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)

Two subtypes of IGF receptors have been identified. Type I IGF receptors have a Mr greater than 300,000 and are composed of disulfide-linked 130,000-dalton (alpha) and approximately 90,000-dalton (beta) subunits. The alpha subunit binds hormone; the beta subunit appears to have intrinsic tyrosine kinase activity and to be autophosphorylated. Type I receptors preferentially bind IGF-I but also bind IGF-II and, more weakly, insulin. Type II IGF receptors consist of a 250,000-dalton protein that contains internal disulfide bonds but is not linked to other membrane components. Type II receptors bind IGF-II with higher affinity than IGF-I. They do not interact with even very high concentrations of insulin. Type I IGF receptors and insulin receptors are homologous structures. They have similar subunit structure. Both receptors bind IGFs and insulin. They have similar (but not identical) antigenic determinants. Both receptors are downregulated by IGFs and insulin. Both receptors are affected in certain patients with genetically determined insulin resistance. Type II IGF receptors do not appear to be homologous to type I receptors. They differ in structure, peptide binding specificity, and antigenic determinants. Type II receptors do not appear to be downregulated. Although type II receptors appear to be phosphorylated in intact cells, they do not possess intrinsic tyrosine protein-kinase activity. Insulin acutely upregulates type II IGF receptors in intact rat adipose cells by effecting a redistribution of receptors cycling between a large intracellular pool and the plasma membrane. Insulin and the IGFs elicit the same biological responses, either by cross-reacting with one of the receptors for the heterologous ligand or by concurrent activation of convergent effector pathways by binding to the homologous receptor. Which mechanism is utilized appears to depend more on the tissue than on the biological response. Insulin desensitizes rat hepatoma cells to the actions of insulin and IGFs, mediated by both insulin and IGF receptors, by mechanisms distal to hormone binding and possibly common to IGF and insulin effector pathways.
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PMID:The nature and regulation of the receptors for insulin-like growth factors. 298 37

The role of the insulin receptor tyrosine kinase (protein-tyrosine kinase, EC 2.7.1.112) in various rapid insulin effects was studied by injecting four different cell types (by osmotic lysis of pinocytotic vesicles) with a monoclonal antibody that specifically inhibits the kinase activity of the insulin receptor and the closely related receptor for insulin-like growth factor (IGF)-I. Injection of this inhibitory antibody resulted in a decreased ability of insulin to stimulate the uptake of 2-deoxyglucose in Chinese hamster ovary cells and freshly isolated rat adipocytes, ribosomal protein S6 phosphorylation in CHO cells, and glycogen synthesis in the human hepatoma cell line HepG2. The ability of insulin, IGF-I, and IGF-II to stimulate glucose uptake in TA1 mouse adipocytes was also inhibited. Studies with CHO cells demonstrated that these effects of the inhibitory antibody were specific, since there was no change in phorbol ester-stimulated glucose uptake and injection of a noninhibiting antibody to the kinase had no effect on insulin action. These studies indicate that the tyrosine kinase activity of the insulin receptor is important in mediating several rapid insulin effects in a variety of different cell types.
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PMID:Acute insulin action requires insulin receptor kinase activity: introduction of an inhibitory monoclonal antibody into mammalian cells blocks the rapid effects of insulin. 354 Sep 58

The insulin-like growth factors (IGF) play an important role in fetal and postnatal development. Recently, the nucleotide sequences of the cDNAs encoding IGF-I and IGF-II and part of the human IGF genes were reported. In this communication we describe two distinct IGF-II cDNAs isolated from a human adult liver and a human hepatoma cDNA library, respectively. Using these two cDNAs, we have established that the human IGF-II gene contains at least 7 exons. Two different IGF-II promoters have been identified, 19 kilobases (kb) apart, which are active in a development-specific manner. The promoter, active in the adult stage, is located only 1.4 kb downstream from the insulin gene.
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PMID:The human insulin-like growth factor II gene contains two development-specific promoters. 356 24

Insulin and the insulinlike growth factors (IGF-I and IGF-II) are members of a family of hormones that regulate the metabolism and growth of many tissues. Cultured HEP-G2 cells (a minimal deviation human hepatoma) have insulin receptors and respond to insulin by increasing their glycogen metabolism. In the present study with HEP-G2 cells, we used 125I-labeled insulin, IGF-I, and IGF-II to identify distinct receptors for each hormone by competition-inhibition studies. Unlabeled insulin was able to inhibit 125I-IGF-I binding but not 125I-IGF-II binding. A mouse monoclonal antibody to the human insulin receptor that inhibits insulin binding and blocks insulin action inhibited 75% of 125I-insulin binding, but inhibited neither 125I-IGF-I nor 125I-IGF-II binding. When glycogen metabolism was studied, insulin stimulated [3H]glucose incorporation into glycogen in a biphasic manner; one phase that was 20-30% of the maximal response occurred over 1-100 pM, and the other phase occurred over 100 pM-100 nM. The anti-receptor monoclonal antibody inhibited the first phase of insulin stimulation but not the second. Both IGF-I and IGF-II stimulated [3H]glucose incorporation over the range of 10 pM-10 nM; IGF-I was three to fivefold more potent. The monoclonal antibody, however, was without effect on IGF regulation of glycogen metabolism. Therefore, these studies indicate that insulin as well as the IGFs at physiological concentrations regulate glycogen metabolism in HEP-G2 cells. Moreover, this regulation of glycogen metabolism is mediated by both the insulin receptor and the IGF receptors.
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PMID:Dual regulation of glycogen metabolism by insulin and insulin-like growth factors in human hepatoma cells (HEP-G2). Analysis with an anti-receptor monoclonal antibody. 609 May 2

We have reported previously that insulin causes a complete but reversible desensitization to insulin action in rat hepatoma HTC cells in tissue culture, and that this insulin resistance is mediated by postbinding mechanisms rather than receptor down-regulation (Heaton, J. H., and Gelehrter, T. D. (1981) J. Biol. Chem. 256, 12257-12262). We report here that insulin causes a similar desensitization to the induction of tyrosine aminotransferase by the insulin-like growth factors IGF-I and IGF-II isolated from human plasma, and by multiplication-stimulating activity, the rat homologue of IGF-II. The results of both competition-binding studies and affinity cross-linking experiments indicate that insulin-like growth factors (IGFs) bind primarily to IGF receptors rather than to insulin receptors. The low concentrations at which these factors induce transaminase is consistent with their acting primarily via IGF receptors. This is confirmed by experiments utilizing anti-insulin receptor antibody which both inhibits 125I-insulin binding and shifts the concentration dependence of insulin induction of tyrosine aminotransferase to the right. This same immunoglobulin does not inhibit 125I-multiplication-stimulating activity binding and only minimally inhibits 125I-IGF-I binding. Anti-insulin receptor antibody also does not significantly shift the concentration dependence for the IGFs, suggesting that IGFs induce transaminase by acting via IGF receptors. Although insulin down regulates insulin receptors, it does not decrease IGF-I or IGF-II binding. We conclude that insulin causes desensitization of HTC cells to IGFs by affecting a postbinding step in IGF action, which may be common to the actions of both insulin and insulin-like growth factors.
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PMID:Insulin regulation of insulin-like growth factor action in rat hepatoma cells. 614 41

The development and application of affinity cross-linking methodology have allowed the identification of receptor subunits for at least seven different polypeptide growth factors. In the case of insulin, a complex disulfide-linked receptor structure has been deduced by this method in conjunction with results obtained from affinity purification of the receptor complex. The minimum subunit structure deduced for this receptor is (beta-S-S-alpha)-S-S-(alpha-S-S-beta), where alpha is a 125,000-dalton glycoprotein subunit and beta is a 90,000-dalton glycoprotein subunit. A receptor species with high affinity for insulinlike growth factor (IGF) I and low affinity for insulin exhibits striking homology to this insulin receptor structure. A third receptor structure has high affinity for IGF-II and lower affinity for IGF-I, with essentially no affinity for insulin. This IGF-II receptor structure has a molecular weight of about 250,000 and shows no evidence of disulfide linkage to other subunits. Receptor polypeptides with high affinity for epidermal growth factor, nerve growth factor, transformation growth factor, or platelet-derived growth factor have been linked to the respective 125I-labeled ligands and exhibit molecular weights of about 160,000, 140,000, 60,000, and 170,000, respectively. None of these receptors appears to be disulfide linked to other subunits. No apparent structural homology among these receptor types has been detected as yet. Recent evidence suggests that there may be important biochemical linkages between certain of the receptor systems. For example, an effect of insulin mediated through its own receptor in intact adipocytes or H-35 hepatoma cells rapidly results in a 5- to 10-fold increase in the affinity of the 250,000-dalton IGF-II receptor for 125I-labeled IGF-II. This may reflect an important mechanism by which insulin can simultaneously mediate rapid effects on cellular enzymes through its own receptor and indirectly promote cellular growth by potentiating growth factor action through this activation of the IGF-II receptor.
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PMID:Interrelationships among receptor structures for insulin and peptide growth factors. 630 63

The regulation of insulin-like growth factor binding protein-1 (IGFBP-1) by its ligands, IGF-I and IGF-II, was studied in continuous cultures of HepG2 human hepatoma cells. Both IGF-I and IGF-II in concentrations as low as 1-10 nmol/l caused significant suppression of IGFBP-I protein levels. This suppression was accompanied by decreased IGFBP-1 mRNA levels occurring within 2-4 h of exposure to IGF-I or IGF-II, and by a significant decrease in IGFBP-1 promoter activity. IGF-I and IGF-II were equipotent in suppressing basal levels of IGFBP-1 protein, mRNA and promoter activity. IGF-I, IGF-II, and IGF-analogs with low IGFBP-1 affinity, (des 1-3)IGF-I and long R3IGF-I, all potently suppressed the previously characterized increase in IGFBP-1 protein levels and promoter activity induced by cAMP and theophylline. In contrast, [Leu-27]IGF-II, which interacts with the type II but not type I IGF receptor, had no effect on IGFBP-1 protein levels or promoter activity. Our data indicate that IGFBP-1 production is inhibited by its ligands, IGF-I and IGF-II, and that this effect is probably mediated at the transcriptional level. The effects of IGF-I and IGF-II apparently occur as a result of binding to the type I IGF receptor, and are similar to the previously characterized suppressive effects of insulin on IGFBP-1 transcription mediated through the insulin receptor. When considered with previous data regarding expression of IGFBP-1 and the type I IGF receptor, our results suggest that IGF regulation of IGFBP-1 may play an as yet undefined role in fetal development and postnatal hepatic regeneration.
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PMID:Insulin-like growth factor (IGF) suppression of IGFBP-1 production: evidence for mediation by the type I IGF receptor. 750 66

[125I]IGF-I binding to chicken hepatoma cell (LMH) membranes was displaced by unlabelled IGF-I or IGF-II, but not by insulin. Cross-linking revealed specific binding sites of 128 and 28-31 kDa, which following solubilization could be separated by wheat germ agglutinin (WGA) chromatography. [125I]IGF-I binding to the WGA eluate (128 kDa) could be displaced by insulin although with a 30-fold lower potency than IGF-I. Binding to the WGA flow-through (28-31 kDa) was not inhibited by insulin. This suggested that IGF binding to LMH was due mainly to membrane bound IGFBP rather than to type 1 IGF receptors. A reverse proportion was observed in normal chicken liver. A predominant 28 kDa IGFBP was synthesized and secreted by LMH cells, together with an unusual 60 kDa IGF binding entity which only bound [125I]IGF-II (with weak affinity). This process was not affected by the presence or absence of glucose, dexamethasone, glucagon, insulin or IGF-I.
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PMID:Preferential binding of insulin-like growth factors to a binding protein rather than to receptors on chicken hepatoma cell (LMH) membranes. 753 43

In this study we investigated the expression of insulin-like growth factor II (IGf-II) to explain a role for this growth factor in concert with hepatitis B virus (HBV) involvement in the development of hepatocellular carcinoma (HCC) from chronic hepatitis type B (CAH-B) and liver cirrhosis (LC). The expressions of IGF-II and HBsAg were tested in tissue samples from 38 patients with CAH-B, 32 with LC, and 31 with HCC, by immunohistochemical staining using monoclonal anti IGF-II and anti HBs. All patients were seropositive for the presence of HBsAg. The expression of IGF-II was observed in 30 out of 32 (93.8%) LC and all 31 (100%) HCC tissue samples tested. IGF-II was expressed in most hepatocytes of regenerating nodules and in tumorous as well as nontumorous cells of HCC tissues. Neither normal liver tissues nor CAH-B tissue samples expressed IGF-II. HBsAg was expressed in 34 out of 38 (89.5%) CAH-B, 24 out of 32 (75%) LC and 13 out of 31 (41.9%) HCC tissue samples. The expression sites of HBsAg were not correlated with those of IGF-II in any tissue samples tested. The present study indicates that IGF-II plays a role in cell proliferation of regenerating nodules as well as in the development of hepatocellular carcinomas. In addition, there was no direct evidence of HBV involvement in the overexpression of this growth factor.
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PMID:Expression of insulin-like growth factor II in chronic hepatitis B, liver cirrhosis, and hepatocellular carcinoma. 766

The insulin-like growth factor-binding proteins (IGFBPs) are a family of six proteins that modulate the biological activity of IGF-I and IGF-II and determine their bioavailability to tissues. One of the IGFBPs, IGFBP-1, is distinctive in the dynamic response of its levels in human plasma to metabolic changes. Parallel changes occur in IGFBP-1 mRNA and IGFBP-1 transcription in rat liver. Using the well differentiated H4-II-E rat hepatoma cell line as a model system, we demonstrated previously that IGFBP-1 transcription is positively regulated by dexamethasone and negatively regulated by insulin. We now examine the effect of the protein synthesis inhibitor, cycloheximide, on the hormonal regulation of IGFBP-1 gene expression. Preincubation of H4-II-E cells with 10.7 microM cycloheximide for 1.5 h did not prevent the induction of IGFBP-1 mRNA and IGFBP-1 transcription (determined in nuclear run-on assays) by dexamethasone. By contrast, cycloheximide treatment abolished the decrease in IGFBP-1 mRNA induced by insulin. Insulin rapidly decreased IGFBP-1 transcription in the absence of cycloheximide (> 50% inhibition in 20 min) and caused a similar decrease in cells pretreated with cycloheximide. Cycloheximide alone also decreased IGFBP-1 transcription. Similar results were observed with a second protein synthesis inhibitor, anisomycin, which also prevented the insulin-induced decrease in IGFBP-1 mRNA without abolishing the insulin-induced inhibition of IGFBP-1 transcription. These results suggest that although insulin decreases IGFBP-1 gene transcription in the presence of protein synthesis inhibitors, IGFBP-1 mRNA levels are maintained because of stabilization of the mRNA. Stabilization was demonstrated directly in actinomycin D-treated cells, where the t1/2 of IGFBP-1 mRNA increased from approximately 2 to approximately 20 h in the presence of cycloheximide; insulin did not affect IGFBP-1 mRNA turnover. Thus, cycloheximide-sensitive labile proteins contribute to the maintenance of basal IGFBP-1 promoter activity and the rapid turnover of IGFBP-1 mRNA, which determine the dynamic regulation of IGFBP-1 gene expression.
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PMID:Cycloheximide stabilizes insulin-like growth factor-binding protein-1 (IGFBP-1) mRNA and inhibits IGFBP-1 transcription in H4-II-E rat hepatoma cells. 768 68


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