Research ArticleCell Biology

Ca2+ signals regulate mitochondrial metabolism by stimulating CREB-mediated expression of the mitochondrial Ca2+ uniporter gene MCU

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Science Signaling  03 Mar 2015:
Vol. 8, Issue 366, pp. ra23
DOI: 10.1126/scisignal.2005673

Maintaining mitochondrial calcium uptake

The calcium uniporter complex, which includes the protein MCU, mediates mitochondrial calcium uptake, a process that buffers excess cytosolic calcium and regulates mitochondrial metabolism. Shanmughapriya et al. examined mitochondrial calcium uptake and function in a B lymphocyte cell line deficient in one or more proteins necessary for mediating two types of calcium signals—IICR, calcium released from the endoplasmic reticulum through the calcium-permeable IP3 receptors, and SOCE, calcium influx through store-operated calcium channels. Without IICR or SOCE, the activity of the transcription factor CREB, which bound to the MCU promoter, and the expression and abundance of MCU were reduced, mitochondrial calcium uptake was compromised, and mitochondrial metabolism was altered. Cells deficient in IICR or SOCE lacked an oscillating basal calcium signal. Thus, IICR and SOCE control the capacity of mitochondria to uptake calcium and therefore regulate mitochondrial metabolism.


Cytosolic Ca2+ signals, generated through the coordinated translocation of Ca2+ across the plasma membrane (PM) and endoplasmic reticulum (ER) membrane, mediate diverse cellular responses. Mitochondrial Ca2+ is important for mitochondrial function, and when cytosolic Ca2+ concentration becomes too high, mitochondria function as cellular Ca2+ sinks. By measuring mitochondrial Ca2+ currents, we found that mitochondrial Ca2+ uptake was reduced in chicken DT40 B lymphocytes lacking either the ER-localized inositol trisphosphate receptor (IP3R), which releases Ca2+ from the ER, or Orai1 or STIM1, components of the PM-localized Ca2+-permeable channel complex that mediates store-operated calcium entry (SOCE) in response to depletion of ER Ca2+ stores. The abundance of MCU, the pore-forming subunit of the mitochondrial Ca2+ uniporter, was reduced in cells deficient in IP3R, STIM1, or Orai1. Chromatin immunoprecipitation and promoter reporter analyses revealed that the Ca2+-regulated transcription factor CREB (cyclic adenosine monophosphate response element–binding protein) directly bound the MCU promoter and stimulated expression. Lymphocytes deficient in IP3R, STIM1, or Orai1 exhibited altered mitochondrial metabolism, indicating that Ca2+ released from the ER and SOCE-mediated signals modulates mitochondrial function. Thus, our results showed that a transcriptional regulatory circuit involving Ca2+-dependent activation of CREB controls the Ca2+ uptake capability of mitochondria and hence regulates mitochondrial metabolism.

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