Bacterial lipopolysaccharide activates nuclear factor-kappaB through interleukin-1 signaling mediators in cultured human dermal endothelial cells and mononuclear phagocytes

Bacterial lipopolysaccharide (LPS)-mediated immune responses, including activation of monocytes, macrophages, and endothelial cells, play an important role in the pathogenesis of Gram-negative bacteria-induced sepsis syndrome. Activation of NF-kappaB is thought to be required for cytokine release from LPS-responsive cells, a critical step for endotoxic effects. Here we investigated the role and involvement of interleukin-1 (IL-1) and tumor necrosis factor (TNF-alpha) signal transducer molecules in LPS signaling in human dermal microvessel endothelial cells (HDMEC) and THP-1 monocytic cells. LPS stimulation of HDMEC and THP-1 cells initiated an IL-1 receptor-like NF-kappaB signaling cascade. In transient cotransfection experiments, dominant negative mutants of the IL-1 signaling pathway, including MyD88, IRAK, IRAK2, and TRAF6 inhibited both IL-1- and LPS-induced NF-kappaB-luciferase activity. LPS-induced NF-kappaB activation was not inhibited by a dominant negative mutant of TRAF2 that is involved in TNF signaling. LPS-induced activation of NF-kappaB-responsive reporter gene was not inhibited by IL-1 receptor antagonist. TLR2 and TLR4 were expressed on the cell surface of HDMEC and THP-1 cells. These findings suggest that a signal transduction molecule in the LPS receptor complex may belong to the IL-1 receptor/toll-like receptor (TLR) super family, and the LPS signaling cascade uses an analogous molecular framework for signaling as IL-1 in mononuclear phagocytes and endothelial cells.

Global fire emissions and the contribution of deforestation, savanna, forest, agricultural, and peat fires (1997–2009)

Abstract. New burned area datasets and top-down constraints from atmospheric concentration measurements of pyrogenic gases have decreased the large uncertainty in fire emissions estimates. However, significant gaps remain in our understanding of the contribution of deforestation, savanna, forest, agricultural waste, and peat fires to total global fire emissions. Here we used a revised version of the Carnegie-Ames-Stanford-Approach (CASA) biogeochemical model and improved satellite-derived estimates of area burned, fire activity, and plant productivity to calculate fire emissions for the 1997–2009 period on a 0.5° spatial resolution with a monthly time step. For November 2000 onwards, estimates were based on burned area, active fire detections, and plant productivity from the MODerate resolution Imaging Spectroradiometer (MODIS) sensor. For the partitioning we focused on the MODIS era. We used maps of burned area derived from the Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) and Along-Track Scanning Radiometer (ATSR) active fire data prior to MODIS (1997–2000) and estimates of plant productivity derived from Advanced Very High Resolution Radiometer (AVHRR) observations during the same period. Average global fire carbon emissions according to this version 3 of the Global Fire Emissions Database (GFED3) were 2.0 Pg C year−1 with significant interannual variability during 1997–2001 (2.8 Pg C year−1 in 1998 and 1.6 Pg C year−1 in 2001). Globally, emissions during 2002–2007 were relatively constant (around 2.1 Pg C year−1) before declining in 2008 (1.7 Pg C year−1) and 2009 (1.5 Pg C year−1) partly due to lower deforestation fire emissions in South America and tropical Asia. On a regional basis, emissions were highly variable during 2002–2007 (e.g., boreal Asia, South America, and Indonesia), but these regional differences canceled out at a global level. During the MODIS era (2001–2009), most carbon emissions were from fires in grasslands and savannas (44%) with smaller contributions from tropical deforestation and degradation fires (20%), woodland fires (mostly confined to the tropics, 16%), forest fires (mostly in the extratropics, 15%), agricultural waste burning (3%), and tropical peat fires (3%). The contribution from agricultural waste fires was likely a lower bound because our approach for measuring burned area could not detect all of these relatively small fires. Total carbon emissions were on average 13% lower than in our previous (GFED2) work. For reduced trace gases such as CO and CH4, deforestation, degradation, and peat fires were more important contributors because of higher emissions of reduced trace gases per unit carbon combusted compared to savanna fires. Carbon emissions from tropical deforestation, degradation, and peatland fires were on average 0.5 Pg C year−1. The carbon emissions from these fires may not be balanced by regrowth following fire. Our results provide the first global assessment of the contribution of different sources to total global fire emissions for the past decade, and supply the community with an improved 13-year fire emissions time series.

An on-demand coherent single-electron source

We report on the electron analog of the single-photon gun. On-demand single-electron injection in a quantum conductor was obtained using a quantum dot connected to the conductor via a tunnel barrier. Electron emission was triggered by the application of a potential step that compensated for the dot-charging energy. Depending on the barrier transparency, the quantum emission time ranged from 0.1 to 10 nanoseconds. The single-electron source should prove useful for the use of quantum bits in ballistic conductors. Additionally, periodic sequences of single-electron emission and absorption generate a quantized alternating current.

Neutralization of TGF-beta by anti-TGF-beta antibody attenuates kidney hypertrophy and the enhanced extracellular matrix gene expression in STZ-induced diabetic mice

Diabetic nephropathy is characterized by renal hypertrophy, thickening of basement membranes, and accumulation of extracellular matrix in the glomerular mesangium and the interstitium. Our previous investigations have shown that high glucose concentration increases transforming growth factor (TGF)-beta1 mRNA in mesangial and proximal tubule cells and that treatment with anti-TGF-beta antibody results in prevention of the effects of high glucose on cell growth (e.g., induction of cellular hypertrophy) and the stimulation of collagen biosynthesis. We evaluated in vivo the functional role of the renal TGF-beta system in diabetic kidney disease by treatment of streptozotocin-induced diabetic mice with either a neutralizing monoclonal antibody against TGF-beta1, -beta2, and -beta3 (alphaT) or nonimmune murine IgG for 9 days. Diabetic mice given IgG demonstrated total kidney and glomerular hypertrophy, significantly elevated urinary TGF-beta1 protein, and increased mRNAs encoding TGF-beta1, type II TGF-beta receptor, alpha1(IV) collagen, and fibronectin. Treatment of diabetic mice with alphaT prevented glomerular hypertrophy, reduced the increment in kidney weight by approximately 50%, and significantly attenuated the increase in mRNA levels without having any effect on blood glucose. The antibody was without significant effect on mRNA levels in nondiabetic mice. This is the first demonstration that the early characteristic features of diabetic renal involvement, which include hypertrophy and increased matrix mRNAs, are largely mediated by increased endogenous TGF-beta activity in the kidney and that they can be significantly attenuated by treatment with neutralizing anti-TGF-beta antibodies.

Coherence and indistinguishability of single electrons emitted by independent sources

The on-demand emission of coherent and indistinguishable electrons by independent synchronized sources is a challenging task of quantum electronics, in particular regarding its application for quantum information processing. Using two independent on-demand electron sources, we triggered the emission of two single-electron wave packets at different inputs of an electronic beam splitter. Whereas classical particles would be randomly partitioned by the splitter, we observed two-particle interference resulting from quantum exchange. Both electrons, emitted in indistinguishable wave packets with synchronized arrival time on the splitter, exited in different outputs as recorded by the low-frequency current noise. The demonstration of two-electron interference provides the possibility of manipulating coherent and indistinguishable single-electron wave packets in quantum conductors.

The liprin protein SYD-2 regulates the differentiation of presynaptic termini in C. elegans

At synaptic junctions, specialized subcellular structures occur in both pre- and postsynaptic cells. Most presynaptic termini contain electron-dense membrane structures, often referred to as active zones, which function in vesicle docking and release. The components of those active zones and how they are formed are largely unknown. We report here that a mutation in the Caenorhabditis elegans syd-2 (for synapse-defective) gene causes a diffused localization of several presynaptic proteins and of a synaptic-vesicle membrane associated green fluorescent protein (GFP) marker. Ultrastructural analysis revealed that the active zones of syd-2 mutants were significantly lengthened, whereas the total number of vesicles per synapse and the number of vesicles at the prominent active zones were comparable to those in wild-type animals. Synaptic transmission is partially impaired in syd-2 mutants. syd-2 encodes a member of the liprin (for LAR-interacting protein) family of proteins which interact with LAR-type (for leukocyte common antigen related) receptor proteins with tyrosine phosphatase activity (RPTPs). SYD-2 protein is localized at presynaptic termini independently of the presence of vesicles, and functions cell autonomously. We propose that SYD-2 regulates the differentiation of presynaptic termini in particular the formation of the active zone, by acting as an intracellular anchor for RPTP signalling at synaptic junctions.

Defective recycling of synaptic vesicles in synaptotagmin mutants of Caenorhabditis elegans

Synaptotagmin, an integral membrane protein of the synaptic vesicle, binds calcium and interacts with proteins of the plasma membrane. These observations suggest several possible functions for synaptotagmin in synaptic vesicle dynamics: it could facilitate exocytosis by promoting calcium-dependent fusion, inhibit exocytosis by preventing fusion, or facilitate endocytosis of synaptic vesicles from the plasma membrane by acting as a receptor for the endocytotic proteins of the clathrin AP2 complex. Here we show that synaptic vesicles are depleted at synaptic terminals in synaptotagmin mutants of the nematode Caenorhabditis elegans. This depletion is not caused by a defect in transport or by increased synaptic vesicle release, but rather by a defect in retrieval or synaptic vesicles from the plasma membrane. Thus we propose that, as well as being involved in exocytosis, synaptotagmin functions in vesicular recycling.

TGF-β1-induced EMT promotes targeted migration of breast cancer cells through the lymphatic system by the activation of CCR7/CCL21-mediated chemotaxis

Tumor cells frequently disseminate through the lymphatic system during metastatic spread of breast cancer and many other types of cancer. Yet it is not clear how tumor cells make their way into the lymphatic system and how they choose between lymphatic and blood vessels for migration. Here we report that mammary tumor cells undergoing epithelial–mesenchymal transition (EMT) in response to transforming growth factor-β (TGF-β1) become activated for targeted migration through the lymphatic system, similar to dendritic cells (DCs) during inflammation. EMT cells preferentially migrated toward lymphatic vessels compared with blood vessels, both in vivo and in 3D cultures. A mechanism of this targeted migration was traced to the capacity of TGF-β1 to promote CCR7/CCL21-mediated crosstalk between tumor cells and lymphatic endothelial cells. On one hand, TGF-β1 promoted CCR7 expression in EMT cells through p38 MAP kinase-mediated activation of the JunB transcription factor. Blockade of CCR7, or treatment with a p38 MAP kinase inhibitor, reduced lymphatic dissemination of EMT cells in syngeneic mice. On the other hand, TGF-β1 promoted CCL21 expression in lymphatic endothelial cells. CCL21 acted in a paracrine fashion to mediate chemotactic migration of EMT cells toward lymphatic endothelial cells. The results identify TGF-β1-induced EMT as a mechanism, which activates tumor cells for targeted, DC-like migration through the lymphatic system. Furthermore, it suggests that p38 MAP kinase inhibition may be a useful strategy to inhibit EMT and lymphogenic spread of tumor cells.

Magnetization directions of individual nanoparticles

The magnetization directions of individual monodomain nanoparticles as small as 5 nanometers in diameter are determined using the Foucault method of Lorentz microscopy. A model is developed to explain the images and diffraction patterns of samarium cobalt nanoparticles as a function of the aperture shift direction. Thermally induced changes in the magnetization direction of superparamagnetic magnetite nanoparticles were observed but with a much slower rate than expected, due to surface anisotropy. When the time scale for magnetization reversal is much shorter than the data acquisition time, as in carbon-coated iron cobalt alloy nanoparticles, the images show an average of such thermally induced changes.

Expression of interleukin 8 and CD54 by human gastric epithelium after Helicobacter pylori infection in vitro

BACKGROUND/AIMS

Helicobacter pylori is associated with neutrophil infiltrates, although the mechanism of their recruitment is only partially defined. The aim of the study was to determine if Kato III, a human gastric epithelial cell line, expressed cytokines and the intercellular adhesion molecule 1 (ICAM-1), which could contribute to the initiation of inflammation during infection with H. pylori.

METHODS

Kato III cells were stimulated with H. pylori and were examined for evidence of infection, cytokine production, and the expression of ICAM-1.

RESULTS

The expression of interleukin 8 messenger RNA and immunoreactive protein by Kato III cells was significantly increased over constitutive levels within 3 hours of infection with H. pylori. Infected Kato III supernatants activated neutrophils as evidenced by increased CD11b/CD18 and decreased L-selectin that could be blocked by anti-interleukin 8. In contrast, Campylobacter jejuni, lipopolysaccharide, killed H. pylori, and supernatants from cultures of H. pylori did not increase interleukin 8. Interleukins 2 and 6; interferons alfa, beta, and gamma; and tumor necrosis factor were not produced by resting or H. pylori-stimulated Kato III cells. In addition to producing interleukin 8, Kato III constitutively expressed surface ICAM-1, which acts as an intercellular adhesion molecule for neutrophils.

CONCLUSIONS

Our results indicate that H. pylori stimulates the gastric epithelium to initiate inflammation and neutrophil recruitment and activation.

Regulation of presynaptic terminal organization by C. elegans RPM-1, a putative guanine nucleotide exchanger with a RING-H2 finger domain

Presynaptic terminals contain highly organized subcellular structures to facilitate neurotransmitter release. In C. elegans, the typical presynaptic terminal has an electron-dense active zone surrounded by synaptic vesicles. Loss-of-function mutations in the rpm-1 gene result in abnormally structured presynaptic terminals in GABAergic neuromuscular junctions (NMJs), most often manifested as a single presynaptic terminal containing multiple active zones. The RPM-1 protein has an RCC1-like guanine nucleotide exchange factor (GEF) domain and a RING-H2 finger. RPM-1 is most similar to the Drosophila presynaptic protein Highwire (HIW) and the mammalian Myc binding protein Pam. RPM-1 is localized to the presynaptic region independent of synaptic vesicles and functions cell autonomously. The temperature-sensitive period of rpm-1 coincides with the time of synaptogenesis. rpm-1 may regulate the spatial arrangement, or restrict the formation, of presynaptic structures.

Biofilm-forming ability of Candida albicans is unlikely to contribute to high levels of oral yeast carriage in cases of human immunodeficiency virus infection

An increased prevalence of candidal carriage and oral candidiasis is common in cases of human immunodeficiency virus (HIV) infection, and the reasons for this may include the enhanced ability of colonizing yeasts to produce biofilms on mucosal surfaces. The aim of the present study was therefore to examine the differences, if any, in the biofilm-forming abilities of 26 Candida albicans yeast isolates from HIV-infected individuals and 20 isolates from HIV-free individuals, as this attribute of yeast isolates from patients with HIV disease has not been examined before. Biofilm formation in microtiter plate wells was quantitatively determined by both the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide (XTT) reduction method and the crystal violet method. Although candidal biofilm formation could be quantitatively evaluated by either technique, the better reproducibility (P < 0.05) of the XTT reduction assay compared with that of the crystal violet method led us to conclude that the former is more reliable. There were no significant quantitative differences in biofilm formation between C. albicans isolates from HIV-infected patients and isolates from HIV-free individuals during in vitro incubation in a multiwell culture system over a period of 66 h. Three of eight host factors in the HIV-infected group were found to be associated with candidal biofilm formation. Thus, yeasts isolated from older individuals and those with higher CD4-cell counts exhibited decreased biofilm formation, while the findings for yeasts from individuals receiving zidovudine showed the reverse (P < 0.05 for all comparison). Our data indicate that attributes other than biofilm formation may contribute to the increased oral yeast carriage rates in cases of HIV infection.

Control of type-D GABAergic neuron differentiation by C. elegans UNC-30 homeodomain protein

The Caenorhabditis elegans gene unc-30 is required for the development and functioning of the 19 inhibitory GABAergic (gamma-aminobutyric-acid-secreting) type D motor neurons, which control locomotion. In unc-30 mutants the D neurons lack GABA and have defects in axonal pathfinding and synaptic connections (J. White, personal communication). We report here that unc-30 encodes a homeodomain protein that is present in the nuclei of the D neurons at high levels in young larvae, in which the motor circuitry is formed, and at low levels in older animals. The UNC-30 protein is also present in six non-GABAergic neurons and is absent from the seven non-D-type GABAergic neurons. Ectopic expression of unc-30 induced GABA expression in cells that are normally not GABAergic. We propose that unc-30 functions as a transcriptional regulator within the type D neurons to control their terminal differentiation and that unc-30 is sufficient in some but not all cell types to induce GABA expression.

UNC-16, a JNK-signaling scaffold protein, regulates vesicle transport in C. elegans

Transport of synaptic components is a regulated process. Loss-of-function mutations in the C. elegans unc-16 gene result in the mislocalization of synaptic vesicle and glutamate receptor markers. unc-16 encodes a homolog of mouse JSAP1/JIP3 and Drosophila Sunday Driver. Like JSAP1/JIP3, UNC-16 physically interacts with JNK and JNK kinases. Deletion mutations in Caenorhabditis elegans JNK and JNK kinases result in similar mislocalization of synaptic vesicle markers and enhance weak unc-16 mutant phenotypes. unc-116 kinesin heavy chain mutants also mislocalize synaptic vesicle markers, as well as a functional UNC-16::GFP. Intriguingly, unc-16 mutations partially suppress the vesicle retention defect in unc-104 KIF1A kinesin mutants. Our results suggest that UNC-16 may regulate the localization of vesicular cargo by integrating JNK signaling and kinesin-1 transport.

Detection of Virulence to Resistance Gene Sr24 Within Race TTKS of Puccinia graminis f. sp. tritici

The stem rust resistance gene Sr24 is effective against most races of Puccinia graminis f. sp. tritici, including race TTKS (syn. Ug99), and is used widely in commercial wheat cultivars worldwide. In 2006, susceptible infection responses were observed on wheat lines and cultivars carrying Sr24 in a field stem rust screening nursery at Njoro, Kenya. We derived 28 single-pustule isolates from stem rust samples collected from the 2006 Njoro nursery. The isolates were evaluated for virulence on 16 North American stem rust differential lines; on wheat lines carrying Sr24, Sr31, Sr38, and SrMcN; and on a wheat cultivar with a combination of Sr24 and Sr31. All isolates were identified as race TTKS with additional virulence on Sr31 and Sr38. These isolates were divided into two groups: group A (seven isolates and the two control isolates), producing a low infection type, and group B (21 isolates), producing a high infection type on Sr24, respectively. Isolates of group B represented a new variant of race TTKS with virulence to Sr24. Eighteen simple sequence repeat (SSR) markers were used to examine the genetic relationship between these two groups of isolates in race TTKS and five North American races (MCCF, QCCQ, RCRS, RTHS, and TPMK) that are representative of distinct lineage groups. All isolates of race TTKS shared an identical SSR genotype and were clearly different from North American races. The virulence and SSR data indicated that the new variant of race TTKS with Sr24 virulence likely has arisen via mutation within the TTKS genetic lineage. We propose to revise the North American stem rust nomenclature system by the addition of four genes (Sr24, Sr31, Sr38, and SrMcN) as the fifth set. This revision recognizes the virulence on Sr31 and differentiates isolates within race TTKS into two separate races: TTKSK and TTKST, with avirulence and virulence on Sr24, respectively. The occurrence of race TTKST with combined virulence on Sr24 and Sr31 has substantially increased the vulnerability of wheat to stem rust worldwide.

Characterisation of fibronectin-mediated FAK signalling pathways in lung cancer cell migration and invasion

Background:

Focal adhesion kinase (FAK) is overexpressed in a variety of cancers, such as breast, colon, prostate, ovary, and lung cancers. However, the mechanism by which extracellular matrix fibronectin stimulates lung cancer cell migration and invasion through FAK remains to be investigated.

Methods:

The signalling pathways in fibronectin-mediated lung cancer cell migration and invasion were examined using western blotting. The metastasis function was detected by wound healing, migration and invasion assays. Further, RNA interference and kinase inhibitors were also used to study the downstream signals.

Results:

In this study, we examined the FAK signalling pathways in relation to calpain-2 and RhoA in fibronectin-mediated lung cancer cell migration and invasion. We found that A549 lung epithelial cells stimulated by fibronectin showed increased phosphorylation of FAK and its downstream targets, Src, ERK1/2, phosphatidylinositol 3′-kinase (PI3K), and Akt. Consistent with this observation, depletion of FAK by siRNA resulted in the inhibition of Src, ERK1/2, PI3K, and Akt activity. In addition, the Src inhibitor, PP2, blocked the phosphorylation of FAK, ERK1/2, PI3K, and Akt. Conversely, inhibition of MEK1/2 using PD98059 reduced the expression of matrix metalloproteinase-9 (MMP9) and calpain-2. The PI3K inhibitor, LY294002, further blocked the expression of MMP9 and RhoA. Inhibition of both MEK1/2 and PI3K caused reduced cell migration and invasion.

Conclusion:

Our data suggest that fibronectin-mediated activation of FAK that leads to lung cancer metastasis could occur through ERK or PI3K/Akt regulation of MMP9/calpain-2 or MMP9/RhoA activity, respectively.

The Impact of Boreal Forest Fire on Climate Warming

We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface albedo. The net effect of all agents was to increase radiative forcing during the first year (34 +/- 31 Watts per square meter of burned area), but to decrease radiative forcing when averaged over an 80-year fire cycle (-2.3 +/- 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate climate warming.

Chromosome analysis of 97 primary breast carcinomas: identification of eight karyotypic subgroups

Chromosome banding analysis of 97 short-term cultured primary breast carcinomas revealed clonal aberrations in 79 tumors, whereas 18 were karyotypically normal. In 34 of the 79 tumors with abnormalities, two to eight clones per case were detected; unrelated clones were present in 27 (34%) cases, whereas only related clones were found in seven. These findings indicate that a substantial proportion of breast carcinomas are of polyclonal origin. Altogether eight abnormalities were repeatedly identified both as sole chromosomal anomalies and as part of more complex karyotypes: the structural rearrangements i(1)(q10), der(1:16)(q10;p10), del(1)(q11-12), del(3)(p12-13p14-21), and del(6)(q21-22) and the numerical aberrations +7, +18, and +20. At least one of these changes was found in 41 (52%) of the karyotypically abnormal tumors. They identify a minimum number of cytogenetic subgroups in breast cancer and are likely to represent primary chromosome anomalies in this type of neoplasia. Other candidates for such a role are translocations of 3p12-13 and 4q21 with various partner chromosomes and inversions of chromosome 7, which also were seen repeatedly. Additional chromosomal aberrations that give the impression of occurring nonrandomly in breast carcinomas include structural rearrangements leading to partial monosomies for 1p, 8p, 11p, 11q, 15p, 17p, 19p, and 19q and losses of one copy of chromosomes X, 8, 9, 13, 14, 17, and 22. The latter changes were seen consistently only in complex karyotypes, however, and we therefore interpret them as being secondary anomalies acquired during clonal evolution.

The JIL-1 tandem kinase mediates histone H3 phosphorylation and is required for maintenance of chromatin structure in Drosophila

To analyze the function of the chromosomal kinase JIL-1, we generated an allelic series of hypomorphic and null mutations. JIL-1 is an essential kinase for viability, and reduced levels of JIL-1 kinase activity lead to a global change in chromatin structure. In JIL-1 hypomorphs, euchromatic regions of polytene chromosomes are severely reduced and the chromosome arms condensed. This is correlated with decreased levels of histone H3 Ser10 phosphorylation. These levels can be restored by a JIL-1 transgene placing JIL-1 directly in the pathway mediating histone H3 phosphorylation. We propose a model where JIL-1 kinase activity is required for maintaining the structure of the more open chromatin regions that facilitate gene transcription.

Cactus protein degradation mediates Drosophila dorsal-ventral signaling

Dorsal-ventral patterning in the Drosophila embryo relies on a signal transduction pathway that is similar to a signaling pathway leading to the activation of the mammalian transcription factor NF-kappa B. Stimulation of this Drosophila pathway on the ventral side of the embryo causes the nuclear translocation of Dorsal, the Drosophila NF-kappa B homolog. Cactus, like its mammalian homolog I kappa B, inhibits nuclear translocation by binding Dorsal and retaining it in the cytoplasm. We show that Cactus, like I kappa B, is rapidly degraded in response to signaling. More importantly, signal-dependent degradation of Cactus does not require the presence of Dorsal, indicating that Cactus degradation is a direct response to signaling, and that disruption of the Dorsal/Cactus complex is a secondary result of Cactus degradation. Mutant alleles of cactus that encode more stable forms of the protein block signaling, showing that efficient degradation is necessary for signaling. We find that Cactus protein stability is regulated by two independent processes that rely on different regions within the protein: signal-dependent degradation requires sequences in the amino terminus or ankyrin repeats, whereas signal-independent degradation of free Cactus requires the carboxy-terminal region of the protein that includes a PEST sequence.

VAMP8/endobrevin is overexpressed in hyperreactive human platelets: suggested role for platelet microRNA

BACKGROUND

Variation in platelet reactivity contributes to disorders of hemostasis and thrombosis, but the molecular mechanisms are not well understood.

OBJECTIVES

To discover associations between interindividual platelet variability and the responsible platelet genes, and to begin to define the molecular mechanisms altering platelet gene expression.

SUBJECTS/METHODS

Two hundred and eighty-eight healthy subjects were phenotyped for platelet responsiveness. Platelet RNA from subjects demonstrating hyperreactivity (n=18) and hyporeactivity (n=11) was used to screen the human transcriptome.

RESULTS

Distinctly different mRNA profiles were observed between subjects with differing platelet reactivity. Increased levels of mRNA for VAMP8/endobrevin, a critical v-SNARE involved in platelet granule secretion, were associated with platelet hyperreactivity (Q=0.0275). Validation studies of microarray results showed 4.8-fold higher mean VAMP8 mRNA levels in hyperreactive than hyporeactive platelets (P=0.0023). VAMP8 protein levels varied 13-fold among platelets from these normal subjects, and were 2.5-fold higher in hyperreactive platelets (P=0.05). Among our cohort of 288 subjects, a VAMP8 single-nucleotide polymorphism (rs1010) was associated with platelet reactivity in an age-dependent manner (P<0.003). MicroRNA-96 was predicted to bind to the 3'-untranslated regionof VAMP8 mRNA and was detected in platelets. Overexpression of microRNA-96 in VAMP8-expressing cell lines caused a dose-dependent decrease in VAMP8 protein and mRNA, suggesting a role in VAMP8 mRNA degradation.

CONCLUSIONS

These findings support a role for VAMP8/endobrevin in the heterogeneity of platelet reactivity, and suggest a role for microRNA-96 in the regulation of VAMP8 expression.