Estrogen binding sites in the nucleus of normal and malignant human tissue: characteristics of the multiple nuclear...

The studies presented here describe the effects of the nonionic detergent, Tween 80 and the reducing agent, dithiothreitol (5 mM), on the quantitation of specific nuclear estrogen binding sites, both estrogen receptors (ER) and type II estrogen binding sites (EBS), in human breast cancer. Neither of these agents had any significant effect on the apparent Kd of the amount of ER measured; however, both had a dramatic effect on the amount of type II EBS measured. Two antiestrogens, tamoxifen and nafoxidine, were also tested for their ability to bind to ER and type II EBS in human breast tumors. Both of the antiestrogens were capable of competing with estradiol for ER and type II EBS. We also present a series of 25 individual human breast cancer specimens which were analyzed for cytoplasmic ER and progesterone receptor by sucrose density gradient centrifugation and for nuclear ER and type II EBS by the sucrose pad assay. Sixty-four % (16 of 25) of the tumors contained nuclear ER and type II EBS when analyzed by the sucrose pad assay. The concentration of type II EBS was strongly correlated to the concentration of cytoplasmic progesterone receptor.