Emerging molecular mechanisms in chemotherapy: Ca2+signaling at the mitochondria-associated endoplasmic reticulum membranes

Inter-organellar communication often takes the form of Ca2+signals. These Ca2+signals originate from the endoplasmic reticulum (ER) and regulate different cellular processes like metabolism, fertilization, migration, and cell fate. A prime target for Ca2+signals are the mitochondria. ER-mitochondrial Ca2+transfer is possible through the existence of mitochondria-associated ER membranes (MAMs), ER structures that are in the proximity of the mitochondria. This creates a micro-domain in which the Ca2+concentrations are manifold higher than in the cytosol, allowing for rapid mitochondrial Ca2+uptake. In the mitochondria, the Ca2+signal is decoded differentially depending on its spatiotemporal characteristics. While Ca2+oscillations stimulate metabolism and constitute pro-survival signaling, mitochondrial Ca2+overload results in apoptosis. Many chemotherapeutics depend on efficient ER-mitochondrial Ca2+signaling to exert their function. However, several oncogenes and tumor suppressors present in the MAMs can alter Ca2+signaling in cancer cells, rendering chemotherapeutics ineffective. In this review, we will discuss recent studies that connect ER-mitochondrial Ca2+transfer, tumor suppressors and oncogenes at the MAMs, and chemotherapy.