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)

The subcellular distribution and regulation of MAP kinase isoforms in chicken hepatoma DU249 cells was investigated with antibodies directed against peptides patterned after sequences in the mitogen-activated protein (MAP) kinases, sea star p44mpk, and rat p44erk1. MonoQ chromatography of cytosol from these cells afforded the resolution of at least four peaks of myelin basic protein (MBP) phosphotransferase activity, but only one of these (peak II) was stimulated in extracts from phorbol ester-treated cells. A 40- to 41-kDa (p41) doublet on Western blots detected with three different MAP kinase antibodies was coincident with peak II, and it probably corresponded to the avian homolog of p42mapk/erk2. Immunofluorescent studies with DU249 cells and chicken embryo fibroblasts revealed that most of the cross-reactive protein with at least two different MAP kinase antibodies was distributed in the nucleus. Subcellular fractionation studies confirmed a predominantly nuclear localization for p41 MAP kinase. Nocodazole arrest of DU249 cells was exploited for the detection of an M-phase-activated MBP kinase that was resolved from p41 MAP kinase by phenyl-Superose chromatography. Western blotting analysis with antibodies for the cdc2-encoded protein kinase and p13suc1-agarose binding studies allowed positive identification of this MBP kinase as p34cdc2.
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PMID:Immunological characterization of avian MAP kinases: evidence for nuclear localization. 132 21

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

Chromium is an important industrial metal, an environmental pollutant, and a human carcinogen. To investigate the mechanisms of chromium-induced carcinogenesis, activation of mitogen-activated protein (MAP) kinases ERK1 and ERK2 was examined in rat hepatoma cells following exposure to hexavalent chromium (Cr(VI)). Cr(VI) was found to activate both forms of MAP kinase in a dose- and time-dependent manner. In contrast to the protein kinase C (PKC) agonist, phorbol 12-myristate 13-acetate, which induced a transient activation of MAP kinases, Cr(VI) caused persistent activation of these enzymes. Furthermore, unlike phorbol 12-myristate 13-acetate, the ability of chromium to activate MAP kinases was found to be independent of PKC since chromium-induced MAP kinase activation occurred in PKC-depleted cells. Stimulation of ERK1 and ERK2 was associated with the ability of Cr(VI) to increase cellular peroxide levels as determined using the H2O2-sensitive fluorescent probe 2',7'-dichlorofluorescein diacetate and flow cytometry. Furthermore, the activation of these kinases by chromium was enhanced in cells treated with the glutathione-depleting agent, L-buthionine-[S,R]-sulfoximine, and attenuated in cells pretreated with an agent that elevates cellular levels of glutathione (i.e., N-acetyl-L-cysteine). The ability of chromium to modulate MAP kinase activity in this manner suggests a mechanism of chromium-induced carcinogenesis that involves the persistent stimulation of cellular regulatory pathways.
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PMID:Chromium induces a persistent activation of mitogen-activated protein kinases by a redox-sensitive mechanism in H4 rat hepatoma cells. 861 49

The mitogen-activated protein kinase (MAPK) cascade acts as a focal point for signal transduction following activation of both G-protein-linked and tyrosine kinase growth factor receptors. A common intermediate between both of these diverse receptor subtypes includes the small guanosine triphosphate (GTP)-binding protein, p21ras. Point mutations of p21ras have been identified in various tumor types and lead to constitutive activation of this protein and subsequent activation of downstream pathways including the MAPK cascade. Using an in vivo model of hepatocellular carcinoma (HCC), we investigated the abundance and function of individual components of the MAPK cascade and the presence of specific p21ras mutations in this model. Expression of components of the MAPK cascade were determined in tumor and adjacent, non-neoplastic liver specimens by Western blot analysis and functional activity confirmed by substrate phosphorylation assays. Mutations in p21ras were analyzed using an enzyme-linked immunosorbent assay. In tumor, extracellular regulated kinases (ERKs) ERK1, ERK2, and mitogen-activated ERK-regulated kinase-1 (MEK1) were elevated by three- to fourfold as compared with adjacent nontumorigenic normal liver. In contrast, MEK2 was elevated by only 28%. Substrate phosphorylation and detection of phosphorylated ERK1/2 proteins showed increased functional activity of these proteins of the same magnitude as that observed for protein expression. Mutations in p21ras were not detected in this experimental model of HCC. We conclude that HCC is associated with marked changes in expression and function of components of the MAPK cascade independent of common p21ras mutations.
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PMID:Altered expression of mitogen-activated protein kinases in a rat model of experimental hepatocellular carcinoma. 939 88

Peroxovanadiums (pVs) are potent protein tyrosine phosphatase (PTP) inhibitors with insulin-mimetic properties in vivo and in vitro. We have established the existence of an insulin receptor kinase (IRK)-associated PTP whose inhibition by pVs correlates closely with IRK tyrosine phosphorylation, activation, and downstream signaling. pVs have also been shown to activate various tyrosine kinases (TKs) that could participate in activation of the insulin-signaling pathway. In the present study we have sought to determine whether pV-induced IRK tyrosine phosphorylation requires the intrinsic kinase activity of the IRK, and whether IRK activation is necessary to realize the early steps in the insulin-signaling cascade. To address this we evaluated the effect of a pure pV compound, bis peroxovanadium 1,10-phenanthroline [bpV(phen)], in HTC rat hepatoma cells overexpressing normal (HTC-IR) or kinase-deficient (HTC-M1030) mutant IRKs. We showed that at a dose of 0.1 mM, but not 1 mM, bpV(phen) induced IRK-dependent events. Thus, 0.1 mM bpV(phen) increased tyrosine phosphorylation and IRK activity in HTC-IR but not HTC-M1030 cells. Tyrosine phosphorylation of insulin signal-transducing molecules was promoted in HTC-IR but not HTC-M1030 cells by bpV(phen). The association of p185 and p60 with the src homology-2 (SH2) domains of Syp and the p85-regulatory subunit of phosphatidylinositol 3'-kinase was induced by bpV(phen) in HTC-IR, but not in HTC-M1030 cells, as was insulin receptor substrate-1-associated phosphatidylinositol 3'-kinase activity. Thus autophosphorylation and activation of the IRK by bpV(phen) is effected by the IRK itself, and the early events in the insulin- signaling cascade follow from this activation event. This establishes a critical role for PTP(s) in the regulation of IRK activity. bpV(phen) could be distinguished from insulin only in its ability to activate ERK1 in HTC-M1030 cells, thus indicating that this event is IRK independent, consistent with our previous hypothesis that bpV(phen) inhibits a PTP involved in the negative regulation of mitogen-activated protein kinases.
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PMID:Early signaling events triggered by peroxovanadium [bpV(phen)] are insulin receptor kinase (IRK)-dependent: specificity of inhibition of IRK-associated protein tyrosine phosphatase(s) by bpV(phen). 941 95

To examine the role of clathrin-dependent insulin receptor internalization in insulin-stimulated signal transduction events, we expressed a dominant-interfering mutant of dynamin (K44A/dynamin) by using a recombinant adenovirus in the H4IIE hepatoma and 3T3L1 adipocyte cell lines. Expression of K44A/dynamin inhibited endocytosis of the insulin receptor as determined by both cell surface radioligand binding and trypsin protection analysis. The inhibition of the insulin receptor endocytosis had no effect on either the extent of insulin receptor autophosphorylation or insulin receptor substrate 1 (IRS1) tyrosine phosphorylation. In contrast, expression of K44A/dynamin partially inhibited insulin-stimulated Shc tyrosine phosphorylation and activation of the mitogen-activated protein kinases ERK1 and -2. Although there was an approximately 50% decrease in the insulin-stimulated activation of the phosphatidylinositol 3-kinase associated with IRS1, insulin-stimulated Akt kinase phosphorylation and activation were unaffected. The expression of K44A/dynamin increased the basal rate of amino acid transport, which was additive with the effect of insulin but had no effect on the basal or insulin-stimulated DNA synthesis. In 3T3L1 adipocytes, expression of K44A/dynamin increased the basal rate of glucose uptake, glycogen synthesis, and lipogenesis without any significant effect on insulin stimulation. Together, these data demonstrate that the acute actions of insulin are largely independent of insulin receptor endocytosis and are initiated by activation of the plasma membrane-localized insulin receptor.
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PMID:Inhibition of clathrin-mediated endocytosis selectively attenuates specific insulin receptor signal transduction pathways. 963 70

The effects of the liver tumor promoters phenobarbital, clofibrate, dieldrin, and DDT on transforming growth factor-beta1 (TGFbeta)-induced apoptosis were studied in FTO-2B hepatoma cells. Inhibition of apoptosis by these compounds was strongly correlated with a decrease in CPP32-like caspase activity. Similar effects were obtained with insulin and dexamethasone. CPP32-like activity may thus provide a useful tool for quantiation of apoptosis under various treatment conditions. Diverse effects on apoptosis-associated cellular signaling proteins were observed: insulin led to an activation of the MAP kinases ERK1/2, of PKB/Akt and of NF-kappaB, phenobarbital and clofibrate enhanced NF-kappaB activity solely, while dexamethasone slightly enhanced NF-kappaB activity and increased the expression of Bcl-xL. Since inhibition of apoptosis was still detectable if the anti-apoptotic compounds were administered more than 10 h after TGFbeta, the diverse primary signals appear to converge at a presumably late stage of apoptosis, but upstream of activation of CPP32 or related caspases.
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PMID:Inhibition of transforming growth factor beta1-induced hepatoma cell apoptosis by liver tumor promoters: characterization of primary signaling events and effects on CPP32-like caspase activity. 1020 May 66

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

Insulin-like growth factor (IGF) binding protein-1 (IGFBP-1) is a 28-kDa plasma protein that binds to IGF-I and IGF-II with high affinity. IGFBP-1 is elevated in the blood as a result of sepsis, AIDS, excessive alcohol consumption, and diabetes and may, in part, be responsible for the wasting observed during these pathophysiological conditions. The liver is the principal site of IGFBP-1 synthesis, and we have previously shown that proinflammatory cytokines can directly stimulate IGFBP-1 secretion in a human hepatoma cell line (HepG2). The purpose of the present study was to investigate the role of the MAP kinase pathway in regulating IGFBP-1 synthesis by IL-1beta. We show that IL-1beta stimulates the phosphorylation of ERK-1 and -2 in a time- and dose-dependent manner. In addition, the MAP kinase-kinase MEK-1 and the ribosomal S6-kinase RSK-1 are also phosphorylated in response to IL-1beta. The transcription factor CREB, a potential substrate of both protein kinase A (PKA) and RSK-1, is phosphorylated in response to IL-1beta and cAMP in HepG2 cells. The ability of IL-1beta to stimulate the expression of IGFBP-1 and the phosphorylation of the above kinases was specifically inhibited by PD98059, a MEK-1 inhibitor. cAMP also stimulated IGFBP-1 synthesis, but PD98059 failed to block the cAMP effect. Conversely, a PKA inhibitor (H-89) inhibited the ability of cAMP, but not IL-1beta to stimulate IGFBP-1 synthesis. The effect of IL-1beta and cAMP on IGFBP-1 messenger RNA (mRNA) accumulation was additive. IL-1beta, cAMP, PD98059, and H-89 had similar effects on the accumulation of IGFBP-1 protein and mRNA. IL-1beta and cAMP did not change the half-life of IGFBP-1 mRNA, but PD98059 and SB202190, a p38 MAP kinase inhibitor, destabilized IGFBP-1 mRNA and blocked the phosphorylation of RSK-1 in response to IL-1beta. Our data demonstrate that the MAP kinase signal transduction pathway plays an important role in the regulation of IGFBP-1 synthesis by IL-1beta.
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PMID:Stimulation of insulin-like growth factor binding protein-1 synthesis by interleukin-1beta: requirement of the mitogen-activated protein kinase pathway. 1096 86


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