title: Uncoupling protein 3 (UCP3) modulates the activity of Sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) by decreasing mitochondrial ATP production.
abstract: The uncoupling proteins UCP2 and UCP3 have been postulated to catalyze Ca(2+) entry across the inner membrane of mitochondria, but this proposal is disputed, and other, unrelated proteins have since been identified as the mitochondrial Ca(2+) uniporter. To clarify the role of UCPs in mitochondrial Ca(2+) handling, we down-regulated the expression of the only uncoupling protein of HeLa cells, UCP3, and measured Ca(2+) and ATP levels in the cytosol and in organelles with genetically encoded probes. UCP3 silencing did not alter mitochondrial Ca(2+) uptake in permeabilized cells. In intact cells, however, UCP3 depletion increased mitochondrial ATP production and strongly reduced the cytosolic and mitochondrial Ca(2+) elevations evoked by histamine. The reduced Ca(2+) elevations were due to inhibition of store-operated Ca(2+) entry and reduced depletion of endoplasmic reticulum (ER) Ca(2+) stores. UCP3 depletion accelerated the ER Ca(2+) refilling kinetics, indicating that the activity of sarco/endoplasmic reticulum Ca(2+) (SERCA) pumps was increased. Accordingly, SERCA inhibitors reversed the effects of UCP3 depletion on cytosolic, ER, and mitochondrial Ca(2+) responses. Our results indicate that UCP3 is not a mitochondrial Ca(2+) uniporter and that it instead negatively modulates the activity of SERCA by limiting mitochondrial ATP production. The effects of UCP3 on mitochondrial Ca(2+) thus reflect metabolic alterations that impact on cellular Ca(2+) homeostasis. The sensitivity of SERCA to mitochondrial ATP production suggests that mitochondria control the local ATP availability at ER Ca(2+) uptake and release sites.
authors.affiliation: Department of Cell Physiology and Metabolism, University of Geneva, rue Michel-Servet, 1, CH-1211 Genève, Switzerland.
authors.forename: Umberto
authors.initials: U
authors.lastname: De Marchi
authors.forename: Cyril
authors.initials: C
authors.lastname: Castelbou
authors.forename: Nicolas
authors.initials: N
authors.lastname: Demaurex
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis* / Q000235:genetics; D002118:Calcium / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D020868:Gene Silencing; D006367:HeLa Cells; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D000071247:Uncoupling Protein 3
chemical_list: D007473:Ion Channels; D024101:Mitochondrial Proteins; C000604392:UCP3 protein, human; D000071247:Uncoupling Protein 3; D000255:Adenosine Triphosphate; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium