We are studying the estrogen receptors (ERs) through which estrogen and the estrogen-related anti-cancer drugs, tamoxifen and raloxifene, act. Our research will help us understand why these drugs have different effects in different parts of the human body. For example, tamoxifen blocks breast cancer, but increases the risk of uterine cancer. Raloxifene, like estrogen, can help to prevent osteoporosis, but without the increased breast cancer risk associated with estrogen. Previous experiments have indicated that different responses by different ER ligands are partly due to the differences in the two ER subtypes, and partly due to different types of DNA sequences where ERs can bind. We want to find ER-regulated genes that are induced by raloxifene or tamoxifen, but not by the natural ligand, 17-estradiol. Cells will be treated with these compounds and used for a genomic screen. Sequences can then be obtained for all the genes that are activated by anti-estrogens but not by estrogen. Genes and promoters will be characterized, and deletion analysis used to isolate the response elements, DNA regions of estrogen receptor interactions. Extensive use of database tools will be necessary for this part of the project. Novel response elements will be of particular interest. These will be analyzed mechanistically by making reporter constructs with the response elements and testing ER alpha verses ER beta effects of transcription. Crystal structures of the ligand binding domain of ER binding these different ligands show significant differences which have been implicated in the different responses. Computer graphics will be important for analyzing mutants and new ligands created to understand these difference more completely. It is our hope that a better understanding of estrogen receptors, the ligands they bind, and the genes they regulate can lead to improved application of known estrogen therapies and can help in the development of new ones.