ORAI1 and ORAI3 in Breast Cancer Molecular Subtypes and the Identification of ORAI3 as a Hypoxia Sensitive Gene and a Regulator of Hypoxia Responses.

Iman Azimi,Sarah Roberts-Thomson,Gregory Monteith,Silke Chalmers,Christopher Henry,Erik Thompson,Mélanie Robitaille,Gregory Baillie,Michael Milevskiy,Kunsala Yapa

doi:10.3390/cancers11020208

Abstract

The remodeling of specific calcium-permeable ion channels is a feature of some breast cancer subtypes. ORAI1 is a protein that forms a calcium-permeable ion channel responsible for store-operated calcium entry (SOCE) in a variety of cell types. ORAI3, a related isoform, is not a regulator of SOCE in most cell types. However, ORAI3 does control SOCE in many estrogen receptor-positive breast cancer cell lines, where it also controls proliferation. ORAI1 is a well-characterized regulator of the proliferation and migration of many basal breast cancer cells; however, the role of ORAI3 in these types of breast cancer cells remains unclear. Here, we sought to define ORAI1 and ORAI3 expression in breast cancer cell lines of different molecular subtypes and assess the potential role and regulation of ORAI3 in basal breast cancer cells. Our study demonstrates that elevated ORAI1 is a feature of basal-like breast cancers, while elevated ORAI3 is a feature of luminal breast cancers. Intriguingly, we found that ORAI3 is over-expressed in the mesenchymal subtype of triple-negative breast cancer. Given this, we assessed ORAI3 levels in the presence of two inducers of the mesenchymal phenotype, hypoxia and epidermal growth factor (EGF). Hypoxia induced ORAI3 levels in basal breast cancer cell lines through a pathway involving hypoxia-inducible factor-1 alpha (HIF1α). The silencing of ORAI3 attenuated hypoxia-associated phosphorylation of the EGF receptor (EGFR) and the expression of genes associated with cell migration and inflammatory/immune responses in the MDA-MB-468 model of basal breast cancer. Although elevated ORAI3 levels were not associated with survival; basal, estrogen receptor-negative and triple-negative breast cancers with high ORAI3 and low ORAI1 levels were associated with poorer clinical outcomes. This study defines ORAI3 as a potential fine-tuner for processes relevant to the progression of basal breast cancers.

Highlights

The remodeling of calcium (Ca2+ ) signaling and/or changes in the expression of specific ion channels occurs in a variety of cancers [1,2]
Consistent with reports from microarray data indicating higher levels of ORAI1 in basal breast cancers compared to non-basal [11], our assessment of five intrinsic PAM50 molecular subtypes showed higher levels of ORAI1 in basal breast cancers compared to HER2-enriched, Luminal A, Luminal B and Normal-like subtypes (Figure 1A), with significantly higher levels of ORAI1 in basal breast cancers compared to all other molecular subtypes (Figure 1(Bi))
The potential importance of the ORAI3/ORAI1 heteromeric channel should be explored in basal breast cancers and triple negative breast cancers (TNBC), as has been assessed in prostate cancer [26]. These studies have defined the remodeling of ORAI1 and ORAI3 in breast cancer molecular subtypes

Summary

Introduction

The remodeling of calcium (Ca2+ ) signaling and/or changes in the expression of specific ion channels occurs in a variety of cancers [1,2]. Signaling, such as the molecular components of store-operated Ca2+ entry (SOCE) are a feature of specific breast cancer subtypes [3]. Breast cancer is a heterogeneous disease with several molecular subtypes including luminal A, luminal B, Her-2 enriched, claudin-low, and basal-like. No targeted therapies for TNBC currently exist, making target identification a major priority to improve the prognosis of this disease [6]. Molecular subtypes of TNBC have been defined and include Basal-Like Immune-Suppressed (BLIS), Basal-Like

Methods

Results

Conclusion