Leukemia inhibitory factor and ciliary neurotrophic factor cause dendritic retraction in cultured rat sympathetic neurons.
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Dendritic retraction occurs in many regions of the developing brain and also after neural injury. However, the molecules that regulate this important regressive process remain largely unknown. Our data indicate that leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) cause sympathetic neurons to retract their dendrites in vitro, ultimately leading to an approximately 80% reduction in the size of the arbor. The dendritic retraction induced by LIF exhibited substantial specificity because it was not accompanied by changes in cell number, in the rate of axonal growth, or in the expression of axonal cytoskeletal elements. An antibody to gp130 blocked the effects of LIF and CNTF, and both cytokines induced phosphorylation and nuclear translocation of stat3. Moreover, addition of soluble interleukin-6 (IL-6) receptor to the medium endowed IL-6 with the ability to cause dendritic regression. These data indicate that ligands activating the gp130 pathway have the ability to profoundly alter neuronal cell shape and polarity by selectively causing the retraction of dendrites. (+info)
Disulfide bond structure and N-glycosylation sites of the extracellular domain of the human interleukin-6 receptor.
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The high affinity interleukin-6 (IL-6) receptor is a hexameric complex consisting of two molecules each of IL-6, IL-6 receptor (IL-6R), and the high affinity converter and signaling molecule, gp130. The extracellular "soluble" part of the IL-6R (sIL-6R) consists of three domains: an amino-terminal Ig-like domain and two fibronectin-type III (FN III) domains. The two FN III domains comprise the cytokine-binding domain defined by a set of 4 conserved cysteine residues and a WSXWS sequence motif. Here, we have determined the disulfide structure of the human sIL-6R by peptide mapping in the absence and presence of reducing agent. Mass spectrometric analysis of these peptides revealed four disulfide bonds and two free cysteines. The disulfides Cys102-Cys113 and Cys146-Cys157 are consistent with known cytokine-binding domain motifs, and Cys28-Cys77 with known Ig superfamily domains. An unusual cysteine connectivity between Cys6-Cys174, which links the Ig-like and NH2-terminal FN III domains causing them to fold back onto each other, has not previously been observed among cytokine receptors. The two free cysteines (Cys192 and Cys258) were detected as cysteinyl-cysteines, although a small proportion of Cys258 was reactive with the alkylating agent 4-vinylpyridine. Of the four potential N-glycosylation sites, carbohydrate moieties were identified on Asn36, Asn74, and Asn202, but not on Asn226. (+info)
Gab-family adapter proteins act downstream of cytokine and growth factor receptors and T- and B-cell antigen receptors.
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We previously found that the adapter protein Gab1 (110 kD) is tyrosine-phosphorylated and forms a complex with SHP-2 and PI-3 kinase upon stimulation through either the interleukin-3 receptor (IL-3R) or gp130, the common receptor subunit of IL-6-family cytokines. In this report, we identified another adapter molecule (100 kD) interacting with SHP-2 and PI-3 kinase in response to various stimuli. The molecule displays striking homology to Gab1 at the amino acid level; thus, we named it Gab2. It contains a PH domain, proline-rich sequences, and tyrosine residues that bind to SH2 domains when they are phosphorylated. Gab1 is phosphorylated on tyrosine upon stimulation through the thrombopoietin receptor (TPOR), stem cell factor receptor (SCFR), and T-cell and B-cell antigen receptors (TCR and BCR, respectively), in addition to IL-3R and gp130. Tyrosine phosphorylation of Gab2 was induced by stimulation through gp130, IL-2R, IL-3R, TPOR, SCFR, and TCR. Gab1 and Gab2 were shown to be substrates for SHP-2 in vitro. Overexpression of Gab2 enhanced the gp130 or Src-related kinases-mediated ERK2 activation as that of Gab1 did. These data indicate that Gab-family molecules act as adapters for transmitting various signals. (+info)
The STAT3-independent signaling pathway by glycoprotein 130 in hepatic cells.
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Interleukin (IL)-6 is a major regulator of hepatic acute-phase plasma protein (APP) genes. The membrane-proximal 133-amino acid cytoplasmic domain of glycoprotein (gp) 130, containing one copy of the Box3 motif, is sufficient to transmit a productive signal to endogenous APP genes in rat hepatoma H-35 cells. In contrast, a mutant gp130 domain lacking the Box3 motif activates Janus kinases to a normal level but fails to activate signal transducer and activator of transcription 3 and to up-regulate a number of APP genes, including thiostatin, fibrinogen, hemopexin, and haptoglobin. However, in the absence of Box3, gp130 still stimulates the expression of alpha2-macroglobulin and synergizes with IL-1 to up-regulate alpha1-acid glycoprotein. The Box3 motif is not required for activation of the SH2-containing protein tyrosine phosphatase 2 or the mitogen-activated protein kinase (MAPK), nor is the immediate induction of egr-1 and junB significantly altered. Surprisingly, gp130 without any functional Box3 stimulates prolonged activation of MAPK, leading to an extended period of up-regulation of egr-1 and to an extracellularly regulated kinase-mediated reduction in the IL-6-stimulated production of thiostatin. IL-6 reduces proliferation of H-35 cells through signaling by the Box3. In addition, cells expressing Box3-deficient gp130 showed distinct morphologic changes upon receptor activation. Taken together, these results indicate that Box3-derived and Box3-independent signals cooperate in the control of hepatic APP genes and that Box3 may be involved in the modulation of MAPK activity in gp130 signaling. (+info)
Identification of a Leu-lle internalization motif within the cytoplasmic domain of the leukaemia inhibitory factor receptor.
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Leukaemia inhibitory factor (LIF) signals via a heterodimeric receptor complex comprised of the LIF receptor (LIFR) and the interleukin (IL)-6 signal transducer gp130. Upon binding to its cognate receptor LIF is internalized. In this study, we show that the LIFR is endocytosed independently of gp130. By using a heterochimaeric receptor system we identified a dileucine-based internalization motif within the cytoplasmic domain of the LIFR. Our findings suggest that a heterodimeric LIFR/gp130 complex and homodimeric gp130/gp130 complex are endocytosed via distinct internalization signals. (+info)
The carboxyl-terminal domains of gp130-related cytokine receptors are necessary for suppressing embryonic stem cell differentiation. Involvement of STAT3.
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Cell type-specific responses to the leukemia inhibitory factor (LIF)/interleukin 6 cytokine family are mediated by dimerization of the LIF receptor alpha-chain (LIFRalpha) with the signal transducer gp130 or of two gp130 molecules followed by activation of the JAK/STAT and Ras/mitogen-activated protein kinase cascades. In order to dissect the contribution of gp130 and LIFRalpha individually, chimeric molecules consisting of the extracellular domain of the granulocyte colony stimulating factor receptor (GCSF-R) and various mutant forms of the cytoplasmic domains of gp130 or LIFRalpha were expressed in embryonic stem (ES) cells to test for suppression of differentiation, or in a factor-dependent plasma cytoma cell line to assess for induction of proliferation. Carboxyl-terminal domains downstream of the phosphatase (SHP2)-binding sites were dispensable for mitogen-activated protein kinase activation and the transduction of proliferative signals. Moreover, carboxyl-terminal truncation mutants which lacked intact Box 3 homology domains showed decreased STAT3 activation, failed to induce Hck kinase activity and suppress ES cell differentiation. Moreover, STAT3 antisense oligonucleotides impaired LIF-dependent inhibition of differentiation. Substitution of the tyrosine residue within the Box 3 region of the GSCF-R abolished receptor-mediated suppression of differentiation without affecting the transduction of proliferative signals. Thus, distinct cytoplasmic domains within the LIFRalpha, gp130, and GCSF-R transduce proliferative and differentiation suppressing signals. (+info)
Fetal liver development requires a paracrine action of oncostatin M through the gp130 signal transducer.
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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)
The signal transducer gp130: solution structure of the carboxy-terminal domain of the cytokine receptor homology region.
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The transmembrane glycoprotein gp130 is the common signal transducing receptor subunit of the interleukin-6-type cytokines. It is a member of the cytokine-receptor superfamily predicted to consist of six domains in its extracellular part. The second and third domain constitute the cytokine-binding module defined by a set of four conserved cysteines and a WSXWS motif, respectively. The three-dimensional structure of the carboxy-terminal domain of this region was determined by multidimensional NMR. The domain consists of seven beta-strands constituting a fibronectin type III-like topology. The structure reveals that the WSDWS motif of gp130 is part of an extended tryptophan/arginine zipper which modulates the conformation of the CD loop. (+info)