Abstract 5276: Secretory pathway calcium ATPase 2 (SPCA2) promotes cell survival and chemoresistance in receptor positive breast cancer cells
Authors: Monish Ram Makena, Donna Dang, Allatah Mekile, Phillip Buckhaults, Rajini Rao
Journal: Cancer Research (2020)

Abstract Introduction: Dysregulation of the Ca2+ toolkit has profound consequences for tumor growth and metastasis, raising hopes for novel avenues of therapeutic intervention. The Secretory Pathway Ca2+-ATPase Isoform 2 (SPCA2) has a dual function in sequestering Ca2+ and Mn2+ into secretory stores as well as eliciting their entry into cells by activating plasma membrane ion channels. We have previously showed that SPCA2 is implicated in breast cancer progression, microcalcifications, epithelial-mesenchymal transition, and metastasis. Methods and Results: High SPCA2 expression was associated with poor overall survival in receptor positive breast cancer patients (n=548, P =8.7e-0.6; KM Plotter). Depletion of SPCA2 (SPCA2 KD) in MCF-7 cells significantly reduced cell proliferation (P &amp;lt; 0.05). Analysis of the cell cycle (PI staining, Flow cytometry) revealed a significant increase (P &amp;lt; 0.05) in the number of cells in the G0/G1 phase, and significant increase in apoptosis (via TUNEL assay) (P &amp;lt; 0.05) in SPCA2 KD cells compared to control. Microarray analysis showed the p53 pathway is the most significantly upregulated pathway (P &amp;lt; 0.05) in SPCA2 KD cells compared to control. P53 knockout abrogated SPCA2 mediated cell cycle arrest and apoptosis. Depletion of SPCA2 increased reactive oxygen species (ROS, measured by DCFDA dye and MitoSox Red using flow cytometry) leading to DNA damage (confocal microscopy), and activation of ATM/ATR pathway (Immunoblotting, P &amp;lt; 0.05). As a consequence, SPCA2 KD cells showed specific hypersensitivity to DNA damaging agents used in breast cancer therapy (carboplatin, radiation, and doxorubicin) (determined by MTT assay) (P &amp;lt; 0.05). Thus SPCA2 is a novel molecular target in breast cancer therapy. Curcumin is currently being evaluated in clinical trials of breast cancer. We show that curcumin causes dose-dependence inhibition of SPCA2 expression (P &amp;lt; 0.05) in multiple receptor-positive cell lines, and that forced overexpression of SPCA2 decreased curcumin cytotoxicity. Interestingly, we did not observe these results with SPCA1, the housekeeping SPCA isoform, revealing isoform-specific function of Golgi calcium pumps in breast cancer subtypes. Conclusion: These novel findings point to a causal link between SPCA2, breast cancer progression, and chemoresistance to DNA damaging agents. Decrease of SPCA2 expression by curcumin may have therapeutic potential in treating receptor positive breast cancer. Citation Format: Monish Ram Makena, Donna Dang, Allatah Mekile, Phillip Buckhaults, Rajini Rao. Secretory pathway calcium ATPase 2 (SPCA2) promotes cell survival and chemoresistance in receptor positive breast cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5276.