Berg, Nicholas J.

Abstract A micro version of a nuclear binding assay to assess the biological activity of receptors for steroid hormones was developed for application to small (needle) biopsies of human tumors for the purpose of predicting responses to steroid therapy. This easier assay requires 10-fold less tissue than the original nuclear binding assay described for progesterone receptors in the avian oviduct, endometrium, and endometrial carcinomas (Spelsberg TC, et al., Endocrinology 1987;121:631). We describe the application of this micro assay to normal avian oviduct and cancers of the human breast, and we demonstrate a tissue specificity and saturation of nuclear binding. The micro assay reliably measured as little as 0.5 mg equivalents of tissue per assay tube. Results for breast tumors determined to be estrogen-receptor-positive by the standard dextran-coated charcoal method were also determined with this nuclear binding assay. As described previously for progesterone receptors in endometrial carcinomas, some receptor-positive breast biopsies displayed negligible capacity for nuclear binding. Therefore, with the present assay we have identified nonfunctional receptors in these biopsies, which may be useful for accurate prediction of patients' responses to therapy with hormones.

In seven strains of cultured normal human osteoblast-like cells, a mean of 1615 molecules of tritium-labeled 17β-estradiol per cell nucleus could be bound to specific nuclear sites. The nuclear binding of the labeled steroid was temperature-dependent, steroid-specific, saturable, and cell type-specific. These are characteristics of biologically active estrogen receptors. Pretreatment with 10 nanomolar estradiol in vitro increased the specific nuclear binding of progesterone in four of six cell strains, indicating an induction of functional progesterone receptors. RNA blot analysis demonstrated the presence of messenger RNA for the human estrogen receptor. The data suggest that estrogen acts directly on human bone cells through a classical estrogen receptor-mediated mechanism.