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)

Activation of the tyrosine kinase activity of the insulin receptor by autophosphorylation leads to phosphorylation of cellular substrates on tyrosine. Thus far, the best characterized is the insulin receptor substrate (IRS) 1, which has been proposed to serve as a docking protein for other molecules involved in signal transduction. A number of other proteins that become phosphorylated in response to insulin have been identified, some of which are reported to be tissue-specific. A 60 kDa phosphoprotein has been detected in adipocytes after insulin stimulation [Lavan and Lienhard (1993) J. Biol. Chem. 268, 5921-5928]. We have identified a protein of similar molecular mass in rat hepatoma cells transfected with the human insulin receptor. The 60 kDa protein in hepatoma cells is tyrosine-phosphorylated in response to insulin in a dose-dependent manner, with maximal phosphorylation occurring at 50 nM insulin. Although the dose-response of p60 phosphorylation mirrors that of IRS-1, the time course is slightly slower, with maximal phosphorylation observed 5 min after addition of insulin. Like the adipocyte protein, the 60 kDa protein detected in liver cells binds to the SH2 domain of the p85 regulatory subunit of phosphatidylinositol 3-kinase, but not to other SH2 domains. Binding of p60 to p85 is similar to the interaction between p85 and IRS-1 in that a tyrosine-phosphorylated peptide containing the YVXM motif can inhibit the association. The presence of this 60 kDa tyrosine-phosphorylated protein in adipocytes and hepatoma cells suggests that it represents another important intermediate in the insulin-receptor signal-transduction pathway.
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PMID:Detection of a 60 kDa tyrosine-phosphorylated protein in insulin-stimulated hepatoma cells that associates with the SH2 domain of phosphatidylinositol 3-kinase. 753 11

Tumor necrosis factor-alpha (TNF) has been suggested to be the mediator of insulin resistance in infection, tumor cachexia, and obesity. We have previously shown that TNF diminishes insulin-induced tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1). The current work examines potential mechanisms that mediate this event. TNF effect on IRS-1 in Fao hepatoma cells was not associated with a significant reduction in insulin receptor tyrosine kinase activity as measured in vitro but impaired the association of IRS-1 with phosphatidylinositol 3-kinase, localizing TNF impact to IRS-1. TNF did not increase protein-tyrosine phosphatase activity and protein-tyrosine phosphatase inhibition by vanadate did not change TNF effect on IRS-1 tyrosine phosphorylation, suggesting that protein-tyrosine phosphatases are not involved in this TNF effect. In contrast, TNF increased IRS-1 phosphorylation on serine residues, leading to a decrease in its electrophoretic mobility. TNF effect on IRS-1 tyrosine phosphorylation was not abolished by inhibiting protein kinase C using staurosporine, while inactivation of Ser/Thr phosphatases by calyculin A and okadaic acid mimicked it. Our data suggest that TNF induces serine phosphorylation of IRS-1 through inhibition of serine phosphatases or activation of serine kinases other than protein kinase C. This increased serine phosphorylation interferes with insulin-induced tyrosine phosphorylation of IRS-1 and impairs insulin action.
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PMID:Tumor necrosis factor alpha-induced phosphorylation of insulin receptor substrate-1 (IRS-1). Possible mechanism for suppression of insulin-stimulated tyrosine phosphorylation of IRS-1. 755 52

Considerable evidence has shown that most physiologic responses to insulin require activation of the intrinsic tyrosine kinase of the insulin receptor. Biochemical studies have also supported the hypothesis that receptor kinase activity can be modulated by cellular protein tyrosine phosphatases (PTPases), which have not yet been identified. To test the hypothesis that the transmembrane PTPase LAR can modulate insulin receptor signaling in vivo, antisense RNA expression was used to specifically suppress LAR protein levels by 63% in the rat hepatoma cell line, McA-RH7777. Hormone-dependent autophosphorylation of the insulin receptor was increased by approximately 150% in the antisense-expressing cells at all insulin concentrations tested. This increase in autophosphorylation was paralleled by a 35% increase in insulin receptor tyrosine kinase activity. Reduced LAR levels did not alter non-hormone-dependent tyrosine phosphorylation nor basal insulin receptor tyrosine phosphorylation and kinase activity. Most significantly, reduced LAR levels resulted in a 350% increase in insulin-dependent phosphatidylinositol 3-kinase activity. These studies provide unique in vivo evidence that LAR is involved in the modulation of insulin receptor signaling in intact cells.
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PMID:Insulin receptor signaling is augmented by antisense inhibition of the protein tyrosine phosphatase LAR. 785 2

Insulin rapidly stimulates tyrosine kinase activity of its receptor, resulting in phosphorylation of the cytosolic substrate, insulin receptor substrate-1 (IRS-1), which, in turn, associates with phosphatidylinositol 3-kinase (PI 3-kinase), thus activating the enzyme. In the present study we have examined these three early postreceptor components of the insulin action pathway in rat hepatoma (Fao) cells and have determined the effects of two hormones that can induce insulin resistance, dexamethasone and insulin. Dexamethasone (1 microM) induced a time- and dose-dependent increase in insulin receptor levels in Fao cells, reaching 135 +/- 3% of basal levels after 24 h (P < 0.05). There was a simultaneous increase in IRS-1 protein to 255 +/- 66% of the control value (P < 0.05) and a parallel increase in IRS-1 phosphorylation. Insulin stimulation of IRS-1-associated PI 3-kinase was also increased by 70% in cells treated with dexamethasone despite only a minimal increase in PI 3-kinase protein, as determined by immunoblotting. Prolonged insulin treatment induced a time- and dose-dependent decrease in insulin receptor and IRS-1 protein levels, reaching nadirs of 40 +/- 4% (P < 0.01) and 15 +/- 6% (P < 0.005) of control levels, respectively, after 24 h with 100 nM insulin. There was also a decrease in the phosphorylation of insulin receptors and IRS-1, a marked decrease in the association between IRS-1 and PI 3-kinase, and an 82% decrease in insulin-stimulated PI 3-kinase activity without a significant change in PI 3-kinase protein levels. When cells were exposed to both insulin and dexamethasone, the effect of insulin to reduce insulin receptor and IRS-1 levels and insulin-stimulated IRS-1 phosphorylation dominated. These data suggest that regulation of the insulin receptor, IRS-1, and PI 3-kinase contributes significantly to the insulin resistance induced by chronic hyperinsulinemia, but that glucocorticoid-induced insulin resistance is located beyond these early steps in insulin action.
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PMID:Insulin and dexamethasone regulate insulin receptors, insulin receptor substrate-1, and phosphatidylinositol 3-kinase in Fao hepatoma cells. 789 67

Antisense-mediated suppression of the transmembrane protein-tyrosine phosphatase (PTPase) LAR has been shown previously to increase insulin-dependent phosphatidylinositol 3-kinase (PI 3-kinase) activation by greater than 300% in the rat hepatoma cell line McA-RH7777. Here, insulin-dependent insulin receptor tyrosine kinase activation was examined with recombinant insulin receptor substrate 1 (IRS-1) as the substrate and shown to be 3-fold greater in cells with suppressed LAR levels. Consistent with a receptor level effect, in vivo insulin-dependent tyrosine phosphorylation of both IRS-1 and Shc was increased by a similar 3-fold with LAR suppression. These increases in IRS-1 and Shc phosphorylation were paralleled by increases in insulin-dependent PI 3-kinase association with IRS-1 and activation of the MAP kinase pathway. Reduced LAR levels also resulted in increases of over 300% and 250% in epidermal growth factor (EGF)- and hepatocyte growth factor (HGF)-dependent receptor autophosphorylation, respectively, as well as a severalfold increase in substrate tyrosine phosphorylation. In a post-receptor response, EGF- and HGF-dependent MAP kinase activation was increased by 300% and 350%, respectively, with LAR suppression. Similarly, growth factor-dependent PI 3-kinase activation was increased in LAR antisense expressing cells when compared to null vector expressing cells. These results demonstrate that the transmembrane PTPase LAR modulates ligand-dependent activation of at least three receptor tyrosine kinases.
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PMID:The transmembrane protein-tyrosine phosphatase LAR modulates signaling by multiple receptor tyrosine kinases. 855 82

Overexpression of the transmembrane protein-tyrosine phosphatase (PTPase) CD45 in nonhematopoietic cells results in decreased signaling through growth factor receptor tyrosine kinases. Consistent with these data, insulin receptor signaling is increased when the CD45-related PTPase LAR is reduced by antisense suppression in a rat hepatoma cell line. To test whether the hematopoietic cell-specific PTPase CD45 functions in a manner similar to LAR by negatively modulating insulin receptor signaling in hematopoietic cells, the insulin-responsive human multiple myeloma cell line U266 was isolated into two subpopulations that differed in CD45 expression. In CD45 nonexpressing (CD45-) cells, insulin receptor autophosphorylation was increased by 3-fold after insulin treatment when compared to CD45 expressing (CD45+) cells. This increase in receptor autophosphorylation was associated with similar increases in insulin-dependent tyrosine kinase activation. These receptor level effects were paralleled by postreceptor responses. Insulin-dependent tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1) and Shc was 3-fold greater in CD45- cells. In addition, insulin-dependent IRS-1/phosphatidylinositol 3-kinase association and MAP kinase activation in CD45- cells were also 3-fold larger. While expression of CD45 was associated with a decrease in the responsiveness of early insulin receptor signaling, interleukin 6-dependent activation of mitogen-activated protein kinase kinase and mitogen-activated protein kinase was equivalent between CD45- and CD45+ cells. These observations indicate that CD45 can function as a negative modulator of growth factor receptor tyrosine kinases in addition to its well-established role as an activator of src family tyrosine kinases.
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PMID:The transmembrane protein-tyrosine phosphatase CD45 is associated with decreased insulin receptor signaling. 855 83

The sphingomyelin pathway is a newly described signal transduction pathway mediating the action of several cytokines including tumor necrosis factor-alpha (TNF). TNF was recently shown to interfere with insulin-induced tyrosine phosphorylation of the insulin receptor substrate-1 (IRS-1). In this work we examined the possible effect of direct activation of the sphingomyelin pathway on insulin-induced tyrosine phosphorylation of IRS-1. Incubation of the insulin-sensitive rat hepatoma Fao cells with bacterial sphingomyelinase (SMase) that causes membrane hydrolysis of sphingomyelin led to a time- and dose-dependent decrease in insulin-induced tyrosine phosphorylation of IRS-1. The effect was apparent after 10 min of incubation and with a dose of 10 milliunits/ml SMase. It was not associated with a decrease in insulin receptor autophosphorylation. In addition, SMase treatment interrupted the association of the 85-kDa catalytic subunit of phosphatidylinositol 3-kinase with IRS-1. A similar impact on IRS-1 tyrosine phosphorylation was observed after addition of cell-permeable ceramide analogs (C2 and C6). Comparable changes in IRS-1 tyrosine phosphorylation and electrophoretic mobility were found after exposure of cells to either TNF, SMase, or ceramide. Our findings suggest that TNF may utilize the sphingomyelin pathway in its effect on the insulin-stimulated tyrosine phosphorylation of IRS-1.
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PMID:Sphingomyelinase and ceramide suppress insulin-induced tyrosine phosphorylation of the insulin receptor substrate-1. 862 23

Tyrosine phosphorylation of cellular proteins is an early and key step after activation of the insulin receptor kinase (IRK). The study of the properties of these proteins should contribute to our understanding of insulin action. In rat hepatoma cells overexpressing human insulin receptors (HTC-IR), insulin treatment resulted in rapid tyrosine phosphorylation of proteins of 180, 94, 68, and 60 kDa. When lysates from insulin-treated cells were immunoprecipitated with anti-Syp antibody, subsequent immunoblotting identified p65 and p68, which reacted with anti-Syp, and p6O and p68, which reacted with antiphosphotyrosine antibody. Thus, insulin treatment yielded tyrosine phosphorylation of both Syp and a Syp-associated p6O molecule. When lysates from insulin-treated cells were adsorbed with a glutathione S-transferase (GST)-Syp-Src homology-2 (SH2) fusion protein, tyrosine- phosphorylated p6O was sequestered. After subjecting lysates to SDS-PAGE, the GST-SypSH2 fusion protein was found to bind to p18O, p94, and p6O. Thus, Syp associates directly with a 60-kDa IRK substrate via its SH2 domains. Syp-associated p6O differed from the 60- to 62-kDa proteins, associating with ras guanosine triphosphatase-activating protein, which also underwent modest tyrosine phosphorylation in response to insulin. Preadsorption of cell lystates with antibody against the 85-kDa subunit (p85) of phosphatidylinositol 3-kinase substantially reduced the amount of p60 subsequently immunoprecipitated by anti-Syp. Thus, p60 associates with both Syp and p85. The amount of tyrosine-phosphorylated p60 exceeded that of p180 in anti-Syp immunoprecipitates, whereas their proportion was comparable in anti-p85 immunoprecipitates. Grb2 was also observed in the anti-Syp immunoprecipitates. When lysates from insulin-treated cells were adsorbed with GST-p85SH2 domains or GST-Grb2, the subsequent eluates contained tyrosine-phosphorylated p60, as determined by immunoblotting with antiphosphotyrosine. Membrane binding assays using GST fusion proteins showed that these associations were direct. Studies in rat liver, muscle, and adipose tissue identified insulin-dependent association of Syp, Grb2, and p85 with tyrosine-phosphorylated p60 in adipose tissue only. We conclude that insulin treatment of HTC-IR cells and rat adipose tissue results in the tyrosine phosphorylation of p60, which might participate in the recruitment of downstream effectors involved in insulin signal transduction.
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PMID:A 60-kilodalton protein in rat hepatoma cells overexpressing insulin receptor was tyrosine phosphorylated and associated with Syp, phophatidylinositol 3-kinase, and Grb2 in an insulin-dependent manner. 877 Aug 81

A 60-kDa protein that undergoes rapid tyrosine phosphorylation in response to insulin and then binds phosphatidylinositol 3-kinase has been previously described in adipocytes and hepatoma cells. We have isolated this protein, referred to as pp60, from rat adipocytes, obtained the sequences of tryptic peptides, and cloned its cDNA. The predicted amino acid sequence of pp60 reveals that it contains an N-terminal pleckstrin homology domain, followed by a phosphotyrosine binding domain, followed by a group of likely tyrosine phosphorylation sites, four of which are in the YXXM motif that binds to the SH2 domains of phosphatidylinositol 3-kinase. The overall architecture of pp60 is thus the same as that of insulin receptor substrates 1 and 2 (IRS-1 and IRS-2), and furthermore both the pleckstrin homology and phosphotyrosine binding domains are highly homologous (about 50% identical amino acids) to these domains in both IRS-1 and IRS-2. Thus, pp60 is a new member of the IRS family, which we have designated IRS-3.
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PMID:The 60-kDa phosphotyrosine protein in insulin-treated adipocytes is a new member of the insulin receptor substrate family. 911 Oct 55

Leptin, an adipocyte-secreted hormone, is one of the central regulators of body weight homeostasis. In humans and rodents, two major forms of leptin receptors (OB-R) are expressed. The short form (OB-RS), considered to lack signaling capability, is detected in many organs. In contrast, OB-R long form (OB-RL) predominates in the hypothalamus, but is also present at low levels in peripheral tissues. Transient transfection experiments have demonstrated that OB-RL transduces an intracellular signaling similar to interleukin (IL)-6 type-cytokine receptors. To define the specificity by which OB-R induces genes and cooperates with signal transduction pathways utilized by other hormones and cytokines, rat and human hepatoma cell lines were generated which stably express human OB-RL. Hepatoma cell lines selected for appreciable levels of OB-RL mRNA display enhanced leptin binding and responded to leptin with an IL-6 receptor-like signaling that includes the activation of STAT proteins, induction of acute-phase plasma proteins, and synergism with IL-1 and tumor necrosis factor-alpha. A leptin-mediated recruitment of phosphatidylinositol 3-kinase to insulin receptor substrate-2 was also detected. However, no significant tyrosine phosphorylation of insulin receptor substrate-2 and modulation of the immediate cell response to insulin were observed. The data suggest that OB-RL action in hepatic cells is equivalent to that of IL-6 receptor. However, leptin does not play a specific role in muting insulin action on hepatoma cells and therefore may not contribute to the diabetic symptoms associated with obesity.
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PMID:Leptin receptor action in hepatic cells. 919 22


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