DNA binding ability of estrogen receptor from human breast cancer

Abstract

DNA binding ability of estrogen receptors (ER) from human breast cancers was examined and clearly demonstrated in 51 of 55 ER positive tumors by using a DNA cellulose slurry. The percentages of ER bound to fixed amounts of DNA varied widely, but the average was lower than that of rat uterine ER. Preheating of ER at 25°C caused increased DNA binding ability in some tumors but significant loss of this ability in other tumors. Mixing rat uterine cytosol with cytosols from 2 tumors, including an endocrine-resistant cancer which showed no DNA binding activity of ER, destroyed DNA binding ability of uterine ER with a minor effect on estradiol binding capacities even at low temperature. Exposure of the tumor cytosol to 56°C for 30 min or dialysis of the tumor cytosol, however, reduced this inhibitory activity. This cytoplasmic factor in the tumor was also found to cleave rat uterine ER into a smaller fragment (3–4S) either in a high salt or in a low salt sucrose density gradient, especially at a relatively high temperature. A significant amount of DNA binding of ER and its enhancement by preheating were observed in all 8 endocrine-responsive tumors, while no DNA binding of ER or temperature-induced decrease in DNA binding ability was observed in 5 of 6 ER positive but endocrine-resistant tumors, suggesting clinical importance of this cytoplasmic factor in the tumor.