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

Abstract Inter-organellar communication often takes the form of Ca 2+ signals. These Ca 2+ signals originate from the endoplasmic reticulum (ER) and regulate different cellular processes like metabolism, fertilization, migration, and cell fate. A prime target for Ca 2+ signals are the mitochondria. ER–mitochondrial Ca 2+ 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 Ca 2+ concentrations are manifold higher than in the cytosol, allowing for rapid mitochondrial Ca 2+ uptake. In the mitochondria, the Ca 2+ signal is decoded differentially depending on its spatiotemporal characteristics. While Ca 2+ oscillations stimulate metabolism and constitute pro-survival signaling, mitochondrial Ca 2+ overload results in apoptosis. Many chemotherapeutics depend on efficient ER–mitochondrial Ca 2+ signaling to exert their function. However, several oncogenes and tumor suppressors present in the MAMs can alter Ca 2+ signaling in cancer cells, rendering chemotherapeutics ineffective. In this review, we will discuss recent studies that connect ER–mitochondrial Ca 2+ transfer, tumor suppressors and oncogenes at the MAMs, and chemotherapy.