title: Antifolate-resistant Chinese hamster cells. Evidence for dihydrofolate reductase gene amplification among independently derived sublines overproducing different dihydrofolate reductases.
abstract: Purification of a cDNA probe specific for dihydrofolate reductase mRNA has allowed the relative quantification of dihydrofolate reductase gene numbers and mRNA levels between a line of Chinese hamster lung fibroblasts sensitive to the antifolate drugs methotrexate and methasquin and sublines which by virtue of their overproduction of the target enzyme dihydrofolate reductase are cross-resistant to these site-specific inhibitors. Previous results have shown that resistant sublines could overproduce one of two molecular weight forms of dihydrofolate reductase, one parental-like (Mr = 21,000) and one nonparental-like (Mr = 20,000), each encoded by a different mRNA present in elevated amounts in resistant cells (Melera, P. W., Wolgemuth, D., Biedler, J. L., and Hession, C. (1980). J. Biol. Chem. 255, 319--322). The cDNA-RNA and cDNA-DNA hybridization experiments reported here confirm the elevated levels of dihydrofolate reductase-specific mRNA in resistant cells and show that the overproduction of either molecular weight form of dihydrofolate reductase is accompanied by amplification in dihydrofolate reductase gene number.
mesh_terms: D000818:Animals; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004247:DNA / Q000378:metabolism*; D004351:Drug Resistance; D005492:Folic Acid / Q000031:analogs & derivatives* / Q000096:biosynthesis; D007700:Kinetics; D008168:Lung; D008727:Methotrexate / Q000494:pharmacology*; D008970:Molecular Weight; D009693:Nucleic Acid Hybridization; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D012335:RNA, Ribosomal / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D012335:RNA, Ribosomal; C010920:dihydrofolate; D004247:DNA; D005492:Folic Acid; D008727:Methotrexate