Identification of human estrogen-inducible transcripts that potentially mediate the apoptotic response in breast cancer

Hormone manipulation has been used for several decades with the purpose of inducing breast cancer regression. On the one hand, hormone ablation and an tiestrogen administration were used on the rationale that estrogens induce proliferation of their tar et cells. Before the advent of the antiestrogen tamoxifen, on the other hand, the estrogen agonist DES was used to obtain c linical remissions. The rationale for the use of diethylstilbestrol (DES) w as totally empirical. In fact, the efficacy of both treatments was comparab le. A mechanistic explanation for estrogen-induced regression is urgently n eeded in order to provide a rationale for its use in therapeutic fields, an d to develop markers to identify this phenotype in order to recognize respo nsive tumors. In this report, we use E8CASS cells (a MCF7 variant) as a mod el to study estrogen-mediated regression. The proliferation late of E8CASS cells is decreased by estrogens. In order to isolate mRNA sequences induced by estradiol, a subtracted library was prepared from E8CASS cells grown in the presence and absence of estrogens. Twenty nine differentially expresse d unique sequences were found. Seven of them were homologous to known genes , 12 of them were homologous to expressed sequence tags (EST), and 10 seque nces had no homologues in the databases. The two sequences showing the high est induction by estradiol (E9 and E43) were chosen for further analysis. T he sequence of the E43 coding region has 96% homology to the bovine actin2 gene and 100% identity to bovine actin? protein, and it is homologous to th e human actin-related protein 3 (Arp3). It has been suggested that Arp3 is involved in actin nucleation. The phenotype of E8CASS cells is clearly affe cted by estrogen treatment. It is likely that E43 may be involved ill these morphological changes. The E9 cDNA is a putative zinc-finger protein of th e PI-ID family of transcriptional transactivators. A member of this family, Requiem, is involved in apoptosis. The E9 mRNA is highly expressed in E8CA SS cells treated with estrogens, a treatment which results in decreased pro liferation rate and increased DNA degradation. This correlation suggests th at E9 may be a mediator of estrogen-induced regression of breast cancer. (C ) 2000 Elsevier Science Ltd. All rights reserved.