Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) is a polypeptide that forms a ternary complex with IGFs and an acid-labile subunit. The hormonal regulation of the components of this complex is highly controversial, and both IGF-I and GH have been shown to mediate the expression/synthesis of IGFBP-3. This study investigates the regulation of IGFBP-3 protein, measured by RIA and Western ligand blot, and messenger RNA (mRNA) expression, measured by Northern analysis and reverse transcriptase-PCR, in SKHEP-1 human hepatocarcinoma cells. SKHEP-1 cells significantly increased the IGFBP-3 concentrations in conditioned medium (CM) when treated with GH (0.1-10 ng/ml), IGF-I (1-100 ng/ml), or Des(1-3)-IGF-I (1-100 ng/ml) in a dose-dependent manner (>3-fold). The increase in IGFBP-3 protein concentrations in CM was accompanied by a corresponding increase in IGFBP-3 mRNA levels. Interestingly, time-course studies showed that the GH-induced increase in IGFBP-3 mRNA preceded the IGF-I-induced increase (6 h for GH-induced IGFBP-3 mRNA; 12 h for IGF-I-induced IGFBP-3 mRNA). The half-life of IGFBP-3 mRNA was evaluated after transcriptional arrest by treatment with a RNA polymerase II inhibitor (5,6-dichloro-1beta-D-ribofuranosylbenzimidazole), and was found to be 14-18 h and unaltered by GH or IGF-I treatment. The induction of IGFBP-3 by GH was not due to the indirect action of locally synthesized IGF-I, because 1) no immunoreactive IGF-I was detected in the CM of control or GH-treated cells; 2) Northern blots revealed no IGF-I mRNA expression in SKHEP-1 cells; 3) reverse transcriptase-PCR did not detect any expression of the IGF-I gene; and 4) time-course studies showed an earlier increase in IGFBP-3 mRNA after GH treatment than after IGF-I treatment. Thus, the results obtained in this study are consistent with an IGF-I-independent regulation of IGFBP-3 gene expression by GH.
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PMID:Evidence for insulin-like growth factor (IGF)-independent transcriptional regulation of IGF binding protein-3 by growth hormone in SKHEP-1 human hepatocarcinoma cells. 907 3

Insulin-like growth factor binding protein-1 (IGFBP-1) modulates the mitogenic actions of IGF-I and IGF-II. Dexamethasone increases IGFBP-1 mRNA abundance and gene transcription in rat liver and in H4-II-E rat hepatoma cells. A glucocorticoid response element (GRE) located at nucleotide (nt) -91/-77 is required for dexamethasone to stimulate rat IGFBP-1 promoter activity in transient transfection assays in H4-II-E cells. Mutagenesis of nt -108/-99 (the M4 region of the insulin response element), however, decreased dexamethasone-stimulated promoter activity despite the presence of an intact GRE, suggesting that regulatory sites in addition to the GRE were required for optimal dexamethasone stimulation. To identify these sites, we introduced 5'-deletion and substitution mutations into rat IGFBP-1 promoter fragments coupled to a luciferase reporter gene and transfected these constructs into H4-II-E cells. Three sites are required for optimal basal promoter activity: a site (nt -62/-50) that binds the liver-enriched transcription factor, hepatocyte nuclear factor-1 (HNF-1), the M4 site, and a putative binding site for transcription factor AP-2 (nt -293/-286). The HNF-1 and M4 sites and an upstream site (nt -252/-236) are also involved in dexamethasone stimulation under some, but not all, circumstances. Mutation of either the HNF-1 site or the M4 site decreased dexamethasone stimulation by more than 80% in constructs whose 5'-end was at nt -92, -135, or -235 but not if the 5' -end was at nt -278 or -327. These results suggest that the nt -278/-236 region can compensate for the loss of the HNF-1 site or the M4 site but that the HNF-1 and M4 sites do not compensate for each other in constructs whose 5'-end was at nt -135 or -235, which lack the nt -278/-236 region. The site within the nt -278/-236 region was localized to nt -252/-236 by deoxyribonuclease I protection and transfection assays. Thus, several cis-elements in the rat IGFBP-1 promoter cooperate, in varying combinations, with the low-affinity GRE to allow optimal dexamethasone-stimulated promoter activity.
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PMID:Dexamethasone stimulation of rat insulin-like growth factor binding protein-1 promoter activity involves multiple cis-elements. 912 90

Insulin receptors (IR) and type 1 IGF receptors (IGF-IR) have been shown to form insulin/IGF-I hybrid receptors in tissues expressing both molecules. The biological function of hybrid receptors is still undefined. To date there is no information about the distribution of hybrid receptors in human tissues. We have applied two microwell-based immunoassays which are capable of quantitating hybrid receptors in small samples of human tissues and cells. Results demonstrated that the proportion of total IGF-IR assembled as hybrids varied between 40 and 60%, thus indicating that hybrid receptors account for a large fraction of total IGF-I binding in human tissues. A significant fraction of total IR was assembled as hybrids in the tissues examined, varying from 37% in placenta to 45% in hepatoma, with the exception of adipose tissue where the fraction of insulin receptors forming hybrids was 17%. Because hybrid receptors bind IGF-I, but not insulin, with high affinity, it is likely that in human tissues hybrid receptors may be primarily activated by IGF-I rather than insulin under physiological conditions. Therefore, differences in hybrid receptors distribution may contribute to regulate tissue sensitivity to insulin and IGF-I by sequestering insulin receptor alphabeta-heterodimer in an IGF-I responsive form.
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PMID:Distribution of insulin/insulin-like growth factor-I hybrid receptors in human tissues. 920 95

Cytochrome P-450 2E1 (CYP2E1) is characterized by a rapid turnover in the liver and some cell lines and the ability of substrates and heme iron ligands to inhibit significantly enzyme degradation. In the Fao hepatoma cell line, CYP2E1 was found to be fairly stable (half-life of 26 h), but serum withdrawal resulted in its rapid disappearance from the microsomal fraction (half-life of about 7 h) as evaluated using cycloheximide chase. The effect of serum withdrawal could be partially reversed by the addition of albumin to the culture medium, whereas insulin and the insulin-like growth factor IGF-I had no additional effect. The effect of serum withdrawal was specific for CYP2E1 since (a) no concomitant fast degradation of CYP2B1 and NADPH-cytochrome P-450 reductase was observed and (b) the CYP2E1 ligands ethanol and imidazole prevented the fast degradation of the enzyme. The lysosomotropic agent ammonium chloride and the inhibitor of autophagocytosis 3-methyladenine slowed down CYP2E1 degradation by about 30%, while leupeptin had no effect. Under the same conditions, the degradation of total long-lived cell protein showed the same sensitivity to ammonium chloride, but was significantly less sensitive to 3-methyladenine and serum and not sensitive to ethanol and imidazole. CYP2E1 degradation was inhibited by combined treatment with brefeldin A and nocodazole, which blocks both anterograde and retrograde vesicular transport between endoplasmic reticulum and the Golgi apparatus. The data point to the existence of a selective mechanism for the degradation of membrane proteins in serum-deprived cells in addition to nonselective autophagocytosis. The selective degradation of CYP2E1 may be attained by means of its selective vesicular transport to an acidic post-endoplasmic reticulum compartment.
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PMID:Selective fast degradation of cytochrome P-450 2E1 in serum-deprived hepatoma cells by a mechanism sensitive to inhibitors of vesicular transport. 924 6

We have established a hepatocarcinoma cell line (LFCI2 A) that produces voluminous tumors when injected subcutaneously into syngeneic Commentry rats. These neoplastic cells express both insulin-like growth factors (IGF) I and II. When transfected with an episomal cassette-expressing IGF-I antisense RNA, the modified LFCI2 A cell lines become poorly tumorigenic and, when injected subcutaneously, are associated with inhibition of the growth of the parental tumoral cells and/or induction of regression of established tumors. By contrast, cell lines isolated after transfection with the IGF-II antisense-expressing vector were as tumorigenic as the parental cell lines. The results are discussed in terms of protective immunity induced by the tumoral cells transfected by the IGF-I antisense vector. In the transfected hepatocarcinoma cells that do not produce IGF-I, the expression of major histocompatibility complex class I antigen was increased at least 4-fold compared with parental cells. The introduction of these cells in vivo induced a tumor-specific immunity that was associated with CD8 T cells.
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PMID:Antisense insulin-like growth factor I transferred into a rat hepatoma cell line inhibits tumorigenesis by modulating major histocompatibility complex I cell surface expression. 934 99

The insulin-like growth factor (IGF) binding proteins (IGFBPs) are a family of proteins that bind IGF-I and IGF-II and modulate their biological activities. IGFBP-1 is distinctive among the IGFBPs in its rapid regulation in response to metabolic and hormonal changes. The synthetic glucocorticoid, dexamethasone, increases IGFBP-1 mRNA abundance and gene transcription in rat liver and in H4-II-E rat hepatoma cells. A glucocorticoid response element (GRE) located at nucleotide (nt) -91/-77 is required for dexamethasone to stimulate rat IGFBP-1 promoter activity in transient transfection assays in H4-II-E cells. In addition to the GRE, three accessory regulatory sites [a putative hepatocyte nuclear factor-1 (HNF-1) site (nt -62/-50), an insulin-response element (nt -108/-99), and an upstream site (nt -252/-236)] are involved in dexamethasone stimulation under some, but not all, circumstances. The present study begins to address the mechanism by which transcription factors bound to the putative HNF-1 site act synergistically with the glucocorticoid receptor (GR) bound to the GRE. In gel shift assays, HNF-1alpha and HNF-1beta in H4-II-E extracts bind to the palindromic HNF-1 site. Both half-sites are required. Overexpression of HNF-1beta enhances dexamethasone-stimulated promoter activity. Both the HNF-1 site and the GRE must be intact for stimulation to occur. By contrast, overexpression of HNF-1alpha does not enhance dexamethasone-stimulated promoter activity, although, as also observed with overexpression of HNF-1beta, it inhibits basal promoter activity. Thus, the synergistic effects of HNF-1beta and the GR on dexamethasone-stimulated promoter activity require that they are bound to the HNF-1 site and the GRE, respectively, and may involve protein-protein interactions between the transcription factors, or between them and the basal transcription machinery or a steroid receptor coactivator. Synergy between the ubiquitously expressed GR and HNF-1, which is developmentally regulated and expressed in a limited number of tissues, provides a possible mechanism for tissue- and development-specific regulation of glucocorticoid action.
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PMID:Hepatocyte nuclear factor 1 and the glucocorticoid receptor synergistically activate transcription of the rat insulin-like growth factor binding protein-1 gene. 936 50

Insulin-like growth factors (IGFs) I and II stimulate growth and expression of specific genes through binding to cell membrane receptors. IGF binding proteins also bind IGF-I with higher affinity than the receptor. They are found in the circulation and tissues and can modulate IGF actions. Human IGFBP-1 is phosphorylated on serine residues, which increases its affinity for IGF-I. An acidic, presumably phosphorylated, form of human IGFBP-1 inhibits IGF-I-stimulated DNA synthesis in cultured cells, while a less acidic, unphosphorylated form potentiates this function. Phosphorylation of human IGFBP-3, however, does not affect its affinity for IGF-I. Previously we found that multiple forms of rat IGFBP-1 are obtained by anion-exchange chromatography, raising the possibility that it also is phosphorylated, which led us to examine its properties. Phosphopeptide analysis of 32P-labeled, immunoprecipitated rat IGFBP-1 synthesized by H-4-II-EC3 rat hepatoma cells indicated that it is phosphorylated on two sites that were deduced to be ser107 and ser132 in the central nonconserved domain. Dephosphorylation of purified phosphorylated rat IGFBP-1 did not affect its affinity for IGF-I or its specific binding activity, and the dephosphorylated form inhibited DNA synthesis in 3T3 cells. Incubation of cells labeled with radioactive proline in the presence of monensin and brefeldin A, which inhibit secretion at different sites, led to intracellular accumulation of the least phosphorylated form of rat IGFBP-1, but prevented further phosphorylation. The results suggested that phosphorylation occurs at two sites in cells, the cis-Golgi and the trans-Golgi network. In summary, these studies have shown that rat IGFBP-1 is phosphorylated on two sites by reactions that occur in different secretory organelles and that similar to human IGFBP-3, but unlike human IGFBP-1, phosphorylation does not affect its affinity for IGF-I.
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PMID:Phosphorylation of rat insulin-like growth factor binding protein-1 does not affect its biological properties. 972 Nov 88

The insulin-like growth factors (IGF-I and -II) are structurally related peptides participating in the regulation of metabolism, growth and cellular differentiation. In the present study, the human hepatoma cell line PLC was studied for the expression of individual components of the IGF axis. Northern blot analysis using IGF-I and -II coding cDNAs failed to detect IGF-I- or -II-specific transcripts in total RNA from PLC cells. Biosynthesis of type I and II IGF receptors was demonstrated by northern blotting and binding studies as well as cross-linking of the respective radiolabeled ligand. Both IGF-I and -II stimulated [3H]-thymidine incorporation dose-dependently. The mitogenic activity of exogenously added IGFs was reduced by the presence of IGF-binding proteins of 24, 30, 34, 41 and 45 kDa in supernatants of PLC cells identified as IGFBP-4, -1, -2 and -3, respectively, by [125I]IGF-I ligand-, immuno- and northern blotting. Biosynthesis of IGFBP-3 was stimulated dose-dependently by IGF-I and -II, while IGFBP-1, -2 and -4 were not affected. The increase of IGFBP-3 in response to IGF-I and -II was due to a stimulation of IGFBP-3 specific mRNA as well as to an inhibition of IGFBP-3 endocytosis. Proteolytic activity for rhIGFBP-3 was detected in media from PLC cells at acidic pH that was inhibited by the aspartyl protease inhibitor pepstatin A as well as after immunodepletion of cathepsin D from media of PLC cells. Thus, a role of cathepsin D for the regulation of IGFBP-3 bioavailability via endocytosis in acidic prelysosomal compartments was suggested. The susceptibility of PLC for IGF-I and -II was restricted by their ability to increase the abundance of inhibitory IGFBPs and to decrease the level of IGF-I receptor expression. The present data point to the IGF axis as a complex regulatory system that self limits the mitogenic activity of exogenous IGFs.
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PMID:Characterization of the insulin-like growth factor axis in a human hepatoma cell line (PLC). 988 66

We observed that all-trans-retinoic acid (RA) down-regulated insulin-like growth factor binding proteins (IGFBPs) in cultured human hepatoma cells (Hep 3B, PLC/PRF/5, and Hep G2); therefore, we characterized the role of this down-regulation in cell growth. Treatment with 10 micromol/L RA revealed a rapid decrease in IGFBP-3 within 2 days, and continued treatment with RA for 6 days resulted in a time-dependent stimulation of Hep 3B cell growth. However, RA treatment decreased IGFBP-1 in PLC/PRF/5 cells and in Hep G2 cells, and the growth-stimulatory activity of RA was transient and less prominent, and was finally obliterated in both cell lines. The addition of 5 ng/mL or 50 ng/mL insulin-like growth factors (IGFs) did not change the growth effects elicited by RA. The addition of IGFBP-3 (1,000 ng/mL) inhibited the growth of Hep 3B cells and counteracted the growth-stimulatory activity of RA, but not completely, suggesting that RA has direct growth-stimulatory activity and that this is enhanced by autocrine down-regulation of IGFBP-3. IGFBP-3 also inhibited the growth of PLC/PRF/5 cells and of Hep G2 cells. Treatment with phosphorylated IGFBP-1 (1,000 ng/mL) alone or with RA did not affect the growth of PLC/PRF/5 cells or Hep G2 cells. However, addition of dephosphorylated IGFBP-1, derived from in vivo dephosphorylation of the phosphorylated form, stimulated the growth of both cell lines, independent of interaction with IGF-I. From these observations, we propose that RA down-regulates IGFBPs, which in turn causes autocrine modulation of cell growth independent of IGF in hepatoma cells in vitro or in vivo. In addition, RA regulates IGFBPs at the posttranscriptional (Hep 3B cells and Hep G2 cells) or transcriptional level (PLC/PRF/5 cells) in a cell-specific manner.
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PMID:Down-regulation of insulin-like growth factor binding proteins and growth modulation in hepatoma cells by retinoic acid. 1009 52

The soluble form of the insulin-like growth factor II (IGF-II)/mannose 6-P (IGF-II/M6P) receptor is released by cells in culture and circulates in the serum. It retains its ability to bind IGF-II and blocks IGF-II-stimulated DNA synthesis in isolated rat hepatocytes. Because these cells are not normally stimulated to divide by IGF-II in vivo, the effect of soluble IGF-II/M6P receptor on DNA synthesis has been further investigated in two cell lines sensitive to IGF-II; mouse 3T3(A31) fibroblasts, stimulated by low levels of IGF-II following priming by epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) and Buffalo rat liver (BRL) cells, which secrete IGF-II and proliferate in the absence of exogenous growth factors. Soluble IGF-II/M6P receptor (0.2-2.0 microgram/ml) purified from a rat hepatoma cell line inhibited DNA synthesis (determined by dThd incorporation) in both cell lines. Basal DNA synthesis was very low in serum-free 3T3 cells, but high in serum-free BRL cells, possibly as a result of autocrine IGF-II production. The inhibitory effect was reversible in cells preincubated with soluble receptor prior to incubation with growth factors and could also be overcome by excess IGF-II. Soluble receptor was more potent in IGF-II-stimulated 3T3 cells and serum-free BRL cells than in BRL cells incubated with serum. Mean inhibition by four preparations of soluble receptor (1 microgram/ml) was 34.7% +/- 4.4% in BRL cells stimulated with fetal calf serum (FCS) (5%) compared to 54.8% +/- 4.2% in serum-free BRL cells (P = 0.05) and 60.6% +/- 6.5% (P = 0.02) in 3T3 cells stimulated by PDGF, EGF, and IGF-II. Soluble receptor had no effect on DNA synthesis in 3T3 cells stimulated with IGF-I. These results demonstrate that soluble receptor, at physiological concentrations, can block proliferation of cells by IGF-II and could therefore play a role in blocking tumor growth mediated by IGF-II.
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PMID:Soluble insulin-like growth factor II/mannose 6-phosphate receptor inhibits DNA synthesis in insulin-like growth factor II sensitive cells. 1056 17


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