Ca2+ flux across the mitochondrial inner membrane regulates bioenergetics, cytoplasmic Ca2+ signals and activation of cell death pathways1–11. Mitochondrial Ca2+ uptake occurs at regions of close apposition with intracellular Ca2+ release sites 12–14, driven by the inner membrane voltage generated by oxidative phosphorylation and mediated by a Ca2+ selective ion channel (MiCa15) called the uniporter16–18 whose complete molecular identity remains unknown. Mitochondrial calcium uniporter (MCU) was recently identified as the likely ion-conducting pore19, 20. In addition, MICU1 was identified as a mitochondrial regulator of uniporter-mediated Ca2+ uptake in HeLa cells 21. Here we identified CCDC90A, hereafter referred to as MCUR1 (Mitochondrial Calcium Uniporter Regulator 1), an integral membrane protein required for MCU-dependent mitochondrial Ca2+ uptake. MCUR1 binds to MCU and regulates ruthenium red-sensitive MCU-dependent Ca2+ uptake. MCUR1 knockdown does not alter MCU localization, but abrogates Ca2+ uptake by energized mitochondria in intact and permeabilized cells. Ablation of MCUR1 disrupts oxidative phosphorylation, lowers cellular ATP, and activates AMP kinase-dependent pro-survival autophagy. Thus, MCUR1 is a critical component of a mitochondrial uniporter channel complex required for mitochondrial Ca2+ uptake and maintenance of normal cellular bioenergetics.

Packaging DNA into condensed structures is integral to the transmission of genomes. The mammalian mitochondrial genome (mtDNA) is a high copy, maternally inherited genome in which mutations cause a variety of multisystem disorders. In all eukaryotic cells, multiple mtDNAs are packaged with protein into spheroid bodies called nucleoids, which are the fundamental units of mtDNA segregation. The mechanism of nucleoid formation, however, remains unknown. Here, we show that the mitochondrial transcription factor TFAM, an abundant and highly conserved High Mobility Group box protein, binds DNA cooperatively with nanomolar affinity as a homodimer and that it is capable of coordinating and fully compacting several DNA molecules together to form spheroid structures. We use noncontact atomic force microscopy, which achieves near cryo-electron microscope resolution, to reveal the structural details of protein-DNA compaction intermediates. The formation of these complexes involves the bending of the DNA backbone, and DNA loop formation, followed by the filling in of proximal available DNA sites until the DNA is compacted. These results indicate that TFAM alone is sufficient to organize mitochondrial chromatin and provide a mechanism for nucleoid formation. INTRODUCTIONMutations affecting mitochondrial oxidative phosphorylation cause a variety of multisystem disorders (DiMauro and Schon, 2003;Taylor and Turnbull, 2005) with an estimated incidence of 1:5000 live births (Thorburn, 2004). The majority of these mutations are found in the mitochondrial genome (mtDNA), which encodes the core hydrophobic proteins involved in oxidative phosphorylation and some of the molecules required for their expression, such as tRNAs and rRNAs. The mutant mtDNA genomes generally coexist alongside wild-type copies in affected patients, a situation referred to as heteroplasmy. The segregation pattern of heteroplasmic DNAs in different tissues is an important determinant of the severity of the clinical phenotype. To develop an animal model of heteroplasmy, our laboratory generated mice containing polymorphisms in otherwise normal mtDNA, and we identified three nuclear quantitative trait loci that affect mtDNA segregation in liver, spleen, and kidney (Jenuth et al., 1997;Battersby et al., 2003). The selection of one variant of the mtDNA over another could be explained by differences in their organization or packaging.Mammalian mtDNA is packaged in protein-DNA complexes termed nucleoids, which can be visualized as small submitochondrial bodies in the matrix (Nass, 1969). The nucleoid contains two to seven genomes, depending on cell type, and it is present as 450 -800 distinct foci in cultured cells (Nass, 1969;Iborra et al., 2004;Legros et al., 2004). Several mammalian mitochondrial nucleoid proteins have been identified after enrichment by sedimentation and immunoprecipitation (Wang and Bogenhagen, 2006;He et al., 2007). However, other than the components of the mitochondrial replisome and transcription apparatus, the only proteins that have been fo...

Fibrosis of the kidney is the final common pathway leading to end stage renal failure. By analyzing kidneys of patients and animal models with fibrosis we observed a significant mitochondrial defect, including the loss of the mitochondrial transcription factor A (TFAM) in kidney tubule cells. Here, we generated mice with tubule-specific deletion of TFAM (Ksp-Cre/ Tfam flox/flox ). While these mice developed severe mitochondrial loss and energetic deficit (ATP *

Background:The BRCA1/2 proteins are involved in regulation of cellular proliferation by DNA damage repair via homologous recombination. Therefore, BRCA1/2 mutation carriers with pancreatic cancer may have distinct biologic outcomes.Methods:Patients with BRCA1/2-associated pancreatic ductal adenocarcinoma (PDAC) diagnosed between January 1994 and December 2012 were identified from databases at three participating institutions. Clinical data were collected. Disease-free survival and overall survival (OS) were analysed.Results:Overall, 71 patients with PDAC and BRCA1 (n=21), BRCA2 (n=49) or both (n=1) mutations were identified. Mean age at diagnosis was 60.3 years (range 33–83), 81.7% (n=58) had any family history of malignancy; 30% (n=21) underwent primary resection. Out of 71 participants, 12 received experimental therapy; one patient had missing data, these 13 cases were excluded from OS analysis. Median OS for 58 patients was 14 months (95% CI 10–23 months). Median OS for patients with stage 1/2 disease has not been reached with 52% still alive at 60 months. Median OS for stage 3/4 was 12 months (95% CI 6–15). Superior OS was observed for patients with stage 3/4 treated with platinum vs those treated with non-platinum chemotherapies (22 vs 9 months; P=0.039).Conclusion:Superior OS was observed for advanced-disease BRCA-associated PDAC with platinum exposure.