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 glycoprotein tissue-type plasminogen activator (t-PA) is subject to hepatic clearance in humans. Here, the interaction of t-PA with a well-differentiated hepatoma cell line (HepG2) was examined. Suspended HepG2 cells bound 125I-t-PA in a specific, saturable, and reversible fashion through a Ca(2+)-dependent, active site-independent mechanism. Binding isotherms indicated a high affinity system with a single class of saturable binding sites (Kd 39 nM; maximum binding capacity 493,000 sites per cell). Bound t-PA was rapidly degraded at 37 degrees C in a manner inhibited by lysosomotropic agents or metabolic inhibitors. Pretreatment of t-PA with monoclonal antibodies against the EGF/fibronectin finger domain, but not kringle 2 or kringle 1, reduced total binding by 86%. Binding of 125I-t-PA to HepG2 cells was inhibited by monosaccharides fucose and galactose and by the neoglycoprotein fucosyl-albumin. Enzymatic removal of alpha-fucose residues, but not alpha-galactose, high mannose, or complex oligosaccharide from 125I-t-PA, reduced specific binding by 60 +/- 5%. Binding was also inhibited by high, but not low, molecular weight urokinase, which contains an EGF-based threonine-linked alpha-fucose homologous to that of t-PA. These data suggest that EGF-associated O-linked alpha-fucose may mediate t-PA binding and degradation by HepG2 cells. This mechanism may be relevant to other proteins with analogous structures.
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PMID:alpha-Fucose-mediated binding and degradation of tissue-type plasminogen activator by HepG2 cells. 811 82

The transcription factor LFB1 (HNF1) involved in the expression of liver-specific genes is characterized by a serine/threonine-rich activation domain whose transactivation potential differs between mammals and Xenopus. Exchanging the activation domain between the Xenopus and rat LFB1, we produced chimeric transactivators whose activities are primarily determined by the origin of the activation domain. By replacing the serine/threonine-rich activation domain of LFB1 with the acidic activation domain of VP16, we generated transcription factors that act as dominant positive interfering mutants on endogenous LFB1 in differentiated hepatoma cells. As these LFB1/VP16 chimeras show no self-squelching as observed with wild-type LFB1 and increase the activity of saturating LFB1, we postulate that acidic and serine/threonine-rich activation domains use different targets of the basal transcription machinery. Stable transfection of various LFB1 derivatives, including those containing the VP16 transactivation domain, into the dedifferentiated C2 hepatoma cell resulted in cell clones stably expressing LFB1 function. However, as in none of these clones the chromosomal albumin genes are activated, we conclude that the presence of functional LFB1 may not be sufficient to reactivate liver-specific functions lost in dedifferentiated hepatoma cells.
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PMID:Chimeric liver transcription factors LFB1 (HNF1) containing the acidic activation domain of VP16 act as positive dominant interfering mutants. 839 59

We have cloned a cDNA for a novel GC box-binding protein designated BTEB2 from a human placenta cDNA library using rat BTEB cDNA (Imataka et al. (1992). EMBO J. 11,3663-3671. as a hybridization probe. BTEB2 consists of 219 amino acids and contains three contiguous zinc finger motifs at its C-terminus. The zinc finger domains showed 59% and 64% sequence similarity to those of Sp1 and BTEB, respectively. Adjacent to the N-terminal of the zinc finger motifs, a short sequence rich in basic amino acids is conserved between BTEB2 and Sp1. Furthermore, This basic sequence concurs with the N-terminal half of the consensus sequence for basic domains of the proteins containing both helix-loop-helix and leucine zipper motifs. The other region of BTEB2 is notably rich in proline, serine, threonine, and alanine residues. BTEB2 expressed in Escherichia coli showed DNA-binding activity whose specificity was closely similar to that of Sp1. Cotransfection experiments using Hepa-1 cells (a mouse hepatoma cell line) with a BTEB2 expression plasmid and GC box-containing reporter plasmids revealed that BTEB2 apparently activated the expression of the CAT activity. Moreover, when BTEB2 was fused to GAL4 DNA-binding domain, the chimeric protein could enhance the transcription through promoters containing GAL4-binding sites. Analysis of the BTEB2 mRNA by RNA blot analysis demonstrated that the mRNA was expressed specifically in testis and placenta with different sizes, 20S and 28S, respectively, among various organs examined.
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PMID:cDNA cloning and transcriptional properties of a novel GC box-binding protein, BTEB2. 847 2

The effect has been studied of various media, hormones and of amino acids on the membrane potential of rat hepatoma cells in culture measured by microelectrode impalement. Cells in Eagle's minimal essential medium plus 5% serum had a value which varied daily from about 5-8 mV, inside negative. The membrane potential of rat hepatocytes was measured to be 8.7 +/- 0.2 mV, inside negative. The membrane potential of the hepatoma cells was decreased by insulin and increased by glucagon. Membrane potential was unaffected by change of medium to Hanks' or Earle's balanced salt solutions or deprivation of serum. It was, however, reduced in cells in phosphate-buffered saline and by reduction of pH. The former effect was shown to be due to the higher [Na+] of phosphate-buffered saline as opposed to the other media. Addition of alanine, glycine, serine, proline and methylaminoisobutyrate all reduced membrane potential by 2-3 mV. Smaller decreases were seen with methionine, leucine and phenylalanine, but none with glutamine, threonine, BCH (2-aminonorborane-2-carboxylic acid) and D-alanine. The results are compared with the effects of similar conditions on aminoisobutyrate uptake. Whilst there was a correlation under some conditions there was not under others. It is concluded that for the hepatoma cells factors additional to the membrane potential must exert some influence on the capacity for amino acid transport.
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PMID:Membrane potential of rat hepatoma cells in culture: influence of factors affecting amino acid transport. 856 68

We have developed a useful strategy for identifying amino acid spin systems and side-chain carbon resonance assignments in small 15N-, 13C-enriched proteins. Multidimensional constant-time pulsed field gradient (PFG) HCC(CO)NH-TOCSY experiments provide side-chain resonance frequency information and establish connectivities between sequential amino acid spin systems. In PFG HCC(CO)NH-TOCSY experiments recorded with a properly tuned constant-time period for frequency labeling of aliphatic 13C resonances, phases of cross peaks provide information that is useful for identifying spin system types. When combined with 13C chemical shift information, these patterns allow identification of the following spin system types: Gly, Ala, Thr, Val, Leu, Ile, Lys, Arg, Pro, long-type (i.e., Gln, Glu and Met), Ser, and AMX-type (i.e., Asp, Asn, Cys, His, Phe, Trp and Tyr).
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PMID:Classification of amino acid spin systems using PFG HCC(CO)NH-TOCSY with constant-time aliphatic 13C frequency labeling. 858 9

Wortmannin is an inhibitor of phosphatidylinositol (PI) 3'-kinase, a cellular kinase activated by docking to phosphotyrosyl residues of insulin receptor substrate-1 (IRS-1) that can also phosphorylate serine residues on IRS-1 in vitro. After treatment of hepatoma cells with 100 nM wortmannin, the tyrosine phosphorylation of IRS-1 in response to insulin was increased by 38.3 +/- 3.3% while its phosphoserine/threonine content was reduced by 19%. Treatment with 1 microM wortmannin further increased IRS-1 tyrosine phosphorylation to 180% of control, while under these conditions, tyrosine phosphorylation of the IR substrate p52 Shc was reduced to less than 50% of control. Thus, alteration of the serine phosphorylation of IR substrates by a wortmannin-sensitive kinase may regulate post-insulin receptor signaling pathways by differential modulation of their insulin-stimulated tyrosine phosphorylation.
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PMID:Differential regulation of insulin-stimulated tyrosine phosphorylation of IRS-1 and SHC by Wortmannin in intact cells. 866 Mar 83

Hepatitis delta virus (HDV) contains two virus-specific delta antigens (HDAgs), large and small forms, which are identical in sequence except that the large one contains 19 extra amino acids at the C terminus. HDAgs are nuclear phosphoproteins with distinct biological functions; the small form activates HDV RNA replication, whereas the large form suppresses this process but is required for viral particle assembly. In this study, we have characterized the phosphorylative property of HDAg in a human hepatoma cell line (HuH-7) and examined the role of phosphorylation in HDAg function. As demonstrated by in vivo labeling and kinase inhibitor experiments, the phosphorylation levels of both HDAgs were diminished by the inhibitor of casein kinase II (CKII). Nevertheless, phosphorylation of only the small form could be markedly reduced by the protein kinase C (PKC) inhibitor, suggesting different phosphorylation properties between the two HDAgs. When these two kinase inhibitors were added separately to the transient-expression system, HDV RNA replication was profoundly suppressed. In contrast, the inhibitors did not affect the assembly of empty HDAg particle from HDAgs and hepatitis B virus surface antigen. To further examine the role of phosphorylation in HDAg function, two conservative CKII recognition sites at Ser-2 and Ser-123 of both HDAgs and one potential PKC recognition site at Ser-210 of the large HDAg were altered to alanine by site-directed mutagenesis. Transfection experiments indicated that mutation at Ser-2, but not Ser-123, significantly impaired the activity of the small HDAg in assisting HDV RNA replication. This property is in accordance with our observation that Ser-2, not Ser-123, was the predominant CKII phosphorylation site in the small HDAg. Our studies also excluded the possibility that the phosphorylation of Ser-2, Ser-123, or Ser-210, had roles in the trans-suppression activity of the large HDAg, in the assembly of empty virus-like HDAg particle, and in the nuclear transport of HDAgs. In conclusion, our results indicate that both CKII and PKC positively modulate HDV RNA replication but not the assembly of empty HDAg particle. The role of CKII in HDV replication may at least in part be accounted for by the phosphorylation of Ser-2 in the small HDAg. The effect of PKC on HDV RNA replication is, however, not to mediate the phosphorylation of the conservative Ser-210 in the large HDAg but rather to act on as-yet-unidentified Ser or Thr residues in the small HDAg or cellular factors. These findings provide the first insight into the roles of phosphorylation of the two HDAgs in the HDV replication cycle.
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PMID:Casein kinase II and protein kinase C modulate hepatitis delta virus RNA replication but not empty viral particle assembly. 870 45

When 7721 human hepatocarcinoma cells were treated with 100 nM phorbol-12-myristate-13-acetate (PMA), the activity of N-acetylglucosaminyltransferase V(GnT-V) in the cells varied in accordance with the activity of membranous protein kinase C (PKC), but not with that of cytosolic PKC. Quercetin, a non-specific inhibitor of Ser/Thr protein kinase, and D-sphingosine and staurosporine, two specific inhibitors of PKC, blocked the activation of membranous PKC and GnT-V by PMA. Among the three inhibitors, quercetin was least effective. The inhibitory rates of quercetin and staurosporine toward membranous PKC and GnTV were proportional to the concentrations of the two inhibitors. The activities of GnTV and membranous protein kinase A (PKA) were also induced in parallel by dibutyryl cAMP (db-cAMP) and this induction was blocked by a specific PKA inhibitor. When cell free preparations of 7721 cells and human kidney were treated with alkaline phosphatase (ALP) to remove the phosphate groups, the GnTV activities were decreased. These results suggest that GnTV may be activated by membranous PKC or PKA, indirectly or directly, via phosphorylation of Ser/Thr residues.
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PMID:Regulation of N-acetylglucosaminyltransferase V by protein kinases. 874 53

A high serum alpha-fetoprotein (AFP) level was found in a patient with endometrial adenocarcinoma of the uterus, which appeared to be hepatoid on histological examination. The AFP of this unusual patient was purified by immunoaffinity chromatography and characterized. The electrophoretic profiles on sodium dodecyl sulfate-polyacrylamide get electrophoresis both before and after glycopeptidase F treatment were indistinguishable from those of a hepatoma AFP. This indicates that the patient's AFP was also composed of a single polypeptide chain of Mr 67,000 and an N-linked sugar chain of Mr 3,000. Amino acid sequence analyses of this AFP, and of AFP from hepatoma and umbilical cord serum indicated that the N-terminal sequences were essentially the same. The sequence, Arg-Thr-Leu-His-Arg-Asn-Glu-Tyr-Gly-Ile, was slightly different from previous reports, but matched that deduced from the cDNA sequence. AFP isoforms due to microheterogeneity of the sugar chain were analyzed by lectin affinity electrophoresis using a series of lectins. The AFP isoform profiles were distinct from those of proteins derived from cord serum, hepatoma, yolk sac tumor and gastric cancer. The reverse-transcription of RNA from the tumor tissue followed by a polymerase chain reaction using primers with AFP-specific sequences gave a product of the size and nucleotide sequence expected for AFP. mRNAs possessing the requisite sequences for albumin and transferrin syntheses were also detected in the tumor. The expression of these hepatocyte-specific proteins supported the hepatoid nature of this tumor.
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PMID:Biochemical characterization of alpha-fetoprotein and other serum proteins produced by a uterine endometrial adenocarcinoma. 876 25

mRNA levels and enzyme activities of the serine/threonine protein phosphatases (EC 3.1.3.16) type 1 (PP1) and 2A (PP2A) in drug-resistant rat ascites hepatoma cells were examined and compared with those in the parental drug-sensitive cell lines, under drug-free conditions. The mRNA levels of PP1 alpha were much higher in all the hepatomas, either sensitive or resistant, compared with normal liver. The mRNA level of PP2C alpha was decreased in the drug-resistant hepatomas compared with the parental drug-sensitive hepatomas, whereas mRNA levels of PP1 alpha, PP1 gamma 1 and PP2A alpha in resistant hepatomas showed diverse deviations, which are not drug-resistance-specific. However, both spontaneous and potential PP1 activities in particulate fractions of the resistant hepatomas were markedly increased compared with those of the sensitive hepatomas and normal rat liver. Western blot analysis showed that the resistant hepatomas contained larger amounts of PP1 alpha in both cytosolic and particulate fractions than the sensitive hepatomas and rat liver. In both groups of hepatomas, spontaneous and potential activities of PP2A were kept lower than those in normal rat liver, but there was no difference between drug-sensitive and -resistant hepatomas. These results suggest an involvement of PP1 in development of drug-resistant phenotype.
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PMID:mRNA levels and enzyme activities of protein phosphatases in drug-resistant rat ascites hepatomas. 886 62


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