title: Uncoupling protein-3 sensitizes cells to mitochondrial-dependent stimulus of apoptosis.
abstract: The mitochondrial uncoupling protein-3 is a member of the mitochondrial carrier protein family. As a homologue of the thermogenic brown fat uncoupling protein-1, it possesses a mitochondrial uncoupling activity and thus can influence cell energy metabolism but its exact biological function remains unclear. In the present study, uncoupling protein-3 was expressed in 293 cells using the tetracycline-inducible system and its impact on cell bioenergetics and responsiveness to the apoptotic stimulus was determined. The induction of uncoupling protein-3 expression in mitochondria did not lead to uncontrolled respiratory uncoupling in intact cells. However, it caused a GDP-inhibition of state 4 respiration and a GDP-induced re-polarization of the inner mitochondrial membrane in the presence of fatty acids, in agreement with its expected physiological behavior as an uncoupling protein (UCP). Uncoupling protein-3 expression did not cause apoptosis per se but increased the responsiveness of the cells to a mitochondrial apoptotic stimulus (i.e., addition of staurosporine in the culture medium). It enhanced caspase 3 and caspase 9 activation and favored cytochrome c release. Moreover, cells in which uncoupling protein-3 expression had been induced showed a higher mitochondrial Bax/Bcl-2 ratio essentially due to enhanced translocation of Bax from cytosol to mitochondria. Finally, the induction of uncoupling protein-3 also increased the sensitivity of mitochondria to open the permeability transition pore in response to calcium. It is concluded that the presence of uncoupling protein-3 in mitochondria sensitizes cells to apoptotic stimuli involving mitochondrial pathways.
authors.affiliation: Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Barcelona, Spain.
authors.forename: Laurent
authors.initials: L
authors.lastname: Dejean
authors.forename: Yolanda
authors.initials: Y
authors.lastname: Cámara
authors.forename: Brigitte
authors.initials: B
authors.lastname: Sibille
authors.forename: Gemma
authors.initials: G
authors.lastname: Solanes
authors.forename: Francesc
authors.initials: F
authors.lastname: Villarroya
mesh_terms: D017209:Apoptosis / Q000502:physiology*; D015153:Blotting, Western; D002352:Carrier Proteins / Q000502:physiology*; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D019069:Cell Respiration / Q000502:physiology*; D045304:Cytochromes c / Q000378:metabolism; D004734:Energy Metabolism; D004789:Enzyme Activation / Q000502:physiology; D015870:Gene Expression; D006153:Guanosine Diphosphate / Q000378:metabolism; D006801:Humans; D007473:Ion Channels; D008928:Mitochondria / Q000502:physiology*; D024101:Mitochondrial Proteins; D021381:Protein Transport / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D014162:Transfection; D000071247:Uncoupling Protein 3; D051028:bcl-2-Associated X Protein
chemical_list: C494826:BAX protein, human; D002352:Carrier Proteins; D007473:Ion Channels; D024101:Mitochondrial Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C000604392:UCP3 protein, human; D000071247:Uncoupling Protein 3; D051028:bcl-2-Associated X Protein; D006153:Guanosine Diphosphate; D045304:Cytochromes c; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases