Cancer is the 2nd leading cause of death in the US. The advent of new treatments such as immunotherapy and targeted therapies have revolutionized the fight against cancer, and when combined with surgery, often result in significant positive therapeutic responses. Unfortunately, some tumor cells gain the ability to resist drug- and immune- therapies, which is often linked to their ability to metastasize. Indeed, metastasis ultimately underlies the majority of patient mortality by cancer. A major unmet need in oncology is the prediction and prevention of metastatic progression. Thus, understanding how tumor cells acquire metastatic potential and develop drug resistance is critical to identifying novel therapeutic options and improving patient outcomes. It is of critical importance to define the signaling mechanisms that contribute to altered growth, metabolism, motility and survival associated with metastasis. Our long-standing goal is to uncover the molecular consequences of Ras/ERK-MAP kinase signaling using biochemical, cell biological and genetic approaches in vitro and in vivo. We have provided the foundational studies revealing how subtle differences in ERK signal strength, location and duration are critical determinants of cellular outcomes. More recently, we demonstrated that different ERK isoforms promote different cell fates. Specifically, we found that different docking domains within ERK2, the CD domain and the DEF binding pocket (DBP), regulate different cellular outcomes, with ERK2 playing a major role in promoting the epithelial-to-mesenchymal transition (EMT) through DBP signaling. Additionally, this EMT-like phenotype was associated with increased motility, survival and metastasis in vivo and in vitro. Understanding these mechanisms are part of the long-term goal of our basic research efforts to discover new potential targets and identify new biomarkers, and to help resolve this currently unmet clinical need of targeting the metastatic process. Thus, this grant application proposes to mechanistically investigate underexplored areas associated with EMT and metastatic progression, taking advantage of discoveries made during the previous 30+ years investigating the ERK pathway in my laboratory. Our goals include an investigation into: (i) the regulation and role of H3.3 histone chaperones and H3.3 modifications, (ii) the role SP1/EGR1-downregulated genes and their characterization as new metastasis suppressors, such as CHAF1b and MCEE; (iii) the function of massive reorganization of endomembrane trafficking, lysosome and autophagosome function and the unexplored regulation and function of various plasma and lysosome membrane transporters in the maintenance of cancer stem cell properties, invasion, survival and chemoresistance during cancer progression and metastasis. In conclusion, there is an essential need for greater understanding of the mechanisms associated with metastatic behavior. Our expectations are that successful completion...