SUMMARY The Hippo and Wnt signaling pathways are intimately associated with tissue homeostasis and tumorigenesis. However, how these two pathways crosstalk remains elusive and has been a matter of intense debate. Both positive and negative regulation of Wnt signaling by YAP/TAZ, the intracellular mediators of Hippo signaling, has been reported, and further studies are clearly required to resolve the controversy regarding the functional and signaling interactions between these two important pathways. In the intestinal epithelium where Wnt signaling plays a pivotal role in controlling stem cell renewal and differentiation, our recent work demonstrated that Lats1/2, the core Hippo kinases, are required for sustaining Wnt signaling in intestinal stem cells. We showed that Lats1/2 removal inhibits Wnt pathway downstream of APC/β-Catenin in the intestine in a cell-autonomous manner. In this grant, we will use a combination of genetic, proteomic and chemical approaches to dissect the molecular basis of the YAP/TAZ-Wnt crosstalk in the intestine. In Specific Aim 1, we will examine the ability of YAP/TAZ to inhibit Wnt/TCF activation in both wild type and APC mutated intestine, using two new conditional alleles of nuclear YAP/TAZ we recently generated. We will also determine the molecular mechanism by which nuclear YAP/TAZ suppress Wnt/TCF transcriptional activation downstream of APC. In Specific Aim 2, we define the Wnt- uncoupled TEAD-dependent downstream programs in APC- and Lats1/2- mutated intestinal epithelium and explore therapeutic targeting TEAD in intestinal tumors using animal models.