Proliferative disorders of the endometrium are common with an estimated 50% of women seeking consultation for abnormal uterine bleeding at some point in their lives. As women age the risk of pre-malignant disorders of the endometrium increases with those not being treated showing an increased risk of endometrial cancer, of which there are approximately 40,000 new cases in the US annually. Furthermore endometriosis a proliferative disease of the endometrium, affects 6-10% of women and 35% with pain or infertility. However, despite this large amount of morbidity and significant mortality, the molecular control of human endometrial cell proliferation is poorly understood. In both human and mouse endometrium estradiol-172 (E2) stimulates epithelial cell proliferation whilst progesterone (P4) inhibits it. In both cases initial signaling is through their respective receptors (ER and PR). In the mouse, our studies have defined two signal transduction pathways stimulated by E2 and inhibited by P4 required for E2 induced uterine epithelial cell proliferation. These are: 1) E2 induced signaling through IGF-1R that stimulates the PI3-kinase pathway to ultimately inhibit GSK-32 with the resultant nuclear localization of CyclinD1/CDK4 active kinase complexes and pRb phosphorylation. 2) Through the control of DNA replication licensing by regulation of Minichromosome Maintenance Proteins that are required for DNA synthesis initiation. Using these studies in the mouse uterus as a guide, we plan to utilize a direct translational approach to elucidate the molecular basis of human uterine epithelial cell proliferation. These studies will use endometrial biopsies form mid-reproductive age women and a novel xenotransplantation model for studying human endometrial function. The specific aims are: 1) Characterize the regulation of the canonical cell cycle and DNA replication licensing regulatory pathways by female sex steroid hormones in human uterine epithelia. 2) Utilize a mouse xenograft model to study the regulation of human endometrial proliferation. 3) Elucidate the cell cycle pathways activated by selective modulation of estrogen and progesterone receptors in xenotransplanted human endometrium. These studies will provide unique insights in humans into the mechanism of action of E2 and P4 as well as for the therapeutically valuable SERMs and SPRMSs. Such data can be applied to a wide range of clinical situations to ameliorate human morbidity and mortality. These include prevention of uterine hyperplasia and cancer in high-risk situations and endometriosis, promotion of optimal growth and differentiation where it is required, for example in fertility, and inhibition of differentiation, when it is not required, for example, contraception and menopausal hormonal therapy. PUBLIC HEALTH RELEVANCE: These studies will provide unique insights in humans into the mechanism of action of E2 and P4 as well as for the therapeutically valuable SERMs and SPERMs. Such data can be applied to a wide range of clinical situations to ameliorate human morbidity and mortality. These include prevention of uterine hyperplasia and cancer in high-risk situations and endometriosis, promotion of optimal growth and differentiation where it is required, for example in fertility, and inhibition of differentiation, when it is not required, for example, contraception and menopausal hormonal therapy. [unreadable] [unreadable] [unreadable]