Regulation of Hippo/YAP signaling and esophageal squamous carcinoma progression by an E3 ubiquitin ligase PARK2

Abstract Background Esophageal squamous cell carcinoma (ESCC) is one of the most lethal malignancies in the world, while the overall five-year survival is less than 20%. Recent genomic sequencing analysis indicated the over-activation of Hippo/YAP signaling might play important roles for the carcinogenic process and progression for ESCC patients. However, little is known about the molecular mechanisms that controls Hippo signaling activity in ESCC. Methods YAP and PARK2 protein level were measured by western blot, while the Hippo classical target genes were measured by real-time PCR. WST1 assay were used to measure cell proliferation, the trans-well and wound healing were used to measure the cell migration and invasion capacity. Protein stability and ubiquitin assay were used to detect the YAP protein ubiquitin and stability. The immuno-precipitation assays were used to detect the protein interactions. Immuno-staining was used to detect the protein localization of YAP and PARK2, while the ubiquitin-based immuno-precipitation assays were used to detect the specific ubiquitination manner of YAP. Results Here, we identify a novel E3 ubiquitin ligase PARK2 as an inhibition factor for Hippo/YAP axis. We find that PARK2 depletion promotes ESCC progression both in vivo and in vitro through Hippo/YAP axis, while PARK2 overexpression suppresses ESCC tumor progression via Hippo signaling. Mechanistic study reveals that PARK2 could interact with YAP in the cytosol and promotes YAP K48-linked ubiquitination at K90 sites, which subsequently promotes YAP protein degradation in ESCC. Clinical sample of ESCC revealed that PARK2 is significantly decreased in ESCC, and relates to good prognosis in ESCC patients. Beside, PARK2 expression negatively correlates with tumor stage and YAP protein expression. Conclusions: Our study identifies an interesting mechanism of Hippo pathway regulation, by which PARK2 modulates ESCC cancer progression, and implies PARK2 could be a novel marker for therapeutics and diagnostics in human ESCC.