bluuebunny/crossref_metadata_2025 huggingface dataset:
Anesthesia Increases Postoperative Pain
Authors: Gough Nancy R.
Published: September 2008

Patients often report a burning sensation when receiving intravenously delivered anesthetics, and respiratory irritation limits the dose of pungent inhalation anesthetics. Matta
et al
. show that the pungent volatile anesthetics isoflurane and desflurane, as well as the intravenous anesthetics propofol and etomidate (collectively referred to as the noxious general anesthetics), activated TRPA1 channels, which are members of the transient receptor potential family that are present on a large proportion of peripheral nociceptive sensory neurons. The nonpungent volatile anesthetics halothane and sevoflurane did not. Electrophysiology experiments revealed that the noxious general anesthetics activated TRPA1 channels, but not TRPV1 or TRPM8 channels, when the channels were heterologously expressed in cultured cells. Calcium imaging experiments on neurons cultured from dorsal root ganglia indicated that these noxious general anesthetics activated nociceptive neurons containing TRPA1. Cells isolated from TRPA1-null mice failed to respond to the noxious general anesthetics. The noxious general anesthetics activated the channels in cell-free patches, which suggests that these drugs may interact directly with the channel and do not require second messenger signaling for channel regulation. The pain response triggered by propofol administered to mice required TRPA1, and coadministration of a neurogenic irritant with isoflurane triggered more swelling than was observed with the irritant alone. Thus, although these central nervous system depressants are important for induction of surgical anesthesia, choosing a general anesthetic that does not activate TRPA1 may minimize postoperative pain and inflammation.

J. A. Matta, P. M. Cornett, R. L. Miyares, K. Abe, N. Sahibzada, G. P. Ahern, General anesthetics activate a nociceptive ion channel to enhance pain and inflammation.
Proc. Natl. Acad. Sci. U.S.A.
105
, 8784-8789 (2008).
[Abstract]
[Full Text]
How Sanshool Produces One Singular Sensation
Authors: Adler Elizabeth M.
Published: September 2008

Szechuan peppers, which are unrelated to black peppers or chili peppers, are harvested from various species

of
Xanthoxylum
, a genus of plants traditionally known as "toothache trees" because of the characteristic tingling, numbing sensation they elicit. Using live-cell calcium imaging, Bautista
et al
. found that hydroxy-α-sanshool (sanshool, the active ingredient) purified from Szechuan pepper excited two main classes of cultured mouse sensory neurons. These comprised a subset of small-diameter unmyelinated neurons that expressed the capsaicin receptor TRPV1 and a subset of large-diameter myelinated neurons that expressed the neurotrophin receptor TrkC and were sensitive to osmotic stimuli. Whole-cell voltage-clamp analysis indicated that sanshool inhibited a background K
+
leak current; sensitivity to pH and pharmacology implicated the KCNK family of two-pore K
+
channels as sanshool targets. When different KCNK subtypes were expressed in
Xenopus
oocytes, only KCNK3, KCNK9, and KCNK18 were inhibited by sanshool; the effects of sanshool were reversible, independent of pH, and apparent on channels in excised membrane patches. In contrast, various excitatory channels, including TRPV1 and TRPA1 (which responds to mustard oil), did not appear to be sanshool targets. Cultured cerebellar granule neurons also showed calcium responses to sanshool; their sensitivity correlated with a temporal increase in expression of transcripts encoding KCNK3 and KCNK9, whereas KCNK18 appeared to play a key role in the sanshool sensitivity of cultured trigeminal ganglion sensory neurons. Thus, the unique sensation elicited by sanshool--described by the authors as "akin to…touching one’s tongue to the terminals of a 9-V battery"--appears to depend on an equally unusual mechanism of sensory neuron activation.

D. M. Bautista, Y. M. Sigal, A. D. Milstein, J. L. Garrison, J. A. Zorn, P. R. Tsuruda, R. A. Nicoll, D. Julius, Pungent agents from Szechuan peppers excite sensory neurons by inhibiting two-pore potassium channels.
Nat. Neurosci.
11
, 772-779 (2008).
[PubMed]
Enhancing Channel Activity
Authors: Foley John F.
Published: September 2008

Alzheimer’s disease (AD) is associated with the accumulation of amyloid β (Aβ) plaques and neurofibrillary tangles in the brain, but whether Aβ is responsible for triggering AD is unclear. Excessive Ca
2+
signaling, which is very toxic to neurons, is another potential culprit. The γ secretase complex, whose core components are the presenilin (PS) proteins, processes the amyloid precursor protein (APP) to produce Aβ. Cells containing mutant PS proteins associated with familial AD (FAD) exhibit excessive Ca
2+
signaling. Because the inositol 1,4,5-trisphosphate receptor (IP
3
R) is the channel responsible for Ca
2+
egress from the endoplasmic reticulum (ER), Cheung
et
al
. investigated a role for PS proteins in modulating IP
3
R activity. Coimmunoprecipitation assays showed the physical association of either wild-type or FAD PS proteins with IP
3
Rs in mouse brain lysates. Single-channel patch-clamp current recordings showed that basal and IP
3
-stimulated channel activity in chick DT40 cells overexpressing FAD PS proteins was enhanced compared with that in cells expressing wild-type PS proteins and was more sensitive to lower concentrations of IP
3
. The increased Ca
2+
flux in FAD PS–expressing cells was associated with the IP
3
R being in an open state for longer durations than was the case in wild-type PS-expressing cells. Similar electrophysiological experiments showed that FAD PS1 enhanced IP
3
R-mediated Ca
2+
signaling in transfected mouse brain cortical neurons. Although overexpression of FAD PS1 increased Aβ production by APP-expressing DT40 cells compared with that observed when wild-type PS1 was overexpressed, this enhancement of APP processing was blocked in DT40 cells deficient in all IP
3
R isoforms. Together, these data suggest that increased Ca
2+
signaling through mutant PS-mediated enhancement of IP
3
R activity may play a role in the pathogenesis of AD.

K.-H. Cheung, D. Shineman, M. Müller, C. Cárdenas, L. Mei, J. Yang, T. Tomita, T. Iwatsubo, V. M.-Y. Lee, J. K. Foskett, Mechanism of Ca
2+
disruption in Alzheimer’s disease by presenilin regulation of InsP
3
receptor channel gating.
Neuron
58
, 871-883 (2008).
[PubMed]
A Ligand, Not a Carrier
Authors: Adler Elizabeth M.
Published: September 2008

Volatile odorants are generally thought to bind to G protein-coupled receptors and thereby activate a downstream signaling pathway, a paradigm challenged by data from Laughlin
et al
. In
Drosophila
, various odorant-binding proteins are secreted into the lymph around subsets of olfactory neurons (where odorants diffuse); the function of these pheromone- and odorant-binding proteins, however, has been unclear (see Stowers and Logan). Laughlin
et al
., from a research group that previously showed that the odorant-binding protein LUSH is required for sensitivity to the pheromone 11-
cis
vaccenyl acetate (cVA), combined structural and in vivo electrophysiological analysis to investigate its function. Comparison of the x-ray crystal structure of LUSH bound to cVA with the previously determined structure of uncomplexed LUSH revealed that binding by cVA (which was almost completely enclosed by LUSH) induced a conformational change in LUSH. A LUSH mutant bearing an amino acid substitution predicted to minimize this conformational change was less effective at conferring cVA sensitivity to T1 neurons (which mediate the response to this pheromone) in flies lacking endogenous LUSH than was wild-type LUSH. In contrast, a mutation predicted to enhance the conformational change produced a more effective form. Moreover, a mutation yielding an uncomplexed LUSH conformation that resembled that of the cVA-bound form stimulated T1 neurons even in the absence of cVA, an ability that depended on the expression in T1 neurons of Or67d and SNMP (which are required for sensitivity to cVA). Thus, the authors conclude that LUSH is an inactive ligand that is converted into an active form through cVA binding.

J. D. Laughlin, T. S. Ha, D. N. M. Jones, D. P. Smith, Activation of pheromone-sensitive neurons is mediated by conformational activation of pheromone-binding protein.
Cell
133
, 1255-1265 (2008).
[PubMed]

L. Stowers, D. W. Logan, LUSH shapes up for a starring role in olfaction.
Cell
133
, 1137-1139 (2008).
[PubMed]
Developing the Lateral Line
Authors: Hines Pamela J.
Published: September 2008

Fish use the lateral line to sense changes in pressure and water movements that may signal the arrival of food or predators. Nechiporuk and Raible now use genetics, cell transplantation, and live imaging to study lateral line development in zebrafish. In zebrafish, the lateral line develops from front to back, with a migrating zone of progenitor cells laying down repeated clusters of hair cells in its wake. Fibroblast growth factor signaling is involved in several aspects of the process--migration, deposition of a primordium, and differentiation.

A. Nechiporuk, D. W. Raible, FGF-dependent mechanosensory organ patterning in zebrafish.
Science
320
, 1774-1777 (2008).
[Abstract]
[Full Text]
p53 Brings a New Twist to the Smad Signaling Network
Authors: Atfi Azeddine , Baron Roland
Published: September 2008

Transforming growth factor beta (TGF-β) signaling regulates a plethora of cellular responses, including specification of developmental fate during embryogenesis, cell proliferation, differentiation, and apoptosis. Components of this pathway are often mutated in cancers and other human disorders. TGF-β signaling involves activation of transcriptional regulators of the Smad family. The tumor suppressor p53 is an essential partner of Smads, affecting TGF-β signaling at various points in the pathway. Inactivation of p53 may contribute to the aberrant behavior of cancer cells that escape the cytostatic action of TGF-β despite the apparent integrity of the TGF-β receptor or Smads. Thus, the discovery that p53 and TGF-β cooperate in cell-fate decisions and cellular homeostatic mechanisms has important pathophysiological implications.
Uncoupling the Role of Sonic Hedgehog in Limb Development: Growth and Specification
Authors: Francis-West Philippa , Hill Robert
Published: September 2008

Sonic hedgehog (Shh) signaling is essential for the anterior-posterior (A-P) patterning of the embryonic limb bud. An additional role for Shh has now been identified in the mouse and chick, in which Shh promotes the proliferation of limb mesenchymal cells, which increases the number of digits that form. Surprisingly, these data are not consistent with any of the previous models in the mouse that described roles for Shh and the zone of polarizing activity in the patterning of the A-P axis. Therefore, new light is shed on the mechanisms of Shh action, which both challenges our understanding of limb development and gives insights into the evolutionary changes that result in digit reductions.
Breaking Through the Basement
Authors: Adler Elizabeth M.
Published: September 2008

At various stages during development, epithelial cells undergo epithelial-mesenchymal transition (EMT), becoming nonadherent and motile, a process that involves coordination of distinct events (such as loss of polarity, disruption of intercellular junctions, and degradation of the basement membrane) and that also occurs in carcinoma progression (see Levayer and Lecuit). Nakaya
et al
. characterized the expression patterns of various EMT markers in gastrulation-stage chick embryos and found that breakdown of the basement membrane was the earliest identifiable EMT event. Electroporation of RhoA into medial epiblast cells (mesoderm precursors) in the primitive streak interfered with their ability to undergo EMT. It led to the retention of the basement membrane marker laminin in nascent mesoderm cells and in mesoderm precursors without affecting laminin expression in lateral epiblast cells. Excess RhoA also led to the formation of aggregates of nascent mesoderm cells at the streak midline. These defects were rescued by concurrent electroporation of the Rho inhibitor C3 exoenzyme. Immunofluorescence analysis revealed RhoA in the epiblast but not the mesoderm; further, whereas RhoA was identified in both apical and basal regions of lateral epiblast cells, it was only apparent in the apical portions of medial cells. Expression of the RhoA guanine nucleotide exchange factor (GEF) Net1 was basally restricted in lateral epiblast cells and down-regulated or absent in medial epiblast cells. Antisense morpholino oligonucleotides directed against
RhoA
and
Net1
elicited premature breakdown of laminin, as did expression of dominant-negative RhoA; moreover, the
Net1
-directed morpholinos reduced basal RhoA activity in epiblast cells without affecting the activity of apical RhoA. Nocodazole, which destabilizes microtubules, promoted breakdown of the basement membrane, whereas taxol, which stabilizes them, promoted retention of the basement membrane in the medial epiblast. Misexpression of RhoA caused the retention in medial epiblast cells of a posttranslationally modified form of β-tubulin, typically found near the basal cell membrane of lateral epiblast cells but absent in medial epiblast cells. Thus, the authors propose that the decreased activity of basal RhoA and destabilization of basal microtubules lead to disruption of interactions between epithelial cells and basement membrane, and thereby trigger basement membrane breakdown, at the onset of the EMT during gastrulation.

Y. Nakaya, E. W. Sukowati, Y. Wu, G. Sheng, RhoA and microtubule dynamics control cell-basement membrane interaction in EMT during gastrulation.
Nat. Cell Biol
.
10
, 765-775 (2008).
[PubMed]

R Levayer, T Lecuit, Breaking down EMT.
Nat. Cell Biol
.
10
, 757-759 (2008).
[PubMed]
Generating a Biological Oscillator
Authors: Ray L. Bryan
Published: September 2008

The components of many of the biochemical circuits that regulate biological functions have been described, and investigators are now able to explore how the components work together and why regulatory networks are connected in a particular way. Tsai
et al
. note that, although a simple negative feedback loop can create an oscillator, biological oscillators like the pacemaker of the heart or the cell cycle include both negative and positive feedback loops. Modeling of the properties of a range of circuits of these types confirms that the "negative plus positive feedback" option is better for biological applications. This circuit design enables a broad range of control of the frequency without changes in the amplitude of the output of the oscillator, whereas negative feedback alone made an oscillator with a more restricted range of function. Even when the frequency of oscillation does not need to be adjusted, there appear to be advantages to the more complicated circuit; it allows oscillating behavior over a much larger range of enzyme concentrations and kinetic constant values, which may contribute to adaptability during evolution.

T. Y.-C. Tsai, Y. S. Choi, W. Ma, J. R. Pomerening, C. Tang, J. E. Ferrell, Jr., Robust, tunable biological oscillations from interlinked positive and negative feedback loops.
Science
321
, 126-129 (2008).
[Abstract]
[Full Text]
Myosins Under Tension
Authors: Vinson Valda J.
Published: September 2008

Myosin I is a single-headed myosin molecule that plays a role in regulating membrane dynamics and structure in eukaryotic cells. Its best-characterized function is to provide tension to sensitize mechanosensitive ion channels responsible for hearing. Myosin I is thought to function by sensing tension and changing its motile properties in response to changes in loads. Laakso
et al
. used single-molecule measurements to characterize the motor activity of myosin I. Small resisting loads (<2 pN) resulted in a 75 times lower rate of myosin I detachment from actin, dramatically changing its motor properties. This acute sensitivity supports models in which myosin I functions as a molecular force sensor.

J. M. Laakso, J. H. Lewis, H. Shuman, E. M. Ostap, Myosin I can act as a molecular force sensor.
Science
321
, 133-136 (2008).
[Abstract]
[Full Text]
The Cytoplasmic Tail of MUC1: A Very Busy Place
Authors: Carson Daniel D.
Published: September 2008

The role of mucin 1 (MUC1) in protecting epithelia from microbial infection, enzymatic digestion, and other irritants has been appreciated for some time. In addition, MUC1 serves as a barrier to embryo implantation. MUC1 is highly abundant in many tumors in which its role in barrier function may serve to protect cells from the host immune system, whereas MUC1 is less abundant in certain other cells—for example, in trophoblasts and hematopoietic cells. Most of the functions of MUC1 depend upon its large, extracellular ectodomain. Nonetheless, a series of studies have demonstrated a surprisingly diverse role for the small, highly conserved cytoplasmic domain of MUC1 in intracellular signaling. These intracellular activities have potential roles in the physiology of both malignant and nonmalignant cells.
Tissue Inhibitors of Metalloproteinases in Cell Signaling: Metalloproteinase-Independent Biological Activities
Authors: Stetler-Stevenson William G.
Published: September 2008

Over the past 20 years, the tissue inhibitors of metalloproteinases (TIMPs) have been implicated in direct regulation of cell growth and apoptosis. However, the mechanisms of these effects have been controversial. Recent work by several laboratories has identified specific signaling pathways and cell surface binding partners for members of the TIMP family. TIMP-2 binding to the integrin α
3
β
1
is the first description of a cell surface receptor for a TIMP family member. TIMP-2 has been shown to induce gene expression, to promote G
1
cell cycle arrest, and to inhibit cell migration. TIMP-1 binding to CD63 inhibits cell growth and apoptosis. These new findings suggest that TIMPs are multifunctional and can act either directly through cell surface receptors or indirectly through modulation of protease activity to direct cell fate. The emerging concept is that TIMPs function in a contextual fashion so that the mechanism of action depends on the tissue microenvironment.
Bone Disease from a Placental Hypoxia Pathway
Authors: Gough Nancy R.
Published: September 2008

Osteoclasts are cells of a hematopoetic lineage that resorb bone, and excessive activity of these cells can lead to low bone mass with an associated increased incidence of fractures. These cells are also implicated in disorders such as Paget's disease of the bone and multiple myeloma. Osteoclast differentiation requires the transcription factor AP-1, which is a heterodimer of a Jun family member and a Fos family member. Bozec
et al
. found that mice deficient for the Fos family member Fra-2, which is encoded by
Fosl2
, exhibited increased osteoclast size (giant osteoclasts), number, and activity. The expression and abundance of the leukemia inhibitory factor (LIF) receptor (LIFR) were also decreased in the bones of
Fosl2
knockout mice. Chromatin immunoprecipitation experiments and reporter gene assays showed that
LIF
was a direct target of Fra-2 and Jun. Although no bone phenotype was reported for
LIF
knockout mice, Bozec
et al
. found that these mice had osteoclasts that were larger and more numerous with increased resorptive activity, which led to decreased bone volume. Fetal liver-derived osteoclast progenitor cells deficient in either Fra-2 or LIF did not differentiate in culture and exhibited increased apoptosis compared with wild-type cells; however, differentiation into osteoclasts was rescued by the addition of LIF. In vivo, the expression of
Bcl-2
, which encodes an antiapoptotic protein, was increased in the bones of Fra-2- or LIF-deficient animals. In vivo, osteoclasts were hypoxic and hypoxia-inducible factor-1α (HIF-1α) was abundant, and the mRNA for PHD2 (prolyl hydroxylase domain 2 protein, which contributes to HIF-1α destabilization) was decreased, suggesting that hypoxia may contribute to the giant osteoclast phenotype. In culture, the Fra-2- or LIF-deficient osteoclast progenitors exhibited decreased
Bcl-2
expression and increased cell death at 21% oxygen, and increased
Bcl-2
expression and less cell death at 3% oxygen. Thus, the loss of LIF signaling appears to alter the sensitivity of the cells to oxygen. Surprisingly, selective knockout of Fra-2 in the macrophage-osteoclast lineage did not show bone phenotypes in vivo, but isolated progenitor cells failed to differentiate in the absence of additional LIF. Instead, it appeared that the Fra-2 knockout mice had impaired placental function, because
LIF
and
LIFR
and
Phd2
expression were decreased in the placenta, and
HIF-1α
and its targets were increased. Thus, proper bone oxygenation in utero requires a functional LIF signaling axis that required Fra-2, and a similar pathway in the bone progenitors was required for proper oxygen responsiveness.

A. Bozec, L. Bakiri, A. Hoebertz, R. Eferl, A. F. Schilling, V. Komnenovic, H. Scheuch, M. Priemel, C. L. Stewart, M. Amling, E. F. Wagner, Osteoclast size is controlled by Fra-2 through LIF/LIF-receptor signalling and hypoxia.
Nature
454
, 221-225 (2008).
[PubMed]
Heading in the Wrong Direction?
Authors: Adler Elizabeth M.
Published: September 2008

The neurotransmitter dopamine is cleared from synapses by presynaptic dopamine transporters, which thus play a key role in regulating dopaminergic signaling. Mazei-Robison
et al
., who previously identified a mutant form of the dopamine transporter in two brothers with attention deficit hyperactivity disorder (ADHD), investigated the effects of this mutation on transporter function. When transfected into human embryonic kidney (HEK) 293T cells, the total and surface abundance of the mutant transporter [in which an alanine at residue 559 is substituted with valine (hDAT A559V)] was similar to that of the transfected wild-type human dopamine transporter (hDAT), as was dopamine uptake. Amperometric recordings of cells preloaded with dopamine, however, revealed that, whereas cells expressing hDAT showed little dopamine efflux, hDAT A559V cells exhibited pronounced dopamine efflux currents. Whole-cell patch clamp analysis combined with experiments in which the intracellular concentrations of Na
+
or dopamine were varied indicated that hDAT A559V showed an exaggerated increase in dopamine efflux in response to depolarization compared with hDAT and an increased sensitivity to intracellular Na
+
. Intriguingly, amphetamine, which is used to treat ADHD, enhanced hDAT-mediated dopamine efflux (as it typically does) but inhibited hDAT A559V–mediated efflux. The authors thus propose that alterations in dopamine efflux through hDAT may play a role in ADHD and perhaps other brain disorders associated with altered dopamine signaling.

M. S. Mazei-Robison, E. Bowton, M. Holy, M. Schmudermaier, M. Freissmuth, H. H. Sitte, A. Galli, R. D. Blakely, Anomalous dopamine release associated with a human dopamine transporter coding variant.
J. Neurosci
.
28
, 7040-7046 (2008).
[Abstract]
[Full Text]
Maintaining Cerebrovascular Integrity
Authors: Adler Elizabeth M.
Published: September 2008

The serine protease tissue plasminogen activator (tPA, a clot-busting enzyme that can be used to treat acute ischemic stroke) must be administered within hours of the onset of stroke symptoms, markedly limiting its clinical utility. With a delay of more than three hours, the risk of catastrophic brain hemorrhage as a complication of intravenous tPA treatment outweighs the potential benefits (see Rieckmann). Su
et al
., a group of researchers who previously showed that tPA increases cerebrovascular permeability independently of plasminogen (a substrate critical to tPA’s thrombolytic effects) and that platelet-derived growth factor-CC (PDGF-CC) is a tPA target, investigated the role of PDGF-CC in regulating cerebrovascular permeability. Intraventricular administration of tPA increased cerebrovascular permeability in mice, as did active PDGF-CC; moreover, the tPA-mediated increase was inhibited by neutralizing antibodies directed against PDGF-CC. tPA and PDGF-CC produced similar morphological changes in cerebral vasculature, predominantly areas of apparent fluid accumulation around arterioles; indeed, tpA, PDGF-CC, and the PDGF receptor-α (PDGFR-α) were all associated with brain arterioles, with PDGFR-α expressed in perivascular astrocytes. Middle cerebral artery occlusion (MCAO, a model of ischemic stroke) led to an increase in PDGFR-α phosphorylation (indicative of activation) in wild-type mice but not in mice lacking endogenous tPA. MCAO elicited an increase in cerebrovascular permeability, and treatment with the PDGFR-α inhibitor imatinib 1 hour after MCAO reduced this response. Imatinib also decreased the volume of infarct seen 72 hours after MCAO and decreased cerebral hemorrhage associated with tPA treatment administered 5 hours after MCAO. Thus, the authors propose that endogenous PDGF-CC may regulate blood-brain barrier permeability after ischemic stroke and that targeting signaling mediated through PDGF-CC and PDGFR-α with agents such as imatinib (an anticancer drug also known as Gleevec) may extend the therapeutic window for tPA treatment.

E. J. Su, L. Fredriksson, M. Geyer, E. Folestad, J. Cale, J. Andrae, Y. Gao, K. Pietras, K. Mann, M. Yepes, D. K. Strickland, C. Betsholtz, U. Eriksson, D. A. Lawrence, Activation of PDGF-CC by tissue plasminogen activator impairs blood-brain barrier integrity during ischemic stroke.
Nat. Med
.
14
, 731-737 (2008).
[PubMed]

P. Rieckmann, Imatinib buys time for brain after stroke.
Nat. Med
.
14
, 712-713 (2008).
[PubMed]
Finding and Building Connections
Authors: Gough Nancy R.
Published: September 2008

Three phases of excitatory glutamatergic synapse formation have been described for the mammalian central nervous system. First, there is a period with a slow rate of synapse formation, then a period with a rapid rate of synapse formation, and finally a maturation and pruning phase. Kayser
et al
. provide evidence in mice that the second phase of fast synapse formation involves EphB2, a receptor tyrosine kinase that is present on the nascent dendrites of the postsynaptic cell. In cortical neuron cultures or in slice preparations from triple-knockout (TKO) mice deficient for EphB1, EphB2, and EphB3, but not double knockouts (DKO) deficient for EphB1 and EphB3, the initial phase of synapse formation appears to proceed normally, but the rapid phase appears to be compromised. Further, the TKO cells exhibited decreased filopodial motility, despite having increased numbers of filopodia and decreased density of mature dendrites, a phenotype that was copied by RNA interference to reduce EphB2 in the postsynaptic cells. RNA interference experiments to decrease EphB2 or EphB2 rescue experiments at specific times during development of cultured neurons suggested that EphB2 may serve a key role in the rapid phase of synapse formation and contribute to maturation of the dendritic spine. In neurons in which EphB2 was knocked down, expression of a constitutively active form of the kinase PAK, which is downstream of EphB2 in the pathway that regulates the cytoskeleton and cell motility, restored filopodial motility but not synaptic density. In cells in which endogenous EphB2 was knocked down, expression of a kinase-defective mutant of EphB2 or a form that could not bind its ligand on the presynaptic neuron EphrinB did not restore synaptic density or filopodial motility. However, coexpression of the kinase-inactive form of EphB2 and PAK in the cells in which endogenous EphB2 was knocked down did restore both motility and synapse formation. Thus, forward signaling by EphB2 appears to control filopodial motility and the ability to find a presynaptic cell, whereas reverse signaling appears to allow a stable connection with the presynaptic cell, thereby promoting synapse formation.

M. S. Kayser, M. J. Nolt, M. B. Dalva, EphB receptors couple dendritic filopodia motility to synapse formation.
Neuron
59
, 56-69 (2008).
[PubMed]
Know Thyself
Authors: Ash Caroline
Published: September 2008

Cells of the pathogenic bacterium
Proteus mirabilis
clump together to form colonies that, on meeting other colonies, can distinguish self from foreigners.
Proteus
detects, then deters, interlopers of the same species using polypeptide weapons called proticines. Gibbs
et al.
investigated the genetic basis of this self-non-self recognition system in
Proteus
and discovered a locus of six genes that seem to constitute general and specific recognition determinants, as well as accessory genes. Within infected hosts,
P. mirabilis
infections are usually clonal, so this recognition system could be a way for an established clone to prevent superinfection by another clone and to avoid competition.

K. A. Gibbs, M. L. Urbanowski, E. P. Greenberg, Genetic determinants of self identity and social recognition in bacteria.
Science
321
, 256-259 (2008).
[Abstract]
[Full Text]
Stopping STIM Stops Strokes
Authors: Ray L. Bryan
Published: September 2008

Proper responses of platelets in the blood to various physiological signals are essential: Unresponsiveness prevents clotting at sites of wounds, but overactivity can contribute to heart attacks or stroke. Platelets respond to a number of factors, but the various signals all feed into activation of phospholipase C and consequent release of calcium from intracellular stores. Depletion of calcium from the intracellular stores then leads to influx of extracellular calcium. The STIM1 protein (stromal interaction molecule 1) functions in detection of store emptying and activation of store-operated channels that allow calcium entry. Varga-Szabo
et al
. used knockout mice in which the
Stim 1
gene was disrupted to study the role of STIM1 in arterial thrombosis and ischemic brain infarction. The
Stim 1
–/–
animals died a few hours after birth, but the authors were able to transplant bone marrow from the knockout animals to lethally irradiated host mice to study platelet function. In two in vivo models of arterial thrombosis induced by injury, formation of occlusive thrombi was inhibited in the
Stim 1
–/–
animals. Similarly, in a model of ischemic brain infarction induced by restriction of blood flow through the middle cerebral artery, infarct size was reduced in the
Stim 1
–/–
animals. Most animals with the
Stim 1
–/–
platelets stopped bleeding from a wound at the tail tip within about 10 minutes, as did wild-type mice. The response was more variable in the

Stim 1
–/–

animals, however, and about 35% of the animals showed longer bleeding. Because of this relatively mild effect on bleeding, the authors propose that inhibitors of Stim 1 might be attractive as antithrombolitics that could help treat stroke patients without the unacceptable side effect of increased intracerebral hemorrhage. As a caveat, the authors do note that results in the mouse models may not necessarily be directly comparable to the situation in humans.

D. Varga-Szabo, A. Braun, C. Kleinschnitz, M. Bender, I. Pleines, M. Pham, T. Renné, G. Stoll, B. Nieswandt, The calcium sensor STIM1 is an essential mediator of arterial thrombosis and ischemic brain infarction.
J. Exp. Med
.
205
, 1583-1591 (2008).
[Abstract]
[Full Text]
Science Signaling
Podcast: 15 July 2008
Authors: Foley John F. , VanHook Annalisa M.
Published: September 2008

This conversation is about research highlighted in the Editors' Choice summary titled, "Macrophages Go Back to School." The highlighted articles are T. Hagemann, T. Lawrence, I. McNeish, K. A. Charles, H. Kulbe, R. G. Thompson, S. C. Robinson, F. R. Balkwill, "Re-educating" tumor-associated macrophages by targeting NF-κB.
J
.
Exp
.
Med
.
205
, 1261-1268 (2008), and C. H. Y. Fong, M. Bebien, A. Didierlaurent, R. Nebauer, T. Hussell, D. Broide, M. Karin, T. Lawrence, An antiinflammatory role for IKKβ through the inhibition of "classical" macrophage activation.
J
.
Exp
.
Med
.
205
, 1269-1276 (2008). (Length: 11 min; file size: 5.00 MB; file format: mp3; location:
http://podcasts.aaas.org/science_signaling/ScienceSignaling_080715.mp3
)
Ethanol’s Molecular Targets
Authors: Harris R. Adron , Trudell James R. , Mihic S. John
Published: September 2008

Ethanol produces a wide variety of behavioral and physiological effects in the body, but exactly how it acts to produce these effects is still poorly understood. Although ethanol was long believed to act nonspecifically through the disordering of lipids in cell membranes, proteins are at the core of most current theories of its mechanisms of action. Although ethanol affects various biochemical processes such as neurotransmitter release, enzyme function, and ion channel kinetics, we are only beginning to understand the specific molecular sites to which ethanol molecules bind to produce these myriad effects. For most effects of ethanol characterized thus far, it is unknown whether the protein whose function is being studied actually binds ethanol, or if alcohol is instead binding to another protein that then indirectly affects the functioning of the protein being studied. In this Review, we describe criteria that should be considered when identifying alcohol binding sites and highlight a number of proteins for which there exists considerable molecular-level evidence for distinct ethanol binding sites.
A Virulent Response to Losing Your Tail
Authors: Adler Elizabeth M.
Published: September 2008

The bacterium
Vibrio cholerae
(which causes the diarrheal disease cholera) secretes and detects signals that lead to the transcriptional repression of virulence genes by means of the regulator HapR; thus, its expression of virulence factors decreases with increased population density. Liu
et al
. used an antibiotic-coupled transposon screen to identify signals that might regulate virulence through this quorum-sensing pathway. Intriguingly, mutation of various genes involved in biosynthesis of
V. cholerae
’s flagellum decreased HapR activity and increased the production of virulence factors. Deletion of
flgD
, which encodes a flagellar rod protein, inhibited transcription of a
hapR
transcriptional reporter and that of a reporter activated by HapR, but promoted transcription of a reporter inhibited by HapR as well as production of virulence factors. Constitutive activation of the gene encoding FliA, which is involved in the activation of some flagellar genes, also promoted virulence factor production. Noting that FliA activity increases with the secretion of its inhibitor FlgM through the flagellar export apparatus, the authors determined that FlgM concentration was greater in supernatants from
flgD
mutant cultures than in those from wild-type cultures. Moreover, the effects of the
flgD
mutant on
hapR
expression were mediated through FliA.
V. cholerae
must traverse a layer of mucus to colonize intestinal epithelial cells, and both flagellar staining and electron microscopic analysis revealed that more than 80% of wild-type
V. cholerae
lost their flagellae while swimming through 1% mucin. The concentration of FlgM was higher in supernatants of cultures containing mucin, and
hapR
expression was decreased in mucin-exposed bacteria. Thus, the authors suggest that signals encountered en route to the epithelial cells may enable
V. cholerae
to jettison HapR-mediated repression of virulence at precisely the right time and place.

Z. Liu, T. Miyashiro, A. Tsou, A. Hsiao, M. Goulian, J. Zhu, Mucosal penetration primes
Vibrio cholerae
for host colonization by repressing quorum sensing.
Proc. Natl. Acad. Sci. U.S.A.
105
, 9769-9774 (2008).
[Abstract]
[Full Text]
Interleukin-15 Delivery Service
Authors: Gough Nancy R.
Published: September 2008

Cytokines are secreted immune signaling molecules, and regulating their release is an important mechanism for controlling their activity. The long form of interleukin-15 (IL-15) is a glycosylated protein that is secreted through the classical secretory pathway from endoplasmic reticulum to Golgi to cell surface. However, in some cells the mRNA for IL-15 is present, yet IL-15 is not secreted. In these cells, the receptor that binds IL-15, IL-15Rα, is not expressed. By expressing IL-15 with or without its receptor IL-15Rα or with variants of the receptor that could not bind IL-15 or were not membrane-associated in COS-7 cells, Duitman
et al
. showed that transit of IL-15 from the endoplasmic reticulum through the Golgi to the surface required IL-15Rα. When the IL-15 binding site was mutated, IL-15 was retained in the cells in a form that was sensitive to the glycanase Endo H, indicating that it did not proceed through the Golgi but had reached the endoplasmic reticulum. When IL-15 was expressed with an IL-15Rα that lacked a transmembrane domain, the proteins were secreted into the supernatant and did not associate with the cell surface. Monocytes stimulated with interferon-γ (IFN-γ) showed increased transcription of both IL-15 and IL-15Rα and increased secretion of IL-15. Release of IL-15 from the surface of cells cotransfected with IL-15 and IL-15Rα, or from IFN-γ-stimulated monocytes, required proteolysis, which was inhibited by general matrix metalloproteinase inhibitor GM6001. Secretion of IL-15 from cells coexpressing the transmembrane-lacking mutant IL-15Rα was unaffected by GM6001. IL-15 acts as a cell surface-associated juxtacrine signal, and this receptor-mediated mechanism of cell surface delivery explains how the cytokine may be presented to adjacent cells.

E. H. Duitman, Z. Orinska, E. Bulanova, R. Paus, S. Bulfone-Paus, How a cytokine is chaperoned through the secretory pathway by complexing with its own receptor: Lessons from interleukin-15 (IL-15)/IL-15 receptor α.
Mol. Cell. Biol.
28
, 4851-4861 (2008).
[Abstract]
[Full Text]
Positive Peroxidation
Authors: Foley John F.
Published: September 2008

Ingestion of the ω-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) reduces inflammation in vivo, which is thought to involve inhibition of nuclear factor κB (NF-κB) signaling; however, the precise mechanisms involved are unknown. To further complicate matters, DHA is highly susceptible to peroxidation by free radicals, which results in the production of a number of bioactive lipid products, thus making it unclear whether DHA or one of its metabolites is the anti-inflammatory agent. The cyclopentenone neuroprostanes (A
4
/J
4
-NPs) form one group of DHA metabolites, and Musiek
et
al
. investigated the effects of a synthetic A
4
/J
4
-NP called A
4
-NP on inflammatory responses in the mouse macrophage cell line RAW267.4. They found that pretreatment of RAW267.4 cells with A
4
-NP dose-dependently blocked lipopolysaccharide (LPS)-induced expression of the genes encoding two proinflammatory proteins, inducible nitric oxide synthase and cyclooxygenase-2. A combination of NF-κB-reporter assays, immunofluorescence staining, and Western blotting analyses demonstrated that A
4
-NP blocked LPS-induced responses by inhibiting the activity of inhibitor of κB (IκB) kinase β (IKKβ), thus preventing the phosphorylation of IκB and the translocation of NF-κB to the nucleus. However, A
4
-NP did not inhibit the activity of a mutant IKKβ that lacked Cys
179
, which suggests that A
4
-NP forms an adduct with the thiol group of this residue to inactivate IKKβ. Elimination of the bioactivity of A
4
-NP through chemical reduction or by complex formation with glutathione prevented it from modifying and inhibiting IKKβ activity. The authors also found that A
4
/J
4
-NPs were more abundant in the brains of patients with Alzheimer’s disease than in those of controls, which suggests that in vivo oxidation of DHA may contribute to its anti-inflammatory role.

E. S. Musiek, J. D. Brooks, M. Joo, E. Brunoldi, A. Porta, G. Zanoni, G. Vidari, T. S. Blackwell, T. J. Montine, G. L. Milne, B. McLaughlin, J. D. Morrow, Electrophilic cyclopentenone neuroprostanes are anti-inflammatory mediators formed from the peroxidation of the ω-3 polyunsaturated fatty acid docosahexaenoic acid.
J
.
Biol
.
Chem
.
283
, 19927-19935 (2008).
[Abstract]
[Full Text]
Phosphorylation Inside-Out
Authors: Ray L. Bryan
Published: September 2008

A signaling pathway called the Hippo pathway has important roles in the control of tissue organization in development and in the regulation of organ size in the fruit fly. Hippo is a protein kinase that appears to pass signals from atypical cadherin molecules Fat and Dachsous at the cell surface to another intracellular kinase, Warts, which then regulates a transcriptional coactivator. Another protein somewhat distantly related to the protein kinases, Four-jointed, has also been implicated genetically in the pathway. Ishikawa
et al
. provide evidence that Four-jointed, which is localized to the Golgi complex, is indeed a kinase and that it appears to phosphorylate the cadherin domains of Fat and Dachsous, which will become extracellular domains at the cell surface.

H. O. Ishikawa, H. Takeuchi, R. S. Haltiwanger, K. D. Irvine, Four-jointed is a Golgi kinase that phosphorylates a subset of cadherin domains.
Science
321
, 401-404 (2008).
[Abstract]
[Full Text]
Sleepless
in
Drosophila
Authors: Kelner Katrina L.
Published: September 2008

All animals sleep, and the longer they are awake, the stronger the drive to sleep. To better understand the process of sleep, Koh
et al
. screened mutagenized
Drosophila
for genes involved in sleep regulation. They found one—
sleepless
—that is required for normal sleep; without
sleepless
, flies sleep much less, about 20% of normal.
Sleepless
is also required for rebound sleep after prolonged waking.
Sleepless
is an allele of
quiver
, a gene that modulates the K
+
channel activity encoded by
Shaker
, which also affects sleep. K
+
channel-associated neuronal sensitivity may thus play a role in the control of sleep, and the SLEEPLESS protein may signal the drive to sleep by decreasing membrane excitability.

K. Koh, W. J. Joiner, M. N. Wu, Z. Yue, C. J. Smith, A. Sehgal, Identification of SLEEPLESS, a sleep-promoting factor.
Science
321
, 372-376 (2008).
[Abstract]
[Full Text]
Nailing a Riboswitch
Authors: Riddihough Guy
Published: September 2008

In bacteria, the second messenger cyclic di-guanosine monophosphate (di-GMP) regulates a wide range of genes and affects diverse physiological (and disease-causing) processes. It has been suggested that cyclic di-GMP may modulate transcription and translation via specific cyclic di-GMP riboswitches. Sudarsan
et al.
now show that this is indeed so and that cyclic di-GMP, and not its closely related breakdown products, binds to the highly conserved GEMM RNA domain, which is found upstream of both cyclic di-GMP synthesis and degradation enzymes, as well as likely target genes. The GEMM RNA constitutes the aptamer domain of the cyclic di-GMP riboswitch. The riboswitch is also found in bacteriophages, which suggests that viruses monitor and respond to the cyclic di-GMP-driven physiological transformations of their hosts.

N. Sudarsan, E. R. Lee, Z. Weinberg, R. H. Moy, J. N. Kim, K. H. Link, R. R. Breaker, Riboswitches in eubacteria sense the second messenger cyclic di-GMP.
Science
321
, 411-413 (2008).
[Abstract]
[Full Text]
Dead but Not Deadly
Authors: Ray L. Bryan
Published: September 2008

The presence of cells dying by the process of necrosis is a signal for activation of the adaptive immune system and a stimulus for an inflammatory response to protect the organism from the threat that is damaging the dying cells. However, billions of cells in the human immune system die every day by apoptosis, a more orderly physiological form of cell death, and these dying cells are actually anti-inflammatory and promote tolerance of antigens by the immune system. Kazama
et al
. show that one key difference that influences the immunogenicity of the dying cells is the disruption of mitochondrial function in apoptotic cells and consequent generation of reactive oxygen species (ROS). The authors used an assay of immunogenicity in which mice exposed to dying cells were subsequently exposed to antigens. Treatment of apoptotic cells with the reducing agent dithiothreitol (DTT) prevented their promotion of tolerance, and exposure of necrotic cells to the oxidant hydrogen peroxide made them promote tolerance rather than inflammation. The authors focused on high-mobility group box-1 (HMGB1), a protein that binds chromatin and acts as a transcription factor but also functions as an inflammatory cytokine. Release of HMGB1 had been proposed to be a marker of necrotic death, but Kazama
et al
. saw release of the protein from both apoptotic and necrotic cells. What differed was the oxidation state of HMGB1. Supernatants from apoptotic cells could promote tolerance, but this effect was prevented if ROS species were neutralized with a scavenger or if oxidation of HMGB1 was prevented by mutation of cysteine residues that likely mediate its response to oxidation. Recombinant human HMGB1 could also eliminate the tolerogenic effect of apoptotic cells if the HMGB1 was first treated with DTT, but not if the HMGB1 was first oxidized with hydrogen peroxide. Peter provides commentary and notes that the studies open the way for exploration of how dendritic cells specifically recognize oxidized HMGB1 and what signaling pathways are activated--work that may allow these new concepts to be exploited to modulate immunological activation in patients.

H. Kazama, J.-E. Ricci, J. M. Herndon, G. Hoppe, D. R. Green, T. A. Ferguson, Induction of immunological tolerance by apoptotic cells requires caspase-dependent oxidation of high-mobility group box-1 protein.
Immunity
29
, 21-32 (2008).
[PubMed]

M. E. Peter, ROS eliminate danger.
Immunity
29
, 1-2 (2008).
[PubMed]
Host-Directed Drug Targeting of Factors Hijacked by Pathogens
Authors: Schwegmann Anita , Brombacher Frank
Published: September 2008

The current paradigm for managing infectious diseases has targeted unique processes or enzymes within pathogens. A serious disadvantage of this pathogen-directed drug targeting strategy has been the development of microbial drug resistance and consequent resurgence of once-contained infectious diseases. A new drug discovery paradigm has therefore emerged focusing on identifying and targeting host factors essential for pathogen entry, survival, and replication. Innovative strategies combining genome-wide computational biology, genomics, proteomics, and traditional forward and reverse genetics have identified host-pathogen interactions and host functions critical for the establishment of infection. Chemogenomics and chemical genetics have allowed rapid identification of new and existing licensed drugs with antimicrobial activity. Although most host-directed drug targeting studies have focused on viral infections, they have provided a proof of concept for similar approaches to bacterial and parasite infections. Future therapies may combine conventional targeting of microbial virulence factors, together with host-directed drug therapy and augmentation of protective host factors, to efficiently eliminate the invading pathogen.