169 research outputs found
Necroptosis-Inducing Rhenium(V) Oxo Complexes
Rhenium(V) oxo complexes of general formula [ReO(OMe)(N^N)Cl₂], where N^N = 4,7-diphenyl-1,10-phenanthroline, 1, or 3,4,7,8-tetramethyl-1,10-phenanthroline, 2, effectively kill cancer cells by triggering necroptosis, a non-apoptotic form of cell death. Both complexes evoke necrosome (RIP1-RIP3)-dependent intracellular reactive oxygen species (ROS) production and propidium iodide uptake. The complexes also induce mitochondrial membrane potential depletion, a possible downstream effect of ROS production. Apparently, 1 and 2 are the first rhenium complexes to evoke cellular events consistent with programmed necrosis in cancer cells. Furthermore, 1 and 2 display low acute toxicity in C57BL/6 mice and reasonable stability in fresh human blood.National Cancer Institute (U.S.) (CA034992
Allosteric Inhibition of Human Ribonucleotide Reductase by dATP Entails the Stabilization of a Hexamer
Ribonucleotide reductases (RNRs) are responsible for all de novo biosynthesis of DNA precursors in nature by catalyzing the conversion of ribonucleotides to deoxyribonucleotides. Because of its essential role in cell division, human RNR is a target for a number of anticancer drugs in clinical use. Like other class Ia RNRs, human RNR requires both a radical-generation subunit (β) and nucleotide-binding subunit (α) for activity. Because of their complex dependence on allosteric effectors, however, the active and inactive quaternary forms of many class Ia RNRs have remained in question. Here, we present an X-ray crystal structure of the human α subunit in the presence of inhibiting levels of dATP, depicting a ring-shaped hexamer (α[subscript 6]) where the active sites line the inner hole. Surprisingly, our small-angle X-ray scattering (SAXS) results indicate that human α forms a similar hexamer in the presence of ATP, an activating effector. In both cases, α[subscript 6] is assembled from dimers (α[subscript 2]) without a previously proposed tetramer intermediate (α[subscript 4]). However, we show with SAXS and electron microscopy that at millimolar ATP, the ATP-induced α[subscript 6] can further interconvert with higher-order filaments. Differences in the dATP- and ATP-induced α[subscript 6] were further examined by SAXS in the presence of the β subunit and by activity assays as a function of ATP or dATP. Together, these results suggest that dATP-induced α[subscript 6] is more stable than the ATP-induced α6 and that stabilization of this ring-shaped configuration provides a mechanism to prevent access of the β subunit to the active site of α.National Institutes of Health (U.S.) (GM100008)National Institutes of Health (U.S.) (Grant GM29595)Massachusetts Institute of Technology. Undergraduate Research Opportunities Progra
Wt1 functions in the development of germ cells in addition to somatic cell lineages of the testis
AbstractThe Wilms' tumor suppressor gene, Wt1, encodes a transcription factor critical for development of the urogenital system. To identify lineages within the developing urogenital system that have a cell-autonomous requirement for Wt1, chimeric mice were generated from Wt1-null ES cells. Males with large contributions of Wt1−/− cells showed hypoplastic and dysgenic testes, with seminiferous tubules lacking spermatogonia. Wt1-null cells contributed poorly to both somatic and germ cell lineages within the developing gonad, suggesting an unexpected role for Wt1 in germ cell development in addition to a role in the development of the somatic lineages of the gonad. Wt1 expression was detected in embryonic germ cells beginning at embryonic day 11.5 after migrating primordial germ cells (PGCs) have entered the gonad. Germ cells isolated from Wt1-null embryos showed impaired growth in culture, further demonstrating a role for Wt1 in germ cell proliferation or survival. Therefore, Wt1 plays important, and in some cases previously unrecognized, roles in multiple lineages during urogenital development
Spacelike Singularities and Hidden Symmetries of Gravity
We review the intimate connection between (super-)gravity close to a
spacelike singularity (the "BKL-limit") and the theory of Lorentzian Kac-Moody
algebras. We show that in this limit the gravitational theory can be
reformulated in terms of billiard motion in a region of hyperbolic space,
revealing that the dynamics is completely determined by a (possibly infinite)
sequence of reflections, which are elements of a Lorentzian Coxeter group. Such
Coxeter groups are the Weyl groups of infinite-dimensional Kac-Moody algebras,
suggesting that these algebras yield symmetries of gravitational theories. Our
presentation is aimed to be a self-contained and comprehensive treatment of the
subject, with all the relevant mathematical background material introduced and
explained in detail. We also review attempts at making the infinite-dimensional
symmetries manifest, through the construction of a geodesic sigma model based
on a Lorentzian Kac-Moody algebra. An explicit example is provided for the case
of the hyperbolic algebra E10, which is conjectured to be an underlying
symmetry of M-theory. Illustrations of this conjecture are also discussed in
the context of cosmological solutions to eleven-dimensional supergravity.Comment: 228 pages. Typos corrected. References added. Subject index added.
Published versio
Variation in optineurin (OPTN) allele frequencies between and within populations
PURPOSE: To evaluate the extent to which mutations in the optineurin (OPTN) glaucoma gene play a role in glaucoma in
different populations.
METHODS: Case-controlled study of OPTN sequence variants in individuals with or without glaucoma in populations of
different ancestral origins and evaluate previous OPTN reports. We analyzed 314 subjects with African, Asian, Caucasian
and Hispanic ancestries included 229 cases of primary open-angle glaucoma, 51 cases of juvenile-onset open-angle glaucoma,
33 cases of normal tension glaucoma, and 371 controls. Polymerase chain reaction-amplified OPTN coding exons
were resequenced and case frequencies were compared to frequencies in controls matched for ancestry.
RESULTS: The E50K sequence variant was identified in one individual from Chile with normal tension glaucoma, and the
691_692insAG variant was found in one Ashkenazi Jewish individual from Russia. The R545Q variant was found in two
Asian individuals with primary open-angle glaucoma; one of Filipino ancestry and one of Korean ancestry. In addition to
presenting OPTN allele frequencies for Caucasian and Asian populations that have been the subject of previous reports,
we also present information for populations of Hispanic and black African ancestries.
CONCLUSIONS: Our study contributes additional evidence to support the previously reported association of the OPTN E50K
mutation with glaucoma. After finding an additional 691_692insAG OPTN variant, we can still only conclude that this
variant is rare. Combined analysis of our data with data from more than a dozen other studies indicates no association of
R545Q with glaucoma in most populations. Those same studies disagree in their conclusions regarding the role of M98K
in glaucoma. Our analysis of the combined data provides statistically significant evidence of association of M98K with
normal tension glaucoma in Asian populations, but not in Caucasian populations; however, the validity of this conclusion
is questionable because of large differences in allele frequencies between and within populations. It is currently not
possible to tell how much of the underlying cause of the allele frequency difference is attributable to demographic, technical, or ascertainment differences among the studies
Superstring Cosmology
Aspects of superstring cosmology are reviewed with an emphasis on the
cosmological implications of duality symmetries in the theory. The string
effective actions are summarized and toroidal compactification to four
dimensions reviewed. Global symmetries that arise in the compactification are
discussed and the duality relationships between the string effective actions
are then highlighted. Higher-dimensional Kasner cosmologies are presented and
interpreted in both string and Einstein frames, and then given in dimensionally
reduced forms. String cosmologies containing both non-trivial
Neveu-Schwarz/Neveu-Schwarz and Ramond-Ramond fields are derived by employing
the global symmetries of the effective actions. Anisotropic and inhomogeneous
cosmologies in four-dimensions are also developed. The review concludes with a
detailed analysis of the pre-big bang inflationary scenario. The generation of
primordial spectra of cosmological perturbations in such a scenario is
discussed. Possible future directions offered in the Horava-Witten theory are
outlined.Comment: 161 pages, latex with epsf, 15 figures. Minor changes, additional
references and figures. Version to appear in Physics Report
Presenilin Is the Molecular Target of Acidic γ-Secretase Modulators in Living Cells
The intramembrane-cleaving protease γ-secretase catalyzes the last step in the generation of toxic amyloid-β (Aβ) peptides and is a principal therapeutic target in Alzheimer's disease. Both preclinical and clinical studies have demonstrated that inhibition of γ-secretase is associated with prohibitive side effects due to suppression of Notch processing and signaling. Potentially safer are γ-secretase modulators (GSMs), which are small molecules that selectively lower generation of the highly amyloidogenic Aβ42 peptides but spare Notch processing. GSMs with nanomolar potency and favorable pharmacological properties have been described, but the molecular mechanism of GSMs remains uncertain and both the substrate amyloid precursor protein (APP) and subunits of the γ-secretase complex have been proposed as the molecular target of GSMs. We have generated a potent photo-probe based on an acidic GSM that lowers Aβ42 generation with an IC50 of 290 nM in cellular assays. By combining in vivo photo-crosslinking with affinity purification, we demonstrated that this probe binds the N-terminal fragment of presenilin (PSEN), the catalytic subunit of the γ-secretase complex, in living cells. Labeling was not observed for APP or any of the other γ-secretase subunits. Binding was readily competed by structurally divergent acidic and non-acidic GSMs suggesting a shared mode of action. These findings indicate that potent acidic GSMs target presenilin to modulate the enzymatic activity of the γ-secretase complex
Unfractionated heparin inhibits live wild type SARS-CoV-2 cell infectivity at therapeutically relevant concentrations
BACKGROUND AND PURPOSE: Currently, there are no licensed vaccines and limited antivirals for the treatment of COVID-19. Heparin (delivered systemically) is currently used to treat anticoagulant anomalies in COVID-19 patients. Additionally, in the United Kingdom, Brazil and Australia, nebulised unfractionated heparin (UFH) is being trialled in COVID-19 patients as a potential treatment. A systematic comparison of the potential antiviral effect of various heparin preparations on live wild type SARS-CoV-2, in vitro, is needed.EXPERIMENTAL APPROACH: Seven different heparin preparations including UFH and low MW heparins (LMWH) of porcine or bovine origin were screened for antiviral activity against live SARS-CoV-2 (Australia/VIC01/2020) using a plaque inhibition assay with Vero E6 cells. Interaction of heparin with spike protein RBD was studied using differential scanning fluorimetry and the inhibition of RBD binding to human ACE2 protein using elisa assays was examined.KEY RESULTS: All the UFH preparations had potent antiviral effects, with IC50 values ranging between 25 and 41 μg·ml-1 , whereas LMWHs were less inhibitory by ~150-fold (IC50 range 3.4-7.8 mg·ml-1 ). Mechanistically, we observed that heparin binds and destabilizes the RBD protein and furthermore, we show heparin directly inhibits the binding of RBD to the human ACE2 protein receptor.CONCLUSION AND IMPLICATIONS: This comparison of clinically relevant heparins shows that UFH has significantly stronger SARS-CoV-2 antiviral activity compared to LMWHs. UFH acts to directly inhibit binding of spike protein to the human ACE2 protein receptor. Overall, the data strongly support further clinical investigation of UFH as a potential treatment for patients with COVID-19.</p
Chaos, decoherence and quantum cosmology
In this topical review we discuss the connections between chaos, decoherence
and quantum cosmology. We understand chaos as classical chaos in systems with a
finite number of degrees of freedom, decoherence as environment induced
decoherence and quantum cosmology as the theory of the Wheeler - DeWitt
equation or else the consistent history formulation thereof, first in mini
super spaces and later through its extension to midi super spaces. The overall
conclusion is that consideration of decoherence is necessary (and probably
sufficient) to sustain an interpretation of quantum cosmology based on the Wave
function of the Universe adopting a Wentzel - Kramers - Brillouin form for
large Universes, but a definitive account of the semiclassical transition in
classically chaotic cosmological models is not available in the literature yet.Comment: 40 page
Re-visiting Meltsner: Policy Advice Systems and the Multi-Dimensional Nature of Professional Policy Analysis
10.2139/ssrn.15462511-2
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