SHARPIN stabilizes estrogen receptor α and promotes breast cancer cell proliferation.

Ting Zhuang,Sifan Yu,Yingxiang Hou,Yuanyuan Shi,Muhammad Sharif Hasni,Hui Wang,Weilong Wang,Xiumin Li,Xuefeng Li,Gang Niu,Huijie Yang,Jian Zhu,Kun Mu,Anqi Li,Juntao Xu,Lichen Zhang,Na Yu,Zhenhua Liu,Xin Li

doi:10.18632/oncotarget.20368

Abstract

Estrogen receptor α is expressed in the majority of breast cancers and promotes estrogen-dependent cancer progression. In our study, we identified the novel E3 ubiquitin ligase SHARPIN function to facilitate ERα signaling. SHARPIN is highly expressed in human breast cancer and correlates with ERα protein level by immunohistochemistry. SHARPIN expression level correlates with poor prognosis in ERα positive breast cancer patients. SHARPIN depletion based RNA-sequence data shows that ERα signaling is a potential SHARPIN target. SHARPIN depletion significantly decreases ERα protein level, ERα target genes expression and estrogen response element activity in breast cancer cells, while SHARPIN overexpression could reverse these effects. SHARPIN depletion significantly decreases estrogen stimulated cell proliferation in breast cancer cells, which effect could be further rescued by ERα overexpression. Further mechanistic study reveals that SHARPIN mainly localizes in the cytosol and interacts with ERα both in the cytosol and the nuclear. SHARPIN regulates ERα signaling through protein stability, not through gene expression. SHARPIN stabilizes ERα protein via prohibiting ERα protein poly-ubiquitination. Further study shows that SHARPIN could facilitate the mono-ubiquitinaiton of ERα at K302/303 sites and facilitate ERE luciferase activity. Together, our findings propose a novel ERα modulation mechanism in supporting breast cancer cell growth, in which SHARPIN could be one suitable target for development of novel therapy for ERα positive breast cancer.

Highlights

Breast cancer causes the most frequent women cancer prevalence and mortality in the world [1]
SHARPIN is higher expressed in breast tumor and correlates with estrogen receptor α (ERα) protein in breast cancer tissues
By analysis of The Cancer Genome Atlas (TCGA) public available database, we observe that SHARPIN mRNA level in breast cancer tissue is higher than normal breast tissue (Figure 1A), and SHARPIN mRNA level in breast cancer tissue is more likely to be higher compared with the adjacent normal breast tissue in individual breast cancer subtype (Figure 1B)

Summary

Introduction

Breast cancer causes the most frequent women cancer prevalence and mortality in the world [1]. It is urgent and necessary to understand the potential mechanisms and insight into the novel facets and modulatory factors for estrogen signaling, which could serve for the development of promising treatment strategies. Several mechanisms were shown to account for hyper-activation of ERα and endocrine resistance in breast cancer [4,5,6]. The others are associated with the modulatory factors, which could include ERα co-activators and protein modulators, including ubiquitination, SUMOlyation and phosphorylation [8,9,10]. The detailed mechanism that how ERα protein and its signaling are controlled by these modulators still remains largely unclear. As a group of ubiquitin ligases have been shown to facilitate estrogen signaling in breast cancer cell, such as BRCA1, CHIP and RNF31, it may suggest ER signaling and turnover is tightly linked to ubiquitin-proteasome system [11,12,13,14]

Methods

Results

Conclusion