The biological significance of estradiol receptor binding to DNA.

MTW9-D, a rat mammary tumor derived from MTW9 by chronic administration of the dopamine antagonist drug R33,812 shows ovariectomy-induced regression (OIR). MTW9-MtT is also a variant of MTW9, grown by coimplantation of a mammosomatotropic tumor MtTW10, but it does not show OIR. However, when the mammosomatotropic tumor (MtT) is resected, the tumor regresses and shows rapid OIR; implantation of MtT into animals bearing MTW9-D prevents OIR following drug withdrawal. The estradiol receptor (ER) from MTW9-D cytosol binds to DNA-cellulose significantly more than that from MTW9-MtT. After MtT resection, the mammary tumor ER binds to DNA-cellulose, as well as ER from MTW9-D, whereas implantation of MtT into animals bearing MTW9-D decreases ER binding to DNA-cellulose. The significance of these findings in relation to possible clinical application is discussed.