Clinical and Biological Significance of ESR1 Gene Alteration and Estrogen Receptors Isoforms Expression in Breast Cancer Patients.

Anna Nagel,Grzegorz Stasilojc,Aleksandra Markiewicz,Jaroslaw Skokowski,Anna Zaczek,Mariola Iliszko,Marzena Welnicka-Jaskiewicz,Rafal Sadej,Jolanta Szade,Julia Elzanowska,Jacek Bigda

doi:10.3390/ijms20081881

Anna Nagel, Grzegorz Stasilojc + Show 9 more

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https://doi.org/10.3390/ijms20081881

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Abstract

The amplification of estrogen receptor alpha (ERα) encoded by the ESR1 gene has been described as having a prognostic role in breast cancer patients. However, increased dosage of the ESR1 gene (tested by real-time PCR) is also observed in ER-negative breast cancers, which might suggest the expression of alternative isoforms of ERα (other than classical ERα of 66 kDa). In the current work, we have investigated the ESR1 gene dosage in 402 primary breast cancer patients as well as the expression of ERα isoforms—ERα66 and ERα36—on mRNA and protein levels. The obtained results were correlated with clinicopathological data of the patients. Results showed that increased ESR1 gene dosage is not related to ESR1 gene amplification measured by fluorescent in situ hybridization (FISH), but it correlates with the decreased expression of ERα66 isoform (p = 0.01). Interestingly, the short ER isoform ERα36 was expressed in samples with increased ESR1 gene dosage, suggesting that genomic aberration might influence the expression of that particular isoform. Similarly to ESR1 increased gene dosage, high ERα36 expression was linked with the decreased disease-free survival of the patients (p = 0.05), which was independent of the status of the classical ERα66 level in breast tumors.

Highlights

Estrogen receptor alpha (ERα) is an important prognostic and predictive factor in breast cancer
As the literature describes the opposite findings, when ESR1 gene status was tested by fluorescent in situ hybridization (FISH), it made us wonder if increased ESR1 gene dosage measured by qPCR would correspond to ESR1 amplification analyzed by the golden standard method for gene amplification testing: FISH
ESR1 gene status measured by qPCR and FISH did not correlate (r = −0.042, p = 0.75, Figure 2), which suggests that both methods detect different types of

Summary

Introduction

Estrogen receptor alpha (ERα) is an important prognostic and predictive factor in breast cancer It is a ligand-activated transcription factor and its signaling governs the growth, proliferation, and survival of cancer cells. We have applied a similar technique for the analysis of ESR1 genomic sequence alteration [6] With this method, we have shown that the ESR1 copy number changes (gene dosage changes) occur in ER-negative patients and have prognostic significance. In 2005, Wang et al described a 36-kDa splicing variant of the ESR1 gene, which was called ERα36 [11,12] It differs from the ERα66 isoform by lacking both transcriptional activation domains, but retains the DNA-binding domains [13,14], new results indicate that it might act as a transcription factor [15]. In vitro studies performed using various breast cancer cells indicate that ERα36 rapidly activates the MAPK signalling pathway, leading to uncontrolled proliferation and anti-apoptotic events [22]

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