Interleukin-6 signals activating junB and TIS11 gene transcription in a B-cell hybridoma

C/EBP-related sites in addition to a STAT site are necessary for ciliary neurotrophic factor-leukemia inhibitory factor-dependent transcriptional activation by the vasoactive intestinal peptide cytokine response element

The neuropoietic cytokines ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) regulate VIP gene expression through a cytokine response element (CyRE) which interacts with members of the STAT transcription factor family. The CyRE STAT site is, however, insufficient to mediate full transcriptional activation by CNTF/LIF, suggesting that other sequences and nuclear proteins are also important. As C/EBP proteins participate in the transcriptional effects of the related cytokine, interleukin-6, we investigated the role of possible C/EBP-binding sites in the response of the VIP CyRE to CNTF/LIF. Using DNase I footprinting, transactivation studies, DNA mobility shift assays, and mutational analysis, three sites within the VIP CyRE were identified as C/EBP-related binding sites and shown to be important to CNTF/LIF-mediated transcriptional activation. The CyRE C/EBP-related sites interact with nuclear proteins from the human neuroblastoma cell line, NBFL, including a novel, protein synthesis-dependent, nuclear protein complex, induced by CNTF treatment. These nuclear proteins are not, however, recognized by antisera to known C/EBP proteins. Therefore, other nuclear proteins regulated by independent pathways act in concert with the JAK-STAT pathway to mediate CNTF/LIF regulation of VIP gene expression through the CyRE.

The conserved box 1 motif of cytokine receptors is required for association with JAK kinases

The JAK2 tyrosine kinase is known to associate with the receptors for growth hormone (GH) and erythropoietin (EPO) and with the interleukin-6 receptor signal transducing protein, gp130. Here we demonstrate that chimeric cytokine receptors which contain the cytoplasmic domain of the receptors for GH and EPO or for gp130 can form complexes with JAK2 when transiently co-expressed in HeLa cells. Mutational analyses of chimeras for the the GH and EPO receptors and gp130 demonstrated that box 1, a motif critical for cytokine receptor signal transduction, was required for the association of JAK2. Although JAK2 was capable of associating with all three of the chimeras, JAK1 co-precipitated only with the gp130 chimera. Association of JAK1 and JAK2 with cytokine receptor proteins, therefore, requires the highly conserved box 1 domain, but other sequences within the receptor proteins may influence the specificity of JAK binding. Mutational analysis of JAK2 revealed that multiple or complex protein sequences within JAK2 are required for association with cytokine receptors.

Interleukin-6-induced serine phosphorylation of transcription factor APRF: evidence for a role in interleukin-6 target gene induction

The cytokine interleukin-6 (IL-6) rapidly activates a latent cytoplasmic transcription factor, acute-phase response factor (APRF), by tyrosine phosphorylation. Activation and DNA binding of APRF are inhibited by inhibitors of protein tyrosine kinases but not serine/threonine kinases. However, immediate-early gene induction by IL-6 and, as we show here, stimulation of the promoters of the genes for alpha 2-macroglobulin, Jun-B, and intercellular adhesion molecule-1 (ICAM-1) are blocked by the serine/threonine kinase inhibitor H7. We now show that IL-6 triggers a delayed phosphorylation of APRF at serine resudues which can be reversed in vitro by protein phosphatase 2A and is also inhibited by H7. Therefore, APRF serine phosphorylation is likely to represent a crucial event in IL-6 signal transduction leading to target gene induction.

Two distinct signalling pathways are involved in the control of the biphasic junB transcription induced by interleukin-6 in the B cell hybridoma 7TD1

We have measured the level of junB mRNA in the B hybridoma cell line 7TD1, under interleukin-6 (IL-6) stimulation. IL-6 increases junB mRNA in a biphasic fashion. The first early-induced peak was transient and likely corresponds to the well documented typical junB mRNA, stimulated in response to numerous growth factors, including IL-6. At variance, the second peak which has never been reported previously, lasted several hours. As a consequence of its effect on junB mRNA, IL-6 stimulated, in a biphasic fashion, the nuclear accumulation of the JunB protein. In this study, we demonstrated that IL-6 regulation occurred exclusively at the transcriptional level and that the bimodal increase of junB mRNA and JunB protein can be accounted for by a biphasic stimulation of junB transcription. Furthermore, our data point to two major differences between the mechanism of control of the early and the late IL-6-induced junB transcription waves. First, cycloheximide strongly potentiated the transcription of the second wave, whereas it failed to affect the early-induced burst. Second, tyrphostin, a tyrosine kinase inhibitor, impaired the expression of the first but not the second junB mRNA peak. Conversely, genistein, another tyrosine kinase inhibitor, totally abolished the expression of the second peak of junB mRNA whereas it did not affect the expression of the first peak. Altogether these data indicate that, in 7TD1 cells, IL-6 controls junB transcription in a biphasic fashion by means of two separate transduction pathways.

Cytokine receptor architecture, structure and genetic assembly

In this review major structural and molecular characteristics of interleukin-6-type cytokine receptors consisting of ligand-specific (e.g., IL-6 receptor) and public (gp130) elements are outlined. The peculiar shedding feature of the ligand-binding receptor subunit provides a possibility to form a receptor-ligand complex in the soluble phase, followed by an autocrine or paracrine re-attaching to the membrane bound gp130. This situation provides a dynamic 4-chain model for IL-6-type receptors, depending on a critical balance between membrane bound and soluble cytokine receptors. The generation and transduction of intracellular signal for IL-6-type cytokine receptors based primarily on generation of phospho-tyrosine proteins. In this set of events kinases of the JAK family are basically involved. Although not all primary substrates are uncovered, gp130 and stat proteins are phosphorylated. The variability of the JAK/Stat system and its still not clear relation to the specificity of cytokine actions are discussed.

Regulation of an oligodendrocyte progenitor cell line by the interleukin-6 family of cytokines

We report pleiotropic actions of the interleukin-6 family of cytokines on a rat cerebral cortical oligodendrocyte cell line, Central Glia-4 (CG-4). This is a bipotential oligodendrocyte type-2 astrocyte (O-2A) progenitor cell line that can be manipulated in vitro to become either a type-2 astrocyte or to follow a linear sequence of events into becoming a mature oligodendrocyte. Using Northern and Western analyses in conjunction with immunocytochemistry we have demonstrated that ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), and interleukin-6 (IL-6) cause a transient increase in glial fibrillary acidic protein (GFAP) in oligodendrocyte type-2 astrocyte (O-2A) progenitor cells. At maximal cytokine concentrations, the largest increase in GFAP protein levels were observed for CNTF and LIF; albeit, IL-6 did increase GFAP but the order of magnitude was 6-7 times less. Moreover, in trophic factor deprived medium, CNTF and LIF protected immature (O4+/MBP-) and mature (MBP+) oligodendrocytes from the apoptotic mode of cell death, while IL-6 had no effect in enhancing oligodendrocyte cell survival. Analysis of the cytokine-induced early response genes (ERGs) revealed a strong degree of overlap for CNTF and LIF. The effect of IL-6 was different in the degree to which the ERGs were up-regulated and in their temporal patterns of expression. These findings suggest that ERGs may be important, at least in part, for determining the extent of functional overlap observed within this cytokine family. Our findings clearly demonstrate differential regulation of oligodendrocyte survival and differentiation by the IL-6 family of cytokines.

Ciliary neurotrophic factor: a review

Ciliary neurotrophic factor (CNTF) is a 22-kDa protein predicted to share with leukemia inhibitory factor (LIF) and interleukin-6 a common amphipathic helical domain. Consistent with this prediction, the CNTF receptor complex is composed of the CNTF alpha receptor, the LIF beta receptor and gp130 a signalling molecule for LIF and interleukin-6. The major sources of synthesis of CNTF are Schwann cells and astrocytes, but it remains unclear how much CNTF is released from these glial cells and by what mechanism. In vitro, CNTF supports the survival of all classes of peripheral nervous system neurons plus many CNS neurons, induces neurite outgrowth, promotes a cholinergic phenotype in sympathetic neurons and arrests division of neuronal precursor cells. Several cell lines also respond to CNTF. In vivo, CNTF rescues several types of neurons from axotomy-induced death. The functions of CNTF in the development and maintenance of the nervous system remain enigmatic.

Control of activator protein-1 and nuclear factor kappa B activity by interleukin-1, interleukin-6 and metals in HEPG2 cells

The intracellular signals induced by IL-1 and IL-6 have been described but there are few details of the signals they induce in liver-derived cells during initiation of acute phase protein synthesis. We therefore used an in vitro system to investigate signalling by IL-1 and IL-6 in the human liver cell line, HepG2. Chloramphenicol acetyl transferase (CAT) expression vectors, under the control of activator protein-1 (pTRE-CAT), nuclear factor kappa B (pNF-CAT) or no enhancer region (pBLCAT2), were transfected into HepG2 cells and the effects of the cytokines on their activity was studied. Profound changes in liver processing of heavy metals and the induction of metal-dependent acute proteins are also seen during the acute phase response. To determine if the supply of metal ions could itself influence signalling we also investigated the effects of cadmium and zinc on the activity of the transfected vectors. Both alpha and beta forms of interleukin-1 increased the expression of pTRE-CAT and pNF-CAT, but not pBLCAT2, while interleukin-6 had no effect, suggesting that activator protein-1 and nuclear factor kappa B activity was induced by interleukin-1, but not interleukin-6. Specificity of the effect of interleukin-1 alpha was confirmed using an anti-interleukin-1 alpha monoclonal antibody. Zinc and cadmium also increased pTRE-CAT expression, but not pNF-CAT or pBLCAT2. Removal of heavy metal ions from the culture medium resulted in decreased pTRE-CAT expression, while pNF-CAT and pBLCAT2 were relatively unaffected, confirming the stimulatory effect of metals on activator protein-1, but not nuclear protein kappa B activity. Therefore, metal and interleukin-1-mediated signal transduction may involve overlapping pathways, whereas interleukin-1 and interleukin-6 act via different pathways in liver cells.

Signal transduction through gp130 that is shared among the receptors for the interleukin 6 related cytokine subfamily

Interleukin 6 (IL-6) and related cytokines, such as leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF) and IL-11 exhibit multiple functions and redundancy in biological activities and play important roles in the immune response, hematopoiesis, the nervous system and acute phase reactions. These IL-6 family cytokines exhibit a similar helical structure, and their receptors are structurally similar and constitute a cytokine receptor super family. In addition, a receptor subunit is shared among these IL-6 related cytokine subfamily receptors, contributing to one of the mechanisms of functional redundancy of cytokine activities and suggesting the presence of a common signal transduction pathway among these receptors. In this review, we describe the structure of the receptors for IL-6 and its related cytokine subfamily members. Furthermore, we propose a novel mechanism for the generation of cytokine diversity, i.e. the complex of a cytokine and one of its receptor subunits act as a novel cytokine on the cells that express the other receptor subunit(s) capable of acting as a receptor for the complex. Finally, we describe a Ras-independent novel signal transduction pathway that utilizes Jak tyrosine kinase family, Stat protein family and yet unidentified H-7-sensitive pathway. This signal transduction pathway is commonly generated through the receptors for a wide range of cytokines and growth factors.

Maintenance of the pluripotential phenotype of embryonic stem cells through direct activation of gp130 signalling pathways

Propagation of the undifferentiated pluripotential phenotype of embryonic stem (ES) cells is dependent on the cytokine differentiation inhibiting activity/leukemia inhibitory factor (DIA/LIF). The DIA/LIF receptor complex is a heterodimer of DIA/LIF receptor (DIA/LIF-R) and gp130. The latter is also a component of the interleukin-6 (IL-6) receptor complex. We report that a combination of IL-6 and soluble IL-6 receptor (sIL-6R), which can induce homodimerisation of gp130 and activation of signalling processes, sustains self-renewal of pluripotential ES cells. Our findings indicate that the IL-6/sIL-6R complex acts on ES cells through gp130 alone, bypassing DIA/LIF-R, and therefore implicate gp130 as the key component in the signalling pathway responsible for stem cell renewal.

Regulation of bone marrow stromal cell differentiation by cytokines whose receptors share the gp130 protein

The bone marrow stroma consists of a heterogeneous population of cells which participate in osteogenic, adipogenic, and hematopoietic events. The murine stromal cell line, BMS2, exhibits the adipocytic and osteoblastic phenotypes in vitro. BMS2 differentiation was examined in response to cytokines which share the gp130 signal transducing protein within their receptor complex. Four of the cytokines (interleukin 6, interleukin 11, leukemia inhibitory factor, and oncostatin M) inhibited hydrocortisone-induced adipocyte differentiation in a dose dependent manner based on lipid accumulation and lipoprotein lipase enzyme activity. Inhibition occurred only when the cytokines were present during the initial 24 h of the induction period; after 48 h their effects were diminished. Likewise, these cytokines increased alkaline phosphatase enzyme activity twofold in preadipocyte BMS2 cells. Both leukemia inhibitory factor and oncostatin M induced early active gene expression in resting preadipocyte BMS2 cells and decreased the steady state mRNA level of a unique osteoblastic gene marker, osteocalcin. A fifth cytokine whose receptor complex shares the gp130 protein, ciliary neurotrophic factor, did not significantly regulate stromal cell differentiation when added by itself. However, with the addition of a missing component of its receptor complex, ciliary neurotrophic factor receptor alpha protein, this cytokine also inhibited BMS2 adipogenesis. Together, these data indicate that the cytokines whose receptors share the gp130 protein can modulate stromal cell commitment to the adipocyte and osteoblast differentiation pathways.

Interleukin 11: an overview

Interleukin (IL)-11 is a bone marrow fibroblast derived cytokine with a wide spectrum of in vitro biological activities in the hematopoietic, lymphopoietic, hepatic, adipose, neuronal and osteoclast systems, either alone or in synergy with other hematopoietic growth factors. In vivo administration of IL-11 in mice, rats and nonhuman primates has demonstrated the thrombopoietic effects of this cytokine. The expression of the human IL-11 gene, which is localized at 19q13.3-13.4, can be controlled at both the transcriptional and post-transcriptional levels. Initial biochemical characterization has identified a 151 kD protein as the potential IL-11 binding subunit of the receptor complex. Like other cytokines such as IL-6, leukemia inhibitory factor (LIF), oncostatin M (ONC) and ciliary neurotrophic factor (CNTF), IL-11 has been shown to utilize IL-6 signal transducer, gp130. Because of the overlapping biological activities, the similarities in the predicted tertiary structures, and the sharing of common signal transducer protein, we have compared the signal transduction pathways mediated by these cytokines in various cell types. Studies of protein tyrosine phosphorylation, primary response gene expression and signaling molecules known to be important in transducing mitogenic signals have suggested that there are convergent and divergent points along the signal transduction pathways utilized by IL-11, IL-6, LIF and ONC. These observations may explain the biological pleiotropy and redundancy of this group of cytokines.

Brequinar sodium inhibits interleukin-6-induced differentiation of a human B-cell line into IgM-secreting plasma cells

Brequinar sodium (BQR) has been shown recently to be a potent immunosuppressive agent. This property has been attributed to the capacity of BQR to inhibit de novo pyrimidine nucleoside biosynthesis and consequently, to blockade the synthesis both of DNA and RNA. The influence of this new immunosuppressant on lymphocyte function has not been fully characterized. To determine the potential efficacy of BQR for the control of antibody-mediated graft rejection, which is of particular significance in the context of xenotransplantation, we have examined the influence of the drug on interleukin-6-dependent IgM production by the human B-cell line, SKW 6.4. At concentrations up to 10 micrograms/ml, BQR did not affect concanavalin A (Con A)-induced human peripheral blood lymphocyte proliferation or IL-6 production by blood mononuclear leucocytes. In contrast, the drug was very effective in inhibiting IL-6-stimulated IgM production by SKW 6.4 cells, with an optimal inhibitory concentration of 0.3 microgram/ml. As expected, addition of exogenous uridine (0.1 mM), the precursor of uridine triphosphate (UTP), reversed the inhibitory effect of BQR on antibody production, while cytidine (0.1 mM) potentiated the inhibitory activity of the drug. It was further demonstrated that the inhibition of IgM production was unrelated to DNA synthesis, indicating that BQR may affect IL-6 signal transduction and IgM production in SKW 6.4 cells independent of any effect on 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.

Effects of interleukin-1 and interleukin-6 on metallothionein and amyloid precursor protein expression in human neuroblastoma cells. Evidence that interleukin-6 possibly acts via a receptor different from the 80-kDa interleukin-6 receptor

Since immunohistochemical studies indicated the presence of interleukin-6 in the cortices of patients with Alzheimer's disease, we were interested in the eventual biological effects of this cytokine on neuronal cells. We found that interleukin-6 and interleukin-1 induced metallothionein expression in a human neuronal (SH-SY5Y neuroblastoma) cell line. In contrast to metallothionein, amyloid precursor protein expression was unaffected by both cytokines. When searching in the same cell line for the expression of the classical 80-kDa interleukin-6 binding protein, which is part of the dimeric interleukin-6 receptor, we were unable to detect the respective mRNA. Our findings either indicate that the interleukin-6 receptor in these cells is expressed in extremely low levels or that interleukin-6 may act upon neuronal cells via a different, yet unknown neuronal receptor.

Nuclear signaling by interleukin-6

The molecular analysis of the regulation of nuclear proteins induced by interleukin-6 has provided new insights into this largely unknown signal transduction pathway. Transcription factors of the CCAAT/enhancer-binding protein and AP-1 families, as well as the octamer-binding proteins and the tumor suppressor gene product pRB, are regulated by interleukin-6 in a cell type specific manner, suggesting that they may play a role in the nuclear signaling by interleukin-6.

The cholinergic stimulating effects of ciliary neurotrophic factor and leukemia inhibitory factor are mediated by protein kinase C

The intracellular mechanisms through which two trophic factors, ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF), regulate cholinergic development were examined in sympathetic neuron cultures. Treatment with CNTF or LIF increased levels of choline acetyltransferase (ChAT) activity by 375 and 350%, respectively. However, in neuronal cultures depleted of protein kinase C (PKC) activity by chronic phorbol ester treatment, neither CNTF nor LIF elevated ChAT activity. Further, the stimulation of ChAT due to increased cell density was not observed in PKC-depleted sympathetic neurons. The inhibition of CNTF-stimulated ChAT by phorbol ester occurred in a dose-dependent manner and chronic phorbol ester treatments did not alter the levels of the catecholamine biosynthetic enzyme tyrosine hydroxylase. Moreover, increased levels of diacylglycerol, an endogenous activator of PKC, were observed in sympathetic neurons treated with CNTF. However, neither CNTF nor LIF stimulated the hydrolysis of phosphatidylinositol 4,5-bisphosphate. These observations suggest that a common PKC-dependent pathway, which is independent of phosphatidylinositol 4,5-bisphosphate hydrolysis, mediates the cholinergic stimulating effects of CNTF, LIF, and cell-cell contact in cultured sympathetic neurons.

Biochemistry of B lymphocyte activation

The activation of B lymphocytes from resting cells proceeds from the events of early activation to clonal proliferation to final differentiation into either an antibody-secreting plasma cell or a memory B cell. This is a complex activation process marked by several alternative pathways, depending on the nature of the initial antigenic stimulus. Over the past 5-10 years, there has been an explosion of studies examining the biochemical nature of various steps in these pathways. Some of that progress is reviewed here. In particular, we have described in detail what is known about the structure and function of the AgR, as this molecule plays a pivotal role in B cell responses of various types. We have also reviewed recent progress in understanding the mechanism of action of contact-dependent T cell help and of the cytokine receptors, particularly the receptors for IL-2, IL-4, and IL-6. Clearly, all of these areas represent active areas of investigation and great progress can be anticipated in the next few years.

Human interleukin-9: a new cytokine in hematopoiesis

IL-9 was first identified in the mouse system as a T cell growth factor while human IL-9 was isolated based on its activity on a human myeloid leukemic cell line. The high sequence homology between mouse and human IL-9 plus the preliminary biological analysis have predicted a wide spectrum of in vitro biological activities for this cytokine. Despite the high sequence homology between mouse and human IL-9, many biological activities, however, have not been demonstrated in both species. In vivo studies therefore become essential to understand the physiological role of IL-9. Increasing evidence have also suggested the possible role of IL-9 in the pathogenesis of HD and LCAL. Detailed analysis of IL-9 expression, autocrine growth and clinical outcome of HD patients will be required to make any speculation on the role of this cytokine in the disease states.

Modulation of GM-CSF receptor beta-subunit and interleukin-6 receptor mRNA expression in a human megakaryocytic leukemia cell line

Our present study was designed to clarify the mechanism by which the same megakaryocyte progenitor cells respond to various cytokines at different stages of megakaryocyte development. We examined the changes in mRNA expression of granulocyte macrophage colony-stimulating factor receptor beta-subunit (GM-CSFR beta-subunit), which was a common subunit of a high-affinity interleukin-3 receptor (IL-3R) and a high-affinity GM-CSFR, and interleukin-6 receptor (IL-6R) during megakaryocyte development in a human megakaryocytic leukemia cell line (CMK) which could proliferate and/or differentiate in the presence of 12-O-tetradecanoylphorbol 13-acetate (TPA), IL-3, GM-CSF, and IL-6. We found that GM-CSFR beta-subunit mRNA was expressed constitutively in CMK cells and was transiently down-regulated by TPA and IL-6, while the expression of IL-6R mRNA was increased by TPA in association with the differentiation of megakaryocytes. Furthermore, the TPA-induced down-regulation of GM-CSFR beta-subunit mRNA expression and its recovery were blocked by cycloheximide (CHX), a protein synthesis inhibitor, suggesting that these modulations required de novo protein synthesis. These findings imply that multi-lineage cytokines such as GM-CSF and IL-3 may contribute preferentially to the regulation of the earlier development of megakaryocyte progenitor cells with high densities of multi-lineage cytokine receptors, while IL-6 may be limited in its action to supporting the maturation of more differentiated megakaryocyte progenitor cells.(ABSTRACT TRUNCATED AT 250 WORDS)

cDNA cloning of rat LRP, a receptor like protein tyrosine phosphatase, and evidence for its gene regulation in cultured rat mesangial cells

Protein tyrosine phosphatases (PTPases) are a family of enzymes that play a crucial role in the regulation of signal transduction mediated by reversible protein tyrosine phosphorylation. To understand the significance of PTPases in physiological and pathophysiological processes in the kidney, we isolated three cDNA segments encoding PTPases (LAR, LRP and a novel PTPase) from rat kidney by polymerase chain reaction (PCR). Using PCR product as a probe, we isolated a full-length cDNA of rat LRP. LRP cDNA encoded a single membrane spanning protein consisted of 796 amino acids, with two tandemly located intracellular PTPase domains. By Northern analysis, a ubiquitous pattern of LRP gene expression in rat tissues was demonstrated. In cultured rat mesangial cells, LRP mRNA was detected and the mRNA level was suppressed by either interleukin-1 or interleukin-6 treatment.

Mitogen-induced expression of the primary response gene cMG1 in a rat intestinal epithelial cell-line (RIE-1)

cMG1 is a primary response gene first identified in a rat intestinal epithelial (RIE-1) cell-line [(1990) Oncogene 5, 1081-1083]. A number of mitogens, including epidermal growth factor (EGF), angiotensin II (AII), serum and insulin rapidly induced 2- to 6-fold increases of cMG1 mRNA in RIE-1 cells, while transforming growth factor-beta caused a small reduction. Cyclic AMP-elevating agents blocked the increase of cMG1 mRNA induced by EGF. The AII-stimulated increase of cMG1 mRNA was blocked by the depletion of protein kinase C, whereas the EGF-stimulated increase was not affected, indicating that protein kinase C-dependent and -independent signalling pathways stimulate cMG1 expression.

CNTF and LIF act on neuronal cells via shared signaling pathways that involve the IL-6 signal transducing receptor component gp130

Ciliary neurotrophic factor (CNTF) has a variety of actions within the nervous system. While some of the actions of leukemia inhibitory factor (LIF) on neurons resemble those of CNTF, LIF also has broad actions outside of the nervous system that in many cases mimic those of interleukin-6 (IL-6). Comparison of the tyrosine phosphorylations and gene activations induced by CNTF and LIF in neuron cell lines reveals that they are indistinguishable and also very similar to signaling events that characterize LIF and IL-6 responses in hematopoietic cells. We provide a basis for the overlapping actions of these three factors by demonstrating that the shared CNTF and LIF signaling pathways involve the IL-6 signal transducing receptor component gp130. Thus, the receptor system for CNTF is surprisingly unlike those used by the nerve growth factor family of neurotrophic factors, but is instead related to those used by a subclass of hematopoietic cytokines.

Interleukin 6-induced differentiation of a human B cell line into IgM-secreting plasma cells is mediated by c-fos

The role of the protooncogene c-fos in interleukin (IL) 6-induced B cell differentiation was assessed. Treatment of SKW 6.4 cells with IL 6 induced a transient and early stimulation of c-fos sense mRNA expression. The effect appeared within 30 min and returned to basal levels after 2 h. The addition of antisense oligonucleotides to c-fos significantly inhibited IL 6-induced IgM production by SKW 6.4 cells (p less than 0.001), whereas control oligonucleotides had no inhibitory effect. These results indicate that activation of c-fos is involved in IL 6-induced differentiation of SKW 6.4 cells into IgM-secreting cells.

Interleukin-11: a novel stroma-derived cytokine

Interleukin-11 (IL-11) is a novel stroma-derived cytokine that acts on both hematopoietic progenitors and stromal cells. IL-11 was originally identified in a medium conditioned by the macaque bone marrow-derived stromal cell line PU-34 and cloned as a growth factor for the IL-6-dependent plasmacytoma cell line T1165. IL-11 stimulates T-cell dependent development of antibody-producing B cells and is synergistic with IL-3 to stimulate megakaryocyte colony formation. Adipogenesis inhibitory factor (AGIF) was cloned from the human bone marrow-derived stromal cell line KM-102. The AGIF cDNA sequence was revealed to be identical to that of the IL-11 cDNA. AGIF inhibits the process of adipogenesis of the bone marrow-derived preadipocyte cell line H-1/A. Other biological activities such as stimulation of stem-cell proliferation, erythropoiesis, lymphohematopoiesis and hepatic acute-phase response are also summarized. The human IL-11 gene consists of five exons and four introns, and was mapped on chromosome 19 at band 19q13.3-q13.4. A single class of high-affinity IL-11 receptor (IL-11R) of 151 kDa is present on 3T3-L1 preadipocytes. A protein-tyrosine kinase pathway may be involved in the initiation of the IL-11R-mediated signal transduction.

Interleukin 6 (IL-6) and its receptor: their role in plasma cell neoplasias

Interleukin 6 (IL-6) is a multifunctional cytokine regulating immune response acute phase reaction and hematopoiesis. IL-6 plays a critical role in B cell differentiation to plasma cells and is a potent growth factor for plasmacytoma and myeloma. Abnormal production of IL-6 has been suggested to be involved in polyclonal plasma cell abnormalities and plasma cell neoplasias. The deregulated expression of the IL-6 gene in transgenic mice resulted in the generation of malignant plasmacytoma. Based on these findings, it could be considered that continuous IL-6 gene expression plays an essential role in a multistep oncogenesis of plasma cell neoplasias. The role of IL-6 and its receptor in the generation of plasma cell neoplasias and the mechanisms of the IL-6 gene expression and IL-6 receptor-mediated signal transduction are described.