Prickle-1 promotes the degradation of dishevelled by ubiquitination in liver cancer

Abstract

Aberrant activation of Wnt signaling with accumulation of β-catenin has been linked to tumorigenesis, particularly in colorectal and liver cancers. Mutations of β-catenin, adenomatous polyposis coli and axins are important factors leading to β-catenin activation but they are not frequent enough to be accountable for the accumulation of β-catenin in human hepatocellular carcinoma (HCC). In this study, we characterized the roles of Prickle-1, a Dishevelled (Dvl)-associated protein, in the regulation of Wnt/β-catenin activity in HCC. We have demonstrated that Prickle-1 interacted with Dvl3 with co-immunoprecipitation assay. In addition, Prickle-1 facilitated Dvl3 ubiquitination/degradation through its destruction box (D-box) motifs. This requirement of D-box for ubiquitination was confirmed by the use of mutant D-box 1 (R557M and L560M) and D-box 2 (R669I and L702M) generated by sequential site-directed mutagenesis. Enforced expression of Prickle-1 significantly reduced the levels of Dvl3 and β-catenin and β-catenin activity in a dose-dependent manner, and inhibited the tumorigenic properties of HCC cells in terms of colony formation and anchorage-independent growth assays. In both HCC cell lines and human HCCs, underexpression of Prickle-1 was significantly associated with overexpression of Dvl3 Prickle-1 underexpression also significantly correlated with β-catenin accumulation in cytosol and/or at membrane (P = 0.023) and tumor size (P = 0.03). Our results have defined a novel mechanistic relationship between Prickle-1 and Dvl3 in Wnt/β-catenin pathway. The enhancement of Dvl3 degradation by Prickle-1 implicates that Prickle-1 is a negative regulator of the Wnt/β-catenin signaling pathway. Our results suggest that Prickle-1 is a putative tumor suppressor in HCC. (This work was supported in part by a University Research Committee of the University of Hong Kong)