Mutant mouse cells with nitrobenzylthioinosine-insensitive nucleoside transport functions

From a mutagenized population of wildtype S49 T lymphoma cells, clones were generated that were resistant to the physiological effects of the potent inhibitor of nucleoside transport, 4-nitrobenzyl-6-thioinosine (NBMPR). NBMPR protected wildtype cells from the cytotoxic effects of a spectrum of nucleosides, whereas two mutant clones, KAB1 and KAB5, were still sensitive to nucleoside-mediated cytotoxicity in the presence of NBMPR. In addition, NBMPR prevented wildtype cells from surviving in hypoxanthine-amethopterin-thymidine containing medium, whereas KAB1 and KAB5 cells grew normally. Rapid sampling transport studies indicated that mutant cells, unlike wildtype parental cells, had acquired a substantial NBMPR-insensitive nucleoside transport component. Binding studies with [3H]NBMPR indicated that KAB5 cells were 70-75% deficient in the number of NBMPR binding sites, whereas KAB1 cells possessed a wildtype complement of NBMPR binding sites. The characterization of the KAB1 and KAB5 cell lines suggested that the NBMPR binding site in wildtype S49 cells is genetically distinguishable from the nucleoside carrier site.