Receptors for B cell stimulatory factor 2. Quantitation, specificity, distribution, and regulation of their expression

Interleukin-6 attenuates agonist-mediated calcium mobilization in murine osteoblastic cells

Interleukin-6 (IL-6) is a multifunctional cytokine which is made by osteoblasts and has diverse effects on bone metabolism. We studied the interaction of IL-6 with the Ca2+ and cAMP signaling systems in the osteoblastic cell line UMR-106 and in primary osteoblastic cultures derived from neonatal rat calvariae. IL-6 did not alter basal intracellular calcium concentration ([Ca2+]i) but inhibited Ca2+ transients induced by parathyroid hormone (PTH), prostaglandin E2 (PGE2), and endothelin-1 in both dose- (100-400 U/ml) and time- (4-48 h) dependent manners. The effect of the cytokine was abolished by the tyrosine kinase inhibitor, herbimycin A (50 ng/ml). The IL-6 effect on the Ca2+ message system was related to suppressed production of hormonally induced inositol 1,4,5-triphosphate and inhibition of Ca2+ release from intracellular stores. Hormonally induced calcium entry pathways (estimated by using Mn2+ as a surrogate for Ca2+) were not, however, altered by the cytokine. IL-6 did not modulate cAMP generation in osteoblasts. With respect to osteoblast function, IL-6, although having no effect on cell proliferation by itself, greatly enhanced the antiproliferative effect of PGE2 and PTH. Because the production of IL-6 in osteoblasts is stimulated by calciotropic hormones (e.g., PTH and PGE2), the suppressive effect of the cytokine on hormonally induced Ca2+ transients may serve as an autocrine/paracrine mechanism for modulating the effect of hormones on bone metabolism.

Roles of disulfide bonds in recombinant human interleukin 6 conformation

Human IL-6 has two disulfide bonds linking Cys45 to Cys51 and Cys74 to Cys84, respectively. Previous site-directed mutagenesis studies have demonstrated that the Cys74-Cys84 bond is essential for full biological and receptor binding activities. To address the structural importance of these disulfide bonds in the formation and stabilization of IL-6 secondary and tertiary structures, we have generated a panel of disulfide bond-deficient rIL-6 analogs both by chemical reduction and alkylation as well as by site-directed mutagenesis. Conformational changes affecting these rIL-6 analogs were probed by circular dichroism spectroscopy, as well as reactivity with monoclonal antibodies, and correlated with changes in biological activities. We have shown that the first disulfide bridge (Cys45-Cys51) is highly sensitive to reduction and, therefore, more solvent-exposed or less thermodynamically stable. Contrary to previous reports, this bridge contributes, although minimally, to the full biological activity of the cytokine. However, no significant changes in secondary or tertiary structures were observed upon removal of this bond. In marked contrast, analogs lacking the disulfide bridge between Cys74 and Cys84 exhibited as little as 0.5% and 0.05% wild-type biological and receptor binding activities, respectively. These dramatic changes correlated with a slight reduction in alpha-helical content and a decreased reactivity with the neutralizing monoclonal antibody mAb8 which recognizes a conformational epitope associated with the active site. Our results suggest that the second disulfide bridge plays a critical role in maintaining the spatial relationship between the putative IL-6 A and D helices.

Interleukin 6 receptor mRNA in prostate carcinomas and benign prostate hyperplasia

We investigated the presence of interleukin 6 (IL6) receptors in human prostate carcinomas and benign prostatic hyperplasias. Interleukin 6 receptor expression was measured at the mRNA level by slot blot analysis using a probe that recognizes mRNA encoding the 80-kDa subunit of the IL6 receptor. Significant expression was found in 29 of 37 (78%) samples of benign prostate hyperplasia (BPH) and in 17 of 17 prostate carcinomas. Quantitative analysis of the expression level revealed that 11 of the 29 positive hyperplasia tissues (38%) and 4 carcinoma samples (23.5%) expressed equal or higher levels of IL6 receptor mRNA than the human hepatoma cell line PLC/PRF5, which contains about 2300 IL6 receptors per cell. We also measured IL6 receptor mRNA levels in three human prostate carcinoma cell lines LNCaP, DU145 and PC3, which are known to contain IL6 receptors because they are sensitive to the cytotoxic action of an IL6-toxin fusion protein. We were not able to detect IL6 receptor expression with the slot blot procedure, but we were able to detect IL6 receptor mRNA using a very sensitive PCR assay. Our data provide evidence that IL6 may play a role in the growth of benign and malignant prostate tumors and suggest that the IL6 receptor could be a target for the delivery of therapeutic agents in prostate cancer.

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.

Regulation of cytokine expression in osteoblasts by parathyroid hormone: rapid stimulation of interleukin-6 and leukemia inhibitory factor mRNA

PTH and other hormones that stimulate resorption affect osteoclasts indirectly by modulating cytokine production by osteoblasts. However, the identity and role of the osteoblast-derived cytokines involved in this process are unclear. To examine which cytokines are regulated by PTH, we assessed cytokine mRNA levels in osteoblasts using the reverse transcription-polymerase chain reaction technique. Of the 16 cytokines we examined, unstimulated MC3T3-E1 osteoblastic cells expressed mRNA for interleukins 5, 6, and 7, macrophage and granulocyte-macrophage colony-stimulating factors, transforming growth factor beta 1, and leukemia inhibitory factor. PTH specifically increased expression of interleukin-6 (approximately 50-fold) and leukemia inhibitory factor (approximately 10-fold). Levels of both IL-6 and LIF mRNA peaked 30-60 minutes after addition of PTH and returned to baseline by 4-6 h. This rapid and transient mRNA response, which resembles that of immediate early genes, was also observed in primary rat osteoblasts. The transient mRNA response was accompanied by increased secretion of IL-6 protein. Lipopolysaccharide, another stimulator of resorption, increased mRNA levels of a group of cytokines that were not induced by PTH, namely interleukin-1 alpha, tumor necrosis factor alpha, and granulocyte-macrophage and granulocyte colony-stimulating factors. We conclude that osteoblasts produce complex networks of cytokines that (1) are regulated by bone-resorptive agents and (2) may be involved in controlling bone resorption.

Differential sensitivity of human myeloma cell lines and normal bone marrow colony forming cells to a recombinant diphtheria toxin-interleukin 6 fusion protein

The cytotoxicity of a recombinant interleukin 6 (IL-6)-diphtheria toxin (DT) fusion protein towards human myeloma cell lines was investigated. DAB389-IL-6 inhibited protein synthesis and methylcellulose colony formation by U266 myeloma cells. In the clonogenic assay, the fusion protein approached the level of cytotoxicity achieved by native DT. The specificity of killing by DAB389-IL-6 was demonstrated by inhibition of cytotoxicity by a molar excess of free rhIL-6. The effect of DAB389-IL-6 on colony formation by six OCI-My cell lines was assessed. Similar to U266 cells, colony growth by the OCI-My 5 and -My 2 cell lines was inhibited in a simple dose dependent manner. However, a biphasic effect was observed for the IL-6 dependent OCI-My 4 cells; DAB389-IL-6 stimulated colony formation at low (< or = 10(-11) M) concentrations, yet was inhibitory at higher doses. Three other cell lines whose growth was not altered by IL-6 were relatively unaffected by DAB389-IL-6, despite their sensitivity to native DT. Flow cytometric analysis for IL-6 receptor expression using phycoerythrin-conjugated IL-6 demonstrated specific binding sites on both DAB389-IL-6 sensitive and certain insensitive cell lines, suggesting that other factors in addition to the expression of IL-6 receptors are involved in killing by the fusion toxin. Despite evidence for a role of IL-6 in myeloid cell development, normal bone marrow was insensitive to the IL-6 fusion toxin. In cultures containing both normal bone marrow and U266 cells DAB389-IL-6 effectively inhibited the growth of U266 myeloma colonies but had little effect on normal bone marrow erythroid, granulocyte and mixed erythroid/granulocyte colony growth. From these experiments we conclude that DAB389-IL-6 is specifically cytotoxic towards a subset of IL-6-responsive human myeloma cell lines and may be useful, in some cases, in the selective elimination of tumour cells from mixed populations of normal and malignant cells.

Inactivation of interleukin-6 in vitro by monoblastic U937 cell plasma membranes involves both protease and peptidyl-transferase activities

Human promonocytic U937 cells have previously been shown to possess at their cell surface specific transmembrane serine proteases and N-terminal amino acid proteases as well as associated enzymes including elastase and cathepsin G. In this study, purified plasma membranes from U937 cells are reported to degrade the recombinant 21-kDa 125I-interleukin-6 (125I-IL-6) into 8-kDa products with loss of biological activity, as monitored by polyacrylamide gel electrophoresis and a cell-proliferation bioassay. Degradation of 125I-IL-6 by plasma membranes was completely prevented by the serine-protease inhibitor diisopropyl fluorophosphate, but was only partially impaired by alpha 1-protease inhibitor and antibody against cathepsin G. A similar incubation of 125I-IL-6 with cathepsin G purified from U937 cells caused hydrolysis of the cytokine into similar inactive 8-kDa fragments, whereas incubation with purified U937 cell elastase failed to degrade the peptide. These findings indicate that U937 cells hydrolyze IL-6 using cell-associated serine-protease activity and that cathepsin G partially participates in this degradation. Prolonged incubation of 8-kDa 125I-IL-6 fragments with purified U937 plasma membranes, led to a complete loss of IL-6 activity related to the transformation of the 8-kDa forms into a higher-molecular-mass complex (16 kDa). This complex was stable in SDS and 2-mercaptoethanol at 100 degrees C and was not dissociated by hydroxylamine treatment, indicating the formation of a covalent non-ester bond between the 8-kDa 125I-IL-6-derived peptide and an undetermined acceptor. An initial oxidative treatment of 125I-IL-6 partially prevented complex formation, suggesting the presence of one or more oxidizable methionine residues at the binding site of 8-kDa 125I-IL-6 peptide. The kinetics of complex formation (time dependence and plasma-membrane-concentration dependence), as well as its inhibition by a specific inhibitor of N-amino-peptidase activity, bestatin, suggest the participation of peptidyl-transferase activity in complex formation. Finally, a plasma-membrane fraction, corresponding to a molecular mass > or = 30 kDa, was able to convert the 8-kDa 125I-IL-6 forms into the 125I-labeled 16-kDa complex, suggesting that a > or = 30-kDa peptidyl-transferase enzyme catalyzes the reaction and provides the 125I-labeled 16-kDa peptide by dimerization of 8-kDa 125I-IL-6-derived intermediates. Further identification of the plasma-membrane-associated peptidyl transferase as a regulator of IL-6 proteolysis may be of physiological relevance for the control of IL-6 biological activity.

Characterization of a CD34+ cell line established from a child with large cell cutaneous lymphoma

BACKGROUND

Lymphoma presenting with skin involvement has heterogeneous morphology and rarely is seen in children. To study the pathogenesis of this disease, lymphoma cells from a child with B-cell large cell lymphoma of the skin were cultured in vitro.

METHODS

Lymphoma cells cultured on a feeder layer under hypoxic conditions grew in vitro after a latency period of 2 weeks. Since interleukin-6 (IL-6) induces final differentiation of activated B-lymphocytes, the cell line was evaluated for the presence of IL-6 receptors and biologic response to IL-6.

RESULTS

An Epstein-Barr virus (EBV)-negative cell line (UoC-B2) was established which expressed CD34, CD45, HLA-DR, CD19, CD20, sIgM, sIgD, and lambda light chain. Good general concordance was observed between the patient's lymphoma and the cell line by comparing the immunophenotype, genotype, and karyotype. The UoC-B2 cells expressed surface IgM but did not secrete IgM into the culture media even in the presence of supplemental IL-6.

CONCLUSIONS

A B-lymphoid cell line (UoC-B2) was established from a child with primary cutaneous lymphoma. The cells expressed cell surface IgM and receptors for IL-6 but supplemental IL-6 had no effect on IgM production or cell proliferation.

Interleukin 6 signal transduction in a human hepatoma cell line (Hep G2)

Interleukin 6 is an important peptide regulatory factor with diverse biological activities including stimulation of acute phase protein synthesis. In this report we describe the effect of signal transduction pathway modulators on interleukin 6 mediated acute phase protein synthesis in a human hepatoma cell line Hep G2. Genistein, a tyrosine kinase inhibitor inhibited the interleukin 6 stimulated synthesis of acute phase proteins suggesting that a tyrosine kinase event participates in the signal transduction pathway. There was no evidence to suggest that protein kinase C had a stimulatory role although this or a related kinase may be involved in down-regulating the interleukin 6 signal.

Effect of recombinant human interleukin-11 on rat megakaryopoiesis and thrombopoiesis in vivo: comparative study with interleukin-6

The ability of recombinant human interleukin-11 (IL-11) to stimulate rat megakaryopoiesis and thrombopoiesis in vivo was investigated. Once daily subcutaneous injections of IL-11 at doses of 2, 8 and 20 micrograms/rat for 5 d caused dose-dependent increases in platelet counts. The chronic administration of 20 micrograms/rat/d for 14 d resulted in biphasic increases in platelet counts with peaks at days 8 and 15 of up to 30% over the control, continuing for more than 5 d after cessation of IL-11 injections. Moreover, a striking increase in megakaryocytic size and ploidy in bone marrow in response to IL-11 was elicited. IL-11 induced a dose-dependent elevation in bone marrow cell numbers but not in splenic weight and cell numbers. Modifications of these parameters were noted as soon as 24 h after the first IL-11 injections. IL-11 had a same potency of thrombopoietic effect in rats as compared with IL-6. However, elevation of acute phase protein such as immunosuppressive acidic protein was 2.2-fold in rats given 20 micrograms/d of IL-6 over those receiving a same dose of IL-11 (470 v 210 micrograms/ml). In addition, the rate of body-weight increase in rats receiving IL-11 for 5 d as well as 14 d did not differ from that in control animals. In IL-6 treated rats, the increase in body weight was significantly slower than the controls, which was observed even in the group given 8 micrograms/d of IL-6. These results suggest that IL-11 may be an effective strategy for the treatment of thrombocytopenia.

Serum soluble interleukin-6 receptor in MRL/lpr mice is elevated with age and mediates the interleukin-6 signal

The characteristics of soluble interleukin-6 receptor (sIL-6R) in murine sera were examined. To investigate a relationship between serum sIL-6R level and autoimmune diseases, quantitative analysis of serum sIL-6R in MRL/lpr mice was performed by an enzyme-linked immunosorbent assay. The serum sIL-6R level in MRL/lpr mice of both sexes was below the detection limit (< 1.0 ng/ml) at 8 weeks of age, but it increased in accordance with age and reached 42 +/- 9.3 ng/ml in female and 31 +/- 13 ng/ml in male mice at 30 weeks of age. In MRL/+ mice, although an age-associated increase in serum sIL-6R level was observed, it was much less extensive than that in MRL/lpr mice. Elevated serum sIL-6R level at the age of 30 weeks was observed in female and male (NZB x NZW)F1 mice (32 +/- 10 ng/ml and 17 +/- 5.0 ng/ml, respectively), and male BXSB/Mpj Yaa mice (42 +/- 18 ng/ml), suggesting that elevated serum sIL-6R in aged mice is one of the characteristics of autoimmune-prone mice. Quantitative analysis of serum IL-6 in MRL/lpr revealed that the serum sIL-6R level correlated well with the serum IL-6 level. We also showed that sIL-6R in the sera from MRL/lpr mice could mediate the IL-6 functions through the IL-6 signal-transducing receptor component gp130, suggesting that elevated production of sIL-6R may partly contribute to development of autoimmune disease in MRL/lpr mice.

Generation of effector cytotoxic T cells from cytotoxic T cell precursors: role of soluble factors

Cytotoxic T lymphocytes (CTL) have long been recognized as playing a major role in the immune response to alloantigens and viral antigens as well as tumor antigens. The progress of the last decade in the identification and characterization of soluble factors involved in the regulation of the immune response has greatly improved our knowledge of the mechanisms of CTL activation and regulation. This review will summarize the data available in the literature regarding different lymphokines and their specific activity on CTL. In addition it will point out a few of the elements of the systems that hamper its full understanding and it will suggest possible directions for future research.

Interleukin-6 undergoes transition from paracrine growth inhibitor to autocrine stimulator during human melanoma progression

The ability to penetrate the dermal basement membrane and subsequently proliferate in the underlying mesenchyme is one of the key steps in malignant progression of human melanomas. We previously undertook studies aimed at assessing how normal dermal fibroblasts (one of the main cellular components of mesenchyme) may affect the growth of human melanoma cells and facilitate the overgrowth of malignant subpopulations (Cornil, I., D. Theodorescu, S. Man, M. Herlyn, J. Jambrosic, and R. S. Kerbel. 1991. Proc. Natl. Acad. Sci. USA. 88:6028-6032). We found that melanoma cell lines from early-stage (metastatically incompetent) lesions were growth inhibited whereas those from advanced-stage (metastatically competent) lesions were stimulated under the same conditions by co-culture with fibroblasts; conditioned medium from such cells gave the same result. Subsequent studies using biochemical purification and neutralizing antibodies revealed the inhibitory activity to be identical to interleukin-6 (IL-6). We now report that addition of purified recombinant human IL-6 resulted in a growth inhibition in vitro by G1/G0 arrest of early, but not advanced stage melanoma cells. Despite this alteration in response there was no significant difference in melanoma cell lines of varying malignancy in respect to their expression of genes encoding the IL-6 receptor, or gp130, the IL-6 signal transducer. Scatchard analysis also revealed similar [125I]IL-6 binding activities in both IL-6 sensitive and resistant groups. However, studies of IL-6 production indicated that five out eight IL-6 melanoma cell lines known to be resistant to exogenous IL-6-mediated growth inhibition constitutively expressed mRNA for IL-6; they also secreted bioactive IL-6 into culture medium. To assess the possible role of this endogenous IL-6 in melanoma cell growth, antisense oligonucleotides to the IL-6 gene were added to cultures of melanoma cells. This resulted in a significant growth inhibition only in cell lines that produced endogenous IL-6. In contrast, neutralizing antibodies to IL-6 were ineffective in causing such growth inhibition. This indicates that endogenous IL-6 may behave as a growth stimulator by an intracellular ("private") autocrine mechanism. Thus, a single cytokine, IL-6, can switch from behaving as a paracrine growth inhibitor to an autocrine growth stimulator within the same cell lineage during malignant tumor progression. Such a switch may contribute to the growth advantage of metastatically competent melanoma cells at the primary or distant organ sites and thereby facilitate progression of disease.

Induction of metallothionein in a human astrocytoma cell line by interleukin-1 and heavy metals

The effects of cytokines and heavy metals on the expression and localization of metallothioneins (MTs) within U373MG astrocytoma cells were analyzed by using indirect immunofluorescence using a monoclonal anti-MT antibody (MT45). IL-1, CdCl2 (50 microM) or ZnCl2 (500 microM) remarkably augmented intracellular MT levels, whereas IL-6 or 10 microM of ZnCl2 showed no inducing activity. From 24 to 48 h after the addition of CdCl2 or IL-1, immunoreactive MTs were found in the cytoplasm and the nucleus. After 72 h, immunoreactive MTs accumulated in a granular form near the cell surfaces in the presence of CdCl2 (50 microM) or IL-1 plus ZnCl2 (10 microM). However, this accumulation was not observed when only IL-1 was added. Thus, Zn2+ facilitated the appearance of the granular form of immunoreactive MTs at a concentration where they do not induce MTs by themselves.

Involvement of the Arg179 in the active site of human IL-6

Three internal-amino acid deletions of amino acids 171-179 of human interleukin 6 (IL-6) were introduced at the cDNA level. While all deletion proteins were biologically inactive, immunoprecipitations with a set of conformation-specific anti-(IL-6) monoclonal antibodies showed that only mutant delta 177-179 does not present major alterations in folding. This finding, together with the observation that delta 177-179 is not able to compete with IL-6 for binding to the soluble human IL-6 receptor, suggested that some or all of these three residues participate to the composition of the receptor-binding site of human IL-6. A large number of single-amino-acid-substitution mutants were generated in residues 177, 178 and 179. Their detailed analysis revealed that Arg179 is crucial for activity in mouse cells, because all amino acid substitutions in this position cause a dramatic drop of biological activity on murine hybridoma cells without affecting the overall protein folding. The only substitution which preserved some residual activity was the conservative Arg to Lys change. This demonstrates the absolute requirement for a positive charge in position 179 for the interaction of human IL-6 with its receptor.

Immunoreactive interleukin-6 in serum of patients with B-lymphoproliferative diseases

Serum immunoreactive interleukin-6 (ir-IL-6) concentration was measured by radioimmunoassay in nine patients with chronic lymphocytic leukaemia (CLL), 16 patients with multiple myeloma (MM), 12 patients with monoclonal gammapathy of undetermined significance (MGUS), 22 patients with primary Sjögren's syndrome (SS), and in 32 control subjects. Measurable quantities of ir-IL-6 were detected in every sample studied. Patients with MGUS and SS had significantly higher serum ir-IL-6 (mean +/- SD) concentrations (337 +/- 92 ng l-1 and 299 +/- 100 ng l-1, respectively) than controls (92 +/- 77 ng l-1) and patients with CLL and MM (120 +/- 32 ng l-1 and 113 +/- 58 ng l-1, respectively). Longitudinal studies of ir-IL-6 concentration in a few patients with MM showed a decrease before remission and an increase prior to relapse, but no consistent pattern was detected. In conclusion, we found that serum ir-IL-6 levels are higher in patients with benign hypergammaglobulinaemic states than in patients with malignant neoplastic B-cell disorders.

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.

A soluble receptor for interleukin-1 beta encoded by vaccinia virus: a novel mechanism of virus modulation of the host response to infection

Vaccinia virus gene B15R is shown to encode an abundant, secretory glycoprotein that functions as a soluble interleukin-1 (IL-1) receptor. This IL-1 receptor has novel specificity since, in contrast with cellular counterparts, it binds only IL-1 beta and not IL-1 alpha or the natural competitor IL-1 receptor antagonist. The vaccinia IL-1 beta receptor is secreted when expressed in a baculovirus system and competitively inhibited binding of IL-1 beta to the natural receptor on T cells. Deletion of B15R from vaccinia virus accelerated the appearance of symptoms of illness and mortality in intranasally infected mice, suggesting that the blockade of IL-1 beta by vaccinia virus can diminish the systemic acute phase response to infection and modulate the severity of the disease. The IL-1 beta binding activity is present in other orthopoxviruses.

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.

Purification and characterization of a recombinant murine interleukin-6. Isolation of N- and C-terminally truncated forms

Murine interleukin-6 (IL-6), when expressed in Escherichia coli using the pUC9 vector, accumulated as insoluble aggregates or 'inclusion bodies'. After selective urea washing of the inclusion bodies, to remove extraneous proteins, murine IL-6 was solubilized with 8 M guanidine hydrochloride and then rapidly purified to homogeneity by gel-permeation chromatography followed by reversed-phase HPLC. It was demonstrated that complete disulfide bond formation in murine IL-6 occurred during the early urea washing/guanidine hydrochloride extraction steps, so no refolding step was required. When fully reduced murine IL-6 was dissolved in 8 M guanidine hydrochloride and allowed to air-oxidize, complete disulfide bond formation, monitored by analytical reversed-phase HPLC, was shown to occur within 13 h at 6 degrees C. About 25 mg pure protein was obtained from 37 g wet cells. This recombinant murine IL-6 had a specific activity in the hybridoma growth factor assay of 2 x 10(8) U/mg, which is equivalent to that of native murine IL-6. During the purification procedure, a number of variant forms of murine IL-6 were isolated and partially characterized. Two of these forms, T1 and T3, were C-terminal deletants of murine IL-6 lacking about 60 and 20 amino acids from the C-terminus, respectively, while the other form, T2, was an N-terminal deletant lacking 37 amino acids from the N-terminus. None of these variant forms of murine IL-6 bound to the murine IL-6 receptor and, consequently, all were inactive in the hybridoma growth factor assay.

Cytokine regulation of interleukin-6 gene expression in astrocytes involves activation of an NF-kappa B-like nuclear protein

The cytokines interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) induce interleukin-6 (IL-6) gene expression in astrocytes. The molecular mechanism(s) by which these cytokines activate IL-6 expression was examined by transient transfection of the human IL-6 promoter linked to the reporter gene CAT (IL-6-CAT) in primary rat astrocytes. We show that both IL-1 beta and TNF-alpha exert their effects through the IL-6 promoter to increase CAT activity, indicating that the cytokines act at the transcriptional level. Use of deletion mutants revealed that the NF-kappa B-like binding site is required for cytokine induction of IL-6 promoter activity. The correlary effects of IL-1 beta and TNF-alpha on DNA-binding proteins specific for this element were examined. Treatment of astrocytes with either cytokine leads to a rapid activation (15 min) of a nuclear protein which specifically complexes with the NF-kappa B-like binding region in the IL-6 promoter. These results suggest that TNF-alpha and IL-1 beta activate IL-6 gene expression in astrocytes by a mechanism(s) involving activation of an NF-kappa B-like protein.

Detection of cytokine receptors by high-sensitivity immunofluorescence/flow cytometry

Cytokines have profound effects on cells, and act through receptors which need only be at low concentrations (around 100 copies per cell) to transmit activation signals. The detection of such low concentrations is possible using monoclonal antibodies and fluorescence/flow cytometry, but only by using specialized techniques. The best results so far have been obtained using biotinylated second antibody followed by phycoerythrin-streptavidin, and batches of these reagents have to be carefully selected. Analysis of the fluorescence is best done using 546 nm excitation from a mercury arc lamp, but 512 nm excitation from an argon-ion laser can also be used. With appropriate alignment, instruments with 488 nm fixed-wavelength lasers can give sensitivity almost as good as the 546 nm system. Working at high sensitivity, background levels also increase, particularly for B lymphocytes. Background staining can be reduced to acceptable levels by blocking the two major mechanisms for non-specific binding. Applications of these methods to the detection of cytokine receptors on normal and malignant cells are reviewed.

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.

Expression of interleukin-6 receptor on blood lymphocytes without in vitro activation

A monoclonal antibody against the interleukin-6 receptor (IL-6R) has been used in a high-sensitivity immunofluorescence technique to study receptor expression on unstimulated blood lymphocytes. Most CD4 cells express IL-6 receptor, whilst a small and variable proportion of CD8 and B cells are positive. CD4+ cells express higher levels of receptor than CD8+ T cells, and CD45RO+ cells express higher levels than CD45RA cells.

Synergistic action of interleukin-6 and glucocorticoids is mediated by the interleukin-6 response element of the rat alpha 2 macroglobulin gene

One class of genes coding for the acute-phase proteins (acute-phase genes) is induced by interleukin 6 (IL-6) through the human transcription factor NF-IL-6 and its rat homolog IL-6-DBP/LAP. A second class, represented by the rat alpha 2 macroglobulin gene, utilizes a different IL-6 response element (IL-6-RE) and different DNA-binding proteins interacting with this element, the so-called IL-6-RE binding proteins (IL-6 RE-BPs). Human Hep3B and HepG2 hepatoma, U266 myeloma, and CESS lymphoblastoid cells contain IL-6 RE-BPs that form complexes, with the IL-6-RE, with gel mobilities indistinguishable from those of the corresponding complexes of rat liver cells. The ability to form these complexes was induced by IL-6 in human hepatoma cells with a maximum reached after 4 h and required ongoing protein synthesis. Multiple copies of an 18-bp element containing the IL-6-RE core were sufficient to confer both induction by IL-6 and a synergistic induction by IL-6 plus glucocorticoids to minimal promoters. The synergism was blocked by the receptor antagonist RU486 and thus was dependent on the glucocorticoid receptor (GR). However, the 18-bp element contained no consensus GR-binding site, and recombinant GR did not bind at this sequence. Therefore, the synergism was probably achieved by an indirect effect of a glucocorticoid-activated intermediate gene on the IL-6 RE-BPs. The rat IL-6 RE-BP had a molecular weight of 102 +/- 10 kDa and was thus distinct from NF-IL-6 and IL-6-DBP/LAP. Therefore, IL-6 must activate two different classes of liver acute-phase genes through at least two different nuclear DNA-binding proteins: NF-IL-6/IL-6-DBP/LAP and the IL-6 RE-BP.

Up-regulation of interleukin (IL)-6 receptor gene expression in vitro and in vivo in IL-6 deprived myeloma cells

Myeloma cells absolutely require interleukin-6 (IL-6) for growing in vivo in patients with multiple myeloma and exogenous IL-6-dependent myeloma cell lines have been reproducibly obtained. In this study we show a dramatic up-regulation of the IL-6 receptor (gp80 chain) gene expression in myeloma cell lines following the removal of exogenous IL-6. Such a regulation was also known to occur in IL-6-deprived myeloma cells in vivo in three patients who were treated with optimal doses of anti-IL-6 monoclonal antibodies. The direct effect of IL-6 on IL-6 receptor gene expression in myeloma cells was further confirmed by adding IL-6 to an autonomously growing myeloma cell line.

Synergistic action of interleukin-6 and glucocorticoids is mediated by the interleukin-6 response element of the rat alpha 2 macroglobulin gene

One class of genes coding for the acute-phase proteins (acute-phase genes) is induced by interleukin 6 (IL-6) through the human transcription factor NF-IL-6 and its rat homolog IL-6-DBP/LAP. A second class, represented by the rat alpha 2 macroglobulin gene, utilizes a different IL-6 response element (IL-6-RE) and different DNA-binding proteins interacting with this element, the so-called IL-6-RE binding proteins (IL-6 RE-BPs). Human Hep3B and HepG2 hepatoma, U266 myeloma, and CESS lymphoblastoid cells contain IL-6 RE-BPs that form complexes, with the IL-6-RE, with gel mobilities indistinguishable from those of the corresponding complexes of rat liver cells. The ability to form these complexes was induced by IL-6 in human hepatoma cells with a maximum reached after 4 h and required ongoing protein synthesis. Multiple copies of an 18-bp element containing the IL-6-RE core were sufficient to confer both induction by IL-6 and a synergistic induction by IL-6 plus glucocorticoids to minimal promoters. The synergism was blocked by the receptor antagonist RU486 and thus was dependent on the glucocorticoid receptor (GR). However, the 18-bp element contained no consensus GR-binding site, and recombinant GR did not bind at this sequence. Therefore, the synergism was probably achieved by an indirect effect of a glucocorticoid-activated intermediate gene on the IL-6 RE-BPs. The rat IL-6 RE-BP had a molecular weight of 102 +/- 10 kDa and was thus distinct from NF-IL-6 and IL-6-DBP/LAP. Therefore, IL-6 must activate two different classes of liver acute-phase genes through at least two different nuclear DNA-binding proteins: NF-IL-6/IL-6-DBP/LAP and the IL-6 RE-BP.

Soluble interleukin-6 receptor is released from receptor-bearing cell lines in vitro

Soluble interleukin-6 receptor (sIL-6R) was found to be spontaneously released from human myeloma cell line U266 cells into culture supernatant, and was quantitatively measured with a fluorescence sandwich enzyme-linked immunosorbent assay employing antibodies specific to IL-6R. The supernatant IL-6R was generated only from IL-6R-positive cell lines; myeloma cell lines RPMI8226 and PRMI1788, and myelomonocytic cell lines U937, THP-1, and HL-60. In contrast, it was not released from the IL-6R-negative cells; T cell line Molt-4 and Burkitt lymphoma cell line Raji. SDS-PAGE analysis of the soluble IL-6R from U266 cells suggested a molecular weight of approximately 50-55 kDa, 25-30 kDa smaller than the mature cell surface receptor. These results suggest that the generation of soluble IL-6R may be a maker of myeloma cells and myelomonocytic cells.

Targeting growth factor receptors with fusion toxins

Recombinant toxins which bind to growth factor receptors have been prepared and used to kill cells responsible for malignant or autoimmune disease. Our strategy has been to genetically fuse ligands to different forms of Pseudomonas exotoxin which due to mutations or deletions do not bind to normal cells. The resulting recombinant chimeric toxins, in concentrations often less than 1 ng/ml, selectively kill cells expressing the appropriate growth factor receptor. The ligand may be a growth factor, such as transforming growth factor alpha (TGF alpha), interleukin 6 (IL6) or interleukin 2 (IL2), or single chain antigen binding proteins, such as the variable heavy and light regions of the monoclonal antibody anti-Tac. These chimeric toxins kill not only established cell lines but also fresh tumor cells from patients and display anti-tumor activity toward human malignant tumors in nude mice. While clinical trials are beginning with some of these agents, work continues to improve the effectiveness of recombinant chimeric toxins, and to widen the scope of disorders which might be treated by this approach.

Interleukin-6 regulates the cytotoxic effect of tumour necrosis factor on U937 cells

In this study, we demonstrate that low but not high concentrations of interleukin-6 (IL-6) potentiate the cytotoxic effect of tumour necrosis factor-alpha (TNF-alpha) on U937 cells, in a dose-dependent manner. Killing of U937 cells by 100 U/ml of TNF-alpha, was maximally potentiated by 50 U/ml of IL-6. No potentiation of cell killing was observed when the concentration of IL-6 was increased to 4000 U/ml. At a concentration of 50 U/ml, IL-6 up-regulated TNF receptor expression but no change in TNF receptor number was observed when the concentration of IL-6 was increased to 4000 U/ml. Low concentrations of IL-6 can also induce sub-cytotoxic doses of TNF-alpha (0.1 and 0.33 U/ml) to kill U937 cells. Up-regulation of TNF receptors by IL-6 is dependent on de novo protein synthesis since receptor induction is abolished in the presence of cycloheximide. Taken together the data suggest that the potentiation of cell killing observed by a combination of these lymphokines is mediated in part by IL-6-induced changes in TNF receptor expression.

The IL-6 signal transducer, gp130: an oncostatin M receptor and affinity converter for the LIF receptor

Leukemia inhibitory factor (LIF) and interleukin-6 (IL-6) are multifunctional cytokines with many similar activities. LIF is structurally and functionally related to another cytokine, Oncostatin M (OSM), that binds to the high-affinity LIF receptor but not to the low-affinity LIF receptor. A complementary DNA was isolated that encodes the high-affinity converting subunit of the LIF receptor. The converter conferred high-affinity binding of both LIF and OSM when expressed with the low-affinity LIF receptor and is identical to the signal transducing subunit of the IL-6 receptor, gp130. The gp130 subunit alone confers low-affinity binding of OSM when expressed in COS-7 cells. This receptor system resembles the high-affinity receptors for granulocyte-macrophage colony-stimulating factor, IL-3, and IL-5, which share a common subunit.

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.

Interleukin-6 can prime THP-1 macrophages for enhanced production of tumor necrosis factor-alpha in response to LPS

Although interferon-gamma has been shown to effectively prime macrophages for enhanced production of tumor necrosis factor-alpha (TNF alpha), it is reasonable to assume that other cytokines present in the extracellular environment may likewise facilitate cytokine biosynthesis. For example, interleukin-6 (IL-6) is synthesized by synovial lining macrophages and fibroblasts, and has been detected (along with TNF alpha) in rheumatoid synovial effusions. Therefore, the purpose of the present study was to determine whether IL-6 influences the production of IL-1 beta and/or TNF alpha by THP-1 macrophages. Although IL-6 treatment alone resulted in only a slight increase in TNF alpha levels, administration of IL-6 followed by Sal. minnesota LPS resulted in a synergistic potentiation of TNF alpha production by THP-1 macrophages. The priming effect of IL-6 could be reversed by boiling, or by the addition of a neutralizing polyclonal antibody against IL-6. Notably, IL-6 only weakly enhanced interleukin-1 beta production. In summary, the ability of IL-6 to potentiate TNF alpha production by THP-1 macrophages may provide insight into the regulation of the cytokine network in inflammatory diseases, such as rheumatoid arthritis.

Search for hepatitis B virus cell receptors reveals binding sites for interleukin 6 on the virus envelope protein

The major target organ for hepatitis B virus (HBV) is the liver. However, cells other than hepatocytes, including peripheral blood lymphocytes and monocytes, may become infected with HBV. The cell receptor binding site was assigned to the preS(21-47) segment of the HBV envelope protein. HBV receptors were detected on human liver and hepatoma cells, on B lymphocytes, and, as shown here, on monocytes, and T cell lines, activated by Escherichia coli lipopolysaccharide and concanavalin A, respectively. The cell receptors for HBV have not been characterized until now. The detection of HBV receptors and their "activation antigen" characteristic on distinct cells suggested paths for identification of the receptors with already defined cell surface proteins. This search revealed that interleukin 6 contains recognition sites for the preS(21-47) sequence and mediates HBV-cell interactions. Thus, HBV belongs to a group of viruses utilizing cytokines or cytokine receptors for replication and interference with the host immune system.

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

Interleukin-6 (IL-6) relays an important signal to hepatocytes during the early stages of an acute inflammatory response, causing an alteration in the expression of several major defense proteins. Additional regulation of this signal could occur either by altering the number of IL-6 receptors (IL-6-R) or of the signal transducing protein, gp130. We employed ribonuclease protection assays to measure the expression of IL-6-R and gp130 mRNA in primary rat hepatocytes in response to IL-6, interleukin-1, dexamethasone, and combinations thereof. Dexamethasone increases receptor mRNA levels 2.7-fold above controls but has no detectable effect on that of gp130. Such treatment increased surface expression of IL-6-R from 600 receptors per cell to greater than 6000, without a change in Kd (2.5-4.6 x 10(-10) M). In contrast to the stimulatory effect of the steroid signal, the inflammatory cytokines, individually and together, down-modulated both the mRNA and the cell surface expression of IL-6-R. These findings demonstrate for the first time that a sensitive control system exists between inflammatory mediators and IL-6-R.

Interleukin-6 and its relation to inflammation and disease

Interleukin-6 (IL-6) is a multifunctional cytokine that regulates the immune response, acute phase reactions, and hematopoiesis. Its receptor system consists of two molecules: a ligand-binding 80-kDa molecule and a non-ligand-binding signal transducer, gp 130, both of which were found to belong to the cytokine receptor family. Deregulated IL-6 gene expression has been implicated as being involved in the pathogenesis of a number of diseases, especially autoimmune diseases and plasma cell neoplasias. In fact, IL-6 transgenic C57BL/6 mice showed a massive polyclonal plasmacytosis with production of autoantibodies and mesangial proliferative glomerulonephritis, indicating that IL-6 plays a critical role in the development of plasma cell abnormalities and glomerulonephritis.

Production of interleukin-6 by human retinal pigment epithelium in vitro and its regulation by other cytokines

Interleukin-6 (IL-6) is a pleiotropic cytokine which produces uveitis if administered intraocularly. It has been demonstrated in the aqueous of patients with various uveitis entities. We have investigated the ability of human retinal pigment epithelium (RPE) to produce IL-6 in vitro, both unstimulated, and in the presence of interleukin-1 (IL-1), tumor necrosis factor alpha (TNF), interferon (IFN) gamma, and lipopolysaccharide (LPS). Five human RPE cell lines were cultured over a 6-day period, both unstimulated and in the presence of these cyokines. IL-6 in the supernatants was measured using an ELISA assay. Unstimulated RPE produced small amounts of IL-6. IL-1 at 100 or 10 U/ml markedly upregulated IL-6 production, and TNF at 1000, 100 or 10 U/ml did so to a lesser extent. Neither IFN gamma or LPS alone increased IL-6 expression, but together gave significant upregulation. Thus human RPE can produce IL-6 and may be the source of this cytokine in ocular inflammatory states.