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)

In KB epidermoid cells, we previously showed that interleukin-1 alpha (IL-1) and various mitogens activate the mitogen-activated protein (MAP) kinases ERK1 and ERK2, which phosphorylate both myelin basic protein (MBP) and a peptide containing Thr669 of the epidermal growth factor receptor. In cell-free extracts made from gingival fibroblasts treated with platelet-derived growth factor or HepG2 hepatoma cells stimulated with phorbol myristate acetate, MBP and Thr669 kinase were both elevated 4-fold, and ERK1 and ERK2 were tyrosine-phosphorylated. In these cells IL-1 activated a kinase(s) that phosphorylated Thr669 peptide but not MBP and failed to cause tyrosine phosphorylation of ERK1/ERK2. Ceramide has been proposed as an intracellular mediator of IL-1 action, but C2-ceramide or sphingosine stimulated predominantly MBP-specific kinase activity in fibroblasts and had no effect in HepG2 cells. p54 MAP kinase (also called stress-activated protein kinase) is a c-Jun kinase first isolated from livers of cycloheximide-treated rats. After IL-1 stimulation, immunoprecipitates of lysates made from all three cell types with specific anti-p54 MAP kinase serum contained Thr669 and c-Jun phosphorylating activity, whereas precipitates from unstimulated cells contained no detectable p54 kinase activity. The major peak of IL-1-stimulated HepG2 Thr669 kinase activity co-chromatographed on Mono Q and phenyl-Superose with immunodetectable p54 MAP kinase. IL-1 did not cause p21ras activation in any cell type. Induction of Thr 669 kinase activity was not abrogated by elevation of cAMP levels, which has been shown to interfere with the activation of Raf-1. We could not detect MAP kinase kinase phosphorylating activity in unfractionated lysates made from IL-1-stimulated fibroblasts or HepG2 cells. KB cells contained a small amount of this activity, but it was not precipitated with an anti-Raf-1 antibody. We conclude that most of the IL-1-activated Thr669 kinase activity in fibroblasts and HepG2 cells, and a portion in KB cells, is due to p54 MAP kinase and that its activation is Ras-, Raf-, and MAP kinase kinase-independent.
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PMID:Interleukin-1 activates p54 mitogen-activated protein (MAP) kinase/stress-activated protein kinase by a pathway that is independent of p21ras, Raf-1, and MAP kinase kinase. 752 98

p44erk1 is a member of a family of tyrosyl-phosphorylated and mitogen-activated protein (MAP) kinases that participate in cell cycle control. A full-length erk1 cDNA was isolated from a human hepatoma cell line (Hep G2) library. The erk1 cDNA clone shared approximately 96% predicted amino acid identity with partial sequences of rodent erk1 cognates, and the erk1 gene was assigned to human chromosome 16 by hybrid panel analysis. Human erk1 expressed in Escherichia coli as a glutathione S-transferase fusion (GST-Erk1) protein was substantially phosphorylated on tyrosine in vivo. It underwent further autophosphorylation in vitro (up to 0.01 mol of P per mol) at the regulatory Tyr-204 site and at additional tyrosine and serine residues. Threonine autophosphorylation, presumably at the regulatory Thr-202 site, was also detected weakly when the recombinant kinase was incubated in the presence of manganese, but not in the presence of magnesium. Before and after cleavage of the GST-Erk1 protein with thrombin, it exhibited a relatively high level of myelin basic protein phosphotransferase activity, which could be reduced eightfold by treatment of the kinase with the protein-tyrosine phosphatase CD45, but not by treatment with the protein-serine/threonine phosphatase 2A. The protein-tyrosine kinase p56lck catalyzed phosphorylation of GST-Erk1 at two autophosphorylations sites, including Tyr-204, and at a novel site. A further fivefold stimulation of the myelin basic protein phosphotransferase activity of the GST-Erk1 was achieved in the presence of a partially purified MAP kinase kinase from sheep platelets. Under these circumstances, there was primarily an enhancement of the tyrosine phosphorylation of GST-Erk1. This MAP kinase kinase also similarly phosphorylated a catalytically compromised version of GST-Erk1 in which Lys-71 was converted to Ala by site-directed mutagenesis.
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PMID:Molecular cloning, expression, and characterization of the human mitogen-activated protein kinase p44erk1. 768 43

The P-glycoprotein (Pgp) reversing agent, reserpine, induces MDR1 mRNA and PGP protein in human colon carcinoma cells (Schuetz, E. G., Beck, W. T., and Schuetz, J. D. (1996) Mol. Pharmacol. 49, 311-318) and in H35 rat hepatoma cells. Reserpine's interference with cellular dopamine utilization suggested that dopamine and dopaminergics might be important physiological regulators of PGP expression. Initial studies demonstrated that the H35 cells express the D2 dopamine receptor. Pgp protein and pgp2/mdr1b mRNA was increased (maximum of 10- and 8-fold, respectively) by the potent D2 dopamine receptor agonists bromocriptine, R(-)-propylnorapomorphine hydrochloride, and quinpirole, and Pgp protein induction was blocked by D2 receptor antagonists spiperone and clozapine. D2 receptor agonist induction of pgp2/mdr1b mRNA was paralleled by transcriptional activation of the pgp2/mdr1b promoter but blocked by pretreatment with the D2 dopamine receptor antagonists, spiperone, eticlopride, and clozapine. Co-transfection of a D2 dopamine receptor expression vector enhanced bromocriptine's transcriptional activation of the pgp2/mdr1b promoter. The G-protein, Galphai2, is required for bromocriptine transcriptional activation because the G-protein inhibitor, pertussis toxin, suppressed bromocriptine's activation of pgp2/mdr1b transcription and co-transfection of a dominant negative Galphai2 abrogated bromocriptine activation of pgp2/mdr1b. Gi proteins can transduce signals by activation of mitogen-activated protein kinases (MAPKs), and because Raf-1 is a known activator of MDR1, we tested for Raf-1 involvement. Co-transfection of a dominant negative Raf-1 failed to block bromocriptine induction of pgp2/mdr1b, and bromocriptine treatment caused no phosphorylation of the MAP kinase kinase substrates p42 and p44, demonstrating that the MAP kinase pathway was not involved. These are the first studies demonstrating transcriptional activation of an MDR gene by dopamine receptor agonists and that this activation occurs by a signal transduction pathway requiring the D2 dopamine receptor coupled to a functional G-protein.
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PMID:Bromocriptine transcriptionally activates the multidrug resistance gene (pgp2/mdr1b) by a novel pathway. 911 Oct 66

After insulin receptor activation, many cytoplasmic enzymes, including mitogen-activated protein (MAP) kinase, MAP kinase kinase (MEK) and casein kinase II (CKII) are activated, but exactly how insulin signalling progresses to the nucleus remains poorly understood. In Chinese hamster ovary cells overexpressing human insulin receptors [CHO(Hirc)], MEK, CKII and the MAP kinases ERK I and ERK II can be detected by immunoblotting in the nucleus, as well as in the cytoplasm, in the unstimulated state. Nuclear localization of MAP kinase is also observed in 3T3-F442A adipocytes, NIH-3T3 cells and Fao hepatoma cells, whereas MEK is found in the nucleus only in Fao and CHO cells. Insulin treatment for 5-30 min induces a translocation of MEK from the cytoplasm to the nucleus, whereas the MAP kinases and CKII are not translocated into the nucleus in response to insulin during this period. However, nuclear MAP kinase and CKII activities increase by 2-3-fold within 1-10 min after stimulation with insulin. By using gel-shift assays, it has been shown that insulin also stimulates nuclear protein binding to an AP-1 site with kinetics similar to MEK translocation and MAP kinase and CKII activation. Treatment of the extracts in vitro with protein phosphatase 2A or treatment of the intact cells with 5, 6-dichloro-1-beta-d-ribofuranosylbenzimidazole, a cell-permeable inhibitor of CKII, almost completely blocks the insulin-induced DNA-binding activity, whereas incubation of cells with a MEK inhibitor produces only a slight decrease. These results suggest that insulin signalling results in the activation of serine kinases in the nucleus via two pathways: (1) insulin stimulates the nuclear translocation of some kinases, such as MEK, which might directly phosphorylate nuclear protein substrates or activate other nuclear kinases, and (2) insulin activates nuclear kinases without translocation. The latter is true of CKII, which seems to regulate the binding of nuclear proteins to the AP-1 site, possibly by phosphorylation of AP-1 transcription factors.
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PMID:Insulin regulation of mitogen-activated protein kinase kinase (MEK), mitogen-activated protein kinase and casein kinase in the cell nucleus: a possible role in the regulation of gene expression. 916 93

The sarcomatoid cells found in cholangiocarcinoma (CC) or hepatocellular carcinoma (HCC) are not well characterized. In this study, a human sarcomatoid CC cell line, ETK-1, was established from a patient, and then morphological and phenotypical characteristics of the ETK-1 cells were evaluated before and after treatment with differentiation-inducing 5-azacytidine (5-azaCR). Phenotypically, the ETK-1 cells appeared immature. Exposure to 5-azaCR induced morphological transformation; a converted cell line, MEK, was successfully established. The MEK cells expressed such hepatocyte-specific proteins as alpha-fetoprotein, albumin, integrin alpha1, and thrombopoietin, but lost such bile duct-specific proteins as integrin alpha3 and integrin beta4. The histopathology of MEK xenografts resembled that of HCC. The ETK-1 cells appeared to be converted into hepatocytes by exposure to 5-azaCR. On the other hand, ETK-1 xenografts were diagnosed as tubular adenocarcinoma, and the tumor cells had a ductal phenotype. This suggests the possibility that ETK-1 cells can differentiate along a biliary epithelial cell lineage. ETK-1 and MEK will be useful in studying hepatocytic differentiation and the transformation from a biliary epithelial cell to a hepatocytic lineage.
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PMID:Hepatocytic phenotypes induced in sarcomatous cholangiocarcinoma cells treated with 5-azacytidine. 925 36

The signaling pathway involved in low density lipoprotein (LDL) receptor gene expression induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was investigated in the human hepatoma HepG2 cell line. Treatment of HepG2 cells with 100 nM TPA resulted in an approximately 20-fold increase in LDL receptor mRNA level, as determined by RT-PCR, which peaked at 2-4 h of treatment and subsequently declined. The protein kinase C (PKC) inhibitors calphostin C and staurosporine prevented TPA-mediated LDL receptor mRNA induction. In contrast, TPA did not affect squalene synthase mRNA expression. Immunoblotting of cell extracts with isozyme-specific PKC antibodies revealed that HepG2 cells expressed PKC alpha, which was mainly cytosolic, and PKC beta, PK epsilon, and PKC zeta, all of which were present in both the cytosolic and particulate fractions. Treatment of HepG2 cells with 100 nM TPA resulted in translocation of cytosolic PKC alpha to the particulate fraction, with a maximum at 30 min-2 h of treatment, but was without effect on the subcellular distribution of the other isozymes. TPA treatment also led to activation of the mitogen-activated protein kinase (MAPK) ERK cascade. The specific MAPK pathway inhibitor PD98059 blocked TPA-induced ERK activation. Furthermore, pretreatment of cells with PD98059 inhibited TPA-induced LDL receptor mRNA induction. Moreover, pretreatment of cells with calphostin C inhibited TPA-mediated ERK activation and LDL receptor mRNA induction in a dose-dependent fashion. Based on a close kinetic correlation between PKC alpha translocation and ERK activation, and the effects of specific inhibitors, these findings suggest that translocation/activation of PKC alpha, and subsequent activation of the Raf-1/MEK/ERK MAPK cascade, represent key events in the transcriptional induction of LDL receptor gene by TPA in HepG2 cells.
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PMID:Phorbol ester-induced low density lipoprotein receptor gene expression in HepG2 cells involves protein kinase C-mediated p42/44 MAP kinase activation. 939 22

Phosphoenolpyruvate carboxykinase (PEPCK) catalyzes the first committed step in hepatic gluconeogenesis. Glucagon and glucocorticoids stimulate PEPCK gene transcription, whereas insulin has a dominant inhibitory effect. We have shown that inhibitors of 1-phosphatidylinositol 3-kinase (PI 3-kinase) block this action of insulin. In contrast, three distinct agents, all of which prevent activation of p42/p44 mitogen-activated protein (MAP) kinase, have no effect on the regulation of PEPCK transcription by insulin. However, a subsequent report has suggested that this pathway is involved in the inhibition of cAMP-induced PEPCK gene transcription by insulin. To address these conflicting data, we re-examined the Ras MAP kinase pathway, not only with respect to regulation of PEPCK gene transcription, but also for regulation of PI 3-kinase and p42/p44 MAP kinase. Overexpression of constitutively active Ras (V61) (or Raf-1 (RafCAAX)) partially represses PEPCK transcription in hepatoma cells. However, an inhibitor of MAP kinase kinase blocks this action of RafCAAX but has no effect on regulation of PEPCK gene transcription by insulin. Second, the action of a dominant negative Ras (N17Ras) on PEPCK gene transcription correlates more closely with the inhibition of PI 3-kinase than with the inhibition of p42/p44 MAP kinase. Third, insulin cannot activate p42/p44 MAP kinase in the presence of cAMP even though cAMP-induced PEPCK gene transcription is inhibited by insulin. This data confirms that the Ras MAP kinase pathway is not required for the regulation of PEPCK gene transcription by insulin and demonstrates the importance of employing multiple techniques when investigating the function of signaling pathways.
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PMID:Activation of the ras mitogen-activated protein kinase-ribosomal protein kinase pathway is not required for the repression of phosphoenolpyruvate carboxykinase gene transcription by insulin. 945 31

Guanine nucleotide regulatory proteins (G-proteins) represent an important transmembrane pathway whereby extra-cellular signals are transduced to intracellular signaling pathways. The mitogen-activated protein kinase (MAPK) cascade has been identified as a key factor in transducing numerous mitogenic stimuli. MAPK activity is regulated via numerous receptor types, including those linked to Gq/G11-proteins, which regulate phospholipase-C activity. We hypothesized that alterations in a Gq/G11-PLC pathway may contribute to the enhanced cellular mitogenesis characteristic of hepatocellular carcinoma (HCC), possibly via a MAPK-dependent pathway. By using an in vivo model of HCC we investigated changes in Gq/G11-protein expression in tumorigenic tissue versus adjacent, non-neoplastic liver. In addition we addressed the role of Gq/G11-proteins in the regulation of MAPK-linked mitogenesis by using rat hepatic tumorigenic cells (H4IIE) and isolated hepatocytes in culture. Western blot analysis showed significant increases in Gqalpha and G11alpha expression in tumorigenic liver versus normal liver specimens, an effect that was augmented in cultured H4IIE cells versus isolated cultured hepatocytes. Furthermore, phosphoinositol specific phospholipase-C (PLC) activity was significantly increased in HCC versus normal liver. A specific PLC inhibitor (Et-18-OCH3) caused a dose-dependent decrease in serum stimulated DNA synthesis in both cultured H4IIE cells and isolated rat hepatocytes, the H4IIE cell line showing greater sensitivity to Et-18-OCH3. In addition, serum-stimulated MAPK activity was significantly enhanced in H4IIE versus cultured hepatocytes. Moreover, treatment with Et-18-OCH3 significantly attenuated serum stimulated MAPK activity in both cultured hepatocytes and H4IIE cells. Furthermore, U73122 (Gqalpha-PLC specific uncoupler) and GP2A (Gqalpha specific inhibitor) mirrored the effects of those observed for Et-18-OCH3 whereas PD98059 (specific MEK inhibitor) completely abolished serum-stimulated DNA synthesis in tumorigenic H4IIE cells. We conclude that HCC is associated with enhanced Gq/G11-PLC expression/activity as compared with normal liver. Furthermore, a PLC-linked MAPK cascade plays a significant role in the progression of the enhanced mitogenesis characteristic of HCC.
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PMID:Altered Gq/G11 guanine nucleotide regulatory protein expression in a rat model of hepatocellular carcinoma: role in mitogenesis. 991 12

Using the differential display polymerase chain reaction osmosensitive regulation of mRNA levels of the nucleolar phosphoprotein of 140 kDa (Nopp140) was found in H4IIE rat hepatoma cells. These levels were downregulated after hypoosmotic exposure in H4IIE cells and primary rat hepatocytes. Hyperosmotic incubation increased Nopp140 mRNA levels in H4IIE cells but not in hepatocytes. Inhibition of p38MAPK or MAP kinase kinase upstream of Erk-1 and Erk-2 decreased Nopp140 mRNA levels but did not prevent their osmosensitivity. Because Nopp140 is involved in the regulation of transcriptional activity it could play a role in the osmosignalling pathway towards gene expression in H4IIE cells and hepatocytes.
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PMID:Anisoosmotic regulation of the Nopp140 mRNA in H4IIE rat hepatoma cells and primary hepatocytes. 1038 2

The proliferation and metabolism of H4IIE hepatoma cells is apparently mediated through the insulin receptor. These cells, however, also have high-affinity binding sites for insulin-like growth factor-I (IGF-I). Addition of insulin to H4IIE cells increased RNA synthesis, DNA synthesis and cell number. IGF-I, on the other hand, was ineffective at concentrations equivalent to the lowest effective insulin dose, although stimulation was observed with concentrations 100-fold higher. Similar results were obtained when glucose uptake was measured. Western blot analysis demonstrated that tyrosine phosphorylation patterns produced by insulin and IGF-I differed. In particular, phosphorylation of insulin receptor substrate-1 (IRS-1) was evident after treatment with insulin, but not after treatment with IGF-I. Correspondingly, insulin, but not IGF-I, stimulated receptor tyrosine kinase activity. In contrast with these results, both insulin and IGF-I induced mitogen-activated protein (MAP) kinase phosphorylation and activity at a concentration of 10 nM. The correlation between insulin-dependent and IGF-I-dependent MAP kinase activation was confirmed by Western blot analysis of phosphorylated MAP kinase kinase (MEK). These results suggest that phosphorylation of IRS-1 is essential for both cell proliferation and glucose metabolism, but is uncoupled from the MAP kinase cascade. Furthermore, stimulation of MEK and MAP kinase is independent of receptor tyrosine kinase activity.
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PMID:Insulin-like growth factor-I (IGF-I)-dependent activation of pp42/44 mitogen-activated protein kinase occurs independently of IGF-I receptor kinase activation and IRS-1 tyrosine phosphorylation. 1058 12


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