Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Interleukin-6 (IL6) exerts its action via a cell surface receptor composed of an 80 kDa IL6-binding protein (gp80) and a 130 kDa polypeptide involved in signal transduction (gp130). We studied the role of gp80 in binding, internalization and down-regulation of the hepatic IL6-receptor (IL6R) by its ligand in human hepatoma cells (HepG2). Comparison of transfected HepG2 cells overexpressing gp80 with parental cells indicate that gp80 is responsible for low affinity binding (Kd = 500 pM) of IL6. Furthermore, gp80 is rate-limiting in internalization and degradation of IL6. Internalization resulted in a rapid down-regulation (t1/2 approximately 15-30 min) of IL6-binding sites at the cell surface. More than 80% of the internalized [125I]rhIL6 was degraded. The reappearance of IL6-binding sites at the cell surface required greater than 8 h and was sensitive to cycloheximide, suggesting that gp80 is not recycled after internalization. The down-regulation of the hepatic IL6R by its ligand might play an important role as a protection against overstimulation.
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PMID:The hepatic interleukin-6 receptor. Down-regulation of the interleukin-6 binding subunit (gp80) by its ligand. 132 36

Interleukin-6 (IL-6) induces changes in gene expression and the N-glycosylation pattern of acute-phase proteins in hepatocytes. IL-6 exerts its action via a cell surface receptor complex consisting of an 80 kDa IL-6 binding protein (gp80) and a 130 kDa glycoprotein (gp130) involved in signal transduction. A genetically engineered gp80-derived soluble human IL-6-receptor (shIL-6-R) significantly enhanced the IL-6 effect on N-glycosylation changes (revealed by reactivity with the lectin-concanavalin A) of a1-protease inhibitor (PI) secreted by human hepatoma cells (HepG2). Stable transfection of IL-6-cDNA into HepG2 cells (HepG2-IL-6) resulting in constitutive secretion of 2 micrograms of IL-6 per 10(6) cells in 24 h led to a down-regulation of surface-bound gp80 and subsequent homologous desensitization of HepG2-IL-6 cells towards IL-6. Soluble human IL-6-R functionally substituted membrane-bound gp80 resulting in a reconstitution of responsiveness of HepG2-IL-6 cells.
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PMID:Soluble human interleukin-6-receptor modulates interleukin-6-dependent N-glycosylation of alpha 1-protease inhibitor secreted by HepG2 cells. 132 38

The receptor for granulocyte colony stimulating factor (G-CSFR) and chimeric receptors consisting of the extracellular domain of G-CSFR and the transmembrane and cytoplasmic domain of the leukemia inhibitory factor receptor, gp130, or c-mpl function as homodimeric complexes. These receptors mediate a similar stimulation of gene transcription via separate regulatory elements of acute phase plasma protein genes. To identify the receptor regions within the cytoplasmic domains necessary for transcriptional regulation, the receptors were transiently expressed in rat hepatoma cells. Each receptor form reconstituted G-CSF-induced expression of a chloramphenicol acetyltransferase gene construct containing the cytokine response element of the rat alpha 1-acid glycoprotein gene. This regulation required the presence of two conserved sequence motifs (referred to as box 1 and box 2) in the cytoplasmic domains of each receptor. With the exception of G-CSFR-MPL chimera, the receptors also mediated a similarly high stimulation via the IL-6 response element of the rat beta-fibrinogen and hemopexin genes. Regulation of the IL-6 response element required, however, in addition to boxes 1 and 2, a third sequence motif (box 3). This motif is absent in the cytoplasmic domain of c-mpl, possibly explaining its inability to activate the IL-6 response element. When cells which express receptor forms with prominent box 3 function were treated with suramin, a ligand-independent gene stimulation via the IL-6 response element was observed. The suramin effect probably involves a receptor dimerization mediated by the extracellular G-CSFR domain and by the intracellular regions that include box 3.
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PMID:Signaling by the cytoplasmic domain of hematopoietin receptors involves two distinguishable mechanisms in hepatic cells. 751 79

The synthesis of the human acute-phase alpha 1-acid glycoprotein (AGP) is primarily controlled by IL-6 and IL-1 in liver cells. In the present study, monoclonal antibodies against human gp80 interleukin-6 receptor (IL-6R) were utilized to study the role of the IL-6R in the control of the IL-6-induced AGP synthesis in the human hepatoma Hep3B cell line. Two of the 4 MAbs used in this study, M164 and M195, identified 2 different epitopes involved in IL-6 binding and two others, M91 and M182, recognized epitopes not involved in IL-6 binding. Dose-response experiments indicated that up to 55% of AGP synthesis was inhibited by 10(5) ng/ml of MAbs 164 or 195 when Hep3B cells were treated by IL-6 for 48h. Kinetics of the inhibition of AGP synthesis after addition of anti-IL-6R indicated that the decrease of the IL-6-induced AGP synthesis by Hep3B cells was obtained immediately after the addition of the anti-IL-6R MAbs. Of the two MAbs not involved in IL-6 binding, M91 was unable to interfere with the IL-6-induced AGP synthesis whereas, surprisingly, M182 decreased it by about 25%. Since M182 was also able to interfere with the proliferative response of an IL-6 dependent plasma cell line, our results suggested that M182 may be directed to a structure involved in the IL-6/IL-6R gp130 complex formation.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:IL-6-induced changes in synthesis of alpha 1-acid glycoprotein in human hepatoma Hep3B cells are distinctively regulated by monoclonal antibodies directed against different epitopes of IL-6 receptor (gp80). 753 7

Interleukin-6 (IL-6) interacts with a system of receptors, which include a 80-kDa IL-6-binding subunit (IL-6R) and a transducing element (gp130). The soluble form of IL-6R (sIL-6R) can bind its ligand and induce cellular responses by association with gp130, thus acting as an IL-6 agonist. We and others have previously shown that the responsiveness to IL-6 is different in hepatoma and human primary hepatocytes. We therefore compared the effects of sIL-6R on the two types of cells, and on the B9 hybridoma, another IL-6-sensitive cell line. Human primary hepatocytes, hepatoma cells PLC/PRF/5, and B9 cells were incubated with different concentrations of IL-6, sIL-6-R, or both. The hepatocyte culture supernatants were tested for their content of acute-phase proteins (APP). The proliferation of B9 cells was assessed by a colorimetric method. Results showed that sIL-6R alone markedly increased the production of APP by hepatoma cells in a dose-dependent manner, but affects only minimally primary hepatocytes and the proliferation of B9 cells. The combinations of IL-6R and its ligand enhanced the effects of Il-6 alone in both PLC/PRF/5 and B9 cells, but had no effect on primary hepatocytes. An immunohistochemical study indicated that the cell-surface expression of IL-6R was dramatically lower in hepatoma cells than in primary hepatocytes. In conclusion, our results show that the expression of IL-6R is low in the hepatoma cell PLC/PRF/5 when compared with primary hepatocytes and that this difference can, at least partly, explain their deficient responsiveness to IL-6. On the other hand, it appears that IL-6R expression by primary hepatocytes is sufficient and that circulating sIL-6R is unlikely to play a significant role in the modulation of IL6 effects.
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PMID:Soluble interleukin-6 receptor strongly increases the production of acute-phase protein by hepatoma cells but exerts minimal changes on human primary hepatocytes. 754 21

Mutagenesis of a region of human interleukin (IL)-6 which is important for triggering signal transduction via the IL-6 receptor beta-chain (gp130) has lead to the isolation of a variant of human IL-6 (IL-6.Q160E/T163P), which could antagonize the biological activity of wild type IL-6 on the human EBV transformed B cell line CESS and the human hepatoma cell line HepG2. Surprisingly this antagonistic IL-6 variant had an agonistic effect on the human myeloma cell line XG-1, albeit at a 1000-fold higher concentration than wild type IL-6. This residual activity of the mutant arose from triggering gp130, because it could be inhibited by a gp130 specific mAb. Extensive mutagenesis of residues between Q153 and H165 of human IL-6, a region which is partly homologous in cytokines which also signal via gp130 (oncostatin M, ciliary neurotrophic factor, leukaemia inhibitory factor, IL-11), did result in the isolation of a second antagonist for IL-6 activity on CESS and HepG2 cells. However on XG-1 cells this variant was active as well. These results suggest that (an) additional region(s) of the IL-6 molecule might be involved in gp130 triggering. Recently we indeed found that residues Lys42-Ala57 are also important for gp130 triggering. Inhibition experiments with neutralizing IL-6R alpha-chain specific mAb show that this region can be functionally separated from the Q153-H165 region. These findings have important implications for the development of receptor antagonists of IL-6 and IL-6 family members.
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PMID:Functional distinction of two regions of human interleukin 6 important for signal transduction via gp130. 757 77

Interleukin-6 (IL-6) triggers the formation of a high affinity receptor complex constituted by the ligand-binding subunit IL-6 receptor alpha (IL-6R alpha) and the signal-transducing beta chain gp130. Since the cytoplasmic region of IL-6R alpha is not required for signal transduction, soluble forms of IL-6R alpha (sIL-6R alpha) show agonistic properties because they are still able to originate IL-6.sIL-6R alpha complexes, which in turn associate with gp130. A three-dimensional model of the human IL-6.IL-6R alpha.gp130 complex has been constructed and verified by site-directed mutagenesis of regions in shIL-6R alpha (where "h" is human) anticipated to contact hgp130, with the final goal of generating receptor variants with antagonistic properties. In good agreement with our structural model, substitutions at Asn-230, His-280, and Asp-281 selectively impaired the capability of shIL-6R alpha to associate with hgp130 both in vitro and on the cell surface, without affecting its affinity for hIL-6. Moreover, the multiple substitution mutant A228D/N230D/H280S/D281V expressed as a soluble protein partially antagonized hIL-6 bioactivity on hepatoma cells.
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PMID:Interleukin-6 (IL-6) antagonism by soluble IL-6 receptor alpha mutated in the predicted gp130-binding interface. 774 75

The cytoplasmic receptor sequences required for the transcriptional control via the IL-6 response element (IL-6RE) and the hematopoietin receptor response element (HRRE) in hepatoma cells were defined by transient expression of wild-type and mutant granulocyte-colony stimulating factor receptor-gp130 chimeric receptors. gp130 generated two separate transcriptional signals, one of which was directed to IL-6RE and required an intact box 3 motif, and another, which was directed to HRRE and was box 3-independent. The activation of DNA-binding of STAT3 required the same gp130 domains as the IL-6RE response. A box 3-independent activation of STAT proteins was achieved by overexpression of the kinases JAK2 or TYK2. The increase in the DNA-binding activity of STAT proteins, however, did not result in a corresponding increase in transcription via either IL-6RE or HRRE. The data indicate that activation of the DNA-binding potential of STAT proteins via gp130 is not sufficient to achieve transcriptional up-regulation of specific target genes.
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PMID:Separate signaling mechanisms are involved in the control of STAT protein activation and gene regulation via the interleukin 6 response element by the box 3 motif of gp130. 779 60

The pleiotropic cytokine interleukin 6 (IL-6) plays a role in the pathogenesis of various diseases, such as multiple myeloma, autoimmune and inflammatory diseases and osteoporosis. Therefore, specific inhibitors of IL-6 may have clinical applications. We previously succeeded in developing receptor antagonists of IL-6 that antagonized wild-type IL-6 activity on the human Epstein-Barr virus (EBV)-transformed B cell line CESS and the human hepatoma cell line HepG2. However, these proteins still had agonistic activity on the human myeloma cell line XG-1. We here report the construction of a novel mutant protein of IL-6 in which two different mutations are combined that individually disrupt the association of the IL-6/IL-6 receptor (R) alpha complex with the signaltransducing "beta" chain, gp130, but leave the binding of IL-6 to IL-6R alpha intact. The resulting mutant protein (with substitutions of residues Gln160 to Glu, Thr163 to Pro, and replacement of human residues Lys42-Ala57 with the corresponding residues of mouse IL-6) was inactive on XG-1 cells and weakly antagonized wild-type IL-6 activity on these cells. By introducing two additional substitutions (Phe171Leu, Ser177Arg), the affinity of the mutant protein for IL-6R alpha was increased fivefold, rendering it capable of completely inhibiting wild-type IL-6 activity on XG-1 cells. Moreover, this mutant also antagonized the activity of IL-6, but not that of leukemia inhibitory factor, oncostatin M, or GM-CSF on the human erythroleukemia cell line TF-1, demonstrating its specificity for IL-6. These data demonstrate the feasibility of developing specific IL-6R antagonists. The availability of such antagonists may offer an approach to specifically inhibit IL-6 activity in vivo.
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PMID:Development of an interleukin (IL) 6 receptor antagonist that inhibits IL-6-dependent growth of human myeloma cells. 796 14

Interleukin-6 (IL-6) exerts its action via a receptor complex composed of a ligand-binding subunit (gp80) and a signal transducer (gp130) which both belong to the hematopoietic receptor super-family. Very little is known about the biosynthesis and the biological half-lives of proteins of this superfamily. Therefore, we studied the biosynthesis and maturation of the interleukin-6 receptor and its signaling subunit gp130 by pulse chase experiments in stably transfected Madin-Darby canine kidney cells. We found that both proteins are synthesized as precursors with apparent molecular masses of 67 kDa and 130 kDa, respectively. These receptor forms are processed within 45-60 min into mature proteins of 82 kDa and 150 kDa containing complex-type oligosaccharides. The signal transducer gp130 shows a similar maturation in human hepatoma cells HepG2. The IL-6 receptor appears at the cell surface 45 min after completion of its synthesis in the endoplasmic reticulum. In both cell types studied, gp80 and gp130 are rapidly turned over with half-lives of 2-3 h. These half-lives were unaffected by the presence of the ligand IL-6.
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PMID:Biosynthesis and half-life of the interleukin-6 receptor and its signal transducer gp130. 803 1


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