The Hippo tumor suppressor pathway plays an important role in development and tumorigenesis. Yes-associated protein (YAP) is a major effector of the Hippo pathway regulating the expression of genes involved in cell proliferation, cell death, and cell differentiation (Pan, 2010; Johnson and Halder, 2014; Piccolo et al., 2014; Yu et al., 2015). In intestine, YAP is mainly expressed in leucine rich repeat containing G protein-coupled receptor 5 (LGR5) marked stem cells, and is required for regeneration following tissue damage and the development of colon cancer in mice (Cai et al., 2010; Barry et al., 2013; Wang et al., 2017). Moreover, in colorectal cancer (CRC) specimens, elevated YAP expression and activity is frequently observed (Steinhardt et al., 2008). It has been shown that high YAP expression is associated with cancer metastasis, poor prognosis, resistance to chemotherapy, and greater possibility of relapse (Johnson and Halder, 2014; Yu et al., 2015). However, the molecular mechanism underlying elevated YAP protein expression in CRC and other cancers remains poorly defined. The ubiquitin-proteasome system (UPS) plays a critical role in tumorigenesis (Popovic et al., 2014). Dysregulated expression of E3 ligases or deubiquitinating enzymes (DUB) is frequently observed in human cancers, including CRC. The protein stability of YAP is mainly regulated by phosphorylation and ubiquitination, and the latter is carried out by beta-transducin repeat containing E3 ubiquitin protein ligase (β-TRCP)(Zhao et al., 2010). However, the DUB responsible for YAP deubiquitination and stabilization in CRC is currently unknown.

It has been shown previously that ubiquitin specific peptidase 7 (USP7, a DUB) interacts with β-TRCP (Peschiaroli et al., 2010). We speculated that β-TRCP and USP47 may work together to fine-tune the ubiquitination and protein stability of YAP. To verify this hypothesis, we first tested the interaction between USP47 and YAP. In co-immunoprecipitation (Co-IP) assays, recombinant USP47 could pull-down YAP and vice versa, suggesting that USP47 and YAP physically interact with each other (Fig. 1 A). The intermolecular interaction was mediated by the peptidase domain (C19C) and coiled coil (CC) domains in USP47 and