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)

Peroxisome proliferator-activated receptor alpha (PPARalpha) is responsible for peroxisome proliferator-induced pleiotropic responses, including the development of hepatocellular carcinoma in rodents. However, it remains to be determined whether activation of PPARalpha only in hepatocytes is sufficient to induce hepatocellular carcinomas. To address this issue, transgenic mice were generated that target constitutively activated PPARalpha specifically to hepatocytes. The transgenic mice exhibited various responses that mimic wild-type mice treated with peroxisome proliferators, including significantly decreased serum fatty acids and marked induction of PPARalpha target genes encoding fatty acid oxidation enzymes, suggesting that the transgene functions in the same manner as peroxisome proliferators to regulate fatty acid metabolism. However, the transgenic mice did not develop hepatocellular carcinomas, even though they exhibited peroxisome proliferation and hepatocyte proliferation, indicating that these events are not sufficient to induce liver cancer. In contrast to the transgenic mice, peroxisome proliferators activate proliferation of hepatic non-parenchymal cells (NPCs). Thus, activation of hepatic NPCs and/or associated molecular events is an important step in peroxisome proliferators-induced hepatocarcinogenesis.
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PMID:Hepatocyte-restricted constitutive activation of PPAR alpha induces hepatoproliferation but not hepatocarcinogenesis. 1733 54

Nuclear receptors (NRs) are a superfamily of transcription factors whose genomic functions are known to be activated by lipophilic ligands, but little is known about how to deactivate them or how to turn on their nongenomic functions. One obvious mechanism is to alter the nuclear localization of the receptors. Here, we show that protein kinase C (PKC) phosphorylates a highly conserved serine (Ser) between the two zinc fingers of the DNA binding domain of orphan receptor hepatocyte nuclear factor 4alpha (HNF4alpha). This Ser (S78) is adjacent to several positively charged residues (Arg or Lys), which we show here are involved in nuclear localization of HNF4alpha and are conserved in nearly all other NRs, along with the Ser/threonine (Thr). A phosphomimetic mutant of HNF4alpha (S78D) reduced DNA binding, transactivation ability, and protein stability. It also impaired nuclear localization, an effect that was greatly enhanced in the MODY1 mutant Q268X. Treatment of the hepatocellular carcinoma cell line HepG2 with PKC activator phorbol 12-myristate 13-acetate also resulted in increased cytoplasmic localization of HNF4alpha as well as decreased endogenous HNF4alpha protein levels in a proteasome-dependent fashion. We also show that PKC phosphorylates the DNA binding domain of other NRs (retinoic acid receptor alpha, retinoid X receptor alpha, and thyroid hormone receptor beta) and that phosphomimetic mutants of the same Ser/Thr result in cytoplasmic localization of retinoid X receptor alpha and peroxisome proliferator-activated receptor alpha. Thus, phosphorylation of this conserved Ser between the two zinc fingers may be a common mechanism for regulating the function of NRs.
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PMID:Phosphorylation of a conserved serine in the deoxyribonucleic acid binding domain of nuclear receptors alters intracellular localization. 1738 49

Persistent infection of hepatitis C virus (HCV) can lead to a high risk for hepatocellular carcinoma (HCC). HCV core protein plays important roles in HCV-related hepatocarcinogenesis, because mice carrying the core protein exhibit multicentric HCCs without hepatic inflammation and fibrosis. However, the precise mechanism of hepatocarcinogenesis in these transgenic mice remains unclear. To evaluate whether the core protein modulates hepatocyte proliferation and apoptosis in vivo, we examined these parameters in 9- and 22-month-old transgenic mice. Although the numbers of apoptotic hepatocytes and hepatic caspase 3 activities were similar between transgenic and nontransgenic mice, the numbers of proliferating hepatocytes and the levels of numerous proteins such as cyclin D1, cyclin-dependent kinase 4 and c-Myc, were markedly increased in an age-dependent manner in the transgenic mice. This increase was correlated with the activation of peroxisome proliferator-activated receptor alpha (PPARalpha). In these transgenic mice, spontaneous and persistent PPARalpha activation occurred heterogeneously, which was different from that observed in mice treated with clofibrate, a potent peroxisome proliferator. We further demonstrated that stabilization of PPARalpha through a possible interaction with HCV core protein and an increase in nonesterified fatty acids, which may serve as endogenous PPARalpha ligands, in hepatocyte nuclei contributed to the core protein-specific PPARalpha activation. In conclusion, these results offer the first suggestion that HCV core protein induces spontaneous, persistent, age-dependent and heterogeneous activation of PPARalpha in transgenic mice, which may contribute to the age-dependent and multicentric hepatocarcinogenesis mediated by the core protein.
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PMID:Hepatitis C virus core protein induces spontaneous and persistent activation of peroxisome proliferator-activated receptor alpha in transgenic mice: implications for HCV-associated hepatocarcinogenesis. 1776 15

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a key regulator in hepatic lipid metabolism and a potential therapeutic target for dyslipidemia. However, in humans hepatic PPARalpha-regulated genes remain unclear. To investigate the effect of PPARalpha agonism on mRNA expressions of lipid metabolism-related genes in human livers, a potent PPARalpha agonist, KRP-101 (KRP), was used to treat the human hepatoma cell line, HepaRG cells. KRP did not affect AOX or L-PBE, which are involved in peroxisomal beta-oxidation. KRP increased L-FABP, CPT1A, VLCAD, and PDK4, which are involved in lipid transport or oxidation. However, the EC(50) values (114-2500 nM) were >10-fold weaker than the EC(50) value (10.9 nM) for human PPARalpha in a transactivation assay. To search for more sensitive genes, we determined the mRNA levels of apolipoproteins, apoA-I, apoA-II, apoA-IV, apoA-V, and apoC-III. KRP had no or little effect on apoA-I, apoC-III, and apoA-II. Interestingly, KRP increased apoA-IV (EC(50), 0.99 nM) and apoA-V (EC(50), 0.29 nM) with high sensitivity. We identified apoA-IV as a PPARalpha-upregulated gene in a study using PPARalpha siRNA. Moreover, when administered orally to dogs, KRP decreased the serum triglyceride level and increased the serum apoA-IV level in a dose-dependent manner. These findings suggest that apoA-IV, newly identified as a highly sensitive PPARalpha-regulated gene in human livers, may be one of the mechanisms underlying PPARalpha agonist-induced triglyceride decrease and HDL elevation.
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PMID:Highly sensitive upregulation of apolipoprotein A-IV by peroxisome proliferator-activated receptor alpha (PPARalpha) agonist in human hepatoma cells. 1790 33

Dehydroepiandrosterone (DHEA), a C19 human adrenal steroid, activates peroxisome proliferator-activated receptor alpha (PPARalpha) in vivo but does not ligand-activate PPARalpha in transient transfection experiments. We demonstrate that DHEA regulates PPARalpha action by altering both the levels and phosphorylation status of the receptor. Human hepatoma cells (HepG2) were transiently transfected with the expression plasmid encoding PPARalpha and a plasmid containing two copies of fatty acyl coenzyme oxidase (FACO) peroxisome-proliferator activated receptor responsive element consensus oligonucleotide in a luciferase reporter gene. Nafenopin treatment increased reporter gene activity in this system, whereas DHEA treatment did not. Okadaic acid significantly decreased nafenopin-induced reporter activity in a concentration-dependent manner. Okadaic acid treatment of primary rat hepatocytes decreased both DHEA- and nafenopin-induced FACO activity in primary rat hepatocytes. DHEA induced both PPARalpha mRNA and protein levels, as well as PP2A message in primary rat hepatocytes. Western blot analysis showed that the serines at positions 12 and 21 were rapidly dephosphorylated upon treatment with DHEA and nafenopin. Results using specific protein phosphatase inhibitors suggested that protein phosphatase 2A (PP2A) is responsible for DHEA action, and protein phosphatase 1 might be involved in nafenopin induction. Mutation of serines at position 6, 12, and 21 to an uncharged alanine residue significantly increased transcriptional activity, whereas mutation to negative charged aspartate residues (mimicking receptor phosphorylation) decreased transcriptional activity. DHEA action involves induction of PPARalpha mRNA and protein levels as well as increased PPARalpha transcriptional activity through decreasing receptor phosphorylation at serines in the AF1 region.
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PMID:Modulation of receptor phosphorylation contributes to activation of peroxisome proliferator activated receptor alpha by dehydroepiandrosterone and other peroxisome proliferators. 1807 79

A uniquely formulated soy phospholipid, phosphatidylinositol (PI), is under development as a therapeutic agent for increasing plasma high-density lipoprotein (HDL) levels. Soy PI has been shown to increase plasma HDL and apolipoprotein A-I (apoA-I) levels in phase I human trials. Low micromolar concentrations of PI increase the secretion of apoA-I in model human hepatoma cell lines, through activation of G-protein and mitogen-activated protein (MAP) kinase pathways. Experiments were undertaken to determine the importance of the PI head group and acyl chain composition on hepatic apoA-I secretion. Phospholipids with choline and inositol head groups and one or more linoleic acid (LA) acyl chains were shown to stimulate apoA-I secretion by HepG2 cells and primary human hepatocytes. Phospholipids containing two LA groups (dilinoleoylphosphatidylcholine, DLPC) were twice as active as those with only one LA group and promoted a 4-fold stimulation in apoA-I secretion. Inhibition of cytosolic phospholipase A2 with pyrrolidine 1 (10 microM) resulted in complete attenuation of PI- and DLPC-induced apoA-I secretion. Pretreatment with the peroxisome proliferator-activated receptor alpha (PPARalpha) inhibitor MK886 (10 microM) also completely blocked PI- and DLPC-induced apoA-I secretion. Hepatic PPARalpha expression was significantly increased by both PI and DLPC. However, in contrast to that seen with the fibrate drugs, PI caused minimal inhibition of catalytic activities of cytochrome P450 and UGT1A1 enzymes. These data suggest that LA-enriched phospholipids stimulate hepatic apoA-I secretion through a MAP kinase stimulation of PPARalpha. LA-enriched phospholipids have a greater apoA-I secretory activity than the fibrate drugs and a reduced likelihood to interfere with concomitant drug therapies.
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PMID:Linoleic acid-enriched phospholipids act through peroxisome proliferator-activated receptors alpha to stimulate hepatic apolipoprotein A-I secretion. 1818 24

Phosphatidylcholine (PC) is synthesized through the Kennedy pathway, but more than 50% of PC is remodeled through the Lands cycle, i.e. the deacylation and reacylation of PC to attain the final and proper fatty acids within PC. The reacylation step is catalyzed by lysophosphatidylcholine acyltransferase (LPCAT), and we report here the identification of a novel LPCAT, which we named LPCAT3. LPCAT3 belongs to the membrane-bound O-acyltransferase (MBOAT) family and encodes a protein of 487 amino acids with a calculated molecular mass of 56 kDa. Membranes from HEK293 cells overexpressing LPCAT3 showed significantly increased LPCAT activity as assessed by thin layer chromatography analysis with substrate preference toward unsaturated fatty acids. LPCAT3 is localized within the endoplasmic reticulum and is primarily expressed in metabolic tissues including liver, adipose, and pancreas. In a human hepatoma Huh7 cells, RNA interference-mediated knockdown of LPCAT3 resulted in virtually complete loss of membrane LPCAT activity, suggesting that LPCAT3 is primarily responsible for hepatic LPCAT activity. Furthermore, peroxisome proliferator-activated receptor alpha agonists dose-dependently regulated LPCAT3 in liver in a peroxisome proliferator-activated receptor alpha-dependent fashion, implicating a role of LPCAT3 in lipid homeostasis. Our studies identify a long-sought enzyme that plays a critical role in PC remodeling in metabolic tissues and provide an invaluable tool for future investigations on how PC remodeling may potentially impact glucose and lipid homeostasis.
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PMID:Identification and characterization of a major liver lysophosphatidylcholine acyltransferase. 1819 19

The nuclear hormone receptors hepatocyte nuclear factor 4 (HNF4) and retinoid X receptor alpha (RXRalpha) plus peroxisome proliferator-activated receptor alpha (PPARalpha) heterodimer support hepatitis B virus (HBV) pregenomic RNA synthesis and viral replication in nonhepatoma cells. Small heterodimer partner (SHP), an orphan nuclear hormone receptor lacking a DNA binding domain, inhibits nuclear hormone receptor-mediated viral transcription and replication. The inhibition of HBV replication by SHP is dependent on the presence of nuclear hormone receptors. HBV replication that is dependent on HNF4 is considerably more sensitive to SHP-mediated inhibition than RXRalpha/PPARalpha-directed viral biosynthesis. SHP inhibition of HBV biosynthesis in HepG2 cells suggests that multiple nuclear hormone receptors mediate viral replication in this human hepatoma cell line. These observations suggest that the physiological regulation of HBV biosynthesis by SHP in the liver will depend on both the level of SHP expression and the relative contribution of HNF4 and RXRalpha/PPARalpha, plus potentially additional nuclear hormone receptors, to HBV RNA synthesis and replication.
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PMID:Differential inhibition of nuclear hormone receptor-dependent hepatitis B virus replication by the small heterodimer partner. 1823 86

The peroxisome proliferator-activated receptor alpha (PPARalpha) belongs to the nuclear receptor family and plays a central role in the regulation of lipid metabolism, glucose homeostasis and inflammatory processes. In addition to its ligand-induced activation, PPARalpha is regulated by phosphorylation via ERK-MAPK, PKA and PKC. In this study we examined the effect of p38-MAPK on PPARalpha transcriptional activity. In COS-7 cells, anisomycin, a p38 activator, induced a dose-dependent phosphorylation of PPARalpha and a 50% inhibition of its transcriptional activity. In H4IIE hepatoma cells, anisomycin-induced p38 phosphorylation decreased both endogenous and PPARalpha ligand-enhanced L-CPTI and ACO gene expression. Interestingly, PPARalpha/p38 interaction required the molecular adapter ZIP/p62. Reducing ZIP/p62 expression by siRNA, partially reversed the inhibitory effect of anisomycin on L-CPTI gene expression. In conclusion, we showed that p38 activation induced PPARalpha phosphorylation and inhibition of its transcriptional activity through a trimeric interaction between p38-MAPK, ZIP/p62 and PPARalpha.
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PMID:Involvement of ZIP/p62 in the regulation of PPARalpha transcriptional activity by p38-MAPK. 1837 65

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a member of the nuclear receptor family of ligand-activated transcription factors. It plays an important role in the regulation of genes involved in lipid metabolism and transport. Compound A is a potent and orally active PPARalpha agonist that activated both human and rat PPARalpha receptors. The compound induced the expression of genes involved in fatty acid metabolism in a rodent hepatoma cell line and in the liver of db/db mouse. The ability of compound A to stimulate fatty acid beta-oxidation was demonstrated in human hepatocytes and human skeletal muscle cells, which confirmed a functional activation of PPARalpha-mediated activities. Compound A was shown to be a more potent and efficacious antidyslipidemic agent in atherogenic rat and db/db mouse models as compared with fenofibrate. The increase in high-density lipoprotein cholesterol levels by compound A was at least partially due to an increase in serum apolipoprotein A-I protein concentrations in human PPARalpha transgenic mouse. The triglyceride-lowering effect was further confirmed in a higher species, obese dog models. In addition, compound A dose-dependently ameliorated hyperglycemia and hyperinsulinemia, and improved glucose tolerance in db/db mice. In a diet-induced obesity mouse model, compound A decreased body weight mainly by increasing energy expenditure and reducing fat deposition. In conclusion, the novel and potent PPARalpha agonist improves lipid profile, insulin sensitivity, and energy balance in animal models.
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PMID:Improvement of dyslipidemia, insulin sensitivity, and energy balance by a peroxisome proliferator-activated receptor alpha agonist. 1894 Mar 88


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