MICU1 encodes a mitochondrial EF hand protein required for Ca2+ uptake

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Abstract

Mitochondrial calcium uptake plays a central role in cell physiology by stimulating ATP production, shaping cytosolic calcium transients, and regulating cell death. The biophysical properties of mitochondrial calcium uptake have been studied in detail, but the underlying proteins remain elusive. Here, we utilize an integrative strategy to predict human genes involved in mitochondrial calcium entry based on clues from comparative physiology, evolutionary genomics, and organelle proteomics. RNA interference against 13 top candidates highlighted one gene that we now call mitochondrial calcium uptake 1 ( MICU1). Silencing MICU1 does not disrupt mitochondrial respiration or membrane potential but abolishes mitochondrial calcium entry in intact and permeabilized cells, and attenuates the metabolic coupling between cytosolic calcium transients and activation of matrix dehydrogenases. MICU1 is associated with the organelle’s inner membrane and has two canonical EF hands that are essential for its activity, suggesting a role in calcium sensing. MICU1 represents the founding member of a set of proteins required for high capacity mitochondrial calcium entry. Its discovery may lead to the complete molecular characterization of mitochondrial calcium uptake pathways, and offers genetic strategies for understanding their contribution to normal physiology and disease.

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Most cited references 42

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STIM1 is a Ca2+ sensor that activates CRAC channels and migrates from the Ca2+ store to the plasma membrane.

Michael D. Cahalan, Kenneth Stauderman, Mark Ellisman … (2005)

As the sole Ca2+ entry mechanism in a variety of non-excitable cells, store-operated calcium (SOC) influx is important in Ca2+ signalling and many other cellular processes. A calcium-release-activated calcium (CRAC) channel in T lymphocytes is the best-characterized SOC influx channel and is essential to the immune response, sustained activity of CRAC channels being required for gene expression and proliferation. The molecular identity and the gating mechanism of SOC and CRAC channels have remained elusive. Previously we identified Stim and the mammalian homologue STIM1 as essential components of CRAC channel activation in Drosophila S2 cells and human T lymphocytes. Here we show that the expression of EF-hand mutants of Stim or STIM1 activates CRAC channels constitutively without changing Ca2+ store content. By immunofluorescence, EM localization and surface biotinylation we show that STIM1 migrates from endoplasmic-reticulum-like sites to the plasma membrane upon depletion of the Ca2+ store. We propose that STIM1 functions as the missing link between Ca2+ store depletion and SOC influx, serving as a Ca2+ sensor that translocates upon store depletion to the plasma membrane to activate CRAC channels.

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Integrated analysis of protein composition, tissue diversity, and gene regulation in mouse mitochondria.

Vamsi K Mootha, Jakob Bunkenborg, Jesper V Olsen … (2003)

Mitochondria are tailored to meet the metabolic and signaling needs of each cell. To explore its molecular composition, we performed a proteomic survey of mitochondria from mouse brain, heart, kidney, and liver and combined the results with existing gene annotations to produce a list of 591 mitochondrial proteins, including 163 proteins not previously associated with this organelle. The protein expression data were largely concordant with large-scale surveys of RNA abundance and both measures indicate tissue-specific differences in organelle composition. RNA expression profiles across tissues revealed networks of mitochondrial genes that share functional and regulatory mechanisms. We also determined a larger "neighborhood" of genes whose expression is closely correlated to the mitochondrial genes. The combined analysis identifies specific genes of biological interest, such as candidates for mtDNA repair enzymes, offers new insights into the biogenesis and ancestry of mammalian mitochondria, and provides a framework for understanding the organelle's contribution to human disease.

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Genome-wide RNAi screen identifies Letm1 as a mitochondrial Ca2+/H+ antiporter.

Dawei Jiang, Linlin Zhao, David Clapham (2009)

Mitochondria are integral components of cellular calcium (Ca2+) signaling. Calcium stimulates mitochondrial adenosine 5'-triphosphate production, but can also initiate apoptosis. In turn, cytoplasmic Ca2+ concentrations are regulated by mitochondria. Although several transporter and ion-channel mechanisms have been measured in mitochondria, the molecules that govern Ca2+ movement across the inner mitochondrial membrane are unknown. We searched for genes that regulate mitochondrial Ca2+ and H+ concentrations using a genome-wide Drosophila RNA interference (RNAi) screen. The mammalian homolog of one Drosophila gene identified in the screen, Letm1, was found to specifically mediate coupled Ca2+/H+ exchange. RNAi knockdown, overexpression, and liposome reconstitution of the purified Letm1 protein demonstrate that Letm1 is a mitochondrial Ca2+/H+ antiporter.

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Author and article information

Journal

Journal ID (nlm-journal-id): 0410462

Journal ID (pubmed-jr-id): 6011

Journal ID (nlm-ta): Nature

Title: Nature

ISSN (Print): 0028-0836

ISSN (Electronic): 1476-4687

Publication date Nihms-submitted: 4 August 2010

Publication date (Electronic): 8 August 2010

Publication date (Print): 16 September 2010

Publication date PMC-release: 16 March 2011

Volume: 467

Issue: 7313

Pages: 291-296

Affiliations

[1 ]Center for Human Genetic Research, Massachusetts General Hospital, Boston, MA U.S.A., Broad Institute, Cambridge, MA U.S.A., Department of Systems Biology, Harvard Medical School, Boston, MA U.S.A.

[2 ]Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO U.S.A.

Author notes

Correspondence and requests for materials should be addressed to V.K.M. ( vamsi@ 123456hms.harvard.edu )

Article

Manuscript ID: nihpa223698

DOI: 10.1038/nature09358

PMC ID: 2977980

PubMed ID: 20693986

SO-VID: e5441f11-cdbc-4dd8-9114-37d7d5c1b7ff

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