Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cellular and molecular mechanisms involved in the resistance to cytotoxic heavy metals remain largely to be characterized in mammalian cells. To this end, we have analyzed a metal-resistant variant of the human lung cancer GLC4 cell line that we have selected by a step-wise procedure in potassium antimony tartrate. Antimony-selected cells, termed GLC4/Sb30 cells, poorly accumulated antimony through an enhanced cellular efflux of metal, thus suggesting up-regulation of a membrane export system in these cells. Indeed, GLC4/Sb30 cells were found to display a functional overexpression of the multidrug resistance-associated protein MRP1, a drug export pump, as demonstrated by Western blotting, reverse transcriptase-polymerase chain reaction and calcein accumulation assays. Moreover, MK571, a potent inhibitor of MRP1 activity, was found to markedly down-modulate resistance of GLC4/Sb30 cells to antimony and to decrease cellular export of the metal. Taken together, our data support the conclusion that overexpression of functional MRP1 likely represents one major mechanism by which human cells can escape the cytotoxic effects of heavy metals.
...
PMID:Overexpression of the multidrug resistance-associated protein (MRP1) in human heavy metal-selected tumor cells. 1002 56

Deletion of the multidrug resistance gene MRP1 has been demonstrated in acute myeloid leukemia (AML) patients with inversion of chromosome 16 (inv[16]). These AML patients are known to have a relatively favorable prognosis, which suggests that MRP1 might play an important role in determining clinical outcome. This study analyzed MRP1 deletion by fluorescent in situ hybridization (FISH), with a focus on inv(16) AML patients. Functional activity of multidrug resistance protein (MRP) was studied in a flow cytometric assay with the use of the MRP substrate carboxyfluorescein (CF) and the inhibitor MK-571. MRP1, MRP2, and MRP6 messenger RNA (mRNA) expression was determined with reverse transcriptase-polymerase chain reaction (RT-PCR). The results were compared with normal bone marrow cells. MRP1 deletion was detected in 7 AML patients; 2 cases showed no MRP1 FISH signals, and 5 cases had 1 MRP1 signal, whereas in 4 AML patients with inv(16) no MRP1 deletions were observed. A variability in MRP activity, expressed as CF efflux-blocking by MK-571, was observed (efflux-blocking factors varied between 1.2 and 3.6); this correlated with the number of MRP1 genes (r = 0.91, P <. 01). MRP activity in the AML cases was not different from normal hematopoietic cells. MRP1 mRNA was detected in patients with 1 or 2 MRP1 FISH signals, but not in patients with no MRP1 signals. MRP2 and MRP6 mRNA were expressed predominantly in AML samples with 1 MRP1 signal, whereas in normal bone marrow cells no MRP2 and MRP6 mRNA was observed. In conclusion, this study shows that MRP activity varies among inv(16) AML cases and does not differ from that in normal hematopoietic cells; this might be in part due to the up-regulation of other MRP genes.
...
PMID:Deletion of the multidrug resistance protein MRP1 gene in acute myeloid leukemia: the impact on MRP activity. 1082 37

It is widely accepted that a prolonged ouabain blockade of the Na(+),K(+)-ATPase makes cells detach from each other and from the substrate, leading to their death and that cellular resistance to ouabain is due to the presence of isoforms of Na(+),K(+)-ATPase with low affinity to this glycoside. In the present work the effect of reduced glutathione in the response of two types of renal cells to ouabain: MDCK, a ouabain-sensitive cell line and Ma104, a ouabain-resistant one, was studied. Glutathione protected MDCK cells from ouabain toxicity and inhibition of glutathione synthesis by L-buthionine-S,R-sulfoximine sensitized Ma104 cells to ouabain. As glutathione is involved with multidrug resistance (MDR) in cells expressing the multidrug resistance-related protein MRP1 and as Ma104 cells have a MDR phenotype, it was investigated whether Ma104 cells express this protein. The expression of the MRP1-mRNA in Ma104 cells was detected by reverse transcriptase-polymerase chain reaction and ribonuclease protection assay, and the protein was detected by Western blotting and immunofluorescence. Treatment of Ma104 cells with ouabain increased MRP1-mRNA expression and altered the localization of MRP1 in these cells. Our results suggest that some cells may have mechanisms to protect themselves from ouabain toxicity and that MRP1 may have a role in controlling the toxic effects of ouabain.
...
PMID:Reduced glutathione protect cells from ouabain toxicity. 1141 Mar 39

Nuclear expression of the Y-box-binding protein (YB-1) has been reported to correlate with the expression of P-glycoprotein in breast cancer and osteosarcoma. Overexpression of the ATP-binding cassette (ABC) superfamily, such as P-glycoprotein/multi-drug resistance (MDR) 1 and MDR-associated protein (MRP) 1, 2 and 3, has been reported in various malignant neoplasms. Fifty-four surgically resected synovial sarcomas were examined immunohistochemically for nuclear expression of YB-1 and intrinsic expression of P-glycoprotein, MRP1, MRP2, and topoisomerase II alpha, and the findings were compared with clinicopathological parameters, proliferative activities as evaluated by MIB-1 labelling index (LI), and the patients' prognoses. In addition, MDR1, MRP1, MRP2, and MRP3 mRNA levels were assessed using a quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method in 22 concordant frozen specimens from these cases and the findings were compared with six control skeletal muscle tissues. Independent prognostic factors were investigated using the Cox proportional hazards regression model. Nuclear expression of YB-1 protein correlated with P-glycoprotein expression (p = 0.0126). Moreover, cases with nuclear expression of YB-1 correlated with poor survival (p = 0.0495) and showed a high topoisomerase II alpha labelling index (topo II alpha LI) (p = 0.0056) and a high MIB-1 LI (p = 0.01). Multivariate Cox analysis showed that only the nuclear expression of YB-1 (p = 0.0136) and high American Joint Committee on Cancer (AJCC) stage (ie stage III or IV) (p < 0.0001) were independent factors for poor prognosis, while the expression of the YB-1 responsive gene products examined was not. These results indicate that the nuclear expression of YB-1 protein is associated with P-glycoprotein expression and proliferative activity as shown by the topo II alpha LI and the MIB-1 LI, and that expression of this protein is an important independent prognostic factor in synovial sarcoma.
...
PMID:Nuclear expression of Y-box-binding protein-1 correlates with P-glycoprotein and topoisomerase II alpha expression, and with poor prognosis in synovial sarcoma. 1253 39

Brain expression of the multidrug resistance proteins (MRPs), a collection of membrane-associated ATP-dependent efflux transporters, is poorly understood. Although several studies have examined the expression of these proteins within the brain barriers (i.e., the blood-brain barrier and choroid plexus), little information is available with respect to brain parenchyma cells such as microglia and astrocytes. Because microglia are the primary brain cells infected by the human immunodeficiency virus type 1 (HIV-1), MRP1 expression within microglia may contribute to lower brain accumulation of anti-HIV drugs. To examine the expression pattern of MRP1 within microglia, we performed reverse transcriptase-polymerase chain reaction analysis and Western blotting on a rat brain microglia cell line MLS-9, and in primary cultures of rat microglia. Both rat MRP1 (rMPR1) mRNA and protein were expressed in the cell line, as well as the primary cultures. We then characterized rMRP1-mediated transport properties in MLS-9 cells using [3H]vincristine, a known MRP1 substrate. Vincristine accumulation by monolayers of MLS-9 cells increased significantly in the presence of several well established MRP1 inhibitors (MK571, genistein, sulfinpyrazone, probenecid, and indomethacin), protease inhibitors, or the ATPase inhibitor sodium azide. In addition, vincristine accumulation was significantly modulated by altering the intracellular concentration of the reduced form of glutathione, further suggesting the involvement of rMRP1-mediated transport. These results provide strong evidence that the MRP1 protein is both expressed and functional in microglia cells. They also suggest that brain parenchyma can act as a "second" barrier to drug permeability and regulate brain distribution/accumulation of various xenobiotics, including protease inhibitors.
...
PMID:Functional expression of the multidrug resistance protein 1 in microglia. 1289 36

It has been proposed that the declining efficiency of antiretroviral agents in human immunodeficiency virus (HIV) infection may also depend on cellular factors at their site of action. Two in particular have been proposed: (i) the defective intracellular metabolism of NRTI in target cells and the altered uptake; and (ii) efflux of nucleoside reverse transcriptase inhibitors (NRTI) and protease inhibitors (PI) by cellular transporter molecules. Several studies have shown that: changes in the activities of various purine and pyrimidine biosynthetic enzymes may occur in lymphocytes of HIV-infected patients; HIV-infected patients on prolonged treatment with nucleoside analogues, e.g. zidovudine, show significantly decreased activity of thymidine kinase (TK) compared with untreated HIV-infected people; and NRTI and PI are substrates for the multidrug membrane transporters. With regard to the latter issue, it is known that the ATP-binding cassette transporter proteins such as the P-glycoprotein (MDR), and the newly discovered family of multidrug resistance-associated proteins (MRP1-6), promote the active extracellular efflux of a wide variety of therapeutics drugs and overexpression of some of them lowers intracellular concentration of PI. In the very near future such mechanisms, also called 'cellular drug resistance', might be taken into account, together with other immunological, virological and behavioural factors, to explain the 'drug failure' and/or the variability of response in HIV patients undergoing antiretroviral treatment.
...
PMID:Cellular issues relating to the resistance of HIV to antiretroviral agents. 1500 May 83

We have evaluated the effects of monensin liposomes on drug resistance reversal, induction of apoptosis and expression of multidrug resistance (MDR) genes in a doxorubicin-resistant human breast tumour (MCF-7/dox) cell line. Monensin liposomes were prepared by the pH-gradient method. MCF-7/dox cells were treated with various anticancer drugs (doxorubicin, paclitaxel and etoposide) alone and in combination with monensin liposomes. The cytotoxicity was assessed using the crystal violet dye uptake method. The induction of apoptosis in MCF-7/dox cells was assessed by established techniques such as TUNEL (terminal deoxynucleotidyl transferase-mediated nick end labelling) staining and caspase-3 assay. The effect of monensin liposomes on doxorubicin accumulation in MCF-7/dox cells was monitored by fluorescent microscopy. Finally, the expression of MDR genes (MDR1 and MRP1) in MCF-7/dox cells following the exposure to doxorubicin alone and in combination with monensin liposomes was evaluated by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Our results indicated that monensin liposomes overcame drug resistance in MCF-7/dox cells to doxorubicin, etoposide and paclitaxel by 16.5-, 5.6- and 2.8-times, respectively. The combination of doxorubicin (2.5 microg mL(-1)) with monensin liposomes (20 x 10(-8)M) induced apoptosis in approximately 40% cells, whereas doxorubicin (2.5 microg mL(-1)) or monensin liposomes (20 x 10(-8)M) alone produced minimal apoptosis (<10%) in MCF-7/dox cells. Fluorescent microscopy revealed that monensin liposomes increased the accumulation of doxorubicin in MCF-7/dox cells. RT-PCR studies demonstrated that the expression of MDR1 and MRP1 was increased by 33 and 57%, respectively, in MCF-7/dox cells following treatment with doxorubicin (2.5 microg mL(-1)) for 72 h as compared with control MCF-7/dox cells. Furthermore, the levels of MDR1 and MRP1 in MCF-7/dox cells exposed to both doxorubicin and monensin liposomes showed a modest decrease as compared with MCF-7/dox cells treated with doxorubicin alone. In conclusion, the delivery of monensin via liposomes provided an opportunity to overcome drug resistance.
...
PMID:Effects of monensin liposomes on the cytotoxicity, apoptosis and expression of multidrug resistance genes in doxorubicin-resistant human breast tumour (MCF-7/dox) cell-line. 1523 69

The phenomenon of multidrug resistance (MDR) in various malignant neoplasms has been reported as being caused by one or multiple expressions of ATP-binding cassette (ABC) superfamily protein, including P-glycoprotein/multidrug resistance (MDR) 1 and the MDR protein (MRP) family. However, their expression levels and distribution within soft tissue sarcomas remain controversial. In 86 cases of surgically resected soft tissue sarcoma, intrinsic mRNA levels of MDR1, MRP1, MRP2 and MRP3 were assessed using a quantitative reverse transcriptase-PCR (RT-PCR) method. Moreover, immunohistochemical protein expressions of P-glycoprotein (P-gp), MRP1, MRP2, MRP3 and p53 protein were evaluated in concordant paraffin-embedded material. The mRNA expression and immunohistochemical expression of ABC superfamily transporters were compared to clinicopathologic parameters and proliferative activities as evaluated by the MIB-1-labeling index (LI). Among the various histologic types, malignant peripheral nerve sheath tumor (MPNST) showed significantly high levels of MDR1 (p=0.017) and MRP3 (p=0.0384) mRNA expression, compared to the other tumor types. When the immunohistochemical method was compared to the RT-PCR technique to assess ABC transported expression at the protein and mRNA levels, a significantly close relationship was found between the 2 methods (p<0.05). P-gp expression was significantly correlated with large tumor size (> or =5 cm, p=0.041) and high AJCC stage (stages III and IV) (p=0.0365). Furthermore, cases with nuclear expression of p53 revealed significantly higher levels of MDR1 mRNA expression, compared to those with negative immunoreaction for p53 (p=0.0328). Our results suggest that MDR1/P-gp expression may have an important role to play in tumor progression in the cases of soft tissue sarcoma, and p53 may be one of the active regulators of the MDR1 transcript. In addition, the high levels of both MDR1 and MRP3 mRNA expression in MPNST may help to explain the poor response of this tumor to anticancer-drugs.
...
PMID:ATP-binding cassette superfamily transporter gene expression in human soft tissue sarcomas. 1560 99

Apart from fusion inhibitors, 'conventional' antiretrovirals such as nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs) act on intracellular targets. Intracellular concentrations of these agents may be an important determinant of antiviral activity, and the pharmacokinetics of intracellular drug accumulation (including binding to cytosolic proteins, intracellular-free fraction, influx and efflux kinetics and intracellular drug metabolism) are likely to impact upon efficacy and toxicity. To date, intracellular drug accumulation has been poorly studied in vivo, due to methodological difficulties and the relatively large volumes of blood required. NRTIs require intracellular conversion to their active phosphorylated metabolites: interactions between these agents, or with other drugs may impact upon efficacy. PIs are metabolised by cytochrome P450 enzymes in gut and liver; some intracellular metabolism by P450 isoforms is also possible. PIs are also substrates for drug efflux transporters such as P-gp and MRP1. We have previously observed a hierarchy of intracellular accumulation of PIs, most probably related to physiochemical characteristics of these drugs such as lipophilicity and plasma protein binding. Comparatively, little is known about the intracellular pharmacokinetics of NNRTIs. These drugs probably do not accumulate inside cells to any significant degree. The study of intracellular pharmacokinetics of HIV drugs is central to investigating putative sanctuary sites where HIV may replicate with little selective pressure. However, stringent methodological procedures need to be applied, and techniques for measuring intracellular drug are in their infancy. Moreover, failure to differentiate between truly intracellular drug and drug bound to cell membranes render results difficult to interpret.
...
PMID:Intracellular pharmacokinetics of antiretroviral agents. 1573 42

Cisplatin (CDDP) is a widely used potent chemotherapeutic agent for many malignancies. However, the mechanism of resistance to CDDP remains unclear. To investigate the molecular mechanism, we established a CDDP-resistant cell line (H-1R) from a CDDP-sensitive cell line (H-1) which was derived from moderately differentiated squamous cell carcinoma of the lower gingiva. The 3-(3,4-dimethyl-thiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay indicated that H-1R had a 10-fold greater resistance to CDDP than H-1. When we compared gene expression levels in the cell lines using an in-house cDNA microarray, which represented 2,201 genes originating from normal oral tissue, primary oral cancer, and oral cancer cell lines, 12 genes showing elevated mRNA expression in H-1R compared with H-1 were identified. Among them, the up-regulated expression of ATP-binding cassette transporter genes (MDR1, MRP1, and MRP2), CD55, and PGK1 and down-regulated expression of Caveolin 1 were further confirmed by semiquantitative reverse transcriptase-polymerase chain reaction (PCR) or real-time PCR. Our results suggest that H-1 and H-1R cell lines could be useful for elucidating the candidate genes responsible for CDDP resistance, including the genes found in this study.
...
PMID:Establishment and characterization of a cisplatin-resistant oral squamous cell carcinoma cell line, H-1R. 1621 Dec 97


1 2 Next >>

---