

Postnatal expression of interleukin-6 (IL-6) and IL-6 receptor (IL-6R) mRNAs in rat sympathetic and sensory ganglia

The postnatal expression of interleukin-6 (IL-6) and IL-6 receptor (IL-6R) mRNAs in superior cervical ganglia (SCG) and dorsal root ganglia (DRG) of normal rats were studied by using RT-PCR. IL-6 and IL-6R transcripts were found in both these peripheral nervous system (PNS) tissues and their expression was differentially regulated. In sensory ganglia, a strong upregulation (12-fold) of the IL-6R mRNA occurred between postnatal day 2 and day 20, staying at this elevated level until adulthood (day 70). During the same period the IL-6 mRNA increased to a lesser extent (3-fold). In SCG, both transcripts undergo only a minor induction (2-fold) during postnatal development. To identify the cellular source of IL-6 and its receptor mRNAs in both PNS tissues, a sensitive non-radioactive in situ hybridization technique was used. Both mRNAs could be localized predominantly in the neuronal cell bodies in the sympathetic and sensory ganglia. In addition, IL-6R mRNA positive cells were found located along the axon outside the DRG, and are likely to be Schwann cells. The same cells were negative for IL-6 mRNA. These findings support the concept of IL-6 as a regulator of neuronal survival and differentiation in the central and peripheral nervous system.

Towards prediction of cognate complexes between the WW domain and proline-rich ligands

The WW domain is a structured protein module found in a wide range of regulatory, cytoskeletal, and signaling molecules. Its ligands contain proline-rich sequences, some of which show a core consensus of XPPXY that is critical for binding. In order to gain a better understanding of the molecular and biological functions of WW domains, we decided to predict their cognate ligands by searching databases for proteins containing the XPPXY consensus. Using several axioms that take into account evolutionary conservation and functional similarity, we have identified four groups of proteins representing candidate ligands that signal through known or unknown WW domains. These include viral Gag proteins, sodium channels, interleukin receptors, and a subgroup of serine/threonine kinases. In addition, we proposed that dystrophin and beta-dystroglycan bind through the WW-XPPXY link and that interference with this interaction could result in muscular dystrophy. Our study provides guidelines for experiments to probe the molecular and biological functions of the WW domain-ligand connection. Should these predictions be proven empirically, the results may have important ramifications for basic research and medicine.

Saturation mutagenesis of the WSXWS motif of the erythropoietin receptor

The WSXWS motif in the extracellular domain defines members of the cytokine receptor family, yet its role in receptor structure and function remains unresolved. To address this question we have generated a panel of 100 mutants within the WSXWS motif of the erythropoietin receptor, which represents all single amino acid substitutions of these five amino acids. All mutants were synthesized at the same level; however, their passage from the endoplasmic reticulum to the Golgi apparatus differed. Because of this, expression of mutant receptors at the cell surface varied more than 300-fold. The tolerance of the tryptophan and serine residues to substitution was quite narrow; as a result, most of these mutants were retained in the endoplasmic reticulum and showed no cell surface expression or reduced cell surface expression. Although many mutants with substitutions at the middle residue of the motif reached the cell surface, it was notable that one mutant, A234E, was processed more efficiently than the wild type receptor and was expressed in elevated numbers at the cell surface. Despite this variation, all mutant receptors that reached the cell surface appeared able to bind erythropoietin and transduce a proliferative signal normally. These results are discussed in terms of a general model for WSXWS function in which the motif contributes to efficient receptor folding.

Transcription factors Stat3 and Stat5b are present in rat liver nuclei late in an acute phase response and bind interleukin-6 response elements

Proteins binding at the interleukin-6 response element of the rat alpha 2 macroglobulin gene were purified by a combination of chromatographic procedures including binding site-specific DNA-affinity chromatography as the principal step. Three polypeptides of 92, 91, and 86 kDa were enriched approximately 6,300-fold from nuclei of rat livers excised 12 h after the induction of an experimental acute phase response. Amino acid sequence analysis identified the 86- and 91-kDa species as two forms of the transcription factor Stat3 and the 92-kDa species as the factor Stat5b. This identification was confirmed by gel mobility shift-supershift experiments using specific antisera for Stat3 and Stat5. Unexpectedly, activated Stat5 was also detected in the nuclei of untreated control rats. cDNA clones representing Stat3 and two isoforms of Stat5b were isolated from a cDNA library prepared with mRNA from rat livers excised at the peak of an experimental acute phase response. Full-length Stat5b, predicted from cDNA, consisted of 786 amino acids, while the variant Stat5b delta 40C lacked 41 amino acids at the COOH terminus. The amino acid sequence of rat Stat5b showed 26.7% overall identity with rat Stat3, 87.3% with sheep Stat5a, 92.5% with murine Stat5a, and 98.7% with murine Stat5b.

Expression of interleukin-6 (IL-6) and IL-6 receptor mRNAs in rat adrenal medulla

Using in situ hybridization and reverse transcription combined with the polymerase chain reaction (RT-PCR) we have studied the expression and developmental regulation of interleukin-6 (IL-6) and its receptor mRNAs in rat adrenal medulla. Labeling for both transcripts was much more intense over the adrenal medulla than over cortical regions at postnatal day 70. Levels of mRNAs of both genes measured by RT-PCR increased from birth to adulthood. In vitro survival and neurite growth of chromaffin cells from early postnatal rats were not affected by IL-6. Even so, the presence and developmental regulation of IL-6 and its receptor are consistent with a possible auto- or paracrine role of IL-6 in rat adrenal medulla.

Regulation of interleukin-6 receptor expression in rat Kupffer cells: modulation by cytokines, dexamethasone and prostaglandin E2

Interleukin-6 has a variety of biological effects, mainly on the immune system. The regulation of this signal at both the site of production and the site of action is necessary to maintain the organism's homeostasis. In the microenvironment of the hepatic sinusoids, Kupffer cells as resident macrophages are the most potent source of interleukin-6 during inflammation. This cytokine is an important signal to hepatocytes during the early stages of the acute-phase response, leading to the expression of several major plasma proteins. Kupffer cells were found to express interleukin-6 receptor constitutively. Interleukin-6 decreased the level of interleukin-6 receptor mRNA, indicating an autocrine pathway by which Kupffer cells regulate their responsiveness to interleukin-6. Furthermore, lipopolysaccharide, tumor necrosis factor-alpha, interferon-gamma, interleukin-1 beta and phorbol ester induced interleukin-6 production and, at the same time, suppressed the level of interleukin-6 receptor mRNA. The existence of an autocrine loop in rat Kupffer cells may be physiologically relevant, as it would contribute to a regulated interleukin-6 signal chain in the liver. The anti-inflammatory mediators dexamethasone or PGE2 and its second messenger, cyclic AMP, increased interleukin-6 receptor mRNA, whereas prostaglandin D2 or the Ca2+ ionophore, A 23187, were without effect. The changes in interleukin-6 mRNA were paralleled by the number of interleukin-6 receptors present on Kupffer cells as detected by binding of 125I-interleukin-6. These results suggest the existence of control mechanisms involving several soluble mediators that help balance the level of interleukin-6-R mRNA in rat liver macrophages.

Cellular localization of interleukin 6 mRNA and interleukin 6 receptor mRNA in rat brain

The distribution of interleukin 6 (IL-6) mRNA and IL-6 receptor (IL-6R) mRNA in the brain of adult male rats was studied at the light microscope level by in situ hybridization histochemistry using 35S-labelled oligonucleotides. The transcripts of both genes were localized in the pyramidal neurons and in the granular neurons of the hippocampus, in neurons of the habenular nucleus as well as in the dorsomedial and ventromedial hypothalamus, in the piriform cortex, in scattered neurons of the cortex and in granular cells of the cerebellum. The medial preoptic nucleus and the anterior tip of the lateral ventricle contained mRNA encoding IL-6 and its receptor. Moreover, white matter areas, such as the internal capsule, which consist of only fibres and glial cells, were found to have autoradiographic signals above background. The mRNAs for IL-6 and IL-6R in hippocampus and cerebellum are not different, as shown by Northern blot analyses of RNA isolated from these tissues. We postulate that the cytokine IL-6 is expressed constitutively in discrete regions of the CNS and that it is involved in the mechanisms coordinating metabolic, behavioural and neuroendocrine changes not only during illness but also under normal physiological conditions. Our results suggest that IL-6 mRNA and IL-6R mRNA are colocalized, thus supporting a role of the cytokine in autocrine and paracrine communication.

The molecular biology of the CNTF receptor

Recently there have been advances in studies of the molecular biology of the receptor for CNTF. In contrast with the receptors for other known neurotrophic factors, which belong to the family of receptor tyrosine kinases, the CNTF receptor belongs to the family of cytokine receptors. This review will describe the structural features and signaling capabilities of the CNTF receptor, and discuss the implications for the biology of CNTF as well as for other neurotrophic factors and cytokines. This review is an updated version of the review that appears in Current Opinion in Neurobiology 1993, 3:20-24.

The soluble interleukin-6 receptor is generated by shedding

The ligand-binding subunit (gp80) of the human interleukin-6 receptor (IL-6R) was transiently expressed in COS-7 cells. The metabolically labeled protein was shown to be quantitatively released from the membrane within 20 h. We identified the protein released from the transfected COS-7 cells after purification to homogeneity and N-terminal sequencing as a soluble form of the gp80/IL-6R. Shedding of the gp80 protein was strongly induced by 4 beta-phorbol-12-myristate-13-acetate, indicating that the process was regulated by protein kinase C (PKC). This was further corroborated by the finding that co-transfection of a PKC expression plasmid led to enhanced shedding of the gp80 protein. Since shedding of gp80 could not be prevented by treatment of the cells with inhibitors of all known classes of proteases, a novel protease seems to be involved. As a control, an unrelated membrane protein (vesicular stomatitis virus glycoprotein) was transfected into COS-7 cells and analyzed for shedding. Since the turnover of this protein was not mediated by shedding, we conclude that the release of gp80 from COS-7 cells is a specific process. The shed gp80 protein specifically binds IL-6, and this complex shows biological activity on human hepatoma cells. Human peripheral blood monocytes released a soluble form of the gp80 protein into the culture medium upon PMA treatment indicating that PKC-regulated shedding is the physiological mechanism of generation of the soluble IL-6R.

The molecular biology of the CNTF receptor

Recently there have been advances in studies of the molecular biology of the receptor for CNTF. In contrast with the receptors for other known neurotrophic factors, which belong to the family of receptor tyrosine kinases, the CNTF receptor belongs to the family of cytokine receptors. This review will describe the structural features and signaling capabilities of the CNTF receptor, and discuss the implications for the biology of CNTF as well as for other neurotrophic factors and cytokines.

Structural, functional and evolutionary implications of the three-dimensional crystal structure of murine interferon-beta

The crystal structure of recombinant murine interferon-beta as elucidated by Senda et al. (Proc. Jap. Acad. 66B: 77-80 (1990); EMBO J. 11: 3193-3201 (1992)) appears to represent the basic structural framework of all Type I interferons including interferons-beta and all subtypes of interferons-alpha of various mammalian origin. Now the huge accumulated data on the structure-activity relationship of Type I interferons using various chemical and genetic techniques can be systematically evaluated in terms of the three-dimensional structure. Structural comparison with other cytokines, for which three-dimensional structures have been established, including interferon-gamma and considerations on the evolution of cytokines and cytokine receptors are also given.

Regulation of IL-6 and the hepatic IL-6 receptor in acute inflammation in vivo

The serum levels of interleukin 6 (IL-6) and the expression (mRNA) of the 80 kDa IL-6 receptor (IL-6R) were examined in three different models of acute inflammation. Rats were treated with either Freund's complete adjuvant (FA) via intraperitoneal injection, LPS via intravenous injection, or turpentine via subcutaneous injection. Using bio- and specific immunoassays, rat serum levels of IL-6, corticosterone, and acute phase proteins were quantified. LPS treatment induced the quickest and greatest serum IL-6 response (> 100 ng/ml within 3 h). In comparison, sera from turpentine and FA-treated rats contained much lower levels of IL-6 activity (< 10 ng/ml). Serum corticosterone levels increased by 3 h after injection in all three models, and equivalent raised serum levels of acute phase proteins were detected within 12-24 h. The expression of IL-6 receptor mRNA in hepatocytes increased markedly as early as 3 h after treatment and message levels began to decline by 6-12 h in all three models. To analyze the individual effects of raised corticosterone and IL-6 on the expression of hepatic IL-6R mRNA, rats were injected with either dexamethasone (Dex) or purified recombinant rat IL-6 (rIL-6) via intraperitoneal injection. Rats injected with rIL-6 showed highly induced IL-6R mRNA levels as early as 1 h after injection, and Dex-injected rats showed a significant but less dramatic rise in IL-6R message levels. Dex- or rIL-6-injected rats demonstrated a distinct profile of acute phase protein response different from that seen in the three experimental models. Regulation of IL-6R gene expression in the liver in vivo depends on a complex interaction between the hepatocyte and a combination of cytokines and other hormones.

The alpha component of the CNTF receptor is required for signaling and defines potential CNTF targets in the adult and during development

We recently proposed that ciliary neurotrophic factor (CNTF) shares two receptor components with a generally acting cytokine, leukemia inhibitory factor (LIF), but that CNTF also requires a third receptor component (CNTFR alpha) that is mostly restricted to the nervous system in its expression. Here we demonstrate that a transfected CNTFR alpha gene is sufficient to confer CNTF responsiveness upon hemopoietic cells normally responsive only to LIF, providing evidence that CNTFR alpha is a required receptor component that uniquely characterizes CNTF-responding cells. Consistent with this notion, CNTFR alpha expression could be localized to neurons within all known peripheral targets of CNTF. CNTFR alpha was also widely expressed within neurons of the CNS, suggesting that CNTF has broader CNS actions than previously appreciated. However, in vivo localization of CNTFR alpha, as well as of CNTF itself, is consistent with a particularly important role for CNTF in motor function as well as during neuropoiesis.

Molecular cloning and characterization of the rat liver IL-6 signal transducing molecule, gp130

Interleukin-6 (IL-6) is a multifunctional cytokine that exerts its effects on different target cells by interacting with a specific receptor. This interaction leads to the association and activation of a second membrane glycoprotein, gp130, which is the IL-6 signal transducing molecule. The nucleotide sequence of gp130 from a human B-cell line has been reported. We report here the cloning and sequence analysis of the gp130 molecule derived from rat liver. Comparison of gp130 molecules from the different species and cell types reveals 78% overall amino acid homology and 94% identity in the growth factor signaling domain. Two gp130 mRNA species, a moderately abundant species of 7.5 kb and a lesser one of 9.0 kb, were present in rat hepatocytes. Ribonuclease protection analyses demonstrated the presence of gp130 mRNA in four different nontransformed cell types: hepatocytes, astrocytes, fibroblasts, and endothelial cells. The sequences between both gp130s in the different cell types are quite similar, supporting the prediction that the different responses initiated by IL-6 on different target cells are modulated by cell-specific proteins distal to the activated gp130 molecule.

Chromosomal localization of the IL-6 receptor signal transducing subunit, gp130 (IL6ST)

Signal transduction in eukaryotic cells is a complex process mediated, normally, by the interaction of soluble extrinsic protein factors and their cognate receptors. One example of this phenomena is the inflammatory cytokine interleukin-6 and the IL-6 receptor. However, the IL-6 receptor, once its ligand is bound, associates with another membrane glycoprotein, gp130, to potentiate the cytokine response. To further understand the basis of this interaction, and its possible implications in cellular transforming events, the corresponding gene(s) must be studied. Here we find that the human gp130 gene product is homologous to two distinct chromosomal loci on chromosomes 5 and 17. Furthermore, the presence of two distinct gp130 gene sequences is restricted to primates and is not found in other vertebrates.

Effects of interleukin-6 on cytochrome P450-dependent mixed-function oxidases in the rat

Intravenous treatment of male rats with recombinant human interleukin-6 (rhIL6) at 50, 100 and 200 micrograms/kg (corresponding to 4, 8 and 16 x 10(4) U/animal, respectively) reduced the activities of hepatic microsomal cytochrome P450-dependent monoxygenases to varying degrees. Ethylmorphine-N-demethylase activity fell to 53% of control values, an effect similar to that induced by 2.5 mg/kg Escherichia coli lipopolysaccharide (LPS). Ethoxycoumarin-O-deethylase activity was also sensitive to inhibition, whereas IL6 had little effect on the activities of other P450-dependent enzymes, including ethoxyresorufin-O-deethylase. Pentoxyresorufin dealkylase activity, which is representative of the cytochrome P450 IIB 1/2 subfamily, was unaffected by IL6 whereas LPS reduced it to 33.7% of control values. Another hepatocyte-related parameter, serum concentration of alpha 1-acid glycoprotein (AGP), was increased by up to 3.5-fold over baseline by IL6 and 10-fold by LPS. Recombinant human interleukin-1 beta (rhIL1 beta) (10 micrograms/kg, corresponding to 5 x 10(4) U/rat) and recombinant human tumor necrosis factor alpha (rhTNF) (150 micrograms/kg corresponding to 24 x 10(4) U/rat) were both as potent as LPS (2.5 mg/kg) in increasing serum AGP levels and reducing hepatic microsomal monoxygenase activities. IL6 did not potentiate the effects of rhIL1 beta. Hepatic microsomal glucuronyltransferase activities were little affected by LPS and unaffected by rhIL6. Finally, rhIL6 was more potent after i.p. injection than after i.v. or s.c. injection. These results suggest that the effects of LPS, TNF and IL1 on the mixed-function oxidase system in vivo may be due partly to an induction of IL6 in vivo. The different sensitivities of the enzymes to IL6 but not to IL1 or TNF may be due to the involvement of two distinct mechanisms.

Localization of interleukin 6 mRNA and interleukin 6 receptor mRNA in rat brain

The cytokine interleukin 6 (IL6) has several effects on the central nervous system in addition to the well established regulation of the acute phase inflammatory response. Therefore, the distribution of IL6- and IL6 receptor mRNA in the rat brain has been investigated by in situ hybridization using [35S]-labeled oligonucleotides. The messages of both genes were found in the CA1-CA4 regions as well as in the dentate gyrus of the hippocampus, in the habenulae, the dorsomedial and the ventromedial hypothalamus, in the internal capsule, the optic tract and in the piriform cortex. These data indicate both neuronal and glial localization of IL6 and IL6 receptor and their involvement in an autocrine or paracrine action of the cytokine in centrally regulated functions including neuroendocrine control.

Up-regulation of the interleukin-6-signal transducing protein (gp130) by interleukin-6 and dexamethasone in HepG2 cells

The hepatic IL-6-receptor is composed of an 80 kDa IL-6-binding protein and a 130 kDa polypeptide (gp130) believed to be involved in signal transduction. Previous experiments have shown that the 80 kDa IL-6-receptor is up-regulated by glucocorticoids, but not by IL-6. Here we demonstrate that IL-6 together with the synthetic glucocorticoid dexamethasone induces the expression of mRNA for gp130 approximately 5-fold in HepG2 cells. The induction was dose- and time-dependent. Dexamethasone alone, interferon-gamma, IL-1 alpha and IL-1 beta had no effect. A possible role for the regulation of the IL-6-signal transducing protein gp130 in various inflammatory states is proposed.

Ciliary neurotrophic factor and its receptor complex

Ciliary neurotrophic factor (CNTF), originally identified for its ability to promote survival of neurons of the ciliary ganglion, is now known to have additional survival and differentiative actions on cells of the nervous system. CNTF is, however, unrelated in structure to the nerve growth factor family of neurotrophic factors. Instead, CNTF is distantly related to, and in fact shares receptor components with, a number of hemopoietic cytokines. This review focuses on the biological actions of CNTF, the shared and unique features of the CNTF receptor complex and signaling pathways, and the distribution of CNTF and its receptor during development, in the adult and in response to injury.

The Interleukin-6-dependent DNA-binding protein gene (transcription factor 5: TCF5) maps to human chromosome 20 and rat chromosome 3, the IL6 receptor locus (IL6R) to human chromosome 1 and rat chromosome 2, and the rat IL6 gene to rat chromosome 4

Using two panels of somatic cell hybrids segregating either human or rat chromosomes, the gene encoding the interleukin-6-dependent DNA-binding protein, also called liver activator protein (designated transcription factor 5: TCF5), was assigned to human chromosome 20 and to rat chromosome 3. The TCF5 gene might be identical with the NF-IL6 gene. The locus encoding the IL6 receptor gene (IL6R) was localized to human chromosome 1 and rat chromosome 2. An IL6R-like (IL6RL) locus was also assigned to human chromosome 9. In addition, the rat interleukin-6 (IL6) gene was assigned to rat chromosome 4. These mapping data allow one to extend comparison between the rat, mouse, and human gene maps.

Gene regulation by interleukin 6

Interleukin 6 (IL-6) is a central alarm hormone of the mammalian body. During acute and chronic inflammations, it induces acute phase plasma protein synthesis by liver hepatocytes, modulates the immune response and participates in the regulation of body temperature (fever). In addition, it is a growth factor for certain tumor cells, such as myeloma cells. The details of the IL-6 signal transduction mechanism are unknown. We have contributed to this problem at 2 levels: (a), we have mapped an IL-6-response element (IL-6-RE) in the 5' flanking region of the alpha 2-macroglobulin gene (alpha 2M), a prototype rat liver acute phase gene. This element, CTGGGA, serves as a binding site for nuclear factors that facilitate hormone induced transcription. We have begun to characterize these factors from hepatic cells and demonstrated that they undergo characteristic IL-6-induced changes. Similar factors were also discovered in human Burkitt tumor derived cell lines (B cells). These bound at the IL-6-RE of the rat alpha 1M gene and formed indistinguishable protein DNA complexes, as the corresponding hepatic factors. Thus, common elements probably operate in the IL-6 signal transduction cascade in liver cells and B cells; (b), we have cloned the rat liver IL-6 receptor (IL-6-R) and derived its amino acid sequence. It was 53% identical to the human leukocyte IL-6-R and all functional domains were highly conserved. Therefore, the cell-type specific responses to IL-6 in liver cells and lymphocytes were probably not due to cell-type specific forms of the receptor, but to other so far unknown elements of the signal transduction cascade.(ABSTRACT TRUNCATED AT 250 WORDS)