Hypomethylation-Linked Activation of PLCE1 Impedes Autophagy and Promotes Tumorigenesis through MDM2-Mediated Ubiquitination and Destabilization of p53.

Yunzhao Chen ,Zhihao Yang ,Jun Li ,Jianming Hu ,Xi Chen ,Zheng Liu ,Jun Yu ,Yi Zheng ,Qi Shi ,Huahua Xin ,Menglu Li ,Xiaobin Cui ,Yousheng Tian ,Hao Peng ,Xiaoxi Huang ,Hong Zhou ,Xiao Han ,Xuan Huang ,Feng Li

doi:10.1158/0008-5472.can-19-1912

Abstract

Esophageal squamous cell carcinoma (ESCC) is one of the deadliest malignant diseases. Multiple studies with large clinic-based cohorts have revealed that variations of phospholipase C epsilon 1 (PLCE1) correlate with esophageal cancer susceptibility. However, the causative role of PLCE1 in ESCC has remained elusive. Here, we observed that hypomethylation-mediated upregulation of PLCE1 expression was implicated in esophageal carcinogenesis and poor prognosis in ESCC cohorts. PLCE1 inhibited cell autophagy and suppressed the protein expression of p53 and various p53-targeted genes in ESCC. Moreover, PLCE1 decreased the half-life of p53 and promoted p53 ubiquitination, whereas it increased the half-life of mouse double minute 2 homolog (MDM2) and inhibited its ubiquitination, leading to MDM2 stabilization. Mechanistically, the function of PLCE1 correlated with its direct binding to both p53 and MDM2, which promoted MDM2-dependent ubiquitination of p53 and subsequent degradation in vitro. Consequently, knockdown of PLCE1 combined with transfection of a recombinant adenoviral vector encoding wild-type p53 resulted in significantly increased levels of autophagy and apoptosis of esophageal cancer in vivo. Clinically, the upregulation of PLCE1 and mutant p53 protein predicted poor overall survival of patients with ESCC, and PLCE1 was positively correlated with p53 in ESCC cohorts. Collectively, this work identified an essential role for PLCE1- and MDM2-mediated ubiquitination and degradation of p53 in inhibiting ESCC autophagy and indicates that targeting the PLCE1-MDM2-p53 axis may provide a novel therapeutic approach for ESCC. SIGNIFICANCE: These findings identify hypomethylation-mediated activation of PLCE1 as a potential oncogene that blocks cellular autophagy of esophageal carcinoma by facilitating the MDM2-dependent ubiquitination of p53 and subsequent degradation. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/11/2175/F1.large.jpg.

Highlights

Esophageal squamous cell carcinoma (ESCC) is one of the most common cancers worldwide, with mortality ranking sixth and morbidity ranking seventh in China [1]
Flow cytometry analyses showed that the inhibition of phospholipase C epsilon 1 (PLCE1) by shPLCE1 increased the number of apoptotic cells compared with their respective controls (Fig. 1D; Supplementary Fig. S2D)
Treatment with sh-PLCE1 or U73122 increased the number of terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling (TUNEL)positive cells (Supplementary Fig. S2E), whereas overexpression of PLCE1 could partially decrease the number of TUNEL-positive cells induced by PLCE1 knockdown (Fig. 1G)

Summary

Introduction

Esophageal squamous cell carcinoma (ESCC) is one of the most common cancers worldwide, with mortality ranking sixth and morbidity ranking seventh in China [1]. Despite improvements in ESCC treatments, the outcomes of patients with ESCC are still dismal due to the limited knowledge about its molecular pathogenesis, the difficulty in detecting the disease at its early stages, and the lack of effective therapies [2, 3]. Studies have indicated that some oncogenes and tumor suppressor genes are involved in the progression of esophageal cancer, the molecular mechanisms remain unclear. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/).

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