The role of deubiquitination in regulating planar cell polarity (PCP) signaling

Abstract

Planar Cell Polarity (PCP) signaling is a crucial, evolutionarily conserved mechanism that governs cell polarity coordination across tissue planes. Disruption of PCP signaling underlies a variety of developmental defects, such as neural tube defects and skeletal anomalies, while its aberrant activation has been implicated in cancer malignancy. Vangl1 and Vangl2, core components of the PCP signaling pathway, are tightly regulated by post-translational modifications (PTMs) such as phosphorylation and ubiquitination. Previously, we have identified the E3 ligase CUL3-KBTBD7 that can regulate Vangl through the endoplasmic reticulum-associated degradation (ERAD) pathway, whereas the deubiquitinase of Vangl still remains unknown. Here, by screening deubiquitinating enzymes (DUBs) that have significant impacts on Vangl protein abundance, we identified two ubiquitin-specific peptidases, USP6 and USP32, which share high similarity in amino acid sequence. Specifically, ectopic expression of USP6/32 increased the protein level of Vangl1 and Vangl2, whereas their depletion promoted Vangl1 and Vangl2 degradation. Furthermore, both USP6 and USP32 reduce the polyubiquitination level of Vangl2. Interestingly, our research also highlights the role of USP32 in regulating Vangl1 in pancreatic cancer. Vangl1 and USP32 are both highly expressed in human pancreatic ductal adenocarcinoma (PDAC) tissues and their expression levels are strongly correlated among various PDAC cell lines. USP32 depletion significantly inhibited the metastasis of PDAC cells to the lung by promoting Vangl1 degradation, while the similar phenotype could also be observed by reducing Vangl1. In mice, we found that loss of USP32 led to a decrease of Vangl expression and thus an increase of the penetrance of loop tail phenotype in Vangl mutant mouse. The defect of pancreatic ductal morphogenesis in USP32 KO and Vangl mutant mouse is also observed. Overall, these findings reveal a new regulatory mechanism of PCP signaling through USP6 and USP32-mediated Vangl deubiquitination, highlighting their significant roles in both development and disease progression.