PROJECT SUMMARY Tumors have been described as wounds that do not heal. Similarities between tumors and wounds include traits such as loss of polarized tissue structure and chronic inflammation. We showed that disruption of tissue polarity induced activation of the NF-?B pathway and macrophage infiltration. However, little is known of how disruption of epithelial cell polarity induces the NF-kB pathway and macrophage infiltration. We have identified the RAR-related orphan nuclear receptor ? (ROR?) as a potent tumor suppressor by analyzing global gene expression profiles in polarized and non-polarized mammary epithelial cells. Our recent findings show that ROR? inhibits NF-?B activation and macrophage infiltration in the syngeneic mouse mammary tumor model. These results suggest that ROR? is a potent suppressor of macrophage infiltration in mammary epithelial cells. We found that knockdown of ROR? significantly induced ROS production in mammary epithelial cells. Reactive oxygen species (ROS) is a driver of cancer progression and a critical regulator of the NF-?B pathway. Based on these novel findings, the central hypothesis of our proposal is that downregulation of ROR? in non-polarized breast cancer cells induces ROS-dependent NF-?B activation, thereby enhancing macrophage infiltration and differentiation in cancer tissue. We will integrate high-throughput metabolic analysis and global gene expression profiling to delineate mechanisms by which ROR? inhibits ROS production. The long-term goal of this proposal is to define the impact of the ROR?/NF-?B axis in mediating mammary epithelial cell-macrophage crosstalk and regulating breast cancer progression. We have proposed following specific aims to test the hypothesis: The first aim is to elucidate the molecular mechanisms by which ROR? inhibits the NF-?B pathway in polarized acinus; the second aim is to determine how reduced ROR? expression in non-polarized breast cancer cells induces macrophage infiltration and differentiation; and the third aim is to define the impact of ROR? in suppressing breast cancer formation and metastasis. This proposed study involves in-depth mechanistic molecular, biochemical and cellular studies, using state-of-the art metabolomics, imaging techniques, and model systems. The results will establish a novel link between disruption of tissue polarity and macrophage infiltration/differentiation, a critical gap in scientific knowledge in this important research area. Expected study outcomes will also provide new insights in function and regulation of the NF-?B pathway during breast cancer development and progression that will facilitate the development of mechanistic based target for cancer therapy.