Project Summary: Breast cancer resistance to anti-estrogens may be caused by cross-talk between growth factor receptor signaling and estrogenic pathways. Our recent data suggest that the enzymatic activity of aromatase can be increased by AKT, a kinase activated by several growth factor receptor tyrosine kinase signaling cascades (e.g., HER2/Neu). Aromatase is the rate-limiting enzyme complex involved in the biosynthesis of estrogens, which exert mitogenic, anti-apoptotic, and growth-stimulatory effects in mammary tissues. Therefore, growth factor receptor signaling may moderate aromatase activity, estrogen production, and the consequent activation of estrogen-responsive pathways. Aim 1- To determine if AKT phosphorylates aromatase to increase its enzymatic activity in vitro. Aim 2- To determine whether active AKT modulates aromatase activity in vivo and aromatase-induced morphological alterations in the mammary gland of transgenic mice. Aim 3- To determine whether over-expression of active AKT or HER2/Neu in the mammary epithelium of transgenic mice confers resistance to aromatase inhibitors. Aim 1 will utilize molecular techniques and cell lines to determine the ability of AKT to phosphoregulate aromatase in vitro. Aims 2 and 3 will use histomorphological, immunohistochemical, and molecular analyses of transgenic mouse models to determine whether active AKT and HER2/Neu can modulate aromatase activity in vivo, and whether these oncogenes confer resistance to aromatase inhibitors. Results from these studies may provide novel drug targets for hormone-dependent cancers while furthering our understanding of the communication between growth factor receptor signaling and estrogenic pathways. Relevance: Aromatase inhibitors are used clinically to decrease the aromatase-mediated production of estrogens for the treatment of estrogen-dependent breast cancers. While aromatase inhibitors are initially very effective, tumors typically exhibit initial or acquired drug resistance, necessitating the development of further therapeutics. Our work will investigate potential mechanisms by which cancer cells mediate escape from aromatase inhibitor therapy to provide new drug targets for the treatment of breast cancer. [unreadable] [unreadable] [unreadable]