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)

One of the major actions of interleukin-6 (IL-6) is the transcriptional activation of acute-phase plasma proteins (APP) genes in liver cells. Signaling by the IL-6 receptor is mediated through the signal transducing subunit gp130 and involves the activation of Janus-associated kinases (JAKs), signal transducer and activator of transcription 3 (STAT3), and mitogen-activated protein (MAP) kinase. Functional analysis of gp130 in rat hepatoma cells by using transduced chimeric G-CSFR-gp130 receptor constructs demonstrates that SHP-2, the Src homology 2 (SH2) domain-containing protein tyrosine phosphatase, acts as a negative regulator of the JAK/STAT signaling in part by downregulating JAK activity, thereby indirectly moderating the induction of STAT3-dependent APP genes. This study shows that in hepatoma cells, the recruitment and tyrosine phosphorylation of SHP-2, but not SHC, is the primary signaling event associated with the activation of MAP kinases (ERK1/2) by gp130. Overexpression of truncated SHP-2 that lacks Grb2-interacting sites, but not the full-length catalytically inactive SHP-2, reduces ERK activation by IL-6, confirming the signal-mediating role of SHP-2. Activation of ERK1/2 is correlated with induction of the immediate-early response genes. Stimulation of the c-fos, c-jun, and egr-1 genes is essentially absent in cells expressing gp130 with a Y759F mutation, which is unable to recruit SHP-2. Interestingly, both JAK/STAT and SHP-2 pathways regulate the induction of the junB gene. Moreover, disengagement of SHP-2 from gp130 signaling not only enhances APP gene induction but also further reduces cell proliferation, in part correlated with the attenuated expression of immediate-early response genes. These results suggest that IL-6 regulation of APP genes is affected by SHP-2 in two ways: SHP-2 acts as a phosphatase on the JAK/STAT pathway and serves as linker to the MAP kinase pathway, which in turn moderates APP production.
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PMID:Dual signaling role of the protein tyrosine phosphatase SHP-2 in regulating expression of acute-phase plasma proteins by interleukin-6 cytokine receptors in hepatic cells. 1040 24

The role of endogenous regucalcin in the regulation of protein tyrosine phosphatase activity in the proliferation of the cloned rat H4-II-E hepatoma cells was investigated. Cells were cultured for 6 to 96 h in a medium containing 1.0 or 10% fetal bovine serum (FBS). Cell numbers were significantly raised by culture with 10% FBS in comparison with that of 1.0% FBS. Protein tyrosine phosphatase activity in the cells was significantly elevated by culture with 10% FBS for 24 to 96 h as compared with that of 1% FBS. Such an increase was not seen in protein phosphatase activity toward phosphoserine or phosphothreonine. The presence of anti-regucalcin monoclonal antibody (50 or 100 ng/ml) in the enzyme reaction mixture caused a remarkable elevation of protein tyrosine phosphatase activity in the cells obtained by culture with 1.0 or 10% FBS. This elevation was completely prevented by the addition of regucalcin (10-6 M). The effect of antibody in elevating protein tyrosine phosphatase activity in the cells was significantly inhibited by the addition of okadaic acid (10-6 M) or vanadate (10(-6) M), an inhibitor of protein phosphatase, in the reaction mixture. The present study suggests that protein tyrosine phosphatase activity in the cloned rat hepatoma cells is increased in serum-stimulated cell proliferation, and that endogenous regucalcin has a suppressive role in the enhancement of the enzyme activity in proliferative cells.
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PMID:Enhancement of protein tyrosine phosphatase activity in the proliferation of cloned rat hepatoma H4-II-E cells: suppressive role of endogenous regucalcin. 1093 98

The transcriptional mechanism of regucalcin gene expression was determined using gel mobility shift assay with TTGGC oligonucleotide (II-b) which is located between position -523 and -506 in the promoter region, containing a nuclear factor I (NF1) consensus motif TTGGC(N)(6)CC. The mutation analysis in this motif showed that TTGGC sequence was a specific binding region of the nuclear protein in rat liver and the cloned rat hepatoma cells (H4-II-E). When liver nuclei were incubated with ATP (1 mM), the nuclear protein binding to TTGGC sequence was increased. This binding was also increased in the nuclei of H4-II-E cells cultured with 10% FBS. Such an increase was also seen by culture with vanadate (100 microM), a potent inhibitor of protein tyrosine phosphatase. Serum-enhanced nuclear protein binding to TTGGC sequence was decreased in the presence of TFP (10 microM), staurosporine (100 nM), genistein (10 microM), PD98059 (10 microM), or wortmannin (10 nM), which are inhibitors of various protein kinases. Treatment of a monoclonal phosphotyrosine antibody (4G10) caused an alteration in the TTGGC oligonucleotide-nuclear protein complex formation, indicating that tyrosine phosphorylation of nuclear protein is partly involved in the binding to TTGGC sequence. Moreover, when H4-II-E cells were cultured with FBS (10%), Bay K 8644 (5 microM), PMA (1 microM), or insulin (20 nM), the protein binding to TTGGC sequence in the nuclei was increased, while it was reduced in the cytoplasm, indicating a nuclear localization of the TTGGC sequence-binding protein. This study demonstrates that hepatic nuclear protein can specifically bind to the TTGGC sequence in rat regucalcin gene promoter region, and that this binding is enhanced by intracellular signaling factors which are partly mediated through protein phosphorylation.
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PMID:Intracellular signaling factors--enhanced hepatic nuclear protein binding to TTGGC sequence in the rat regucalcin gene promoter: involvement of protein phosphorylation. 1111 52

Regucalcin, a regulatory protein of Ca2+ signaling, is mainly present in liver cells. The role of regucalcin in hepatoma cells, however, has not been clarified. The role of endogenous regucalcin in the regulation of protein tyrosine phosphatase activity in the cloned rat hepatoma cells (H4-II-E) was investigated. Hepatoma cells were cultured for 3 days in a medium containing serum (10% fetal bovine serum). After subconfluency, the cells were used for the assay of protein phosphatase activity toward phosphotyrosine. The expression of regucalcin in hepatoma cells was detected by Western blotting using anti-regucalcin antibody. Protein tyrosine phosphatase activity was exhibited in the cytosol of hepatoma cells. The enzyme activity in the cytosol of hepatoma cells was significantly elevated by the addition of calcium chloride (10(-6)-10(-4) M) in the reaction mixture. This elevation was completely blocked by the addition of trifluoperazine (TFP: 2.5 x 10(-6) M), an antagonist of calmodulin. The addition of regucalcin (10(-7) M) caused a complete inhibition of the calcium (10(-4) M)-increased enzyme activity. The presence of anti-regucalcin monoclonal antibody (25, 50, and 100 ng/ml) in the enzyme reaction mixture produced a significant increase in protein tyrosine phosphatase activity in the cytosols of hepatoma cells and normal liver cells. This increase was completely prevented by regucalcin addition. The effect of antibody (50 ng/ml) in elevating the enzyme activity was partly inhibited by vanadate (10(-4) M). Protein tyrosine phosphatase activity was significantly elevated by the culture with Bay K 8644, a Ca2+-channel agonist. This increase was blocked by TFP addition in the enzyme reaction mixture, and it was enhanced in the presence of anti-regucalcin antibody. The present study demonstrates that regucalcin is expressed in hepatoma cells (H4-II-E), and that the protein may have an inhibitory effect on Ca2+/calmodulin-dependent protein tyrosine phosphatase activity in the cells.
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PMID:Role of endogenous regucalcin in protein tyrosine phosphatase regulation in the cloned rat hepatoma cells (H4-II-E). 1112 57

Thioalkyl containing K vitamin analogs have been shown to be potent inhibitors of hepatoma cell growth and antagonizers of protein tyrosine phosphatase activity. We now show that they inhibit the activity of specific protein tyrosine phosphatases (PTP) in cell-free conditions in vitro, particularly the dual specificity phosphatase Cdc25A. Using primary cultures of adult rat hepatocytes that are in G0/G1 phase until stimulated into DNA synthesis by epidermal growth factor, we found that 2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone or Compound 5 (Cpd 5) inhibited hepatocyte DNA synthesis and PTP activity in cell culture and in vivo after a two-thirds partial hepatectomy. We found a selective inhibition of Cdc25A activity in vitro, using both synthetic substrates and authentic cellular substrate, immunoprecipitated phospho-Cdk4. Intact Cpd 5-treated cells had decreased cellular Cdc25A activity and increased tyrosine phosphorylation of Cdk4, resulting in decreased phosphorylation of retinoblastoma (Rb). Loss of Cdk4 activity was confirmed using Cdk4 immunoprecipitates from either Cpd 5-treated or untreated cells and measuring its kinase activity using GST-Rb as target. We found a similar order of activity for inhibition of growth and Cdc25A activity using several thiol-containing analogs. Cdc25A inhibitors may thus be useful for defining biochemical pathways involving protein tyrosine phosphorylation that mediate cell growth inhibition.
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PMID:A Cdc25A antagonizing K vitamin inhibits hepatocyte DNA synthesis in vitro and in vivo. 1258 35

A comparison was made between two K vitamin analogs. Growth in vitro of Hep G2 hepatoma cells was inhibited both by Compound 5 (Cpd 5), a recently synthesized thioalkyl analog of vitamin K or 2-(2-mercaptoethanol)-3-methyl-1, 4-naphthoquinone, as well as by synthetic vitamin K3 (menadione). Using synchronized Hep G2 hepatoma cells, the actions of both Cpd 5 and vitamin K3 on cell cycle regulating proteins were examined. Cpd 5 decreased the levels of cyclin D1, Cdk4, p16, p21 and cyclin B1. By contrast, VK3 only decreased the level of cyclin D1, but had no effect on the levels of Cdk4, p16 or p21. Interestingly, both VK3 and VK2 increased the levels of p21. The naturally occurring K vitamins had little effect on cell growth and none on the cyclins or Cdks. Amounts and activity of the G1/S phase controlling Cdc25A were measured. We found that Cpd 5 directly inhibited both Cdc25A activity and its protein expression, whereas VK3 did not. Thus, the main effects of Cpd 5 were on G1 and S phase proteins, especially Cdk4 and Cdc25A amounts in contrast to VK3. Computer docking studies of Cpd 5 and VK3 to Cdc25A phosphatase showed three binding sites. In the best conformation, Cpd 5 was found to be closer to the enzyme active site than VK3. These findings show that Cpd 5 represents a new class of anticancer agent, being a protein tyrosine phosphatase (PTP) antagonist, that binds to Cdc25A with suppression of its activity. Tumors expressing high levels of oncogenic Cdc25A phosphatase may thus be susceptible to the growth inhibitory activities of this class of compound.
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PMID:Differential effects of two growth inhibitory K vitamin analogs on cell cycle regulating proteins in human hepatoma cells. 1267 93

Peroxisome proliferator activated receptor (PPAR)-alpha controls the expression of multiple genes involved in lipid metabolism, and activators of PPAR-alpha, such as fibrates, are commonly used drugs in the treatment of hypertriglyceridemia and other dyslipidemic states. Recent data have also suggested a role for PPAR-alpha in insulin resistance and glucose homeostasis. In the present study, we have assessed the transcriptional and physiological responses to PPAR-alpha activation in a diet-induced rat model of insulin resistance. The two PPAR-alpha activators, fenofibrate and Wy-14643, were dosed at different concentrations in high-fat fed Sprague-Dawley rats, and the transcriptional responses were examined in liver using cDNA microarrays. In these analyses, 98 genes were identified as being regulated by both compounds. From this pool of genes, 27 correlated to the observed effect on plasma insulin, including PPAR-alpha itself and the leukocyte antigen-related protein tyrosine phosphatase (PTP-LAR). PTP-LAR was downregulated by both compounds, and showed upregulation as a result of the high-fat feeding. This regulation was also observed at the protein level. Furthermore, downregulation of PTP-LAR by fenofibric acid was demonstrated in rat FaO hepatoma cells in vitro, indicating that the observed regulation of PTP-LAR by fenofibrate and Wy-14643 in vivo is mediated as a direct effect of the PPAR agonists on the hepatocytes. PTP-LAR is one of the first genes involved in insulin receptor signaling to be shown to be regulated by PPAR-alpha agonists. These data suggest that factors apart from skeletal muscle lipid supply may influence PPAR-alpha-mediated amelioration of insulin resistance.
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PMID:Identification of hepatic transcriptional changes in insulin-resistant rats treated with peroxisome proliferator activated receptor-alpha agonists. 1279 Aug 2

SAP-1 (stomach cancer-associated protein tyrosine phosphatase-1) is a transmembrane-type protein tyrosine phosphatase that has been implicated as a negative regulator of integrin-mediated signaling. The potential role of this enzyme in hepatocarcinogenesis has now been investigated by examining its expression in 32 surgically excised human hepatocellular carcinoma (HCC) specimens. Both immunohistochemical and immunoblot analyses revealed that normal liver tissue, as well as tissue affected by chronic hepatitis or cirrhosis, contained substantial amounts of SAP-1. The expression level of SAP-1 in 75% of well-differentiated HCCs was similar to or higher than that observed in the surrounding noncancerous tissue. In contrast, the abundance of SAP-1 in 85.7% of moderately differentiated HCCs and in all poorly differentiated HCCs was greatly reduced compared with that in the adjacent tissue. Indeed, SAP-1 was almost undetectable in 83.3% of poorly differentiated HCCs. Furthermore, expression of recombinant SAP-1 in two highly motile human HCC cell lines resulted in a change in morphology and a marked reduction in both migratory activity and growth rate. In conclusion, these results indicate that SAP-1 expression is downregulated during the dedifferentiation of human HCC, and that this downregulation may play a causal role in disease progression.
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PMID:Downregulation of stomach cancer-associated protein tyrosine phosphatase-1 (SAP-1) in advanced human hepatocellular carcinoma. 1287 10

A diet lacking folic acid and choline and low in methionine (folate/methyl deficient diet, FMD diet) fed to rats is known to produce preneoplastic nodules (PNNs) after 36 weeks and hepatocellular carcinomas (tumors) after 54 weeks. FMD diet-induced tumors exhibit global hypomethylation and regional hypermethylation. Restriction landmark genome scanning analysis with methylation-sensitive enzyme NotI (RLGS-M) of genomic DNA isolated from control livers, PNNs and tumor tissues was performed to identify the genes that are differentially methylated or amplified during multistage hepatocarcinogenesis. Out of the 1250 genes analysed, 2 to 5 genes were methylated in the PNNs, whereas 5 to 45 genes were partially or completely methylated in the tumors. This analysis also showed amplification of 3 to 12 genes in the primary tumors. As a first step towards identifying the genes methylated in the PNNs and primary hepatomas, we generated a rat NotI-EcoRV genomic library in the pBluescriptKS vector. Here, we describe identification of one methylated and downregulated gene as the rat protein tyrosine phosphatase receptor type O (PTPRO) and one amplified gene as rat C-MYC. Methylation of PTPRO at the NotI site located immediate upstream of the trancription start site in the PNNs and tumors, and amplification of C-MYC gene in the tumors were confirmed by Southern blot analyses. Bisulfite genomic sequencing of the CpG island encompassing exon 1 of the PTPRO gene revealed dense methylation in the PNNs and tumors, whereas it was methylation free in the livers of animals on normal diet. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed significant decrease in the expression of PTPRO in the tumors and in a transplanted rat hepatoma. The expression of PTPRO mRNA in the transplanted hepatoma after demethylation with 5-azacytidine, a potent inhibitor of DNA methyltransferases, further confirmed the role of methylation in PTPRO gene expression. These results demonstrate alteration in methylation profile and expression of specific genes during tumor progression in the livers of rats in response to folate/methyl deficiency, and further implicate the potential role of PTPRO as a novel growth regulatory gene at least in the hepatocellular carcinomas.
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PMID:Suppression of the protein tyrosine phosphatase receptor type O gene (PTPRO) by methylation in hepatocellular carcinomas. 1450 12

Leptin has been shown to improve insulin sensitivity and glucose metabolism in obese diabetic ob/ob mice, yet the mechanisms remain poorly defined. We found that 2 d of leptin treatment improved fasting but not postprandial glucose homeostasis, suggesting enhanced hepatic insulin sensitivity. Consistent with this hypothesis, leptin improved in vivo insulin receptor (IR) activation in liver, but not in skeletal muscle or fat. To explore the cellular mechanism by which leptin up-regulates hepatic IR activation, we examined the expression of the protein tyrosine phosphatase PTP1B, recently implicated as an important negative regulator of insulin signaling. Unexpectedly, liver PTP1B protein abundance was increased by leptin to levels similar to lean controls, whereas levels in muscle and fat remained unchanged. The ability of leptin to augment liver IR activation and PTP1B expression was also observed in vitro in human hepatoma cells (HepG2). However, overexpression of PTP1B in HepG2 cells led to diminished insulin-induced IR phosphorylation, supporting the role of PTP1B as a negative regulator of IR activation in hepatocytes. Collectively, our results suggest that leptin acutely improves hepatic insulin sensitivity in vivo with concomitant increases in PTP1B expression possibly serving to counterregulate insulin action and to maintain insulin signaling in proper balance.
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PMID:Leptin increases hepatic insulin sensitivity and protein tyrosine phosphatase 1B expression. 1497 21


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