The identification of therapeutically actionable genetic lesions in malignancies has transformed patient care. However, there remain many individuals who either do not possess these targetable alterations or who relapse following therapeutic intervention. Therefore, it is imperative to identify novel mechanisms that control the critical biological processes that impact clinical outcomes. RNA-binding proteins (RBPs) have emerged as fundamental regulators of a plethora of biological processes, and their dysregulation has been established in a variety of solid and heme malignancies, making them attractive candidates for study. This application will focus on the role of a mutation in an RNA-binding protein, PCBP1, in colorectal cancer initiation and progression. Poly-C binding protein 1, PCBP1, is a tumor suppressor that is recurrently mutated in 3% of all colorectal cancers. These hotspot missense mutations have been identified as putative cancer drivers in several unbiased studies. Critically, a recent study identified PCBP1 mutations as a resistance mechanism to cetuximab therapy in colorectal cancer patients. These observations necessitate an in-depth investigation into the pathogenic role of PCBP1 mutations. Our preliminary data suggest that the L100Q mutation attenuates the tumor suppressive function of PCBP1 and activates oncogenic signaling cascades. Our central hypothesis is that the L100Q mutation in the RNA-binding domain of PCBP1 abrogates its tumorsuppressive function and promotes malignant phenotypes due to its ability to activate diverse signaling cascades. In this proposal we will 1) determine the impact of PCBP1 mutation on the cellular signaling landscape, and 2) determine whether the PCBP1 mutants can drive oncogenic transformation and progression. Completion of this study will provide insights into the mechanisms by which PCBP1 mutations impact cancer signaling pathways, as well as help identify therapeutic vulnerabilities in these pathways. Furthermore, these studies will have exciting implications for other structurally-related RBPs implicated in disease. Finally, completion of these studies will lend credence to the role of RBPs as therapeutically actionable drivers of disease.