Clinical Significance of Ubiquitin Specific Protease 7 (USP7) in Predicting Prognosis of Hepatocellular Carcinoma and its Functional Mechanisms.

BACKGROUND Hepatocellular carcinoma (HCC) accounts for one of the most prevalent cancer types in the world. The ubiquitin specific protease 7 (USP7), a kind of deubiquitylating enzyme, has been reported to play multifaceted roles in different tumor types. The aim of this study was to investigate the expression and function of USP7 in HCC. MATERIAL AND METHODS Immunohistochemical staining and quantitative PCR were performed to explore the expression of USP7 in both HCC tissues and adjacent normal liver tissues. Chi-square test, univariate analysis, and multivariate analysis were conducted to statistically evaluate the clinical significance of USP7 in HCC. Proliferation, migration, and invasion capacities of HCC cells were assessed after overexpressing or silencing USP7. RESULTS Both the RNA and protein levels of USP7 were upregulated in HCC tissues compared to normal liver tissues. High expression of USP7 was correlated with advanced tumor stage and poor overall survival. Moreover, USP7 was identified as a novel independent prognostic factor for HCC patients. Cellular studies showed that USP7 could enhance the proliferation, migration, and invasion capacities of HCC cells, thereby promoting tumor progression. CONCLUSIONS High expression of USP7 is frequent in HCC tissues, which promotes tumor proliferation and invasion, and is correlated with a poor overall survival. Targeting USP7 may be a novel direction for the drug development of HCC therapy.

Characterization of naturally occurring pentacyclic triterpenes as novel inhibitors of deubiquitinating protease USP7 with anticancer activity in vitro.

Deubiquitinating protease USP7 is a promising therapeutic target for cancer treatment, and interest in developing USP7 inhibitors has greatly increased. In the present study, we reported a series of natural pentacyclic triterpenes with USP7 inhibitory activity in vitro. Among them, both the ursane triterpenes and oleanane triterpenes were more active than the lupine triterpenes, whereas ursolic acid was the most potent with IC50 of 7.0±1.5 µmol/L. Molecular docking studies showed that ursolic acid might occupy the ubiquitin binding pocket of USP7, with the 17-carboxyl group and 3-hydroxyl group playing a vital role in the USP7-ursolic acid interaction. Using the cellular thermal shift assay, we demonstrated that ursolic acid interacted with USP7 in RPMI8226 human myeloma cells. Ursolic acid dose-dependently inhibited the proliferation of the myeloma cells with IC50 of 6.56 µmol/L, accompanied by reductions in USP7 substrates such as MDM2, UHRF1 and DNMT1. Overexpression of USP7 partially, but significantly attenuated ursolic acid-induced cell death as well as downregulation of MDM2, UHRF1 and DNMT1. In conclusion, we demonstrate for the first time that pentacyclic triterpenes represent a novel scaffold for developing USP7 inhibitors and that USP7 inhibition contributes to the anti-cancer effect of ursolic acid.