Differential regulation of interleukin-6 receptor and gp130 gene expression in rat hepatocytes

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.

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.

Modeling Therapeutic Antibody-Small Molecule Drug-Drug Interactions Using a Three-Dimensional Perfusable Human Liver Coculture Platform

Traditional in vitro human liver cell culture models lose key hepatic functions such as metabolic activity during short-term culture. Advanced three-dimensional (3D) liver coculture platforms offer the potential for extended hepatocyte functionality and allow for the study of more complex biologic interactions, which can improve and refine human drug safety evaluations. Here, we use a perfusion flow 3D microreactor platform for the coculture of cryopreserved primary human hepatocytes and Kupffer cells to study the regulation of cytochrome P450 3A4 isoform (CYP3A4) activity by chronic interleukin 6 (IL-6)-mediated inflammation over 2 weeks. Hepatocyte cultures remained stable over 2 weeks, with consistent albumin production and basal IL-6 levels. Direct IL-6 stimulation that mimics an inflammatory state induced a dose-dependent suppression of CYP3A4 activity, an increase in C-reactive protein (CRP) secretion, and a decrease in shed soluble interleukin-6 receptor (IL-6R) levels, indicating expected hepatic IL-6 bioactivity. Tocilizumab, an anti-IL-6R monoclonal antibody used to treat rheumatoid arthritis, has been demonstrated clinically to impact small molecule drug pharmacokinetics by modulating cytochrome P450 enzyme activities, an effect not observed in traditional hepatic cultures. We have now recapitulated the clinical observation in a 3D bioreactor system. Tocilizumab was shown to desuppress CYP3A4 activity while reducing the CRP concentration after 72 hours in the continued presence of IL-6. This change in CYP3A4 activity decreased the half-life and area under the curve up to the last measurable concentration (AUClast) of the small molecule CYP3A4 substrate simvastatin hydroxy acid, measured before and after tocilizumab treatment. We conclude that next-generation in vitro liver culture platforms are well suited for these types of long-term treatment studies and show promise for improved drug safety assessment.

Activation of the IL-6R/Jak/stat pathway is associated with a poor outcome in resected pancreatic ductal adenocarcinoma

BACKGROUND AND OBJECTIVE

Chronic localized pancreatic inflammation in the form of chronic pancreatitis is an established risk factor for human pancreatic ductal adenocarcinoma (PDAC) development. Constitutive activation of inflammation-related signal transducer and activator of transcription (Stat)3 signaling has been implicated in the development and progression a number of malignancies, including PDAC. Although, the Janus Kinase (Jak)/Stat pathway is a potential drug target, clinicopathological, molecular, and prognostic features of Stat3-activated PDAC remain uncertain. Our aim was to determine the clinicopathological impact of this inflammatory pathway in resectable PDAC.

METHODS

Using a tissue microarray-based cohort of PDAC from 86 patients undergoing pancreaticoduodenectomy with curative intent and complete clinicopathological data available, we evaluated expression of the interleukin-6 receptor (IL-6R)/Jak/Stat pathway by immunohistochemistry. IL-6R, Jak, phospho (p)-Jak, Stat3, pStat3(Tyr705), and pStat3(Ser727) were assessed in PDAC and pancreatic intraepithelial neoplasia. A Cox regression multivariate analysis model was used to determine factors influencing survival. Activation of the IL-6R/Jak/Stat3 pathway was compared with the systemic inflammatory response as measured by serum C-reactive protein levels.

RESULTS

High pJak was associated with reduced overall survival in multivariate analysis when compared with those with moderate or low expression (p = 0.036; hazard ratio (HR) = 1.68) as was pStat3(Tyr705) (p < 0.001; HR = 2.66) independent of lymph node status and tumor grade. Patients with a combination of pJakhigh/pStat3(Tyr705) high expression had an especially poor prognosis (median survival of 8.8 months; 95 % CI, 4.4-13.2). While the IL-6R/Jak/Stat pathway did not correlate with serum C-reactive protein levels, high pStat3 expression was associated with a reduction in the density of the local tumoral immune response.

CONCLUSION

Activation of the Jak/Stat3 pathway via phosphorylation was associated with adverse outcome following resection of PDAC with curative intent supporting potential roles for pJak and pStat3 as prognostic biomarkers markers and therapeutic targets.

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.

Corticosteroids in sepsis: from bench to bedside?

The use of corticosteroids in patients with septic shock has been recently revisited and the use of low dose corticosteroids led to very promising results, particularly in patients with corticosteroid insufficiency. We review the different mechanisms that can account for their beneficial effects in patients. Glucocorticoids display a wide spectrum of anti-inflammatory properties that have been identified in in vitro and in vivo experimental models (e.g., inhibition of production of pro-inflammatory cytokines, free radicals, prostaglandins and inhibition of chemotaxis, and adhesion molecule expressions.) In addition, glucocorticoids have profound effects on the cardiovascular system (e.g., increasing mean blood pressure, increasing pressor sensitivity, and therefore decreasing the duration of use of catecholamines during septic shock.) Through these anti-inflammatory and cardiovascular effects, low doses of glucorticoids may improve septic shock survival.

Long-term stable cultures of rat hepatocytes: an in vitro model to study acute and chronic hepatic inflammation

Engineered tissues provide an opportunity to investigate important physiological processes difficult to study in whole perfused organs and animal models. For example, a hepatocyte culture model consisting of rat hepatocytes cultured in a collagen sandwich configuration, which exhibits stable differentiated liver-specific functions, may be useful to investigate liver pathophysiology. To investigate systemic inflammation-related hepatic failure, we chronically exposed hepatocytes to the inflammatory mediators interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) for up to 4 weeks. IL-6 (2.5 ng/mL) transiently suppressed albumin (-90%) and chronically increased fibrinogen (+6-fold) production. IL-6 inhibited urea synthesis at 2.5 ng/mL and stimulated it at 0.025 ng/mL. IL-1beta (10 ng/mL) inhibited albumin (-90%), urea (-40 to 50%), and IL-6-stimulated fibrinogen (-90%) secretion. The inhibitory effect of IL-1beta on urea secretion was dose-dependent. Furthermore, IL-1beta transiently stimulated nitric oxide (NO) synthesis; however, NO did not mediate the effect of IL-1beta on albumin and fibrinogen production, and played a minor role in IL-1beta-mediated urea synthesis suppression. In conclusion, IL-1beta and IL-6 exert, via a direct effect on hepatocytes, long-term inhibitory effects on hepatic functions that are potentially important for the survival of the host, which may contribute to hepatic dysfunction in prolonged inflammatory states.

Acute activation of gp130 gene expression in bone marrow stromal cells by contact with myeloma-derived lymphoblastic cell line ARH77 cell membranes

Cell-cell contact of myeloma-derived cell lines (MDCL) or fresh myeloma cells with bone marrow stromal cells (BMSC) is known to induce interleukin-6 (IL-6) and matrix metalloproteinase-1 (MMP-1) production by a marrow stromal cell line. To determine if other BMSC transcripts are altered during cell-cell contact between BMSC and tumor cells, we have used cell lines ARH77 and U266 in an in vitro model. Using mRNA differential display and reverse transcriptase-polymerase chain reaction (RT-PCR), it was determined that a total of 141 transcripts were either upregulated or downregulated in the BMSC on contact with cell membrane from cell lines ARH77 and U266. Induction of two of these transcripts, interleukin-6 (IL-6) and gp130 in the BMSC by ARH77 cell membranes was studied in greater detail. Real-time PCR was used to quantitate transcript levels of gp130, IL-6, and 36b4, a housekeeping gene. Cycloheximide (CHX) alone increased both gp130 and IL-6 transcripts in the BMSC. In addition, CHX caused a superinduction of these transcripts in BMSC exposed to ARH77 cell membranes. The induction of gp130 was independent of the increase in IL-6 mRNA. Upregulation of gp130, a component of the membrane receptors for the IL-6 superfamily, can have profound effects on the response of BMSC to the IL-6 superfamily of cytokines.

Interleukin-6 stimulates hepatic insulin-like growth factor binding protein-4 messenger ribonucleic acid and protein

Sepsis and bacterial lipopolysaccharide (LPS) injection decrease circulating concentrations of insulin-like growth factor (IGF)-I and induce an increase in IGFBP-1 and IGFBP-4 that may have impact upon IGF-I anabolic actions. Although the mechanisms responsible for the IGFBP-1 increase in response to LPS have already been unraveled, the cause for the IGFBP-4 elevation is still unknown. The aim of this study was to characterize the regulation of IGFBP-4 by proinflammatory cytokines and glucocorticoids. In rat primary cultured hepatocytes, interleukin (IL)-6 strongly stimulated IGFBP-4 messenger RNA (mRNA) and protein levels in a dose- and time-dependent way (mRNA levels: 9-fold, P: < 0.01 and protein levels: approximately 3-fold at 24 h, with IL-6 10 ng/ml). Interleukin (IL)-1ss and tumor necrosis factor (TNF)-alpha blunted the IL-6 stimulation of IGFBP-4 mRNA (66% and 46% decrease, respectively) and protein levels (82% and 68% decrease, respectively). In contrast, dexamethasone induced IGFBP-4 mRNA and protein and potentiated the effect of IL-6 on IGFBP-4 mRNA (2.5-fold, P: < 0.01 vs. IL-6 alone). Both actinomycin and cycloheximide prevented the IL-6 induction of IGFBP-4 mRNA suggesting that the IL-6 effect on IGFBP-4 gene occurs probably at the transcriptional level and needs an ongoing protein synthesis. Administration of IL-6 to rats caused a 3-fold increase in liver IGFBP-4 mRNA (P: < 0.001) reflected in serum levels of IGFBP-4 (P: < 0.05). In conclusion, our results show that IL-6 stimulates hepatic IGFBP-4 gene expression and production in vitro and in vivo, thereby suggesting another mechanism by which cytokines could control IGF-I action.

Distinct effects of Broncho-Vaxom (OM-85 BV) on gp130 binding cytokines

BACKGROUND

Broncho-Vaxom (OM-85 BV) is known to support respiratory tract resistance to bacterial infections. In vivo and in vitro studies in animals and humans have shown that the action of the drug is based on the modulation of the host immune response, and it has been found to upregulate interferon gamma (IFN-gamma) and interleukin (IL)-2, IL-6, and IL-8. These immunomodulatory effects of the compound may explain its stimulation on T helper cells and natural killer cells. Following earlier findings that OM-85 BV induces the synthesis of IL-6, a study was undertaken to investigate its possible effect on other gp130 binding cytokines including IL-11, IL-12, leukaemia inhibitory factor (LIF), oncostatin M (OSM), and ciliary neutrophil factor (CNTF). Its modulation of the corresponding receptors of the above mentioned cytokines and of the signal transducer gp130 in human pulmonary fibroblasts and peripheral blood lymphocytes was also studied.

METHODS

Transcription of cytokines was assessed by Northern blot analysis. Secretion of cytokines was analysed using commercially available enzyme linked immunosorbent assay kits. Cytokine receptors and gp130 proteins were determined by Western blot analysis.

RESULTS

OM-85 BV increased the expression of IL-11 in human lung fibroblasts, but not in lymphocytes, in a dose and time dependent manner by maximal fivefold within 20 hours. The compound inhibited serum induced IL-12 expression in peripheral blood lymphocytes but did not induce OSM, LIF, or CNTF at any concentration. In lung fibroblasts the expression of the IL-6 receptor was enhanced fourfold at a concentration of 10 microg/ml OM-85 BV while that of the IL-11 receptor was not altered. In peripheral blood lymphocytes LIF receptor alpha expression was downregulated in the presence of 10 microg/ml OM-85 BV. At a concentration of 10 microg/ml OM-85 BV enhanced gp130 gene transcription fivefold and increased gp130 protein accumulation in cell membranes by 2.5 times.

CONCLUSION

In vitro OM-85 BV exerts immunomodulatory action via modulation of the signal transducer gp130 and gp130 binding cytokines. The increase of IL-6 and IL-11 may explain enhanced T and B cell activity, immunoglobulin synthesis, and IgM to IgG switch. Suppression of IL-12 and LIF receptor-alpha further contributes to organ protection. With regard to gp130 mediated signalling of the investigated cytokines, OM-85 BV modifies the host immune response towards an increased sensitisation of cells to gp130 binding proteins.

Augmentation of Type I IL-1 Receptor Expression and IL-1 Signaling by IL-6 and Glucocorticoid in Murine Hepatocytes

IL-1 signal is transduced through type I receptor (IL-1RI). We have recently reported that LPS augments IL-1RI mRNA expression in the hepatocytes of mice in vivo, and the augmentation is mediated by the interaction of IL-1, IL-6, and glucocorticoid (GC). In this study, we examined whether IL-1RI mRNA expression level in the hepatocytes reflects those of cell surface molecule and IL-1 signaling. When primary cultured murine hepatocytes were treated with dexamethasone (Dex) or IL-6, these two reagents synergistically up-regulated IL-1RI mRNA expression in the cells. 125I-labeled IL-1 binding experiment showed that the level of binding was also up-regulated by the treatment with Dex and IL-6. Scatchard analysis revealed that the number of IL-1R increased. The increased binding of IL-1 was completely inhibited by an Ab against murine IL-1RI, indicating that Dex and IL-6 augmented the expression of cell surface IL-1RI molecule. When hepatocytes were pretreated with Dex and IL-6, the activation of IL-1R-associated kinase was augmented in response to IL-1, indicating that IL-1 signaling was also augmented. In addition, IL-1 treatment following administration of the combination of Dex and IL-6 into mice markedly increased the serum level of serum amyloid A. These results indicate that GC and IL-6 augment the expression of cell surface IL-1RI in hepatocytes, as well as IL-1 signaling and IL-1R-associated kinase activation, through up-regulation of IL-1RI mRNA level, which represents a novel regulatory network between IL-1, GC, and IL-6.

Effect of IL-6 overexpression on the metastatic potential of rat hepatocellular carcinoma cells

BACKGROUND

Previous studies demonstrated that excess IL-6 production correlated with the metastatic potential of rat hepatocellular carcinoma cells. In the work reported here a retroviral construct containing the gene for murine IL-6 was introduced into otherwise nonmetastatic tumor cells to directly determine the effect of IL-6 overexpression on tumor metastatic potential.

METHODS

The clonal cell lines 1682.C.2.9.L0 (L0, poorly metastatic) and 1682.C.2.9.L10 (L10, highly metastatic) were selected from a parental hepatocellular carcinoma induced in ACI rats by feeding an ethionine-containing diet. Viral supernatant was used to infect the PA317 amphotropic cell line, and retrovirus produced from these cells infected the poorly metastatic L0 hepatocellular carcinoma cell line. Neomycin-resistant cells were selected in G418 and designated L0-IL-6.

RESULTS

As determined by bioassay, L0 cells produce 10 +/- 1.2 U/mL IL-6 in culture, whereas L10 cells release 95 +/- 11 U/mL (P < 0.01, Student's t-test). Retroviral-mediated IL-6 gene transfer resulted in the production of 1266 +/- 48 U/mL IL-6 by L0-IL-6 cells under identical culture conditions. When an inoculum of 5 x 10(6) cells is injected subcutaneously, both L0 and L10 cell lines result in primary tumors with equivalent rates of growth; only L10 cells metastasize to the lung, however. A similar inoculation of L0-IL-6 cells produced local tumors in all 24 animals tested. Interestingly, 15 of 24 (62%) animals presented with metastatic nodules in the abdominal cavity, whereas no such tumors were found in animals receiving L10 cells.

CONCLUSION

Overexpression of IL-6 increases metastatic potential of tumor cells, with preferential metastases to the abdominal cavity when compared with tumor cells elaborating endogenous IL-6.

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.

Role of glucocorticoid in the upregulation of type I interleukin-1 receptor mRNA expression in hepatocytes of endotoxin-administrated mice

The interleukin-1 (IL-1) signal is transduced through type I IL-1 receptor (IL-1RI). We have recently reported that lipopolysaccharide (LPS) upregulated IL-1RI mRNA expression in mouse liver in vivo and that IL-1 and IL-6 directly upregulated IL-1RI mRNA expression in primary cultured mouse hepatocytes. Glucocorticoid (GC) has been reported to increase IL-1 binding to the cell surface and the expression level of IL-1R mRNA in a variety of cell types. As serum GC level is elevated in an inflammatory response, we evaluated the role of GC in LPS-induced upregulation of IL-1RI mRNA in the mouse liver. When LPS was administered to adrenalectomized (ADX) mice, IL-1RI mRNA was upregulated at a level comparable to those of untreated or sham-operated mice. A high dose of dexamethasone (Dex), however, caused upregulation of the mRNA. When primary cultured mouse hepatocytes were treated with Dex, only a weak upregulation of IL-1RI mRNA was observed. However, Dex in combination with IL-1 or IL-6 markedly enhanced the IL-1RI mRNA expression. A marked upregulation of the mRNA was also induced by treatment with a combination of IL-1 and IL-6 in the absence of Dex, reflecting the observation in ADX mice. These results suggest that the upregulation of IL-1RI mRNA in response to LPS is induced by the interaction of IL-1 and IL-6 and that GC augments their effect.

Interleukin-6 in the injured patient. Marker of injury or mediator of inflammation?

OBJECTIVE

The effects of interleukin (IL)-6 in the injured patient are examined in an attempt to clarify the potential pathophysiologic role of IL-6 in the response to injury.

SUMMARY BACKGROUND DATA

Interleukin-6 is an integral cytokine mediator of the acute phase response to injury and infection. However, prolonged and excessive elevations of circulating IL-6 levels in patients after trauma, burns, and elective surgery have been associated with complications and mortality. The mechanistic role of IL-6 in mediating these effects is unclear.

METHODS

A review of current literature is performed to summarize the origins, mechanisms of action, and biologic effects of IL-6 and to characterize the IL-6 response to injury.

RESULTS

Interleukin-6 is a multifunctional cytokine expressed by a variety of cells after a multitude of stimuli, under complex regulatory control mechanisms. The IL-6 response to injury is uniquely consistent and related to the magnitude of the insult. Moreover, the early postinjury IL-6 response correlates with complications as well as mortality.

CONCLUSIONS

Interleukin-6 appears to play an active role in the postinjury immune response, making it an attractive therapeutic target in attempts to control hyperinflammatory provoked organ injury.

Glucocorticoid-dependent induction of interleukin-6 receptor expression in human hepatocytes facilitates interleukin-6 stimulation of amino acid transport

OBJECTIVE

The authors studied the effects of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) on glutamine and alanine transport in isolated human hepatocytes. They also evaluated the role of dexamethasone in modulating this response and its effects on the expression of the plasma membrane high-affinity IL-6 receptor.

SUMMARY BACKGROUND DATA

Animal studies indicate that cytokines are important mediators of the increased hepatic amino acid uptake that occurs during cancer and sepsis, but studies in human tissues are lacking. The control of transport by cytokines and cytokine receptor expression in the liver may provide a mechanism by which hepatocytes can modulate amino acid availability during catabolic disease states.

METHODS

Human hepatocytes were isolated from wedge biopsy specimens and plated in 24-well trays. Interleukin-6 and TNF-alpha, in combination with the synthetic glucocorticoid dexamethasone, were added to hepatocytes in culture, and the transport of radiolabeled glutamine and alanine was measured. Fluorescent-activated cell sorter (FACS) analysis was used to study the effects of dexamethasone on IL-6 receptor number in the well-differentiated human hepatoma HepG2.

RESULTS

Both IL-6 and TNF-alpha exerted a small stimulatory effect on alanine and glutamine transport. Dexamethasone alone did not alter transport rates, but pretreatment of cells augmented the effects of both cytokines on carrier-mediated amino acid uptake. Dexamethasone pretreatment and a combination of IL-6 and TNF-alpha resulted in a greater than twofold increase in transport activity. Fluorescent-activated cell sorter analysis demonstrated that dexamethasone induced a threefold increase in the expression of high-affinity IL-6 receptors.

CONCLUSIONS

Interleukin-6 and TNF-alpha work coordinately with glucocorticoids to stimulate amino acid uptake in human hepatocytes. Dexamethasone exerts a permissive effect on cytokine-mediated increases in transport by increasing IL-6 receptor expression on the cell surface. It is likely that this upregulation of IL-6 receptors "primes" human liver cells for subsequent stimulation by cytokines. The resulting increase in hepatic amino acid transport provides the liver with substrate to support key metabolic pathways during catabolic states.

D1 cap region involved in the receptor recognition and neural cell survival activity of human ciliary neurotrophic factor

Human ciliary neurotrophic factor (hCNTF), which promotes the cell survival and differentiation of motor and other neurons, is a protein belonging structurally to the alpha-helical cytokine family. hCNTF was subjected to three-dimensional structure modeling and site-directed mutagenesis to analyze its structure-function relationship. The replacement of Lys-155 with any other amino acid residue resulted in abolishment of neural cell survival activity, and some of the Glu-153 mutant proteins had 5- to 10-fold higher biological activity. The D1 cap region (around the boundary between the CD loop and helix D) of hCNTF, including both Glu-153 and Lys-155, was shown to play a key role in the biological activity of hCNTF as one of the putative receptor-recognition sites. In this article, the D1 cap region of the 4-helix-bundle proteins is proposed to be important in receptor recognition and biological activity common to alpha-helical cytokine proteins reactive with gp130, a component protein of the receptors.

Interleukin-6 and ciliary neurotrophic factor trigger janus kinase activation and early gene response in rat hepatocytes

Interleukin-6 (IL-6) and ciliary neurotrophic factor (CNTF) share a signal-transducing molecule called gp130. Previous studies showed that CNTF regulates fibrinogen gene expression in rat hepatocytes by competitive binding to the IL-6 receptor. This report explores the post ligand-binding events in the control of fibrinogen and early response gene production stimulated by IL-6 and CNTF in primary rat hepatocytes. Metabolic labeling, using [32P]orthophosphate or anti-phosphotyrosine antibody (Ab) blot experiments revealed that both IL-6 and CNTF induced tyrosine phosphorylation of gp130, and the Jak1 and Jak2 kinases in a dose- and time-dependent manner. Additional experiments revealed that only one of the early response genes, junb, but not c-myc or c-fos, was stimulated by the addition of either IL-6 or CNTF. These data suggest that activation of Jak kinases and stimulation of junb reflect a divergence of the IL-6/CNTF signaling pathway and further suggest that junb may participate in cytokine control of acute-phase protein production in the inflammatory response.

Interferon-alpha down-regulates the interleukin-6 receptor in a human multiple myeloma cell line, U266

The effects of interferon-alpha (IFN-alpha) on the interleukin-6 (IL-6) receptor in a multiple myeloma cell line, U266, have been examined. IFN-alpha inhibits [3H]thymidine incorporation in U266 cells in a time- and dose-dependent manner. Furthermore, IFN-alpha inhibits the ability of IL-6 to induce increases in [3H]thymidine incorporation. While IFN-alpha suppresses the ability of 125I-IL-6 to bind to the IL-6 receptor on U266 cells, this effect is not due to competition of IFN-alpha with IL-6 for the IL-6 receptor. Although IFN-alpha induces IL-6 synthesis in the U266 cell, inhibition of IL-6 binding occurs when IL-6 synthesis is minimal. Furthermore, after pretreatment of U266 cells with neutralizing anti-IL-6 antibodies, IFN-alpha still inhibits 125I-IL-6 binding. These data suggest that IFN-alpha inhibition of 125I-IL-6 binding does not involve IL-6 synthesis. IFN-alpha reduces 125I-IL-6 binding without affecting its affinity, suggesting that IFN-alpha inhibits IL-6 receptor expression. Although pretreatment with cycloheximide inhibits 125I-IL-6 binding, IFN-alpha does not cause a selective decrease in the levels of gp130 or IL-6 receptor mRNA at times when 125I-IL-6 binding is inhibited. These observations indicate that IFN-alpha lowers IL-6 receptor density on U266 cells by mechanisms other than competitive binding or lowering IL-6 receptor mRNA production. Receptor down-regulation may be a mechanism of IFN-alpha-induced inhibition of growth in U266 cells.

Differential regulation of astrocyte TNF-alpha expression by the cytokines TGF-beta, IL-6 and IL-10

In this study, we demonstrate that transforming growth factor-beta (TGF-beta), interleukin-10 (IL-10) and interleukin-6 (IL-6) inhibit tumor necrosis factor-alpha expression by primary rat astrocytes. Treatment of astrocytes with TGF-beta alone had no effect on TNF-alpha expression, however, TGF-beta suppressed induction of TNF-alpha expression at both the protein and mRNA level. In contrast, IL-10 and IL-6 both inhibited TNF-alpha protein expression by astrocytes, but had no effect on mRNA levels. The extent of IL-6-mediated inhibition was greatest when astrocytes were pretreated with IL-6 for 12-24 hr, then exposed to the inducing stimuli, while IL-10 was an effective inhibitor even when added simultaneously with the inducing stimuli. Collectively, these data indicate that TGF-beta, IL-6 and IL-10 are all capable of inhibiting TNF-alpha expression by astrocytes, although these immunosuppressive cytokines act at different levels of gene expression; i.e. TGF-beta at the transcriptional level and IL-10/IL-6 at the translational level. These results indicate that TGF-beta, IL-6 and IL-10 are important regulators of cytokine production by astrocytes under inflammatory conditions in the brain, and can contribute to controlling the production of detrimental cytokines such as TNF-alpha.

Biosynthetic and glycosylation events of the IL-6 receptor beta-subunit, gp130

It is now recognized that the beta-subunit of the interleukin-6 (IL-6) receptor, also known as gp130, is a common signal transducer shared by other cytokines, including ciliary neurotrophic factor, leukemia inhibitor factor, oncostatin M, and IL-11. In this study, the biosynthesis and glycosylation of hepatic gp130 were investigated using a specific polyclonal antibody to the 287 amino acid cytoplasmic domain of gp130. Immunoprecipitation and metabolic labeling experiments demonstrate, in addition to a mature surface expressed gp130, the presence of a major immature form of the molecule within the cell. The immature form can shift to become a functional gp130 only after being terminally glycosylated. The kinetics of gp130 maturation and surface expression were determined. When both forms of gp130 are deglycosylated the resulting core peptides migrate to identical positions in a denatured protein gel, indicating that the principal difference between the two forms resides in the extent of their glycosylation. IL-6 and other members of this cytokine family activate only the mature form, demonstrating its location at the membrane surface. Protein and mRNA turnover studies reveal gp130 to be a stable, slowly renewing population under nonstimulated conditions. These findings provide novel information on the intracellular events leading to the expression of this critically important signal transducing protein.

Disruption by interferon-alpha of an autocrine interleukin-6 growth loop in IL-6-dependent U266 myeloma cells by homologous and heterologous down-regulation of the IL-6 receptor alpha- and beta-chains

IL-6 is an autocrine growth factor for U266 myeloma cells and their growth is inhibited by IFN-alpha or IL-6 mAb. We asked, therefore, whether IFN-alpha-induced growth inhibition involved IL-6. IFN-alpha and mAb against IL-6, the IL-6R alpha-(gp80) or beta-chain (gp130) potently inhibited U266 cells. Remarkably, this effect occurred despite IFN-alpha-augmented secretion of endogenous IL-6. However, examining the IL-6R revealed that IFN-alpha drastically curtailed expression of the IL-6R alpha- and beta-chain. This effect occurred on two different levels (protein and mRNA) and by two different mechanisms (directly and indirectly through IL-6). First, IFN-alpha, but not IL-6, greatly decreased gp80 and, to a lesser extent, gp130 mRNA levels which resulted in a loss of IL-6 binding sites. Second, IFN-alpha-induced IL-6 predominantly down-regulated membrane-bound gp130. IFN-alpha-mediated decrease of gp80 levels was not detected on IL-6-independent myeloma (RPMI 8226) or myeloid cells (U937). We conclude that IFN-alpha inhibited IL-6-dependent myeloma cell growth by depriving U266 cells of an essential component of their autocrine growth loop, a functional IL-6R.

Effect of acute and chronic alcohol administration to rats on the expression of interleukin-6 cell-surface receptors of hepatic parenchymal and nonparenchymal cells

Rats were treated with alcohol either acutely (continuous, 7-hr intravenous infusion; blood alcohol levels approximately 35 mM) or chronically (liquid diet, 12-14 weeks). Three hr before killing, the animals received Gram-negative bacterial lipopolysaccharide (LPS) or saline. Hepatocytes, Kupffer cells, and liver sinusoidal endothelial cells were isolated by liver collagenase perfusion and centrifugal elutriation, and used for measurements of recombinant human [125I]interleukin-6 binding. Dissociation constant (Kd) and the amount of cell-surface receptors (Bmax) were measured on whole cells, at 4 degrees C. Two binding sites were detected on all three cell types: high-affinity (Kd1, from 20 to 125 pM) and low-affinity (Kd2, from 0.2 to 2 nM), with low Bmax (Bmax, from 0.4 to 12 fmol/10(6) cells) and high Bmax (Bmax2, from 10 to 210 fmol/10(6) cells). Hepatocytes displayed an 8-fold higher binding capacity for high-affinity sites (Bmax1) than the other two cell types. Acute ethanol treatment induced the following significant changes in the binding parameters: a decrease in Kd1 for hepatocytes and Kupffer cells, an increase in Bmax2 for hepatocytes, and a decrease in Bmax1 for Kupffer cells. Although the control (nonalcoholic) liquid diet per se completely suppressed the high-affinity binding sites, alcohol-containing diet induced only one change: a significant increase in Kd2 for hepatocytes. No changes in the binding parameters were seen after LPS administration to the chronically treated group. In the acute group, LPS mimicked alcohol action on hepatocyte binding parameters. Alcohol blunted LPS effects.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Phosphorylation and internalization of gp130 occur after IL-6 activation of Jak2 kinase in hepatocytes

Recent evidence has shown that members of the Jak kinase family are activated after IL-6 binds to its receptor complex, leading to a tyrosine phosphorylation of gp130, the IL-6 signal-transducing subunit. The different members of the IL-6 cytokine subfamily induce distinct patterns of Jak-Tyk phosphorylation in different cell types. Using monospecific antibodies to gp130, Jak2 kinase, and phosphotyrosine, we investigated the kinetics of IL-6 stimulation of members of this pathway in primary hepatocytes. Our findings show that Jak 2 is maximally activated within 2 min of exposure to IL-6, followed by gp130 phosphorylation that reaches its peak in another 2 min then declines to basal level by 60 min. In vitro phosphorylation experiments show that activated Jak 2 is able to phosphorylate both native gp130 and a fusion peptide containing its cytoplasmic domain, demonstrating gp130 is a direct substrate of Jak 2 kinase. Experiments designed to explore the cell surface expression of gp130 show that > or = 2 h are required to get a second round of phosphorylation after the addition of more cytokines. This finding suggests that activated gp130 is internalized from the cell surface after IL-6 stimulation. Additional experiments using protein synthesis inhibitors reveal that new protein synthesis is required to get a second cycle of gp130 phosphorylation indicating gp130 must be synthesized de novo and inserted into the membrane. These findings provide strong evidence that down regulation of the IL-6 signal in hepatocytes involves the internalization and cytosol degradation of gp130.

Differential regulation of interleukin-6 receptors by interleukin-6 and interferons in multiple myeloma cell lines

Interleukin-6 (IL-6) mediates pleiotropic functions through specific receptors (IL-6R) composed of an 80-kDa binding protein, associated with a non-ligand binding protein (gp130) which transduces the signal. Because IL-6 is the major tumor growth factor in multiple myeloma, we investigated the regulation of IL-6R in two human multiple myeloma cell lines. Binding experiments with 125I-labeled IL-6 showed that IL-6R were expressed at a high density on RPMI-8226 cells (15 000 receptors/cell), but no specific binding was detected on XG-1 cells, whose growth depends on the presence of exogenous IL-6. However, when IL-6 was removed from the culture medium, high-affinity IL-6R appeared on the surface of XG-1 cells (5300 sites/cell). Treatment of RPMI-8226 cells with IL-6 reduced the number of IL-6R without changing their affinity. This reduction was dose dependent and was not affected by acid treatment which dissociates ligand-receptor complexes. Cross-linking experiments showed that the formation of one IL-6/receptor complex of 160 kDa markedly decreased upon IL-6 treatment, while the other complex of 190 kDa became undetectable. These data provide evidence for ligand-induced down-regulation of membrane IL-6R expression in myeloma cells. Treatment of RPMI-8226 cells with interferon-alpha (IFN-alpha), which inhibits the growth of these cells, stimulated IL-6R expression and increased the formation of the 160-kDa IL-6/receptor complex. This stimulation was specific for IFN-alpha, since IFN-gamma reduced the number of IL-6R. These data indicate that, in myeloma cells, IL-6R are differentially regulated by IL-6 and IFN-alpha.

Increased fibrinogen synthesis in mice during the acute phase response: co-operative interaction of interleukin 1, interleukin 6, and interleukin 1 receptor antagonist

Interleukin 6 (IL-6) stimulates fibrinogen (Fg) gene expression both in vivo and in vitro; while interleukin 1 (IL-1) paradoxically stimulates in vivo, yet inhibits in vitro, Fg synthesis. The naturally occurring interleukin 1 receptor antagonist (IL-1ra) and passive immunization with anti-IL-6 antiserum were used to study the in vivo mechanism of action of IL-1 on Fg gene expression. Changes in plasma Fg and hepatic Fg mRNA concentrations were measured following administration of exogenous IL-1ra together with IL-6 or IL-1 to CD2F1 mice. Our results suggest that in vivo, IL-1 per se inhibits Fg production since when IL-1ra was co-administered with IL-6, greater concentrations of Fg were observed than when IL-6 was administered alone. The data suggest that IL-1 stimulates Fg production through intermediate production of IL-6, since stimulation was abrogated when either IL-1ra or anti-IL-6 antiserum was co-administered with IL-1. An in vivo role for IL-1ra in the stimulation of Fg by IL-1 was supported by the observation that within 1 h of IL-1 administration to mice, IL-1ra mRNA was detectable in liver. It appears that IL-1, an early mediator of inflammation, inhibits constitutive expression of Fg genes and stimulates the IL-1ra and IL-6 genes. The inhibitory effect of IL-1 is reversed by endogenous IL-1ra and by the direct stimulation of Fg gene expression by IL-6.

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.

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.

Enhancement of IL-6 receptor beta chain (gp130) expression by IL-6, IL-1 and TNF in human epithelial cells

Analysis of the IL-6 Receptor beta chain (gp130) mRNA expression on the two human epithelial cell lines UAC and Hep3B reveals that it is enhanced by IL-6, IL-1 and TNF treatment. In the case of UAC cells, TNF action might be mediated by IL-6. For Hep3B cells, TNF seems to exert a direct effect on gp130, as no IL-6 expression is detected after stimulation by this cytokine. On the same cells, increase of the binding of an anti-gp130 monoclonal antibody was observed after treatment by TNF, which denotes the effective appearance of new gp130 molecules on the cell surface. All this cytokines seem to act selectively on the beta chain of the IL-6 receptor. This probably reflects the importance for some cells to have gp130 represented on their membrane in inflammatory contexts.