Focus of the Laboratory:
First, we are using molecular techniques to determine the mechanisms whereby estrogen receptors repress gene transcription by identifying coregulatory proteins involved in transcriptional repression pathways in response to estrogens and phytoestrogens. Whereas tremendous progress has been made in understanding the molecular mechanisms whereby estrogen receptors activate gene transcription, little is known about how ERs repress genes. However, the repression of genes, such as tumor necrosis factor (TNF-a) may be the major pathway whereby estrogens prevent osteoporosis and other menopausal conditions. Estrogens exert their effects by activating or repressing gene transcription after binding to two distinct estrogen receptors (ERs), ERa and ERb. We have demonstrated that ERb is more potent than ERa at repressing the TNF-a promoter, whereas it is weaker than ERa at activating an estradiol (E2) response element. We also demonstrated that E2-mediated repression requires interactions between ERa and ERb and coregulators. Thus, the coregulatory proteins are the key factors that couple the ERs to the basic transcriptional machinery, and therefore required to elicit biological responses to estrogens. Our focus is to identify the coregulator proteins that trigger transcriptional repression and the molecular mechanisms whereby coregulator protein/ER interactions lead to repression. We believe the coregulators will provide important therapeutic targets for estrogenic compounds that may be safer than the current estrogens used in HRT.
Second, we are identifying the target genes regulated by estrogens and selective estrogen receptors modulators with ERa and ERb using microarrays. Remarkably, we found that most genes regulated by ERa or ERb are different in stable cell lines transfected with ERa or ERb. This observation is surprising, because the DNA binding domain (DBD) of ERa and ERb are almost identical. We are now investigating the mechanism whereby ERa and ERb regulate different genes. We believe that understanding how estrogenic compounds differentially regulate the transcriptional activity of ERa and ERb is key to discovering the role of ERa and ERb in breast cancer and new generation of estrogens for HRT.
Third, we are studying the role of ERs in breast cancer. Although evidence indicates that estrogens promote breast cancer, paradoxically the ingestion of phytoestrogens is associated with a low incidence of breast cancer in Asian women. We hypothesize that the divergent actions of estrogens and phytoestrogens can be explained by differences in their ability to trigger transcriptional functions of ERa and ERb. We have found that E2 is a potent agonist at both ERs, whereas phytoestrogens are strong agonists at ERb and weak agonists at ERa. We have prepared an adenovirus that expresses human ERb, which is being used to infect MCF-7 cells that express exclusively ERa. These studies will help to determine the role of ERb in breast cancer. We are also correlating the expression of ERa and ERb in human breast tumor slides by immunohistochemistry to the patient information to determine the role of ERb in the initiation and progression of breast cancer as well as the response to tamoxifen treatment.
Fourth, we are identifying Chinese herbs that have estrogenic activity, which may be useful for preventing breast cancer. High intake of plant estrogens (phytoestrogens) is associated with a low incidence of breast cancer whereas estrogens increase the risk of. A key question is: Why do estrogens increase the risk of breast cancer whereas phytoestrogens might decrease the risk of breast cancer. Our studies with isoflavones suggest that the divergent action of estrogens and phytoestrogens on breast may result from differences in their ability to trigger transcriptional functions of ERa or ERb. Based on these studies, we have hypothesize that estrogens increase breast cancer by interacting with ERa to stimulate cell proliferation, whereas phytoestrogens may prevent breast cancer by interacting with ERb. We have hypothesized that Chinese herbs that are used in traditional Chinese Medicine to prevent and treat breast cancer may contain natural estrogenss that selectively interact with ERa or ERb. Our preliminary data with 71 herbs indicates that like, isoflavones, some Chinese herbs also possess estrogenic activity and interact selectively with ERa or ERb. The major goal of our studies is to identify Chinese herbs that selectively trigger ERb or block ERa transcriptional pathways, because we hypothesize that these herbs will be less likely to elicit proliferative effects on breast cells, compared to estrogens. To accomplish this goal, we our determining the effects of herbs on: (a) proliferation of breast cancer cells (b) transcriptional repression and activation by ERa or ERb (c) binding to purified ERa or ERb (d) recruitment of coregulator proteins to ERa or ERb and (e) expression of growth promoting genes. These studies have the potential to determine the molecular mechanism whereby herbs differentially interact with ERa or ERb to regulate gene transcription and cell proliferation. This translational research project can provide a scientific basis to prioritize herbs to evaluate in clinical trials for their ability to prevent and treat breast cancer.