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 liver is remarkably insensitive to a variety of cytotoxins and expresses a number of known drug resistance genes. To isolate new P-glycoprotein (Pgp)-related genes, we screened a normal rat liver cDNA library at low stringency with a MDR1 cDNA fragment containing the P-loop and ATP binding site. We isolated a novel cDNA closely related to the Pgps that is dramatically increased in hepatic neoplasia and refer to it as P-glycoprotein-related protein (PRP). The predicted protein shows PRP to be a member of the ATP-Binding Cassette (ABC) family of proteins, and a multisequence comparison of the nucleotide binding domain and the ABC family signature sequences reveals that PRP sequences are highly conserved with the greatest similarity to the yeast heavy metal transporter encoded by hmtl. However, the hydropathy plot analysis suggests that PRP does not have any prominent membrane-spanning domains and thus is not typical of ABC transporters. The PRP transcript is detected in many normal tissues. In the H35 hepatoma cell line, PRP was overexpressed compared to normal liver. Southern blot analysis of DNA from the H35 rat hepatoma cells reveals that the PRP gene was amplified compared to normal liver. The orotic acid model of hepatocarcinogenesis was used to determine if during stepwise progression to liver cancer, PRP changed with hepatocarcinogenesis. At the hyperplastic nodule stage, PRP expression was increased over its expression in normal surrounding liver. More dramatic increases in PRP expression were found in frank hepatic carcinomas. Cumulatively, these studies are the first to link a novel ABC family member to the hepatic neoplastic process, a role that may be recapitulated in other cells, considering the ubiquitous expression of PRP.
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PMID:Identification of a new P-glycoprotein-like ATP-binding cassette transporter gene that is overexpressed during hepatocarcinogenesis. 928 77

Hepatocellular carcinoma (HCC) frequently overexpresses the MDR1 gene and is resistant to drugs transported by the multidrug-resistance efflux pump. A xanthine analog, 1-(11-dodecylamino-10-hydroxyundecyl)-3,7-dimethylxanthine (CT-2584,CTI), is cytotoxic to many tumors in culture and was four times more effective than verapamil in inhibiting Rhodamine 123 secretion in MDR1-overexpressing Chinese hamster ovary cells. However, studies using PRF/PLC/5 (Alexander) cells revealed that CT-2584 is cytotoxic by another mechanism not involving inhibition of MDR1 function. Alexander cells have integrated the hepatitis B surface antigen (HBsAg) gene and quantitatively secrete HBsAg. The parent cell line, Alex 0, has low MDR1 expression and is drug-sensitive, whereas a derived line, Alex 0.5, is drug-resistant and overexpresses MDR1 100 times. Both cell lines were similarly killed within 24 or 48 hours by CT-2584. Freshly isolated rat and human hepatocytes were considerably more resistant to killing by CT-2584. In vivo, CT-2584 significantly reduced tumor growth in SCID mice bearing Alex 0 or 0.5 xenografts as determined by serial measurements of HBsAg. Hepatic parenchyma was normal, whereas apoptosis and cellular loss were observed in xenografts. The xenograft model is useful for testing pharmacological therapy of HCC.
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PMID:Effect of a xanthine analog on human hepatocellular carcinoma cells (Alexander) in culture and in xenografts in SCID mice. 936 62

Loss of functional p53 paradoxically results in either increased or decreased resistance to chemotherapeutic drugs. The inconsistent relationship between p53 status and drug sensitivity may reflect p53's selective regulation of genes important to cytotoxic response of chemotherapeutic agents. We reasoned that the discrepant effects of p53 on chemotherapeutic cytotoxicity is due to p53-dependent regulation of the multidrug resistance gene (MDR1) expression in tumors that normally express MDR1. To test the hypothesis that wild-type p53 regulates the endogenous mdr1 gene we stably introduced a trans-dominant negative (TDN) p53 into rodent H35 hepatoma cells that express P-glycoprotein (Pgp) and have wild-type p53. Levels of Pgp and mdr1a mRNA were markedly elevated in cells expressing TDN p53 and were linked to impaired p53 function (both transactivation and transrepression) in these cells. Enhanced mdr1a gene expression in the TDN p53 cells was not secondary to mdr1 gene amplification and Pgp was functional as demonstrated by the decreased uptake of vinblastine. Cytotoxicity assays revealed that the TDN p53 cell lines were selectively insensitive to Pgp substrates. Sensitivity was restored by the Pgp inhibitor reserpine, demonstrating that only drug retention was the basis for loss of drug sensitivity. Similar findings were evident in human LS180 colon carcinoma cells engineered to overexpress TDN p53. Therefore, the p53 inactivation seen in cancers likely leads to selective resistance to chemotherapeutic agents because of up-regulation of MDR1 expression.
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PMID:p53-dependent regulation of MDR1 gene expression causes selective resistance to chemotherapeutic agents. 938 Jul 55

The goal of our study was to obtain direct evidence of co-ordinated regulation of P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) and differentiation in tumour cells and to study some signalling pathways involved in joint regulation of these two cell phenotypes. The sublines of human melanoma (mS) and hepatoma (human HepG2 and rat McA RH 7777) cell lines were obtained by retroviral infection of the wild-type cells with the cDNA of the human retinoic acid receptor alpha (RAR alpha). The resulting sublines stably overexpressed exogenous RAR alpha gene. The infectants became more differentiated than the parental cells as determined by a decrease in the synthesis of the embryo-specific alpha-fetoprotein in HepG2 and McA RH 7777 hepatoma cells and by an increase in melanin synthesis in mS cells. The differentiation of human cells was accompanied by an increase in the amounts of MDR1 mRNA but not by an increase in P-gp activity as a drug transporter, in contrast, in the rat RAR alpha overexpressing cells P-gp functional activity was elevated. Treatment with cytotoxic drug (colchicine) or retinoic acid (RA) resulted in a slight increase in P-gp activity in the parental and RAR alpha-infected melanoma cells, whereas the increase in P-gp function in the infected hepatoma cells (both human and rat) was very prominent. Thus, we provide new evidence that cell differentiation caused by the overexpression of the gene participating in the differentiation programme leads to overexpression of MDR1 gene and drug resistance and that this effect is tissue and species specific. These data imply that the activation of the RA-controlled signalling pathway up-regulates MDR1 gene expression.
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PMID:Influence of exogenous RAR alpha gene on MDR1 expression and P-glycoprotein function in human and rodent cell lines. 966 38

We previously showed that combined neoadjuvant doxorubicin (DOX) treatment and orthotopic liver transplantation produced a 3-year tumor-free survival rate of 54% in stage II-IVa nonresectable hepatocellular carcinomas (HCCs). These patients received posttransplant immunosuppressive doses of cyclosporin A (CsA). CsA has been shown to modify the function of a membrane P-glycoprotein (Pgp) whose overexpression is associated with a multidrug-resistant (MDR1) phenotype. This study utilized HCC cell lines to characterize the in vitro chemomodulatory properties of CsA as found in posttransplant patient plasma to consider the hypothesis that CsA may prolong posttransplant survival by enhancing the therapeutic efficacy of DOX against multidrug-resistant hepatoma cells. We characterized Pgp expression in the HCC lines Hep3B, Hep G2, and SK-HEP-1 by immunohistochemistry and the reverse transcription-polymerase chain reaction. The combined cytotoxicity of DOX + CsA was examined by [3H]thymidine uptake and flow cytometric drug-retention assays. Pgp expression was assessed further after prolonged (10-day) treatment with CsA. Hep3B and Hep G2 cells expressed low to moderate levels of Pgp. The effective DOX dose required for inhibiting MDR1(+) Hep3B and Hep G2 cell proliferation by 50% (DOX IC50) was 44.5 ng/ml and 43.5 microgram/ml, as compared with 10.7 ng/ml for Pgp-negative SK-HEP-1 cells. Optimal concentrations of CsA (0.8 micrometer) lowered DOX IC50 for Hep3B cells and Hep G2 cells by 6-fold and 4-fold, respectively. Similarly, plasma from patients containing immunosuppressive levels of CsA lowered DOX IC50 of the MDR1(+) Hep G2 cells by up to 4-fold. Prolonged exposure to CsA did not affect its chemosensitizing capacity or Pgp expression of HCC cells. PSC-833, a nonimmunosuppressive analogue of CsA, was equally effective in reducing the DOX IC50 of MDR1(+) HCC cells. CsA and PSC-833 increased drug retention by approximately 75%, but did not significantly affect hepatoma cell viability or Pgp expression. Pharmacological concentrations of cyclosporin analogues, including one nonimmunosuppressive form, enhance DOX cytotoxicity of MDR1(+) HCC cells by modulating drug retention. CsA as found in posttransplant patient plasma enhanced DOX cytotoxicity to human MDR1(+) hepatoma cells in vitro, albeit at less than optimal chemosensitizing concentrations. Prolonged exposure to CsA did not affect its chemosensitizing properties or block Pgp expression of HCC cells. These findings support our hypothesis that in vivo immunosuppressive levels of CsA may enhance DOX chemotherapeutic efficacy on MDR1(+) HCC cells.
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PMID:Chemosensitization of human hepatocellular carcinoma cells with cyclosporin A in post-liver transplant patient plasma. 981

The human multidrug resistance gene MDR1 encodes a membrane-bound protein, referred to as P-glycoprotein, that acts as a pump to extrude toxins from cells. The 3' untranslated region (3'UTR) of the human MDR1 mRNA is very AU-rich (70%) and contains AU-rich sequences similar to those shown to confer rapid decay on c-myc, c-fos, and lymphokine mRNAs. We tested the ability of the MDR1 3'UTR to act as an mRNA destabilizing element in the human hepatoma cell line HepG2. The MDR1 mRNA has an intermediate half-life of 8 h in HepG2 cells compared to a half-life of 30 min for c-myc mRNA. The MDR1 mRNA half-life was prolonged to >20 h upon treatment with the protein synthesis inhibitor cycloheximide. We constructed expression vectors containing the human beta-globin coding region with the 3'UTR from either MDR1 or c-myc. The c-myc 3'UTR increased the decay of the chimeric mRNA, but the MDR1 3'UTR had no effect. We tested the ability of MDR1 3'UTR sequences to compete for interaction with AU-binding proteins in cell extracts; MDR1 RNA probes had a fivefold lower affinity for AU-binding proteins that interact with the c-myc AU-rich 3'UTR. Overall, our data suggest that the MDR1 3'UTR does not behave as an active destabilizing element in HepG2 cells.
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PMID:The AU-rich 3' untranslated region of human MDR1 mRNA is an inefficient mRNA destabilizer. 1044 77

Export of L-T3 out of the cell is one factor governing the cellular T3 content and response. We previously observed in liver-derived cells that T3 export was inhibited by verapamil, suggesting that it is due to either ATP-binding cassette/multidrug resistance (MDR1/mdr1b) or multidrug resistance-related (MRP1/mrp1) proteins. To test this hypothesis we measured T3 export in FRTL-5, NIH-3T3, and rat hepatoma (HTC) cells that varied in expression of these proteins. FRTL-5 and NIH-3T3 cells were found to contain a T3 efflux mechanism that is verapamil inhibitable, saturable, and stereospecific. By contrast, T3 efflux in HTC cells was slow and unaffected by verapamil. Neither FRTL-5 nor NIH-3T3 cells express mdrlb, but all three cell types express mrpl, as assessed by immunoblotting. Overexpression of MDR1 in NIH-3T3 cells did not enhance verapamil-inhibitable T3 efflux. Photoaffinity labeling of FRTL-5 and NIH-3T3 cells with [125I]L-T3 revealed a labeled 90- to 100-kDa protein that was not present in HTC cells. Verapamil and excess nonradioactive L-T3, but not D-T3, inhibited labeling of this protein. The lack of correlation between T3 efflux and MDR1 and mrpl expression and the finding of a photoaffinity-labeled putative transport protein smaller than MDR1 or mrp1 protein (approximately 170 kDa) suggest that a novel protein is involved in the transport of T3 out of cells.
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PMID:Thyroid hormone export in rat FRTL-5 thyroid cells and mouse NIH-3T3 cells is carrier-mediated, verapamil-sensitive, and stereospecific. 1053 18

Recent studies have shown that expression levels of the multidrug resistance gene MDR1, which encodes the drug transporter P-glycoprotein, correlate with prognostic outcomes of certain tumor types. These findings suggest that expression of MDR1 may affect tumor behaviors. To address this issue further, we investigated the expression of mdr1a, a human MDR1 homolog, on the development of hepatocellular carcinoma in a transgenic mouse model carrying the liver-targeted expression of human hepatitis-B virus (HBV) surface antigen. The pathogenetic program was compared in HBV mice carrying either mdr1a(+/+) or mdr1a(-/-). We found that the expressions of proliferative activity markers, Ki67 nuclear antigen, and proliferating cell nuclear antigen were elevated in mdr1a(-/-) mice younger than 10 wk in comparison with those in the same age group of wild-type animals. Replication in the hepatic population as determined by bromodeoxyuridine incorporation tended to support observation that mdr1a(-/-) mice exhibited elevated labeling indices in this age group. Moreover, histologic staining and flow-cytometric analysis showed that the mdr1a(-/-) animals exhibited a higher cell population with polyploidy than did the mdr1a(+/+) counterparts of the same age. However, no significant differences in the expression of the liver-injury markers serum alanine transaminase and aspartate transaminase were observed. Although our results showed that absence of mdr1a expression is correlated with modest enhanced proliferative characteristics in the livers at stage before the development of hepatocellular carcinoma, the overall life spans between these two strains of mice were not significantly different. The implication of these findings to the role of P-glycoprotein in tumor development and cancer chemotherapy is discussed.
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PMID:Elevated expression of hepatic proliferative markers during early hepatocarcinogenesis in hepatitis-B virus transgenic mice lacking mdr1a-encoded P-glycoprotein. 1107 7

The objective of this study was to examine effects of interleukin-6 (IL-6) on the expression and activity of the drug resistance transporters (MDR1 and MRP) in human hepatoma cell lines. Expression and activity of MDR1 and MRP transporters were examined in IL-6-treated and control HuH 7 and HepG2 cells using semi-quantitative RT-PCR analysis and by rhodamine 123 and 5-carboxyfluorescin efflux assays. Results from RT-PCR demonstrated expression of MRP3, MRP6, and MDR1 in HuH 7 cells and expression of MRP1, MRP2, MRP3, MRP6, and MDR1 in HepG2 cells. Compared with controls, treatment of HuH 7 cells with IL-6 (10 ng/mL, 24 h) resulted in a 1.8-fold increase in MRP-mediated efflux of 5-CF with a corresponding 1.5-fold induction of MRP3 mRNA levels (p < 0.05). Similarly, in HepG2 cells, a 2-fold increase in MRP functional activity and a 1.8-fold induction of MRP1 mRNA levels were seen in the IL-6 treated cells (p < 0.05). Treatment of cells with IL-6 was also found to cause significant reductions in the expression and activity of MDR1 in HuH 7 cells, but not in HepG2 cells. Our data suggest that IL-6 induces MRP expression and activity in human hepatoma cell lines. Suppressive effects of IL-6 on MDR1 expression and activity were also observed in HuH 7 cells. This underscores the importance of examining the regulation of multiple drug resistance proteins as these proteins may have opposing regulatory mechanisms in malignant cells.
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PMID:Influence of IL-6 on MDR and MRP-mediated multidrug resistance in human hepatoma cells. 1169 47

The expression of P-glycoprotein encoded by the multidrug resistance (MDR1) gene is associated with the emergence of the MDR phenotype in cancer cells. Human MDR1 and its rodent homolog mdr1a and mdr1b are frequently overexpressed in liver cancers. However, the underlying mechanisms are largely unknown. The hepatocarcinogen 2-acetylaminofluorene (2-AAF) efficiently activates rat mdr1b expression in cultured cells and in Fisher 344 rats. We recently reported that activation of rat mdr1b in cultured cells by 2-AAF involves a cis-activating element containing a NF-kappaB binding site located -167 to -158 of the rat mdr1b promoter. 2-AAF activates IkappaB kinase (IKK), resulting in degradation of IkappaBbeta and activation of NF-kappaB. In this study, we report that 2-AAF could also activate the human MDR1 gene in human hepatoma and embryonic fibroblast 293 cells. Induction of MDR1 by AAF was mediated by DNA sequence located at -6092 which contains a NF-kappaB binding site. Treating hepatoma cells with 2-AAF activated phosphoinositide 3-kinase (PI3K) and its downstream effectors Rac1, and NAD(P)H oxidase. Transient transfection assays demonstrated that constitutively activated PI3K and Rac1 enhanced the activation of the MDR1 promoter by 2-AAF. Treatment of hepatoma cells with 2-AAF also activated another PI3K downstream effector Akt. Transfection of recombinant encoding a dominant activated Akt also enhanced the activation of MDR1 promoter activation by 2-AAF. These results demonstrated that 2-AAF up-regulates MDR1 expression is mediated by the multiple effectors of the PI3K signaling pathway.
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PMID:Induction of human MDR1 gene expression by 2-acetylaminofluorene is mediated by effectors of the phosphoinositide 3-kinase pathway that activate NF-kappaB signaling. 1196 Mar 67


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