Isolation and Characterization of a Rat Liver Epithelial Cell Line Resistant to the Antiproliferative Effects of Transforming Growth Factor β (Type 1)

Rat liver epithelial cells resistant to the growth-inhibitory effects of transforming growth factor β1 (TGF-β#x03B2;1) were isolated after 3 h exposure to 1.5 μg/ml of N-methyl-.N′-nitro-N-nitrosoguanidine followed by continuous treatment with 1 ng/ml TGF-β#x03B2;1 for 6 weeks. In comparison to the parental or N-methyl-N′-nitro-N-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 TGF-β1 and exhibited resistance to growth inhibition by a highly purified liver-derived growth inhibitor, recombinant human tumor necrosis factor, and transforming growth factor β2. 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-β, treatment. Binding of 125I-labeled TGF-β, 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 S-transferase-P, TGF-β1, and c-myc genes. The data presented here suggest an association between resistance to the growth-inhibitory effects of TGF-β1- and MDR-1-mediated multidrug resistance.