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 role of plasminogen activator inhibitor type 1 (PAI-1) in the clearance of tissue-type plasminogen activator (t-PA) by hepatocyte-like cells was studied. Rat (Novikoff) hepatoma cells were able to bind and degrade t-PA in a PAI-1 independent fashion, but PAI-1 markedly increased the rate of degradation and t-PA/PAI-1 was a more efficient inhibitor of 125I-t-PA or of 125I-t-PA/PAI-1 degradation than free t-PA. Competition studies revealed that the effect of PAI-1 is unlikely to involve determinants located on the PAI-1 part of the complex: 1) an excess of free PAI had no effect on the rate of degradation of 125I-t-PA/PAI-1.2) Complexes of PAI-1 with urokinase-type PA or with a t-PA mutant lacking the finger and growth factor domains were unable to compete for the binding and degradation of free or PAI-1-complexed 125I-t-PA.3) t-PA KHRR296-299AAAA, a mutant which reacts 2 orders of magnitude slower with PAI-1 than wild type t-PA, behaved similar to wild type t-PA. The clearance via both the PAI-1-dependent and the PAI-1-independent mechanisms was inhibited by the receptor-associated protein, a general inhibitor of clearance mediated by the LDL receptor-related protein. We conclude that t-PA can be cleared by rat hepatoma cells in a PAI-1 independent fashion, but after complex formation with PAI-1, binding of t-PA to the cells is increased and clearance accelerated. Both mechanisms seem to involve the same receptor.
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PMID:The role of plasminogen activator inhibitor type 1 in the clearance of tissue-type plasminogen activator by rat hepatoma cells. 811 17

Because of the frequent occurrence of premature cardiovascular disease in patients with non-insulin-dependent, type II diabetes mellitus (NIDDM), the attenuated fibrinolytic activity of plasma from type II diabetic patients with increased concentrations of plasminogen activator inhibitor type-1 (PAI-1), and the fact that insulin stimulates synthesis of PAI-1 by human hepatic cells in vitro, we and others have hypothesized that accelerated vascular disease in type II diabetes may result in part from impaired fibrinolysis secondary to excessive elaboration of PAI-1 stimulated by insulin. Alternatively, the hyperglycemia associated with type II diabetes could influence the synthesis and secretion of PAI-1 directly. The present study was performed to determine whether PAI-1 secretion is or is not sensitive to the prevailing concentration of glucose in the conditioned medium of endothelial and liver cells, which are thought to be the major sources of circulating PAI-1 in vivo. Confluent cells were exposed to 0, 2.8, 5.6, 11.1, or 22.2 mmol/L (0, 50, 100, 200, or 400 mg/dL) glucose in medium without serum and subsequently to media with or without insulin (7.3 nmol/L). Secretion of PAI-1 by highly differentiated human hepatoma (Hep G2) cells did not increase as a function of increasing concentrations of glucose, whether or not insulin was present. In contrast, with pig aortic endothelial cells, the secretion of PAI-1 increased significantly with extracellular glucose with or without insulin. The increases in PAI-1 were specific (as shown by metabolic labeling experiments) and not attributable to osmotic effects (as shown by replacement of glucose by sorbitol).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Augmentation of synthesis of plasminogen activator inhibitor type-1 in arterial endothelial cells by glucose and its implications for local fibrinolysis. 824 Nov 3

Type 1 plasminogen activator inhibitor (PAI-1) is the major physiological inhibitor of plasminogen activation, inhibiting both tissue- and urokinase-type plasminogen activators. In HTC rat hepatoma cells, glucocorticoids increase PAI-1 activity, antigen and mRNA accumulation 3- to 5-fold; this increase is due solely to an increase in the rate of PAI-1 gene transcription. We have identified the cis-acting sequences in the 5'-flanking sequence of the HTC PAI-1 gene that mediate this induction. Analysis of a series of hybrid genes containing various portions of the PAI-1 5'-flanking region fused to the chloramphenicol acetyltransferase reporter gene transfected into HTC cells localized the region involved in the transcriptional regulation by glucocorticoids to between -1237 and -764. Electrophoretic mobility shift assays and DNase-I protection assays showed that a glucocorticoid response element (GRE) 15-mer located at -1212 bound the glucocorticoid receptor DNA-binding domain protein in a concentration-dependent manner. Mutations created within this GRE eliminated its ability both to confer a glucocorticoid response and to bind the glucocorticoid receptor. When placed upstream of a heterologous promoter in either orientation, this GRE conferred glucocorticoid inducibility. We, therefore, conclude that the sole cis-acting sequence required for the glucocorticoid response of the PAI-1 gene in rat HTC hepatoma cells is the GRE at -1212.
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PMID:Mechanism of glucocorticoid induction of the rat plasminogen activator inhibitor-1 gene in HTC rat hepatoma cells: identification of cis-acting regulatory elements. 824 19

Hepatic parenchymal cells play an essential role in the clearance of circulating tissue-type plasminogen activator (t-PA) in vivo as a major pathway in the regulation of plasma fibrinolytic activity. Previous studies have identified plasminogen activator inhibitor type 1 (PAI-1)-dependent t-PA-binding sites in the human hepatoma cell line HepG2. In this study, we demonstrate that receptor-mediated binding and endocytosis of the t-PA-PAI-1 complex are largely mediated by a recently identified low density lipoprotein receptor-related protein (LRP). A 39-kDa LRP receptor-associated protein that modulates ligand binding to LRP was found to bind specifically to HepG2 cells and to inhibit approximately 70-80% of specific 125I-t-PA.PAI-1 binding. This inhibition by the 39-kDa protein was not due to inhibition of complex formation between 125I-t-PA and PAI-1; instead, the 39-kDa protein inhibited 125I-t-PA.PAI-1 binding to LRP. Polyclonal anti-LRP antibody raised against purified human LRP also inhibited 70-80% of specific 125I-t-PA.PAI-1 binding. A similar extent of inhibition by the 39-kDa protein was also observed for 125I-t-PA.PAI-1 endocytosis and degradation. Chemical cross-linking experiments demonstrated the direct interaction between 125I-t-PA.PAI-1 and LRP on HepG2 cells as anti-LRP antibody, in addition to anti-t-PA and anti-PAI-1 antibodies, was able to immunoprecipitate the 125I-t-PA.PAI-1 complex following binding of 125I-t-PA.PAI-1 to HepG2 cells and cross-linking. This interaction of the t-PA.PAI-1 complex with LRP on HepG2 cells was also observed when the unlabeled t-PA.PAI-1 complex was cross-linked to [35S]methionine-labeled HepG2 cells. In addition, the direct binding of the 39-kDa protein to LRP on HepG2 cells was demonstrated by similar cross-linking experiments. Thus, these data clearly show that LRP is the major cell-surface receptor responsible for t-PA.PAI-1 complex binding and endocytosis on human hepatoma HepG2 cells and extend the multifunctional nature of LRP as an endocytosis receptor for several structurally and functionally distinct ligands.
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PMID:Receptor-mediated endocytosis of tissue-type plasminogen activator by low density lipoprotein receptor-related protein on human hepatoma HepG2 cells. 838 67

Using the Northern blot technique, we screened 6 human hepatoma cell lines to investigate the regulation mechanism of heparin cofactor II (HC II) biosynthesis. We found that HuH-7 and Hep G2 cells constitutively expressed the HC II gene. In conditioned medium, HuH-7 cells constantly produced HC II that was functionally active and formed a complex with thrombin in the presence of dermatan sulfate. HC II is thought be an acute phase reactant, and, therefore, we examined the effects of the major inflammatory cytokines, IL-6, IL-1 beta, and TNF-alpha, on the regulation of HC II production in HuH-7 and Hep G2 cells. In HuH-7 cells, the antigen and mRNA levels of plasminogen activator inhibitor type-1 (PAI-1), an acute phase protein produced by hepatocytes, were increased in response to stimulation with either IL-6 or IL-1 beta or both, but HC II antigen and mRNA levels were not changed by the same stimulation. Even when Hep G2 cells were treated with a combination of three cytokines, IL-6, IL-1 beta, and TNF-alpha, HC II antigen and mRNA levels were not changed; however, PAI-1 antigen and mRNA levels were clearly increased. These results suggest that the production of HC II in hepatoma cells is not regulated by the major inflammatory mediators, IL-6, IL-1 beta, and TNF-alpha.
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PMID:The production of heparin cofactor II is not regulated by inflammatory cytokines in human hepatoma cells: comparison with plasminogen activator inhibitor type-1. 881 80

The conformation and degree of multimerization of vitronectin (Vn) appears to be of critical importance for its functions, but little is known about the underlying mechanisms that control Vn multimerization. We report that Vn secreted by cultured hepatoma cells is present as a mixture of monomeric and multimeric forms. A single protein of Mr 45,000 co-purified with hepatoma cell-derived Vn, which was immunologically identified as type 1 plasminogen activator inhibitor (PAI-1). The possibility that PAI-1 may modulate Vn multimerization was investigated. The addition of active PAI-1 to unfractionated plasma containing Vn monomers resulted in the formation of covalently and noncovalently associated Vn multimers and expression of conformationally sensitive epitopes. In contrast, inactive forms of PAI-1 did not efficiently induce Vn multimerization and conformational change. Gel filtration analysis revealed that Vn remained multimeric after dissociation from PAI-1. Vn multimers were also assembled using purified monomeric Vn and PAI-1, suggesting that a plasma cofactor was not required to induce Vn multimerization. This study provides insights into physiological mechanism responsible for the generation of homomultimeric Vn, a multimeric form of Vn that is not in complex with other proteins and which expresses a functional repertoire distinct from that of plasma Vn.
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PMID:Type 1 plasminogen activator inhibitor induces multimerization of plasma vitronectin. A suggested mechanism for the generation of the tissue form of vitronectin in vivo. 893 96

Transforming growth factor-beta (TGF-beta) is a potent inducer of programmed cell death in liver as well as some hepatoma cell lines. To explore the mechanism by which TGF-beta induces apoptosis, we investigated the role of caspase family proteases in the apoptotic death of a human hepatoma cell line, Hep3B. We showed that TGF-beta-induced apoptosis was blocked by expression of the cowpox virus protein CrmA, a serpin-like pseudosubstrate for some of the caspase family proteases. CrmA expression, however, did not affect TGF-beta-induced regulation of promoter activities of the cyclin A and plasminogen activator inhibitor type I genes. These results indicate that CrmA inhibits a step specific for the apoptotic effect of TGF-beta. In addition to CrmA, a tripeptide caspase-protease inhibitor, z-Val-Ala-Asp-fluoromethylketone could also suppress TGF-beta-induced apoptosis in a dose-dependent manner. In TGF-beta-treated Hep3B cells, we observed a specific degradation of the catalytic subunit of DNA-dependent protein kinase, which was previously shown to be a substrate of caspase-3 but not several other members of the caspase family. This degradation was not seen in Hep3B cells transfected with CrmA nor in Hep3B cells pretreated with the tripeptide caspase inhibitor. Our study indicates a requirement of caspase family proteases in TGF-beta-induced apoptosis.
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PMID:Involvement of caspase family proteases in transforming growth factor-beta-induced apoptosis. 921 76

The transforming growth factor-beta (TGF-beta) family of cytokines mediates multiple biological effects by regulating the expression of target genes. The Smad family proteins function as intracellular signal transducers downstream of the receptors to transmit the TGF-beta signal from cell membrane to nucleus. The mechanisms by which Smads mediate transcriptional activation of target genes is largely unknown. Here we report the identification of a novel TGF-beta-responsive element in the human type 1 plasminogen activator inhibitor promoter that is required for mediating strong transcriptional activation of this gene by TGF-beta. Smad3 and Smad4 are incorporated into a TGF-beta-inducible complex formed on this element following TGF-beta stimulation of human hepatoma cells. Both Smad3 and Smad4 bind directly to this TGF-beta-responsive element through their conserved MH1 domains. These results indicate that Smad3 and Smad4 mediate TGF-beta signaling by directly interacting with a specific response element in a physiological target gene.
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PMID:Smad4/DPC4 and Smad3 mediate transforming growth factor-beta (TGF-beta) signaling through direct binding to a novel TGF-beta-responsive element in the human plasminogen activator inhibitor-1 promoter. 979 26

Whether the phenotypes of drug resistance and metastatic activity in cancer are dependent on each other or not is controversial. We compared in vitro invasive properties of human hepatoma cells resistant to epirubicin and rich in P-glycoprotein (Pgp) (HB8065/R) with the parental epirubicin-sensitive, Pgp-poor cells (HB8065/S). The HB8065/R cells displayed elevated capacity to migrate in a transwell chamber assay (three- to fourfold compared to the HB8065/S cells), both in the absence and presence of a reconstituted basement membrane extract (Matrigel). In the presence of the P-gp inhibitor PSC 833 (1.5 micrograms/ml) the capacity of the HB8065/R cells to cross Matrigel-coated filters was attenuated by approximately 25%. Compared to the HB8065/S cells, the resistant cell line expressed higher level of plasminogen activator inhibitor (PAI)-1 mRNA (approximately threefold), which was reflected by a approximately fivefold increase in secreted PAI-1 immunoactivity (approximately 50 ng/10(6) HB8065/R cells). Furthermore, treatment with PSC 833 was associated with upregulation of PAI-1 mRNA (approximately 3.5-fold) and immunoactivity (approximately twofold) in the HB8065/R cells. Level of tissue inhibitor of metalloproteinases (TIMP)-1 was also significantly increased in the HB8065/R cells compared to the HB8065/S cells, whereas both cell lines showed low constitutive expression of TIMP-2. Levels of TIMPs were not altered by PSC 833. These data suggest that overexpression of Pgp in these hepatoma cells may covariate with the phenotypes of both enhanced in vitro invasiveness and high PAI-1 expression, whether randomly acquired or not.
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PMID:Human hepatoma cells rich in P-glycoprotein display enhanced in vitro invasive properties compared to P-glycoprotein-poor hepatoma cells. 980 60

The serum concentration of transforming growth factor beta (TGF-beta) is elevated as tumors progress in hepatocellular carcinoma (HCC) patients. In this study, we examined whether modulation of tumor-derived TGF-beta signal transduction contributes to malignant progression. We investigated the production of TGF-beta1, the biological effects of TGF-beta and neutralizing antibody on HCC cells, activation of Smad 2, Smad 3, and Smad 4, induction of antagonistic Smads (Smad 6 and Smad 7), and promoter activities of two target genes, plasminogen activator inhibitor type 1 (PAI-1) and p15INK4B. In human cell lines HCC-M and HCC-T, TGF-beta accelerates their proliferation. Smad 2 was activated constitutively by an autocrine mechanism, because in the absence of exogenous TGF-beta, a high level of Smad 2 phosphorylation, induction of PAI-1 transcripts, and nuclear localization of Smad 2 were observed. This constitutive activation of Smad 2 was, at least in part, attributable to the lack of induction of antagonistic Smads by TGF-beta. However, Smads activated by tumor-derived TGF-beta constantly suppressed p151NK4B expression. In addition, 3 of 10 human HCC tissues showed nuclear localization of Smad 2 and low mRNA levels of p15INK4B and antagonistic Smads but a high level of PAI-1. Our observations suggest that this constant suppression of the p15INK4B gene could be involved in the malignant progression of HCC.
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PMID:Autocrine stimulatory mechanism by transforming growth factor beta in human hepatocellular carcinoma. 1072 5


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