Deletion of mitochondrial calcium uniporter enhances calcium signals by slowing calcium clearance and triggers adaptive transcriptomic remodeling

Mitochondrial Ca 2+ uptake via the mitochondrial Ca 2+ uniporter (MCU) following store-operated Ca 2+ entry (SOCE) supports cellular bioenergetics, yet how mitochondria shape SOCE and cytosolic Ca 2+ signaling remains incompletely understood. Combining gene deletion and functional Ca 2+ imaging techniques with a rigorous transcriptomic filter, we find larger cytosolic Ca 2+ signals in CRISPR/Cas9-generated Mcu knockout cells. This increase arises primarily from slower cytosolic Ca 2+ clearance rather than increased store-operated Ca 2+ release-activated Ca 2+ (CRAC) channel activity. Compensatory upregulation of cytosolic Ca 2+ regulators, such as the plasma membrane Ca 2+ ATPase (PMCA) pump that extrudes excess cytosolic Ca 2+ , is insufficient to restore normal Ca 2+ homeostasis. Re-expression of wild-type MCU restored the cytosolic Ca 2+ dynamics but a channel pore-dead MCU mutant did not. Deletion of Mcu resulted in major alterations in the transcriptome and re-expression of the protein significantly restored 15% of more than 200 common genes that showed differential expression in two independent knockout clones. Our results identify a set of candidate MCU-dependent genes that may contribute to the regulation of cellular Ca 2+ signaling, and show how cytosolic Ca 2+ signals can be enhanced in the absence of MCU without an increase in CRAC channel activity.