Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.5.1.3 (dihydrofolate reductase)
 5,819 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mouse mdr gene family is composed of three members designated mdr1, mdr2, and mdr3. A full-length mdr2 complementary DNA clone has been introduced in an amplifiable eukaryotic expression vector (pEMC2b1) which directs amplification and overexpression of a bicistronic mdr2-dihydrofolate reductase mRNA after stepwise methotrexate selection of transfected mutant dihydrofolate reductase Chinese hamster ovary DUK cells. Independent cell clones expressing low to high amounts of mdr2 cellular mRNA and Mdr2 protein in their membrane fraction could be obtained by this selection procedure. Comparison of drug survival characteristics of cell clones expressing similar amounts of either Mdr1 or Mdr2 proteins revealed that Mdr1 but not Mdr2 could confer readily detectable levels of colchicine or vinblastine resistance. Labeling experiments using membrane-enriched fractions and a photoactivatable analogue of ATP showed that the Mdr2 protein was properly inserted in the membrane of transfected cells and could bind this ligand with an apparent affinity similar to that of Mdr1. However, labeling studies with the photoactivatable drug analogue iodoarylazidoprazosin showed considerably reduced binding of this ligand to Mdr2 as compared to Mdr1. Our findings demonstrate that Mdr2 cannot confer drug resistance and suggest that this inability is linked to reduced drug binding to the Mdr2 protein.
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PMID:The inability of the mouse mdr2 gene to confer multidrug resistance is linked to reduced drug binding to the protein. 791 94

Various gene alterations are involved in the drug resistance of leukemia cells. To understand the mechanism that underlies the emergence of cells with such gene alterations in human leukemia, we performed clonal analysis of the gene expression of mutant dihydrofolate reductase (DHFR) and mdr1 in trimetrexate-resistant human leukemia MOLT-3 cells. Trimetrexate-resistant (70- and 60-fold) sublines were developed in the presence or absence of an exogenous supply of thymidine (MOLT-3/TMQ70/Th+, MOLT-3/TMQ60/Th-, respectively). Ten clonal lines were isolated by methyl cellulose cloning from each of the 2 trimetrexate-resistant MOLT-3 sublines. All the clonal lines from the 2 sublines expressed mutated DHFR mRNA, with a base change (T --> C) at the second position of codon 31, as well as the wild-type mRNA, in accordance with cross-resistance to methotrexate. On the other hand, mdr1 mRNA expression was demonstrated by reverse-transcription polymerase chain reaction only in clonal lines from MOLT-3/TMQ70/Th+ cells. mdr1 mRNA expression in clonal lines from MOLT-3/TMQ70/Th+ cells and subclonal lines subsequently obtained from the 3 clonal lines with different mdr1 mRNA expression levels was heterogeneous, and its high expression levels were correlated with acquisition of the multidrug resistance (MDR) phenotype. Polymerase chain reaction-based assay for separate microsatellites, mfd27 and mfd41, demonstrated genomic instability among clonal and subclonal lines of MOLT-3. The clonal analysis of polymorphic microsatellites also suggested that emergence of MDR in trimetrexate-resistant MOLT-3 cells in thymidine was not only heterogeneous but also progressively expanding among clones. Genomic instability may play a role in the establishment and clonal evolution of drug resistance in leukemia cells.
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PMID:Microsatellite instability and clonal heterogeneity of MDR1 messenger RNA expression in trimetrexate-resistant human leukemia MOLT-3 cells developed in thymidine. 1036 Aug 22