Influence of subunit combinations on signaling by receptors for oncostatin M, leukemia inhibitory factor, and interleukin-6

Oncostatin M: Dual Regulator of the Skeletal and Hematopoietic Systems

PURPOSE OF THE REVIEW

The bone and hematopoietic tissues coemerge during development and are functionally intertwined throughout mammalian life. Oncostatin M (OSM) is an inflammatory cytokine of the interleukin-6 family produced by osteoblasts, bone marrow macrophages, and neutrophils. OSM acts via two heterodimeric receptors comprising GP130 with either an OSM receptor (OSMR) or a leukemia inhibitory factor receptor (LIFR). OSMR is expressed on osteoblasts, mesenchymal, and endothelial cells and mice deficient for the Osm or Osmr genes have both bone and blood phenotypes illustrating the importance of OSM and OSMR in regulating these two intertwined tissues.

RECENT FINDINGS

OSM regulates bone mass through signaling via OSMR, adaptor protein SHC1, and transducer STAT3 to both stimulate osteoclast formation and promote osteoblast commitment; the effect on bone formation is also supported by action through LIFR. OSM produced by macrophages is an important inducer of neurogenic heterotopic ossifications in peri-articular muscles following spinal cord injury. OSM produced by neutrophils in the bone marrow induces hematopoietic stem and progenitor cell proliferation in an indirect manner via OSMR expressed by bone marrow stromal and endothelial cells that form hematopoietic stem cell niches. OSM acts as a brake to therapeutic hematopoietic stem cell mobilization in response to G-CSF and CXCR4 antagonist plerixafor. Excessive OSM production by macrophages in the bone marrow is a key contributor to poor hematopoietic stem cell mobilization (mobilopathy) in people with diabetes. OSM and OSMR may also play important roles in the progression of several cancers. It is increasingly clear that OSM plays unique roles in regulating the maintenance and regeneration of bone, hematopoietic stem and progenitor cells, inflammation, and skeletal muscles. Dysregulated OSM production can lead to bone pathologies, defective muscle repair and formation of heterotopic ossifications in injured muscles, suboptimal mobilization of hematopoietic stem cells, exacerbated inflammatory responses, and anti-tumoral immunity. Ongoing research will establish whether neutralizing antibodies or cytokine traps may be useful to correct pathologies associated with excessive OSM production.

The Human GP130 Cytokine Receptor and Its Expression-an Atlas and Functional Taxonomy of Genetic Variants

Genetic variants in IL6ST encoding the shared cytokine receptor for the IL-6 cytokine family GP130 have been associated with a diverse number of clinical phenotypes and disorders. We provide a molecular classification for 59 reported rare IL6ST pathogenic or likely pathogenic variants and additional polymorphisms. Based on loss- or gain-of-function, cytokine selectivity, mono- and biallelic associations, and variable cellular mosaicism, we grade six classes of IL6ST variants and explore the potential for additional variants. We classify variants according to the American College of Medical Genetics and Genomics criteria. Loss-of-function variants with (i) biallelic complete loss of GP130 function that presents with extended Stüve-Wiedemann Syndrome; (ii) autosomal recessive hyper-IgE syndrome (HIES) caused by biallelic; and (iii) autosomal dominant HIES caused by monoallelic IL6ST variants both causing selective IL-6 and IL-11 cytokine loss-of-function defects; (iv) a biallelic cytokine-specific variant that exclusively impairs IL-11 signaling, associated with craniosynostosis and tooth abnormalities; (v) somatic monoallelic mosaic constitutively active gain-of-function variants in hepatocytes that present with inflammatory hepatocellular adenoma; and (vi) mosaic constitutively active gain-of-function variants in hematopoietic and non-hematopoietic cells that are associated with an immune dysregulation syndrome. In addition to Mendelian IL6ST coding variants, there are common non-coding cis-acting variants that modify gene expression, which are associated with an increased risk of complex immune-mediated disorders and trans-acting variants that affect GP130 protein function. Our taxonomy highlights IL6ST as a gene with particularly strong functional and phenotypic diversity due to the combinatorial biology of the IL-6 cytokine family and predicts additional genotype-phenotype associations.

Molecular Signature of Neuroinflammation Induced in Cytokine-Stimulated Human Cortical Spheroids

Crucial in the pathogenesis of neurodegenerative diseases is the process of neuroinflammation that is often linked to the pro-inflammatory cytokines Tumor necrosis factor alpha (TNFα) and Interleukin-1beta (IL-1β). Human cortical spheroids (hCSs) constitute a valuable tool to study the molecular mechanisms underlying neurological diseases in a complex three-dimensional context. We recently designed a protocol to generate hCSs comprising all major brain cell types. Here we stimulate these hCSs for three time periods with TNFα and with IL-1β. Transcriptomic analysis reveals that the main process induced in the TNFα- as well as in the IL-1β-stimulated hCSs is neuroinflammation. Central in the neuroinflammatory response are endothelial cells, microglia and astrocytes, and dysregulated genes encoding cytokines, chemokines and their receptors, and downstream NFκB- and STAT-pathway components. Furthermore, we observe sets of neuroinflammation-related genes that are specifically modulated in the TNFα-stimulated and in the IL-1β-stimulated hCSs. Together, our results help to molecularly understand human neuroinflammation and thus a key mechanism of neurodegeneration.

The barrier hypothesis and Oncostatin M: Restoration of epithelial barrier function as a novel therapeutic strategy for the treatment of type 2 inflammatory disease

Mucosal epithelium maintains tissue homeostasis through many processes, including epithelial barrier function, which separates the environment from the tissue. The barrier hypothesis of type 2 inflammatory disease postulates that epithelial and epidermal barrier dysfunction, which cause inappropriate exposure to the environment, can result in allergic sensitization and development of type 2 inflammatory disease. The restoration of barrier dysfunction once it's lost, or the prevention of barrier dysfunction, have the potential to be exciting new therapeutic strategies for the treatment of type 2 inflammatory disease. Neutrophil-derived Oncostatin M has been shown to be a potent disrupter of epithelial barrier function through the induction of epithelial-mesenchymal transition (EMT). This review will discuss these events and outline several points along this axis at which therapeutic intervention could be beneficial for the treatment of type 2 inflammatory diseases.

Oncostatin M promotes mucosal epithelial barrier dysfunction, and its expression is increased in patients with eosinophilic mucosal disease

BACKGROUND

Epithelial barrier dysfunction is thought to play a role in many mucosal diseases, including asthma, chronic rhinosinusitis (CRS), and eosinophilic esophagitis.

OBJECTIVE

The objective of this study was to investigate the role of oncostatin M (OSM) in epithelial barrier dysfunction in human mucosal disease.

METHODS

OSM expression was measured in tissue extracts, nasal secretions, and bronchoalveolar lavage fluid. The effects of OSM stimulation on barrier function of normal human bronchial epithelial cells and nasal epithelial cells cultured at the air-liquid interface were assessed by using transepithelial electrical resistance and fluorescein isothiocyanate-dextran flux. Dual-color immunofluorescence was used to evaluate the integrity of tight junction structures in cultured epithelial cells.

RESULTS

Analysis of samples from patients with CRS showed that OSM mRNA and protein levels were highly increased in nasal polyps compared with those seen in control uncinate tissue (P < .05). OSM levels were also increased in bronchoalveolar lavage fluid of allergic asthmatic patients after segmental allergen challenge and in esophageal biopsy specimens from patients with eosinophilic esophagitis. OSM stimulation of air-liquid interface cultures resulted in reduced barrier function, as measured by decreased transepithelial electrical resistance and increased fluorescein isothiocyanate-dextran flux (P < .05). Alterations in barrier function by OSM were reversible, and the viability of epithelial cells was unaffected. OSM levels in lysates of nasal polyps and uncinate tissue positively correlated with levels of α2-macroglobulin, a marker of epithelial leak, in localized nasal secretions (r = 0.4855, P < .05).

CONCLUSIONS

These results suggest that OSM might play a role in epithelial barrier dysfunction in patients with CRS and other mucosal diseases.

A novel small molecular STAT3 inhibitor, LY5, inhibits cell viability, cell migration, and angiogenesis in medulloblastoma cells

Signal transducers and activators of transcription 3 (STAT3) signaling is persistently activated and could contribute to tumorigenesis of medulloblastoma. Numerous studies have demonstrated that inhibition of the persistent STAT3 signaling pathway results in decreased proliferation and increased apoptosis in human cancer cells, indicating that STAT3 is a viable molecular target for cancer therapy. In this study, we investigated a novel non-peptide, cell-permeable small molecule, named LY5, to target STAT3 in medulloblastoma cells. LY5 inhibited persistent STAT3 phosphorylation and induced apoptosis in human medulloblastoma cell lines expressing constitutive STAT3 phosphorylation. The inhibition of STAT3 signaling by LY5 was confirmed by down-regulating the expression of the downstream targets of STAT3, including cyclin D1, bcl-XL, survivin, and micro-RNA-21. LY5 also inhibited the induction of STAT3 phosphorylation by interleukin-6 (IL-6), insulin-like growth factor (IGF)-1, IGF-2, and leukemia inhibitory factor in medulloblastoma cells, but did not inhibit STAT1 and STAT5 phosphorylation stimulated by interferon-γ (IFN-γ) and EGF, respectively. In addition, LY5 blocked the STAT3 nuclear localization induced by IL-6, but did not block STAT1 and STAT5 nuclear translocation mediated by IFN-γ and EGF, respectively. A combination of LY5 with cisplatin or x-ray radiation also showed more potent effects than single treatment alone in the inhibition of cell viability in human medulloblastoma cells. Furthermore, LY5 demonstrated a potent inhibitory activity on cell migration and angiogenesis. Taken together, these findings indicate LY5 inhibits persistent and inducible STAT3 phosphorylation and suggest that LY5 is a promising therapeutic drug candidate for medulloblastoma by inhibiting persistent STAT3 signaling.

Interleukin 6 and rheumatoid arthritis

Interleukin-6 (IL-6) is a representative cytokine featuring pleiotropic activity and redundancy. A transient synthesis of IL-6 contributes to host defense against infectious agents and tissue injuries by inducing acute phase reactions and immunological and hematopoietic responses. However, uncontrolled persistent production of IL-6 may lead to the development of several immune-mediated diseases. Rheumatoid arthritis (RA) is a chronic disease with joint and systemic inflammation resulting from immunological abnormalities and it has been found that IL-6 plays a key role in the development of this disease. Clinical trials in various parts of the world of tocilizumab, a humanized anti-IL-6 receptor antibody, have proved its efficacy and tolerable safety either as monotherapy or in combination with disease-modifying antirheumatic drugs. As a result, it is currently used as a first-line biologic for the treatment of moderate-to-severe RA in more than 100 countries. Clarification of the mechanism(s) through which tocilizumab exerts its effect on RA and of the reason(s) why IL-6 is continuously produced in RA can be expected to lead to the best use of this agent for RA patients and aid in investigations into the pathogenesis of RA.

Oncostatin M decreases interleukin-1 β secretion by human synovial fibroblasts and attenuates an acute inflammatory reaction in vivo

Oncostatin M (OSM) is a pleiotropic cytokine of the IL-6 family and displays both pro-inflammatory and anti-inflammatory activities. We studied the impact of OSM on the gene activation profile of human synovial cells, which play a central role in the progression of inflammatory responses in joints. In synovial cells stimulated with lipopolysaccharide and recombinant human granulocyte-macrophage colony-stimulating factor, recombinant human OSM and native OSM secreted by human granulocytes both reduced the gene expression and secretion of IL-1β and CXCL8, but increased that of IL-6 and CCL2. This impact on synovial cell activation was not obtained using IL-6 or leukaemia inhibitory factor. Signal transducer and activator of transcription-1 appeared to mediate the effects of OSM on stimulated human synovial fibroblasts. In the murine dorsal air pouch model of inflammation, OSM reduced the expression of the pro-inflammatory cytokines IL-1β and TNF-α in lining tissues, and their presence in the cavity. These results as a whole suggest an anti-inflammatory role for OSM, guiding inflammatory processes towards resolution.

Oncostatin M promotes STAT3 activation, VEGF production, and invasion in osteosarcoma cell lines

Background

We have previously demonstrated that both canine and human OSA cell lines, as well as 8 fresh canine OSA tumor samples, exhibit constitutive phosphorylation of STAT3, and that this correlates with enhanced expression of matrix metalloproteinase-2 (MMP2). While multiple signal transduction pathways can result in phosphorylation of STAT3, stimulation of the cytokine receptor gp130 through either IL-6 or Oncostatin M (OSM) is the most common mechanism through which STAT3 is activated. The purpose of this study was to evaluate the role of IL-6 and OSM stimulation on both canine and human OSA cell lines to begin to determine the role of these cytokines in the biology of OSA.

Methods

RT-PCR and Western blotting were used to interrogate the consequences of OSM and IL-6 stimulation of OSA cell lines. OSA cells were stimulated with OSM and/or hepatocyte growth factor (HGF) and the effects on MMP2 activity (gel zymography), proliferation (CyQUANT), invasion (Matrigel transwell assay), and VEGF production (Western blotting, ELISA) were assessed. The small molecule STAT3 inhibitor LLL3 was used to investigate the impact of STAT3 inhibition following OSM stimulation of OSA cells.

Results

Our data demonstrate that the OSM receptor (OSMR), but not IL-6 or its receptor, is expressed by all human and canine OSA cell lines and canine OSA tumor samples; additionally, OSM expression was noted in all tumor samples. Treatment of OSA cell lines with OSM induced phosphorylation of STAT3, Src, and JAK2. OSM stimulation also resulted in a dose dependent increase in MMP2 activity and VEGF expression that was markedly reduced following treatment with the small molecule STAT3 inhibitor LLL3. Lastly, OSM stimulation of OSA cell lines enhanced invasion through Matrigel, particularly in the presence of rhHGF. In contrast, both OSM and HGF stimulation of OSA cell lines did not alter their proliferative capacity.

Conclusions

These data indicate OSM stimulation of human and canine OSA cells induces STAT3 activation, thereby enhancing the expression/activation of MMP2 and VEGF, ultimately promoting invasive behavior and tumor angiogenesis. As such, OSM and its receptor may represent a novel target for therapeutic intervention in OSA.

A dual role for oncostatin M signaling in the differentiation and death of mammary epithelial cells in vivo

Recent studies in breast cancer cell lines have shown that oncostatin M (OSM) not only inhibits proliferation but also promotes cell detachment and enhances cell motility. In this study, we have looked at the role of OSM signaling in nontransformed mouse mammary epithelial cells in vitro using the KIM-2 mammary epithelial cell line and in vivo using OSM receptor (OSMR)-deficient mice. OSM and its receptor were up-regulated approximately 2 d after the onset of postlactational mammary regression, in response to leukemia inhibitory factor (LIF)-induced signal transducer and activator of transcription-3 (STAT3). This resulted in sustained STAT3 activity, increased epithelial apoptosis, and enhanced clearance of epithelial structures during the remodeling phase of mammary involution. Concurrently, OSM signaling precipitated the dephosphorylation of STAT5 and repressed expression of the milk protein genes beta-casein and whey acidic protein (WAP). Similarly, during pregnancy, OSM signaling suppressed beta-casein and WAP gene expression. In vitro, OSM but not LIF persistently down-regulated phosphorylated (p)-STAT5, even in the continued presence of prolactin. OSM also promoted the expression of metalloproteinases MMP3, MMP12, and MMP14, which, in vitro, were responsible for OSM-specific apoptosis. Thus, the sequential activation of IL-6-related cytokines during mammary involution culminates in an OSM-dependent repression of epithelial-specific gene expression and the potentiation of epithelial cell extinction mediated, at least in part, by the reciprocal regulation of p-STAT5 and p-STAT3.

Box 2 region of the oncostatin M receptor determines specificity for recruitment of Janus kinases and STAT5 activation

Human and murine oncostatin M (OSM) induce their bioactivities through a heterodimeric receptor complex consisting of gp130 and the OSM receptor (OSMR), which initiates a signaling pathway involving Janus kinases (JAKs) and transcription factors of the signal transducers and activators of transcription (STAT) family. In contrast to the signal transducing receptor subunit gp130, the OSMR allows strong activation of STAT5B. The underlying molecular mechanism, however, remained unclear. Here we demonstrate that the human and murine OSM receptors use distinct mechanisms for STAT5B activation. The human receptor contains a STAT5B recruiting tyrosine motif (Tyr837/Tyr839) C-terminal to the box 1/2 region, which is absent in the mouse receptor. In contrast, the murine receptor initiates STAT5 activation directly via the receptor bound Janus kinases. Intriguingly, the murine receptor preferentially recruits JAK2, whereas the human receptor seems to have a higher affinity for JAK1. We identify a single amino acid (Phe820) in the human receptor that is responsible for this preference. Exchange by the murine counterpart (Cys815) allows recruitment of JAK2 by the human receptor and consequently activation of STAT5B independently of receptor tyrosine motifs. STAT5B interacts directly with JAK2 only in response to activation of the murine OSMR or the mutated human OSMR. Additionally, we show that OSM-induced STAT1 phosphorylation occurs independently of receptor tyrosine motifs and is mediated directly by Janus kinases, whereas the two C-terminally located tyrosine residues Tyr917/Tyr945 of the OSMR are crucial for STAT3 activation.

Crif1 is a novel transcriptional coactivator of STAT3

Signal transducer and activator of transcription 3 (STAT3) is a transcriptional factor that performs a broad spectrum of biological functions in response to various stimuli. However, no specific coactivator that regulates the transcriptional activity of STAT3 has been identified. Here we report that CR6-interacting factor 1 (Crif1) is a specific transcriptional coactivator of STAT3, but not of STAT1 or STAT5a. Crif1 interacts with STAT3 and positively regulates its transcriptional activity. Crif1-/- embryos were lethal around embryonic day 6.5, and manifested developmental arrest accompanied with defective proliferation and massive apoptosis. The expression of STAT3 target genes was markedly reduced in a Crif1-/- blastocyst culture and in Oncostatin M-stimulated Crif1-deficient MEFs. Importantly, the key activities of constitutively active STAT3-C, such as transcription, DNA binding, and cellular transformation, were abolished in the Crif1-null MEFs, suggesting the essential role of Crif1 in the transcriptional activity of STAT3. Our results reveal that Crif1 is a novel and essential transcriptional coactivator of STAT3 that modulates its DNA binding ability, and shed light on the regulation of oncogenic STAT3.

Interleukin-6 cytokine family member oncostatin M is a hair-follicle-expressed factor with hair growth inhibitory properties

The activation of receptor complexes containing glycoprotein 130 (gp130) identifies the interleukin (IL)-6 cytokine family. We examined members of this family for their expression and activity in hair follicles. Quantitative polymerase chain reaction using mRNA derived from microdissected, anagen-stage human hair follicles and comparison to non-follicular skin epithelium revealed higher levels of IL-6 (15.5-fold) and oncostatin M (OSM, 3.4-fold) in hair follicles. In contrast, expression of all mRNAs coding for IL-6 cytokine family receptors was reduced. Immunohistology suggested expression of OSM, gp130, leukaemia inhibitory factor receptor (LIFr) and IL-11r in the hair follicle root sheaths and dermal papilla, while IL-11, IL-6r and OSMr were expressed in root sheaths alone. IL-6 was expressed in the dermal papilla while cardiotrophin-1 (CT-1) and LIF were not observed. OSM and to a lesser extent CT-1 exhibited a dose-dependent growth inhibition capacity on human hair follicles in vitro. OSM and CT-1 incubated with agarose beads and injected subcutaneously at 1 mug per mouse into telogen skin of 65-day-old mice revealed no capacity to induce anagen hair growth. In contrast, injection of 65-day-old mice in which anagen had been induced by hair plucking revealed a moderate hair growth inhibitory capacity for OSM, but no significant effect for CT-1. The data identify OSM as a modulator of hair follicle growth and suggest other family members may also have some degree of hair growth inhibitory effect. In principle, increased expression of some IL-6 cytokine family members in cutaneous inflammation might contribute to the promotion of hair loss.

Gene expression profiling of long-term changes in rat liver following burn injury

The inflammatory response initiated upon burn injury is also associated with extensive metabolic adjustments. While there is a significant body of literature on the characterization of these changes at the metabolite level, little is known on the mechanisms of induction, especially with respect to the role of gene expression. We have comprehensively analyzed changes in gene expression in rat livers during the first 7 d after 20% total body surface area burn injury using Affymetrix microarrays. A total of 740 genes were significantly altered in expression at 1, 2, 4, and 7 d after burn injury compared to sham-burn controls. Functional classification based on gene ontology terms indicated that metabolism, transport, signaling, and defense/inflammation response accounted for more than 70% of the significantly altered genes. Fisher least-significant difference post-hoc testing of the 740 differentially expressed genes indicated that over 60% of the genes demonstrated significant changes in expression either on d 1 or on d 7 postburn. The gene expression trends were corroborated by biochemical measurements of triglycerides and fatty acids 24 h postburn but not at later time points. This suggests that fatty acids are used, at least in part, in the liver as energy substrates for the first 4 d after injury. Our data also suggest that long-term regulation of energy substrate utilization in the liver following burn injury is primarily at the posttranscriptional level. Last, relevance networks of significantly expressed genes indicate the involvement of key small molecules in the hepatic response to 20% total body surface area burn injury.

Molecular and Functional Characterization of a Soluble Form of Oncostatin M/Interleukin-31 Shared Receptor

Activation of the signaling transduction pathways mediated by oncostatin M (OSM) requires the binding of the cytokine to either type I OSM receptor (leukemia inhibitory factor receptor/gp130) or to type II OSM receptor (OSMR/gp130). In the present work we have developed an enzyme-linked immunosorbent assay detecting a soluble form of OSMR (sOSMR) secreted by glioblastoma, hepatoma, and melanoma tumor cell lines. sOSMR was also present in sera of healthy individuals, with increased levels in multiple myeloma. Molecular cloning of a corresponding cDNA was carried out, and it encoded for a 70-kDa protein consisting of a half cytokine binding domain containing the canonical WSXWS motif, an immunoglobulin-like domain, and the first half of a second cytokine binding domain with cysteines in fixed positions. Analysis of the soluble receptor distribution revealed a preferential expression in lung, liver, pancreas, and placenta. sOSMR was able to bind OSM and interleukin-31 when associated to soluble gp130 or soluble interleukin-31R, respectively, and to neutralize both cytokine properties. We have also shown that OSM could positively regulate the synthesis of its own soluble receptor in tumor cells.

Progenitor cells in liver regeneration: molecular responses controlling their activation and expansion

Although normally quiescent, the adult mammalian liver possesses a great capacity to regenerate after different types of injuries in order to restore the lost liver mass and ensure maintenance of the multiple liver functions. Major players in the regeneration process are mature residual cells, including hepatocytes, cholangiocytes and stromal cells. However, if the regenerative capacity of mature cells is impaired by liver-damaging agents, hepatic progenitor cells are activated and expand into the liver parenchyma. Upon transit amplification, the progenitor cells may generate new hepatocytes and biliary cells to restore liver homeostasis. In recent years, hepatic progenitor cells have been the subject of increasing interest due to their therapeutic potential in numerous liver diseases as alternative or supportive/complementary tools to liver transplantation. While the first investigations on hepatic progenitor cells have focused on their origin and phenotypic characterization, recent attention has focused on the influence of the hepatic microenvironment on their activation and proliferation. This microenvironment comprises the extracellular matrix, epithelial and non-epithelial resident liver cells, and recruited inflammatory cells as well as the variety of growth-modulating molecules produced and/or harboured by these elements. The cellular and molecular responses to different regenerative stimuli seem to depend on the injury inflicted and consequently on the molecular microenvironment created in the liver by a certain insult. This review will focus on molecular responses controlling activation and expansion of the hepatic progenitor cell niche, emphasizing similarities and differences in the microenvironments orchestrating regeneration by recruitment of progenitor cell populations or by replication of mature cells.

Expression of oncostatin M and its receptors in normal and cirrhotic human liver

BACKGROUND/AIMS

In the cirrhotic liver, gene expression of the multifunctional cytokine oncostatin M (OSM) is up-regulated, but its cellular origin is unknown. Therefore, we investigated the expression of OSM protein and its specific receptor subunits, OSMRbeta and LIFRbeta in normal and cirrhotic human liver using immunohistochemical and Western blot analysis.

RESULTS

OSM protein was expressed in Kupffer cells, variably in normal liver but consistently in cirrhosis. OSMRbeta was expressed at low level in hepatocytes of all normal livers examined, but in no cirrhotic sample. In contrast, LIFRbeta receptor was expressed weakly in normal livers, but much more intensely in cirrhosis, in reactive ductules, bile duct epithelial cells and perisinusoidal areas. Double immunostaining showed co-localization of LIFRbeta with cytokeratin 7, proliferating cell nuclear antigen (PCNA) and leukemia inhibitory factor (LIF), in bile duct epithelial cells, but not with alpha-smooth muscle actin, a myofibroblast marker.

CONCLUSIONS

In human liver, OSM protein is expressed in Kupffer cells, variably in normals but universally in cirrhosis. The differential expression pattern of OSM and its receptors could allow for differential OSM signaling by alternative utilization of receptors to promote hepatocyte proliferation in acute injury and, with its homologue LIF, for the bile ductular reaction in cirrhosis.

Immunocytochemical detection and reverse transcription polymerase chain reaction expression of oncostatin M (OSM) and its receptor (OSM-Rbeta) in human fetal and adult ovaries

OBJECTIVE

To investigate the immunocytochemical expression and presence of mRNA transcripts of oncostatin M (OSM) and its exclusive receptor (OSM-Rbeta) in ovaries from human adults and fetuses.

DESIGN

Immunocytochemical and reverse transcription polymerase chain reaction (RT-PCR) study.

SETTING

Major tertiary care and referral academic centers.

PATIENT(S)

Ten women and girls undergoing laparoscopic ovarian biopsy and 30 women undergoing second-trimester and third-trimester pregnancy terminations.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Microscopic morphometric analysis, immunocytochemistry for OSM and OSM-Rbeta, and RT-PCR analyses.

RESULT(S)

There was strong to moderate immunocytochemical staining for OSM in both oocytes and granulosa cells of follicles from primordial stages onwards in ovaries from both fetuses and adults/adolescents. OSM-Rbeta was detected mainly in the oocytes. Transcripts of OSM and OSM-Rbeta RNA were detected by RT-PCR analyses.

CONCLUSION(S)

The expression of OSM and its receptor in ovarian tissue from fetuses and women suggests a possible role of OSM in growth initiation of human primordial follicles.

Characterization of the Signaling Capacities of the Novel gp130-like Cytokine Receptor

The gp130-like receptor (GPL) is a recently cloned member of the family of type I cytokine receptors. The name reflects its close relationship to gp130, the common receptor subunit of the interleukin (IL)-6-type cytokines. Indeed, the recently proposed ligand for GPL, IL-31, is closely related to the IL-6-type cytokines oncostatin M, leukemia inhibitory factor, and cardiotrophin-1. The second signal transducing receptor for IL-31 seems to be the oncostatin M receptor beta (OSMRbeta). The present study characterizes in depth the molecular mechanisms underlying GPL-mediated signal transduction. GPL is a strong activator of STAT3 and STAT5, whereas STAT1 is only marginally tyrosine-phosphorylated. We identify tyrosine residues 652 and 721 in the cytoplasmic region of the longest isoform of GPL (GPL(745)) as the major STAT5- and STAT3-activating sites, respectively. Additionally, we demonstrate Jak1 binding to GPL and its activation in heteromeric complexes with the OSMRbeta but also in a homomeric receptor complex. Most interesting, unlike OSMRbeta and gp130, GPL is insufficient to mediate ERK1/2 phosphorylation. We propose that this is due to a lack of recruitment of the tyrosine phosphatase SHP-2 or the adaptor protein Shc to the cytoplasmic domain of GPL.

Principles of interleukin (IL)-6-type cytokine signalling and its regulation

The IL (interleukin)-6-type cytokines IL-6, IL-11, LIF (leukaemia inhibitory factor), OSM (oncostatin M), ciliary neurotrophic factor, cardiotrophin-1 and cardiotrophin-like cytokine are an important family of mediators involved in the regulation of the acute-phase response to injury and infection. Besides their functions in inflammation and the immune response, these cytokines play also a crucial role in haematopoiesis, liver and neuronal regeneration, embryonal development and fertility. Dysregulation of IL-6-type cytokine signalling contributes to the onset and maintenance of several diseases, such as rheumatoid arthritis, inflammatory bowel disease, osteoporosis, multiple sclerosis and various types of cancer (e.g. multiple myeloma and prostate cancer). IL-6-type cytokines exert their action via the signal transducers gp (glycoprotein) 130, LIF receptor and OSM receptor leading to the activation of the JAK/STAT (Janus kinase/signal transducer and activator of transcription) and MAPK (mitogen-activated protein kinase) cascades. This review focuses on recent progress in the understanding of the molecular mechanisms of IL-6-type cytokine signal transduction. Emphasis is put on the termination and modulation of the JAK/STAT signalling pathway mediated by tyrosine phosphatases, the SOCS (suppressor of cytokine signalling) feedback inhibitors and PIAS (protein inhibitor of activated STAT) proteins. Also the cross-talk between the JAK/STAT pathway with other signalling cascades is discussed.

GPL, a novel cytokine receptor related to GP130 and leukemia inhibitory factor receptor

We describe a novel cytokine receptor named GP130 Like receptor, or GPL, that displays similarities with the interleukin-6 and interleukin-12 family of signaling receptors. Four different isoforms diverging in their carboxyl terminus were isolated, corresponding to proteins encompassing 560, 610, 626, and 745 amino acids. Sequences included a signal peptide of 32 amino acids, followed by a cytokine binding domain containing four conserved cysteines, a WSDWS motif, and a region consisting of three fibronectin type III domain repeats. No immunoglobulin-like module was identified in the GPL sequences. The intracellular part of longer isoforms contained a proline-rich region defining a box1 motif for interaction with the Janus kinases. The Gpl gene is organized in 15 exons and is located on 5q11.2 in tandem with the gp130 gene. Both genes were only separated by 24 kilobases, with opposite transcriptional orientations. The GPL receptor displayed a 28% identity with gp130. Specific GPL transcripts were observed in tissues involved in reproduction. Transcripts were also found in blood cells and in bone marrow, revealing expression of GPL in all of the myelomonocytic lineage, from hematopoietic stem cells to activated dendritic cells. In monocytes and dendritic cells, expression of GPL was strongly up-regulated by interferon-gamma, indicating a possible involvement of GPL in Th1-type immune responses. The molecular basis of cell signaling mediated by GPL was studied using chimeric receptors where external portions of alpha or beta interleukin-5 receptor subunits were fused to the internal portion of GPL or of related receptors. Results indicated that association of GPL to the intracellular portions of gp130, or LIF receptor, allowed the signaling cascade.

Principles of interleukin (IL)-6-type cytokine signalling and its regulation

The IL (interleukin)-6-type cytokines IL-6, IL-11, LIF (leukaemia inhibitory factor), OSM (oncostatin M), ciliary neurotrophic factor, cardiotrophin-1 and cardiotrophin-like cytokine are an important family of mediators involved in the regulation of the acute-phase response to injury and infection. Besides their functions in inflammation and the immune response, these cytokines play also a crucial role in haematopoiesis, liver and neuronal regeneration, embryonal development and fertility. Dysregulation of IL-6-type cytokine signalling contributes to the onset and maintenance of several diseases, such as rheumatoid arthritis, inflammatory bowel disease, osteoporosis, multiple sclerosis and various types of cancer (e.g. multiple myeloma and prostate cancer). IL-6-type cytokines exert their action via the signal transducers gp (glycoprotein) 130, LIF receptor and OSM receptor leading to the activation of the JAK/STAT (Janus kinase/signal transducer and activator of transcription) and MAPK (mitogen-activated protein kinase) cascades. This review focuses on recent progress in the understanding of the molecular mechanisms of IL-6-type cytokine signal transduction. Emphasis is put on the termination and modulation of the JAK/STAT signalling pathway mediated by tyrosine phosphatases, the SOCS (suppressor of cytokine signalling) feedback inhibitors and PIAS (protein inhibitor of activated STAT) proteins. Also the cross-talk between the JAK/STAT pathway with other signalling cascades is discussed.

The oncogenic fusion protein-tyrosine kinase ZNF198/fibroblast growth factor receptor-1 has signaling function comparable with interleukin-6 cytokine receptors

The reciprocal t(8;13) chromosome translocation results in a fusion gene (FUS) in which the N-terminal half of the zinc finger protein ZNF198 is combined with the cytoplasmic domain of the fibroblast growth factor receptor-1 (FGFR1). Expression of FUS is suggested to provide growth-promoting activity to myeloid cells similar to the activity of hematopoietic cytokine receptors. This study determined the specificity of FUS to activate signal transduction pathways. Because no tumor cell line expressing FUS was available, the mode of FUS action was identified in cells transiently and stably transfected with an expression vector for FUS. FUS acted as a constitutively active protein-tyrosine kinase and mediated phosphorylation of STAT1, 3, and 5 but not STAT4 and 6. The same specificity but lower activity was determined for normal FGFR1. STAT activation by FUS, similar to that by interleukin-6-type cytokines, promoted STAT-specific induction of genes. The functionality of FUS, as well as the relative recruitment of STAT isoforms, was determined by the dimerizing function of the zinc finger domain. Replacement of the ZNF198 portion by the Bcr portion as present in the t(8;22) translocation shifted the signaling toward a more prominent STAT5 activation. This study documents that both gene partners forming the fusion oncogene define the activity and the signaling specificity of the protein-tyrosine kinase of FGFR1.

Molecular basis of the cell specificity of cytokine action

The molecular cloning and biological analyses of cytokines have led us to a general understanding of their pleiotropism and redundancy. These features have been ascribed to the composition of cytokine receptor complexes, which include a signal-transducing receptor subunit that is used by all members of a cytokine family and a binding subunit that is specific for each cytokine. Even though a given cytokine uses the same receptor complex when binding to various cell types, the cytokine elicits quite specific and distinct biological responses in different types of cells. Even in the same type of cell, the responses to a given cytokine could vary depending on the location of the cell and the condition of its microenvironment. Important mediators for the main cytokine signal-transduction pathway are the Janus kinases (Jaks) and signal transducer and activator of transcription (STATs). Selective usage of members of the Jak and STAT families by a given cytokine receptor is partly responsible for the specificity of cytokine action. In addition to the Jak-STAT pathway, a cytokine receptor complex can simultaneously operate multiple signal-transduction pathways, which usually express contradictory properties. These contradictory signals from a single cytokine are orchestrated to evoke a unified biological response in the cell. Here we discuss the molecular mechanisms that regulate how the cell specificity of cytokine signals is regulated, especially focusing on the IL-6/gp130 system.

Novel role of Janus kinase 1 in the regulation of oncostatin M receptor surface expression

The oncostatin M receptor (OSMR) is part of a heterodimeric receptor complex that mediates signal transduction of the pleiotropic cytokine OSM via a signaling pathway involving Janus kinases (Jaks) and transcription factors of the signal transducers and activators of transcription (STAT) family. Upon heterologous expression of the OSMR in several cell lines, we observed that its surface expression was significantly enhanced by coexpression of the Janus kinases Jak1, Jak2, and Tyk2 but not Jak3. Chimeric receptors consisting of the extracellular region of the interleukin-5 receptor beta chain and the transmembrane and intracellular part of the OSMR were similarly up-regulated on the plasma membrane when Jak1 was coexpressed. The overall expression level of these constructs did not change significantly, but Jak1 coexpression increased the amount of endoglycosidase H-resistant, fully processed OSMR chimeras. Using mutated receptor and Jak1 constructs, we were able to demonstrate that association of Jak1 with the membrane proximal region of the receptor, but not its kinase activity, is necessary for this effect. Moreover, deletion of the OSMR box1/2 region also resulted in an improved surface expression indicating that this region may contain a signal preventing efficient receptor surface expression in the absence of associated Jaks. Finally we demonstrate that in Jak1-deficient cells, the endogenous OSMR is significantly down-regulated, an effect that can be reversed by transient expression of Jak1 in these cells.

Coexpression of oncostatin M and its receptors and evidence for STAT3 activation in human ovarian carcinomas

The expression of oncostatin M and leukemia inhibitory factor (LIF), JAK-STAT activators and members of the interleukin-6 family of cytokines, were examined in a series of primary ovarian carcinomas using immunohistochemistry. The malignant epithelial cells of all 29 ovarian carcinomas examined expressed oncostatin M; none expressed LIF. Oncostatin M can activate two related receptors, one consisting of a low-affinity LIF receptor subunit, LIFR beta, which forms a heterocomplex with the gp130 signal transducing protein and can recognize both oncostatin M and LIF, and a second heterocomplex consisting of a subunit that specifically recognizes oncostatin M, OSMR beta, and the gp130 protein. By immunohistochemistry, 25 of 25 ovarian carcinomas examined expressed the LIFR beta subunit in the malignant epithelial cells (all samples express gp130), and two-thirds the ovarian carcinomas studied expressed OSMR beta mRNA as determined by RT-PCR. Thus oncostatin M and its receptors are commonly coexpressed in malignant ovarian epithelial cells, and represent a potential autocrine loop in this tumor type. STAT3, of one the signaling proteins downstream of the oncostatin M/LIF receptors, was found in its phosphorylated, activated form (phosphotyrosine 705 STAT3) in the malignant epithelial cells of 17 of 23 ovarian carcinomas examined (74%) as determined by immunohistochemistry; this suggests that this protein is constitutively activated in most ovarian carcinomas, as it is in many other human malignancies. Recombinant human Oncostatin M (rhOSM) can induce the transient tyrosine 705 phosphorylation of STAT3 in serum-starved LIFR beta/OSMR beta expressing ovarian carcinoma cell lines, but does not alter cell growth and effects only a modest increase in the apoptotic rate in these cultured cells. Oncostatin M and its receptors may be part of a network of cytokine systems within ovarian carcinomas that may act to maintain STAT3 in its activated form, a phenomenon associated with the malignant phenotype.

Involvement of tyrosine phosphatase PTP1D in the inhibition of interleukin-6-induced Stat3 signaling by alpha-thrombin

We previously demonstrated that exposure of CCL39 lung fibroblasts to alpha-thrombin inhibits interleukin-6 (IL-6)-induced tyrosine phosphorylation of Stat3 (signal transducers and activators of transcription 3) via activation of mitogen-activated protein (MAP) kinase kinase 1 [Bhat et al. (1998) Arch. Biochem. Biophys. 350, 307-314]. In this study, using CCL39/MRC-5 cells, we investigated if additional signaling intermediates are involved in alpha-thrombin's inhibitory effects on IL-6-induced Stat3 signaling. We also determined if alpha-thrombin inhibits oncostatin M (OSM)-induced Stat3/Stat1, and interferon-gamma (IFN-gamma)-induced Stat1 tyrosine phosphorylation. We demonstrate that, although both IL-6 and OSM belong to the same cytokine family, alpha-thrombin inhibited only the IL-6-induced Stat3 tyrosine phosphorylation. The tyrosine phosphatase PTP1D coprecipitated with Stat3 from alpha-thrombin + IL-6, but not from alpha-thrombin + OSM-treated cells. Pretreatment of cells with a phosphatase inhibitor reversed the inhibitory actions of alpha-thrombin, suggesting a role for PTP1D in alpha-thrombin-mediated inhibition of IL-6-induced Stat3 signaling. Interestingly, alpha-thrombin failed to inhibit OSM- and IFN-gamma-induced Stat1 tyrosine phosphorylation. Cytokine-specific inhibition of the Stat3 signaling involving MAP kinase kinase 1 and PTP1D by alpha-thrombin may play an important role in regulation of gene expression.

Differential effects of oncostatin M and leukaemia inhibitory factor expression in astrocytoma cells

The effects of the production of two closely related cytokines, oncostatin M (OSM) and leukaemia inhibitory factor (LIF), by astrocytoma cells were investigated using the stable cell line human U373-MG, which expressed and secreted both biologically active polypeptides. The expression of LIF by these cells caused resistance to this cytokine due to loss of the LIF receptor (LIFR), from the cell surface, suggesting its retention. In contrast, cells expressing OSM were stimulated by this cytokine, utilizing an autocrine mechanism, and possessed receptors for OSM, but not LIF, on the cell surface. In these cells the continuous up-regulation of OSM-induced gene expression was found even though the Janus kinase-signal transducer and activator of transcription ('JAK/STAT') pathway was almost exhausted due to long-term autocrine stimulation of the cells by OSM. The amount of LIFR was down-regulated in both LIF- and OSM-producing cells and this effect was not found in wild-type U373-MG cells treated with externally added cytokines. To investigate the mechanism of autocrine stimulation by OSM we constructed a stable cell line expressing a form of OSM that is retained in the endoplasmic reticulum (ER). This biologically active cytokine was not secreted, but was localized in the ER. In addition, it did not stimulate the astrocytoma cells in an autocrine manner. We conclude that expression of LIF causes resistance of astrocytoma cells to this cytokine, whereas expression of OSM leads to autocrine stimulation.

Coupling of inflammatory cytokine signaling pathways probed by measurements of extracellular acidification rate

There is a growing interest in the mechanisms of how cells integrate the multitude of signals that emanate during inflammatory stimuli, such as the hepatic acute phase response to burn or trauma. We have used measurements of extracellular acidification rate (ECAR) of HepG2 cells cultured on microporous membranes to probe the coupling between signaling pathways for gp130 family cytokines (interleukin-6, oncostatin M) and IL-1, each of which is considered to play a significant role in the hepatic acute phase response. We found that brief (30 min or less) exposure to any of these cytokines desensitized the HepG2 cells to subsequent exposure with the same cytokine. Furthermore, we found that this property serves as a probe of the coupling of signaling pathways: exposure to IL-1 did not desensitize the cells to exposure to OSM and vice versa. However, cells exposed to IL-6 with soluble gp80, which together share with OSM the use of gp130 as a signal transducing receptor, were subsequently unable to respond to OSM, and vice versa. Simultaneous exposure of cells to moderate concentrations (near their respective EC50 values) of both IL-1 and OSM resulted in synergistic effects on the ECAR, but simultaneous exposure to saturating concentrations of IL-1 and OSM resulted in a response that tracked that of OSM alone. These results suggest that the signaling pathways of IL-1 and OSM may be simultaneously activated in HepG2 cells under moderate inflammatory cytokine challenge but that the cells must prioritize their response under extreme cytokine challenges.

Non-redundant signal transduction of interleukin-6-type cytokines. The adapter protein Shc is specifically recruited to rhe oncostatin M receptor

The common use of the cytokine receptor gp130 has served as an explanation for the extremely redundant biological activities exerted by interleukin (IL)-6-type cytokines. Indeed, hardly any differences in signal transduction initiated by these cytokines are known. In the present study, we demonstrate that oncostatin M (OSM), but not IL-6 or leukemia inhibitory factor, induces tyrosine phosphorylation of the Shc isoforms p52 and p66 and their association with Grb2. Concomitantly, OSM turns out to be a stronger activator of ERK1/2 MAPKs. Shc is recruited to the OSM receptor (OSMR), but not to gp130. Binding involves Tyr(861) of the OSMR, located within a consensus binding sequence for the Shc PTB domain. Moreover, Tyr(861) is essential for activation of ERK1/2 and for full activation of the alpha(2)-macroglobulin promoter, but not for an exclusively STAT-responsive promoter. This study therefore provides evidence for qualitative differential signaling mechanisms exerted by IL-6-type cytokines.

Expression levels of gp130 in bone marrow stromal cells determine the magnitude of osteoclastogenic signals generated by IL-6-type cytokines

Interleukin-6 (IL-6)-type cytokines stimulate osteoclast formation by activating the glycoprotein 130 (gp130) receptor subunit on stromal/osteoblastic cells, which in turn leads to signal transducer and activator of transcription 3 (STAT3)-mediated expression of receptor activator of NF-kappaB ligand (RANKL). Based on evidence that gp130 expression is regulated by a variety of cytokines and hormones, we have determined here whether changes in gp130 levels directly contribute to the magnitude of the osteoclastogenic stimulus delivered by IL-6-type cytokines. To accomplish this, gp130 protein levels were modulated using a tetracycline-regulated expression system in a stromal/osteoblastic cell line, UAMS-32, which supports osteoclast formation. Removal of doxycycline from the culture medium elevated gp130 expression and increased the responsiveness of a STAT-responsive promoter-luciferase construct to IL-6 complexed with its soluble receptor (IL-6+sIL-6R), but diminished the responsiveness to oncostatin M (OSM). IL-6+sIL-6R-stimulated osteoclast formation was greater when osteoclast precursors were cocultured with the cells expressing elevated gp130 levels than when cells expressing low gp130 levels were used. However, increased gp130 levels reduced OSM-stimulated osteoclast formation. These results establish that the level of gp130 in stromal/osteoblastic cells directly modulates the magnitude of the osteoclastogenic response to IL-6-type cytokines such that an increase in gp130 increases the cellular responsiveness to IL-6+sIL-6R but reduces responsiveness to OSM.

Receptor subunit-specific action of oncostatin M in hepatic cells and its modulation by leukemia inhibitory factor

The related cytokines, interleukin-6 (IL-6), oncostatin M (OSM), and leukemia inhibitory factor (LIF) direct the formation of specific heteromeric receptor complexes to achieve signaling. Each complex includes the common signal-transducing subunit gp130. OSM and LIF also recruit the signaling competent, but structurally distinct OSMRbeta and LIFRalpha subunits, respectively. To test the hypothesis that the particularly prominent cell regulation by OSM is due to signals contributed by OSMRbeta, we introduced stable expression of human or mouse OSMRbeta in rat hepatoma cells which have endogenous receptors for IL-6 and LIF, but not OSM. Both mouse and human OSM engaged gp130 with their respective OSMRbeta subunits, but only human OSM also acted through LIFR. Signaling by OSMRbeta-containing receptors was characterized by highest activation of STAT5 and ERK, recruitment of the insulin receptor substrate and Jun-N-terminal kinase pathways, and induction of a characteristic pattern of acute phase proteins. Since LIF together with LIFRalpha appear to form a more stable complex with gp130 than OSM with gp130 and OSMRbeta, co-activation of LIFR and OSMR resulted in a predominant LIF-like response. These results suggest that signaling by IL-6 cytokines is not identical, and that a hierarchical order of cytokine receptor action exists in which LIFR ranks as dominant member.

Crystal structure and functional dissection of the cytostatic cytokine oncostatin M

BACKGROUND

The cytokine oncostatin M (OSM) inhibits growth of certain tumour-derived cells, induces proliferation in other cell types (e.g. haemangioblasts) and is a mediator of inflammatory responses. Its mechanism of action is via specific binding to gp130 and either the leukaemia inhibitory factor receptor (LIFR) or oncostatin M receptor (OSMR) systems at the cell surface to form an active signalling complex.

RESULTS

We report here the crystal structure of human oncostatin M (hOSM) along with mutagenesis data which map the receptor-binding epitopes of the molecule. The structure was determined to a resolution of 2.2 A and conforms to the haematopoietin cytokine up-up-down-down four-helix bundle topology. The site 2 epitope, responsible for gp130 binding, is centred around Gly120 which forms a 'dimple' on the surface of the molecule located on helices A and C. The site 3 motif, responsible for LIFR and OSMR binding, consists of a protruding Phe160/Lys163 pair located at the start of helix D.

CONCLUSIONS

The data presented allow functional dissection of the receptor-binding interfaces to atomic resolution. Modelling suggests that the gp130 residue Phe169 packs into the site 2 dimple in an analogous fashion to structurally equivalent residues at the growth hormone-growth hormone receptor interface, implying that certain key features may underlie recognition across the whole cytokine/receptor superfamily. Conversely, detailed comparison of the available structures suggests that variations on a common theme dictate the specificity of receptor-ligand interactions within the gp130 family of cytokines.

Leukemia-inhibitory factor-neuroimmune modulator of endocrine function

Leukemia-inhibitory factor (LIF) is a pleiotropic cytokine expressed by multiple tissue types. The LIF receptor shares a common gp130 receptor subunit with the IL-6 cytokine superfamily. LIF signaling is mediated mainly by JAK-STAT (janus-kinase-signal transducer and activator of transcription) pathways and is abrogated by the SOCS (suppressor-of cytokine signaling) and PIAS (protein inhibitors of activated STAT) proteins. In addition to classic hematopoietic and neuronal actions, LIF plays a critical role in several endocrine functions including the utero-placental unit, the hypothalamo-pituitary-adrenal axis, bone cell metabolism, energy homeostasis, and hormonally responsive tumors. This paper reviews recent advances in our understanding of molecular mechanisms regulating LIF expression and action and also provides a systemic overview of LIF-mediated endocrine regulation. Local and systemic LIF serve to integrate multiple developmental and functional cell signals, culminating in maintaining appropriate hormonal and metabolic homeostasis. LIF thus functions as a critical molecular interface between the neuroimmune and endocrine systems.

Early cortical precursors do not undergo LIF-mediated astrocytic differentiation

Multipotential stem cells have been isolated from the developing and adult CNS. Similar identified factors control the differentiation of these cells. A striking example is the instructive action of CNTF/LIF activating the JAK/STAT pathway to induce astrocytic differentiation in both fetal and adult CNS stem cells. Here we show that E12 cortical precursors express functional LIF receptors but do not exhibit this differentiation response to CNTF/LIF either in explant or in dissociated cell culture. The lack of response to LIF-induced astrocytic differentiation is maintained in cocultures with LIF responsive cells derived from E15 cortex. This suggests cell intrinsic differences between early and late stage precursors in the interpretation of LIF-mediated signaling; however, the early nestin-positive precursor population differentiates into both neurons and neural crest derivatives. These data define differences between CNS stem cells from different stages of cortical development. J. Neurosci. Res. 59:301-311, 2000. Published 2000 Wiley-Liss, Inc.

Oncostatin M: a cytokine upregulated in human cirrhosis, increases collagen production by human hepatic stellate cells

BACKGROUND/AIMS

Hepatic stellate cells are predominantly responsible for the increased extracellular matrix seen in cirrhosis. The cytokine oncostatin M has been implicated in fibrogenesis in vitro in other cell types and in vivo in other tissues, although its effect on hepatic stellate cells or in cirrhosis is unknown.

METHODS

To examine the effect of oncostatin M on collagen production by human hepatic stellate cells in culture, collagen protein was measured and collagen alpha2(1) mRNA was quantified by Northern analysis. Tissue inhibitor of metalloproteinase-1 (an inhibitor of collagen degradation) mRNA was measured in response to oncostation M stimulation. To explore the potential biological significance of this work to human liver disease, oncostatin M messenger RNA in normal and cirrhotic human liver was measured.

RESULTS

Oncostatin M induced in a 2-fold increase in collagen secretion. The potency of induction of collagen protein secretion was equal to that observed after transforming growth factor beta stimulation. An increase in endogenous collagen alpha2(1) mRNA could not be detected. This suggested a post-transcriptional mechanism for the increase in collagen protein. In response to oncostatin M stimulation, there was a 2-fold increase in the tissue inhibitor or metalloproteinase-1 mRNA. Oncostatin M mRNA was detected in 6/6 cirrhotic livers and 1/7 normal livers after 28 PCR cycles.

CONCLUSION

These results suggest that oncostatin M expression is upregulated in cirrhosis where it may have a role as a profibrogenic cytokine in hepatic stellate cells.

Contributions of Leukemia Inhibitory Factor Receptor and Oncostatin M Receptor to Signal Transduction in Heterodimeric Complexes with Glycoprotein 130

Leukemia inhibitory factor (LIF), cardiotrophin-1, ciliary neurotrophic factor, and oncostatin M (OSM) lead to heterodimerization of LIF receptor (LIFR) or the OSM-specific receptor (OSMR) with glycoprotein (gp) 130, the common receptor subunit for IL-6-type cytokines. Thereby intracellular signaling via Janus kinases (Jaks) and STAT transcription factors is initiated. We investigated the contributions of LIFR and OSMR to signal transduction in the context of heterodimers with gp130. Chimeric receptors based on the extracellular parts of the IL-5R α- and β-chains were generated, allowing the induced heterodimerization of two different cytoplasmic tails. Our studies demonstrate that upon heterodimerization with the gp130 cytoplasmic region, the cytoplasmic parts of both LIFR and OSMR were critical for activation of an acute phase protein promoter in HepG2 hepatoma cells. The membrane-proximal region of LIFR or OSMR was crucial for the ability of such receptor complexes to induce DNA binding of STAT1 and STAT3 in COS-7 cells. Membrane-distal regions of LIFR and OSMR contributed to STAT activation even in the absence of gp130 STAT recruitment sites. We further show that the Janus kinases Jak1 and Jak2 constitutively associated with receptor constructs containing the cytoplasmic part of LIFR, OSMR, or gp130, respectively. Homodimers of the LIFR or OSMR cytoplasmic regions did not elicit responses in COS-7 cells but did in HepG2 cells and in MCF-7 breast carcinoma cells. Thus, in spite of extensive functional similarities, differential signaling abilities of gp130, LIFR, and OSMR may become evident in a cell-type-specific manner.

Stat5a and Stat5b: fraternal twins of signal transduction and transcriptional activation

Stat5a and Stat5b are discretely encoded transcription factors that mediate signals for a broad spectrum of cytokines. Their activation is often an integral component of redundant cytokine signal cascades involving complex cross-talk and pleiotropic gene regulation by Stat5 has been implicated in cellular functions of proliferation, differentiation and apoptosis with relevance to processes of hematopoiesis and immunoregulation, reproduction, and lipid metabolism. Although Stat5a and Stat5b show peptide sequence similarities of > 90%, targeted gene disruptions in mice yield distinctive phenotypes. Prolactin-directed mammary gland maturation fails without functional Stat5a, while disruption of Stat5b in males mitigates growth hormone effects on hepatic function and body mass. The molecular basis for this biologic dichotomy is probably multifaceted. Limited structural dissimilarities between the Stat5a and Stat5b transactivation domains, or subtle differences in the DNA-binding affinities of Stat5 dimer pairs undoubtedly influence gene regulation, but cell-dependent asymmetries in availability of phosphorylated Stat5 can be an underlying factor. Differences in serine phosphorylation(s) of Stat5a and Stat5b, or Stat5 associations with adaptor proteins or co-transcription factors are other potential sources of functional disparity and the signal amplitude, frequency or duration also can be significant. In addition to Stat5 signal attenuation by phosphatase actions or classical feedback inhibition, truncated forms of Stat5 lacking in transactivation capacity may compete upstream for activation and diminish access of full length molecules to DNA binding sites.

Oncostatin M transforms lymphoid tissue function in transgenic mice by stimulating lymph node T-cell development and thymus autoantibody production

Oncostatin M (OM) is a member of the IL-6 subfamily of cytokines that is expressed in primary lymphoid tissues such as bone marrow and thymus, as well as in secondary lymphoid tissues and activated leukocytes. We produced transgenic mice that overexpressed the human, bovine, or mouse OM genes and compared their relative ability to modulate lymphopoiesis. Each species of cytokine induced a similar extrathymic pathway of T-cell development involving the accumulation of immature T cells within lymph nodes. Reconstitution experiments utilizing lethally irradiated athymic mice indicated that OM had caused hematopoietic precursors within fetal liver and bone marrow to initiate lymph node T-cell development in the absence of a thymic environment. Breeding experiments with IL6-/- and IL-7r(alpha)-/- deficient mice, indicated that induction of this extrathymic pathway by the OM transgene occurred in the absence of IL-6, but was strictly dependent on IL-7 receptor signaling. Separately, OM stimulated the accumulation of immature B cells within the transgenic thymus and caused the subcapsular regions of the thymus to expand with mature B and T cells. This thymus conversion to secondary lymphoid tissue was responsible for a lethal autoimmune-like disease marked by high titers of circulating autoantibodies, proteinuria, and glomerulonephritis. The conserved phenotypes elicited by these three forms of OM indicate that this potent hematopoietic cytokine can regulate lymphoid tissue function and morphogenesis.

Cytoplasmic Domains of the Leukemia Inhibitory Factor Receptor Required for STAT3 Activation, Differentiation, and Growth Arrest of Myeloid Leukemic Cells

Leukemia inhibitory factor (LIF) induces growth arrest and macrophage differentiation of mouse myeloid leukemic cells through the functional LIF receptor (LIFR), which comprises a heterodimeric complex of the LIFR subunit and gp130. To identify the regions within the cytoplasmic domain of LIFR that generate the signals for growth arrest, macrophage differentiation, and STAT3 activation independently of gp130, we constructed chimeric receptors by linking the transmembrane and intracellular regions of mouse LIFR to the extracellular domains of the human granulocyte macrophage colony-stimulating factor receptor (hGM-CSFR)  and βc chains. Using the full-length cytoplasmic domain and mutants with progressive C-terminal truncations or point mutations, we show that the two membrane-distal tyrosines with the YXXQ motif of LIFR are critical not only for STAT3 activation, but also for growth arrest and differentiation of WEHI-3B D+ cells. A truncated STAT3, which acts in a dominant negative manner was introduced into WEHI-3B D+ cells expressing GM-CSFR-LIFR and GM-CSFRβc-LIFR. These cells were not induced to differentiate by hGM-CSF. The results indicate that STAT3 plays essential roles in the signals for growth arrest and differentiation mediated through LIFR.

Reconstitution of the Functional Mouse Oncostatin M (OSM) Receptor: Molecular Cloning of the Mouse OSM Receptor β Subunit

Oncostatin M (OSM) is a member of the interleukin-6 (IL-6) family of cytokines that share the gp130 receptor subunit. Of these family members, leukemia inhibitory factor (LIF) is most closely related to OSM, and various overlapping biologic activities have been described between human LIF and OSM (hLIF and hOSM). Two types of functional hOSM receptors are known: the type I OSM receptor is identical to the LIF receptor that consists of gp130 and the LIF receptor β subunit (LIFRβ), and the type II OSM receptor consists of gp130 and the OSM receptor β subunit (OSMRβ). It is thus conceivable that common biologic activities between hLIF and hOSM are mediated by the shared type I receptor and OSM-specific activities are mediated by the type II receptor. However, in contrast to the human receptors, recent studies have demonstrated that mouse OSM (mOSM) does not activate the type I receptor and exhibits unique biologic activity. To elucidate the molecular structure of the functional mOSM receptor, we cloned a cDNA encoding mOSMRβ, which is 55.5% identical to the hOSMRβ at the amino acid level. mOSM-responsive cell lines express high-affinity mOSM receptors, as well as mOSMRβ, whereas embryonic stem cells, which are responsive to LIF but not to mOSM, do not express mOSMRβ. mOSMRβ alone binds mOSM with low affinity (kd = 13.0 nmol/L) and forms a high-affinity receptor (kd = 606 pmol/L) with gp130. Ba/F3 transfectants expressing both mOSMRβ and gp130 proliferated in response to mOSM, but failed to respond to LIF and human OSM. Thus, the cloned mOSMRβ constitutes an essential and species-specific receptor component of the functional mOSM receptor. Reminiscent of the colocalization of the mOSM and mLIF genes, the mOSMRβ gene was found to be located in the vicinity of the LIFRβ locus in the proximal end of chromosome 15.

Reconstitution of the Functional Mouse Oncostatin M (OSM) Receptor: Molecular Cloning of the Mouse OSM Receptor β Subunit

Oncostatin M (OSM) is a member of the interleukin-6 (IL-6) family of cytokines that share the gp130 receptor subunit. Of these family members, leukemia inhibitory factor (LIF) is most closely related to OSM, and various overlapping biologic activities have been described between human LIF and OSM (hLIF and hOSM). Two types of functional hOSM receptors are known: the type I OSM receptor is identical to the LIF receptor that consists of gp130 and the LIF receptor β subunit (LIFRβ), and the type II OSM receptor consists of gp130 and the OSM receptor β subunit (OSMRβ). It is thus conceivable that common biologic activities between hLIF and hOSM are mediated by the shared type I receptor and OSM-specific activities are mediated by the type II receptor. However, in contrast to the human receptors, recent studies have demonstrated that mouse OSM (mOSM) does not activate the type I receptor and exhibits unique biologic activity. To elucidate the molecular structure of the functional mOSM receptor, we cloned a cDNA encoding mOSMRβ, which is 55.5% identical to the hOSMRβ at the amino acid level. mOSM-responsive cell lines express high-affinity mOSM receptors, as well as mOSMRβ, whereas embryonic stem cells, which are responsive to LIF but not to mOSM, do not express mOSMRβ. mOSMRβ alone binds mOSM with low affinity (kd = 13.0 nmol/L) and forms a high-affinity receptor (kd = 606 pmol/L) with gp130. Ba/F3 transfectants expressing both mOSMRβ and gp130 proliferated in response to mOSM, but failed to respond to LIF and human OSM. Thus, the cloned mOSMRβ constitutes an essential and species-specific receptor component of the functional mOSM receptor. Reminiscent of the colocalization of the mOSM and mLIF genes, the mOSMRβ gene was found to be located in the vicinity of the LIFRβ locus in the proximal end of chromosome 15.

The box-1 region of the leukemia inhibitory factor receptor alpha-chain cytoplasmic domain is sufficient for hemopoietic cell proliferation and differentiation

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine that acts on a variety of cell types and regulates cell proliferation and differentiation. The functional receptor for LIF is composed of LIFR alpha-chain (LIFRalpha) and gp130 both of which are shared in the functional receptors for oncostatin M, ciliary neurotrophic factor, and cardiotrophin-1. By using stable transfection of wild-type or cytoplasmic deletion mutants of LIFRalpha together with full-length gp130 into Ba/F3 cells, we found that cells expressing gp130 and an extensively deleted mutant LIFRalpha containing only the box-1 region were capable of proliferating in response to LIF, although LIF-dependent long term growth of these cells was seriously impaired. Using a similar strategy to generate WEHI-3BD+ cells expressing gp130 and wild-type or truncation mutants of LIFRalpha, studies revealed that the box-1 region of the LIFRalpha was also sufficient for LIF-dependent induction of different aspects of differentiation, including up-regulation of macrophage surface marker expression, morphological change, and cell migration in agar culture. However, the C-terminal region of the LIFRalpha, although not essential for intracellular signaling, was important for efficient receptor-mediated ligand internalization. In summary, the membrane-proximal box-1 region plays a dominant role in LIF-induced signal transduction of both proliferation and differentiation.

Activation of signal transducers and activators of transcription 1 and 3 by leukemia inhibitory factor, oncostatin-M, and interferon-gamma in adipocytes

We have recently demonstrated that signal transducers and activators of transcription (STATs) 1, 3, 5A, 5B, and 6 are expressed in both cultured and native adipocytes. Our current studies have focused on the activation of STATs 1 and 3 by leukemia inhibitory factor (LIF), oncostatin-M (OSM), and interferon-gamma (IFNgamma) in 3T3-L1 adipocytes. IFNgamma is shown to be a potent activator of STAT 1 as indicated by both tyrosine phosphorylation and nuclear translocation. However, LIF and OSM, which are potent inducers of STAT 3, are less potent activators of STAT 1 as measured by both tyrosine phosphorylation and nuclear translocation. Both STATs 1 and 3 were translocated to the nucleus in a time-dependent fashion following LIF treatment. In addition, IFNgamma resulted in a time- and dose-dependent effect on STATs 1 and 3 nuclear translocation. Growth hormone, a potent activator of STATs 5A and 5B, had a minimal effect on STAT 1 and STAT 3 tyrosine phosphorylation. Preincubation with either insulin or growth hormone had no detectable effects on the tyrosine phosphorylation or nuclear translocation of STATs 1 and 3 induced by LIF, OSM, or IFNgamma. The effects of LIF and IFNgamma on STAT 1 and 3 tyrosine phosphorylation and nuclear translocation were confirmed in native rat adipocytes. In 3T3-L1 adipocytes, a low level of serine phosphorylation of STAT 3 on residue 727 was observed and was markedly enhanced by insulin, LIF, or OSM. This increase in STAT 3 Ser727 phosphorylation was dependent upon the activation of MAPK, since the MAPK kinase inhibitor (PD98059) reduced STAT 3 Ser727 phosphorylation to basal levels. The inhibition of MAPK had no effect on the ability of STATs 1 and 3 to be tyrosine-phosphorylated or translocate to the nucleus. These studies demonstrate the highly specific and quantitative activation of STATs 1 and 3 by LIF, OSM, and IFNgamma in adipocytes and indicate that STAT 3 is a substrate for MAPK in adipocytes.

Interleukin-6-type cytokine signalling through the gp130/Jak/STAT pathway

The family of cytokines signalling through the common receptor subunit gp130 comprises interleukin (IL)-6, IL-11, leukaemia inhibitory factor, oncostatin M, ciliary neurotrophic factor and cardiotrophin-1. These so-called IL-6-type cytokines play an important role in the regulation of complex cellular processes such as gene activation, proliferation and differentiation. The current knowledge on the signal-transduction mechanisms of these cytokines from the plasma membrane to the nucleus is reviewed. In particular, we focus on the assembly of receptor complexes after ligand binding, the activation of receptor-associated kinases of the Janus family, and the recruitment and phosphorylation of transcription factors of the STAT family, which dimerize, translocate to the nucleus, and bind to enhancer elements of respective target genes leading to transcriptional activation. The important players in the signalling pathway, namely the cytokines and the receptor components, the Janus kinases Jak1, Jak2 and Tyk2, the signal transducers and activators of transcription STAT1 and STAT3 and the tyrosine phosphatase SHP2 [SH2 (Src homology 2) domain-containing tyrosine phosphatase] are introduced and their structural/functional properties are discussed. Furthermore, we review various mechanisms involved in the termination of the IL-6-type cytokine signalling, namely the action of tyrosine phosphatases, proteasome, Jak kinase inhibitors SOCS (suppressor of cytokine signalling), protein inhibitors of activated STATs (PIAS), and internalization of the cytokine receptors via gp130. Although all IL-6-type cytokines signal through the gp130/Jak/STAT pathway, the comparison of their physiological properties shows that they elicit not only similar, but also distinct, biological responses. This is reflected in the different phenotypes of IL-6-type-cytokine knock-out animals.

Enhancing Effect of IL-17 on IL-1-Induced IL-6 and Leukemia Inhibitory Factor Production by Rheumatoid Arthritis Synoviocytes and Its Regulation by Th2 Cytokines

IL-17 is a cytokine produced by CD4 T cells that activates the production of inflammatory mediators by synoviocytes. To study the contribution of soluble factors in the interaction between T cells and synoviocytes in rheumatoid arthritis (RA), we looked at the effect of IL-17 on these cells in the presence of cytokines classified as pro (IL-1)- and anti-inflammatory (IL-4, IL-13, IL-10). Both human rIL-1β and rIL-17 induced IL-6 and leukemia inhibitory factor (LIF) production by synovial fibroblasts in a dose-dependent manner. After 7 days of culture, optimal concentrations of IL-1β increased IL-6 (33-fold) and LIF (10-fold) production by synoviocytes, while IL-17 showed a lesser effect on IL-6 (17-fold) and LIF (4-fold) production. Using low concentrations of IL-17 and IL-1β in combination, a synergistic effect was observed on the production of IL-6, whereas an additive effect was observed for LIF production. Production of biologically active IL-17 was demonstrated in RA synovium supernatants with the use of a blocking anti-IL-17 Ab. Both IL-4 and IL-13 had a modest stimulatory effect on IL-1- and IL-17-induced production of IL-6, but inhibited that of LIF. In contrast, IL-10 had a limited inhibitory effect on IL-6 production and no effect on that of LIF. These findings indicate that low levels of cytokines produced by monocytes (IL-1) and T cells (IL-17) can act together on synoviocytes. Thus, some RA synovium T cells producing IL-17 can activate mesenchymal cells leading to an increased proinflammatory pattern sensitive to Th2 cytokine regulation.

Highly specific and quantitative activation of STATs in 3T3-L1 adipocytes

We have recently demonstrated that STATs 1, 3, 5A, 5B, and 6 are expressed in adipocytes. Using the 3T3-L1 cell line, we have examined the activation of all adipocyte expressed STATs by 23 different factors which are either potent regulators of adipocyte gene expression or known STAT activators in other cell types. STAT activation was assessed by examining nuclear translocation and tyrosine phosphorylation in serum deprived, fully differentiated 3T3-L1 adipocytes. Unlike other adipocyte-expressed STATs, STAT 5A was present in the nucleus under basal conditions. Of all the activators examined, only growth hormone was capable of causing STATs 5A and 5B to translocate to the nucleus. None of the activators were capable of affecting the cellular distribution of STAT 6. Furthermore, our results indicate that there is a quantitative activation of STATs 1 and 3 by LIF, OSM, and IFN-gamma as measured by both nuclear translocation and tyrosine phosphorylation in whole cell extracts. IFN-gamma is a potent activator of STAT 1 and a weaker activator of STAT 3, whereas LIF and OSM are potent activators of STAT 3 and weaker activators of STAT 1. These studies demonstrate that STAT activation in adipocytes is highly specific, quantitative, and distinct.

Regulation of the type II oncostatin M receptor expression in lung-derived epithelial cells

Oncostatin M (OSM) is a potent modulator of human lung-derived epithelial cell function. This cytokine binds two distinct receptor complexes: type I OSM receptor which is also a functional receptor for leukemia inhibitory factor (LIF), and type II OSM-specific receptor. The role of these two distinct receptors in mediating the response of individual cell types to OSM has not been delineated. In contrast to LIF, OSM induces synthesis of alpha1-antichymotrypsin and alpha1-antiproteinase inhibitor in lung-derived epithelial cells. The differential responsiveness to LIF and OSM suggested that the response of lung epithelial cells to OSM may be mediated by the OSM-specific receptor. Therefore, we characterized lung-derived epithelial cells for the expression of type II OSM receptor mRNAs, and the regulation of the mRNAs encoding the components of the OSM-specific receptor by cytokines and dexamethasone.