Down‐regulation of Orai3 arrests cell‐cycle progression and induces apoptosis in breast cancer cells but not in normal breast epithelial cells

Abstract

Breast cancer (BC) is the leading cancer in the world in terms of incidence and mortality in women. However, the mechanism by which BC develops remains largely unknown. The increase in cytosolic free Ca(2+) can result in different physiological changes including cell growth and death. Orai isoforms are highly Ca(2+) selective channels. In the present study, we analyzed Orai3 expression in normal and cancerous breast tissue samples, and its role in MCF-7 BC and normal MCF-10A mammary epithelial cell lines. We found that the expression of Orai3 mRNAs was higher in BC tissues and MCF-7 cells than in normal tissues and MCF-10A cells. Down-regulation of Orai3 by siRNA inhibited MCF-7 cell proliferation and arrested cell cycle at G1 phase. This phenomenon is associated with a reduction in CDKs 4/2 (cyclin-dependent kinases) and cyclins E and D1 expression and an accumulation of p21(Waf1/Cip1) (a cyclin-dependent kinase inhibitor) and p53 (a tumor-suppressing protein). Orai3 was also involved in MCF-7 cell survival. Furthermore, Orai3 mediated Ca(2+) entry and contributed to intracellular calcium concentration ([Ca(2+)](i)). In MCF-10A cells, silencing Orai3 failed to modify [Ca(2+)](i), cell proliferation, cell-cycle progression, cyclins (D1, E), CDKs (4, 2), and p21(Waf1/Cip1) expression. Our results provide strong evidence for a significant effect of Orai3 on BC cell growth in vitro and show that this effect is associated with the induction of cell cycle and apoptosis resistance. Our study highlights a possible role of Orai3 as therapeutic target in BC therapy.

Remodelling of Ca2+transport in cancer: how it contributes to cancer hallmarks?

“…In MCF-7 breast cancer cells, G1 phase progression and G1/S transition were shown to depend on the ORAI3 Ca 2þ -permeable channel that contributes to store-operated Ca 2þ entry (SOCE) in these cells [23,24]. It positively regulates the expression of cyclins (D1, E), CDK4 and 2, and suppresses cyclin-dependent kinase inhibitors (CDKIs) such, p21 and p53 by regulating the expression and the activity of c-myc [24,25].…”

Emerging roles of Orai3 in pathophysiology

“…25 Indeed, Orai1 has been reported to mediate SOCE in the ER − breast cancer cell line MDA-MB231 and was shown to contribute to breast cancer metastasis. 19 Studies on Orai3 were subsequently confirmed by other groups; Faouzi et al showed that store depletion activated SOCE through Orai3 channels in ER + MCF7 cells, 23 whereas an earlier report by Feng et al reported that Orai1 is not involved in mediating SOCE in MCF7 cells. 63 Faouzi et al also showed that Orai3 plays an important role in cell cycle regulation of ER + breast cancer cells but not normal breast epithelial cells.…”

“…1). There are reported instances where Orai3 was shown to encode SOCE in a subset of breast cancer cells, expressing the estrogen receptors [23][24][25][26] and in mature effector T cells, 27 but in general SOCE is mediated by Orai1 homomultimeric channels. In fact, in the absence of functional Orai1 channels, ectopically expressed Orai3 can only partially compensate for Orai1 in mediating SOCE in HEK 293 and human fibroblasts.…”

Components of Intracellular Calcium Movements in Cancer Cells: Review

“…44 Kanser sebebi olarak gösterilebilecek asıl bilgi ise, MCF-7 meme kanseri hücrelerinde ORAI3'ün susturulması ile G1 hücre döngüsünün durduğu ve proliferasyonun inhibe olduğu çalışmadan gelmektedir. 45 Verilen bu ör-nekler ORAI-aracılı Ca +2 girişinin bir yukarı regülasyon olduğunu işaret eder iken, apoptotik direnç kazanması ile birlikte bu yolağın aşağı regülasyon olduğunu gösteren bazı kanser tipleri de mevcuttur. 6 LNCaP prostat kanser hücrelerinde ORAI izoformlarının susturulması, hücre çoğal-masını azaltmıştır ve G1 hücre fazında yer alan ve onkojenik hücre döngü proteini olan siklin D1'in aşağı regülasyonuna aracı olmuştur.…”