bluuebunny/crossref_metadata_2025 huggingface dataset:
Slow Breathing
Authors: Adler Elizabeth M.
Published: June 2008

The mitochondrial scaffolding protein A-kinase anchor protein 121 (AKAP121) assembles a signaling complex that includes components of the cAMP (adenosine 3',5'-monophosphate) and Src signaling pathways, facilitating their stimulation of mitochondrial metabolism. Carlucci
et al
. identified the E3-ubiquitin ligase Siah2 as an AKAP121 binding partner in a yeast two-hybrid screen and confirmed the interaction through in vitro assays, coimmunoprecipitation from human embryonic kidney (HEK) 293 cell lysates, and immunostaining of mouse fibroblasts. Cotransfection of HEK293 cells with AKAP121 increased association of a Siah2 mutant that lacked E3-ubiquitin ligase activity (Siah2
rm
) with mitochondria, and cotransfection with Siah2 (but not Siah2
rm
) markedly decreased AKAP121 abundance. Hypoxia promotes
Siah2
transcription, and oxygen and glucose deprivation (OGD) stimulated a Siah2-dependent decrease in the abundance of AKAP121 transfected into HEK293 cells and of endogenous AKAP121 in cultured rat hippocampal neurons and mouse fibroblasts. AKAP121 was a substrate for Siah2 ubiquitination in vitro, and Siah2 overexpression promoted the ubiquitination and proteasomal degradation of AKAP121 in HEK293 cells, as did OGD. When transfected into HEK293 cells, AKAP121 increased mitochondrial membrane potential (ΔΨ
m
) and metabolic activity and opposed decreases in ΔΨ
m
and mitochondrial metabolic activity produced by OGD; Siah2 decreased basal ΔΨ
m
and metabolic activity and opposed the effects of AKAP121. Further, siRNA directed against Siah2 increased metabolic activity in cells exposed to OGD. Occlusion of the middle cerebral artery in rats (which causes ischemic damage to the frontal cortex) led to a decrease in AKAP121 immunoreactivity in neurons in the ischemic region, which was blocked by siRNA directed against Siah2. The authors thus conclude that degradation of AKAP121 by Siah2 provides a mechanism whereby mitochondrial respiration can be slowed under hypoxic conditions.

A. Carlucci, A. Adornetto, A. Scorziello, D. Viggiano, M. Foca, O. Cuomo, L. Annunziato, M. Gottesman, A. Feliciello, Proteolysis of AKAP121 regulates mitochondrial activity during cellular hypoxia and brain ischaemia.
EMBO J.
27
, 1073-1084 (2008).
[PubMed]
Balancing Stability and Dynamics
Authors: VanHook Annalisa M.
Published: June 2008

During collective migration events, groups of cells must balance adhesion to one another with the ability to make and break contacts with the substrate. Border cell migration in
Drosophila
oogenesis is a collective migration in which six to eight cells delaminate from the epithelium surrounding the egg chamber and migrate as a cluster to the anterior end of the oocyte. New studies from Melani
et al.
and Llense and Martín-Blanco show that the Jun N-terminal kinase (JNK) and signal transducer and activator of transcription (STAT) signaling pathways are required to fine-tune the balance between adhesion and migration in border cells. In the first study, Melani
et al.
found that border cells lacking Hindsight (Hnt), a transcription factor that inhibits JNK signaling, failed to delaminate and had greater than normal amounts of the adhesion proteins Armadillo (Arm, a β-catenin homolog) and DE-Cadherin (Cad) on their surfaces. When Hnt was overexpressed in border cells, the amount of Arm and Cad on the cell surfaces was less than normal, and the clusters dissociated so completely that migration failed. The Llense and Martín-Blanco study found that JNK signaling modulated abundance of the adherens junction component Bazooka and the cytoskeletal adapter D-Paxillin in border cells. Both studies showed that mutations in JNK pathway components caused border cell clusters to dissociate without completely disrupting their migration, indicating that precise control of JNK signaling is required to regulate adhesion between border cells but not between the border cells and the substrate. Melani
et al
. also determined that Hnt overexpression reduced STAT activation in the border cells, and mutations in STAT pathway components caused migration defects without dissociation. Finally, the authors demonstrated that the human homolog of Hnt was required for collective migration of breast epithelial cells in a wound-healing assay. These papers provide evidence that the JNK and STAT signaling pathways contribute to distinct aspects of collective migration and that the strength of adhesion between migrating cells is proportional to JNK signaling activity.

M. Melani, K. J. Simpson, J. S. Brugge, D. Montell, Regulation of cell adhesion and collective cell migration by Hindsight and its human homolog RREB1.
Curr. Biol
.
18
, 532-537 (2008).
[PubMed]

F. Llense, E. Martín-Blanco, JNK signaling controls border cell cluster integrity and collective cell migration.
Curr. Biol
.
18
, 538-544 (2008).
[PubMed]
Bcl2 Blocks DNA Repair
Authors: Gough Nancy R.
Published: June 2008

Bcl2 is an oncogenic protein best known for its role as an inhibitor of apoptosis through its actions at the mitochondria. However, Bcl2 was initially identified as associated with a chromosomal breakpoint, not as a mitochondrial protein, which suggests that it has additional functions beyond those at the mitochondria. Zhao
et al
. report that a nuclear function of Bcl2 appears to be inhibition of the DNA repair enzyme APE1, which mediates the repair of apurinic/apyrimidinic (also known as abasic) sites that occur thousands of times each day in a cell due to various environmental stresses. Abasic sites are produced by the carcinogen nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which is found in cigarette smoke. First the authors compared the abasic site repair activity in human lung cancer cell lines and found that there was an inverse correlation between the repair activity and the abundance of Bcl2. When Bcl2 was overexpressed in cells in which endogenous Bcl2 was undetectable, APE1 activity was reduced. Furthermore, in the Bcl2-overexpressing cells, abasic sites induced by NNK were more abundant than in cells transfected with vector alone. Cell lines in which endogenous Bcl2 was abundant exhibited nuclear accumulation, without loss of Bcl2 from the mitochondria, in response to exposure to NNK, and in NNK-treated cells Bcl2 and APE1 coimmunoprecipitated. The interaction between Bcl2 and APE1 and the ability of Bcl2 to inhibit APE1 activity in vitro and abasic site repair in cultured cells required all four BH3 domains of Bcl2. Finally, the endonuclease activity of APE1 is enhanced by interaction with XRCC1, and this interaction was diminished in cells overexpressing Bcl2, and the APE1-XRCC1 complex was dissociated in vitro when purified Bcl2 was added. Thus, inhibition of DNA repair may contribute to the oncogenic properties of Bcl2.

J. Zhao, F. Gao, Y. Zhang, K. Wei, Y. Liu, X. Deng, Bcl2 inhibits abasic site repair by down-regulating APE1 endonuclease activity.
J. Biol. Chem.
283
, 9925-9932 (2008).
[Abstract]
[Full Text]
Fast Receptors in Every Respect
Authors: Stern Peter
Published: June 2008

Lateral diffusion of receptors has been characterized as an important process for receptor trafficking in and out of synapses. The demonstration of this role has been limited to relatively slow events (in the range of minutes) that occur during development or turnover of receptors, during basal transmission, or during certain forms of neuronal plasticity. Heine
et al.
(see the Perspective by Silver and Kanichay) now report that receptor lateral movements are also involved in fast (tens of milliseconds) regulation of synaptic transmission. Recovery from synaptic depression involves exchange of desensitized receptors with functional ones through lateral movements within or from nearby the postsynaptic density.

M. Heine, L. Groc, R. Frischknecht, J.-C. Béïque, B. Lounis, G. Rumbaugh, R. L. Huganir, L. Cognet, D. Choquet, Surface mobility of postsynaptic AMPARs tunes synaptic transmission.
Science
320
, 201-205 (2008).
[Abstract]
[Full Text]

R. A. Silver, R. T. Kanichay, Refreshing connections.
Science
320
, 183-184 (2008).
[Summary]
[Full Text]
GABA Effects on Neurogenesis: An Arsenal of Regulation
Authors: Yuan Ti-Fei
Published: June 2008

The well-known inhibitory neurotransmitter GABA is excitatory to immature neurons during development as well as to neural progenitor cells during adult neurogenesis. Recent evidence indicates that GABA plays a role in regulating neurogenesis in various situations. This journal club paper aims to provide a skeleton description of GABA regulation of neurogenesis, describing some of the disparate mechanisms and scenarios in which it is involved.
Eph, a Protein Family Coming of Age: More Confusion, Insight, or Complexity?
Authors: Lackmann Martin , Boyd Andrew W.
Published: June 2008

Since the mid-1980s, Eph receptors have evolved from being regarded as orphan receptors with unknown functions and ligands to becoming one of the most complex "global positioning systems" that regulates cell traffic in multicellular organisms. During this time, there has been an exponentially growing interest in Ephs and ephrin ligands, coinciding with important advances in the way biological function is interrogated through mapping of genomes and manipulation of genes. As a result, many of the original concepts that used to define Eph signaling and function went overboard. Clearly, the need for progress in understanding Eph-ephrin biology and the underlying molecular principles involved has been compelling. Many cell-positioning programs during normal and oncogenic development—in particular, the patterning of skeletal, vascular, and nervous systems—are modulated in some way by Eph-ephrin function. Undeniably, the complexity of the underlying signaling networks is considerable, and it seems probable that systems biology approaches are required to further improve our understanding of Eph function.
Don’t Try This at Home
Authors: Ray L. Bryan
Published: June 2008

The most common source of genetic variation that can lead to evolution is certainly single-nucleotide mutations. But less frequent events like gene duplication are likely also important, as they allow more dramatic changes that result in rewiring of genetic regulatory networks. Isalan
et al
. explored in bacteria the repercussions of duplication events that would allow splicing of a regulatory promoter sequence of one gene with the open reading frame of another gene. They engineered almost 600 such events in genes encoding transcription factors and monitored effects on survival, growth, and evolvability of the bacterial strains. The remarkable robustness of gene regulatory networks was confirmed by the fact that over 95% of these changes did not prevent viability of the bacteria. Only 16% of the strains showed any change in growth, and some grew even better than wild-type bacteria. The authors also subjected the strains to selective pressures in the lab over many generations and found that even their relatively small (in evolutionary terms) sampling of 600 new networks yielded a dozen or so with apparent evolutionary advantages in fitness. Although some of the rewiring events caused new positive or negative transcriptional feedback loops, these did not cause changes in the amounts of green fluorescent protein–tagged proteins produced from the experimental genes. This suggests that the regulatory networks themselves can compensate for such a change and emphasize that posttranscriptional mechanisms should not be underestimated in comparison with transcriptional control mechanisms. Bennett and Hasty add valuable commentary, noting that you would not want to try such rewiring of processing units in your home computer (analogies between biological control mechanism and systems design in modern technology go only so far) and that advocates of "intelligent design" who claim that the complexity of biological systems would cause them to fail in the presence of randomly generated changes will have to take into account these new data to the contrary.

M. Isalan, C. Lemerle, K. Michalodimitrakis, C. Horn, P. Beltrao, E. Raineri, M. Garriga-Canut, L. Serrano, Evolvability and hierarchy in rewired bacterial gene networks.
Nature
452
, 840-845 (2008).
[PubMed]

M. R. Bennett, J. Hasty, Genome rewired.
Nature
452
, 824-825 (2008).
[PubMed]
Enhancing the Immune Response
Authors: Adler Elizabeth M.
Published: June 2008

Although aluminum-containing adjuvants are widely used in vaccines, the mechanisms whereby they potentiate the immune response have been unclear. Various agents with adjuvant activity stimulate maturation of dendritic cells (DCs), which are critical to activating adaptive immune responses; however, in vitro studies have not found any effect of aluminum-containing adjuvants on DC maturation. Kool
et al
. used mice that had received fluorescently labeled T cells that recognized ovalbumin (OVA) to establish that OVA emulsified with a suspension of aluminum hydroxide and magnesium hydroxide (OVA-alum) elicited a larger and more prolonged immune response than did OVA alone. Intraperitoneal (i.p.) injection of OVA-alum stimulated the rapid recruitment to the peritoneal cavity of inflammatory monocytes as well as a later increase in myeloid and plasmacytoid DCs, neutrophils, and eosinophils. OVA-alum stimulated more OVA uptake and processing by peritoneal CD11c
+
DCs than did OVA. Further, it stimulated DC maturation, ability to stimulate T cell proliferation, and migration to draining lymph nodes. Indeed, OVA-alum stimulated OVA uptake by inflammatory monocytes and their stimulation of T cell proliferation, as well as their migration to draining lymph nodes, expression of CD11c, and conversion to DCs. Depletion of DCs resident in specific lymph nodes abolished stimulation of T cell proliferation in those nodes by i.p. OVA, but not OVA-alum, whereas systemic depletion of CD11c
+
cells during immunization abolished OVA-alum’s adjuvant activity. Unlike saline or OVA, i.p. injection of OVA-alum increased peritoneal uric acid concentration. Uricase abolished OVA-alum–dependent recruitment of inflammatory monocytes to lymph nodes (also lost in mice lacking MyD88, which has been implicated in the inflammatory response to uric acid) and its adjuvant effect. The authors thus conclude that the immunostimulatory activity of aluminum-containing adjuvants depends on activation of DCs by uric acid.

M. Kool, T. Soullié, M. van Nimwegen, M. A. M. Willart, F. Muskens, S. Jung, H. C. Hoogsteden, H. Hammad, B. N. Lambrecht, Alum adjuvant boosts adaptive immunity by inducing uric acid and activating inflammatory dendritic cells.
J. Exp. Med.
205
, 869-882 (2008).
[Abstract]
[Full Text]
Receptor-dsRNA-Receptor
Authors: Vinson Valda J.
Published: June 2008

Toll-like receptors recognize molecules associated with pathogens and initiate inflammatory responses. For example, Toll-like receptor 3 (TLR3) recognizes double-stranded RNA (dsRNA), an intermediate viral replication. The TLR3 ectodomain binds as a dimer to dsRNA, but the molecular basis for signaling remains unclear. Liu
et al
. now report the structure of a complex between two mouse TLR3 ectodomains and dsRNA. Two horseshoe-shaped TLR3-ectodomain monomers bind to opposite faces of the dsRNA through their N and C termini and dimerize through their C termini so that the N termini are at opposite ends of the linear dsRNA molecule. This dimerization mode could mediate signal transduction by facilitating dimerization of the receptor cytoplasmic domains.

L. Liu, I. Botos, Y. Wang, J. N. Leonard, J. Shiloach, D. M. Segal, D. R. Davies, Structural basis of Toll-like receptor 3 signaling with double-stranded RNA.
Science
320
, 379-381 (2008).
[Abstract]
[Full Text]
Nuclear Lamin for Gene Silencing
Authors: Gough Nancy R.
Published: June 2008

In the
Drosophila
ovary, germline stem cells (GSCs) divide to produce one cell that differentiates (a cystoblast) and one stem cell. The stem cell population is maintained by the release of Decapentaplegic (Dpp, a member of the bone morphogenetic protein family) from the stromal somatic cap cells (niche cells), which silences the gene
bag-of-marbles
(
bam
), which is required for cystoblast differentiation. Jiang
et al
. identified
otefin
(
ote
), which encodes a nuclear lamin protein of the LEM family (containing an LEM domain), in a screen for female sterile flies. The germaria (the site of the stem cell population and cystoblast formation) of the mutant flies contained very few germ cells. When GSCs were marked with green fluorescent protein (GFP), the authors found that the number of GSCs declined to nearly absent in Ote-deficient GSCs, whereas wild-type GSCs persisted, which is consistent with excessive differentiation and lack of self-renewal of the GSC population in the
ote
mutants. Ote was required in the GSCs because reintroduction of
ote
into the somatic cells only failed to rescue the mutant ovary phenotype of the Ote-deficient animals. Overexpression of Ote led to an increased number of GSC-like cells, which suggests that excess Ote may suppress or delay differentiation. Bam was detected by expression of a fusion protein, and in Ote-deficient GSCs Bam-GFP was abundant, whereas in wild-type GSCs Bam-GFP was undetectable.
Bam
expression is inhibited by Dpp signaling. The authors showed that a genetic interaction occurred between signaling components of the Dpp pathway and Ote, and that when an inhibitor of Dpp signaling was overexpressed, forced overexpression of Ote led to a loss of GSCs. Thus, Dpp signaling appeared to be required for Ote to stimulate stem cell self-renewal. Ote required nuclear membrane localization and the LEM domain to function in the GSCs because introduction of Ote lacking the transmembrane domain or the LEM domain or targeted to the plasma membrane with a different transmembrane domain failed to rescue the mutant ovary phenotype. Endogenous Ote and Smad4 (called Medea in flies) coimmunoprecipitated when a tagged form of Medea was transfected into S2 cells; this interaction required the LEM domain of Ote. Ote and Medea were also found bound to the
Bam
silencer region in chromatin immunoprecipitation experiments with S2 cells, and the binding of Ote was lost if endogenous Medea was knocked down with siRNA. Thus, signal-dependent gene silencing in the GSCs appears to involve an interaction between the chromatin, the nuclear envelope through Ote, and the transcription factor Medea.

X. Jiang, L. Xia, D. Chen, Y. Yang, H. Huang, L. Yang, Q. Zhao, L. Shen, J. Wang, D. Chen, Otefin, a nuclear membrane protein, determines the fate of germline stem cells in
Drosophila
via interaction with Smad complexes.
Dev. Cell
14
, 494-506 (2008).
[PubMed]
Autonomous Tracheal Sprouting
Authors: VanHook Annalisa M.
Published: June 2008

Hypoxia-inducible factor (HIF) signaling is important for regulating the oxidative stress response as well as for branching morphogenesis of tubular oxygen-delivering tissues such as vertebrate blood vessels. Centanin
et al
. investigated the role of Similar (Sima), a homolog of the transcription factor HIF-α, and its repressor Fatiga (Fga) in
Drosophila
tracheal development. Under normal oxygen conditions, Sima is marked for degradation by Fga-mediated hydroxylation; under hypoxic conditions, this oxygen-dependent reaction slows and Sima accumulates, stimulating transcription of hypoxia-inducible genes. Trachea of
fga
loss-of-function mutants sprouted more branches than wild-type trachea, and overexpression of
sima
in the trachea, but not in tissues surrounding the trachea, was sufficient to induce extra branching.
sima
loss-of-function mutants, however, had wild-type tracheal branching when reared in normoxic conditions. Under hypoxic conditions,
sima
induced expression of the fibroblast growth factor (FGF) receptor
breathless
(
btl
) in trachea and the FGF
branchless
(
bnl
) in tissue around the trachea. In normal development, Btl and Bnl are essential for tracheal branching:
btl
-expressing tracheal cells are attracted to target tissues that secrete Bnl. These data suggest that all aspects of
Drosophila
tracheal branching are genetically programmed but that under hypoxic conditions the HIF pathway stimulates extra tracheal branching via the well-characterized Btl/Bnl chemoattraction system. Thus, the Sima-Fga oxygen sensor is required in both trachea and surrounding tissues for hypoxia-induced branching, and the trachea may initiate branching independently of signaling from the target tissue.

L. Centanin, A. Dekanty, N. Romero, M. Irisarri, T. A. Gorr, P. Wappner, Cell autonomy of HIF effects in
Drosophila
: Tracheal cells sense hypoxia and induce terminal branch sprouting.
Dev. Cell
14
, 547-558 (2008).
[PubMed]
The Yin and Yang of Neuronal Maintenance
Authors: Ray L. Bryan
Published: June 2008

During development, more peripheral neurons project to target organs than are ultimately needed. The neurons then compete for neurotrophic factors that are secreted by target cells. Deppmann
et al
. now explain how some neurons manage to survive, whereas others die, even though they have similar access to sustaining growth factors. The answer appears to depend on a series of feedback loops. Nerve growth factor (NGF) secreted by target cells not only stimulates expression of its own receptor but also promotes expression of other factors that can cause neuronal cell death. The surviving neurons appear to have sufficiently strong NGF signaling to withstand the antagonistic signals.

C. D. Deppmann, S. Mihalas, N. Sharma, B. E. Lonze, E. Niebur, D. D. Ginty, A model for neuronal competition during development.
Science
320
, 369-373 (2008).
[Abstract]
[Full Text]
Thinking Globally, Acting Locally
Authors: VanHook Annalisa M.
Published: June 2008

Semaphorins function in neuronal pathfinding by stimulating the translation of transcripts localized to the growth cone. Targets of semaphorin-induced translation include cofilin and other proteins that promote depolymerization of F-actin and growth cone collapse. New findings from Nukazuka
et al
. (see commentary by Chisholm) suggest that semaphorin signaling is also required for the proper positioning of epithelial sensory organs called rays in the male
C. elegans
tail. In animals that carry loss-of-function mutations in both
semaphorin-1
(
smp-1)
and
smp-2
or in the semaphorin receptor
plexin-1
(
plx-1
), the anteriormost ray is mispositioned, and this phenotype can be rescued by mutation of
gcn-1
, which encodes a translational repressor. GCN1 activates GCN2, a kinase that represses eukaryotic translation initiation factor 2α (eIF2α). In a series of genetic interaction and overexpression experiments coupled with Western analysis, the authors demonstrated that phosphorylation of eIF2α (P-eIF2α) increased upon semaphorin signaling and decreased in
gcn-1
mutants. They also showed that expression of a constitutively active form of eIF2α phenocopied the defects observed in the
plx
and
smp
mutants. Because P-eIF2α is a known translational stimulator, they examined expression and translation of the
C. elegans
cofilin
homolog
unc-60
in tail ray development. Semaphorin signaling stimulated
unc-60
translation through indirect repression of eIF2α activity. Thus, semaphorin-mediated translational regulation is not limited to cells with highly asymmetric shapes such as neurons. Semaphorin signaling may also play a role in positioning epithelial cells, which, although polarized, are not as irregularly shaped as migrating neurons.

A. Nukazuka, H. Fujisawa, T. Inada, Y. Oda, S. Takagi, Semaphorin controls epidermal morphogenesis by stimulating mRNA translation via eIF2α in
Caenorhabditis elegans
.
Genes Dev.
22
, 1025-1036 (2008).
[Abstract]
[Full Text]

A. D. Chisholm, Semaphorin signaling in morphogenesis: Found in translation.
Genes Dev.
22
, 955-959 (2008).
[Abstract]
[Full Text]
Cellular Orienteering
Authors: Ray L. Bryan
Published: June 2008

How do cells control membrane retraction and the direction of cell movement? Witze
et al.
(see the Perspective by Bowerman) examined cells responding to the developmental signaling protein Wnt. Cultured human melanoma cells responded to Wnt5A by accumulating a cluster of receptor, adhesion, cytoskeletal, and motor proteins near the cell surface. When cells were orienting in a gradient of chemokine concentration, the protein cluster was localized asymmetrically at the posterior of the cell. This structure may help cells integrate the actions of receptors that mediate cell adhesion and cell signaling with cytoskeletal components to control membrane retraction and the direction of cell movement.

E. S. Witze, E. S. Litman, G. M. Argast, R. T. Moon, N. G. Ahn, Wnt5a control of cell polarity and directional movement by polarized redistribution of adhesion receptors.
Science
320
, 365-369 (2008).
[Abstract]
[Full Text]

B. Bowerman, Wnt moves beyond the canon.
Science
320
, 327-328 (2008).
[Summary]
[Full Text]
Putting β-Catenin on the Rac
Authors: Foley John F.
Published: June 2008

Canonical Wnt signaling results in the stabilization and nuclear translocation of β-catenin, which activates the transcription of Wnt-responsive genes; however, the mechanism involved is poorly understood. Noting that Rho family guanosine triphosphatases (GTPases) mediate noncanonical Wnt signaling, Wu
et
al
. examined the effects of Wnt3a (canonical) on Rho GTPase activation in a murine bone marrow stromal cell line. Western blot analyses showed that Wnt3a stimulated the accumulation of activated (GTP-bound) Rac1. Small inhibitory RNA (siRNA) specific for Rac1 reduced Wnt3a-induced activity of a reporter plasmid compared with that in control siRNA-treated cells. Cell fractionation experiments and confocal microscopy showed that dominant-negative Rac1 (dnRac1) blocked Wnt3a-dependent nuclear accumulation of β-catenin but not stabilization of cytosolic β-catenin. Inhibitor and siRNA experiments showed that Wnt3a-stimulated Rac1 activation required phosphoinositide 3-kinase (PI3K) activity. Wnt3a stimulated the phosphorylation and activation of c-Jun N-terminal kinase 2 (JNK2), which was blocked by dnRac1. An inhibitor of JNK or JNK-specific siRNA blocked Wnt3a-stimulated reporter activity and nuclear translocation of β-catenin. Coimmunoprecipitation experiments showed that Rac1, JNK2, and β-catenin constitutively formed a complex in the cytosol and that Wnt3a treatment resulted in the incorporation of phosphorylated JNK2 in this complex. In vitro kinase assays showed that JNK2 phosphorylated β-catenin. Deletion of
Rac1
in the embryonic limb bud resulted in complete loss of the hindlimb and in various truncations of the forelimb in mouse embryos, a phenotype identical to that in mice with deletion of β-
catenin
in the same location. Together, these data suggest that canonical Wnt signaling activates a PI3K-Rac1-JNK2 pathway to phosphorylate β-catenin and mediate its translocation to the nucleus.

X. Wu, X. Tu, K. S. Joeng, M. J. Hilton, D. A. Williams, F. Long, Rac1 activation controls nuclear localization of β-catenin during canonical Wnt signaling.
Cell
133
, 340-353 (2008).
[PubMed]
Genetics of Schizophrenia
Authors: Jasny Barbara R.
Published: June 2008

Although complex disorders such as schizophrenia have a heritable component, identifying the genetic components associated has been very difficult. Walsh
et al.
found that multiple, individually rare, structural mutations (genomic microdeletions and -duplications) occurred more frequently in 150 individuals with schizophrenia than in controls. The enrichment was more than threefold among schizophrenia cases generally and more than fourfold among schizophrenia cases with onset by age 18. The genes disrupted by the genomic breakpoints of mutations in the schizophrenia patients were not random but were disproportionately members of pathways controlling neuronal signaling and brain development.

T. Walsh, J. M. McClellan, S. E. McCarthy, A. M. Addington, S. B. Pierce, G. M. Cooper, A. S. Nord, M. Kusenda, D. Malhotra, A. Bhandari, S. M. Stray, C. F. Rippey, P. Roccanova, V. Makarov, B. Lakshmi, R. L. Findling, L. Sikich, T. Stromberg, B. Merriman, N. Gogtay, P. Butler, K. Eckstrand, L. Noory, P. Gochman, R. Long, Z. Chen, S. Davis, C. Baker, E. E. Eichler, P. S. Meltzer, S. F. Nelson, A. B. Singleton, M. K. Lee, J. L. Rapoport, M.-C. King, J. Sebat, Rare structural variants disrupt multiple genes in neurodevelopmental pathways in schizophrenia.
Science
320
, 539-543 (2008).
[Abstract]
[Full Text]
Damage Control
Authors: Adler Elizabeth M.
Published: June 2008

In the soil bacterium
Bacillus subtilis
, the checkpoint protein DisA (DNA integrity scanning protein A) scans the bacterial chromosome at the onset of sporulation; it localizes at sites of DNA damage to temporarily block sporulation and allow the bacterium to repair the damage before proceeding. Witte
et al
. performed structural analysis of
Thermotoga maritima
DisA and determined that it formed an octameric complex; intriguingly, they found bis-(3′,5′)-cyclic dimeric adenosine monophosphate (c-di-AMP) bound to the purified complex. When nucleotide-deprived DisA was crystallized in the presence of Mg
2+
-ATPγS, the crystals were again bound to c-di-AMP, indicating that DisA could act as a diadenylate cyclase. c-di-GMP is known to act as a signaling molecule in bacteria; however, fluorescence anisotropy titration analysis revealed that the binding affinity of fluorescently labeled ATP for both
T. maritima
and
B. subtilis
DisA was about 20 times greater than that of fluorescently labeled GTP. Furthermore, nucleotide cyclase assays revealed that both
T. maritima
and
B. subtilis
DisA converted ATP to c-di-AMP but did not convert GTP to c-di-GMP. DisA thus appears to be the first protein identified with specific diadenylate cyclase activity. Although neither single-stranded nor double-stranded DNA affected DisA cyclase activity, branched DNA bound to DisA and inhibited its cyclase activity. The authors thus propose that DisA uses c-di-AMP to signal the existence of structures that would interfere with chromosomal segregation, allowing c-di-AMP to join the list of naturally occurring purine-based signaling nucleotides.

G. Witte, S. Hartung, K. Büttner, K.-P. Hopfner, Structural biochemistry of a bacterial checkpoint protein reveals diadenylate cyclase activity regulated by DNA recombination intermediates.
Mol. Cell
30
, 167-178 (2008).
[PubMed]
From Dendrite to Dendritic
Authors: Foley John F.
Published: June 2008

Naïve T cell activation by dendritic cells (DCs) is a critical step in the adaptive immune response. Activation occurs as a result of prolonged contact between the cells through the formation of an immunological synapse (IS). The IS involves interactions between peptide major histocompatibility complexes (pMHCs) on the DC and T cell receptor (TCR) complexes on the naïve cell and between adhesion molecules on both cells. Although much is known about the cytoplasmic events that occur in T cells during IS formation, little is known about what occurs in DCs. Bloom
et al
. hypothesized that molecules involved in the formation of neuronal synapses might also play a role in IS formation. Immunofluorescence studies showed that the scaffold protein spinophilin, well known for its role in neuronal dendritic spines, was present in the cytoplasm of immature mouse DCs but was colocalized with MHC at the plasma membrane of mature DCs. When mature DCs that expressed a fusion protein of spinophilin and green fluorescent protein (GFP) were cocultured with antigen-specific T cells in the presence of antigen, live confocal microscopy showed that spinophilin-GFP was quickly distributed to the plasma membrane at the side of the DC closest to TCR clusters in the T cells. Antigen-specific T cells transferred to spinophilin-deficient mice were less efficiently activated than were those transferred to wild-type mice. Lack of spinophilin had no effect on MHC localization or on antigen uptake. This study provides a glimpse into the DC during IS formation and suggests that spinophilin is important for efficient antigen presentation to T cells. As Seed and Xavier discuss, this study raises important new questions about what other partners spinophilin might have.

O. Bloom, J. J. Unternaehrer, A. Jiang, J.-S. Shin, L. Delamarre, P. Allen, I. Mellman, Spinophilin participates in information transfer at immunological synapses.
J
.
Cell
Biol
.
181
, 203-211 (2008).
[Abstract]
[Full Text]

B. Seed, R. Xavier, Spinophilin and the immune synapse.
J
.
Cell
Biol
.
181
, 181-183 (2008).
[Abstract]
[Full Text]
Gamete Interactions
Authors: Purnell Beverly A. , Gough Nancy R.
Published: June 2008

Two articles this week reveal that sexual reproduction of the invasive aquatic organism
Ciona intestinalis
, which is hermaphroditic, and the malaria-causing parasite
Plasmodium
appears to involve processes similar to those used by flowering plants. Self-incompatibility is a mechanism by which hermaphroditic plants and animals prevent self-fertilization. Although insights have been made for self-incompatibility systems of plants, relatively little is known about animal mechanisms. Harada et al. show that self-sterility in the chordate
C. intestinalis
is controlled by two genetic loci. The self/nonself-discriminating gamete interaction takes place on the basis of allele-specific molecular interactions between fibrogen-like ligands on the egg coat and polycystin 1-like receptors on the sperm. Genes for the receptors and ligands are linked and are polymorphic, similar to self-sterility genes in plants. In a second example of similarity to flowering plant reproduction, Hirai
et al.
found that sexual reproduction of
Plasmodium berghei
, which infects rodents, involves a male-specific role for GENERATIVE CELL SPECIFIC 1 (PbGCS1), which is also important for male fertility in angiosperms and is conserved in the
Plasmodium
species that infect humans. Experiments with PbGCS1-deficient
P. berghei
indicated that gametogenesis occurred correctly but that male fertility was compromised. PbGCS1 was essential for the mosquito phases of the life cycle, and interference with gamete interactions may provide a new target for the prevention of malaria.

Y. Harada, Y. Takagaki, M. Sunagawa, T. Saito, L. Yamada, H. Taniguchi, E. Shoguchi, H. Sawada, Mechanism of self-sterility in a hermaphroditic chordate.
Science
320
, 548-550 (2008).
[Abstract]
[Full Text]

M. Hirai, M. Arai, T. Mori, S.-y. Miyagishima, S. Kawai, K. Kita, T. Kuroiwa, O. Terenius, H. Matsuoka, Male fertility of malaria parasites is determined by GCS1, a plant-type reproduction factor.
Curr. Biol.
18
, 607-613 (2008).
[PubMed]
NO Link Between Notch and Inflammation?
Authors: VanHook Annalisa M.
Published: June 2008

Both nitric oxide (NO) and Notch signaling have been implicated in inflammation, although the details of their roles have not been determined. A study by Kim
et al.
presents evidence that NO may repress Notch signaling by nitrating the Notch intracellular domain (NICD, a transcription factor that is released from the membrane and translocates to the nucleus upon stimulation of the Notch pathway). Immortalized macrophages were exposed to lipopolysaccharide (LPS), a bacterial cell wall component, to induce an inflammatory response, and the effect on expression of three different NICD-responsive reporter genes was measured. The expression of each reporter decreased in cells exposed to LPS and in cells treated with the NO donor S-nitro-N-acetyl-penicillamine (SNAP). LPS-treated cells secreted NO into the culture medium, and pharmacological inhibitors of NO synthesis blocked the LPS-induced repression of the reporters. The amount of NICD bound to the reporter promoters decreased as the extracellular NO concentration increased, and high NO concentrations prevented NICD from associating with its DNA-binding partner RBP-Jk. An antibody that recognizes nitrotyrosine confirmed that nitrated NICD was present in extracts from LPS-treated cells. The fluorescence emission profile of NICD indicated that its conformation changed upon exposure to NO, so the authors postulated that nitration represses NICD activity by rendering it incapable of binding to its transcriptional coactivator(s). It had been previously reported that the glycosylation state of the Notch extracellular domain affects its ligand-binding activity, and now it appears that activity of the intracellular domain can also be modulated by covalent modification.

M.-Y. Kim, J.-H. Park, J.-S. Mo, E.-J. Ann, S.-O. Han, S.-H. Baek, K.-J. Kim, S.-Y. Im, J.-W. Park, E.-J. Choi, H.-S. Park, Downregulation by lipopolysaccharide of Notch signaling, via nitric oxide.
J. Cell Sci.
121
, 1466-1476 (2008).
[Abstract]
[Full Text]
Keeping the Balance
Authors: Foley John F.
Published: June 2008

Stimulation of Toll-like receptors (TLRs) by microbial molecules is important in innate immune responses. Most TLRs signal through the adaptor molecule myeloid differentiation marker 88 (MyD88) to sequentially activate interleukin-1 receptor (IL-1R)-associated kinase 4 (IRAK4), IRAK1, extracellular signal-regulated kinase (ERK) 1 and 2, and the transcription factor nuclear factor κB (NF-κB), which leads to the production of proinflammatory cytokines. TLR3 uses the adaptor molecule TRIF. TLR-mediated stimulation of interferon regulatory factors (IRFs) leads to the production of type I interferons (IFNs), which can be anti-inflammatory. TLR signaling must be carefully modulated to prevent excessive inflammation or autoimmune responses. An
et al
. found that stimulation of individual TLRs in splenocytes from mice deficient in the tyrosine phosphatase SHP-1 resulted in increased production of proinflammatory cytokines but decreased production of type I IFNs compared to that in splenocytes from wild-type mice. TLR-stimulated activation of NF-κB and ERK1/2 was higher in SHP-1–deficient splenocytes than in wild-type splenocytes, whereas that of IRF3 and IRF7 was lower. TLR-meditated activation of IRAK1 in splenocytes was inhibited by overexpression of SHP-1, although this did not require its phosphatase activity. The authors found a physical association between IRAK1 and SHP-1 in macrophages that was enhanced upon TLR stimulation. Finally, overexpression of IRAK1 inhibited both MyD88- and TRIF-dependent activation of IRFs, whereas inactivation of IRAK1 had the opposite effect. Although some aspects of the mechanism involved remain unclear, these data suggest that SHP-1 serves to balance the outcome of TLR signaling by binding to and inhibiting IRAK1. As O’Neill points out in commentary, a more complete understanding of both the positive and negative regulators of TLR signaling will help in the design of more effective therapeutics.

H. An, J. Hou, J. Zhou, W. Zhao, H. Xu, Y. Zheng, Y. Yu, S. Liu, X. Cao, Phosphatase SHP-1 promotes TLR- and RIG-I-activated production of type I interferon by inhibiting the kinase IRAK1.
Nat
.
Immunol
.
9
, 542-550 (2008).
[PubMed]

L. A. J. O’Neill, ‘Fine tuning’ TLR signaling.
Nat
.
Immunol
.
9
, 459-461 (2008).
[PubMed]
Integrating Different Signals
Authors: Adler Elizabeth M.
Published: June 2008

Migrating cells need to integrate promigratory diffusible signals that act through heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) with integrin-mediated cues from the extracellular matrix. Penela
et al
. found that overexpression of GPCR kinase 2 (GRK2, a serine/threonine kinase implicated in GPCR regulation) in epithelial-derived cell lines promoted migration toward fibronectin. A catalytically inactive mutant had effects similar to those of wild-type GRK2, whereas knockdown of endogenous GRK2 decreased migration toward fibronectin (but not collagen), which was also attenuated in fibroblasts derived from GRK2
+/–
mouse embryos. Indeed, wound healing in skin was decreased in the GRK2
+/–
mice. Pharmacological analysis indicated that GRK2-dependent stimulation of migration toward fibronectin depended on a pertussis toxin-sensitive GPCR and on the lipid messenger sphingosine 1-phosphate (S1P). Fibronectin promoted internalization of the S1P
1
receptor (indicative of its occupancy by S1P) and increased S1P concentration (both in cytosol and in conditioned medium). Moreover, cells overexpressing GRK2 migrated more rapidly in response to exogenous S1P than did control cells, whereas S1P-induced migration was decreased in cells with decreased GRK2 abundance. Increased or decreased GRK2 expression was paralleled by activation of extracellular signal-regulated kinase (ERK1/2) in response to either S1P or adhesion to fibronectin; further, treatment with pertussis toxin or a sphingosine kinase inhibitor decreased the latter response. The effects of GRK2 on S1P-dependent ERK1/2 signaling and migration were independent of β-arrestin-1 and -2; rather, they involved the dynamic phosphorylation of GRK2 and its association with the scaffolding protein GIT1. The authors thus conclude that GRK2 integrates adhesion- and S1P-based signals to promote epithelial cell migration.

P. Penela, C. Ribas, I. Aymerich, N. Eijkelkamp, O. Barreiro, C. J. Heijnen, A. Kavelaars, F. Sánchez-Madrid, F. Mayor Jr., G protein-coupled receptor kinase 2 positively regulates epithelial cell migration.
EMBO J.
27
, 1206-1218 (2008).
[PubMed]
Back from the Dormant Stage: Second Messenger Cyclic ADP-Ribose Essential for
Toxoplasma gondii
Pathogenicity
Authors: Guse Andreas H.
Published: June 2008

Cyclic adenosine diphosphoribose (cADPR) is an endogenous Ca
2+
-mobilizing second messenger found in cells of animals, plants, and protozoans. It is formed by a specific class of enzymes, the ADP-ribosyl cyclases. cADPR stimulates Ca
2+
release by means of ryanodine receptors located in the sarcoplasmic and endoplasmic reticulum. Recently, a role for cADPR has been demonstrated in the obligate intracellular protozoan pathogen
Toxoplasma gondii
. In
T. gondii
, stress conditions evoked synthesis of the plant hormone abscisic acid by the apicoplast, a remnant organelle of an algal endosymbiont of
T. gondii
. Abscisic acid in turn activated formation of cADPR within
T. gondii
, resulting in Ca
2+
release and secretion of proteins involved in egress of
T. gondii
from its host cell. Evidence for a synthetic pathway of plant origin was obtained with the ABA synthesis inhibitor fluridone, which antagonized cellular egress and induced differentiation of long-lived semidormant cystic forms of
T. gondii.
Moreover, fluridone protected mice from toxoplasmosis.
Kinases in the Polyadenylation Complex
Authors: Gough Nancy R.
Published: June 2008

After transcription of a gene, the abundance of a protein in a cell can be controlled through various mechanisms operating on the mRNA, including regulation of alternative splicing, polyadenylation, stability and degradation, nuclear export, and accessibility to translation factors. Star-PAP is a noncanonical poly(A) polymerase that has a proline-rich region (PRR), which splits the catalytic domain. Star-PAP functions as part of a larger macromolecular complex. However, in addition to the common proteins found in other polyadenylation complexes, the Star-PAP complex includes phosphatidylinositol-4-phosphate 5 kinase Iα (PIPKIα), and Star-PAP activity is stimulated by phosphatidylinositol 4,5-bisphosphate [PI(4,5)P
2
]. Gonzales
et al
. showed that the Star-PAP complex isolated from transfected cells also includes protein kinase activity and that Star-PAP is phosphorylated by the associated kinase. The protein kinase activity of the Star-PAP complex was inhibited by the addition of PI(4,5)P
2
, which led the authors to identify the kinase as casein kinase Iα (CKIα), which is known to be inhibited by PI(4,5)P
2
. CKIα and Star-PAP colocalized in nuclear speckles, which are a site of pre-mRNA processing, and inhibitors of CKIα blocked Star-PAP phosphorylation in vitro. Star-PAP is responsible for increasing the abundance of many mRNAs based on microarray experiments; however, CKIα and PIPKIα appear to control the targeting of Star-PAP to a subset of mRNAs involved in oxidative stress. Cells in which CKIα or PIPKIα was decreased using siRNA showed a specific decrease in the abundance of a subset of mRNAs processed by Star-PAP, including two that encode enzymes involved in the response to oxidative stress (HO-1 and NQO1), without affecting other transcripts targeted by Star-PAP. Thus, the presence of a lipid kinase and a protein kinase in the Star-PAP complex appears to target Star-PAP to specific mRNA targets and connects nuclear lipid signaling to mRNA processing.

M. L. Gonzales, D. L. Mellman, R. A. Anderson, CKIα is associated with and phosphorylates Star-PAP and is also required for expression of select Star-PAP target messenger RNAs.
J. Biol. Chem.
283
, 12665-12673 (2008).
[Abstract]
[Full Text]
A Sense of Danger in the Air
Authors: Simpson Stephen J.
Published: June 2008

Particulate airborne pollutants, such as asbestos and silica, are notorious for their negative effects on health, including lung inflammation and cancer, yet information on how such substances exert their effects is lacking. Dostert
et al.
(see the Perspective by O’Neill) reveal that a multiprotein complex known as the Nalp3 inflammasome can signal exposure of cells to internalized particles of asbestos and silica, which leads to the activation of a potent inflammatory response. In the absence of Nalp3, mice responded less vigorously to asbestos, supporting the idea that this inflammatory sensing complex plays a key role in the response to respiratory pollutants.

C. Dostert, V. Pétrilli, R. Van Bruggen, C. Steele, B. T. Mossman, J. Tschopp, Innate immune activation through Nalp3 inflammasome sensing of asbestos and silica.
Science
320
, 674-677 (2008).
[Abstract]
[Full Text]

L. A. J. O'Neill, How frustration leads to inflammation.
Science
320
, 619-620 (2008).
[Summary]
[Full Text]
Signaling Survival Strategies
Authors: Ray L. Bryan
Published: June 2008

Along with its role in control of metabolism, the enzyme glycogen synthase kinase 3β (GSK3β) functions in a signaling mechanism that controls transcription. When GSK3β is active, it phosphorylates β-catenin and promotes degradation of the β-catenin protein. Inhibition of GSK3 permits accumulation of β-catenin, which works in the nucleus with transcription factors to promote expression of target genes. Thornton
et al
. show that activation of the p38 mitogen-activated protein kinase (MAPK) appears to directly phosphorylate and thereby inhibit GSK3β. Mouse embryo fibroblasts lacking enzymes that lead to activation of p38 were deficient in phosphorylation of GSK3β. The authors propose that such a signaling pathway may allow cellular stresses and cytokines that activate p38 MAPK to influence cell survival.

T. M. Thornton, G. Pedraza-Alva, B. Deng, C. D. Wood, A. Aronshtam, J. L. Clements, G. Sabio, R. J. Davis, D. E. Matthews, B. Doble, M. Rincon, Phosphorylation by p38 MAPK as an alternative pathway for GSK3β inactivation.
Science
320
, 667-670 (2008).
[Abstract]
[Full Text]
Unintentional Uptake
Authors: Simpson Stephen J.
Published: June 2008

In many respects, our understanding of innate immune responses to protozoan parasites still lags behind that for other infectious organisms. However, recent work has shown that an important part of the armory against African trypanosomes is serum apolipoprotein L-I (apoL1), which can kill the parasite by causing lysis—why, then, would the parasites take it in? Vanhollebeke
et al
. show that apoL1 is taken up by the parasite via a specific glycoprotein receptor, which the parasite normally uses to supply heme for its growth and resistance to oxidative stress within the host. In human serum, however, the receptor also inadvertently recognizes a component of certain high-density lipoprotein complexes, of which apoL1 is a part, explaining how the uptake of this detrimental host protein is triggered.

B. Vanhollebeke, G. De Muylder, M. J. Nielsen, A. Pays, P. Tebabi, M. Dieu, M. Raes, S. K. Moestrup, E. Pays, A haptoglobin-hemoglobin receptor conveys innate immunity to
Trypanosoma brucei
in humans.
Science
320
, 677-681 (2008).
[Abstract]
[Full Text]