Browsing by Subject "Mitochondrial Proteins"

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    Features of programmed cell death in intact Xenopus oocytes and early embryos revealed by near-infrared fluorescence and real-time monitoring.
    (Cell Death Differ, 2010-01) Johnson, CE; Freel, CD; Kornbluth, S
    Factors influencing apoptosis of vertebrate eggs and early embryos have been studied in cell-free systems and in intact embryos by analyzing individual apoptotic regulators or caspase activation in static samples. A novel method for monitoring caspase activity in living Xenopus oocytes and early embryos is described here. The approach, using microinjection of a near-infrared caspase substrate that emits fluorescence only after its proteolytic cleavage by active effector caspases, has enabled the elucidation of otherwise cryptic aspects of apoptotic regulation. In particular, we show that brief caspase activity (10 min) is sufficient to cause apoptotic death in this system. We illustrate a cytochrome c dose threshold in the oocyte, which is lowered by Smac, a protein that binds thereby neutralizing the inhibitor of apoptosis proteins. We show that meiotic oocytes develop resistance to cytochrome c, and that the eventual death of oocytes arrested in meiosis is caspase-independent. Finally, data acquired through imaging caspase activity in the Xenopus embryo suggest that apoptosis in very early development is not cell-autonomous. These studies both validate this assay as a useful tool for apoptosis research and reveal subtleties in the cell death program during early development. Moreover, this method offers a potentially valuable screening modality for identifying novel apoptotic regulators.
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    Incongruence between primary sequence data and the distribution of a mitochondrial atp1 group II intron among ferns and horsetails.
    (Molecular phylogenetics and evolution, 2005-09) Wikström, N; Pryer, KM
    Using DNA sequence data from multiple genes (often from more than one genome compartment) to reconstruct phylogenetic relationships has become routine. Augmenting this approach with genomic structural characters (e.g., intron gain and loss, changes in gene order) as these data become available from comparative studies already has provided critical insight into some long-standing questions about the evolution of land plants. Here we report on the presence of a group II intron located in the mitochondrial atp1 gene of leptosporangiate and marattioid ferns. Primary sequence data for the atp1 gene are newly reported for 27 taxa, and results are presented from maximum likelihood-based phylogenetic analyses using Bayesian inference for 34 land plants in three data sets: (1) single-gene mitochondrial atp1 (exon+intron sequences); (2) five combined genes (mitochondrial atp1 [exon only]; plastid rbcL, atpB, rps4; nuclear SSU rDNA); and (3) same five combined genes plus morphology. All our phylogenetic analyses corroborate results from previous fern studies that used plastid and nuclear sequence data: the monophyly of euphyllophytes, as well as of monilophytes; whisk ferns (Psilotidae) sister to ophioglossoid ferns (Ophioglossidae); horsetails (Equisetopsida) sister to marattioid ferns (Marattiidae), which together are sister to the monophyletic leptosporangiate ferns. In contrast to the results from the primary sequence data, the genomic structural data (atp1 intron distribution pattern) would seem to suggest that leptosporangiate and marattioid ferns are monophyletic, and together they are the sister group to horsetails--a topology that is rarely reconstructed using primary sequence data.
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    Individuals with mutations in XPNPEP3, which encodes a mitochondrial protein, develop a nephronophthisis-like nephropathy.
    (J Clin Invest, 2010-03) O'Toole, JF; Liu, Y; Davis, EE; Westlake, CJ; Attanasio, M; Otto, EA; Seelow, D; Nurnberg, G; Becker, C; Nuutinen, M; Kärppä, M; Ignatius, J; Uusimaa, J; Pakanen, S; Jaakkola, E; van den Heuvel, LP; Fehrenbach, H; Wiggins, R; Goyal, M; Zhou, W; Wolf, MT; Wise, E; Helou, J; Allen, SJ; Murga Zamalloa, CA; Ashraf, S; Chaki, M; Heeringa, S; Chernin, G; Hoskins, BE; Chaib, H; Gleeson, J; Kusakabe, T; Suzuki, T; Isaac, RE; Quarmby, LM; Tennant, B; Fujioka, H; Tuominen, H; Hassinen, I; Lohi, H; van Houten, JL; Rotig, A; Sayer, JA; Rolinski, B; Freisinger, P; Madhavan, SM; Herzer, M; Madignier, F; Prokisch, H; Nurnberg, P; Jackson, PK; Jackson, P; Khanna, H; Katsanis, N; Hildebrandt, F
    The autosomal recessive kidney disease nephronophthisis (NPHP) constitutes the most frequent genetic cause of terminal renal failure in the first 3 decades of life. Ten causative genes (NPHP1-NPHP9 and NPHP11), whose products localize to the primary cilia-centrosome complex, support the unifying concept that cystic kidney diseases are "ciliopathies". Using genome-wide homozygosity mapping, we report here what we believe to be a new locus (NPHP-like 1 [NPHPL1]) for an NPHP-like nephropathy. In 2 families with an NPHP-like phenotype, we detected homozygous frameshift and splice-site mutations, respectively, in the X-prolyl aminopeptidase 3 (XPNPEP3) gene. In contrast to all known NPHP proteins, XPNPEP3 localizes to mitochondria of renal cells. However, in vivo analyses also revealed a likely cilia-related function; suppression of zebrafish xpnpep3 phenocopied the developmental phenotypes of ciliopathy morphants, and this effect was rescued by human XPNPEP3 that was devoid of a mitochondrial localization signal. Consistent with a role for XPNPEP3 in ciliary function, several ciliary cystogenic proteins were found to be XPNPEP3 substrates, for which resistance to N-terminal proline cleavage resulted in attenuated protein function in vivo in zebrafish. Our data highlight an emerging link between mitochondria and ciliary dysfunction, and suggest that further understanding the enzymatic activity and substrates of XPNPEP3 will illuminate novel cystogenic pathways.
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    Pharmacological targeting of the mitochondrial phosphatase PTPMT1.
    (2009) Doughty-Shenton, Dahlia
    The dual specificity protein tyrosine phosphatases comprise the largest and most diverse group of protein tyrosine phosphatases and play integral roles in the regulation of cell signaling events. The dual specificity protein tyrosine phosphatases impact multiple cellular processes including mitogenesis, differentiation, adhesion, migration, insulin secretion and programmed cell death. Thus, the dysregulation of these enzymes has been implicated in a myriad of human disease states. While the large volume of genetic data that has become available following genome sequencing efforts over the last decade has led to the rapid identification of many new dual specificity protein tyrosine phosphatases, the elucidation of the cellular function and substrates of these enzymes has been much slower. Hence, there is a need for new tools to study the dual specificity protein tyrosine phosphatases and the identification of inhibitors of these enzymes is regarded as an attractive prospect, potentially affording not only new means of studying these enzymes, but also possible therapeutics for the treatment of diseases caused by their dysregulation. However, the identification of potent, selective inhibitors of the dual specificity protein tyrosine phosphatases has proven somewhat difficult. PTPMT1, Protein Tyrosine Phosphatase Localized to the Mitochondrion 1 is a recently discovered, mitochondrion-localized, dual specificity phosphatase which has been implicated in the regulation of insulin secretion. However, the details of the mechanism by which PTPMT1 impacts insulin secretion, as well as its substrate in the pancreatic β-cell, have yet to be uncovered. Thus, the identification of a potent, selective inhibitor of the enzyme would aid in further study of PTPMT1. This work describes the identification of such an inhibitor of PTPMT1 following an in vitro screen of small molecule, chemical compounds using an artificial substrate. Following the screen, the lead compound emerged as a potent and potentially selective inhibitor of PTPMT1 both in vitro and in cells. Studies using this compound have shown that the compound induces increased secretion of insulin in a dose-dependent manner and thus support the notion that PTPMT1 may serve as a potential target for the treatment of Type II diabetes.
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    RanBP2 modulates Cox11 and hexokinase I activities and haploinsufficiency of RanBP2 causes deficits in glucose metabolism.
    (PLoS Genet, 2006-10) Aslanukov, Azamat; Bhowmick, Reshma; Guruju, Mallikarjuna; Oswald, John; Raz, Dorit; Bush, Ronald A; Sieving, Paul A; Lu, Xinrong; Bock, Cheryl B; Ferreira, Paulo A
    The Ran-binding protein 2 (RanBP2) is a large multimodular and pleiotropic protein. Several molecular partners with distinct functions interacting specifically with selective modules of RanBP2 have been identified. Yet, the significance of these interactions with RanBP2 and the genetic and physiological role(s) of RanBP2 in a whole-animal model remain elusive. Here, we report the identification of two novel partners of RanBP2 and a novel physiological role of RanBP2 in a mouse model. RanBP2 associates in vitro and in vivo and colocalizes with the mitochondrial metallochaperone, Cox11, and the pacemaker of glycolysis, hexokinase type I (HKI) via its leucine-rich domain. The leucine-rich domain of RanBP2 also exhibits strong chaperone activity toward intermediate and mature folding species of Cox11 supporting a chaperone role of RanBP2 in the cytosol during Cox11 biogenesis. Cox11 partially colocalizes with HKI, thus supporting additional and distinct roles in cell function. Cox11 is a strong inhibitor of HKI, and RanBP2 suppresses the inhibitory activity of Cox11 over HKI. To probe the physiological role of RanBP2 and its role in HKI function, a mouse model harboring a genetically disrupted RanBP2 locus was generated. RanBP2(-/-) are embryonically lethal, and haploinsufficiency of RanBP2 in an inbred strain causes a pronounced decrease of HKI and ATP levels selectively in the central nervous system. Inbred RanBP2(+/-) mice also exhibit deficits in growth rates and glucose catabolism without impairment of glucose uptake and gluconeogenesis. These phenotypes are accompanied by a decrease in the electrophysiological responses of photosensory and postreceptoral neurons. Hence, RanBP2 and its partners emerge as critical modulators of neuronal HKI, glucose catabolism, energy homeostasis, and targets for metabolic, aging disorders and allied neuropathies.
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    Smac mimetic Birinapant induces apoptosis and enhances TRAIL potency in inflammatory breast cancer cells in an IAP-dependent and TNF-α-independent mechanism.
    (Breast Cancer Res Treat, 2013-01) Allensworth, Jennifer L; Sauer, Scott J; Lyerly, H Kim; Morse, Michael A; Devi, Gayathri R
    X-linked inhibitor of apoptosis protein (XIAP), the most potent mammalian caspase inhibitor, has been associated with acquired therapeutic resistance in inflammatory breast cancer (IBC), an aggressive subset of breast cancer with an extremely poor survival rate. The second mitochondria-derived activator of caspases (Smac) protein is a potent antagonist of IAP proteins and the basis for the development of Smac mimetic drugs. Here, we report for the first time that bivalent Smac mimetic Birinapant induces cell death as a single agent in TRAIL-insensitive SUM190 (ErbB2-overexpressing) cells and significantly increases potency of TRAIL-induced apoptosis in TRAIL-sensitive SUM149 (triple-negative, EGFR-activated) cells, two patient tumor-derived IBC models. Birinapant has high binding affinity (nM range) for cIAP1/2 and XIAP. Using isogenic SUM149- and SUM190-derived cells with differential XIAP expression (SUM149 wtXIAP, SUM190 shXIAP) and another bivalent Smac mimetic (GT13402) with high cIAP1/2 but low XIAP binding affinity (K (d) > 1 μM), we show that XIAP inhibition is necessary for increasing TRAIL potency. In contrast, single agent efficacy of Birinapant is due to pan-IAP antagonism. Birinapant caused rapid cIAP1 degradation, caspase activation, PARP cleavage, and NF-κB activation. A modest increase in TNF-α production was seen in SUM190 cells following Birinapant treatment, but no increase occurred in SUM149 cells. Exogenous TNF-α addition did not increase Birinapant efficacy. Neutralizing antibodies against TNF-α or TNFR1 knockdown did not reverse cell death. However, pan-caspase inhibitor Q-VD-OPh reversed Birinapant-mediated cell death. In addition, Birinapant in combination or as a single agent decreased colony formation and anchorage-independent growth potential of IBC cells. By demonstrating that Birinapant primes cancer cells for death in an IAP-dependent manner, these findings support the development of Smac mimetics for IBC treatment.