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)

Transforming growth factor-beta1 (TGF-beta1) can induce rapid growth arrest and apoptosis in hepatic cells. Its growth suppressive effects appear to be linked to decreased phosphorylation of the protein product of the retinoblastoma gene, pRb. To characterize the role of pRb in apoptosis, we examined endogenous retinoblastoma gene (Rb) expression following treatment with TGF-beta1, okadaic acid, or antisense Rb S-oligonucleotides in cultured primary rat hepatocytes and human hepatoma HuH-7 cells. We also investigated the effects on apoptosis of Rb overexpression following transfection with vectors containing wild-type Rb in HuH-7 cells. Our results indicated that transfection with Rb antisense S-oligonucleotides blocked the expression of pRb in cultured primary hepatocytes and induced apoptosis. Treatment of HuH-7 cells with TGF-beta1 inhibited expression and phosphorylation of pRb, and also induced apoptosis. Furthermore, 93% of viable preapoptotic cells were arrested in the G1 phase of the cell cycle. Incubation with the phosphatase inhibitor okadaic acid maintained pRb in its phosphorylated state, and resulted in significant apoptosis. Overexpression of wild-type Rb inhibited TGF-beta1 induced apoptosis in HuH-7 cells. In contrast, overexpression of transcription factor E2F-1, a known target for the activity of pRb, caused significant apoptosis. However, coexpression of Rb suppressed E2F-1 induced apoptosis in HuH-7 cells. Our results suggest that inhibition of pRb expression is associated with hepatocyte apoptosis. Furthermore, E2F-1 appears to be a target in the pathway through which pRb modulates the apoptotic threshold in hepatic cells. Finally, the data suggest that these cells exit the cell cycle during the G1 phase before progressing into apoptosis and pRb may be a negative regulator of this process.
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PMID:The retinoblastoma gene product inhibits TGF-beta1 induced apoptosis in primary rat hepatocytes and human HuH-7 hepatoma cells. 864 52

Using rats with hepatocellular carcinoma induced by 3'-methyl-4-dimethylamino-azobenzene (3'-MeDAB), we evaluated the expression of a protein tyrosine phosphatase (PTPase) in the tumor region, non-tumorous region and control rat liver. The expression of SHPTP2 increased 4.1 fold (p < 0.05) in mRNA, 2.1 fold (p < 0.01) in cytosol fraction, and 5.1 fold (p < 0.05) in membrane fraction, respectively, at a protein level in the tumor region compared with control liver. The expression of other phosphatases, LAR, LRP, and PTPase1B, did not change significantly. SHPTP2 phosphatase activity in the tumor region from rats also increased compared with control, suggesting that an increase of this activity may parallel the expression of SHPTP2. This increase of expression of SHPTP2 may contribute to the progression of hepatocellular carcinoma in this rat model.
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PMID:Changes of expressions of phosphotyrosine phosphatases in rat hepatocellular carcinoma induced by 3'-methyl-4-dimethylamino-azobenzene. 887 28

We applied the technique of mRNA differential display to normal liver tissue and hepatoma cell line Hep3B. One of the isolated cDNA clones was expressed in human normal liver tissue but not in the human hepatocarcinoma cell line. Northern Blot analysis confirmed that high level of mRNA was expressed in human normal liver tissue but the level was decreased in non-cancerous liver tissue from hepatoma patients. Low level or no expression was observed in human hepatoma tissue. One of these transcripts was about 1.8 kb in length. Southern Blot analysis showed that it was a single copy gene. We obtained a full length cDNA clone of 2,395 bp by screening human liver 5'-stretch plus cDNA library. Nucleotide sequence indicated that this clone was highly homologous to aryl-dialkyl-phosphatase and possessed two polymorphic sites. Aryl-dialkyl-phosphatase which has a prominent role in the metabolism of several toxic, synthetic compounds, may be potentially related to human hepatocarcinoma susceptibility. The biological significance of its differential expression in normal versus malignant tissue is discussed.
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PMID:Differential expression of a cDNA clone in human liver versus hepatic cancer--highly homologous to aryl-dialkyl-phosphatase. 926 65

The human insulin receptor substrate-1 (hIRS-1) is a key intracellular protein involved in various cytokine signaling pathways associated with cell growth. We have previously demonstrated that stable transfection and overexpression of hIRS-1 in human hepatoblastoma cells in vitro leads to the constitutive activation of the mitogen-activated protein kinase (MAPK) cascade. In this setting, hIRS-1 acts as a dominant oncogene and will induce neoplastic transformation of NIH 3T3 cells. In the present study, the biologic effects of hIRS-1 overexpression in the liver was analyzed using both clinical tumor samples and a newly developed transgenic mouse model. We have found that approximately 40% of 22 human hepatocellular carcinoma (HCC) tumors had enhanced (>200%) hIRS-1 gene expression compared with adjacent non-involved liver tissue. There was a significant relationship between the level of hIRS-1 overexpression and the tumor size; this finding suggests a possible role for hIRS-1 in tumor progression. To determine if downstream signal transduction cascades were activated by overexpression of hIRS-1 in hepatocytes, we established a transgenic mouse model using an hIRS-1 construct driven by an albumin promoter/enhancer element to direct liver specific expression. The overexpressed hIRS-1 protein was found to be tyrosyl phosphorylated and interacted with downstream SH2-containing molecules such as the p85 subunit of phosphatidylinositol-3 kinase (PI3K), Grb2 adaptor, and SHP2 phosphatase proteins. The functional consequences of hIRS-1 overexpression were reflected by constitutive activation of both the MAPK and PI3K signal transduction cascades. More important, overexpression of hIRS-1 in the transgenic liver led to increased hepatocyte DNA synthesis. Our findings indicate that hIRS-1 overexpression induces downstream signaling molecules associated with hepatocyte growth and may potentially enhance tumor progression of HCC.
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PMID:Biological effects of human insulin receptor substrate-1 overexpression in hepatocytes. 930 88

In this study we have investigated the molecular mechanism by which sodium butyrate modulates gene expression when added to cultured cells. As a model system we used hepatoma tissue culture cells in which sodium butyrate treatment increases histone H1(0) mRNA level and decreases c-myc mRNA level. Because we observed that stimulation of histone H1(0) gene expression could take place in the absence of protein neosynthesis, we hypothesized that sodium butyrate induced a post-translational modification of a factor involved in the transcription process. Using different types of well known kinase and phosphatase inhibitors, we studied the implication of kinase or phosphatase activity in this pathway. Interestingly, cell treatment with potent serine-threonine-phosphatase inhibitors, calyculin A or okadaic acid, prevented the regulation of both histone H1(0) and c-myc gene expressions by sodium butyrate. On the other hand, the tyrosine phosphatase inhibitor, vanadate, or the protein kinase C inhibitor, staurosporine, did not significantly modify sodium butyrate effects. Using protein phosphatase 1 and 2A for in vitro assays, we found a 45% increase of phosphatase activity after cell treatment by sodium butyrate, possibly due to a protein phosphatase 1-type protein phosphatase. These data strongly suggest that signaling pathway(s) triggered by sodium butyrate to modulate gene expression involve(s) a serine-threonine-phosphatase activity.
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PMID:The effects of sodium butyrate on transcription are mediated through activation of a protein phosphatase. 930 63

Insulin binding to its receptor induces the phosphorylation of cytosolic substrates, insulin receptor substrate (IRS)-1 and IRS-2, which associate with several Src homology-2 domain-containing proteins. To identify unique IRS-1-binding proteins, we screened a human heart cDNA library with 32P-labeled recombinant IRS-1 and obtained two isoforms (epsilon and zeta) of the 14-3-3 protein family. 14-3-3 protein has been shown to associate with IRS-1 in L6 myotubes, HepG2 hepatoma cells, Chinese hamster ovary cells, and bovine brain tissue. IRS-2, a protein structurally similar to IRS-1, was also shown to form a complex with 14-3-3 protein using a baculovirus expression system. The amount of 14-3-3 protein associated with IRS-1 was not affected by insulin stimulation but was increased significantly by treatment with okadaic acid, a potent serine/threonine phosphatase inhibitor. Peptide inhibition experiments using phosphoserine-containing peptides of IRS-1 revealed that IRS-1 contains three putative binding sites for 14-3-3 protein (Ser-270, Ser-374, and Ser-641). Among these three, the motif around Ser-270 is located in the phosphotyrosine binding domain of IRS-1, which is responsible for the interaction with the insulin receptor. Indeed, a truncated mutant of IRS-1 consisting of only the phosphotyrosine binding domain retained the capacity to bind to 14-3-3 protein in vivo. Finally, the effect of 14-3-3 protein binding on the insulin-induced phosphorylation of IRS-1 was investigated. Phosphoamino acid analysis revealed that IRS-1 coimmunoprecipitated with anti-14-3-3 antibody to be weakly phosphorylated after insulin stimulation, on tyrosine as well as serine residues, compared with IRS-1 immunoprecipitated with anti-IRS-1 antibody. Thus, the association with 14-3-3 protein may play a role in the regulation of insulin sensitivity by interrupting the association between the insulin receptor and IRS-1.
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PMID:14-3-3 protein binds to insulin receptor substrate-1, one of the binding sites of which is in the phosphotyrosine binding domain. 931 43

The action of hyperosmotic stress on the MAP kinase phosphatase MKP-1 mRNA expression was studied in H4IIE rat hepatoma cells. Hyperosmotic (405 mosmol/L) challenge of the cells led to a transient expression of MKP-1 mRNA, which was maximal after 6-8 h and disappeared completely after 24 h. Hyperosmotic MKP-1 mRNA induction was preceded by a transient activation of the MAP kinases Erk-1, Erk-2, and JNK-2, which were not prerequisite for MKP-1 mRNA accumulation. However, the hyperosmolarity-induced MKP-1 mRNA expression was sensitive to antioxidants and to inhibition of p38 by SB203580. A reduced sensitivity of Erk-1/Erk-2 to other stimuli was found after prolonged hyperosmotic exposure. The data are consistent with a hyperosmolarity-induced MKP-1 expression via reactive oxygen intermediates and p38, which may participate in the termination of MAP kinase activation and contribute to desensitization of the MAP kinases after prolonged hyperosmotic exposure of the cells.
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PMID:Hyperosmotic induction of the mitogen-activated protein kinase phosphatase MKP-1 in H4IIE rat hepatoma cells. 950 Aug 41

Given the important relationship between O2 and iron (Fenton chemistry) a study was undertaken to characterize the effects of hypoxia, as well as subsequent reoxygenation, on the iron-regulatory proteins 1 and 2 (IRP1 and IRP2) in a rat hepatoma cell line. IRP1 and IRP2 are cytosolic RNA-binding proteins that bind RNA stem-loops located in the 5'- or 3'-untranslated regions of specific mRNAs encoding proteins that are involved in iron homeostasis. In cells exposed to hypoxia, IRP1 RNA binding was decreased approximately 2. 8-fold after a 6-h exposure to 3% O2. Hypoxic inactivation of IRP1 was abolished when cells were pretreated with the iron chelator desferrioxamine, indicating a role for iron in inactivation. IRP1 inactivation was reversible since re-exposure of hypoxically-treated cells to 21% O2 increased RNA binding activity approximately 7-fold after 21 h with an increase in activity seen as early as 1-h post-reoxygenation. IRP1 protein levels were unaffected during hypoxia as well as during reoxygenation. Whereas the protein synthesis inhibitor cycloheximide did not block IRP1 inactivation during hypoxia, it completely blocked IRP1 reactivation during subsequent reoxygenation. Reactivation of IRP1 during reoxygenation was also partially blocked by the phosphatase inhibitor okadaic acid. Finally, reactivated IRP1 was found to be resistant to inactivation by exogenous iron known to down-regulate its activity during normoxia. These data demonstrate that IRP1 RNA binding activity is post-translationally regulated during hypoxia and hypoxia/reoxygenation. Regulation of IRP1 by changing oxygen tension may provide a novel mechanism for post-transcriptionally regulating gene expression under these stresses.
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PMID:Regulation of iron regulatory protein 1 during hypoxia and hypoxia/reoxygenation. 951 62

Treatment of cells with sodium butyrate is known to increase histone acetylation by inhibiting deacetylases. Here we have observed, in cultured hepatoma cells, that the potent serine-threonine phosphatase inhibitors, okadaic acid or calyculin A, inhibited phosphatase activity and concomitantly decreased the histone acetylation classically maintained by sodium butyrate. These results suggest that a protein phosphatase may mediate the sodium butyrate effect on deacetylases. Since we have previously found that such a protein would also mediate the sodium butyrate effect on gene expression, we propose that a phosphatase activity constitutes an early and essential step in the sodium butyrate-triggered signalling pathway.
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PMID:A protein phosphatase is involved in the inhibition of histone deacetylation by sodium butyrate. 961 85

pp120, a plasma membrane glycoprotein, is phosphorylated on Tyr488 by the insulin receptor tyrosine kinase. This requires basal phosphorylation on Ser503 by cAMP-dependent serine kinase. Phe513, the other tyrosine residue in the intracellular domain, does not undergo insulin-stimulated phosphorylation. Phe488 mutation abolished basal and insulin-stimulated phosphorylation, whereas, Phe513 plus Phe488 mutation markedly decreased the effect of insulin on pp120 phosphorylation without altering basal phosphorylation in intact cells. To investigate whether basal phosphorylation of pp120 is regulated by a phosphatase activity that requires Tyr513, in vitro phosphorylation assays using partially purified glycoproteins from stably transfected NIH 3T3 cells were performed in the absence of phosphatase inhibitors. Wild-type pp120 was promptly dephosphorylated, whereas, Y513F pp120 was not. Decreasing pp120 expression by antisense cDNA transfection proportionally decreased phosphatase activity in H4-II-E hepatoma cells measured by the p-nitrophenyl phosphate assay. This suggests that pp120 is associated with phosphatase activity that requires an intact Tyr513 residue.
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PMID:pp120, a substrate of the insulin receptor tyrosine kinase, is associated with phosphatase activity. 964 50


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