Store Independent Ca2+ Entry Regulates the DNA Damage Response Pathway in Breast Cancer Cells

The mainstay of treatment for hormone responsive breast tumors is chemotherapy, followed by targeted endocrine therapy. The vast majority (80%) of estrogen receptor positive tumors also express wild type p53 protein that is the main determinant of the DNA damage response. Tumors that are ER+ and p53WT respond poorly to chemotherapy, although the underlying mechanisms are not completely understood. We describe a novel link between store independent Ca2+ entry (SICE) and resistance to DNA damaging drugs, mediated by the secretory pathway Ca2+-ATPase, SPCA2. In luminal ER+/PR+ breast cancer subtypes, SPCA2 levels are high and correlate with poor survival prognosis. Independent of ion pump activity, SPCA2 elevates baseline Ca2+ levels through SICE and drives cell proliferation. Attenuation of SPCA2 led to increased mitochondrial ROS production, DNA damage and activation of the ATM/ATR-p53 axis leading to G0/G1 phase cell cycle arrest and apoptosis. Resistance to DNA damaging agents including doxorubicin, carboplatin, and ionizing radiation could be reversed by downregulation of SPCA2 expression using curcumin. In conclusion, elevated SPCA2 drives pro-survival and chemotherapy resistance in ER+ p53WT breast tumors by suppressing the DNA damage response. Attenuation of SPCA2 expression by curcumin may have therapeutic potential in treating receptor positive breast cancer. The goal of this study is to investigate store Independent Ca2+ entry regulation of the DNA Damage Response pathway in breast cancer cells MCF-7 cells were treated with either control shRNA or shRNA constructs targeting ATP2C2 to determine the effect of SPCA2 knockdown on the MCF-7 transcriptome. RNA was extracted from two biological replicates per sample class and used as the input on an Affymetrix microarray to determine changes in gene expression; thus the comparison was two biological replicates each for experimental versus control.