A mechanism decreasing oxidative metabolism during normal cell division and growth is expected to direct substrates toward biosyntheses rather than toward complete oxidation to CO(2). Hence, any event decreasing oxidative phosphorylations (OXPHOS) could provide a proliferating advantage to a transformed or tumor cell in an oxidative tissue. To test this hypothesis, we studied mitochondrial enzymes, DNA and OXPHOS protein content in three types of renal tumors from 25 patients. Renal cell carcinomas (RCCs) of clear cell type (CCRCCs) originate from the proximal tubule and are most aggressive. Chromophilic RCCs, from similar proximal origin, are less aggressive. The benign renal oncocytomas originate from collecting duct cells. Mitochondrial enzyme and DNA contents in all tumor types or grades differed significantly from normal tissue. Mitochondrial impairment increased from the less aggressive to the most aggressive RCCs, and correlated with a considerably decreased content of OXPHOS complexes (complexes II, III, and IV of the respiratory chain, and ATPase/ATP synthase) rather than to the mitochondrial content (citrate synthase and mitochondrial (mt)DNA). In benign oncocytoma, some mitochondrial parameters (mtDNA, citrate synthase, and complex IV) were increased 4- to 7-fold, and some were slightly increased by a factor of 2 (complex V) or close to normal (complexes II and III). A low content of complex V protein was found in all CCRCC and chromophilic tumors studied. However F(1)-ATPase activity was not consistently decreased and its impairment was associated with increased aggressiveness in CCRCCs. Immunodetection of free F(1)-sector of complex V demonstrated a disturbed assembly/stability of complex V in several CCRCC and chromophilic tumors. All results are in agreement with the hypothesis that a decreased OXPHOS capacity favors faster growth or increased invasiveness.

We showed that the human respiratory chain is organized in supramolecular assemblies of respiratory chain complexes, the respirasomes. The mitochondrial complexes I (NADH dehydrogenase) and III (cytochrome c reductase) form a stable core respirasome to which complex IV (cytochrome c oxidase) can also bind. An analysis of the state of respirasomes in patients with an isolated deficiency of single complexes provided evidence that the formation of respirasomes is essential for the assembly/stability of complex I, the major entry point of respiratory chain substrates. Genetic alterations leading to a loss of complex III prevented respirasome formation and led to the secondary loss of complex I. Therefore, primary complex III assembly deficiencies presented as combined complex III/I defects. This dependence of complex I assembly/stability on respirasome formation has important implications for the diagnosis of mitochondrial respiratory chain disorders.

F1-ATPase assembly has been studied in human °c ells devoid of mitochondrial DNA (mtDNA). Since, in these cells, oxidative phosphorylation cannot provide ATP, their growth relies on glycolysis. Despite the absence of the mtDNA-coded F0 subunits 6 and 8, °cells possessed normal levels of F1-ATPase ␣ and ␤ subunits. This F1-ATPase was functional and azide-or aurovertinsensitive but oligomycin-insensitive. In addition, aurovertin decreased cell growth in °cells and also reduced their mitochondrial membrane potential, as measured by rhodamine 123 fluorescence. Therefore, a functional F1-ATPase was important to maintain the mitochondrial membrane potential and the growth of these °c ells. Bongkrekic acid, a specific adenine nucleotide translocator (ANT) inhibitor, also reduced °cell growth and mitochondrial membrane potential. In conclusion, °cells need both a functional F1-ATPase and a functional ANT to maintain their mitochondrial membrane potential, which is necessary for their growth. ATP hydrolysis catalyzed by F1 must provide ADP 3؊ at a sufficient rate to maintain a rapid exchange with the glycolytic ATP 4؊ by ANT, this electrogenic exchange inducing a mitochondrial membrane potential efficient enough to sustain cell growth. However, since the effects of bongkrekic acid and of aurovertin were additive, other electrogenic pumps should cooperate with this pathway.The biogenesis of mitochondrial proteins is controlled by both nuclear and mitochondrial genomes. The proteins coded by the mtDNA are subunits of enzyme complexes involved in oxidative phosphorylation. Since all these complexes also contain proteins coded by the nuclear genome, mechanisms regulating the coordinated expression and assembly of the subunits of nuclear and mitochondrial origin must exist. In yeast cells, nuclear DNA-coded components continue to be synthesized and imported into mitochondria, even when the synthesis of mtDNA-coded subunits is blocked (cf. for review, Refs. 1 and 2). The groups of Schatz and co-workers (3) and Neupert (4) have shown that a mitochondrial membrane potential is a key requirement for protein import into mitochondria (5). In normal cells, the mitochondrial membrane potential is mainly maintained by transmembrane proton pumping occurring during electron transfer or during ATP hydrolysis catalyzed by the ATPase-ATP synthase. In °cells depleted of mtDNA, these complexes cannot be functional since all complexes involved in proton pumping contain mtDNA-coded subunits (6). However, proteins of nuclear origin are imported into the °cell mitochondria (7). Therefore, the mitochondrial membrane potential must be maintained by other electrogenic pumps. In yeast, it has been suggested that the adenine nucleotide translocator (ANT) 1 mediates an exchange of ATP 4Ϫ synthesized in the cytosol during glycolysis for ADP 3Ϫ to maintain this mitochondrial membrane potential (8). However, the exact mechanism that maintains this potential has not been thoroughly investigated. Since the mtDNA-coded subunits are essential components for ...