CDDO-Me reveals USP7 as a novel target in ovarian cancer cells.

Dongjun Qin,Fenghou Gao,Weiwei Wang,Haiyan Cai,Jin Jin,Hu Lei,Hao Luo,Weilie Xiao,Yunzhao Wu,Hanzhang Xu,Ying-Li Wu,Jinfu Zhang,Caixia Tang,Yingying Wang,Tongdan Wang,Chunmin Ma

doi:10.18632/oncotarget.12801

Abstract

Deubiquitinating enzyme USP7 has been involved in the pathogenesis and progression of several cancers. Targeting USP7 is becoming an attractive strategy for cancer therapy. In this study, we identified synthetic triterpenoid C-28 methyl ester of 2-cyano-3, 12-dioxoolen-1, 9-dien-28-oic acid (CDDO-Me) as a novel inhibitor of USP7 but not of other cysteine proteases such as cathepsin B and cathepsin D. CDDO-Me inhibits USP7 activity via a mechanism that is independent of the presence of α, β-unsaturated ketones. Molecular docking studies showed that CDDO-Me fits well in the ubiquitin carboxyl terminus-binding pocket on USP7. Given that CDDO-Me is known to be effective against ovarian cancer cells, we speculated that CDDO-Me may target USP7 in ovarian cancer cells. We demonstrated that ovarian cancer cells have higher USP7 expression than their normal counterparts. Knockdown of USP7 inhibits the proliferation of ovarian cancer cells both in vitro and in vivo. Using the cellular thermal shift assay and the drug affinity responsive target stability assay, we further demonstrated that CDDO-Me directly binds to USP7 in cells, which leads to the decrease of its substrates such as MDM2, MDMX and UHRF1. CDDO-Me suppresses ovarian cancer tumor growth in an xenograft model. In conclusion, we demonstrate that USP7 is a novel target of ovarian cancer cells; targeting USP7 may contribute to the anti-cancer effect of CDDO-Me. The development of novel USP7 selective compounds based on the CDDO-Me-scaffold warrants further investigation.

Highlights

Ovarian cancer is one of the most common gynecological malignancies in women [1]
Using the cellular thermal shift assay and the drug affinity responsive target stability assay, we further demonstrated that CDDO-Me directly binds to USP7 in cells, which leads to the decrease of its substrates such as MDM2, MDMX and UHRF1
The results showed that CDDO-Me (Figure 1A) markedly inhibited the USP7mediated cleavage of GST-UBA52 (Figure 1B) in an in vitro gel-based assay

Summary

Introduction

Ovarian cancer is one of the most common gynecological malignancies in women [1]. Despite great advances in chemotherapy and surgical treatment of this disease, the 5-year survival remains approximately 36% [2]. Over 80% of patients with advanced ovarian cancer will relapse and eventually die of their disease [3]. Identification of novel target to conquer this disease is urgently required. Protein ubiquitination is a dynamic reversible process. Ubiquitinspecific enzymes (USP) constitute the largest subfamily of DUBs, with more than 60 human member proteins. USPs can release poly-Ub chains from proteins targeted for degradation, recycle monomeric Ub, liberate Ub from Ub-fusion precursors, reverse regulatory ubiquitylation and edit inappropriately ubiquitylated proteins [4,5]

Methods

Results

Conclusion