title: Selective overproduction of human dihydrofolate reductase in a methotrexate-resistant human-mouse somatic cell hybrid.
abstract: The development of methotrexate (MTX) resistance in cultured cells results in increased levels of the drug's target enzyme dihydrofolate reductase (DHFR). Stepwise-selected MTX-resistant sublines originating from an MTX-sensitive human-mouse hybrid expressed elevated DHFR levels and human-DHFR specific gene sequence amplification. By high resolution two-dimensional polyacrylamide gradient electrophoresis, human DHFR was shown to be selectively overproduced in VB2a-100 MTX-resistant cells whereas mouse DHFR protein "spots" present in MTX-sensitive parental hybrid were absent in these cells exhibiting 100 microM MTX resistance. These findings and those in a parallel study indicate that concurrent with overproduction of human DHFR and amplification DHFR sequences in VB2a-100, a loss of mouse-specific DHFR gene sequences occurred.
mesh_terms: D000818:Animals; D004351:Drug Resistance; D004591:Electrophoresis, Polyacrylamide Gel; D005784:Gene Amplification; D006801:Humans; D006822:Hybrid Cells / Q000187:drug effects / Q000378:metabolism*; D008727:Methotrexate / Q000494:pharmacology*; D051379:Mice; D013762:Tetrahydrofolate Dehydrogenase / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate