IL-6 cytokine family and signal transduction: a model of the cytokine system

Expression of interleukin-6 and its receptor in the sciatic nerve and cultured Schwann cells: relation to 18-kD fibroblast growth factor-2

Expression of interleukin-6 (IL-6) and fibroblast growth factor-2 (FGF-2) in Schwann cells is modulated by external stimuli. To study possible interactions of both factors we have analyzed mutual effects of exogenous IL-6 and FGF-2 on the expression of each other and the corresponding receptor (R) molecules IL-6R and FGFR1 after peripheral nerve lesion in vivo and in vitro using cultured Schwann cells. Using rat Schwann cells we found that IL-6 did not exert any effects on the expression of FGF-2 and FGF receptor type 1 (R1) whereas exogenously applied 18-kD FGF-2 strongly increased the expression of the mRNAs of IL-6 and its receptor. In addition, immortalized Schwann cells over-expressing the 18-kD FGF-2 isoform showed elevated levels of IL-6 and IL-6R whereas immortalized Schwann cells over-expressing the high-molecular-weight isoforms (21 kD and 23 kD) displayed unaltered IL-6 and IL-6R expression levels. According to in situ hybridization studies of intact and crushed sciatic nerves in vivo, Schwann cells seems to be the main source of IL-6 and IL-6R. Following sciatic nerve crush, the FGF-2 and the IL-6 system are upregulated after the first hours. Furthermore, we showed that the early increase of the FGF-2 protein is mainly confined to the 18-kD isoform. These results are consistent with the idea of a functional coupling of FGF-2 and the IL-6 system in the early reaction of Schwann cells to nerve injury.

Bone morphogenetic protein-2 induces apoptosis in human myeloma cells with modulation of STAT3

Bone morphogenetic proteins (BMPs), members of the transforming growth factor (TGF)–β superfamily, are a group of related proteins that are capable of inducing the formation of cartilage and bone but are now regarded as multifunctional cytokines. We show in this report a novel function of BMPs in hematopoietic cells: BMP-2 induces apoptosis not only in human myeloma cell lines (U266, RPMI 8226, HS-Sultan, IM-9, OPM-2, and KMS-12 cells), but also in primary samples from patients with multiple myeloma. The mechanism of BMP-2–induced apoptosis was investigated with the use of U266 cells, which are dependent on the interleukin-6 autocrine loop. We showed that BMP-2 caused cell-cycle arrest in the G1 phase and the subsequent apoptosis of myeloma cells. BMP-2 up-regulated the expression of cyclin-dependent kinase inhibitors (p21CIP1/WAF1 and p27KIP1) and caused hypophosphorylation of retinoblastoma (Rb) protein. In studies of apoptosis-associated proteins, BMP-2 was seen to down-regulate the expression of Bcl-xL; however, BMP-2 had no effects on the expression of Bcl-2, Bax, or Bad. Therefore, BMP-2 induces apoptosis in various human myeloma cells by means of the down-regulation of Bcl-xL and by cell-cycle arrest through the up-regulation of p21CIP1/WAF1 and p27KIP1 and by the hypophosphorylation of Rb. Further analysis showed that the signal transducer and activator of transcription 3 (STAT3) was inactivated immediately after BMP-2 treatment. We conclude that BMP-2 would be useful as a novel therapeutic agent in the treatment of multiple myeloma both by means of its antitumor effect of inducing apoptotis and through its original bone-inducing activity, because bone lesions are frequently seen in myeloma patients.

Bone morphogenetic protein-2 induces apoptosis in human myeloma cells with modulation of STAT3

Bone morphogenetic proteins (BMPs), members of the transforming growth factor (TGF)–β superfamily, are a group of related proteins that are capable of inducing the formation of cartilage and bone but are now regarded as multifunctional cytokines. We show in this report a novel function of BMPs in hematopoietic cells: BMP-2 induces apoptosis not only in human myeloma cell lines (U266, RPMI 8226, HS-Sultan, IM-9, OPM-2, and KMS-12 cells), but also in primary samples from patients with multiple myeloma. The mechanism of BMP-2–induced apoptosis was investigated with the use of U266 cells, which are dependent on the interleukin-6 autocrine loop. We showed that BMP-2 caused cell-cycle arrest in the G1 phase and the subsequent apoptosis of myeloma cells. BMP-2 up-regulated the expression of cyclin-dependent kinase inhibitors (p21CIP1/WAF1 and p27KIP1) and caused hypophosphorylation of retinoblastoma (Rb) protein. In studies of apoptosis-associated proteins, BMP-2 was seen to down-regulate the expression of Bcl-xL; however, BMP-2 had no effects on the expression of Bcl-2, Bax, or Bad. Therefore, BMP-2 induces apoptosis in various human myeloma cells by means of the down-regulation of Bcl-xL and by cell-cycle arrest through the up-regulation of p21CIP1/WAF1 and p27KIP1 and by the hypophosphorylation of Rb. Further analysis showed that the signal transducer and activator of transcription 3 (STAT3) was inactivated immediately after BMP-2 treatment. We conclude that BMP-2 would be useful as a novel therapeutic agent in the treatment of multiple myeloma both by means of its antitumor effect of inducing apoptotis and through its original bone-inducing activity, because bone lesions are frequently seen in myeloma patients.

Effect of pressure overload on angiotensin receptor expression in the rat heart during early postnatal life

The development of cardiac hypertrophy during neonatal life and in adults implies different processes. The angiotensin II (Ang II) system is involved in the development of cardiac hypertrophy in adults, but its role in neonates remains unclear. The aim of this study was to estimate the influence of increased hemodynamic load on the developmental pattern of the AT1/AT2 receptor expression in the heart. Two-day-old rats submitted to abdominal aortic constriction (AC) or sham operation were sacrificed 2 h, and 1, 3, and 8 days after surgery. Ang II was evaluated in sera and immunohistology was performed to define the cardiac hypertrophy process. The Ang II receptor subtypes 1 and 2 were quantified at the receptor and mRNA levels by(125)I-Ang II binding and RT-PCR, respectively. Ang II content in sera increased transiently 2 h after surgery in the AC group. In sham-operated, AT1 and AT2 decreased throughout the period studied at both mRNA and receptor levels. However, the AT1 mRNA level decrease was more pronounced than that of AT2 (by 57% and 27%, respectively). AC not only prevented the postnatal decrease in AT mRNA level but resulted in an increase in AT1 mRNA 8 days after surgery (P<0.05). Besides in the AC groups, AT2 mRNA levels but not those of AT1 mRNA were linearly correlated with the left ventricular mass. At the receptor level, a significant transient (1 day after surgery) increase in both AT1 and AT2 was observed. In conclusion, our data demonstrated that imposition of pressure overload soon after birth altered the pattern of AT receptor expression.

Oncostatin M regulation of interleukin-6 expression in astrocytes: biphasic regulation involving the mitogen-activated protein kinases ERK1/2 and p38

Oncostatin M (OSM) is a member of the interleukin (IL)-6 family of cytokines and has both pro- and anti-inflammatory properties. Of interest, OSM has functional effects within the CNS. We have shown recently that OSM can modulate expression of the cytokine IL-6 in astrocytes. Herein we characterize the molecular mechanisms and signaling cascades involved in this response. OSM induces IL-6 protein expression in a dose- and time-dependent manner in astrocytes. In addition, OSM can synergize with the cytokines tumor necrosis factor-alpha, IL-1beta, and transforming growth factor-beta for enhanced IL-6 expression. Using neutralizing antibodies to gp 130, the OSM receptor (OSMR), and the leukemia inhibitory factor receptor (LIFR), we document that OSM exclusively uses the OSMR/gp 130 heterodimer in signaling events, rather than the LIFR/gp 130 heterodimer. Kinetic analysis of OSM-induced IL-6 mRNA reveals two up-regulatory events. The first, peaking at 1 h, is transient, does not require protein synthesis, and is regulated at the transcriptional level. The second, peaking between 6 and 8 h, is prolonged and sensitive to puromycin, suggesting a requirement for de novo protein synthesis, and also is transcriptionally regulated. OSM-induced IL-6 mRNA and protein expression is inhibited by the mitogen-activated protein kinase (MAPK) inhibitors U0126 and SB202190, suggesting a requirement for the MAPKs ERK1/2 and p38 in this response. Finally, we show that the MAPKs ERK1/2 and p38 are activated by OSM in astrocytes and that this activation is reduced by the MAPK inhibitors. These data demonstrate that OSM induces IL-6 expression in astrocytes and that the MAPKs ERK1/2 and p38 participate in this response.

Regulation of interleukin 6 production in a human gastric epithelial cell line MKN-28

Interleukin (IL-) 6 is closely related to gastrointestinal diseases. The question of whether gastric epithelial cell contributes to IL-6 production remains undefined. We aim to evaluate the regulatory pathway of IL-6 expression in gastric epithelial cells, by using different inflammatory cytokines, endotoxin, or protein kinase modulators. IL-6 was measured by ELISA. Phorbol-12-myristate-13-acetate (PMA), calcium ionophore A23187, TNF-alpha, IL-1beta, oncostatin M (OSM) but not lipopolysaccharide stimulated IL-6 production from gastric epithelial cell line MKN-28. Blocking protein tyrosine kinase (PTK) activation by herbimycin A or genistein, or blocking NF-kappaB activation by pyrrolidinedithiocarbamate, reduced the IL-6 expression induced by TNF-alpha, IL-1beta and OSM. Dexamethasone mimicked this effect. Protein kinase (PK) C inhibitor only reduced the PMA and OSM induced IL-6 production. Both inhibitors and activators for PKA and G-protein as well as IL-10 had no effects on IL-6 expression. These results indicate that inflammatory cytokines are crucial for IL-6 regulation in gastric epithelial cells. The IL-6 signal pathway is mediated through PTK, NF-kappaB, and also involve PKC, intracellular calcium and sensitive to dexamethasone, but is not related to PKA, G-protein and IL-10.

Control of myeloid differentiation and survival by Stats

Hematopoiesis involves a complex array of growth factors that regulate the survival and proliferation of immature progenitors, influence differentiation commitment, and modulate end-stage cell functions. This mini-review is focused on the role of Stat activation in the development of myeloid cells in response to hematopoietic cytokines. Much of the evidence implicating Stats in these cellular processes comes from studies of mutant cytokine receptors selectively uncoupled from Stat activation, dominant-inhibitory Stat mutants, and mice with targeted disruptions of Stat genes. Together these approaches provide strong evidence that Stat activation, particularly of Stat3 and Stat5, plays an important role in myeloid differentiation and survival. Oncogene (2000).

Interleukin-6 stimulates clonogenic growth of primary and metastatic human colon carcinoma cells

Interleukin-6 (IL-6) is a pleiotropic cytokine which exerts biological activities on various cell types including neoplastic cells. We have investigated the biological effect of IL-6 and the expression of IL-6 receptors (IL-6R) on human colorectal carcinoma cell lines. Isreco-1 was derived from the primary site of a colon cancer while Isreco-2 and Isreco-3 were established from a liver and peritoneal metastasis of the same patient. IL-6 stimulated colony formation in methylcellulose of Isreco-1 cells to 150% (P < 0.05). The effect was even more pronounced on the metastatic Isreco-2 line where colony numbers in the presence of IL-6 were enhanced up to four-fold (P < 0.0001) in a dose-dependent fashion. An anti-IL-6 antibody completely abolished this growth stimulatory effect of IL-6. RT-PCR analysis revealed transcripts for IL-6Ralpha and gp 130 in these cell lines. Experiments with additional cell lines confirmed the general expression of gp130 but showed limited expression of the IL-6Ralpha chain. Surprisingly, about half of the cell lines tested expressed IL-6 mRNA at low levels which was not translated into protein. Our results suggest that IL-6 can potently stimulate anchorage-independent growth of some colorectal carcinoma cells. This stimulation appears to occur through a paracrine mechanism.

Immunohistochemical detection of leukemia inhibitory factor after focal cerebral ischemia in rats

The cytokine leukemia inhibitory factor (LIF) modulates neuronal function during development and promotes neuronal survival after peripheral nerve injury, but little is known about LIF expression after cerebral ischemia. In the present study, the localization of LIF protein was immunohistochemically examined in rats after 3.5, 12, 24, 48, and 96 hours of reperfusion following 1.5 hours of middle cerebral artery occlusion (MCAO) induced by the intraluminal suture method. Double-staining immunohistochemistry with microtubule-associated protein-2 (MAP2), glial fibrillary acidic protein (GFAP), lectin histochemistry, and interleukin (IL) 6 was also performed. The sham group and immunosorption test did not show any clear LIF immunoreactivity. Definite LIF immunoreactivity was first detected after 12 hours of reperfusion in each of the brain regions examined: ischemic core, periinfarct region, and contralateral cortex. However, expression of LIF was most prominent in the periinfarct region at each time point, peaked at 24 hours, and then gradually declined until 96 hours of reperfusion. Some LIF-positive neurons in the periinfarct region expressed IL-6. At 96 hours of reperfusion, GFAP-labeled astrocytes around the infarct core also expressed LIF protein. Induction of LIF mRNA and protein was also confirmed by reverse transcription polymerase chain reaction and western blot analysis, respectively. These findings suggest that LIF expression in ischemically threatened neurons may reflect a repair or defense mechanism against the ischemic insult.

IL-6 up-regulates mcl-1 in human myeloma cells through JAK / STAT rather than ras / MAP kinase pathway

Mcl-1 is an anti-apoptotic member of the Bcl-2 family which is tightly regulated during myeloid and B cell differentiation. We have recently reported that Mcl-1 is expressed in human myeloma cells and that Mcl-1 and Bcl-x(L) expression are correlated. In the current study, we demonstrate that IL-6, a survival factor for the human myeloma cell line MDN, rapidly up-regulates Mcl-1 whereas it has no effect on Bcl-2 protein level. In MDN cells, IL-6 induces both extracellular signal-regulated protein kinase (ERK)1,2 and STAT3 activation whereas STAT1 and STAT5 activation remains undetectable. Furthermore, while investigating the IL-6 signaling pathway leading to Mcl-1 up-regulation, we show that a janus kinase (JAK)-2 inhibitor is able to inhibit both STAT3 activation and Mcl-1 up-regulation whereas an MAP/ERK kinase (MEK) inhibitor has no effect. In conclusion, our data suggest the involvement of the JAK / STAT pathway but not of the Ras / mitogen-activated protein (MAP) kinase pathway in IL-6-induced Mcl-1 up-regulation.

Interleukin-6 expression and regulation in astrocytes

The physiological function of interleukin-6 (IL-6) within the central nervous system (CNS) is complex; IL-6 exerts neurotrophic and neuroprotective effects, and yet can also function as a mediator of inflammation, demyelination, and astrogliosis, depending on the cellular context. In the normal brain, IL-6 levels remain low. However, elevated expression occurs in injury, infection, stroke, and inflammation. Given the diverse biological functions of IL-6 and its expression in numerous CNS conditions, it is critical to understand its regulation in the brain in order to control its expression and ultimately its effects. Accumulating data demonstrate that the predominant CNS source of IL-6 is the activated astrocyte. Furthermore, a wide range of factors have been demonstrated to be involved in IL-6 regulation by astrocytes. In this review, we summarize information concerning IL-6 regulation in astrocytes, focusing on the role of proinflammatory factors, neurotransmitters, and second messengers.

Oncostatin M: signal transduction and biological activity

Oncostatin M (OSM) is a multifunctional cytokine produced by activated T lymphocytes and monocytes that is structurally and functionally related to the subfamily of cytokines known as the IL-6-type cytokine family. OSM shares properties with all members of this family of cytokines, but is most closely related structurally and functionally to LIE OSM acts on a wide variety of cells and elicits diversified biological responses in vivo and in vitro which suggest potential roles in the regulation of gene activation, cell survival, proliferation and differentiation. OSM and LIF can bind to the same functional receptor complex (LIF-receptor beta and gp130 heteromultidimers) and thus mediate overlapping spectra of biological activities. There is a second specific beta receptor that binds OSM with high affinity and also involves the subunit gp130. The two receptors for OSM can be functionally different and be coupled to different signal transduction pathways. OSM-specific receptors are expressed in a wide variety of cell types and do not possess an intrinsic tyrosine kinase domain, but the JAK/STAT tyrosine kinase pathway mediates signal transduction.

Inhibitory roles for SHP-1 and SOCS-3 following pituitary proopiomelanocortin induction by leukemia inhibitory factor

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine that stimulates the hypothalamo-pituitary-adrenal (HPA) axis through JAK-STAT activation. We show here that LIF-induced JAK2 and STAT3 tyrosine phosphorylation is transient, disappearing within 20 and 40 minutes, respectively. LIF activates the SH2 domain-containing tyrosine phosphatase, SHP-1, with maximal stimulation observed at 30 minutes. SHP-1 is constitutively associated with JAK2, and LIF induces recruitment of phosphorylated STAT3 to this complex. Overexpression of wild-type or dominant negative forms of SHP-1 shows decreased or increased LIF-induced proopiomelanocortin (POMC) promoter activity, respectively. LIF-induced JAK2 and STAT3 dephosphorylation is delayed until after 60 minutes in cells that overexpress the mutant SHP-1. In addition, SOCS-3, a negative regulator of LIF signaling, binds to JAK2 after 60 minutes of LIF stimulation, after which the complex is degraded by the proteasome. SOCS-3 overexpression blocks LIF-induced JAK2 tyrosine phosphorylation, confirming a role for SOCS-3 in deactivating JAK2 by direct association. Using SOCS-3 fusion proteins, we also define regions of the SOCS-3 protein that are critical for inhibition of LIF-induced POMC promoter activity. Corticotrophic signaling by LIF is thus subject to 2 forms of negative autoregulation: dephosphorylation of JAK2 and STAT3 by the SHP-1 tyrosine phosphatase, and SOCS-3-dependent inactivation of JAK2.

CSF and serum levels of soluble interleukin-6 receptors (sIL-6R and sgp130), but not of interleukin-6 are altered in multiple sclerosis

Interleukin-6 (IL-6) has recently been implicated in multiple sclerosis (MS), since IL-6 deficient mice were resistant to a demyelinating form of experimental autoimmune encephalomyelitis and IL-6 expression was upregulated in MS. The cytokine IL-6 and its action mediating soluble receptors (sIL-6R and sgp130) were measured in cerebrospinal fluid (CSF) and serum of 61 MS patients and 39 controls. In the presence of unchanged IL-6 concentrations, sIL-6R and sgp130 serum levels were significantly increased in MS and correlated with disease severity. Furthermore, sgp130 CSF levels were decreased in MS, suggesting a possibly altered IL-6 regulation in the CSF.

The oncostatin M signalling pathway: reversing the neoplastic phenotype?

Oncostatin M (OSM) is a member of the interleukin 6 (IL-6) family of cytokines and was originally identified by its ability to inhibit proliferation of melanoma cells but augment the growth of normal fibroblasts. OSM has pleiotropic effects on many different cell types, but here we focus on its ability to inhibit the proliferation of cell lines derived from several tumour types, including breast carcinoma, ovarian cancer, melanoma, glioma and lung carcinoma. The inhibition of proliferation of several cancer cell lines by OSM is associated with alterations in cellular morphology and with phenotypic changes that are consistent with the induction of differentiation of these cells. These observations raise the possibility that OSM could have therapeutic potential.

Cardiotrophin-1 attenuates endotoxin-induced acute lung injury

Cardiotrophin-1 (CT-1) is a recently discovered member of the gp130 cytokine family, which includes IL-6, IL-11, leukemia inhibitory factor, ciliary neurotrophic factor, and oncostatin M. Recent evidence suggests that, like other members of this family, CT-1 may possess anti-inflammatory properties. We hypothesized that in vivo CT-1 administration would attenuate endotoxin (ETX)-induced acute lung injury. We studied the effects of CT-1 (100 microgram/kg ip, 10 min prior to ETX) in a rat model of ETX-induced acute lung injury (Salmonella typhimurium lipopolysaccharide, 20 mg/kg ip). Six hours after ETX, lungs were harvested for determination of neutrophil accumulation (myeloperoxidase, MPO, assay) and lung edema (wet-to-dry weight ratio). Mechanisms of pulmonary vasorelaxation were examined in isolated pulmonary artery rings at 6 h by interrogating endothelium-dependent (response to acetylcholine) and endothelium-independent (response to sodium nitroprusside) relaxation following alpha-adrenergic (phenylephrine)-stimulated preconstriction. CT-1 abrogated the endotoxin-induced lung neutrophil accumulation: 2.3 +/- 0.2 units MPO/g wet lung (gwl) vs 6. 3 +/- 0.3 units MPO/gwl in the ETX group (P < 0.05 vs ETX, P > 0.05 vs control). Similarly, CT-1 prevented ETX-induced lung edema: wet-to-dry-weight ratio, 4.473 +/- 0.039 vs 4.747 +/- 0.039 in the ETX group (P < 0.05 vs ETX, P > 0.05 vs control). Endotoxin caused significant impairment of both endothelium-dependent and -independent pulmonary vasorelaxation, and CT-1 attenuated this injury. Thus, cardiotrophin-1 possesses significant anti-inflammatory properties in a model of endotoxin-induced acute lung injury.

Human germ cell tumor cell lines express novel leukemia inhibitory factor transcripts encoding differentially localized proteins

The polyfunctional cytokine leukemia inhibitory factor (LIF) has been implicated in the maintenance of many stem and progenitor cell populations and as an autocrine growth factor for many tumor cell populations, including germ cell tumors. Studies of LIF transcript expression in germ cell tumor cell lines identified two novel human LIF transcripts, hLIF-M and hLIF-T, containing noncoding alternate first exons that are conserved among all reported LIF genes. Embryonal carcinoma (EC) cell lines expressed these transcripts at consistent levels and hLIF-M was generally the predominant LIF transcript in these cells. This expression pattern was characteristic of EC cells since variable independently regulated expression of these transcripts was evident in other cell lines. Overexpression analysis demonstrated that each alternate hLIF transcript generated different levels of extracellular LIF activity as a consequence of the translation of distinct but partially overlapping sets of proteins. Secreted LIF proteins translated from alternate initiation codons were expressed from the hLIF-D and hLIF-M transcripts. Intracellular, potentially cell-autonomous, proteins were encoded by the hLIF-M and hLIF-T transcripts. Since EC cell lines also expressed LIF receptor transcripts, the novel LIF transcription profiles and proteins identified here suggest a role for autocrine and/or cell-autonomous LIF signaling during germ cell tumorigenesis.

Generation of 'truncated' interleukin-6 receptor (IL-6R) mRNA by alternative splicing; a possible source of soluble IL-6R

Receptors for interleukin-6 (IL-6) occur in body fluids in soluble form, as well. This is an approx. 50 kDa protein with the ability to bind IL-6. The soluble IL-6 receptor (sIL-6R)/IL-6 complex can attach to membrane anchored gp130, a molecule associated with the signal transduction induced by IL-6 and by other related cytokines. Earlier we described the appearance of sIL-6R in various body fluids of autoimmune patients. In this study using reverse transcriptase polymerase chain reaction (RT-PCR) we isolated and characterised a truncated form of amplified cDNA reverse-transcribed from IL-6 receptor mRNA both from human hepatoma cell line HepG2 and mononuclear cells from inflammatory bowel disease (IBD) patients. Using digestion by Pvu II restriction endonuclease and direct nucleotide sequencing we conclude that alternative splicing is likely involved in generation of sIL-6R. Our further experiments suggest that IL-6 and recombinant sIL-6R themselves do not influence the alternative splicing of IL-6 receptor gene.

The IL-6/sIL-6R fusion protein hyper-IL-6 promotes neurite outgrowth and neuron survival in cultured enteric neurons

The undisturbed development of the enteric nervous system depends on the supply of various neurotrophic factors during ontogenesis. Besides glial cell line-derived neurotrophic factor (GDNF), leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) take part in its development. CNTF and LIF belong to the interleukin-6 (IL-6) family of cytokines. The combination of IL-6 and the soluble IL-6 receptor accelerates peripheral nerve regeneration. In this study, we examined the effect of the fusion protein Hyper-IL-6, which consists of IL-6 and the soluble receptor sIL-6R, on neurite outgrowth and neuronal survival in vitro. Myenteric plexus of newborn rats was dissected and dissociated. Cells were grown in either serum-free chemically defined medium alone or medium supplemented with sIL-6R, IL-6, sIL-6+IL-6, Hyper-IL-6, CNTF, LIF, or GDNF. Average neurite outgrowth per neuron was highest in GDNF-treated and Hyper-IL-6-treated cultures. The number of neurite-bearing neurons was reduced in GDNF cultures compared with Hyper-IL-6-treated cells, so that the total neurite outgrowth was maximal after Hyper-IL-6 stimulation. Hyper-IL-6 furthermore stimulated neuronal survival and morphologic differentiation of the enteric glia.

Complex Conserved Organization of the Mammalian Leukemia Inhibitory Factor Gene: Regulated Expression of Intracellular and Extracellular Cytokines

Leukemia inhibitory factor (LIF) is a member of the IL-6 family of pleiotropic cytokines, which are extensively involved in modulating hematopoiesis and immunity. We have undertaken a detailed analysis of LIF genomic organization and gene transcription and investigated the proteins expressed from alternate transcripts. Previously unidentified LIF transcripts, containing alternate first exons spliced onto common second and third exons, were cloned from murine embryonic stem cells, human embryonal carcinoma cells, and primary porcine fibroblasts. Based on sequence homology and position within the genomic sequence, this confirmed the existence of the LIF-M transcript in species other than the mouse and identified a new class of transcript, designated LIF-T. Thus, a complex genomic organization of the LIF gene, conserved among eutherian mammals, results in the expression of three LIF transcripts (LIF-D, LIF-M, and LIF-T) differentially expressed from alternate promoters. The first exon of the LIF-T transcript contained no in-frame AUG, causing translation to initiate downstream of the secretory signal sequence at the first AUG in exon two, producing a truncated LIF protein that was localized within the cell. Enforced secretion of this protein demonstrated that it could act as a LIF receptor agonist. Regulated expression of biologically active intracellular and extracellular LIF cytokine could thus provide alternate mechanisms for the modulation of hematopoiesis and immune system function.

Discriminant power of combined cerebrospinal fluid tau protein and of the soluble interleukin-6 receptor complex in the diagnosis of Alzheimer's disease

Alzheimer's disease (AD) still can only be definitively diagnosed with certainty by examination of brain tissue. There is a great need for a noninvasive, sensitive and specific in vivo test for AD. We combined cerebrospinal fluid analyses of tau protein (levels were significantly increased in AD patients [p=0.0001]), a putative marker of neuronal degeneration, with components of the soluble interleukin-6 receptor complex (sIL-6RC: IL-6, soluble IL-6 receptor and soluble gp130), putative markers of neuroregulatory and inflammatory processes in the brain. A stepwise multivariate discriminant analysis revealed that tau protein and soluble gp130 (levels were significantly reduced in AD subjects [p=0.007]), the affinity converting and signal-transducing receptor of neuropoietic cytokines, maximized separation between the investigated groups. The discriminant function predicted 23 of 25 clinically diagnosed AD patients (sensitivity 92%) with mild to moderate dementia correctly as having AD. Furthermore, 17 of 19 physically and cognitively healthy age-matched control subjects (specificity 90%) were accurately distinguished by this test. Later predicting with the jackknife procedure each case in turn through the remaining patient group, the discriminant function remained stable. Our data suggest that multivariate discriminant analysis of combined CSF tau protein and sIL-6RC components may add more certainty to the diagnosis of AD, however, the method will need to be extended to an independent group of patients, comparisons and control subjects to assess the true applicability.

Both Stat3-Activation and Stat3-Independent BCL2 Downregulation Are Important for Interleukin-6–Induced Apoptosis of 1A9-M Cells

A unique subclone of a bone marrow-derived stromal cell line, BMS2.4, produces soluble factors that inhibit proliferation of several types of hematopoietic cell lines. An understanding of these molecules may be informative about negative regulatory circuits that can potentially limit blood cell formation. We used expression cloning to identify interleukin-6 (IL-6) as one factor that suppressed growth of a pre-B–cell variant line, 1A9-M. Moreover, IL-6 induced macrophage-differentiation and apoptosis of 1A9-M cells. During this process, IL-6 downregulated expression of BCL2 in 1A9-M cells and stimulated BCL-XL expression, but had no effect on p53, Bax, or Bak gene expression. Mechanisms for transduction of IL-6–induced signals were then evaluated in IL-6–stimulated 1A9-M cells. Whereas the signal transducer and activator of transcription 3 (Stat3) was phosphorylated and activated, there was no effect on either Stat1 or Stat5. The importance of BCL2 and Stat3 on IL-6–induced macrophage-differentiation and apoptosis was studied with 1A9-M cells expressing human BCL2 or a dominant-negative form of Stat3, respectively. IL-6–induced apoptosis, but not macrophage-differentiation, was blocked by continuously expressed BCL2. A dominant-negative form of Stat3 inhibited both macrophage-differentiation and apoptosis induced by IL-6. However, diminished Stat3 activity did not prevent IL-6–induced downregulation of the BCL2 gene. Therefore, activation of Stat3 is essential for IL-6–induced macrophage-differentiation and programmed cell death in this model. Whereas overexpression of BCL2 abrogates the apoptotic response, Stat3-independent signals appear to downregulate expression of the BCL2 gene.

Both Stat3-Activation and Stat3-Independent BCL2 Downregulation Are Important for Interleukin-6–Induced Apoptosis of 1A9-M Cells

A unique subclone of a bone marrow-derived stromal cell line, BMS2.4, produces soluble factors that inhibit proliferation of several types of hematopoietic cell lines. An understanding of these molecules may be informative about negative regulatory circuits that can potentially limit blood cell formation. We used expression cloning to identify interleukin-6 (IL-6) as one factor that suppressed growth of a pre-B–cell variant line, 1A9-M. Moreover, IL-6 induced macrophage-differentiation and apoptosis of 1A9-M cells. During this process, IL-6 downregulated expression of BCL2 in 1A9-M cells and stimulated BCL-XL expression, but had no effect on p53, Bax, or Bak gene expression. Mechanisms for transduction of IL-6–induced signals were then evaluated in IL-6–stimulated 1A9-M cells. Whereas the signal transducer and activator of transcription 3 (Stat3) was phosphorylated and activated, there was no effect on either Stat1 or Stat5. The importance of BCL2 and Stat3 on IL-6–induced macrophage-differentiation and apoptosis was studied with 1A9-M cells expressing human BCL2 or a dominant-negative form of Stat3, respectively. IL-6–induced apoptosis, but not macrophage-differentiation, was blocked by continuously expressed BCL2. A dominant-negative form of Stat3 inhibited both macrophage-differentiation and apoptosis induced by IL-6. However, diminished Stat3 activity did not prevent IL-6–induced downregulation of the BCL2 gene. Therefore, activation of Stat3 is essential for IL-6–induced macrophage-differentiation and programmed cell death in this model. Whereas overexpression of BCL2 abrogates the apoptotic response, Stat3-independent signals appear to downregulate expression of the BCL2 gene.

Oncostatin M in the normal human testis and several testicular disorders

The immunohistochemical reaction to oncostatin M (OSM) was studied in normal human testes at different ages (fetuses, newborns, children, pubertal boys, adults, and elderly men), as well as in several testicular disorders including carcinoma-in-situ cells (CIS), germ cell tumors, benign functioning Leydig cell tumor, androgen insensitivity syndrome, Klinefelter's syndrome, and cryptorchidism. Positive OSM immunostained Sertoli cells were only observed in fetuses. In normal testes, intense OSM immunoreaction was found in the Leydig cells of fetuses, newborns, and adults. Leydig cell immunoreaction was weak in elderly men and absent in children and pubertal boys. In some testicular disorders (Leydig cell tumor, cryptorchidism, and CIS), Leydig cell immunoreaction was as intense as in normal adult testes. This immunoreaction was heterogeneous in androgen insensitivity syndrome and was absent in Klinefelter's syndrome and intratubular seminoma. No recognizable Leydig cells were observed in the other testicular tumors. The findings of our study suggest that, in humans, the down-regulation of OSM immunoexpression in Sertoli cells occurs early, and that OSM immunoreaction in the Leydig cells is associated with functionally active and differentiated Leydig cells.

Signal transduction through cytokine receptors

Receptors for interleukins, colony stimulating factors, and hormones have a homology in their extracellular regions, characterized by the conserved cysteine residues and the tryptophan-serine-x-tryptophan-serine motif, thus, they are classified to the type 1 cytokine receptor superfamily. Janus tyrosine kinase (JAKs) have been found to be involved in the signal transduction through type I cytokine receptors. JAKs associate with the membrane proximal region in the cytoplasmic domain having box1 and box2, which are conserved among the family, and upon the stimulation JAKs can be aggregated following the receptor dimerization and activated probably by transphosphorylation. JAKs then phosphorylate the receptor and various signal transducing molecules, including STATs (signal transducer and activator of transcriptions) and other SH2-containing adapter molecules. STATs were initially identified as transcription factors containing a SH2 domain and regulating interferons-inducible genes. STATs can be tyrosine phosphorylated by JAKs and form dimer (either hetero- or homo-dimers) to enter the nucleus, resulting in the expression of a set of genes. On the other hand, adapter molecules such as Shc, GRB2, and SHP-2 have been shown to link the cytokine receptors to Ras, followed by the activation of the Raf-MEK-MAP kinase pathway, leading to the activation of various transcription factors in the nucleus. These two signals are generated by different ways upon the stimulation of the receptors and they elicit a variety of biological functions in various cell types. In this review, we will discuss the mechanism by which cytokines activate JAKs, STATs, and a variety of adapter molecules. We further discuss the roles of each signal transduction pathways in the expression of biological activities of cytokines.

Interleukin-6 and the soluble IL-6 receptor are decreased in cerebrospinal fluid of geriatric patients with major depression: no alteration of soluble gp130

Interleukin-6 (IL-6) is hypothesized to play an important role in the interaction between immune mechanisms and the central nervous system. We investigated whether cerebrospinal fluid (CSF) concentrations of interleukin-6 (IL-6), the soluble IL-6 receptor (sIL-6R) and the soluble form of the signal transducing and affinity converting receptor gp130 (sgp130) are altered in geriatric patients with major depression (MD). In 20 geriatric patients with MD and 20 age-matched healthy control subjects CSF concentrations of the three components of the sIL-6R complex were analyzed by enzyme-linked immunosorbent assays (ELISA). All patients except one were treated with psychotropic drugs. We found statistically significant decreased CSF concentrations of IL-6 (P<0.001) and of the sIL-6R (P<0.001) of patients with MD. Levels of sgp130 showed no statistically significant difference between patients and controls.

Anterograde transport of leukemia inhibitory factor within transected sciatic nerves

Disappointing functional recovery following peripheral nerve repair can be improved by neurotrophic growth factors. Leukemia inhibitory factor (LIF) is unique in that it has independent neurotrophic and myotrophic actions. The aim of this study was to explain this finding by establishing the existence of anterograde axonal transport of LIF from the site of nerve division to denervated muscles. Using 125I LIF, administered topically via an entubulation repair of divided rat sciatic nerve, we monitored its subsequent distribution by measuring the radioactivity associated with nerve segments and denervated muscles. We established that LIF preferentially accumulated in denervated muscles, a process we could reduce by 70% after tightly ligating the intervening nerve, confirming the presence of anterograde axonal transport. This was most likely an active mode of transport that ceased approximately 24 h after nerve division, establishing a narrow clinical time frame within which the myotrophic action of LIF could be optimized following nerve repair.

Hematopoietic support and cytokine expression of murine-stable hepatocyte cell lines (MMH)

It was recently reported that transgenic expression in the liver of truncated human Met renders hepatocytes constitutively resistant to apoptosis and reproducibly permits their immortalization. The derived stable cell lines (MMH from Met murine hepatocyte) are highly differentiated and nontransformed. In this report, the capacity of MMHs to support in vitro hematopoiesis is characterized. By reverse-transcription polymerase chain reaction, the expression by MMHs of cytokines involved in the survival and self-renewal of early progenitor cells (stem cell factor and FLT3 ligand) as well as those acting at different stages of progenitor differentiation (interleukin [IL] 1beta, IL-3, leukemia inhibitory factor, IL-6, granulocyte-macrophage colony-stimulating factor, granulocyte colony-stimulating factor, macrophage colony-stimulating factor, and thrombopoietin) was shown. A ribonuclease protection assay further substantiated the presence of at least six cytokine transcripts in MMH lines. Cocultures between MMH layers and progenitor-enriched fetal liver hematopoietic cells resulted in a 40-fold to 80-fold expansion of total hematopoietic cells and in a 2.5-fold expansion of clonogenic progenitors after 1 to 2 weeks. Hematopoiesis was maintained for up to 6 weeks with formation of typical cobblestone cell areas and continuous differentiation of precursor into cells at various degrees of maturation. At 5 weeks of coculture, clonogenic progenitors were maintained at 20% of the input level in coculture with embryonic-derived hepatocytes, showing the ability of hepatocyte feeder layer to support survival and possibly self-renewal of clonogenic progenitors. Therefore, the data emphasize a direct role of the hepatocyte in sustaining hematopoietic cell proliferation and differentiation.

In Vivo and In Vitro Activities of the gp130-Stimulating Designer Cytokine Hyper-IL-6

IL-6 is a multifactorial cytokine mediating acute inflammatory responses in the liver. When IL-6 binds to a specific receptor (IL-6R), the IL-6/IL-6R complex associates with the signal transducer gp130, initiating intracellular signaling. A soluble form of the IL-6R (sIL-6R) renders target cells sensitive to IL-6 that do not express the IL-6R on their surfaces. A designer cytokine, termed Hyper-IL-6, consisting of IL-6 covalently linked to the sIL-6R was fully active on gp130-expressing cells at 100- to 1000-fold lower concentrations than unlinked IL-6 and IL-6R. Mice were injected i.p. with Hyper-IL-6 or IL-6. Upon injection of Hyper-IL-6 into mice, the acute phase response, as measured by haptoglobin mRNA expression in the liver, was markedly increased and lasted significantly longer compared with that in mice injected with a 10-fold higher dose of IL-6 alone. On human hepatoma cells, Hyper-IL-6 caused similar effects, indicating that the longer lasting response to the fusion protein could not only be explained by the longer plasma half-life of the fusion protein. Experiments using iodinated IL-6 and Hyper-IL-6 revealed that Hyper-IL-6 bound with high affinity to gp130 and was less efficiently internalized. This effect might explain the longer lasting activity of this protein on cells. The highly active IL-6/sIL-6R designer protein might be of significant clinical importance for the stimulation of cells that are more responsive to the IL-6/sIL-6R complex than to IL-6 alone. Such cells include hemopoietic progenitor cells and hepatocytes.

LIF (AM424), a promising growth factor for the treatment of ALS

Growth factors are theoretically promising agents for ALS therapy, but have been disappointing in subcutaneous delivery due to either toxicity or lack of major efficacy. Leukaemia inhibitory factor (LIF), was named after its effect on haemopoietic cells, and belongs to a group of cytokines which includes CNTF, IL-6, CT-1, OM and IL-11. All group members use the gp130 signal transducing subunit for intracellular signalling, but show differences in biological effect. In vitro and in vivo studies on axotomy and nerve crush models demonstrate a powerful effect of LIF in the survival of both motor and sensory neurones, while reducing denervation induced muscle atrophy. Its effects in muscle also include stimulating myoblast proliferation in vitro, and up-regulation after muscle injury. LIF will also stimulate muscle regeneration in vivo when applied exogenously after injury. In published studies of both axotomy induced neuronal death and in the Wobbler mouse models LIF is active at doses of 10 microg/kg delivered systemically, well below the expected maximum tolerated dose suggested by primate safety studies. LIF is expressed in low levels by spinal cord neurones with significant up-regulation when the neurones are damaged by BOAA toxin, an excitatory amino acid associated with a form of ALS. This augments other evidence suggesting LIF is a trauma factor playing a role in the injury response of adult neuronal tissue, and may be more effective than related growth factors. Taken together, the data suggests LIF is a physiologically relevant trophic factor with implications in clinical medicine as a therapy for ALS, and a human recombinant form (AM424), entered human clinical trials during 1998.

Hepatocellular hyperplasia, plasmacytoma formation, and extramedullary hematopoiesis in interleukin (IL)-6/soluble IL-6 receptor double-transgenic mice

Cytokines interact not only with membrane anchored receptors, but also with specific soluble receptors which circulate in the bloodstream. In general, soluble cytokine receptors such as soluble tumor necrosis factor receptor, soluble interleukin 1 receptor, and soluble interleukin 4 receptor compete with their membrane-bound counterparts for the ligands and therefore act as antagonists. In contrast, soluble receptors for cytokines of the interleukin-6 (IL-6) family complex with their ligands act agonistically. Interestingly, the complex of IL-6 and the soluble interleukin 6 receptor (sIL-6R) activates target cells that do not express the membrane-bound IL-6R and therefore cannot respond to IL-6. To identify cellular responses that are due to IL-6/sIL-6R but not to IL-6 alone, IL-6/sIL-6R double-transgenic mice were generated and compared with IL-6 single-transgenic mice. IL-6/sIL-6R transgenic mice develop a severe phenotype showing 1) marked hepatocellular hyperplasia frequently surrounded by peliosis and necrosis, 2) significant acceleration and aggravation of plasmacytoma formation, and 3) excessive activation of extramedullary hematopoiesis in spleen and liver followed by a subsequent increase of all cellular components in the peripheral blood. These in vivo data suggest that the sIL-6R recruits primarily unresponsive cell populations such as hematopoietic progenitor cells and hepatocytes to IL-6-induced proliferation, but also enhances the known mitogenic effect of IL-6 on plasma cells and thereby contributes to plasmacytoma formation.

Gab1 acts as an adapter molecule linking the cytokine receptor gp130 to ERK mitogen-activated protein kinase

Gab1 has structural similarities with Drosophila DOS (daughter of sevenless), which is a substrate of the protein tyrosine phosphatase Corkscrew. Both Gab1 and DOS have a pleckstrin homology domain and tyrosine residues, potential binding sites for various SH2 domain-containing adapter molecules when they are phosphorylated. We found that Gab1 was tyrosine phosphorylated in response to various cytokines, such as interleukin-6 (IL-6), IL-3, alpha interferon (IFN-alpha), and IFN-gamma. Upon the stimulation of IL-6 or IL-3, Gab1 was found to form a complex with phosphatidylinositol (PI)-3 kinase and SHP-2, a homolog of Corkscrew. Mutational analysis of gp130, the common subunit of IL-6 family cytokine receptors, revealed that neither tyrosine residues of gp130 nor its carboxy terminus was required for tyrosine phosphorylation of Gab1. Expression of Gab1 enhanced gp130-dependent mitogen-activated protein (MAP) kinase ERK2 activation. A mutation of tyrosine 759, the SHP-2 binding site of gp130, abrogated the interactions of Gab1 with SHP-2 and PI-3 kinase as well as ERK2 activation. Furthermore, ERK2 activation was inhibited by a dominant negative p85 PI-3 kinase, wortmannin, or a dominant negative Ras. These observations suggest that Gab1 acts as an adapter molecule in transmitting signals to ERK MAP kinase for the cytokine receptor gp130 and that SHP-2, PI-3 kinase, and Ras are involved in Gab1-mediated ERK activation.

Intestinal IgA plasma cells of the B1 lineage are IL-5 dependent

Two lineages of B cells, designated B1 and B2 cells, have been identified based upon their origins, anatomical distribution, cell surface markers, antibody repertoire and self-replenishing potential. B1 cells are maintained by self-renewal of cells resident in the peritoneal cavity (PerC) and they utilize a limited repertoire of germline V-region genes, mostly directed against ubiquitous bacterial antigens such as phosphoryl choline (PC). B2 cells are replenished from bone marrow precursors and use a larger repertoire of immunoglobulin V-region genes. Whereas most immunoglobulin A (IgA) plasma cells in the intestine derive from B2 lineage precursors in the Peyer's patch, a subpopulation of Per C-derived B1 cells populate the intestinal lamina propria where they mature into IgA plasma cells. In previous in vivo studies we have shown that whereas IgA+ B2 cells are interleukin (IL)-6 dependent, B1 cells are IL-6 independent. In view of the in vitro evidence that IL-5 is also involved in IgA expression, in the studies reported here we have used IL-5-deficient mice to evaluate the role of IL-5 in vivo in IgA expression in the gut. The results demonstrate that although total IgA cell numbers are only marginally depressed in IL-5-deficient mice, there is a marked selective depletion of IgA+ cells of the B1 lineage in the gut and a corresponding depression in the capacity of these mice to mount an intestinal response to a B1 antigen (PC) but not to a B2 antigen (oralbumin; OVA), reflecting intact B2-derived IgA cell function but a defect in the B1 cell contribution to IgA responses in IL-5 deficient mice. Collectively these data demonstrate differential cytokine regulation of subsets of IgA+ cells in the gut in that IgA+ cells of the B2 lineage are IL-6 dependent but IL-5 independent, but B1-derived IgA+ cells are IL-5 dependent and IL-6 independent.

Interleukin 6 and its receptor: ten years later

Ten years have passed since the molecular cloning of interleukin 6 (IL-6) in 1986. IL-6 is a typical cytokine, exhibiting functional pleiotropy and redundancy. IL-6 is involved in the immune response, inflammation, and hematopoiesis. The IL-6 receptor consists of an IL-6 binding alpha chain and a signal transducer, gp130, which is shared among the receptors for the IL-6 related cytokine subfamily. The sharing of a receptor subunit is a general feature of cytokine receptors and provides the molecular basis for the functional redundancy of cytokines. JAK tyrosine kinase is a key molecule that can initiate multiple signal-transduction pathways by inducing the tyrosine-phosphorylation of the cytokine receptor, gp130 in the case of IL-6, on which several signaling molecules are recruited, including STAT, a signal transducer and activator of transcription, and SHP-2, which links to the Ras-MAP kinase pathway. JAK can also directly activate signaling molecules such as STAT and Tec. These multiple signal-transduction pathways intimately regulate the expression of several genes including c-myc, c-myb, junB, IRF1, egr-1, and bcl-2, leading to the induction of cell growth, differentiation, and survival. The deregulated expression of IL-6 and its receptor is involved in a variety of diseases.

Sympathetic neurons can produce and respond to interleukin 6

Neuronal expression of cytokines is an area of active investigation in the contexts of development, disease, and normal neural function. Although cultured rat sympathetic neurons respond very weakly to exogenous interleukin 6 (IL-6), we find that addition of soluble IL-6 receptor (sIL-6R) and IL-6 enhances neuronal survival in the absence of nerve growth factor. Neutralizing monoclonal antibodies against IL-6 block these effects. Addition of IL-6 and sIL-6R also induces a subset of neuropeptide and transmitter synthetic enzyme mRNAs identical to that demonstrated for leukemia inhibitory factor, ciliary neurotrophic factor, and oncostatin M. Both of these effects are duplicated by addition of a highly active fusion protein of sIL-6R and IL-6, covalently linked by a flexible peptide chain, which is designated H-IL-6. In addition, we show that sympathetic neurons produce IL-6. In situ hybridization indicates a neuronal localization of IL-6 mRNA in superior cervical ganglia, and bioactive IL-6 protein is detected in ganglion culture supernatants. Interestingly, the IL-6 produced by sympathetic neurons does not lead to survival of these cells in culture unless sIL-6R is added. Thus, sympathetic neurons can produce IL-6 and may respond to it in an autocrine/paracrine manner if sIL-6R is present. Moreover, the prior findings of sIL-6R in serum and inflammatory fluids now have added interest in the context of neuro-immune interactions.

LIF, but not IL-6, regulates osteoprogenitor differentiation in rat calvaria cell cultures: modulation by dexamethasone

Cytokines of the interleukin 6 (IL-6) subfamily are a group of factors produced by osteoblasts and acting through the same transducing element, membrane protein gp130. We have previously shown that exogenous (added to the culture medium) leukemia inhibitory factor (LIF) inhibits bone nodule formation and expression of osteoblast-associated genes in fetal rat calvaria (RC) cell cultures and that dexamethasone (Dex) increases the ID50 of LIF. To investigate the respective roles of IL-6-related cytokines and receptors in osteprogenitor differentiation, and their regulatory interplay with Dex, we used reverse transcribed polymerase chain reaction, bioassay, and blocking antibody techniques to assess the time courses of LIF, IL-6, LIF transmembrane receptor, IL-6 receptor, and gp130 expression in RC cell cultures grown with and without Dex. The levels of the mRNAs for IL-6, LIF, and gp130 decreased concomitantly with the formation of bone nodules. Dex treatment, which stimulates bone nodule formation, reduced the expression of LIF and IL-6 mRNAs and IL-6 bioactivity in the culture medium. LIF treatment strongly stimulated the expression of IL-6. Incubation with anti-LIF antibodies increased the number of nodules, while an antibody blocking IL-6 activity had little or no effect on nodule numbers and did not antagonize the action of exogenous LIF, indicating that IL-6 does not mediate the action of LIF in this system. Moreover, although exogenously added IL-6 was active in the cultures as noted by a reduction of nodule mineralization, it had no effect on nodule numbers, i.e., on osteoprogenitor differentiation, in the presence or absence of Dex. In conclusion, IL-6, LIF, and their receptors are expressed throughout the time-course of osteogenesis in RC cell cultures. However, only LIF, but not IL-6, appears to play a significant role in autocrine regulation of osteoblastic differentiation in this system. The antagonist action of Dex on the effects of exogenously added LIF, as well as the bone-promoting action of Dex in RC cell cultures, could be exerted partly through the down-regulation of the expression of endogenous LIF.

Decreased soluble interleukin-6 receptor in cerebrospinal fluid of patients with Alzheimer's disease

The function of the cytokine interleukin-6 (IL-6) is augmented by soluble IL-6 receptors (sIL-6R). We investigated cerebrospinal fluid sIL-6R concentrations in patients with Alzheimer's disease (AD) compared to age-matched healthy subjects and individuals with at least one first degree relative with AD. We found a statistically significant decrease in sIL-6R levels in the AD group compared to controls. Complete analysis of the IL-6R complex seems crucial to better understand the impact of IL-6 in AD pathophysiology.

Activation of gp130 by IL-6/soluble IL-6 receptor induces neuronal differentiation

Interleukin-6 (IL-6) on target cells binds to the specific IL-6 receptor (IL-6R) and subsequently induces homodimerization of the signal-transducing protein gp130. Cells which express gp130 but no IL-6R and which therefore do not respond to IL-6 can be stimulated by the complex of IL-6 and soluble IL-6R (slL-6R). Here we show that on rat pheochromocytoma cells (PC12), the combination of IL-6 and slL-6R but not IL-6 alone induces expression of c-fos, GAP-43 and neuron-specific enolase followed by neuron-specific differentiation and formation of a neuronal network. The differentiation was dose-and time-dependent and followed the same kinetics as nerve-growth factor (NGF)-induced differentiation. The responses of PC12 cells to IL-6/sIL-6R and NGF were additive, suggesting independent signaling pathways. We demonstrate that activation of gp130 generates a neuronal differentiation signal that is equivalent to and independent of trk/NGF receptor tyrosine kinase. Interestingly, the failure of IL-6 to induce differentiation of PC12 cells is not due to lack of surface expression of IL-6R as IL-6 alone triggered expression of GAP-43 mRNA and protein. We hypothesize that PC12 cells express more gp130 than IL-6R and that the extent of activated gp130 molecules determines the quality of the response.

Signaling mechanisms through gp130: a model of the cytokine system

The interleukin-6 cytokine family plays roles in a wide variety of tissues and organs, including the immune hematopoietic and nervous systems. Gp130 is a signal-transducing subunit shared by the receptors for the IL-6 family of cytokines. The binding of a ligand to its receptor induces the dimerization of gp130, leading to the activation of JAK tyrosine kinase and tyrosine phosphorylation of gp130. These events lead to the activation of multiple signal-transduction pathways, such as the STAT, Ras-MAPK and PI-3 kinase pathways whose activation is controlled by distinct regions of gp130. We propose a model showing that the outcome of the signal transduction depends on the balance or interplay among the contradictory signal transduction pathways that are simultaneously generated through a cytokine receptor in a given target cell.

Interleukin-6-dependent and -independent regulation of the human C-reactive protein gene

We have investigated the function of different mediators of the regulation of the human C-reactive protein (hCRP) gene in transgenic mice. hCRP was induced by lipopolysaccharide and wounding in interleukin-6 (IL-6) +/+ mice, but not in IL-6 -/- mice. This finding suggested that IL-6 is necessary for the induction of hCRP. However, injection of IL-6 did not induce the hCRP gene. Thus, the induction of hCRP by IL-6 seems to require an additional cofactor. Therefore, we screened different cytokines for their activity in IL-6 +/+ and IL-6 -/- mice. Surprisingly, interleukin-1beta, as well as oncostatin M or leukaemia inhibitory factor, led to an induction of hCRP in both genetic backgrounds. These results indicate an IL-6-dependent and -independent regulation of hCRP. These hCRP transgenic mice therefore represent a novel model system for defining the cytokine network involved in the regulation of acute-phase genes during the course of inflammation.

Involvement of STAT3 in the granulocyte colony-stimulating factor-induced differentiation of myeloid cells

Granulocyte colony-stimulating factor (G-CSF) stimulates proliferation and differentiation of the progenitor cells of neutrophilic granulocytes. The binding of G-CSF to its receptor specifically activates JAK1 and JAK2 kinases, as well as STAT3, a signal transducer and activator of transcription (STAT). To examine the role of STAT3 in G-CSF receptor-mediated signal transduction, two different forms of the dominant negative STAT3 were introduced into a mouse myeloid cell line that exogenously expresses the mouse G-CSF receptor. In response to G-CSF, the parental myeloid cells grew for about 4 days, and then they stopped dividing and differentiated into cells with lobulated nuclei. During this period, the expression of the myeloperoxidase (MPO) gene was induced, while c-myc gene expression was down-regulated. In contrast, in the cells expressing the dominant negative STAT3, G-CSF could induce neither growth arrest nor morphological change. However, the induction of the MPO gene by G-CSF was not affected by the dominant negative STAT3. These results indicate that STAT3 activation is responsible for part of the G-CSF-induced differentiation of neutrophils but that another pathway, involving the expression of the MPO gene, that does not utilize the activated STAT3, is also required to fully differentiate the cells.

A primer on cytokines: sources, receptors, effects, and inducers

Protection against pathogens is a prerequisite for survival of most organisms. To cope with this continuous challenge, complex defense mechanisms have evolved. The construction, adaptation, and maintenance of these mechanisms are under control of an extensive network of regulatory proteins called cytokines. A great number of cytokines have been described over the last 2 decades. This review consists of an overview of cytokines that are involved in immune responses and describes some historical and general aspects as well as prospective clinical applications. Major biological effects together with information on cytokine receptors, producers, inducers, and biochemical and molecular characteristics are listed in tables. In addition, some basic information is given on cytokine receptor signal transduction. Finally, the recent discoveries of cytokine receptors functioning as coreceptors in the pathogenesis of human immunodeficiency virus are summarized.

Indomethacin Is a Potent Inhibitor of Pristane and Plastic Disc Induced Plasmacytomagenesis in a Hypersusceptible BALB/c Congenic Strain

Continuous indomethacin (INDO) administration in the drinking water (10 to 20 μg/mL) profoundly inhibited plasmacytoma (PCT) development initiated by three 0.2- or 0.5-mL intraperitoneal (i.p.) injections of pristane in hypersusceptible BALB/c.DBA/2-Idh1-Pep3 congenic mice. The most effective inhibitions were obtained with continuous INDO treatment. When treatment was delayed until 50 to 60 days after the first pristane injection, there was approximately a 50% reduction in PCT incidence. The primary action of pristane is the induction of a chronic inflammation in the peritoneal connective tissues and the formation of a microenvironment where PCTs develop. INDO, a powerful inhibitor of prostaglandin synthases (cyclooxygenases 1 and 2), did not inhibit the formation of mesenteric oil granuloma nor the appearance of cells in this chronic inflammatory tissue carrying c-myc illegitimately joined to an Ig heavy chain switch region, ie, the t(12; 15) chromosomal translocation. INDO inhibited PCT induction by the i.p. implantation of 21 × 2 mm polycarbonate discs. These solid objects predominantly induce the formation of a patchy fibroplastic tissue on contacting peritoneal surfaces. These and previous data indicate that indomethacin inhibits an intermediate stage in PCT development after the arrival of cells bearing the T(12; 15) translocation in the oil granuloma and before these cells acquire transplantability to a pristane-conditioned host. The biological mechanism that explains how INDO inhibits PCT development is not yet established but appears to result from decreased production of prostaglandins in chronic inflammatory tissues (oil granuloma, fibroplasia), suggesting that prostaglandins play an active role in oil and solid plastic induced PCT formation.

Indomethacin Is a Potent Inhibitor of Pristane and Plastic Disc Induced Plasmacytomagenesis in a Hypersusceptible BALB/c Congenic Strain

Continuous indomethacin (INDO) administration in the drinking water (10 to 20 μg/mL) profoundly inhibited plasmacytoma (PCT) development initiated by three 0.2- or 0.5-mL intraperitoneal (i.p.) injections of pristane in hypersusceptible BALB/c.DBA/2-Idh1-Pep3 congenic mice. The most effective inhibitions were obtained with continuous INDO treatment. When treatment was delayed until 50 to 60 days after the first pristane injection, there was approximately a 50% reduction in PCT incidence. The primary action of pristane is the induction of a chronic inflammation in the peritoneal connective tissues and the formation of a microenvironment where PCTs develop. INDO, a powerful inhibitor of prostaglandin synthases (cyclooxygenases 1 and 2), did not inhibit the formation of mesenteric oil granuloma nor the appearance of cells in this chronic inflammatory tissue carrying c-myc illegitimately joined to an Ig heavy chain switch region, ie, the t(12; 15) chromosomal translocation. INDO inhibited PCT induction by the i.p. implantation of 21 × 2 mm polycarbonate discs. These solid objects predominantly induce the formation of a patchy fibroplastic tissue on contacting peritoneal surfaces. These and previous data indicate that indomethacin inhibits an intermediate stage in PCT development after the arrival of cells bearing the T(12; 15) translocation in the oil granuloma and before these cells acquire transplantability to a pristane-conditioned host. The biological mechanism that explains how INDO inhibits PCT development is not yet established but appears to result from decreased production of prostaglandins in chronic inflammatory tissues (oil granuloma, fibroplasia), suggesting that prostaglandins play an active role in oil and solid plastic induced PCT formation.

The role of leukemia inhibitory factor in skeletal muscle regeneration

Although a number of cytokines have been implicated in tissue regeneration, it is unknown which ones actually function in vivo. Here, we use mice with a targeted mutation in the leukemia inhibitory factor (LIF) gene to examine the role of LIF in muscle regeneration. Using a muscle crush model, we show that muscle regeneration in LIF knockout mice is significantly, reduced compared to control littermates. Further, targeted infusion of LIF in both normal and LIF knockout animals stimulated muscle regeneration, but the stimulation observed was much greater in the mutant animals than in controls. In contrast, interleukin-6 and transforming growth factor-alpha, which also stimulate myoblast proliferation in vitro, had no effect on regeneration. These findings demonstrate directly that LIF is involved in regeneration of injured muscle and points to the use of LIF as a therapeutic agent in the treatment of neuromuscular disease.

Differential regulation of chemokines by leukemia inhibitory factor, interleukin-6 and oncostatin M

M. Leukemia inhibitory factor (LIF). oncostatin M (OsM) and interleukin-6 (IL-6) are members of a cytokine family, which are produced by activated macrophages and glomerular mesangial cells. These cytokines have been implicated in the pathogenesis of glomerular inflammation, but their action on glomerular cells is presently unclear. Therefore, we examined the effects of IL-6, OsM and LIF on chemokine synthesis of rat mesangial cells in culture. While LIF as well as IL-6 up-regulated monocyte chemotactic protein-1 (MCP-1) mRNA expression, OsM showed no such effect. The induction of MCP-1 mRNA by LIF and IL-6 was transient, peaking at one to two hours and two to three hours, respectively, and returning to background levels within several hours. Induction of MCP-1 mRNA by LIF and IL-6 was strongly inhibited by dexamethasone. LIF activated STAT factors in mesangial cells, suggesting their involvement in signal transduction pathways that lead to LIF-stimulated up-regulation of MCP-1 mRNA. By contrast, LIF. IL-6 and OsM failed to affect the expression of the chemokines, macrophage inflammatory protein-2 (MIP-2) and RANTES. The rapid, transient and differential regulation of MCP-1 expression induced by LIF and IL-6 contrasted with uniformly powerful effects of the proinflammatory cytokines IL-1 beta and TNF alpha that induced all tested chemokines for prolonged time periods. These results suggest that the selective and transient induction of MCP-1 by LIF and IL-6 may play a role in the preferential attraction of monocytes to the injured glomerulus.

Interleukin-6: structure-function relationships

Interleukin-6 (IL-6) is a multifunctional cytokine that plays a central role in host defense due to its wide range of immune and hematopoietic activities and its potent ability to induce the acute phase response. Overexpression of IL-6 has been implicated in the pathology of a number of diseases including multiple myeloma, rheumatoid arthritis, Castleman's disease, psoriasis, and post-menopausal osteoporosis. Hence, selective antagonists of IL-6 action may offer therapeutic benefits. IL-6 is a member of the family of cytokines that includes interleukin-11, leukemia inhibitory factor, oncostatin M, cardiotrophin-1, and ciliary neurotrophic factor. Like the other members of this family, IL-6 induces growth or differentiation via a receptor-system that involves a specific receptor and the use of a shared signaling subunit, gp130. Identification of the regions of IL-6 that are involved in the interactions with the IL-6 receptor, and gp130 is an important first step in the rational manipulation of the effects of this cytokine for therapeutic benefit. In this review, we focus on the sites on IL-6 which interact with its low-affinity specific receptor, the IL-6 receptor, and the high-affinity converter gp130. A tentative model for the IL-6 hexameric receptor ligand complex is presented and discussed with respect to the mechanism of action of the other members of the IL-6 family of cytokines.

Experimental plasmacytomagenesis in mice

This article discusses some of the mechanistic aspects of plasma cell tumor development. Plasmacytomagenesis, much like other forms of neoplastic development, is a highly complex process that develops in the B cell differentiation lineage. As more is learned about the molecular genetics of multiple myeloma and PCTs in mice, a unifying concept will emerge that possibly can explain the phenotypic differences in the two neoplastic cell processes as variants of a common process.