Using a radiometric assay the effects of estradiol upon the activity of estradiol 2- and 16α-hydroxylases in MCF-7 human breast cancer cells in culture were studied. After 5 days of treatment and 36 h of withdrawal, incubation in the presence of either 2- or 16α-tritiated substrate was carried out. Estradiol (10 nM) significantly increased 16α-hydroxylase activity (21%, P < 0.01), while no effects on 2-hydroxylase activity was observed. Treatment for 6 weeks caused a major increase in 16α-hydroxylation (65%, P < 0.001) and a significant reduction in 2-hydroxylation (21%, P < 0.05). These effects were not observed in estrogen receptor-negative MDA-MB-231 human breast cancer cells. Our observations suggest that these two metabolic pathways in MCF-7 cells are independently regulated and that this regulation is affected via the estrogen receptor.
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