Leucine Zipper EF Hand-containing Transmembrane Protein 1 (Letm1) and Uncoupling Proteins 2 and 3 (UCP2/3) Contribute to Two Distinct Mitochondrial Ca ²⁺ Uptake Pathways*

Abstract

Cytosolic Ca ²⁺ signals are transferred into mitochondria over a huge concentration range. In our recent work we described uncoupling proteins 2 and 3 (UCP2/3) to be fundamental for mitochondrial uptake of high Ca ²⁺ domains in mitochondria-ER junctions. On the other hand, the leucine zipper EF hand-containing transmembrane protein 1 (Letm1) was identified as a mitochondrial Ca ²⁺/H ⁺ antiporter that achieved mitochondrial Ca ²⁺ sequestration at small Ca ²⁺ increases. Thus, the contributions of Letm1 and UCP2/3 to mitochondrial Ca ²⁺ uptake were compared in endothelial cells. Knock-down of Letm1 did not affect the UCP2/3-dependent mitochondrial uptake of intracellularly released Ca ²⁺ but strongly diminished the transfer of entering Ca ²⁺ into mitochondria, subsequently, resulting in a reduction of store-operated Ca ²⁺ entry (SOCE). Knock-down of Letm1 and UCP2/3 did neither impact on cellular ATP levels nor the membrane potential. The enhanced mitochondrial Ca ²⁺ signals in cells overexpressing UCP2/3 rescued SOCE upon Letm1 knock-down. In digitonin-permeabilized cells, Letm1 exclusively contributed to mitochondrial Ca ²⁺ uptake at low Ca ²⁺ conditions. Neither the Letm1- nor the UCP2/3-dependent mitochondrial Ca ²⁺ uptake was affected by a knock-down of mRNA levels of mitochondrial calcium uptake 1 (MICU1), a protein that triggers mitochondrial Ca ²⁺ uptake in HeLa cells. Our data indicate that Letm1 and UCP2/3 independently contribute to two distinct, mitochondrial Ca ²⁺ uptake pathways in intact endothelial cells.

Journal

Journal ID (nlm-ta): J Biol Chem

Journal ID (hwp): jbc

Journal ID (pmc): jbc

Journal ID (publisher-id): JBC

Title: The Journal of Biological Chemistry

Publisher: American Society for Biochemistry and Molecular Biology (9650 Rockville Pike, Bethesda, MD 20814, U.S.A. )

ISSN (Print): 0021-9258

ISSN (Electronic): 1083-351X

Publication date (Print): 12 August 2011

Publication date (Electronic): 25 May 2011

Publication date PMC-release: 25 May 2011

Volume: 286

Issue: 32

Pages: 28444-28455

Affiliations

From the [‡ ]Institute of Molecular Biology and Biochemistry, Molecular and Cellular Physiology Research Unit, Center of Molecular Medicine, Medical University Graz, Harrachgasse 21/III, 8010 Graz, Austria and

the [§ ]Precursory Research for Embryonic Science, Japan Science and Technology Agency, 5 Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan

Author notes

[1 ] To whom correspondence should be addressed: Institute of Molecular Biology and Biochemistry, Molecular and Cellular Physiology Research Unit, Center of Molecular Medicine, Medical University Graz, Harrachgasse 21/III, 8010 Graz, Austria. Tel.: [phone]; Fax: [phone]; E-mail: wolfgang.graier@ 123456medunigraz.at .

Article

Publisher ID: M111.244517

DOI: 10.1074/jbc.M111.244517

PMC ID: 3151087

PubMed ID: 21613221

Copyright statement: © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.

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Categories

Subject: Cell Biology