Orai1 and Orai3 act through distinct signalling axes to promote stemness and tumorigenicity of breast cancer stem cells
Duan Zhuo, Zhenchuan Lei, Dong Lin, Andrew M. Chan, Jiacheng Lin, Liwen Jiang, Beibei Qiu, Xiaohua Jiang, Youhua Tan, Xiaoqiang Yao
Abstract
One of major challenges in breast tumor therapy is the existence of breast cancer stem cells (BCSCs). BCSCs are a small subpopulation of tumor cells that exhibit characteristics of stem cells. BCSCs are responsible for progression, recurrence, chemoresistance and metastasis of breast cancer. Ca 2+ signalling plays an important role in diverse processes in cancer development. However, the role of Ca 2+ signalling in BCSCs is still poorly understood. A highly effective 3D soft fibrin gel system was used to enrich BCSC-like cells from ER+ breast cancer lines MCF7 and MDA-MB-415. We then investigated the role of two Ca 2+ -permeable ion channels Orai1 and Orai3 in the growth and stemness of BCSC-like cells in vitro, and tumorigenicity in female NOD/SCID mice in vivo. Orai1 RNA silencing and pharmacological inhibition reduced the growth of BCSC-like cells in tumor spheroids, decreased the expression levels of BCSC markers, and reduced the growth of tumor xenografts in NOD/SCID mice. Orai3 RNA silencing also had similar inhibitory effect on the growth and stemness of BCSC-like cells in vitro, and tumor xenograft growth in vivo. Mechanistically, Orai1 and SPCA2 mediate store-operated Ca 2+ entry. Knockdown of Orai1 or SPCA2 inhibited glycolysis pathway, whereas knockdown of Orai3 or STIM1 had no effect on glycolysis. We found that Orai1 interacts with SPCA2 to mediate store-independent Ca 2+ entry, subsequently promoting the growth and tumorigenicity of BCSC-like cells via glycolysis pathway. In contrast, Orai3 and STIM1 mediate store-operated Ca 2+ entry, promoting the growth and tumorigenicity of BCSC-like cells via a glycolysis-independent pathway. Together, our study uncovered a well-orchestrated mechanism through which two Ca 2+ entry pathways act through distinct signalling axes to finely control the growth and tumorigenicity of BCSCs.