Assessment of cytosolic free calcium changes during ceramide-induced cell death in MDA-MB-231 breast cancer cells expressing the calcium sensor GCaMP6m

John J. Bassett, Alice H.L. Bong, Ellen K. Janke, Mélanie Robitaille, Sarah J. Roberts-Thomson, Amelia A. Peters, Gregory R. Monteith

Alterations in Ca2+ signaling can regulate key cancer hallmarks such as proliferation, invasiveness and resistance to cell death. Changes in the regulation of intracellular Ca2+ and specific components of Ca2+ influx are a feature of several cancers and/or cancer subtypes, including the basal-like breast cancer subtype, which has a poor prognosis. The development of genetically encoded calcium indicators, such as GCaMP6, represents an opportunity to measure changes in intracellular free Ca2+ during processes relevant to breast cancer progression that occur over long periods (e.g. hours), such as cell death. This study describes the development of a MDA-MB-231 breast cancer cell line stably expressing GCaMP6m. The cell line retained the key features of this aggressive basal-like breast cancer cell line. Using this model, we defined alterations in relative cytosolic free Ca2+ ([Ca2+]CYT) when the cells were treated with C2-ceramide. Cell death was measured simultaneously via assessment of propidium iodide permeability. Treatment with ceramide produced delayed and heterogeneous sustained increases in [Ca2+]CYT. Where cell death occurred, [Ca2+]CYT increases preceded cell death. The sustained increases in [Ca2+]CYT were not related to the rapid morphological changes induced by ceramide. Silencing of the plasma membrane Ca2+ ATPase isoform 1 (PMCA1) was associated with an augmentation in ceramide-induced increases in [Ca2+]CYT and also cell death. This work demonstrates the utility of GCaMP6 Ca2+ indicators for investigating [Ca2+]CYT changes in breast cancer cells during events relevant to tumor progression, which occur over hours rather than minutes.