A Cereblon Signaling Network in Wnt-driven Cancers Abstract The long-term objective of this study is to investigate how Cereblon (CRBN) regulates the Wnt signal transduction pathway and to demonstrate how this can be exploited to target Wnt-driven colorectal cancers (CRCs). Wnt signaling is essential for intestinal stem cell maintenance and aberrant activation of this pathway drives the initiation and progression of nearly all CRCs. To date, no drugs that inhibit the Wnt pathway have been FDA- approved, partly due to the lack of druggable targets that can bypass common Wnt pathway mutations in CRC. In a conceptual breakthrough, our recently published findings reveal that Cereblon (CRBN), the substrate receptor of the CRL4CRBN E3 ubiquitin ligase that is a drug target in hematological malignancies, plays a critical role in Wnt signal transduction. We found that CRBN promotes the degradation of a subset of substrates, including Casein kinase 1α (CK1α), a negative regulator of Wnt signaling and a key component of the β-Catenin destruction complex. Moreover, Wnt stimulation induces the interaction of CRBN with CK1α to promote its ubiquitination and degradation. Furthermore, we showed that the role of CRBN in Wnt signaling is conserved in human cells, mouse intestinal organoids, zebrafish, and Drosophila. These studies demonstrate the first endogenous mechanism of CRBN regulation and provide a novel means of controlling Wnt pathway activity, with relevance for animal development and disease. The goal of this project is to use in vitro, ex vivo, and in vivo approaches to gain a better understanding of how the clinically relevant anti-cancer target, CRBN, promotes Wnt signal transduction. The three specific aims are to: 1) Identify the mechanisms by which Wnt stimulation activates CRBN; 2) Identify Wnt-stimulated CRBN interactors that regulate tumorigenesis; and 3) elucidate the role of CRBN in Wnt-dependent cancer progression. Because CRBN is a well-studied target for the development of drugs to treat hematological malignancies, the knowledge gained from this study will aid in the development of more selective small molecules as well as suggest innovative treatment strategies for CRC and other Wnt-driven cancers.

Project Narrative A Cereblon Signaling Network in Wnt-driven Cancers In the United States, colorectal cancer is the second leading cause of cancer-related death. The goal of this study is to determine how a network of signaling proteins results in the initiation and growth of colorectal cancers, to discover what happens to colorectal cancer cells when proteins from this network are blocked, and to identify new strategies to inhibit the growth of colorectal cancer cells based on these discoveries. Therefore, the knowledge gained from this study may provide new ways to treat colorectal cancer.