Elevated amounts of methotrexate-binding protein, different from normal dihydrofolate reductase, in a petunia MTXR-cell line

Abstract

A petunia cell line, 1ECB, was previously isolated by the stepwise selection procedure, for resistance to methotrexate (MTX), an antimetabolite for the enzyme dihydrofolate reductase (DHFR). Using ammonium sulfate precipitates of cell lysates of cell line 1ECB and its parental cell line (WT), it was found that the mutant has an increase of 400 fold in (3)H-MTX binding capacity and a decrease in the affinity for MTX binding, at two orders of magnitude, in comparison with the WT. In addition, the DHFR specific activity in the mutant increased only moderately (5- to 10-fold), this activity is extremely sensitive to MTX inhibition as compared to the WT. It is evident that the MTX resistance of line 1ECB results mainly from overproduction of an MTX-binding protein which differs from the WT DHFR by four biochemical criteria. This protein may serve as a trap for the excess amounts of MTX to which the cells are exposed.

Methotrexate Resistance in Datura innoxia (Uptake and Metabolism of Methotrexate in Wild-Type and Resistant Cell Lines)

“…fied that are associated with acquired resistance to MTX in plants, namely (a) an increase in a MTX-binding protein(s) that is different from DHFR (Barg et al, 1987;Shabtai et al, 1992); (b) a decrease in the uptake of MTX (Cella et al, 1984;Barg and Shabtai, 1991); and (c) an increase in the target enzyme, DHFR (Shimamoto and Nelson, 1981;Cella et al, 1987;Lazar et al, 1989). However, no DHFR gene amplification in plant cells has been demonstrated.…”