Inhibitory Effect of Estrogens on GCDFP-15 mRNA Levels and Secretion in ZR-75-1 Human Breast Cancer Cells

Abstract

In order to better understand the mechanisms responsible for the antagonism between steroids in human breast cancer cells, we have studied the effect of 17 beta-estradiol (E2), dihydrotestosterone (DHT), and dexamethasone (DEX) alone or in combination on the expression of the breast gross cystic disease fluid protein-15 (GCDFP-15) in ZR-75-1 cells. Incubation with E2 markedly decreased basal GCDFP-15 mRNA levels accompanied by a parallel inhibition of the secretion of this tumor marker, the estrogenic effect being exerted at a half-maximal concentration of about 44 pM E2. The inhibitory effect of E2 on GCDFP-15 expression was competitively reversed by the antiestrogen LY156758. In addition, 1 nM E2 inhibited the marked stimulation induced by 1 nM DHT or 300 nM DEX on GCDFP-15 mRNA accumulation and on the secretion of the glycoprotein. However, at the concentration used, E2 reversed by only 65% the stimulation achieved by the combination of DHT and DEX on GCDFP-15 mRNA levels. It is of interest to mention that the effect of DHT, DEX, and E2 on GCDFP-15 expression is opposite to the respective effect of each steroid on ZR-75-1 cell proliferation. The present data on the regulation of GCDFP-15 mRNA demonstrate an estrogen-induced inhibition of mRNA levels under physiological conditions, thus offering a unique opportunity to study the mechanisms involved in the down-regulation of gene expression by estrogens and to achieve a better understanding of the antagonism between estrogens, androgens, glucocorticoids, and progestins in breast cancer cells. Furthermore, GCDFP-15 could well be a good marker for monitoring the response to androgens and antiestrogens during the course of breast cancer therapy.