Project Summary/Abstract Metastasis is the process in which disseminated tumor cells (DTCs) spread to distal tissues and organs, and it is the leading cause of cancer-related deaths. In order to complete the metastatic cascade, DTCs must be able to invade distal sites, initiate tumor growth, proliferate, and promote a tumor microenvironment (TME) to evade immune surveillance and promote angiogenesis. Elucidating novel mechanisms that underlie these metastatic phenotypes in DTCs can identify key drivers of metastasis, as well as potential therapeutic vulnerabilities which can better target metastatic tumors. My dissertation research focuses on elucidating the mechanisms in which the lncRNA BORG (BMP/OP-Responsive Gene) drives breast cancer (BC) metastasis. My studies determined that metastatic BC cells are reliant upon BORG complexing with E3 SUMO ligase TRIM28 to induce breast cancer stem cells (BCSCs) to expand and self-renew both in vitro and in vivo. This work establishes BORG as a novel driver of BCSCs, and therefore increases our understanding of the mechanisms driving the accumulation of these malignant cell populations. My recent preliminary data suggests BORG:TRIM28 complexes downregulate the expression of splicing factors in BC cells, which contributes to BCSC phenotypes. Interestingly, accumulating evidence indicates that dysregulation of RNA splicing, a complex molecular tool that can control cellular phenotypes through transcriptomic regulatory mechanisms, contributes to a variety of tumorigenic phenotypes and even metastatic relapse. Therefore, during the F99 portion of this proposal, I seek to elucidate the mechanism whereby BORG:TRIM28 complexes dysregulate RNA splicing operant in driving metastatic and BCSC phenotypes in BC. To complete this research during my dissertation, I will (i) determine which splicing factors dysregulated by BORG:TRIM28 complexes drive metastatic phenotypes in BC in vitro and in vivo, and (ii) use RNAseq and subsequent validation to determine the specific alternative splicing events affected by a subset of these splicing factors in BORG-expressing cells. This work will identify novel mechanisms of RNA splicing regulation that play key roles in metastatic phenotypes of BC cells. During the K00 phase of this proposal, I plan to work closely with my postdoctoral mentor to elucidate the mechanisms in which RNA splicing contributes to tumor cell crosstalk with the TME to promote immune evasion and subsequent metastatic outgrowth. Specifically, I plan to elucidate (i) how alternative splicing in tumor cells drive changes in the metastatic TME to promote immune evasion, and (ii) how alternative splicing changes in TME cells, such as T cells and fibroblasts, contribute to the metastatic niche and subsequent metastatic outgrowth. The current and future goals of my research are to elucidate mechanisms in which dysregulated RNA splicing contributes to metastatic seeding and outgrowth in aggressive cancers. My predoct...