Resistant to the Antiproliferative Effects of Transforming Isolation and Characterization of a Rat Liver Epithelial Cell Line

Rat liver epithelial cells resistant to the growth-inhibitory effects of transforming growth factor 0, (TGF-^i) were isolated after 3 h exposure to 1.5 Mg/mlof TV-methyl-iV'-nitro-A'-nitrosoguanidine followed by con tinuous treatment with 1 ng/ml TGF-/?i for 6 weeks. In comparison to the parental or /V-methyU/V'-nitro-A'-nitrosoguanidine-exposed rat liver epithelial cells (concentration causing 50% inhibition of the rate of DNA synthesis, 0.25 ng/ml), these cells were 10-fold more resistant to the antiproliferative effects of I(.!•-/•>', and exhibited resistance to growth inhibition by a highly purified liver-derived growth inhibitor, recombinant human tumor necrosis factor, and transforming growth factor /¿.,. Single cell cloning of these resistant cells led to the isolation of a nontransformed clonal cell population (clone 11) which maintained stable resistance in the absence of TGF-/3, treatment. Binding of 125I-labeledTGF-/3, to rat liver epithelial cells and clone 11 cells was similar. Clone 11 cells exhibited a 5-10-fold resistance to the cytotoxins Adriamycin and vinblastine as assessed by a clonogenic assay. This drug resistance was accompanied by an increase in the steady state levels of the mRNAs for multidrug resistance gene (MDR-1), glutathione 5-transferase-P, TGF/8|, and c-myc genes. The data presented here suggest an association between resistance to the growth-inhibitory effects of TGF-/9]and MDR/-mediated multidrug resistance.