The Mitochondrial Ca2+ uniporter is a central regulator of interorganellar Ca2+ transfer and NFAT activation
Mitochondrial Ca 2+ uptake tailors the strength of stimulation of plasma membrane phospholipase C-coupled receptors to that of cellular bioenergetics. However, how Ca 2+ uptake by the mitochondrial Ca 2+ uniporter (MCU) shapes receptorevoked interorganellar Ca 2+ signaling is unknown. Here, we used CRISPR/Cas9 gene knockout, subcellular Ca 2+ imaging, and mathematical modeling to show that MCU is a universal regulator of intracellular Ca 2+ signaling across mammalian cell types. MCU activity sustains cytosolic Ca 2+ signaling by preventing Ca 2+ -dependent inactivation of store-operated Ca 2+ release-activated Ca 2+ channels and by inhibiting Ca 2+ extrusion. Paradoxically, MCU knockout (MCU-KO) enhanced cytosolic Ca 2+ responses to store depletion. Physiological agonist stimulation in MCU-KO cells led to enhanced frequency of cytosolic Ca 2+ oscillations, endoplasmic reticulum Ca 2+ refilling, nuclear translocation of nuclear factor for activated T cells transcription factors, and cell proliferation, without altering inositol-1,4,5-trisphosphate receptor activity. Our data show that MCU has dual counterbalancing functions at the cytosol-mitochondria interface, whereby the cell-specific MCU-dependent cytosolic Ca 2+ clearance and buffering capacity of mitochondria reciprocally regulate interorganellar Ca 2+ transfer and nuclear factor for activated T cells nuclear translocation during receptor-evoked signaling. These findings highlight the critical dual function of the MCU not only in the acute Ca 2+ buffering by mitochondria but also in shaping endoplasmic reticulum and cytosolic Ca 2+ signals that regulate cellular transcription and function.