A cell line derived from H35 hepatoma cells resistant to methotrexate (MTX) as a result of a defective transport systern for M T X has been examined to determine how closely the variant resembles the parent cells with regard to other cells to catalyze the poly-y-glutamylation of M T X was approxdence of similarity between wild-type and H35 R ~. ~ cells was corticoid-dependent TAT induction and the presence of yGGT. derived from the equitoxic activity to both cell lines of non-The results show that several of the Phenotypic Properties are classical antifolates and other miscellaneous antineoDlastics maintained but rGGT is absent in the drug-resistant cells. The agents, suggesting that the transport-resistant sublines are similar to the parent cells except for those processes related to resistance (Mini et al., 1985). In order to evaluate this further we examined a ,,umber of the phenotypic properties in wildbiochemical properties. The capacity Of extracts Of resistant imately twice as great as that of wild-type cell extracts. Evi-type and transport-resistant H35 cells. These include sensitivity to a variety Of antineoplastic agents, Am gluC0which act by a variety of mechanisms. Two phenotypi; markers of hepatic cell function, a-aminoisobutyric acid (AIB) transport and tyrosine aminotransferase (TAT) activity inducibility, were present in both cell types, demonstrating the maintenance of these phenotypic properties in the H35 R0.3 cells. y-Glutamyltransferase (GGT, EC 2.3.2.2) activity differed in that it was present in wild-type cells and barely detectable in H35 %,3 cells. The GGT activity reappeared in the H35 cells when they regained MTX sensitivity after incubation for 14-20 weeks in MTX-free media. Although defective M T X transport appeared to be correlated with the disappearance of GGT activity in an H35 variant cell line, no functional relationship between them is apparent at this time. It is possible that a lack of GGT activity may be evidence of a more differentiated phenotype in the transport-resistant cell line.
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