Isolation of Retinole Acid-resistant Clones from Human Breast Cancer Cell Line MCF-7 with Altered Activity of Cellular Retinoic Acid-binding Protein1

After ethyl methane sulfonate mutagenesis of the mammary carcinoma cell line, MCF-7, we have isolated three clones, U-2, U-3, and U-9, resistant to retinole acid. These three clones showed more than a 1000-fold higher level of resistance to retinoic acid than the parental MCF-7 cells when assayed by colony formation in monolayer culture system or by growth curves. The three resistant clones showed a 200-fold higher resistance to 13-c/s-retinoic acid, about 10-fold higher resistance to retino!, and about 2-fold higher resistance to retinyl acetate, respectively, than MCF-7. Binding of [3H]retinoic acid or [3H]retinol to a cellular fraction in situ showed apparent decrease of the specific binding of retinoic acid in U-2, but there was no such specific fraction bound to retinol in U-2 and MCF-7. Sucrose gradient analysis with cytoplasmic fraction showed little, if any, cellular retinoic acid-binding protein in U-2, but a significant amount of the cellular retinoic acid-binding protein could be found in MCF-7. By contrast, there was no activity of cellular retinolbinding protein in both MCF-7 and U-2. The sensitivity or resist ance of mammalian cells in culture to retinoic acid is discussed in relation with cellular binding activity for vitamin A.