ER\u03b1-36 regulates progesterone receptor activity in breast cancer

Henri-Philippe Konan,Coralie Poulard,Loay Kassem,Ausra Surmieliova-Garnès,Amélie Rezza,Muriel Le Romancer,Elodie Cascales,Julien Jacquemetton,Isabelle Treilleux,Olivier Trédan,Soleilmane Omarjee

doi:10.1186/s13058-020-01278-7

Abstract

BackgroundAlterations in estrogen and progesterone signaling, via their respective receptors, estrogen receptor alpha (ERα) and progesterone receptor (PR), respectively, are largely involved in the development of breast cancer (BC). The recent identification of ERα-36, a splice variant of ERα, has uncovered a new facet of this pathology. Although ERα-36 expression is associated with poor prognosis, metastasis development, and resistance to treatment, its predictive value has so far not been associated with a BC subtype and its mechanisms of action remain understudied.MethodsTo study ERα-36 expression in BC specimens, we performed immunochemical experiments. Next, the role of ERα-36 in progesterone signaling was investigated by generating KO clones using the CRISPR/CAS9 technology. PR signaling was also assessed by proximity ligation assay, Western blotting, RT-QPCR, and ChIP experiments. Finally, proliferation assays were performed with the IncuCyte technology and migration experiments using scratch assays.ResultsHere, we demonstrate that ERα-36 expression at the plasma membrane is correlated with a reduced disease-free survival in a cohort of 160 BC patients, particularly in PR-positive tumors, suggesting a crosstalk between ERα-36 and PR. Indeed, we show that ERα-36 interacts constitutively with PR in the nucleus of tumor cells. Moreover, it regulates PR expression and phosphorylation on key residues, impacting the biological effects of progesterone.ConclusionsERα-36 is thus a regulator of PR signaling, interfering with its transcriptional activity and progesterone-induced anti-proliferative effects as well as migratory capacity. Hence, ERα-36 may constitute a new prognostic marker as well as a potential target in PR-positive BC.

Highlights

Alterations in estrogen and progesterone signaling, via their respective receptors, estrogen receptor alpha (ERα) and progesterone receptor (PR), respectively, are largely involved in the development of breast cancer (BC)
Clinico-pathological characteristics We evaluated estrogen receptor α (ERα)-36 expression in a cohort of patients displaying invasive breast cancer using our polyclonal antibody recognizing the ERα-36 isoform, which has already been validated for IHC experiments [10]
We found that the inhibitory effect of R5020 on serum-induced proliferation was lost in ERα-36 KO compared to wild type (WT) clones (Fig. 6a)

Summary

Introduction

Alterations in estrogen and progesterone signaling, via their respective receptors, estrogen receptor alpha (ERα) and progesterone receptor (PR), respectively, are largely involved in the development of breast cancer (BC). More than 75% of breast tumors express the estrogen receptor α (ERα) in the nucleus and predominantly belong to the luminal subtype. ERα-36 was shown to activate ERK1/2 through the protein kinase C delta signaling pathway, leading to an increase in the expression of cyclin D1/CDK4, which increases cell cycle progression [9]. Binding of ERα-36 to ERK prevents its dephosphorylation by MKP3 and enhances a paxillin/cyclin D1 pathway [10]. It was reported that ERα-36-mediated estrogen signaling plays an important role in the maintenance of ERα-positive and ERα-negative breast cancer stem/progenitor cells [12]. Overexpression of ERα-36 in normal mammary epithelial cells causes loss of adhesion, enhanced migration, and resistance to apoptosis [13]

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