Sample records for 甲氨喋呤 (methotrexate)
from WorldWideScience.org

Sample records 1 - 20 shown. Select sample records:



75

Transient hypoxia enhances the frequency of dihydrofolate reductase gene amplification in Chinese hamster ovary cells.

Rice, G C; Schimke, R T; Hoy, C

Exposure of Chinese hamster cells to reduced oxygen partial pressure results in a marked enhancement in the frequency of methotrexate resistance and dihydrofolate reductase gene amplification. The frequency of enhanced resistance is a function of the length of exposure to hypoxic conditions and the ...

DRIVER (Chinese)

76

Transformation of mammalian cells with an amplifiable dominant-acting gene.

Dana, S; Wigler, M; Kurtz, D; Perucho, M; Pellicer, A; Axel, R; Silverstein, S

We have transferred a mutant hamster gene coding for an altered dihydrofolate reductase to wild-type cultured mouse cells by using total genomic DNA from methotrexate-resistant Chinese hamster ovary A29 cells as donor. By demonstrating the presence of hamster gene sequences in transformants we have ...

DRIVER (Chinese)

77

Transfer of codominant markers by isolated metaphase chromosomes in Chinese hamster ovary cells.

Spandidos, D A; Siminovitch, L

Codominant mutations to methotrexate and ouabain resistance in Chinese hamster ovary cells can be transferred to recipient Chinese hamster ovary cells by isolated metaphase chromosomes. For methotrexate, both the structural change and the increased activity of dihydrofolate reductase (5,6,7,8-tetrah...

DRIVER (Chinese)

78

The dihydrofolate reductase amplicons in different methotrexate-resistant Chinese hamster cell lines share at least a 273-kilobase core sequence, but the amplicons in some cell lines are much larger and are remarkably uniform in structure.

Flintoff, W F; Looney, J E; Leu, T H; Ma, C; Troutman, W B; Hamlin, J L

We have previously cloned and characterized two different dihydrofolate reductase amplicon types from a methotrexate-resistant Chinese hamster ovary cell line (CHOC 400). The largest of these (the type I amplicon) is 273 kilobases (kb) in length. In the present study, we utilized clones from the typ...

DRIVER (Chinese)

82

Similar 150-kilobase DNA sequences are amplified in independently derived methotrexate-resistant Chinese hamster cells.

Montoya-Zavala, M; Hamlin, J L

We have isolated overlapping recombinant cosmids that represent 150 kilobases of contiguous DNA sequence from the amplified dihydrofolate reductase domain of a methotrexate-resistant Chinese hamster ovary cell line (CHOC 400). This sequence includes the 25-kilobase dihydrofolate reductase gene and a...

DRIVER (Chinese)

83

S phase-specific synthesis of dihydrofolate reductase in Chinese hamster ovary cells.

Mariani, B D; Schimke, R T; Slate, D L

We investigated the cell cycle modulation of dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase, 7,8-dihydroxyfolate:NADP+ oxidoreductase, EC 1.5.1.3) levels in methotrexate-resistant Chinese hamster ovary cells synchronized by mitotic selection. DNA content and DHFR concentration were an...

DRIVER (Chinese)

84

Replication in the amplified dihydrofolate reductase domain in CHO cells may initiate at two distinct sites, one of which is a repetitive sequence element.

Anachkova, B; Hamlin, J L

To study initiation of DNA replication in mammalian chromosomes, we have established a methotrexate-resistant Chinese hamster ovary cell line (CHOC 400) that contains approximately 1,000 copies of the early replicating dihydrofolate reductase (DHFR) domain. We have previously shown that DNA replicat...

DRIVER (Chinese)

85

Poly(L-lysine) has different membrane transport and drug-carrier properties when complexed with heparin.

Shen, W C; Ryser, H J

Methotrexate (MTX) conjugated to a Mr 3000 poly(L-Lys) markedly inhibits the growth of Pro-3 MtxRII5-3 Chinese hamster ovarian cells, a mutant line known to be drug resistant because of defective MTX transport. In these cells, membrane transport of [3H]MTX-poly(Lys) is sharply decreased by addition ...

DRIVER (Chinese)

86

Overproduction of dihydrofolate reductase and gene amplification in methotrexate-resistant Chinese hamster ovary cells.

Essani, A K; Flintoff, W F; Nagainis, C R; Weber, M K; Robertson, D; Salser, W

Stable isolates of Chinese hamster ovary cells that are highly resistant to methotrexate have been selected in a multistep selection process. Quantitative immunoprecipitations have indicated that these isolates synthesize dihydrofolate reductase at an elevated rate over its synthesis in sensitive ce...

DRIVER (Chinese)

87

Organization of a Chinese hamster ovary dihydrofolate reductase gene identified by phenotypic rescue.

Hamlin, J L; Milbrandt, J D; Greisen, K S; Azizkhan, J C

We have constructed a genomic DNA library from a methotrexate-resistant Chinese hamster ovary cell line (CHOC 400) in the cosmid vector pHC79. By utilizing a murine dihydrofolate reductase (DHFR) cDNA clone, we have identified 66 DHFR+ clones among the 11,000 colonies screened by colony hybridizatio...

DRIVER (Chinese)

88

Organization and genesis of dihydrofolate reductase amplicons in the genome of a methotrexate-resistant Chinese hamster ovary cell line.

Hamlin, J L; Ma, C; Leu, T H; Looney, J E

We have recently isolated overlapping recombinant cosmids that represent the equivalent of two complete dihydrofolate reductase (dhfr) amplicon types from the methotrexate-resistant Chinese hamster ovary (CHO) cell line CHOC 400. In the work described in this report, we used pulse-field gradient gel...

DRIVER (Chinese)

89

Multiple origins of replication in the dihydrofolate reductase amplicons of a methotrexate-resistant chinese hamster cell line.

Ma, C; Hamlin, J L; Leu, T H

We recently showed that replication initiates in the early S period at two closely spaced zones in the 240-kilobase (kb) dihydrofolate reductase (DHFR) amplicon of the methotrexate-resistant Chinese hamster ovary cell line CHOC 400. Both of these initiation loci (ori-beta and ori-gamma) have previou...

DRIVER (Chinese)

90

Moderate-level gene amplification in methotrexate-resistant Chinese hamster ovary cells is accompanied by chromosomal translocations at or near the site of the amplified DHFR gene.

Worton, R G; Flintoff, W F; Duff, C; Livingston, E

In previous studies, we have described several classes of methotrexate-resistant Chinese hamster ovary cell lines. Although the RI class is resistant because of an altered target enzyme, dihydrofolate reductase, the RIII class derived from RI cells is somewhat more resistant because of a moderate am...

DRIVER (Chinese)

91

Microcell-mediated cotransfer of genes specifying methotrexate resistance, emetine sensitivity, and chromate sensitivity with Chinese hamster chromosome 2.

Worton, R; Flintoff, W; Duff, C

Many selectable mutants of somatic Chinese hamster cells have been described, but very few of the mutations have been mapped to specific chromosomes. We have utilized the microcell-mediated gene transfer technique to establish the location of three selectable genetic markers on chromosome 2 of Chine...

DRIVER (Chinese)

92

Methotrexate-resistant Chinese hamster ovary cells have amplified a 135-kilobase-pair region that includes the dihydrofolate reductase gene.

Rothman, S M; Milbrandt, J D; White, W C; Heintz, N H; Hamlin, J L

For the eventual purpose of isolating and studying a single animal cell replicon, we have developed a methotrexate-resistant Chinese hamster ovary cell line that has amplified an early-replicating DNA sequence approximately 500 times; this sequence includes the gene coding for dihydrofolate reductas...

DRIVER (Chinese)

93

Isolation of the origin of replication associated with the amplified Chinese hamster dihydrofolate reductase domain.

Burhans, W C; Heintz, N H; Selegue, J E

Autoradiography of restriction digests of DNA labeled in early S phase indicates that replication of the amplified dihydrofolate reductase (DHFR) domain of methotrexate-resistant CHOC 400 cells initiates within a 6.1-kilobase pair (kb) EcoRI-doublet located on the 3' side of the DHFR gene. To locali...

DRIVER (Chinese)

94

Isolation of the amplified dihydrofolate reductase domain from methotrexate-resistant Chinese hamster ovary cells.

Looney, J E; Hamlin, J L

We isolated overlapping recombinant cosmids that represent the equivalent of two complete dihydrofolate reductase amplicon types from the methotrexate-resistant CHO cell line CHOC400. The type I amplicons are 260 kilobases long, are arranged in head-to-tail fashion, and represent 10 to 15% of the am...

DRIVER (Chinese)

95

Identification of methotrexate transport deficiency in mammalian cells using fluoresceinated methotrexate and flow cytometry.

Assaraf, Y G; Schimke, R T

We have studied the frequency of transport mutations in methotrexate-resistant Chinese hamster ovary cells using a rapid-flow cytometric technique. After saturating cells with fluoresceinated methotrexate, we examined the ability of hydrophilic and lipophilic antifolates to displace fluoresceinated ...

DRIVER (Chinese)

96

Identification and characterization of a gene that is coamplified with dihydrofolate reductase in a methotrexate-resistant CHO cell line.

Foreman, P K; Hamlin, J L

As part of an effort to characterize the spatial and functional relationships among genetic elements within the amplified dihydrofolate reductase (DHFR) domain in Chinese hamster cells, we have used a variation of the differential hybridization approach to identify cDNA clones whose genes are coampl...

DRIVER (Chinese)

98

Frequencies of independent and simultaneous selection of Chinese hamster cells for methotrexate and doxorubicin (adriamycin) resistance.

Rice, G C; Schimke, R T; Ling, V

We have determined the frequency with which Chinese hamster cells become resistant to either methotrexate or doxorubicin (former generic name, adriamycin) alone or to the two drugs simultaneously. We find that the frequency of acquisition of simultaneous resistance is 10-100 times higher than that p...

DRIVER (Chinese)

99

Expression of the plasmid-encoded type I dihydrofolate reductase gene in cultured mammalian cells: a novel selectable marker.

Simonsen, C S; Levinson, A D; Walter, M

A recombinant plasmid has been designed to express the gene encoding a type I methotrexate-resistant dihydrofolate reductase, derived from the bacterial plasmid R483, in DHFR- Chinese hamster ovary cells. Vectors containing the wild type gene, whose coding sequence initiates with a GTG codon, fail t...

DRIVER (Chinese)

100

Effect of cycloheximide on development of methotrexate resistance of Chinese hamster ovary cells treated with inhibitors of DNA synthesis.

Sherwood, S W; Schimke, R T; Schumacher, R I

We examined the effects of 18 h of incubation of Chinese hamster ovary (CHO K1) cells with cycloheximide, hydroxyurea, and aphidicolin. Treatment of cells with cycloheximide alone at a concentration adequate to inhibit DNA synthesis to less than 10% of control was significantly less cytotoxic and cl...

DRIVER (Chinese)

101

Complementation of a methotrexate uptake defect in Chinese hamster ovary cells by DNA-mediated gene transfer.

Underhill, T M; Flintoff, W F

A methotrexate-resistant Chinese hamster ovary cell line deficient in methotrexate uptake has been complemented to methotrexate sensitivity by transfection with DNA isolated from either wild-type Chinese hamster ovary or human G2 cells. Primary and secondary transfectants regained the ability to tak...

DRIVER (Chinese)

102

Chromosomal localization of the murine RFC-1 gene encoding a folate transporter and its amplification in an antifolate resistant variant overproducing the transporter

Roy, K; Chiao, JH; Spengler, BA; Tolner, B; Yang, CH; Biedler, JL; Sirotnak, FM

\A variant of the L1210 cell (L1210/R83) selected in the presence of the lipophilic antifolate, metoprine, and a concentration of the natural diastereoisomer of 5-formyltetrahydrofolate, lLCHO-folateH(4), suboptimum for growth exhibited a 35-fold increase compared to parental L1210 cells in one-carb...

DRIVER (Chinese)

103

Carcinogen-mediated methotrexate resistance and dihydrofolate reductase amplification in Chinese hamster cells.

Kleinberger, T; Lavi, S; Etkin, S

We have investigated different parameters characterizing carcinogen-mediated enhancement of methotrexate resistance in Chinese hamster ovary (CHO) cells and in simian virus 40-transformed Chinese hamster embryo (C060) cells. We show that this enhancement reflects dihydrofolate reductase (dhfr) gene ...

DRIVER (Chinese)

104

An amplified chromosomal sequence that includes the gene for dihydrofolate reductase initiates replication within specific restriction fragments.

Heintz, N H; Hamlin, J L

We have developed a methotrexate-resistant Chinese hamster ovary cell line (CHOC 400) containing a 500-fold amplification of a 135-kilobase chromosomal DNA sequence. This sequence includes the gene for dihydrofolate reductase (tetrahydrofolate dehydrogenase, 5,6,7,8-tetrahydrofolate: NADP+ oxidoredu...

DRIVER (Chinese)

105

Amplified inverted duplications within and adjacent to heterologous selectable DNA.

Heartlein, M W; Latt, S A

Plasmids containing a dihydrofolate reductase (DHFR) expression unit were transfected into DHFR-deficient Chinese hamster ovary (CHO) cells. Methotrexate exposure was used to select cells with amplified DHFR sequences. Three cell lines were isolated containing amplified copies of transfected DNA tha...

DRIVER (Chinese)

106

Amplified dihydrofolate reductase genes are localized to a homogeneously staining region of a single chromosome in a methotrexate-resistant Chinese hamster ovary cell line.

Urlaub, G; Nunberg, J H; Schimke, R T; Kaufman, R J; Chasin, L A

Methotrexate-resistant Chinese hamster ovary cells selected for high resistance by progressive increments of methotrexate in the culture medium have levels of dihydrofolate reductase (tetrahydrofolate dehydrogenase, 7,8-dihydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) 200 times that of sensitive cel...

DRIVER (Chinese)

107

Amplification and loss of dihydrofolate reductase genes in a Chinese hamster ovary cell line.

Kaufman, R J; Schimke, R T

During stepwise increases in the methotrexate concentration in culture medium, we selected Chinese hamster ovary cells that contained elevated dihydrofolate reductase levels which were proportional to the number of dihydrofolate reductase gene copies (i.e., gene amplification). We studied the dihydr...

DRIVER (Chinese)

109

Activation of a mammalian origin of replication by chromosomal rearrangement.

Leu, T H; Hamlin, J L

The methotrexate-resistant Chinese hamster cell line DC3F/A3-4K (A3/4K) contains at least two prominent dihydrofolate reductase amplicon types. The type I amplicons, constituting approximately 80% of the total, are at least 650 kb in length, but the endpoints have not yet been characterized. The typ...

DRIVER (Chinese)

110

A STRATEGY FOR THE DESIGN OF MEMBRANE-PERMEABLE FOLYLPOLY-GAMMA-GLUTAMATE SYNTHETASE INHIBITORS - BAY-REGION-SUBSTITUTED 2-DESAMINO-2-METHYL-5,8-DIDEAZAFOLATE ANALOGS

SANGHANI, PC; JACKMAN, A; EVANS, VR; THORNTON, T; HUGHES, L; CALVERT, AH; MORAN, RG

Previous attempts to design inhibitors of mammalian folylpolyglutamate synthetase (FPGS) have resulted in three classes of active compounds, all of which have charged moieties in the side chain, but structural alteration of the rest of the folate molecule has not seemed to be an avenue for drug disc...

DRIVER (Chinese)