Increased dihydrofolate reductase activity in methotrexate-resistant human promyelocytic-leukaemia (HL-60) cells. Lack of correlation between increased activity and overproduction.
Methotrexate(MTX)-resistant human promyelocytic-leukaemia cells (HL-60) derived from MTX-sensitive cells have a 20-fold increase in dihydrofolate reductase (DHFR) activity as compared with the sensitive cells. This increase is not associated with a concomitant increase in DHFR protein as determined by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and by immunological methods using mouse anti-DHFR antibody. The rate of DHFR synthesis is similar in both cell lines. Furthermore, both the sensitive and resistant cells have similar amounts of RNA hybridizing to a DHFR complementary-DNA probe, correlating well with the lack of increase in DHFR protein. DHFR-gene dosages were similar in both types of cells. We conclude that the 20-fold increase in DHFR activity present in these MTX-resistant cells is not due to the overproduction of DHFR but due to the expression of a more active form of the enzyme.
D002460:Cell Line; D004351:Drug Resistance; D004591:Electrophoresis, Polyacrylamide Gel; D005796:Genes; D006367:HeLa Cells / Q000201:enzymology; D006801:Humans; D007122:Immunoelectrophoresis; D015470:Leukemia, Myeloid, Acute / Q000201:enzymology*; D008727:Methotrexate / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate