Extended Synaptotagmins 1 and 2 Are Required for Store-Operated Calcium Entry, Cell Migration and Viability in Breast Cancer Cells

Simple Summary Breast cancer is one of the most common types of cancer in women. Breast tumors can be grouped in, at least, three different molecular subtypes, including luminal, HER2+ and triple negative subtypes. Store-operated Ca2+ entry (SOCE) is a mechanism for Ca2+ influx that supports a variety of cancer hallmarks in breast cancer cells. The key molecular players of SOCE are the endoplasmic reticulum Ca2+ sensor STIM1 and the highly Ca2+-selective Orai1 channels in the plasma membrane. The aim of the present study is to elucidate the functional role of extended synaptotagmins 1 and 2 in the activation of SOCE by facilitating the tethering of the plasma membrane and the membrane of the endoplasmic reticulum. Our results indicate that extended synaptotagmins 1 and 2 are required for SOCE, migration and viability in luminal MCF7 and triple negative breast cancer cells, without having any effect on SOCE in non-tumoral breast epithelial cells.Abstract Extended synaptotagmins (E-Syts) are endoplasmic reticulum (ER)-associated proteins that facilitate the tethering of the ER to the plasma membrane (PM), participating in lipid transfer between the membranes and supporting the Orai1-STIM1 interaction at ER-PM junctions. Orai1 and STIM1 are the core proteins of store-operated Ca2+ entry (SOCE), a major mechanism for Ca2+ influx that regulates a variety of cellular functions. Aberrant modulation of SOCE in cells from different types of cancer has been reported to underlie the development of several tumoral features. Here we show that estrogen receptor-positive (ER+) breast cancer MCF7 and T47D cells and triple-negative breast cancer (TNBC) MDA-MB-231 cells overexpress E-Syt1 and E-Syt2 at the protein level; the latter is also overexpressed in the TNBC BT20 cell line. E-Syt1 and E-Syt2 knockdown was without effect on SOCE in non-tumoral MCF10A breast epithelial cells and ER+ T47D breast cancer cells; however, SOCE was significantly attenuated in ER+ MCF7 cells and TNBC MDA-MB-231 and BT20 cells upon transfection with siRNA E-Syt1 or E-Syt2. Consistent with this, E-Syt1 and E-Syt2 knockdown significantly reduced cell migration and viability in ER+ MCF7 cells and the TNBC cells investigated. To summarize, E-Syt1 and E-Syt2 play a relevant functional role in breast cancer cells.