UCP2 modulates single-channel properties of a MCU-dependent Ca(2+) inward current in mitochondria.
The mitochondrial Ca(2+) uniporter is a highly Ca(2+)-selective protein complex that consists of the pore-forming mitochondrial Ca(2+) uniporter protein (MCU), the scaffolding essential MCU regulator (EMRE), and mitochondrial calcium uptake 1 and 2 (MICU1/2), which negatively regulate mitochondrial Ca(2+) uptake. We have previously reported that uncoupling proteins 2 and 3 (UCP2/3) are also engaged in the activity of mitochondrial Ca(2+) uptake under certain conditions, while the mechanism by which UCP2/3 facilitates mitochondrial Ca(2+) uniport remains elusive. This work was designed to investigate the impact of UCP2 on the three distinct mitochondrial Ca(2+) currents found in mitoplasts isolated from HeLa cells, the intermediate- (i-), burst- (b-) and extra-large (xl-) mitochondrial/mitoplast Ca(2+) currents (MCC). Using the patch clamp technique on mitoplasts from cells with reduced MCU and EMRE unveiled a very high affinity of MCU for xl-MCC that succeeds that for i-MCC, indicating the coexistence of at least two MCU/EMRE-dependent Ca(2+) currents. The manipulation of the expression level of UCP2 by either siRNA-mediated knockdown or overexpression changed exclusively the open probability (NPo) of xl-MCC by approx. 38% decrease or nearly a 3-fold increase, respectively. These findings confirm a regulatory role of UCP2 in mitochondrial Ca(2+) uptake and identify UCP2 as a selective modulator of just one distinct MCU/EMRE-dependent mitochondrial Ca(2+) inward current.
Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010, Graz, Austria.
Alexander I
AI
Bondarenko
Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010, Graz, Austria.
Warisara
W
Parichatikanond
Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010, Graz, Austria.
Corina T
CT
Madreiter
Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010, Graz, Austria.
Rene
R
Rost
Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010, Graz, Austria.
Markus
M
Waldeck-Weiermair
Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010, Graz, Austria.
Roland
R
Malli
Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University of Graz, Harrachgasse 21/III, 8010, Graz, Austria. wolfgang.graier@medunigraz.at.
Wolfgang F
WF
Graier
D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism / Q000502:physiology; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D000071246:Uncoupling Protein 2
D015220:Calcium Channels; D007473:Ion Channels; C582650:MICU2 protein, human; D024101:Mitochondrial Proteins; C000604389:UCP2 protein, human; D000071246:Uncoupling Protein 2; D002118:Calcium
Mitochondrial Ca2+ channels; Mitochondrial Ca2+ currents; Mitochondrial Ca2+ uniporter; Mitoplast; Patch clamp; Uncoupling protein 2