The overall objective of this project is to gain further understanding of the endocrinology of hormonal responses in women in order to provide a rational basis for the design of therapies directed toward the clinical problems of endometriosis, pregnancy loss, and fertility. The steroid hormone estrogen is central to many reproductive processes; we have therefore focused on those factors capable of modulating estrogen responsive genes in estrogen-responsive tissues. Previously, we have demonstrated that the retinoid X receptor (RXR) is capable of modulating estrogen-dependent gene activation. Advances during the current period include: 1) Demonstration that estrogen responsive genes may be specifically activated by cotransfection of the RXR and the peroxisome proliferator-activated receptor (PPAR). This activation was specific for the estrogen responsive DNA element, since mutation of the element prevented activation. Of note, estrogen responsive gene activation by these receptors occurred in the absence of the estrogen receptor. In addition, this activation was found to be augumented by addition of either 9 cis-retinoic acid or arachidonic acid; 2) Demonstration that the RXR and the PPAR bind specifically to an estrogen responsive DNA element in a heterodimeric complex; 3) Demonstration of several RXR-binding proteins in breast cancer cells; and 4) establishment of a method to isolate these RXR-binding proteins using an interactional cloning strategy. We plan to further characterize the role of PPAR in the activation of estrogen responsive genes. In addition, we plan to utilize an interactional cloning method to isolate and identify those proteins that may contribute to RXR modulation of estrogen responsive genes.