Breast cancer is the most common cancer in women in the United States, causing ~40,000 deaths each year. In the proposed study, we will focus on breast cancer and determine what epigenomic changes cause breast cancer to acquire metastatic activity and how the changes are established. Epigenetic modifications of chromatin are associated with the expression status of individual genes. Here we propose a paradigm-shifting idea that a single molecule involved in global gene regulation underlies the massive epigenetic changes that drive the transformation of a tumor cell to aggressive metastastic tumor cells through binding to a subset of specialized DNA sequence that functions as chromosomal marks. We identified SATB1, a genome organizer in thymocytes, to be a key determinant in breast cancer metastasis by altering expression of ~1000 genes, including many associated with poor prognosis. We will test a hypothesis that SATB1 causes progression of non-aggressive breast cancer to metastatic cancer by establishing genome-wide changes in epigenetic marks through global re-organization of higher-order chromatin structure. We further hypothesize that such re-organization involves SATB1 interaction with highly conserved, specialized DNA sequences called base unpairing regions (BURs), distributed throughout the human genome. These BURs may function as chromosome marks to which chromatin modifiers are recruited, thus resulting in specific epigenetic modifications throughout the genome characteristic of aggressive breast cancer. We will adopt a global mapping approach by high-throughput sequencing to map all putative BURs across the human genome and identify those that are bound by SATB1in aggressive breast cancer cells versus those in activated human T helper cells, a non cancerous cell-type where SATB1 is normally expressed. We will subsequently determine genome-wide histone modifications in SATB1-expressing metastatic cancer and SATB1-deficient, non- aggressive breast cancer cells to determine whether aggressive cancer-associated changes in epigenetic marks are centered at SATB1-bound BURs. From the proposed research, we will define the role of BURs in establishing metastatic breast cancer-specific epigenetic marks through interaction with SATB1. These experiments will provide fundamental insight into disease progression that should be useful for developing future therapies.