Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We examined the genetic and biochemical bases for drug resistance and the order of appearance of different mechanisms underlying the increasingly more resistant murine erythroleukemia cell lines established in Adriamycin (ADR). In the first-step low-level resistant cell line PC4-A5 (able to grow in 5 ng/mL ADR), there was a 2-fold reduction in topoisomerase IIalpha and topoisomerase IIbeta mRNA levels, as well as topoisomerase IIalpha protein and activity levels as compared with the parental cell line. The topoisomerase IIalpha activity levels remained reduced as the cells became increasingly more resistant. In contrast, the topoisomerase II mRNA and protein levels returned to approximately the parental levels in resistant cells growing in higher drug concentrations (40-160 ng/mL). Parental cells expressed the multidrug resistance protein (MRP), but beginning with PC4-A5 MRP expression decreased and remained reduced in increasingly resistant cell lines. At high levels of ADR resistance, the cells expressed the mdr3 gene concomitant with the appearance of vincristine resistance and energy-dependent daunomycin and vincristine efflux. Glutathione levels, internal pH, and expression of the major vault protein (MVP) remained unchanged in all cell lines. Fluorescence microscopy revealed no alterations in daunomycin distribution or vesicle numbers between the parental and resistant cell lines. Different resistance mechanisms emerge sequentially as cells become more resistant to ADR; the mechanisms are retained during the development of multidrug resistance (MDR). In intermediate-level MDR cell lines (PC4-A10 and PC4-A20), resistance involves an as yet undetermined mechanism(s).
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PMID:Emergence of different mechanisms of resistance in the evolution of multidrug resistance in murine erythroleukemia cell lines. 939 72

Cytoplasmic replication of poxviruses dictates the encoding of most, if not all, of the trans-acting factors required for faithful genome duplication. Several of these proteins have been identified through genetic and biochemical evaluation, including the catalytic DNA polymerase (E9), an essential and stoichiometric component of the processive polymerase (A20), a single-strand DNA-binding protein (I3), a type I topoisomerase (H6), the uracil DNA glycosylase (D4), a nucleic acid-independent nucleoside triphosphatase (D5), a serine/threonine protein kinase (B1), and a Holliday Junction resolvase (A22). All of these factors work in concert to faithfully duplicate the viral genome. Although a replication origin has not been defined for the poxviruses, cis-acting sequences found within the telomeric 200 bp have been implicated as necessary and sufficient for minichromosome replication. Replication occurs within cytoplasmic foci from approx 3 to 12 h postinfection. This chapter includes several methodologies to assay and quantitate replication in vivo, visualize replication foci microscopically, and test the integrity of central replication enzymes in vitro.
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PMID:Methods for analysis of poxvirus DNA replication. 1511 16

In murine erythroleukemia (MEL) A20 cells (grown in 20 ng/ml adriamycin), mutation(s) producing 10-fold adriamycin (doxorubicin) resistance emerged via an unknown mechanism. Exposure of A20 cells to further stepwise increasing concentrations of ADR in combination with MDR modulators (PSC833 and verapamil) aimed to amplify the undetermined A20 mechanism while controlling P-glycoprotein (P-gp) overexpression. The growth of the derived cell lines A30P, A40P and A60P (grown in 30, 40 and 60 ng/ml ADR with PSC833 and verapamil) was initially slow, but eventually reached near WT rates. The new cell lines A30P and A40P were only 1.3- and 1.6-fold more resistant to adriamycin than PC4 A20. Resistance to vincristine was unchanged, but resistance to etoposide (VP-16) was 3.7-fold higher in A40P than A20 (itself 97-fold higher than wild-type). Expression of mdr3 and mrp mRNA tested by RT-PCR showed no increase. Daunorubicin and etoposide accumulation was not different among the cell lines, and no changes were detected in the number of daunorubicin fluorescent lysosomes. In comparison to WT, reduced topoisomerase IIalpha (EC 5.99.1.3) activity (20%) and protein expression (80%) was similar to the parental A20 cells. No mutations in the coding sequence of topoisomerase IIalpha could be located to account for the high etoposide resistance levels. The inhibitor combination of verapamil and PSC833 prevented the emergence of transporter mediated MDR, but not ADR selection of cell lines highly resistant to etoposide.
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PMID:Selection of non-P-glycoprotein mediated high-level etoposide resistant cell lines by adriamycin with P-gp inhibitors. 1646 81