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  • 1
    Publication Date: 2015-09-30
    Description: Small RNAs (sRNAs) are important regulators of gene expression during bacterial stress and pathogenesis. sRNAs act by forming duplexes with mRNAs to alter their translation and degradation. In some bacteria, duplex formation is mediated by the Hfq protein, which can bind the sRNA and mRNA in each pair in a random order. Here we investigate the consequences of this random-order binding and experimentally demonstrate that it can counterintuitively cause high Hfq concentrations to suppress rather than promote sRNA activity in Escherichia coli . As a result, maximum sRNA activity occurs when the Hfq concentration is neither too low nor too high relative to the sRNA and mRNA concentrations (‘Hfq set-point’). We further show with models and experiments that random-order binding combined with the formation of a dead-end mRNA–Hfq complex causes high concentrations of an mRNA to inhibit its own duplex formation by sequestering Hfq. In such cases, maximum sRNA activity requires an optimal mRNA concentration (‘mRNA set-point’) as well as an optimal Hfq concentration. The Hfq and mRNA set-points generate novel regulatory properties that can be harnessed by native and synthetic gene circuits to provide greater control over sRNA activity, generate non-monotonic responses and enhance the robustness of expression.
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 2
    Publication Date: 2011-01-19
    Description: Small RNAs (sRNAs) regulate diverse pathways, including stress responses, virulence, and metabolism in Escherichia coli. At the center of this large sRNA regulatory network is the Hfq protein. Hfq mediates the binding of sRNAs to their target mRNAs; without Hfq, most sRNAs cannot efficiently regulate target mRNA expression. Here, we show in vivo that Hfq can be a limiting factor for sRNA activity and that it can be easily depleted, causing disruption of the sRNA network. Depletion of the available Hfq can occur when sRNAs and target mRNAs are transcribed at high levels without their partners, resulting in the sequestration of Hfq into sRNA–Hfq and target mRNA–Hfq complexes. This can be avoided by coordinating the transcription of sRNAs with their target mRNAs so that they are turned on and off together to maximize duplex formation and minimize Hfq sequestration. Therefore, the limited availability of Hfq results in a highly interdependent sRNA network, wherein the activity of each sRNA depends on the activity of the other sRNAs and target mRNAs in the network.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 3
    Publication Date: 2012-01-05
    Description: Radiolabeled diacetylbis(4-methylthiosemicarbazonato)copperII [CuII(atsm)] is an effective positron-emission tomography imaging agent for myocardial ischemia, hypoxic tumors, and brain disorders with regionalized oxidative stress, such as mitochondrial myopathy, encephalopathy, and lactic acidosis with stroke-like episodes (MELAS) and Parkinson’s disease. An excessively elevated reductive state is common to these conditions and has been proposed as an important mechanism affecting cellular retention of Cu from CuII(atsm). However, data from whole-cell models to demonstrate this mechanism have not yet been provided. The present study used a unique cell culture model, mitochondrial xenocybrids, to provide whole-cell mechanistic data on cellular retention of Cu from CuII(atsm). Genetic incompatibility between nuclear and mitochondrial encoded subunits of the mitochondrial electron transport chain (ETC) in xenocybrid cells compromises normal function of the ETC. As a consequence of this impairment to the ETC we show xenocybrid cells upregulate glycolytic ATP production and accumulate NADH. Compared to control cells the xenocybrid cells retained more Cu after being treated with CuII(atsm). By transfecting the cells with a metal-responsive element reporter construct the increase in Cu retention was shown to involve a CuII(atsm)-induced increase in intracellular bioavailable Cu specifically within the xenocybrid cells. Parallel experiments using cells grown under hypoxic conditions confirmed that a compromised ETC and elevated NADH levels contribute to increased cellular retention of Cu from CuII(atsm). Using these cell culture models our data demonstrate that compromised ETC function, due to the absence of O2 as the terminal electron acceptor or dysfunction of individual components of the ETC, is an important determinant in driving the intracellular dissociation of CuII(atsm) that increases cellular retention of the Cu.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 4
  • 5
    Publication Date: 2012-08-23
    Description: Small RNAs (sRNAs) and proteins acting as transcription factors (TFs) are the principal components of gene networks. These two classes of signaling molecules have distinct mechanisms of action; sRNAs control mRNA translation, whereas TFs control mRNA transcription. Here, we directly compare the properties of sRNA and TF signaling using mathematical models and synthetic gene circuits in Escherichia coli . We show the abilities of sRNAs to act on existing target mRNAs (as opposed to TFs, which alter the production of future target mRNAs) and, without needing to be first translated, have surprisingly little impact on the dynamics. Instead, the dynamics are primarily determined by the clearance rates, steady-state concentrations and response curves of the sRNAs and TFs; these factors determine the time delay before a target gene’s expression can maximally respond to changes in sRNA and TF transcription. The findings are broadly applicable to the analysis of signaling in gene networks, and we demonstrate that they can be used to rationally reprogram the dynamics of synthetic circuits.
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
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  • 6
    Publication Date: 2016-01-07
    Description: Endothelial cells (ECs) are plastic cells that can switch between growth states with different bioenergetic and biosynthetic requirements. Although quiescent in most healthy tissues, ECs divide and migrate rapidly upon proangiogenic stimulation. Adjusting endothelial metabolism to the growth state is central to normal vessel growth and function, yet it is poorly understood at the molecular level. Here we report that the forkhead box O (FOXO) transcription factor FOXO1 is an essential regulator of vascular growth that couples metabolic and proliferative activities in ECs. Endothelial-restricted deletion of FOXO1 in mice induces a profound increase in EC proliferation that interferes with coordinated sprouting, thereby causing hyperplasia and vessel enlargement. Conversely, forced expression of FOXO1 restricts vascular expansion and leads to vessel thinning and hypobranching. We find that FOXO1 acts as a gatekeeper of endothelial quiescence, which decelerates metabolic activity by reducing glycolysis and mitochondrial respiration. Mechanistically, FOXO1 suppresses signalling by MYC (also known as c-MYC), a powerful driver of anabolic metabolism and growth. MYC ablation impairs glycolysis, mitochondrial function and proliferation of ECs while its EC-specific overexpression fuels these processes. Moreover, restoration of MYC signalling in FOXO1-overexpressing endothelium normalizes metabolic activity and branching behaviour. Our findings identify FOXO1 as a critical rheostat of vascular expansion and define the FOXO1-MYC transcriptional network as a novel metabolic checkpoint during endothelial growth and proliferation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Wilhelm, Kerstin -- Happel, Katharina -- Eelen, Guy -- Schoors, Sandra -- Oellerich, Mark F -- Lim, Radiance -- Zimmermann, Barbara -- Aspalter, Irene M -- Franco, Claudio A -- Boettger, Thomas -- Braun, Thomas -- Fruttiger, Marcus -- Rajewsky, Klaus -- Keller, Charles -- Bruning, Jens C -- Gerhardt, Holger -- Carmeliet, Peter -- Potente, Michael -- K08CA090438/CA/NCI NIH HHS/ -- Cancer Research UK/United Kingdom -- England -- Nature. 2016 Jan 14;529(7585):216-20. doi: 10.1038/nature16498. Epub 2016 Jan 6.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Angiogenesis &Metabolism Laboratory, Max Planck Institute for Heart and Lung Research, D-61231 Bad Nauheim, Germany. ; Laboratory of Angiogenesis and Neurovascular Link, Vesalius Research Center, Department of Oncology, University of Leuven, Leuven 3000, Belgium. ; Laboratory of Angiogenesis and Neurovascular Link, Vesalius Research Center, VIB, Leuven 3000, Belgium. ; Vascular Biology Laboratory, London Research Institute, Cancer Research UK, London WC2A 3LY, UK. ; Vascular Morphogenesis Laboratory, Instituto de Medicina Molecular, Faculdade de Medicina da Universidade de Lisboa, Lisbon 1649-028, Portugal. ; Department of Cardiac Development and Remodeling, Max Planck Institute for Heart and Lung Research, D-61231 Bad Nauheim, Germany. ; UCL Institute of Ophthalmology, University College London, London EC1V 9EL, UK. ; Max Delbruck Center for Molecular Medicine (MDC), D-13125 Berlin, Germany. ; Children's Cancer Therapy Development Institute, Beaverton, Oregon 97005, USA. ; Max Planck Institute for Metabolism Research, Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD) and Center of Molecular Medicine Cologne (CMMC), Center for Endocrinology, Diabetes and Preventive Medicine (CEDP), University of Cologne, D-50931 Cologne, Germany. ; Vascular Patterning Laboratory, Vesalius Research Center, VIB and University of Leuven, Leuven 3000, Belgium. ; DZHK (German Center for Cardiovascular Research), partner site Berlin, D-13347 Berlin, Germany. ; Berlin Institute of Health (BIH), D-10117 Berlin, Germany. ; International Institute of Molecular and Cell Biology, 02-109 Warsaw, Poland. ; DZHK (German Center for Cardiovascular Research), partner site Frankfurt Rhine-Main, D-13347 Berlin, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26735015" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Cell Proliferation ; Cell Respiration ; Endothelium, Vascular/cytology/*growth & development/*metabolism ; Female ; Forkhead Transcription Factors/deficiency/genetics/*metabolism ; Glycolysis ; Human Umbilical Vein Endothelial Cells/cytology/metabolism ; Humans ; Male ; Mice ; Mice, Inbred C57BL ; Proto-Oncogene Proteins c-myc/deficiency/genetics/metabolism ; Signal Transduction
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 7
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 1984-03-30
    Description: Astroblasts in culture proliferated when exposed to glia maturation factor for at least 2 hours and then to insulin, but not when exposed in the reverse order. The sequential relation suggests that glia maturation factor is a competence factor.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lim, R -- Miller, J F -- CA-31796/CA/NCI NIH HHS/ -- New York, N.Y. -- Science. 1984 Mar 30;223(4643):1419-20.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/6367047" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Astrocytes/drug effects/physiology ; Cell Division/drug effects ; Cells, Cultured ; Drug Interactions ; Glia Maturation Factor ; Growth Substances/*pharmacology/physiology ; Insulin/*pharmacology/physiology ; Mice ; Mice, Inbred BALB C ; Nerve Tissue Proteins/*pharmacology/physiology ; Rats
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 8
    Publication Date: 2018-05-31
    Description: Pipecolic acid (Pip), a non-proteinaceous product of lysine catabolism, is an important regulator of immunity in plants and humans alike. In plants, Pip accumulates upon pathogen infection and has been associated with systemic acquired resistance (SAR). However, the molecular mechanisms underlying Pip-mediated signaling and its relationship to other known SAR inducers remain unknown. We show that in plants, Pip confers SAR by increasing levels of the free radicals, nitric oxide (NO), and reactive oxygen species (ROS), which act upstream of glycerol-3-phosphate (G3P). Plants defective in NO, ROS, G3P, or salicylic acid (SA) biosynthesis accumulate reduced Pip in their distal uninfected tissues although they contain wild-type–like levels of Pip in their infected leaves. These data indicate that de novo synthesis of Pip in distal tissues is dependent on both SA and G3P and that distal levels of SA and G3P play an important role in SAR. These results also suggest a unique scenario whereby metabolites in a signaling cascade can stimulate each other’s biosynthesis depending on their relative levels and their site of action.
    Electronic ISSN: 2375-2548
    Topics: Natural Sciences in General
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  • 9
    Publication Date: 2016-09-21
    Description: Vascular pericytes, an important cellular component in the tumor microenvironment, are often associated with tumor vasculatures, and their functions in cancer invasion and metastasis are poorly understood. Here we show that PDGF-BB induces pericyte–fibroblast transition (PFT), which significantly contributes to tumor invasion and metastasis. Gain- and loss-of-function experiments demonstrate that...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 10
    Publication Date: 2013-04-24
    Description: Parkin E3 ubiquitin-ligase activity and its role in mitochondria homeostasis are thought to play a role in Parkinson's disease (PD). We now report that AF-6 is a novel parkin interacting protein that modulates parkin ubiquitin-ligase activity and mitochondrial roles. Parkin interacts with the AF-6 PDZ region through its C-terminus. This leads to ubiquitination of cytosolic AF-6 and its degradation by the proteasome. On the other hand, endogenous AF-6 robustly increases parkin translocation and ubiquitin-ligase activity at the mitochondria. Mitochondrial AF-6 is not a parkin substrate, but rather co-localizes with parkin and enhances mitochondria degradation through PINK1/parkin-mediated mitophagy. On the other hand, several parkin and PINK1 juvenile disease-mutants are insensitive to AF-6 effects. AF-6 is present in Lewy bodies and its soluble levels are strikingly decreased in the caudate/putamen and substantia nigra of sporadic PD patients, suggesting that decreased AF-6 levels may contribute to the accumulation of dysfunctional mitochondria in the disease. The identification of AF-6 as a positive modulator of parkin translocation to the mitochondria sheds light on the mechanisms involved in PD and underscores AF-6 as a novel target for future therapeutics.
    Print ISSN: 0964-6906
    Electronic ISSN: 1460-2083
    Topics: Biology , Medicine
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