bluuebunny/crossref_metadata_2025 huggingface dataset:
Skeletal muscle expresses the extracellular cyclic AMP–adenosine pathway
Authors: Chiavegatti T , Costa V L , Araújo M S , Godinho R O
Published: December 2007

Background and purpose:

cAMP is a key intracellular signalling molecule that regulates multiple processes of the vertebrate skeletal muscle. We have shown that cAMP can be actively pumped out from the skeletal muscle cell. Since in other tissues, cAMP efflux had been associated with extracellular generation of adenosine, in the present study we have assessed the fate of interstitial cAMP and the existence of an extracellular cAMP‐adenosine signalling pathway in skeletal muscle.

Experimental approach:

cAMP efflux and/or its extracellular degradation were analysed by incubating rat cultured skeletal muscle with exogenous cAMP, forskolin or isoprenaline. cAMP and its metabolites were quantified by radioassay or HPLC, respectively.

Key results:

Incubation of cells with exogenous cAMP was followed by interstitial accumulation of 5′‐AMP and adenosine, a phenomenon inhibited by selective inhibitors of ecto‐phosphodiesterase (DPSPX) and ecto‐nucleotidase (AMPCP). Activation of adenylyl cyclase (AC) in cultured cells with forskolin or isoprenaline increased cAMP efflux and extracellular generation of 5′‐AMP and adenosine. Extracellular cAMP‐adenosine pathway was also observed after direct and receptor‐dependent stimulation of AC in rat extensor muscleex vivo. These events were attenuated by probenecid, an inhibitor of ATP binding cassette family transporters.

Conclusions and implications:

Our results show the existence of an extracellular biochemical cascade that converts cAMP into adenosine. The functional relevance of this extracellular signalling system may involve a feedback modulation of cellular response initiated by several G protein‐coupled receptor ligands, amplifying cAMP influence to a paracrine mode, through its metabolite, adenosine.

British Journal of Pharmacology(2008)153, 1331–1340; doi:10.1038/sj.bjp.0707648; published online 24 December 2007
α7 nicotinic acetylcholine receptor agonist properties of tilorone and related tricyclic analogues
Authors: Briggs C A , Schrimpf M R , Anderson D J , Gubbins E J , Grønlien J H , Håkerud M , Ween H , Thorin‐Hagene K , Malysz J , Li J , Bunnelle W H , Gopalakrishnan M , Meyer M D
Published: December 2007

Background and purpose:

The α7 nicotinic acetylcholine receptor (nAChR) has attracted considerable interest as a target for cognitive enhancement in schizophrenia and Alzheimer's Disease. However, most recently described α7 agonists are derived from the quinuclidine structural class. Alternatively, the present study identifies tilorone as a novel α7‐selective agonist and characterizes analogues developed from this lead.

Experimental approach:

Activity and selectivity were determined from rat brain α7 and α4β2 nAChR binding, recombinant nAChR activation, and native α7 nAChR mediated stimulation of ERK1/2 phosphorylation in PC12 cells.

Key results:

Tilorone bound α7 nAChR (IC50110 nM) with high selectivity relative to α4β2 (IC5070 000 nM), activated human α7 nAChR with an EC50value of 2.5 μMand maximal response of 67% relative to acetylcholine, and showed little agonist effect at human α3β4 or α4β2 nAChRs. However, the rat α7 nAChR maximal response was only 34%. Lead optimization led to 2‐(5‐methyl‐hexahydro‐pyrrolo[3,4‐c]pyrrol‐2‐yl)‐xanthen‐9‐one (A‐844606) with improved binding (α7 IC5011 nM, α4β2 IC50>30 000 nM) and activity at both human and rat α7 nAChR (EC50s 1.4 and 2.2 μMand apparent efficacies 61 and 63%, respectively). These compounds also activated native α7 nAChR, stimulating ERK1/2 phosphorylation in PC12 cells.

Conclusions and implications:

Tilorone, known as an interferon inducer, is a selective α7 nAChR agonist, suggesting utility of the fluorenone pharmacophore for the development of α7 nAChR selective agonists. Whether α7 stimulation mediates interferon induction, or whether interferon induction may influence the potential anti‐inflammatory properties of α7 nAChR agonists remains to be elucidated.

British Journal of Pharmacology(2008)153, 1054–1061; doi:10.1038/sj.bjp.0707649; published online 24 December 2007
Quantum wave packet dynamics of N(D2)+H2 reaction
Authors: Jayachander Rao B. , Mahapatra S.
Published: December 2007

The quantum wave packet dynamics of the title reaction within the coupled state approximation is examined here and initial state-selected reaction probabilities, integral reaction cross sections, and thermal rate constants are reported. The ab initio potential energy surface of the electronic ground state (1A″2) of the system recently reported by Ho et al. [J. Chem. Phys., 119, 3063 (2003)] is employed in this investigation. All partial wave contributions up to the total angular momentum J=55 were necessary to obtain converged integral reaction cross sections up to a collision energy of 1.0eV. Thermal rate constants are calculated from the reaction cross sections and compared with the available theoretical and experimental results. Typical resonances formed during the course of the reaction and elucidating the insertion type mechanism for the product formation are calculated. Vibrational energy levels supported by the deep well (∼5.5eV) of the 1A″2 potential energy surface of NH2 are also calculated for the total angular momentum J=0. A statistical analysis of the spacing between the adjacent levels of this energy spectrum is performed and the extent of irregularity in the spectral sequence is assessed.
The electronic nonadiabatic coupling term: Can it be ignored in dynamic calculations?
Authors: Halász G. J. , Vibók A. , Suhai S. , Baer M.
Published: December 2007

Whereas the search for the degeneracy points which are better known as conical intersections (or ci-points) is usually carried out with a lot of devotion, the nonadiabatic coupling terms (NACTs) which together with the adiabatic potential energy surfaces appear in the nuclear Born-Oppenheimer-Schrödinger equation are ignored in most dynamical calculations. In the present article we consider two well known frameworks, namely, the semiclassical surface hopping method and the vibrational coupling model Hamiltonian that avoid the NACTs and examine to what extent, this procedure is justified.
Modified interfacial statistical associating fluid theory: A perturbation density functional theory for inhomogeneous complex fluids
Authors: Jain Shekhar , Dominik Aleksandra , Chapman Walter G.
Published: December 2007

A density functional theory based on Wertheim’s first order perturbation theory is developed for inhomogeneous complex fluids. The theory is derived along similar lines as interfacial statistical associating fluid theory [S. Tripathi and W. G. Chapman, J. Chem. Phys. 122, 094506 (2005)]. However, the derivation is more general and applies broadly to a range of systems, retaining the simplicity of a segment density based theory. Furthermore, the theory gives the exact density profile for ideal chains in an external field. The general avail of the theory has been demonstrated by applying the theory to lipids near surfaces, lipid bilayers, and copolymer thin films. The theoretical results show excellent agreement with the results from molecular simulations.
Calculation of the magnetic circular dichroism B term from the imaginary part of the Verdet constant using damped time-dependent density functional theory
Authors: Krykunov Mykhaylo , Seth Michael , Ziegler Tom , Autschbach Jochen
Published: December 2007

A time-dependent density functional theory (TDDFT) formalism with damping for the calculation of the magnetic optical rotatory dispersion and magnetic circular dichroism (MCD) from the complex Verdet constant is presented. For a justification of such an approach, we have derived the TDDFT analog of the sum-over-states formula for the Verdet constant. The results of the MCD calculations by this method for ethylene, furan, thiophene, selenophene, tellurophene, and pyrrole are in good agreement with our previous theoretical sum-over-states MCD spectra. For the π→π* transition of propene, we have obtained a positive Faraday B term. It is located between the two negative B terms. This finding is in agreement with experiment in the range of 6–8eV.
Analogy of silicon clusters with deltahedral boranes: How far can it go? Reexamining the structure of Sin and Sin2−, n=5–13 clusters
Authors: Zdetsis Aristides D.
Published: December 2007

Silicon clusters of 5 up to 13 atoms, Sin, n=5–13, and their dianions are studied in the light of an anticipated analogy with the corresponding isoelectronic boranes suggested recently by Zdetsis [J. Chem. Phys. 127, 014314 (2007)]. It is demonstrated that this analogy is a fruitful and powerful concept which allows the straightforward determination of the structures of silicon clusters, based on the structure of corresponding closo-boranes, meeting the requirements of well known structural rules. All lowest-lying structures of Sin, n=5–13 clusters, have been obtained through a systematic way on the basis of this analogy. For magic clusters, such as Si6 and Si10, characterized by special stability, the analogy to boranes seems to be much stronger.
The support of the limit distribution of optimal Riesz energy points on sets of revolution in R3
Authors: Brauchart J. S. , Hardin D. P. , Saff E. B.
Published: December 2007

Let A be a compact point set in the right half of the xy plane and Γ(A) the set in R3 obtained by rotating A about the y axis. We investigate the support of the limit distribution of minimal energy point charges on Γ(A) that interact according to the Riesz potential 1∕rs, 0<s<1, where r is the Euclidean distance between points. Potential theory yields that this limit distribution coincides with the equilibrium measure on Γ(A) which is supported on the outer boundary of Γ(A). We show that there are sets of revolution Γ(A) such that the support of the equilibrium measure on Γ(A) is not the complete outer boundary, in contrast to the Coulomb case s=1. However, the support of the limit distribution on the set of revolution Γ(R+A) as R goes to infinity is the full outer boundary for certain sets A, in contrast to the logarithmic case (s=0).
Accurate model including Coulomb-enhanced and Urbach-broadened absorption spectrum of direct-gap semiconductors
Authors: Lin E. Y. , Lay T. S. , Chang T. Y.
Published: December 2007

An accurate absorption model including Coulomb interaction and Urbach-broadened band edge has been demonstrated for direct bandgap semiconductors. We propose a steep-edged compound Lorentzian line-shape function for modeling the Urbach tail and the line broadening of exciton absorptions. The results of applying this fitting procedure to room-temperature and low-temperature absorption spectra of GaAs, InP, and InAs are presented, and a consistent set of band parameters are extracted. The analytical absorption model is suitable for a complete closed-form Kramers-Kronig transform of the absorption spectrum to obtain the refractive-index spectrum.
Tomographic phase-space mapping of intense particle beams using solenoids
Authors: Stratakis D. , Tian K. , Kishek R. A. , Haber I. , Reiser M. , O’Shea P. G.
Published: December 2007

Tomography based on quadrupole scans has been successfully applied to reconstruct the phase space of intense charged particle beams. This letter develops a tomographic technique based on solenoid scans, which is advantageous for solenoidal systems and injectors. The technique is generalized to the diagnosis of beams that are not axisymmetric, and validated through simulation. Solenoidal tomography is applied experimentally to a system with a nonequilibrium initial distribution, demonstrating its detailed evolution in phase space.
Simple finite non-Abelian flavor groups
Authors: Luhn Christoph , Nasri Salah , Ramond Pierre
Published: December 2007

The recently measured unexpected neutrino mixing patterns have caused a resurgence of interest in the study of finite flavor groups with two- and three-dimensional irreducible representations. This paper details the mathematics of the two finite simple groups with such representations, the icosahedral group A5, a subgroup of SO(3), and PSL2(7), a subgroup of SU(3).
Bias dependent dual band response from InAs∕Ga(In)Sb type II strain layer superlattice detectors
Authors: Khoshakhlagh A. , Rodriguez J. B. , Plis E. , Bishop G. D. , Sharma Y. D. , Kim H. S. , Dawson L. R. , Krishna S.
Published: December 2007

We report on the multispectral properties of infrared photodetectors based on type II InAs∕Ga(In)Sb strain layer superlattices using an nBn heterostructure design. The optical and electrical properties of the midwave and long wave infrared (MWIR-LWIR) absorbing layers are characterized using spectral response and current-voltage measurements, respectively. The dual band response is achieved by changing the polarity of applied bias. The spectral response shows a significant change in the LWIR to MWIR ratio within a very small bias range (∼100mV), making it compatible with commercially available readout integrated circuits.
Force measurements in dusty plasmas under microgravity by means of laser manipulation
Authors: Wolter Matthias , Melzer André , Arp Oliver , Klindworth Markus , Piel Alexander
Published: December 2007

Experiments in a dusty plasma under the microgravity conditions of parabolic flights are presented. Under microgravity, extended dust structures and a central dust-free region (“void”) are formed. Here, the forces and the force balance at the void boundary are studied by means of laser manipulation of the dust particles: A focused laser beam is moved in a controlled way to drive particles in the extended dust cloud and at the void boundary. From the observed particle motion, the forces on the particles in the dust cloud and at the void boundary are derived. Together with Langmuir probe measurements, a quantitative description of the force balance has been achieved. Special attention has been paid to the ion drag force, which is crucial in understanding the void formation. The results are compared to prevalent ion drag models.
Impact of strain on free-exciton resonance energies in wurtzite AlN
Authors: Ikeda Hirokatsu , Okamura Takahiro , Matsukawa Kodai , Sota Takayuki , Sugawara Mariko , Hoshi Takuya , Cantu Pablo , Sharma Rajat , Kaeding John F. , Keller Stacia , Mishra Umesh K. , Kosaka Kei , Asai Keiichiro , Sumiya Shigeaki , Shibata Tomohiko , Tanaka Mitsuhiro , Speck James S. , DenBaars Steven P. , Nakamura Shuji , Koyama Takahiro , Onuma Takeyoshi , Chichibu Shigefusa F.
Published: December 2007

The strain dependence of the free-exciton resonance energies in AlN epilayers is presented and the values are analyzed using an appropriate Hamiltonian assuming equibiaxial stress for the wurtzite crystal structure in order to obtain valence band parameters. Based on the results, we study the strain dependence of the valence band ordering, optical transition probability, and free-exciton binding energy. As a result of these calculations, the following strain-free values are obtained for the energy gap, averaged dielectric constants, and ordinary and extraordinary dielectric constants: Eg=6.095 eV at T=11 K, ϵ=7.87, ϵ⊥=7.33, and ϵ∥=8.45, respectively. A brief discussion of the valence band ordering in bulk AlxGa1−xN is also presented.
A model for radial modes in piezoelectric disk exhibiting Bessel polarizations
Authors: Calás H. , Figueredo J. , Moreno E. , Eiras J. A. , Leija L. , Vera A.
Published: December 2007

In this contribution, a model for radial modes in nonhomogeneus poled piezoelectric disk is being presented. Such a model is achieved by assuming a direct correspondence between the piezoelectric coefficients and the poling profile. This model was applied to a piezoelectric disk poled following a zeroth-order first-kind Bessel function, which depends on a scaling parameter, with the purpose of clarify the modal behavior in Bessel transducers. The influence of such parameter on the electrical response of the disk was studied numerically. The theoretical results were verified by the comparison with experimental results obtained for three modal Bessel transducers.
Electronic structure of Fe-doped In2O3 magnetic semiconductor with oxygen vacancies: Evidence for F-center mediated exchange interaction
Authors: Hu Shu-jun , Yan Shi-shen , Lin Xue-ling , Yao Xin-xin , Chen Yan-xue , Liu Guo-lei , Mei Liang-mo
Published: December 2007

Based on the first-principles calculations, the electronic structure and magnetic properties of Fe-doped In2O3 were theoretically investigated. The presence of the predominating defects in oxide, i.e., oxygen vacancies, can lead to strong ferromagnetic coupling between the nearest neighboring Fe cations. Spin density and band-projected charge distribution in the vicinity of the oxygen vacancies reveal that the ferromagnetic exchange is mediated by the donor impurity state, which mainly consists of Fe:3d and Fe:4s electrons trapped in oxygen vacancies. Such results provide direct evidence for the F-center mediated exchange interaction in oxide-based magnetic semiconductors.
Er
As
:
(
In
Ga
As
)
1
−
x
(
In
Al
As
)
x
alloy power generator modules
Authors: Zeng Gehong , Bahk Je-Hyeong , Bowers John E. , Zide Joshua M. O. , Gossard Arthur C. , Bian Zhixi , Singh Rajeev , Shakouri Ali , Kim Woochul , Singer Suzanne L. , Majumdar Arun
Published: December 2007

We report a wafer scale approach for the fabrication of 400 element power generator modules composed of 200 n-type ErAs:(InGaAs)0.8(InAlAs)0.2 and 200 p-type ErAs:InGaAs alloy thermoelectric elements. The thermoelectric properties of the materials were characterized. Two sets of generator modules with the element thicknesses of 20 and 10μm, respectively, were fabricated. The 20μm module had an output power density of 2.5W∕cm2 and 3.5V open circuit voltages, and the 10μm generator modules had an output power density of 1.12W∕cm2 and open circuit voltage of 2.1V. The performance of thermoelectric generator modules can further be improved by increasing the thicknesses of the elements and reducing the electrical and thermal parasitic resistances.
Improved temperature characteristics of single-wall carbon nanotube single electron transistors using carboxymethylcellulose dispersant
Authors: Mori Takahiro , Omura Kazuo , Sato Shunsuke , Suzuki Masaki , Uchida Katsumi , Yajima Hirofumi , Ishibashi Koji
Published: December 2007

Single-wall carbon nanotube (SWNT) based single electron transistors were fabricated by the dispersion method using carboxymethylcellulose (CMC) as a dispersant to make SWNT suspension. The temperature characteristics were improved compared to the one fabricated with a Triton X-100/water SWNT suspension, so that the regular Coulomb oscillations were observed up to 80K. This could be due to the increased barrier height, which may be originated from extra dipoles induced by the adsorbed CMC molecules at the SWNT/metal interface.
Single-molecule tracking of mRNA exiting from RNA polymerase II
Authors: Andrecka Joanna , Lewis Robert , Brückner Florian , Lehmann Elisabeth , Cramer Patrick , Michaelis Jens
Published: December 2007

Single-pair fluorescence resonance energy transfer was used to track RNA exiting from RNA polymerase II (Pol II) in elongation complexes. Measuring the distance between the RNA 5′ end and three known locations within the elongation complex allows us determine its position by means of triangulation. RNA leaves the polymerase active center cleft via the previously proposed exit tunnel and then disengages from the enzyme surface. When the RNA reaches lengths of 26 and 29 nt, its 5′ end associates with Pol II at the base of the dock domain. Because the initiation factor TFIIB binds to the dock domain and exit tunnel, exiting RNA may prevent TFIIB reassociation during elongation. RNA further extends toward the linker connecting to the polymerase C-terminal repeat domain (CTD), which binds the 5′-capping enzyme and other RNA processing factors.
Stepwise dynamics of epitaxially growing single amyloid fibrils
Authors: Kellermayer Miklós S. Z. , Karsai Árpád , Benke Margit , Soós Katalin , Penke Botond
Published: December 2007

The assembly mechanisms of amyloid fibrils, tissue deposits in a variety of degenerative diseases, is poorly understood. With a simply modified application of the atomic force microscope, we monitored the growth, on mica surface, of individual fibrils of the amyloid β25–35 peptide with near-subunit spatial and subsecond temporal resolution. Fibril assembly was polarized and discontinuous. Bursts of rapid (up to 300-nm
−1
) growth phases that extended the fibril by ≈7 nm or its integer multiples were interrupted with pauses. Stepwise dynamics were also observed for amyloid β1–42 fibrils growing on graphite, suggesting that the discontinuous assembly mechanisms may be a general feature of epitaxial amyloid growth. Amyloid assembly may thus involve fluctuation between a fast-growing and a blocked state in which the fibril is kinetically trapped because of intrinsic structural features. The used scanning-force kymography method may be adapted to analyze the assembly dynamics of a wide range of linear biopolymers.
The RCK2 domain of the human BK
Ca
channel is a calcium sensor
Authors: Yusifov Taleh , Savalli Nicoletta , Gandhi Chris S. , Ottolia Michela , Olcese Riccardo
Published: December 2007

Large conductance voltage and Ca
2+
-dependent K
+
channels (BK
Ca
) are activated by both membrane depolarization and intracellular Ca
2+
. Recent studies on bacterial channels have proposed that a Ca
2+
-induced conformational change within specialized regulators of K
+
conductance (RCK) domains is responsible for channel gating. Each pore-forming α subunit of the homotetrameric BK
Ca
channel is expected to contain two intracellular RCK domains. The first RCK domain in BK
Ca
channels (RCK1) has been shown to contain residues critical for Ca
2+
sensitivity, possibly participating in the formation of a Ca
2+
-binding site. The location and structure of the second RCK domain in the BK
Ca
channel (RCK2) is still being examined, and the presence of a high-affinity Ca
2+
-binding site within this region is not yet established. Here, we present a structure-based alignment of the C terminus of BK
Ca
and prokaryotic RCK domains that reveal the location of a second RCK domain in human BK
Ca
channels (hSloRCK2). hSloRCK2 includes a high-affinity Ca
2+
-binding site (Ca bowl) and contains similar secondary structural elements as the bacterial RCK domains. Using CD spectroscopy, we provide evidence that hSloRCK2 undergoes a Ca
2+
-induced change in conformation, associated with an α-to-β structural transition. We also show that the Ca bowl is an essential element for the Ca
2+
-induced rearrangement of hSloRCK2. We speculate that the molecular rearrangements of RCK2 likely underlie the Ca
2+
-dependent gating mechanism of BK
Ca
channels. A structural model of the heterodimeric complex of hSloRCK1 and hSloRCK2 domains is discussed.
Instructive role of aPKCζ subcellular localization in the assembly of adherens junctions in neural progenitors
Authors: Ghosh Sourav , Marquardt Till , Thaler Joshua P. , Carter Nigel , Andrews Shane E. , Pfaff Samuel L. , Hunter Tony
Published: December 2007

In the neurogenic phase of CNS development, the proliferating progenitors are found medially within the neuroepithelium. The adherens junctions on the apical membrane of proliferating neural progenitors allow for cell–cell adhesion and medial stratification. In contrast, differentiating neuronal precursors delaminate and migrate laterally, establishing the laminar layers. Apical adherens junctions also establish the apical–basal polarity in neural progenitors, which in turn is postulated to lead to asymmetric inheritance of cell fate determinants during neurogenic divisions. The signaling pathways and cellular mechanisms that regulate the assembly and asymmetric localization of adherens junctions in neural progenitors remain elusive. Here we show that atypical PKCζ/λ (aPKCζ/λ) localizes at the apical membrane of proliferating neural stem cells, but not postmitotic neuronal precursors, in the developing chicken neural tube. This precise subcellular compartmentalization of the kinase activity provides an instructive signal for apical assembly of adherens junctions in a PI3K, Rac/Cdc42 signaling-dependent pathway. Apical aPKCζ coordinates neural stem cell proliferation and the overall stratification of cell types within the neural tube.
The varitint-waddler (Va) deafness mutation in TRPML3 generates constitutive, inward rectifying currents and causes cell degeneration
Authors: Nagata Keiichi , Zheng Lili , Madathany Thomas , Castiglioni Andrew J. , Bartles James R. , García-Añoveros Jaime
Published: December 2007

Varitint-waddler (Va and Va
J
) mice are deaf and have vestibular impairment, with inner ear defects that include the degeneration and loss of sensory hair cells. The semidominant Va mutation results in an alanine-to-proline substitution at residue 419 (A419P) of the presumed ion channel TRPML3. Another allele, Va
J
, has the A419P mutation in addition to an I362T mutation. We found that hair cells, marginal cells of stria vascularis, and other cells lining the cochlear and vestibular endolymphatic compartments express TRPML3. When heterologously expressed in LLC-PK1-CL4 epithelial cells, a culture model for hair cells, TRPML3 accumulated in lysosomes and in espin-enlarged microvilli that resemble stereocilia. We also demonstrated that wild-type TRPML3 forms channels that are blocked by Gd
3+
, have a conductance of 50–70 pS and, like many other TRP channels, open at very positive potentials and thus rectify outwardly. In addition to this outward current, TRPML3(419P) and (I362T+A419P) generated a constitutive inwardly rectifying current that suggests a sensitivity to hyperpolarizing negative potentials and that depolarized the cells. Cells expressing TRPML3(A419P) or (I362T+A419P), but not wild-type TRPML3, died and were extruded from the epithelium in a manner reminiscent of degenerating hair cells in Va mice. The increased open probability of TRPML3(A419P) and (I362T+A419P) at physiological potentials likely underlies hair cell degeneration and deafness in Va and Va
J
mice.
Costs and benefits of cold acclimation in field-released
Drosophila
Authors: Kristensen Torsten N. , Hoffmann Ary A. , Overgaard Johannes , Sørensen Jesper G. , Hallas Rebecca , Loeschcke Volker
Published: December 2007

One way animals can counter the effects of climatic extremes is via physiological acclimation, but acclimating to one extreme might decrease performance under different conditions. Here, we use field releases of
Drosophila melanogaster
on two continents across a range of temperatures to test for costs and benefits of developmental or adult cold acclimation. Both types of cold acclimation had enormous benefits at low temperatures in the field; in the coldest releases only cold-acclimated flies were able to find a resource. However, this advantage came at a huge cost; flies that had not been cold-acclimated were up to 36 times more likely to find food than the cold-acclimated flies when temperatures were warm. Such costs and strong benefits were not evident in laboratory tests where we found no reduction in heat survival of the cold-acclimated flies. Field release studies, therefore, reveal costs of cold acclimation that standard laboratory assays do not detect. Thus, although physiological acclimation may dramatically improve fitness over a narrow set of thermal conditions, it may have the opposite effect once conditions extend outside this range, an increasingly likely scenario as temperature variability increases under global climate change.
Replication stress induces tumor-like microdeletions in
FHIT
/FRA3B
Authors: Durkin Sandra G. , Ragland Ryan L. , Arlt Martin F. , Mulle Jennifer G. , Warren Stephen T. , Glover Thomas W.
Published: December 2007

Common fragile sites (CFSs) are loci that preferentially exhibit metaphase chromosome gaps and breaks after partial inhibition of DNA synthesis. The fragile site FRA3B, which lies within the
FHIT
tumor-suppressor gene, is a site of frequent heterozygous and homozygous deletions in many cancer cells and precancerous lesions. The great majority of
FHIT
and other CFS-associated gene rearrangements in tumors are submicroscopic, intralocus deletions of hundreds of kilobases that often result in inactivation of associated genes. Although CFS instability leads to chromosome gaps and breaks and translocations, there has been no direct evidence showing that CFS instability or replication stress can generate large submicroscopic deletions of the type seen in cancer cells. Here, we have produced FHIT/FRA3B deletions closely resembling those in tumors by exposing human–mouse chromosome 3 somatic hybrid cells to aphidicolin-mediated replication stress. Clonal cell populations were analyzed for deletions by using PCR, array comparative genomic hybridization (aCGH), and FISH. Thirteen percent to 23% of clones exhibited submicroscopic
FHIT
deletions spanning ≈200–600 kb within FRA3B. Chromosomes with FRA3B deletions exhibited significantly decreased fragility of this locus, with a 2- to 12-fold reduction in metaphase gaps and breaks compared with controls. Sequence analysis showed no regions of homology at breakpoints and suggests involvement of NHEJ in generating the deletions. Our results demonstrate that replication stress induces a remarkably high frequency of tumor-like microdeletions that reduce fragility at a CFS in cultured cells and suggests that similar conditions during tumor formation lead to intralocus deletion and inactivation of genes at CFSs and perhaps elsewhere in the genome.
Synthetic heterovalent inhibitors targeting recognition E3 components of the N-end rule pathway
Authors: Lee Min Jae , Pal Krishnendu , Tasaki Takafumi , Roy Sayantani , Jiang Yonghua , An Jee Young , Banerjee Rajkumar , Kwon Yong Tae
Published: December 2007

Multivalent binding allows high selectivity and affinity in a ligand–protein interaction. The N-end rule pathway is a ubiquitin (Ub)-dependent proteolytic system in which specific E3s, called N-recognins, mediate ubiquitylation through the recognition of types 1 and 2, destabilizing N-terminal residues of substrates. We recently identified a set of E3 Ub ligases (named UBR1–UBR7) containing the 70-residue UBR box, and we demonstrated that UBR1, UBR2, UBR4, and UBR5 can bind to destabilizing N-terminal residues. To explore a model of heterovalent interaction to the N-recognin family, we synthesized the small-molecule compound RF-C11, which bears two heterovalent ligands designed to target N-recognins, together with control molecules with two homovalent ligands. We demonstrate that heterovalent ligands of RF-C11 selectively and cooperatively bind cognate-binding sites of multiple N-recognins and thereby inhibit both types 1 and 2 N-end rule activities. Furthermore, the efficacy of heterovalent RF-C11 was substantially higher than homovalent inhibitors, which can target either a type 1 or type 2 site, providing the molecular basis of designing multivalent inhibitors for the control of specific intracellular pathways. In addition, RF-C11 exhibited higher efficacy and stability, compared with dipeptides bearing destabilizing N-terminal residues, which are known competitive inhibitors of the pathway. We also used the heterovalent compound to study the function of N-recognins in cardiac signaling. Using mouse and rat cardiomyocytes, we demonstrate that the N-end rule pathway has a cell-autonomous function in cardiac proliferation and hypertrophy, explaining our earlier results implicating the pathway in cardiac development and proteolysis of multiple cardiovascular regulators.
Synthetic antibodies for specific recognition and crystallization of structured RNA
Authors: Ye Jing-Dong , Tereshko Valentina , Frederiksen John K. , Koide Akiko , Fellouse Frederic A. , Sidhu Sachdev S. , Koide Shohei , Kossiakoff Anthony A. , Piccirilli Joseph A.
Published: December 2007

Antibodies that bind protein antigens are indispensable in biochemical research and modern medicine. However, knowledge of RNA-binding antibodies and their application in the ever-growing RNA field is lacking. Here we have developed a robust approach using a synthetic phage-display library to select specific antigen-binding fragments (Fabs) targeting a large functional RNA. We have solved the crystal structure of the first Fab–RNA complex at 1.95 Å. Capability in phasing and crystal contact formation suggests that the Fab provides a potentially valuable crystal chaperone for RNA. The crystal structure reveals that the Fab achieves specific RNA binding on a shallow surface with complementarity-determining region (CDR) sequence diversity, length variability, and main-chain conformational plasticity. The Fab–RNA interface also differs significantly from Fab–protein interfaces in amino acid composition and light-chain participation. These findings yield valuable insights for engineering of Fabs as RNA-binding modules and facilitate further development of Fabs as possible therapeutic drugs and biochemical tools to explore RNA biology.
Pressure-induced metallization of silane
Authors: Chen Xiao-Jia , Struzhkin Viktor V. , Song Yang , Goncharov Alexander F. , Ahart Muhtar , Liu Zhenxian , Mao Ho-kwang , Hemley Russell J.
Published: December 2007

There is a great interest in electronic transitions in hydrogen-rich materials under extreme conditions. It has been recently suggested that the group IVa hydrides such as methane (CH
4
), silane (SiH
4
), and germane (GeH
4
) become metallic at far lower pressures than pure hydrogen at equivalent densities because the hydrogen is chemically compressed in group IVa hydride compounds. Here we report measurements of Raman and infrared spectra of silane under pressure. We find that SiH
4
undergoes three phase transitions before becoming opaque at 27–30 GPa. The vibrational spectra indicate the material transforms to a polymeric (framework) structure in this higher pressure range. Room-temperature infrared reflectivity data reveal that the material exhibits Drude-like metallic behavior above 60 GPa, indicating the onset of pressure-induced metallization.
The N-end rule pathway is a sensor of heme
Authors: Hu Rong-Gui , Wang Haiqing , Xia Zanxian , Varshavsky Alexander
Published: December 2007

The conjugation of arginine, by arginyl-transferase, to N-terminal aspartate, glutamate or oxidized cysteine is a part of the N-end rule pathway of protein degradation. We report that arginyl-transferase of either the mouse or the yeast
Saccharomyces cerevisiae
is inhibited by hemin (Fe
3+
-heme). Furthermore, we show that hemin inhibits arginyl-transferase through a redox mechanism that involves the formation of disulfide between the enzyme's Cys-71 and Cys-72 residues. Remarkably, hemin also induces the proteasome-dependent degradation of arginyl-transferase
in vivo
, thus acting as both a “stoichiometric” and “catalytic” down-regulator of the N-end rule pathway. In addition, hemin was found to interact with the yeast and mouse E3 ubiquitin ligases of the N-end rule pathway. One of substrate-binding sites of the yeast N-end rule's ubiquitin ligase UBR1 targets CUP9, a transcriptional repressor. This site of UBR1 is autoinhibited but can be allosterically activated by peptides that bear destabilizing N-terminal residues and interact with two other substrate-binding sites of UBR1. We show that hemin does not directly occlude the substrate-binding sites of UBR1 but blocks the activation of its CUP9-binding site by dipeptides. The N-end rule pathway, a known sensor of short peptides, nitric oxide, and oxygen, is now a sensor of heme as well. One function of the N-end rule pathway may be to coordinate the activities of small effectors, both reacting to and controlling the redox dynamics of heme, oxygen, nitric oxide, thiols, and other compounds, in part through conditional degradation of specific transcription factors and G protein regulators.
Tamoxifen-stimulated growth of breast cancer due to p21 loss
Authors: Abukhdeir Abde M. , Vitolo Michele I. , Argani Pedram , De Marzo Angelo M. , Karakas Bedri , Konishi Hiroyuki , Gustin John P. , Lauring Josh , Garay Joseph P. , Pendleton Courtney , Konishi Yuko , Blair Brian G. , Brenner Keith , Garrett-Mayer Elizabeth , Carraway Hetty , Bachman Kurtis E. , Park Ben Ho
Published: December 2007

Tamoxifen is widely used for the treatment of hormonally responsive breast cancers. However, some resistant breast cancers develop a growth proliferative response to this drug, as evidenced by tumor regression upon its withdrawal. To elucidate the molecular mediators of this paradox, tissue samples from a patient with tamoxifen-stimulated breast cancer were analyzed. These studies revealed that loss of the cyclin-dependent kinase inhibitor p21 was associated with a tamoxifen growth-inducing phenotype. Immortalized human breast epithelial cells with somatic deletion of the
p21
gene were then generated and displayed a growth proliferative response to tamoxifen, whereas p21 wild-type cells demonstrated growth inhibition upon tamoxifen exposure. Mutational and biochemical analyses revealed that loss of p21's cyclin-dependent kinase inhibitory property results in hyperphosphorylation of estrogen receptor-α, with subsequent increased gene expression of estrogen receptor-regulated genes. These data reveal a previously uncharacterized molecular mechanism of tamoxifen resistance and have potential clinical implications for the management of tamoxifen-resistant breast cancers.
Down-regulation of 14-3-3ζ suppresses anchorage-independent growth of lung cancer cells through anoikis activation
Authors: Li Zenggang , Zhao Jing , Du Yuhong , Park Hae Ryoun , Sun Shi-Yong , Bernal-Mizrachi Leon , Aitken Alastair , Khuri Fadlo R. , Fu Haian
Published: December 2007

The family of 14-3-3 proteins has emerged as critical regulators of diverse cellular responses under both physiological and pathological conditions. Here, we report an important role of 14-3-3ζ in tumorigenesis through a mechanism that involves anoikis resistance. 14-3-3ζ is up-regulated in a number of cancer types, including lung cancer. Through an RNAi approach using human lung adenocarcinoma-derived A549 cells as a model system, we have found that knockdown of a single ζ isoform of 14-3-3 is sufficient to restore the sensitivity of cancer cells to anoikis and impair their anchorage-independent growth. Enhanced anoikis appears to be mediated in part by up-regulated BH3-only proteins, Bad and Bim, coupled with decreased Mcl-1, resulting in the subsequent activation of Bax. This study suggests a model in which anchorage-independent growth of lung cancer cells requires the presence of 14-3-3ζ. This work not only reveals a critical role of 14-3-3ζ in anoikis suppression in lung cancer cells, but also identifies and validates 14-3-3ζ as a potential molecular target for anticancer therapeutic development.
A model for obesity and gigantism due to disruption of the
Ankrd26
gene
Authors: Bera Tapan K. , Liu Xiu-Fen , Yamada Masanori , Gavrilova Oksana , Mezey Eva , Tessarollo Lino , Anver Miriam , Hahn Yoonsoo , Lee Byungkook , Pastan Ira
Published: December 2007

Obesity is a major health hazard that is caused by a combination of genetic and behavioral factors. Several models of obesity have been described in mice that have defects in the production of peptide hormones, in the function of cell membrane receptors, or in a transcription factor required for neuronal cell development. We have been investigating the function of a family of genes (
POTE
and
ANKRD26
) that encode proteins that are associated with the inner aspect of the cell membrane and that contain both ankyrin repeats and spectrin helices, motifs known to interact with signaling proteins in the cell. To assess the function of
ANKRD26
, we prepared a mutant mouse with partial inactivation of the
Ankrd26
gene. We find that the homozygous mutant mice develop extreme obesity, insulin resistance, and an increase in body size. The obesity is associated with hyperphagia with no reduction in energy expenditure and activity. The Ankrd26 protein is expressed in the arcuate and ventromedial nuclei within the hypothalamus and in the ependyma and the circumventricular organs that act as an interface between the peripheral circulation and the brain. In the enlarged hearts of the mutant mice, the levels of both phospho-Akt and mTOR were elevated. These results show that alterations in an unidentified gene can lead to obesity and identify a molecular target for the treatment of obesity.
A novel insertion pathway of mitochondrial outer membrane proteins with multiple transmembrane segments
Authors: Otera Hidenori , Taira Yohsuke , Horie Chika , Suzuki Yurina , Suzuki Hiroyuki , Setoguchi Kiyoko , Kato Hiroki , Oka Toshihiko , Mihara Katsuyoshi
Published: December 2007

The central channel Tom40 of the preprotein translocase of outer membrane (TOM) complex is thought to be responsible for the import of virtually all preproteins synthesized outside the mitochondria. In this study, we analyze the topogenesis of the peripheral benzodiazepine receptor (PBR), which integrates into the mitochondrial outer membrane (MOM) through five hydrophobic transmembrane segments (TMSs) and functions in cholesterol import into the inner membrane. Analyses of in vitro and in vivo import into TOM component–depleted mitochondria reveal that PBR import (1) depends on the import receptor Tom70 but requires neither the Tom20 and Tom22 import receptors nor the import channel Tom40, (2) shares the post-Tom70 pathway with the C-tail–anchored proteins, and (3) requires factors of the mitochondrial intermembrane space. Furthermore, membrane integration of mitofusins and mitochondrial ubiquitin ligase, the MOM proteins with two and four TMSs, respectively, proceeds through the same initial pathway. These findings reveal a previously unidentified pathway of the membrane integration of MOM proteins with multiple TMSs.
Sequential roles for myosin-X in BMP6-dependent filopodial extension, migration, and activation of BMP receptors
Authors: Pi Xinchun , Ren Rongqin , Kelley Russell , Zhang Chunlian , Moser Martin , Bohil Aparna B. , DiVito Melinda , Cheney Richard E. , Patterson Cam
Published: December 2007

Endothelial cell migration is an important step during angiogenesis, and its dysregulation contributes to aberrant neovascularization. The bone morphogenetic proteins (BMPs) are potent stimulators of cell migration and angiogenesis. Using microarray analyses, we find that myosin-X (Myo10) is a BMP target gene. In endothelial cells, BMP6-induced Myo10 localizes in filopodia, and BMP-dependent filopodial assembly decreases when Myo10 expression is reduced. Likewise, cellular alignment and directional migration induced by BMP6 are Myo10 dependent. Surprisingly, we find that Myo10 and BMP6 receptor ALK6 colocalize in a BMP6-dependent fashion. ALK6 translocates into filopodia after BMP6 stimulation, and both ALK6 and Myo10 possess intrafilopodial motility. Additionally, Myo10 is required for BMP6-dependent Smad activation, indicating that in addition to its function in filopodial assembly, Myo10 also participates in a requisite amplification loop for BMP signaling. Our data indicate that Myo10 is required to guide endothelial migration toward BMP6 gradients via the regulation of filopodial function and amplification of BMP signals.
Type I phosphatidylinositol 4-phosphate 5-kinase controls neutrophil polarity and directional movement
Authors: Lacalle Rosa Ana , Peregil Rosa M. , Albar Juan Pablo , Merino Ernesto , Martínez-A Carlos , Mérida Isabel , Mañes Santos
Published: December 2007

Directional cell movement in response to external chemical gradients requires establishment of front–rear asymmetry, which distinguishes an up-gradient protrusive leading edge, where Rac-induced F-actin polymerization takes place, and a down-gradient retractile tail (uropod in leukocytes), where RhoA-mediated actomyosin contraction occurs. The signals that govern this spatial and functional asymmetry are not entirely understood. We show that the human type I phosphatidylinositol 4-phosphate 5-kinase isoform β (PIPKIβ) has a role in organizing signaling at the cell rear. We found that PIPKIβ polarized at the uropod of neutrophil-differentiated HL60 cells. PIPKIβ localization was independent of its lipid kinase activity, but required the 83 C-terminal amino acids, which are not homologous to other PIPKI isoforms. The PIPKIβ C terminus interacted with EBP50 (4.1-ezrin-radixin-moesin (ERM)-binding phosphoprotein 50), which enabled further interactions with ERM proteins and the Rho-GDP dissociation inhibitor (RhoGDI). Knockdown of PIPKIβ with siRNA inhibited cell polarization and impaired cell directionality during dHL60 chemotaxis, suggesting a role for PIPKIβ in these processes.
Local cortical pulling-force repression switches centrosomal centration and posterior displacement in C. elegans
Authors: Kimura Akatsuki , Onami Shuichi
Published: December 2007

Centrosome positioning is actively regulated by forces acting on microtubules radiating from the centrosomes. Two mechanisms, center-directed and polarized cortical pulling, are major contributors to the successive centering and posteriorly displacing migrations of the centrosomes in single-cell–stage Caenorhabditis elegans. In this study, we analyze the spatial distribution of the forces acting on the centrosomes to examine the mechanism that switches centrosomal migration from centering to displacing. We clarify the spatial distribution of the forces using image processing to measure the micrometer-scale movements of the centrosomes. The changes in distribution show that polarized cortical pulling functions during centering migration. The polarized cortical pulling force directed posteriorly is repressed predominantly in the lateral regions during centering migration and is derepressed during posteriorly displacing migration. Computer simulations show that this local repression of cortical pulling force is sufficient for switching between centering and displacing migration. Local regulation of cortical pulling might be a mechanism conserved for the precise temporal regulation of centrosomal dynamic positioning.
PR-Set7–dependent lysine methylation ensures genome replication and stability through S phase
Authors: Tardat Mathieu , Murr Rabih , Herceg Zdenko , Sardet Claude , Julien Eric
Published: December 2007

PR-Set7/SET8 is a histone H4–lysine 20 methyltransferase required for normal cell proliferation. However, the exact functions of this enzyme remain to be determined. In this study, we show that human PR-Set7 functions during S phase to regulate cellular proliferation. PR-Set7 associates with replication foci and maintains the bulk of H4-K20 mono- and trimethylation. Consistent with a function in chromosome dynamics during S phase, inhibition of PR-Set7 methyltransferase activity by small hairpin RNA causes a replicative stress characterized by alterations in replication fork velocity and origin firing. This stress is accompanied by massive induction of DNA strand breaks followed by a robust DNA damage response. The DNA damage response includes the activation of ataxia telangiectasia mutated and ataxia telangiectasia related kinase–mediated pathways, which, in turn, leads to p53-mediated growth arrest to avoid aberrant chromosome behavior after improper DNA replication. Collectively, these data indicate that PR-Set7–dependent lysine methylation during S phase is an essential posttranslational mechanism that ensures genome replication and stability.