Genetic and Molecular Dissection of Wnt Pathway Activation

Dartmouth College, Hanover NH

Investigators

Linked publications & trials

Abstract

PROJECT SUMMARY Tissue specification, growth, maintenance, and regeneration rely on spatiotemporal cues provided by the evolutionarily conserved Wnt morphogen pathway. Many developmental disorders and cancers, including nearly all colorectal cancers, arise when the normal regulation of Wnt signal transduction is lost; yet key mechanisms that mediate essential steps in this pathway remain poorly understood. An improved mechanistic understanding of Wnt pathway activation is therefore crucial, as no drugs that target Wnt-driven disease have yet been approved by the FDA. The long-term goals of the PI’s research program are to uncover the foundational mechanisms that control Wnt signaling during animal development and to use this knowledge to identify vulnerabilities in the pathway that are susceptible to therapeutic targeting in Wnt-driven diseases. To support these goals, the PI and her laboratory group have developed innovative, cost-effective approaches in the fruit fly Drosophila that provide three major strengths to surmount existing obstacles in the field: cutting- edge genetic tools, limited functional redundancy, and robust in vivo assays for Wnt signaling gradients. Research by the PI’s group identified two novel roles for the tumor suppressor Adenomatous polyposis coli (APC) in Wnt signaling, two novel transcription cofactors required for nearly all consequences of APC loss, the dual mechanisms by which the therapeutic target Tankyrase activates Wnt signaling, and a Wnt receptor regulatory mechanism required to tune signaling strength throughout the morphogen gradient. This project will address major questions centered on the three multi-protein complexes that control Wnt signaling: 1) How is the activity of the membrane-associated signalosome complex controlled by regulation of the Wnt receptor LRP6/Arrow?; 2) How are the components of the nuclear beta-catenin-TCF transcription complex activated by phosphorylation and ubiquitylation?; and 3) How is the activity of the two key kinases in the cytosolic beta- catenin destruction complex, GSK3 and CK1, modulated under basal conditions and following Wnt stimulation? To address these questions, the research capitalizes on state-of-the-art genetic and proteomic screens that have identified six new enzymatic regulators that control the activity of these essential complexes. The function of each will be defined using a combination of genetic, cell biological, and biochemical assays. The impact of this research is enhanced by long-term collaborations that incorporate complementary experimental approaches, including biochemical reconstitution, quantitative phosphoproteomics, and vertebrate models that test evolutionarily conserved functions. The successful completion of this work will provide a strong mechanistic understanding of this fundamental signaling pathway and highlight new therapeutic strategies to target Wnt-driven diseases.