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(1/60) Fetal liver development requires a paracrine action of oncostatin M through the gp130 signal transducer.

Fetal liver, the major site of hematopoiesis during embryonic development, acquires additional various metabolic functions near birth. Although liver development has been characterized biologically as consisting of several distinct steps, the molecular events accompanying this process are just beginning to be characterized. In this study, we have established a novel culture system of fetal murine hepatocytes and investigated factors required for development of hepatocytes. We found that oncostatin M (OSM), an interleukin-6 family cytokine, in combination with glucocorticoid, induced maturation of hepatocytes as evidenced by morphological changes that closely resemble more differentiated hepatocytes, expression of hepatic differentiation markers and intracellular glycogen accumulation. Consistent with these in vitro observations, livers from mice deficient for gp130, an OSM receptor subunit, display defects in maturation of hepatocytes. Interestingly, OSM is expressed in CD45(+) hematopoietic cells in the developing liver, whereas the OSM receptor is expressed predominantly in hepatocytes. These results suggest a paracrine mechanism of hepatogenesis; blood cells, transiently expanding in the fetal liver, produce OSM to promote development of hepatocytes in vivo.  (+info)

(2/60) 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 alpha- and beta-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.  (+info)

(3/60) Different epitopes are required for gp130 activation by interleukin-6, oncostatin M and leukemia inhibitory factor.

Gp130 is the common signal transducing receptor subunit of interleukin (IL)-6, IL-11, leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor and cardiotrophin-1. IL-6 and IL-11 induce gp130 homodimerization whereas the others lead to the formation of heterodimers with LIFR or OSMR. Binding epitopes for IL-6 and IL-11 are located in the immunoglobulin-like domain and the cytokine binding module (CBM). Here we show that a gp130 mutant lacking domain 1, although unresponsive to IL-6 and IL-11, can still activate signal transducer and activator of transcription (STAT) transcription factors in response to LIF or OSM. Moreover, point mutations in the CBM of gp130 (F191E and V252D) that severely impair signal transduction in response to IL-6 and IL-11 differentially interfere with gp130 activation in response to LIF and OSM. Thus, epitopes involved in gp130 homodimerization are distinct from those leading to the formation of gp130/LIFR or gp130/OSMR heterodimers. These findings may serve as the base for rational design of gp130 antagonists that specifically interfere with bioactivity of distinct IL-6-type cytokines.  (+info)

(4/60) 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.  (+info)

(5/60) Differential inhibition of IL-6-type cytokine-induced STAT activation by PMA.

Prior activation of mitogen-activated protein kinases by phorbol 13-myristate 12-acetate (PMA) results in an inhibition of interleukin (IL)-6-induced activation of the Janus kinase/signal transducer and activator of transcription (STAT) signaling pathway which is most likely mediated by the induction of suppressor of cytokine signaling-3 and requires the specific SHP2 binding site Y759 of the IL-6 signal transducer gp130. In this study, we demonstrate that PMA inhibits STAT activation by IL-6 and the related cytokine leukemia inhibitory factor (LIF) but not by oncostatin M (OSM). Since the LIF receptor also contains an SHP2 recruitment site whereas the OSM receptor lacks such a module, we propose that two SHP2 binding modules within a homo- or heterodimeric receptor are necessary to mediate the PMA inhibitory effect.  (+info)

(6/60) Signal transduction of IL-6, leukemia-inhibitory factor, and oncostatin M: structural receptor requirements for signal attenuation.

Stimulation of the IL-6R complex leads to Src homology domain containing tyrosine phosphatase 2 (SHP2) recruitment to the receptor subunit gp130 and its subsequent tyrosine phosphorylation. SHP2 is a two-SH2 domain-containing protein tyrosine phosphatase that is activated by many cytokines and growth factors. SHP2 counteracts the activation of transcription factors of the STAT family and the induction of IL-6-responsive genes. Tyrosine 759 of gp130, the signal transducing subunit of the IL-6R complex, is essential for the phosphorylation of SHP2. Mutation of tyrosine 759 to phenylalanine leads to an enhanced inducibility of IL-6-dependent genes. Here we demonstrate that no further tyrosines in the cytoplasmic part of gp130 are required for the phosphorylation of SHP2. We also tested whether the tyrosine 759 motifs in both subunits of the gp130 dimer are required for SHP2 association and tyrosine phosphorylation. Interestingly, one SHP2-recruiting phosphotyrosine motif in a single chain of the gp130 dimer is sufficient to mediate SHP2 association to the gp130 receptor subunit and its tyrosine phosphorylation as well as to attenuate IL-6-dependent gene induction. Furthermore, we show that repression of gene induction via Y759 does not require the presence of the SHP2 and STAT recruitment sites within the same receptor subunit, but within the same receptor complex. The Y759 motif in gp130 also attenuates gene induction mediated by the oncostatin M and leukemia inhibitory factor receptor complexes, which both contain gp130 as the shared subunit.  (+info)

(7/60) Oncostatin M synergises with house dust mite proteases to induce the production of PGE(2) from cultured lung epithelial cells.

The release of PGE(2) and nitric oxide (NO) from the respiratory epithelium may act to dampen inflammation. In other tissues, oncostatin M (OSM), a potent inducer of epithelial antiproteases, has also been shown to interact with IL-1beta to stimulate PGE(2) release. However, whether OSM interacts with pro-inflammatory cytokines and proteases in the production of anti-inflammatory eicosanoids and NO from airway epithelium is unknown. The effect of OSM and the related cytokine leukaemia inhibitory factor (LIF) on PGE(2) and NO production by the respiratory epithelial cell line, A549 in response to pro-inflammatory cytokines as well as protease-rich house dust mite (HDM) fractions and a protease-deficient rye grass pollen extract was examined by immunohistochemistry, cell culture, ELISA and enzyme-immunoassay. Cells treated with a mixture of IL-1beta, IFNgamma and LPS for 48 h produced a 9 fold increase in PGE(2) and a 3 fold increase in NO levels (both P<0.05). Both OSM and LIF were without effect. However, OSM added together with the cytokine mixture synergistically enhanced PGE(2) production (22 fold, P<0.05). OSM also synergistically enhanced PGE(2) production in response to a cysteine protease-enriched, but not serine protease-enriched HDM fraction (P<0.05). Rye grass extract, neither alone nor in combination with OSM, induced PGE(2) or NO production, although it did induce the release of GM-CSF. These observations suggest that OSM is an important co-factor in the release of PGE(2) and NO from respiratory epithelial cells and may play a role in defense against exogenous proteases such as those derived from HDM.  (+info)

(8/60) 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.  (+info)