PROJECT SUMMARY Colorectal cancer (CRC) remains the third leading cause of cancer related deaths in the US. Although the over- all incidence is declining, the incidence in the younger population has been steadily increasing over the past thirty years. While a western diet and a sedentary lifestyle are among contributing environmental factors to early onset colorectal cancer (EOCRC; as defined in individuals <50 years old), genetic research has also implicated the Wnt/ß-catenin signaling pathway as a driver of EOCRC. Mutations in the adenomatous polyposis coli (APC) gene, which is a tumor suppressor and encodes a negative regulatory protein of the pathway, are highly prevalent in spontaneous CRC. These mutations drive an oncogenic gene expression program controlled by the ß-catenin transcriptional co-regulator. APC mutations, and other regulators of Wnt/ß-catenin signaling, are also found in EOCRC tumor samples, but the role of deregulated Wnt/ß-catenin signaling in EOCRC is not understood. The goals of this proposal are to elucidate critical downstream Wnt/ß-catenin gene targets and to identify novel Wnt- pathway modulators that drive EOCRC. In Aim 1, we will use RNA-seq to define differential gene expression signatures in patient-matched colonic segments and tumors. We will focus on known downstream target genes of Wnt/ß-catenin signaling and test their role(s) in driving EOCRC using human-derived tumoroids. In Aim 2, we will use a CRISPR/Cas9 knockout screen to identify novel proteins that negatively regulate Wnt/ß-catenin signaling in human colonic organoid cultures derived from EOCRC patients. This work will identify novel drivers of EOCRC which is needed to better understand disease pathogenesis and to reveal new avenues for potential therapeutic intervention.

PROJECT NARRATIVE Over the past three decades, the incidence of early onset colorectal cancer (EOCRC) has been steadily increasing. Genetic analysis of patient-derived colonic tissues and tumors indicate that deregulation of the Wnt/ß- catenin signaling pathway may contribute to colorectal carcinogenesis in this patient population. Work in this proposal will define critical downstream targets of aberrant Wnt/ß-catenin signaling and identify novel pathway interactors that drive EOCRC. This research is needed to support targeting this pathway, or genes whose expression it regulates, to improve patient care.