Transport of methotrexate in Chinese hamster ovary cells: a mutant defective in methotrexate uptake and cell binding.
The uptake of several folate compounds has been investigated in wild-type and one class of methotrexate-resistant Chinese hamster ovary cells. The wild-type cells can take up methotrexate, folic acid, and 5-methyl tetrahydrofolate. The uptake of methotrexate is characterized by a KT of 1.9 +/- 0.2 microM and a Vmax of 1 +/- 0.8 pmol/min/mg protein, is competitively inhibited by folic acid and 5-methyl tetrahydrofolate, and is sensitive to p-hydroxymercuriphenyl sulfonic acid. The resistant cells are unable to take up methotrexate, folic acid, and 5-methyl tetrahydrofolate. In addition, the resistant cells are unable to bind methotrexate specifically, whereas the wild-type cells bind the drug with an apparent KD of 2 +/- 0.4 microM and a Vmax of 1.3 +/- 0.3 pmol/mg protein. These data indicate that the resistant cells are resistant because of an inability to take up the drug resulting from a defective membrane-binding component. The data also suggest that both methotrexate and folic acid are transported by the same system in Chinese hamster ovary cells.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004351:Drug Resistance; D005260:Female; D005492:Folic Acid / Q000378:metabolism; D007700:Kinetics; D008727:Methotrexate / Q000378:metabolism*; D009154:Mutation; D010053:Ovary; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013763:Tetrahydrofolates / Q000378:metabolism
D013439:Sulfhydryl Reagents; D013763:Tetrahydrofolates; D005492:Folic Acid; C005984:5-methyltetrahydrofolate; D008727:Methotrexate