bluuebunny/crossref_metadata_2025 huggingface dataset:
"Waiter, There’s a Fly in My Beer!"
Authors: Ray L. Bryan
Published: September 2007

There are five well-known, distinct tastes that organisms can detect--sweet, bitter, sour, salty, and umami. Fischler
et al
. explored the taste neurons of the fruit fly
Drosophila melanogaster
and discovered a set of neurons that signal detection of a different taste: beer, or, more precisely, carbonated liquids. The authors used immunohistochemistry to detect a set of neurons that expressed a particular gene enhancer probe. These neurons ran from the taste sensors on the proboscis to a region of the brain that processes taste signals. They then expressed a calcium sensor in these neurons that allowed imaging of neuronal activation by confocal microscopy in living flies. The usual taste cues got no response from these neurons, but application of beer or a yeast culture gave strong activation. The authors immediately suspected ethanol or carbon dioxide as potential sensory ligands, and their experiments implicated the latter. Solutions containing dissolved CO
2
were the primary stimulants of the cells. The detection of carbonation also influenced the flies’ behavior. They preferred a solution of sodium bicarbonate at pH 6.5 (in which about half the carbonate is converted to CO
2
) over the same solution at pH 8.5 (in which less than 1% of the carbonate is present as CO
2
). Overexpression of an inwardly rectifying potassium channel (which hyperpolarizes and inactivates the neurons) in the CO
2
-detecting taste neurons showed reduced behavioral preference for CO
2
-containing solutions. Fruit flies have recently been shown to be able to smell CO
2
, but such detection is mediated by a different system and stimulates avoidance behavior. Thus, the same molecule can produce distinct behaviors in the animal, depending on the mode of detection. The authors point out that these results make good sense when related to the fly’s lifestyle. Carbonated solutions that the fly encounters may well have microorganisms like yeast in them and may be full of nutrients. High concentrations of CO
2
in the air, on the other hand, may be associated with unfavorable or stressful conditions and hypoxia. The findings also raise the question whether other organisms might also sense and be attracted to carbonated solutions…Cheers!

W. Fischler, P. Kong, S. Marella, K. Scott, The detection of carbonation by the
Drosophila
gustatory system.
Nature
448
, 1054-1057 (2007).
[Online Journal]
Autophagy and Innate Immunity
Authors: Foley John F.
Published: September 2007

The cytoplasmic contents of the cell are targeted to lysosomes for degradation or recycling by a process known as autophagy. Jounai
et al
. investigated the role of autophagy in the response to infection by vesicular stomatitis virus (VSV). Whereas mouse embryonic fibroblasts (MEFs) from wild-type mice were efficiently infected with VSV, as assessed by measurement of virus in infected cell cultures, MEFs from mice deficient in Atg5 (Atg5 KO), a critical component of the autophagic process, produced much lower amounts of virus. Real-time reverse transcription polymerase chain reaction and Western blotting analyses demonstrated that VSV infection of Atg5 KO MEFs resulted in the higher abundance of interferon-β (IFN-β) mRNA and increased phosphorylation and activation of interferon regulatory factor 3 (IRF-3), a transcription factor that activates IFN gene expression, than did infection of wild-type MEFs. Viral RNA is recognized by DExD/H box RNA helicases, such as retinoic acid-inducible gene I (RIG-I), which then associates with and activates the adaptor molecule IFN-β promoter stimulator 1 (IPS-1). This association is mediated by interactions between the caspase recruitment domains (CARDs) of RIG-I and IPS-1 and leads to IRF-3 activation. Reporter assays in 293 cells demonstrated that RIG-1-induced activation of the IFN promoter was inhibited by both Agt5 and a conjugate of Agt5 and Agt12 (the physiologically relevant form of Atg5). Atg5-Atg12 coimmunoprecipitated with RIG-I and IPS-1 in 293 cells, and VSV infection enhanced the association between Atg5-Atg12 and IPS-1. Experiments with mutant forms of IPS-1 and RIG-I showed that the CARD domains were the targets of Atg5-Atg12. This study suggests that Atg5-Atg12 blocks the interaction between RIG-I and IPS-1 and thus inhibits the innate immune response to viral infection.

N. Jounai, F. Takeshita, K. Kobiyama, A. Sawano, A. Miyawaki, K.-Q. Xin, K. J. Ishii, T. Kawai, S. Akira, K. Suzuki, K. Okuda, The Atg5-Atg12 conjugate associates with innate antiviral immune responses.
Proc. Natl. Acad. Sci. U.S.A.
104
, 14050-14055 (2007).
[Abstract]
[Full Text]
Vesicular Trafficking in Meiotic Arrest
Authors: Gough Nancy R.
Published: September 2007

A constitutively active G protein-coupled receptor (GPCR) resulting in the production of adenosine 3',5'-monophosphate (cAMP) has been implicated in maintaining meiotic arrest. El-Jouni
et al
. investigated whether vesicular trafficking at the plasma membrane may be involved in this process. Using
Xenopus
oocytes, they inhibited exocytosis with a dominant-negative form of SNAP25 (a protein that functions as a critical component of the SNARE machinery that allows vesicles to fuse with the plasma membrane) and found that the oocytes were released from meiotic arrest in the absence of hormonal stimulation (progesterone). Membrane capacitance was monitored as an indicator of exocytosis. Forskolin, which directly activates adenylyl cyclase in the absence of receptor stimulation, and cholera toxin, which activates Gα
s
proteins, prevented progesterone and the dominant-negative SNAP25 from triggering maturation, suggesting that these two agents act upstream of adenylyl cyclase and Gα
s
. Oocytes have constitutive endocytosis as well as clathrin-mediated endocytosis. Blocking constitutive endocytosis had no effect on oocyte maturation, whereas blocking clathrin-mediated endocytosis with monodansylcadaverine delayed progesterone-mediated oocyte maturation. Thus, membrane trafficking, which presumably includes internalization and recycling of the GPCR, may contribute to the receptor’s constitutive activity. Inhibiting exocytosis may be one mechanism that contributes to the maturation process. A role for a block in exocytosis in
Xenopus
is consistent with the morphological changes and decrease in surface area associated with maturation. It will be interesting to understand how the physiological stimuli that trigger maturation are connected to changes in vesicular traffic.

W. El-Jouni, S. Haun, R. Hodeify, A. H. Walker, K. Machaca, Vesicular traffic at the cell membrane regulates oocyte meiotic arrest.
Development
134
, 3307-3315 (2007).
[PubMed]
TNF and Alzheimer’s Disease
Authors: Foley John F.
Published: September 2007

Alzheimer’s disease (AD) is associated with the accumulation in the brain of plaques of amyloid β protein (Aβ), which is produced by the processing of amyloid precursor protein (APP) by the enzymes β-secretase (BACE1) and γ-secretase. He
et al
. pursued their earlier finding that overexpression of tumor necrosis factor (TNF) receptor 1 (TNFR1) promoted Aβ-induced neuronal death by examining the role of TNFR1 in Aβ production. They crossed transgenic APP23 mice, which express a mutant APP and develop Aβ plaques, with

TNFR1
–/–

mice (APP23/

TNFR1
–/–

). Immunhistochemical analyses of the brains of 14-month-old animals showed a decreased number and size of Aβ plaques in APP23/

TNFR1
–/–

mice compared with those in APP23 mice. Real-time reverse transcription polymerase chain reaction assays, together with Western blotting, showed that the abundance of BACE1 mRNA and protein were lower in APP23/

TNFR1
–/–

mice compared with APP23 mice, which suggests that TNFR1 signaling promotes the production of BACE1. Experiments in 293 cells transfected with a reporter plasmid showed that TNF-α treatment induced BACE1 promoter activity, which was blocked by a specific inhibitor of the transcription factor nuclear factor κB (NF-κB). Immunohistochemistry demonstrated the presence of fewer neurons in the brains of APP23 mice than in brains from APP23/

TNFR1
–/–

mice. In learning and object recognition tests, APP23 mice performed poorly; APP23/

TNFR1
–/–

mice performed better, with abilities similar to those of wild-type mice. Together, these data implicate TNFR1 in promoting abnormal APP processing, Aβ plaque formation, and learning defects and suggest that TNFR1 might be an effective therapeutic target in treating AD.

P. He, Z. Zhong, K. Lindholm, L. Berning, W. Lee, C. Lemere, M. Staufenbiel, R. Li, Y. Shen, Deletion of tumor necrosis factor death receptor inhibits amyloid β generation and prevents learning and memory deficits in Alzheimer’s mice.
J. Cell Biol.
178
, 829-841 (2007).
[Abstract]
[Full Text]
Not Lost In Translation
Authors: Riddihough Guy
Published: September 2007

Protein synthesis by ribosomes normally requires that the messenger RNA (mRNA) template be capped at its 5′ end with a modified nucleotide. Starved yeast can undergo a developmental switch to an invasive phenotype, during which most mRNAs are decapped, which prevents their translation by ribosomes. The genes responsible for the switch must therefore be translated in a cap-independent manner. Gilbert
et al
. now show that invasive growth-specific genes have internal ribosome entry sites (IRESs) in the unusually long 5′ untranslated regions of their mRNAs that allow their translation. Unlike viral IRESs, these cellular IRESs seem to consist of an unstructured sequence of adenosines that recruits the poly-A binding protein, a configuration that can substitute for the 5′ cap.

W. V. Gilbert, K. Zhou, T. K. Butler, J. A. Doudna, Cap-independent translation is required for starvation-induced differentiation in yeast.
Science
317
, 1224-1227 (2007).
[Abstract]
[Full Text]
The Aryl Hydrocarbon Receptor: An Illuminating Effector of the UVB Response
Authors: Agostinis Patrizia , Garmyn Marjan , Van Laethem An
Published: September 2007

The aryl hydrocarbon receptor (AhR) is a cytosolic ligand-activated transcription factor that mediates most of the toxic and carcinogenic effects of drugs and environmental toxins collectively known as xenobiotics. Ligand activation of the AhR stimulates the transcription of genes that encode several xenobiotic-metabolizing enzymes. The molecular mechanisms and signaling pathways evoked by the activation of the AhR are becoming increasingly understood and underscore the participation of the AhR in crucial processes, including cellular stress response, proliferation, differentiation, inflammation, and carcinogenesis. Studies now implicate the AhR as an integral part of the multifaceted signal transduction pathway initiated by the exposure of keratinocytes to ultraviolet B radiation (UVB), which is the most ubiquitous hazard to human skin and the principal risk factor for skin cancer. Ligand-dependent activation of the AhR in the cytosol provides a molecular bridge that links cytoplasmic events to nuclear signals, thus unmasking a previously unknown role for this transcription factor in the complex cellular response to UVB.
Hedgehog Signaling: Cooking with Gas1
Authors: Kang Jong-Sun , Zhang Wei , Krauss Robert S.
Published: September 2007

The mechanisms by which morphogens, such as Sonic hedgehog (Shh), specify distinct cell fates in a concentration-dependent manner are not fully understood. Shh signaling is regulated by a feedback network that comprises Shh-binding factors, the expression of which is controlled by the Hedgehog pathway itself. Recent studies have identified the hedgehog-binding protein growth arrest–specific gene 1 (Gas1) as a component of this network. Gas1 binds Shh to promote signaling, but its expression is subsequently inhibited by pathway activity.
Gas1
−/−
mice display Shh dosage–dependent phenotypes in the neural tube, midface, and digits. Ectopic expression and in vitro assays indicate that Gas1 binds Shh synergistically with the Hedgehog receptor Patched1 and promotes signaling in a cell-autonomous fashion. Furthermore, Gas1 cooperates with another component of the feedback network, Cdo, in patterning the neural tube and midface. The coordinate regulation of the activity and expression of several different positively and negatively acting Shh binding proteins should result in fine-tuned modulation of graded Shh signaling.
Scaffold Succumbs to Caspase Cleavage
Authors: Ray L. Bryan
Published: September 2007

Activation of the ERK (extracellular signal-regulated kinase) members of the mitogen-activated protein (MAP) kinase family is associated with cell survival signaling. In cells stimulated to undergo apoptosis, such survival signaling is often disrupted. McKay and Morrison provide insight into molecular mechanisms by which ERK signaling may be shut down in apoptotic cells. The protein known as kinase suppressor of Ras 1 (KSR1) is a scaffold that contributes to ERK activation by bringing together the kinases that participate in a cascade of sequential activation to ultimately stimulate the phosphorylation and activation of ERKs. The authors noted that KSR1 has a characteristic caspase cleavage site that would be expected to effectively break up KSR1’s scaffolding function by separating the C-terminal domain that binds to MEK (MAP kinase or ERK kinase) from the N-terminal domain that binds ERK (a substrate for MEK) and a domain that mediates targeting of the whole complex to the plasma membrane. An epitope-tagged version of KSR1 expressed in KSR
–/–
mouse embryo fibroblasts was indeed cleaved in cells stimulated to undergo apoptosis by treatment with tumor necrosis factor α and cycloheximide. Although the N-terminal fragment of KSR1 appeared to be further degraded, immunoblotting showed that the C-terminal fragment of KSR1 accumulated in apoptotic cells. This fragment can potentially act as a dominant-negative inhibitor, and expression of this fragment in KSR1
–/–
cells resulted in increased apoptotic signaling and reduced amounts of active, phosphorylated ERK. On the other hand, expression of a cleavage-resistant version of KSR1 in the knockout cells led to accumulation of more activated ERK and diminished apoptotic signaling. Cleavage of KSR1 was also observed in a natural model of apoptosis--the involuting mammary gland. The authors propose that caspase-dependent dismantling of KSR1 may provide a one-two punch to the cell’s survival signaling by removing a scaffold that facilitates ERK activation and, at the same time, generating an inhibitor of ERK activation.

M. M. McKay, D. K. Morrison, Caspase-dependent cleavage disrupts the ERK cascade scaffolding function of KSR1.
J. Biol. Chem.
282
, 26225-26234 (2007).
[Abstract]
[Full Text]
Sequestered at the Golgi
Authors: Gough Nancy R.
Published: September 2007

Feng
et al
. identified a Golgi-localized protein with seven putative transmembrane domains as an interacting partner for Raf-1. This protein, which was previously cloned and named PAQR3, they renamed as Raf kinase trapping to Golgi (RKTG). In overexpression assays, RKTG inhibited growth factor-induced signaling and responses in HEK293T (human embryonic kidney) cells and PC12 cells (a pheochromocytoma cell line). RKTG did not inhibit the mitogen-activated protein kinase (MAPK) pathway if a plasma membrane-targeted mutant of Raf-1 was coexpressed or if the pathway was directly activated at the level of the MAPK kinase MEK. Transfected cells exhibited colocalization of RKTG and Raf-1 at the Golgi, and endogenous RKTG and Raf-1 from HEK293T cells coimmunoprecipitated. When overexpressed, RKTG decreased the interaction between tagged Raf-1 and its downstream target MEK and its upstream activator Ras. In RKTG knockout mice, the basal phosphorylation of the MAPK ERK was increased in brain and liver. Mouse embryo fibroblasts from the knockout mice exhibited enhanced ERK phosphorylation (both the amount and duration) in response to growth factor stimulation. Given that spatial regulation of the MAPK pathway is well known for other components in the pathway, it will be interesting to determine whether RKTG-mediated sequestration of Raf-1 not only inhibits signaling to ERK but also may redirect signaling through a different path to other effectors.

L. Feng, X. Xie, Q. Ding, X. Luo, J. He, F. Fan, W. Liu, Z. Wang, Y. Chen, Spatial regulation of Raf kinase signaling by RKTG.
Proc. Natl. Acad. Sci. U.S.A.
104
, 14348-14353 (2007).
[Abstract]
[Full Text]
The Molecular Machinery of Mood Swings
Authors: Chin Gilbert
Published: September 2007

The action of monoamine neurotransmitters that serve as signaling molecules in mood and motivation begins when they are released from the presynaptic nerve terminal and ends when they are transported from the extracellular space back into the cytoplasm via dedicated sodium-dependent plasma membrane transporters. Zhou
et al
.

describe the crystal structure of a bacterial homolog (LeuT) of the mammalian monoamine transporters in complex with its substrate (leucine) and an inhibitor of norepinephrine transport (the antidepressant desipramine). On the basis of homology modeling of the human transporters for serotonin, norepinephrine, and dopamine (hSERT, hNET, and hDAT), they construct mutants of hSERT and hDAT and show that these exhibit the predicted sensitivity of serotonin and dopamine uptake to desipramine inhibition.

Z. Zhou, J. Zhen, N. K. Karpowich, R. M. Goetz, C. J. Law, M. E. A. Reith, D.-N. Wang, LeuT-desipramine structure reveals how antidepressants block neurotransmitter reuptake.
Science
317
, 1390-1393 (2007).
[Abstract]
[Full Text]
Toll-Like Receptors and Neural Stem Cells
Authors: Foley John F.
Published: September 2007

The mechanisms underlying the development of new neurons in the adult brain, a process known as neurogenesis, are unclear. Rolls
et al
. found that Toll-like receptor 2 (TLR2) was abundant in neurogenic niches of the adult human brain, such as the hippocampus, and so investigated the role of TLR2 in neurogenesis. TLR2-deficient (TLR2D) mice showed similar incorporation of the cell proliferation marker 5-bromodeoxyuridine (BrdU) in the dentate gyrus compared with wild-type mice, as determined by microscopic analysis of brain slices. Immunohistochemical analyses showed that neural progenitor cells (NPCs) from TLR2D mice differentiated into fewer neurons but more astrocytes than did NPCs from wild-type mice. TLR2 was detected in wild-type NPCs, and experiments involving wild-type or TLR2D NPCs cocultured with wild-type or TLR2D glial cells showed that it was the TLR2 in NPCs that was important in determining NPC fate. Treatment of wild-type, but not TLR2D, NPCs with the TLR2 agonist Pam3 [
N
-palmitoyl-
S
-(2,3-bis(palmitoyloxy)-(2
RS
)-propyl)-Cys-Ser-Lys
4
] resulted in differentiation into neurons. Western blotting and immunohistochemistry showed that Pam3 activated IκB kinase and stimulated the nuclear translocation of nuclear factor κB (NF-κB). TLR4 was also detected in NPCs, and their treatment with the TLR4 agonist lipopolysaccharide (LPS) inhibited their differentiation into neurons. NPCs in the hippocampi of TLR4D mice showed increased proliferation and neuronal differentiation compared with those in the hippocampi of wild-type (and TLR2D) mice. Applying neutralizing antibodies against both TLR2 and TLR4 resulted in the increased proliferation and differentiation of wild-type NPCs into neurons, suggesting that TLR4 is the dominant receptor. Together, these data suggest that whereas TLR2 modulates differentiation of NPCs, TLR4 affects both their proliferation and differentiation. Martino and Pluchino provide commentary.

A. Rolls, R. Shechter, A. London, Y. Ziv, A. Ronen, R. Levy, M. Schwartz, Toll-like receptors modulate adult hippocampal neurogenesis.
Nat. Cell Biol.
9
, 1081-1088 (2007).
[PubMed]

G. Martino, S. Pluchino, Neural stem cells: guardians of the brain.
Nat. Cell Biol.
9
, 1031-1034 (2007).
[PubMed]
MyD88-5 and Neuronal Toxicity
Authors: Foley John F.
Published: September 2007

The first four members of the myeloid differentiation marker 88 (MyD88) family of cytosolic adaptor proteins are well known for their roles in mediating Toll-like receptor (TLR) signaling in the immune system. Kim
et al
. set out to characterize the more enigmatic fifth member of this family, MyD88-5. Northern and Western blotting demonstrated a higher abundance of MyD88-5 mRNA and protein in the brains of mice and humans than in any other organ. In human blood, real-time reverse transcription polymerase chain reaction (RT-PCR) assays showed that MyD88-5 mRNA was preferentially found in lymphocytes and not in myeloid cells. The authors developed a transgenic mouse that expressed a green fluorescent protein (GFP)-tagged MyD88-5 protein. Confocal microscopic analysis of brain sections showed that GFP fluorescence was strongest in the hippocampus and cerebellum and found only in neurons, within which MyD88-5-GFP was cytoplasmic and had a punctate distribution. When expressed in COS-1 cells, MyD88-5-GFP strongly colocalized with mitochondria. In cotransfected COS-1 cells, the authors demonstrated the colocalization of MyD88-5-GFP with c-Jun N-terminal kinase 3 (JNK3) at mitochondria, an association that was also shown in coimmunoprecipitation studies in COS-1 cells and in hippocampal lysates. JNK3 promotes apoptosis in hippocampal cells after cerebral ischemia (oxygen and nutrient deprivation), and the authors found that cell death was reduced in ischemic hippocampal slices from MyD88-5-deficient mice compared with those from wild-type mice. This study reveals the role of MyD88-5 in mediating neuronal cell death after injury and raises the interesting question of what role MyD88-5 might play in lymphocytes.

Y. Kim, P. Zhou, L. Qian, J.-Z. Chuang, J. Lee, C. Li, C. Iadecola, C. Nathan, A. Ding, MyD88-5 links mitochondria, microtubules, and JNK3 in neurons and regulates neuronal survival.
J. Exp. Med.
204
, 2063-2074 (2007).
[Abstract]
[Full Text]
Mitochondria at the Immunological Synapse
Authors: Gough Nancy R.
Published: September 2007

Quintana
et al
. noted that beads coated with antibodies to CD3, a constituent of the T cell receptor (TCR) complex, produced a larger and more sustained calcium signal in the Jurkat T cell line and primary human T cells than did the same antibodies in solution. This difference correlated with the antibody-coated beads’ ability to stimulate the formation of the immune synapse, a macromolecular structure that forms at the plasma membrane at the site of TCR activation and that is involved in T cell activation. Calcium influx across the plasma membrane in response to TCR activation involves the activation of calcium release-activated calcium (CRAC) channels, the Orai1 channels, in response to depletion of calcium from intracellular stores. Quintana
et al
. found that when mitochondrial calcium uptake was pharmacologically inhibited, calcium signaling was decreased in response to the antibody-coated beads. Indeed, TCR activation triggered the relocation of mitochondria to within 200 nm of the plasma membrane at the site of the immune synapse (based on total internal reflection microscopy), and these mitochondria that were close to the immune synapse exhibited enhanced calcium uptake compared with that of mitochondria distant from the immune synapse. The authors suggest that the relocation of the mitochondria to the immune synapse and their uptake of calcium prevent calcium-induced inactivation of the Orai1 channels, thereby allowing sustained calcium influx in response to stimuli that induce the formation of the immune synapse.

A. Quintana, C. Schwindling, A. S. Wenning, U. Becherer, J. Rettig, E. C. Schwarz, M. Hoth, T cell activation requires mitochondrial translocation to the immunological synapse.
Proc. Natl. Acad. Sci. U.S.A.
104
, 14418-14423 (2007).
[Abstract]
[Full Text]
Reciprocal Regulation of DAPK
Authors: Foley John F.
Published: September 2007

The tumor suppressor death-associated protein kinase (DAPK) functions by inhibiting cell adhesion and migration and promoting apoptosis. It is positively regulated by calmodulin and is thought to inactivate integrins, thus preventing cell adhesion-induced survival signals. Wang
et al
. sought to determine the mechanism of regulation of DAPK. Yeast two-hybrid screening identified leukocyte common antigen-related protein (LAR), a receptor-like tyrosine phosphatase, as a binding partner for the ankyrin repeat domain of DAPK. This interaction was confirmed by coimmunoprecipitation studies in 293T cells. Western blotting showed that DAPK was a substrate for LAR and, using DAPK mutants, the authors identified Tyr
491
and Tyr
492
as the target dephosphorylation sites. In vitro kinase assays demonstrated that the kinase activity of DAPK was increased in 293T transfectants coexpressing LAR but not in cells expressing a phosphatase-deficient mutant LAR. 293T cells cotransfected with DAPK and LAR performed poorly in adhesion assays compared with 293T cells transfected with DAPK alone. Adhesion of cells to fibronectin resulted in the phosphorylation of DAPK, which was reduced by inhibitors of Src tyrosine kinases. Western blotting revealed that Src phosphorylated DAPK at the same residues targeted by LAR, and Src-mediated phosphorylation of DAPK promoted cell adhesion and migration. Epidermal growth factor (EGF) activates Src and decreases the abundance of LAR at the membrane. Treatment of epithelial carcinoma cells with EGF resulted in DAPK inactivation and increased EGF-stimulated migration. Immunohistochemistry demonstrated a correlation between the incidence of hyperphosphorylated, inactivated DAPK and increased Src activity in tumor cells. Together, these data establish a possible link between EGF-induced tumorigenesis and DAPK inactivation through the reciprocal regulation of DAPK by LAR and Src.

W.-J. Wang, J.-C. Kuo, W. Ku, Y.-R. Lee, F.-C. Lin, Y.-L. Chang, Y.-M. Lin, C.-H. Chen, Y.-P. Huang, M.-J. Chiang, S.-W. Yeh, P.-R. Wu, C.-H. Shen, C.-T. Wu, R.-H. Chen, The tumor suppressor DAPK is reciprocally regulated by tyrosine kinase Src and phosphatase LAR.
Mol. Cell
27
, 701-716 (2007).
[PubMed]
Helping Plants Survive Heat Stress
Authors: Gough Nancy R.
Published: September 2007

Plants rely on microorganisms in the local environment for various important processes. One of the most commonly known is nitrogen fixation by symbiotic bacteria that colonize the roots of some plants. McLellan
et al
. provide evidence that fungi in the rhizosphere (the soil surrounding the roots of plants) may also contribute to heat tolerance. Previously, two inhibitors of mammalian heat shock protein 90 (HSP90) were discovered in extracts from Sonoran desert plant-associated fungi, McLellan
et al
. follow up on this result and show that one of these, monocillin I (MON), specifically binds and inhibits the chaperone activity of
Arabidopsis
HSP90 in vitro. Exposure of
Arabidopsis
seedlings to MON increased the expression and abundance of the heat shock response protein AtHSP101. Pretreatment of seedlings with MON before what would be a lethal heat stress in untreated plants increased the survival of the MON-exposed seedlings. The rescue of growth by MON required HSP101, consistent with MON’s triggering the heat shock response. When
Arabidopsis
seedlings were cultured with the fungus that produces MON, hypocotyl elongation was decreased compared with that in plants grown in the absence of MON; however, the plants tolerated heat stress much better in the presence of the fungus.

C. A. McLellan, T. J. Turbyville, E. M. K. Wijeratne, A. Kerschen, E. Vierling, C. Queitsch, L. Whitesell, A. A. L. Gunatilaka, A rhizosphere fungus enhances Arabidopsis thermotolerance through production of an HSP90 inhibitor.
Plant Physiol.
145
, 174-182 (2007).
[Abstract]
[Full Text]
β-Actin: A Regulator of NOS-3
Authors: Su Yunchao , Kondrikov Dmitry , Block Edward R.
Published: September 2007

β-actin is traditionally considered a structural protein that organizes and maintains the shape of nonmuscle cells, although data now indicate that β-actin is also a signaling molecule. β-actin is directly associated with nitric oxide synthase type 3 (NOS-3) in endothelial cells and platelets, and this interaction increases NOS-3 activity and the affinity of NOS-3 for heat shock protein 90 kD (Hsp90). The β-actin–induced increase in NOS-3 activity may be caused directly by β-actin, the binding of Hsp90 to NOS-3, or both. Alterations in the interaction between β-actin and NOS-3 could be caused by changes either in the availability of β-actin or in the affinity of NOS-3 for β-actin, and these alterations probably contribute to vascular complications and platelet aggregation. Studies examining the interactions between NOS-3, β-actin, and Hsp90 could potentially lead to the discovery of effective peptides for the treatment of diseases associated with impaired NOS-3 activity and nitric oxide release, such as systemic and pulmonary hypertension, atherosclerosis, and thrombotic diseases.
Endogenous Enhancers of Toll-Like Receptor 4
Authors: Foley John F.
Published: September 2007

Lipopolysaccharide (LPS) is a bacterial component that triggers an inflammatory response that can lead to sepsis and death. Myeloid-related protein 8 (Mrp8) and Mrp14 interact with each other and are secreted by activated phagocytes, with Mrp8 as the active subunit of the complex. Vogl
et al
. investigated the role of these proteins in sepsis. Using DNA microarrays, they found that a number of genes encoding proinflammatory molecules were more highly expressed in LPS-treated bone marrow cells (BMCs) from wild-type mice than in those of

Mrp14
–/–

mice. (

Mrp8
–/–

mice die as embryos.) Enzyme-linked immunosorbant assays revealed that LPS-treated

Mrp14
–/–

BMCs secreted lower quantities of tumor necrosis factor-α (TNF-α) than did LPS-treated wild-type BMCs. Addition of recombinant Mrp8-Mrp14 increased the responsiveness of

Mrp14
–/–

BMCs to LPS. Immunofluorescence and Western blotting analyses in human epithelial cells showed that Mrp8 stimulated the recruitment of the adaptor protein myeloid differentiation marker 88 to the plasma membrane and the phosphorylation of interleukin-1 receptor (IL-1R)-associated kinase-1 (IRAK-1), both of which are necessary for Toll-like receptor 4 (TLR4) signaling. Luciferase reporter assays performed in 293 cells transfected with TLR4 and its co-receptors MD2 and CD14 revealed that Mrp8 stimulated the activity of the transcription factor nuclear factor κB. Surface plasmon resonance studies showed that Mrp8 bound to the TLR4-MD2 complex. Administration of LPS and galactosamine, which sensitizes mice to LPS-induced TNF-α, to

Mrp14
–/–

mice resulted in less severe effects and better survival than did similar treatment of wild-type mice. The addition of Mrp8 to the

Mrp14
–/–

mice treated with LPS and galactosamine resulted in an outcome similar to that of LPS-treated wild-type mice. The role of Mrp8-Mrp14 as an endogenous enhancer of TLR4-induced TNF-α production in response to LPS thus reveals a new possible therapeutic target in the treatment of sepsis.

T. Vogl, K. Tenbrock, S. Ludwig, N. Leukert, C. Ehrhardt, M. A. D. van Zoelen, W. Nacken, D. Foell, T. van der Poll, C. Sorg, J. Roth, Mrp8 and Mrp14 are endogenous activators of Toll-like receptor 4, promoting lethal, endotoxin-induced shock.
Nat. Med
.
13
, 1042-1049 (2007).
[PubMed]
Receptor Swapping
Authors: Ray L. Bryan
Published: September 2007

The signals that a cell receives from its environment can be altered if cells acquire new receptors on their cell surface. In fact, cells appear to be able to acquire receptors that they themselves are not programmed to express through incorporation of membrane-derived microparticles released from other cells. In particular, during inflammatory responses, platelet-derived microparticles (PMPs) are released that can transfer molecules to cells in the blood vessel walls or to cells in the blood, like neutrophils. Salanova
et al.
discovered that the integrin glycoprotein IIb/IIIa (GPIIb/IIIa), which recognizes various adhesion proteins and thus contributes to platelet aggregation, can be transferred in PMPs to circulating neutrophils. After treatment of whole human blood with adenosine diphosphate to activate platelets, the authors used flow cytometry and fluorescence microscopy to show that neutrophils, which originally showed little evidence of GPIIb/IIIa on their cell surface, acquired small patches on the cell surface that contained the integrin. These receptors appeared to be transferred by PMPs, because they were also present when PMPs were isolated and then applied to purified neutrophils. Neutrophils activate the transcription factor NF-κB when they receive integrin signals together with stimulation by cytokines. Salanova
et al
. observed that neutrophils treated with the cytokine GM-CSF (granulocyte-macrophage colony-stimulating factor) that had also acquired GPIIb/IIIa from PMPs activated NF-κB in response to antibodies that stimulated GPIIb/IIIa or the native integrin CD18. Blocking activation of either one of the integrins inhibited activation of NF-κB. Similarly treated cells that didn’t acquire PMPs did not activate NF-κB in response to activation of either integrin. Fluorescence microscopy indicated that the two integrins were localized together on the cell surface of the neutrophils. Thus, transferred GPIIb/IIIa appears to act together with native integrins of the neutrophil. Inflammation is thought to contribute to the deleterious effects of vascular injury, and inhibition of such responses may be of therapeutic value. In this regard, Salanova
et al
. showed that inhibitors of GPIIb/IIIa already in use clinically to limit platelet aggregation prevented activation of NF-κB in neutrophils that had acquired GPIIb/IIIa and were exposed to GM-CSF and fibronectin (an integrin ligand).

B. Salanova, M. Choi, S. Rolle, M. Wellner, F. C. Luft, R. Kettritz, β2-integrins and acquired glycoprotein IIb/IIIa (GPIIb/IIIa) receptors cooperate in NF-κB activation of human neutrophils.
J. Biol Chem.
282
, 27960-27969 (2007).
[Abstract]
[Full Text]
Regulating Glucose
Authors: Adler Elizabeth M.
Published: September 2007

Increased extracellular glucose stimulates firing of a subset of proopiomelanocortin (POMC)-containing neurons in the hypothalamus through a mechanism thought to depend, like insulin secretion in pancreatic β cells, on the adenosine 5′-triphosphate (ATP)-dependent closure of ATP-sensitive potassium (K
ATP
) channels in the plasma membrane. Parton
et al
. generated transgenic mice (POMC-mut-Kir6.2 mice) that expressed a mutant K
ATP
Kir6.2 subunit under the transcriptional control of the POMC promoter, so that relatively ATP-insensitive K
ATP
channels were selectively expressed in hypothalamic POMC neurons (and in the pituitary). Although the body weight of POMC-mut-Kir6.2 mice was normal, glucose homeostasis was impaired so that they showed an exaggerated increase in blood glucose after intraperitoneal glucose injection. Whereas the firing rate of about half the POMC neurons in wild-type mice was stimulated by physiologically relevant increases in glucose concentration, only 1 of 27 POMC neurons in POMC-mut-Kir6.2 mice was glucose-sensitive. Glucose stimulated release of α-melanocyte–stimulating hormone (α-MSH) from hypothalamic slices from wild-type, but not POMC-mut-Kir6.2, mice. Moreover, it failed to stimulate the release of α-MSH from hypothalamic slices of wild-type mice fed a high-fat diet, and its effect on the firing rate of their POMC neurons was severely attenuated. Expression of the mRNA encoding uncoupling protein 2 (UCP2, a mitochondrial protein that decreases ATP production from glucose) was increased in the hypothalami of obese mice, and pharmacological inhibition of UCP with genipin stimulated firing in glucose-sensitive POMC neurons from wild-type mice. Genipin had little effect on POMC neuronal firing in POMC-mut-Kir6.2 mice, but it restored glucose-dependent release of hypothalamic α-MSH in mice fed a high-fat diet. Furthermore, although mice lacking UCP2 became obese when fed a high-fat diet, the ability of glucose to elicit release of their hypothalamic α-MSH was intact. Thus, the authors conclude that glucose sensing by hypothalamic POMC neurons is implicated in systemic glucose homeostasis, a sensitivity that is lost through a mechanism involving UCP2 in obese mice fed a high-fat diet. They further note that these findings may be pertinent to the pathogenesis of type 2 diabetes.

L. E. Parton, C. P. Ye, R. Coppari, P. J. Enriori, B. Choi, C.-Y. Zhang, C. Xu, C. R. Vianna, N. Balthasar, C. E. Lee, J. K. Elmquist, M. A. Cowley, B. B. Lowell, Glucose sensing by POMC neurons regulates glucose homeostasis and is impaired in obesity.
Nature
449
, 228-232 (2007).
[PubMed]
Establishing Asymmetry
Authors: Adler Elizabeth M.
Published: September 2007

Fertilization of the
Xenopus
egg leads to the asymmetrical distribution of components of the Wnt/β-catenin pathway to what will become the dorsal side of the embryo. This leads to asymmetric signaling by Nodal, a transforming growth factor–β ligand critical to embryonic axis specification and to mesoderm induction. Martello
et al
. found that microRNAs (miRNAs) from gastrula-stage
Xenopus
embryos inhibited embryonic Nodal signaling. Computational analysis revealed binding sites for two related miRNAs, miR-15 and miR-16, in the 3′ untranslated region (3′ UTR) of mRNA encoding the type II Nodal receptor Acvr2a. Activity of a reporter containing a wild-type miR-15–binding site was reduced in
Xenopus
embryos and human HepG2 cells compared with that of a reporter containing a mutated binding site. In addition, activity of the former was further decreased by overexpression of miR-15 or its primary precursor (pri-miR-15/16). Injection of miR-15 inhibited endogenous Nodal signaling and attenuated downstream sequelae such as mesoderm induction and development of Spemann’s organizer, phenotypic defects that were rescued by coinjection of
Acvr2a
mRNA lacking the 3′ UTR. In contrast, inhibitory oligonucleotides directed against miR-15 and miR-16 increased Acvr2a abundance and promoted expansion of Spemann’s organizer. The abundance and activity of miR-15 and miR-16 were greatest ventrally; Acvr2a abundance and Smad2 phosphorylation (p-Smad2, a marker for Nodal signaling) were greatest dorsally. Injection of pri-miR-15/16 led to a decrease in dorsal p-Smad2, whereas inhibition of miR-15 and miR-16 led to an increase in ventral p-Smad2. Overexpression of
Xwnt-8
or
β-catenin
mRNA decreased the abundance and activity of miR-15 and miR-16, whereas β-catenin knockdown increased them. Thus, miR-15 and miR-16 appear to constitute a link between asymmetry in Wnt/β-catenin and asymmetry in Nodal signaling and, thereby, to play a crucial role in the regulation of embryonic patterning.

G. Martello, L. Zacchigna, M. Inui, M. Montagner, M. Adorno, A. Mamidi, L. Morsut, S. Soligo, U. Tran, S. Dupont, M. Cordenonsi, O. Wessely, S. Piccolo, MicroRNA control of Nodal signalling.
Nature
449
, 183-188 (2007).
[PubMed]
Functional Evolution of Proteins
Authors: Vinson Valda J.
Published: September 2007

The direct identification of protein evolution mechanisms requires comparing proteins through evolutionary time. The sequence of the 450-million-year-old ancestor of vertebrate mineralocorticoid (MR) and glucocorticoid (GR) receptors was previously determined by phylogenetic analysis, and the ancestor was shown to have MR-like hormone specificity. Ortlund
et al
. used structural, functional, and phylogenetic analysis to determine how specific mutations resulted in a change from MR-like to GR hormone specificity. They find evidence for epistatic interactions where a substitution changed the conformation at another site. Substitutions that had no immediate functional effect, but affected stability to allow subsequent function-switching mutations, played an important role in GR evolution.

E. A. Ortlund, J. T. Bridgham, M. R. Redinbo, J. W. Thornton, Crystal structure of an ancient protein: Evolution by conformational epistasis.
Science
317
, 1544-1548 (2007).
[Abstract]
[Full Text]
Further refinement to the timing of Mesoproterozoic magmatism, Lake Nipigon region, Ontario
Authors: Heaman L M , Easton R M , Hart T R , Hollings P , MacDonald C A , Smyk M
Published: September 2007

The Midcontinent Rift in the Lake Superior region of North America is one of the best preserved examples of an aborted Precambrian intercontinental rift, one that hosts a diverse suite of rock types in addition to the well-studied and voluminous rift-fill flood basalts. Although there is a growing database of high-precision age information for the main volcanic packages and the largest mafic intrusions, there is relatively little information available on the absolute timing of mafic-ultramafic intrusions, dyke swarms, and alkaline complexes, especially in the Ontario portion of the rift. We report new high-precision U–Pb ages for 29 samples, primarily collected in the Lake Nipigon area, Ontario. From these new age results, it is now possible to expand the known distribution of Geon 15 magmatism in the region, confirm an early stage of Midcontinent Rift mafic magmatism between 1150 and 1130 Ma, provide evidence that significant mafic–ultramafic magmatism occurred in the Lake Nipigon region slightly earlier (~1115–1110 Ma) than the main stage of rift magmatism (1108–1094 Ma), and further document synchronous ~1110–1100 Ma tholeiitic and alkaline magmatism.
Geochemistry of the Mesoproterozoic intrusive rocks of the Nipigon Embayment, northwestern Ontario: evaluating the earliest phases of rift development
Authors: Hart Thomas , Richardson Adam , MacDonald Carole Anne , Hollings Pete
Published: September 2007

The intrusive rocks of the Nipigon Embayment comprise a series of four mafic to ultramafic intrusions and a number of laterally extensive diabase sills that are among the oldest expression of the ~1.1 Ga Mesoproterozoic Mid-continent Rift. New geochemical data indicate that the sills can be subdivided into five distinct groups: three mafic sills (Nipigon, Inspiration, and McIntyre diabase sills), with the Nipigon sills forming the bulk of the outcrop, and two spatially restricted ultramafic to mafic sills (Jackfish and Shillabeer sills). The latter mafic sills are typically massive, medium-grained, intergranular textured gabbros ranging in thickness from a few metres to more than 250 m. Two of the ultramafic intrusions included in this study (Disraeli and Hele) consist of a core of pyroxene peridotite with olivine gabbro along the margins. The geochemical characteristics of the ultramafic intrusions and diabase sills are consistent with plume-derived melts that have undergone subsequent fractionation and been contaminated by continental crust, likely at depth, but a few samples from the Hele and Disraeli intrusions have the characteristics of primary, uncontaminated melts that have been rapidly transported through the lithosphere with little interaction with wall rocks. The field and geochemical characteristics of the intrusions and sills are consistent with the ultramafic intrusions having been emplaced before the diabase sills and indicate that the history of the Midcontinent Rift is more complex and protracted than previously recognized.
Radiogenic isotope characteristics of the Mesoproterozoic intrusive rocks of the Nipigon Embayment, northwestern Ontario
Authors: Hollings Pete , Richardson Adam , Creaser Robert A , Franklin James M
Published: September 2007

The ca. 1110–1120 Ma diabase sills of the Nipigon Embayment represent the oldest phase of the Midcontinent Rift recognized to date. The sills can be subdivided into five geochemically distinct suites: Nipigon, McIntyre, Inspiration, Shillabeer, and Jackfish. Sm–Nd, Rb–Sr, and Pb–Pb isotope data for the sills can be used to evaluate the source regions and emplacement histories of these sills. The εNdT values for all the sill suites are consistently negative (–0.5 to –6.6) but show coherent variations both within and between suites. The negative εNdT values can be interpreted as the result of contamination of a plume-related mantle source by older crustal material. The initial strontium (Sri) values (0.7032–0.7068) for the sills indicate that at least two distinct contaminants are required: (1) a source with strongly negative εNdT and lower Sri, likely Archean metasediment or granite, and (2) one with elevated Sri, likely sedimentary rocks of the Proterozoic Sibley Group. The Pb data for the Nipigon and Inspiration sills form distinct linear arrays consistent with variable contamination of a source comparable to that of other igneous suites of the Midcontinent Rift. The radiogenic isotopes preserve a complex contamination history best interpreted as the result of <5% contamination by a variety of Archean and Proterozoic sources. The ultramafic Jackfish sill shows the least evidence of contamination and is interpreted to have been emplaced along a crustal-scale fault with little interaction with crustal material. In contrast, the other sill suites have undergone complex contamination histories requiring variable crustal residence times and assimilation of material both at depth in large magma chambers and during emplacement.
Overburden geochemical signature of the Lac des Iles platinum group element deposit, northwestern Ontario, Canada
Authors: Barnett Peter J
Published: September 2007

Many previously published studies of the behaviour of Pt and Pd in till and soils have been done in areas of complex stratigraphy or very thin overburden cover, making the interpretation of soil results difficult because of the many variables associated with these settings. At the Lac des Iles mine site in northwestern Ontario, there are excellent exposures of the overburden in a series of exploration trenches. Glacial dispersal trains can be observed in till (C horizon) geochemistry (e.g., Ni, Cr, Cu, and Co). Regional geochemical dispersal trains of elements, such as Ni, Cr, Mg, and Co associated with the North Lac des Iles intrusion, can be detected for about 4 km beyond the western margin of the Mine Block intrusion. Entire dispersal trains range from 5 to 7 km in length and about 1 to 2 km in width. The dispersal of North Lac des Iles intrusion rock fragments tends to mask the response of the Mine Block intrusion. Dispersal trains of Pt and Pd are not well defined and tend to be very short, <1 km in length, due to the initial low concentrations of these elements in C-horizon till samples from the Lac Des Iles area. An exception to this is the Pd dispersal train originating from the high-grade zone that is up to 3 km long. Pd, Pt, Ni, and Cu appear to be moving both within and out of the soil system downslope into surface and shallow groundwater. It is suggested that these elements, to varying degrees, are moving in solution. Airborne contamination from mine operations of the humus has adversely affected the ability to determine the effectiveness of humus sampling for mineral exploration at Lac des Iles. The airborne contamination likely influences the geochemical results from surface water, shallow groundwater, and near-surface organic bog samples, particularly for the elements Pd and Pt.