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 insulin's actions is the induction of DNA synthesis and cell division, but little is known about the molecular mechanisms involved. Previous studies indicate that insulin stimulates cell division and regulates the expression of several genes in rat H4IIE (H4) hepatoma cells. One of these genes is the proto-oncogene c-fos, a cellular gene whose deregulation has been implicated in the process of cellular differentiation and division. We have shown that insulin induces transcription of the c-fos gene in H4 cells. In the present study, the phorbol ester, phorbol 12-myristate 13-acetate (PMA), stimulated c-fos transcription in a rapid and dose-dependent manner with an 800% increase in transcription following 15-30 min of addition. This increase in c-fos transcription was transitory, returning towards baseline transcription rates within 120 min. PMA stimulated the translocation of protein kinase C (PKC) from the cytoplasm to the membrane in H4 hepatoma cells, as evidenced by a 77% decrease in cytosolic PKC and a 29% increase in membrane PKC activity following 10 min of treatment. Insulin addition to H4 cells for 10 min also resulted in a 31% decrease in cytosolic PKC activity, suggesting a translocation response. When H4 cells were pretreated with PMA for 24 h, there was a decrease of 20-45% in both cytosolic and membrane PKC activity and a complete loss of PMA's induction of c-fos transcription. Thus, the cells were functionally desensitized to further PMA addition. When cells were pretreated with PMA for 24 h, the insulin-induced increase in transcription of c-fos was reduced by 50%. Western blot analysis indicated that the PKC-beta isozyme followed a translocation pattern almost identical with that of total PKC activity. These results suggest that a PMA-sensitive form of PKC is preferentially lost upon PMA pretreatment and that this PKC subtype may be necessary for insulin to fully induce c-fos gene expression.
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PMID:Role of protein kinase C in insulin's regulation of c-fos transcription. 157 56

Glucocorticoids induce growth inhibition in certain sensitive hepatoma cells. To investigate how glucocorticoids interact with growth-factor-dependent pathways, we studied the effects of dexamethasone (Dex) on the DNA synthesis, protein kinase C (PKC) activity and phospholipid turnover in mouse hepatoma 22 cells. Dex was found to reduce DNA synthesis in slowly growing hepatoma cells, whereas exponentially growing cells were Dex-insensitive. Direct measurements of PKC activity in the hormone-sensitive hepatoma 22 cells showed a rapid inhibition (within 30 min) when treated with Dex. Dex addition to hormone-sensitive but not to hormone-insensitive hepatoma 22 cells for 30 min caused a significant decrease of 32P-incorporation into the major cellular phospholipids: phosphatidylcholine, phosphatidylglycerol and phosphoinositides. At the same time, the analysis of the correlation between changes in PKC activity and phospholipid turnover showed that synthesis of phosphatidylcholine and phosphatidylglycerol was under positive control of PKC activity. The data suggest that suppression of phospholipid turnover in hormone-sensitive hepatoma 22 cells is one of the early events caused by glucocorticoids, whereas the decrease of PKC activity induced by the hormone is mediated, probably, via changes in phospholipid metabolism.
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PMID:Glucocorticoid regulation of phospholipid turnover and protein kinase C activity in mouse hepatoma 22 cells. 159 Dec 75

Among environmental pollutants, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) is one of the most potent tumor promoters and teratogens known. The molecular mechanisms responsible for the biological activity of TCDD, however, remain largely unknown. In this report, we show that the first observable effects of TCDD in cultured murine hepatoma cells are a rapid, transient increase in Ca2+ influx and a minor but significant elevation of activated, membrane-bound protein kinase C. These changes are then followed by induction of the immediate early proto-oncogenes c-fos, jun-B, c-jun, and jun-D, and by large increases in AP-1 transcription factor activity. Induction of these changes by TCDD is delayed compared with that by phorbol esters, although the magnitude of the effects caused by both treatments is similar, and both induction processes can be blocked by staurosporine, a protein kinase C inhibitor. In cultured cells, proto-oncogene induction by TCDD appears to be independent of the presence of a functional aryl hydrocarbon (Ah) receptor or nuclear translocation protein. These results reveal early events that may lead to the elucidation of the molecular basis of TCDD-induced tumor promotion.
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PMID:Dioxin induces expression of c-fos and c-jun proto-oncogenes and a large increase in transcription factor AP-1. 160 50

The role of protein kinase C and phospholipid turnover in the realization of the cytostatic effect of dexamethasone on hormone-sensitive cells of mouse hepatoma 22 has been studied. It was found that dexamethasone added to hepatoma cells induces a rapid (within 30 min) inhibition of the protein kinase C activity with a simultaneous decrease of the 32P incorporation into the major phospholipids (phosphatidylglycerol, phosphatidylcholine, and phosphoinositides). Analysis of correlation between the protein kinase C activity and phospholipid turnover rate revealed that phosphatidylglycerol and phosphatidylcholine synthesis is under the positive control of protein kinase C, whereas that of phosphoinositides is not controlled by the enzyme. A proportional decrease in the rates of metabolism of all the three major phospholipids after addition of the hormone to hepatoma cells suggests that inhibition of phospholipid turnover is one of the primary manifestations of the dexamethasone effect. The hormone-induced decrease in the protein kinase C activity may be regarded as being due to these changes.
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PMID:[Regulation of the phospholipid turnover rate and protein kinase C activity as a necessary stage in the realization of the growth-inhibiting effect of dexamethasone on hepatoma 22 cells]. 163 23

Haemopexin receptors from mouse hepatoma (Hepa) cells were affinity-labelled by cross-linking to haem-125I-haemopexin complexes using two homo-[disuccinimidyl suberate (DSS) and 3,3'-dithiobis(succinimidyl propionate) (DTSSP)] and one hetero-[sulphosuccinimidyl 4-(p-maleimidophenyl)butyrate (sulpho-SMPB)] bifunctional cross-linking agents. Analysis of the cross-linked products by SDS/PAGE in the absence of reducing agents revealed that 125I-haemopexin was cross-linked specifically to a protein of apparent molecular mass 85-90 kDa. Upon reduction, haemopexin remained cross-linked to a protein of 20 kDa, suggesting that the murine haemopexin receptor has a subunit structure. Two subunits were identified: alpha (p65) and beta (p20). Furthermore, because haemopexin was cross-linked by all three agents to p20, the shortest cross-linker arm being 1.1 nm (11 A), we propose that the haem-haemopexin-binding site resides on this subunit. In addition, a cysteine residue of p20 is located near the haemopexin-binding site, since haemopexin, which has no free thiol groups, is cross-linked to this subunit by the hetero-bifunctional agent sulpho-SMPB. Exposure of Hepa cells to the tumour-promoting phorbol ester 4 alpha-phorbol 12-myristate 13-acetate (PMA) causes a rapid redistribution of haemopexin receptors from the cell surface to the cell interior. Within 2-4 min of incubation with 100 nM-PMA, there was an approx. 50% decrease in cell-surface haemopexin receptors, as judged by ligand binding at 0 degrees C and affinity labelling of the receptor. This time- and dose-dependent down-regulation was fully reversible within 60-90 min after removal of PMA, and the affinity of the remaining receptors was unaltered by PMA. The specificity of PMA was demonstrated by comparison with the non-tumour-promoter 4 alpha-phorbol, which did not affect any of the parameters examined. The amine H-7, a specific inhibitor of protein kinase C, antagonised the receptor redistribution effect of PMA, suggesting that the down-regulation of haemopexin receptors on the cell surface was a consequence of protein kinase C activation. The PMA-induced decrease in surface haemopexin receptors was due to a 2-fold increase in the rate of internalization (from 0.73 min-1 to 1.32 min-1), whereas the rate of exocytosis (0.6 min-1) was unchanged. PMA treatment, like binding of the natural ligand, haem-haemopexin, results in a lower steady-state level of surface haemopexin receptors independent of receptor synthesis, and the receptors were not degraded but were recycled back to the cell surface.
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PMID:The murine haemopexin receptor. Evidence that the haemopexin-binding site resides on a 20 kDa subunit and that receptor recycling is regulated by protein kinase C. 164 99

In man, the plasminogen activator inhibitor 1 (PAI-1) gene codes for two mRNA species, one of 3.2 kilobases (kb) and the other of 2.4 kb. We report that the protein kinase C activating phorbol ester, phorbol 12-myristate-13-acetate (PMA), causes a different induction of the two PAI-1 mRNA species in the human hepatoma cell line, HepG2. Upon addition of 100 nM PMA, the level of the 3.2-kb PAI-1 mRNA species increased to 25-fold after 3 h, and then declined rapidly. The level of the 2.4-kb species increased more slowly and reached a maximal 18-fold stimulation after 6 h, followed by a gradual decrease towards control levels. Run-on analysis showed that PMA induces a transient 40-fold increase in PAI-1 gene transcription rate. The relative concentration of the two PAI-1 mRNA species in the nuclei of PMA-treated HepG2 cells shifted towards the 2.4-kb form, suggesting that changes in transcription termination site and/or post-transcriptional nuclear processing might contribute to their different accumulation. Also, the two mRNAs differ in turnover rate, with a half-life of about 0.85 h for the 3.2-kb form and a half-life of about 2.5 h for the 2.4-kb form. By itself, cycloheximide had no effect on PAI-1 gene transcription rate or PAI-1 mRNA levels in HepG2. When added 1 h prior to PMA, however, cycloheximide prevented the induction of PAI-1 mRNA, which suggests that PMA exerts its stimulating transcriptional activity through a newly synthesized regulatory protein. When cycloheximide was added 2 h after PMA, when the PAI-1 gene transcription rate was maximally increased, the two PAI-1 mRNAs reached even higher levels than with PMA alone and maximal mRNA levels were maintained for a much longer period (up to 8 h). Thus, ongoing protein synthesis is required for both the induction and the transient nature of the PMA-induced PAI-1 mRNA accumulation. We conclude that the differential accumulation of the two PAI-1 mRNAs by PMA in serum-starved HepG2 cells is due both to changes in transcription termination and/or post-transcriptional nuclear processing and to differences in half-life between the two mRNAs in a process that requires ongoing protein synthesis.
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PMID:Different induction of two plasminogen activator inhibitor 1 mRNA species by phorbol ester in human hepatoma cells. 165 29

The role of protein kinase C (PKC) in the control of erythropoietin (Epo) production was studied using the human hepatoma cell line HepG2. Inhibition of PKC by staurosporine and the selective PKC inhibitor CGP 41251 significantly reduced Epo formation. No inhibition occurred with the inactive staurosporine derivative CGP 42700. Treatment with phorbol 12-myristate 13-acetate (PMA) for 24 h dose-dependently inhibited Epo formation, thus suggesting that down-regulation of PKC might be responsible for this inhibition. Immunoblotting experiments showed that incubation of HepG2 cells with PMA for 24 h resulted in a selective and almost complete down-regulation of PKC-alpha. Thus, PKC-alpha may play a permissive role in Epo synthesis in HepG2 cells.
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PMID:Inhibition of erythropoietin production by phorbol ester is associated with down-regulation of protein kinase C-alpha isoenzyme in hepatoma cells. 165 52

In this study we describe the activation of a protein kinase which phosphorylates a peptide, T669, comprising amino acids 663-681 of the epidermal growth factor receptor and containing the phosphate acceptor site Pro-Leu-Thr669-Pro. In the human epidermoid carcinoma cell line KB, T669 kinase activity in cytosolic extracts peaked (up to 15-fold compared with basal levels) 15-30 min after addition of interleukin-1 (IL-1) and closely paralleled receptor occupancy with a half-maximally effective concentration of approximately 100 pM IL-1 alpha. IL-1 treatment elevated T669 kinase activity to a variable extent in selected fibroblast lines, the hepatoma cell line HepG2, and the murine thymoma EL4 6.1. An IL-1 receptor-negative EL4 variant and the B cell lines 70Z/3, CB23, and RPMI 1788 did not respond in this way. All of the cell lines except 70Z/3 showed increased levels of T669 kinase when treated with the protein kinase C activator phorbol myristate acetate and/or with epidermal growth factor. This finding is in agreement with a previous study (Countaway, J. L., Northwood, I. C., and Davis, R. J. (1989) J. Biol. Chem. 264, 10828-10835). Activators of protein kinase A did not mimic the ability of IL-1 to stimulate T669 kinase activity, nor did the protein kinase C inhibitor staurosporine abrogate the effect of IL-1. T669 kinase activity from IL-1-stimulated KB cells was partially purified by ion exchange, hydrophobic interaction, and size exclusion chromatography. The partially purified enzyme phosphorylated myelin basic protein, a characteristic substrate of microtubule-associated protein-2 kinase (MAP-2 kinase) and the peptide Arg-Arg-Arg-(Tyr-Ser-Pro-Thr-Ser-Pro-Ser)4 from RNA polymerase II. Western blotting of chromatographic fractions revealed that T669 kinase activity corresponded with two proteins of 43 and 45 kilodaltons which cross-reacted with antibodies raised against peptide sequences of rat extracellular signal-regulated kinase-1/microtubule-associated protein-2 kinase. T669 kinase activity was critically dependent on the presence of phosphatase inhibitors. Since both the 43- and 45-kDa proteins, immunoprecipitated from [32P]phosphate-labeled cells, demonstrated a dramatic increase in their levels of serine, threonine, and tyrosine phosphorylation after brief treatment with IL-1, we conclude that IL-1 modulates the activity of these extracellular signal-regulated kinase/microtubule-associated protein-2 kinases by altering the level of their phosphorylation.
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PMID:Interleukin-1 represents a new modality for the activation of extracellular signal-regulated kinases/microtubule-associated protein-2 kinases. 165 5

PLC/PRF/5 human hepatoma cells cultured with teleocidin reduced the rate of cell proliferation and were transformed into large cells with many vacuole-like subcellular structures. In these vacuolated cells, the protein content per cell increased without changing the total cellular protein synthesis. Cytokeratin was one of the proteins which increased quantitatively. This intermediate filament formed fibrous network structures throughout the enlarged cytoplasm. The assembly of other cytoskeletal proteins such as actin, tubulin, and vimentin was not altered remarkably, suggesting that teleocidin morphologically transformed the hepatoma cells by changing the assembly of cytokeratin protein selectively. On the other hand, the alterations of cell proliferation, cell morphology, and cytokeratin assembly induced by teleocidin were not associated with either down-regulation of protein kinase C or reduced number of epidermal growth factor receptors. In addition, these teleocidin effects were not mimicked by the protein kinase C agonist 1-oleoyl-2-acetylglycerol or inhibited by the protein kinase C inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine. From these results it can be speculated that the morphological transformation and reduced cell proliferation induced by teleocidin may be mediated by still unknown mechanisms unrelated to protein kinase C.
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PMID:Vacuole formation and cytokeratin rearrangement of hepatoma cells induced by teleocidin are not associated with down-regulation of protein kinase C. 170 98

We applied Southwestern and Western blotting and gel retardation techniques to investigate the changes that occur in the cyclic adenosine monophosphate (cAMP)-responsive element (CRE) binding (CREB) proteins in rapidly growing, chemically induced 5123tc and 5123D Morris hepatomas. Using the CRE sequences from the c-fos, E2A, and somatostatin gene promoters, we identified in the nuclear proteins from normal unstimulated or proliferating rat liver cells six different protein factors of Mr 34,000, 36,000, 40,000, 47,000, 56,000, and 72,000 capable of binding to the element. The Mr 47,000 protein had the highest specificity for the core CRE, suggesting its importance in cAMP-mediated gene expression. We could not find the Mr 47,000 CREB protein in the 5123tc and 5123D hepatomas. Our efforts to detect this protein in the tumors by (a) using the CRE sequence from different gene promoters, (b) altering the protocol for extracting nuclear proteins, or (c) attempting to restore its DNA-binding property by phosphorylation [with endogenous protein kinase(s), a catalytic subunit of cAMP-dependent protein kinase, and protein kinase C/dephosphorylation (with alkaline phosphatase)] were unsuccessful. The loss of tje Mr 47,000 CREB protein from solid tumors of the Morris hepatoma is likely to be related to the neoplastic properties of the tumor cell rather than to cell growth because the level of this protein remained unchanged during a 6-day period of liver regeneration. The nuclear extract from the Morris hepatoma that did not have the Mr 47,000 CRE-binding factor contained proteins immunologically related to the CREB, c-Jun, and c-Fos proteins. We conclude that the Mr 47,000 factor represents a distinct member of the CRE-binding protein family and that its absence from the hepatomas may lead to aberrant expression of cAMP-inducible genes.
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PMID:Changes in cyclic adenosine monophosphate-responsive element binding proteins in rat hepatomas. 182 83


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