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Identification of human estrogen-inducible transcripts that potentially mediate the apoptotic response in breast
1Department of Anatomy and Cell Biology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA.
Abstract:
Hormone manipulation has been used for several decades with the purpose of inducing breast cancer regression. On the one hand, hormone ablation and antiestrogen administration were used on the rationale that estrogens induce proliferation of their target cells. Before the advent of the antiestrogen tamoxifen, on the other hand, the estrogen agonist DES was used to obtain clinical remissions. The rationale for the use of diethylstilbestrol (DES) was totally empirical. In fact, the efficacy of both treatments was comparable. A mechanistic explanation for estrogen-induced regression is urgently needed in order to provide a rationale for its use in therapeutic fields, and to develop markers to identify this phenotype in order to recognize responsive tumors. In this report, we use E8CASS cells (a MCF7 variant) as a model to study estrogen-mediated regression. The proliferation rate 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 expressed unique sequences were found. Seven of them were homologous to known genes, 12 of them were homologous to expressed sequence tags (EST), and 10 sequences had no homologues in the databases. The two sequences showing the highest induction by estradiol (E9 and E43) were chosen for further analysis. The sequence of the E43 coding region has 96% homology to the bovine actin2 gene and 100% identity to bovine actin2 protein, and it is homologous to the human actin-related protein 3 (Arp3). It has been suggested that Arp3 is involved in actin nucleation. The phenotype of E8CASS cells is clearly affected by estrogen treatment. It is likely that E43 may be involved in these morphological changes. The E9 cDNA is a putative zinc-finger protein of the PHD family of transcriptional transactivators. A member of this family, Requiem, is involved in apoptosis. The E9 mRNA is highly expressed in E8CASS cells treated with estrogens, a treatment which results in decreased proliferation rate and increased DNA degradation. This correlation suggests that E9 may be a mediator of estrogen-induced regression of breast cancer.
Insights
Estrogen therapy can induce breast cancer regression by decreasing cell proliferation. Researchers identified two key genes, E9 and E43, involved in estrogen-mediated regression, potentially aiding in identifying responsive tumors.
Area of Science:
- Molecular Biology
- Cancer Research
- Endocrinology
Background:
- Hormone manipulation, including hormone ablation and antiestrogen therapy, has been used for decades to induce breast cancer regression.
- Estrogen agonist diethylstilbestrol (DES) was empirically used for clinical remissions, with efficacy comparable to antiestrogens.
- A mechanistic understanding of estrogen-induced regression is needed to guide therapeutic use and identify responsive tumors.
Purpose of the Study:
- To investigate the molecular mechanisms underlying estrogen-mediated breast cancer regression.
- To identify specific genes and pathways involved in estrogen-induced regression using a cellular model.
Main Methods:
- Utilized E8CASS cells, a variant of MCF7 breast cancer cells, known to decrease proliferation in response to estrogens.
- Prepared a subtracted cDNA library from cells treated with and without estradiol to isolate differentially expressed mRNA sequences.
- Analyzed and selected highly induced sequences (E9 and E43) for further characterization.
Main Results:
- Identified 29 differentially expressed unique sequences, including homologs to known genes, ESTs, and novel sequences.
- Sequence E43 showed high homology to actin-related protein 3 (Arp3), implicated in actin nucleation and potential morphological changes.
- Sequence E9, a putative zinc-finger protein, was highly expressed upon estrogen treatment, correlating with decreased proliferation and increased DNA degradation, suggesting a role in apoptosis and regression.
Conclusions:
- Estrogen treatment significantly impacts the phenotype of E8CASS cells, with E43 potentially mediating morphological changes.
- The gene E9 may act as a mediator of estrogen-induced breast cancer regression by promoting apoptosis.
- Further research into E9 and E43 could lead to the development of biomarkers for identifying estrogen-responsive breast tumors.