The crystal structure of a complex between the protein biosynthesis elongation factor eEF1A (formerly EF-1alpha) and the catalytic C terminus of its exchange factor, eEF1Balpha (formerly EF-1beta), was determined to 1.67 A resolution. One end of the nucleotide exchange factor is buried between the switch 1 and 2 regions of eEF1A and destroys the binding site for the Mg(2+) ion associated with the nucleotide. The second end of eEF1Balpha interacts with domain 2 of eEF1A in the region hypothesized to be involved in the binding of the CCA-aminoacyl end of the tRNA. The competition between eEF1Balpha and aminoacylated tRNA may be a central element in channeling the reactants in eukaryotic protein synthesis. The recognition of eEF1A by eEF1Balpha is very different from that observed in the prokaryotic EF-Tu:EF-Ts complex. Recognition of the switch 2 region in nucleotide exchange is, however, common to the elongation factor complexes and those of Ras:Sos and Arf1:Sec7.

Non-fibrillar soluble oligomeric forms of amyloid-β peptide (oAβ) and tau proteins are likely to play a major role in Alzheimer’s disease (AD). The prevailing hypothesis on the disease etiopathogenesis is that oAβ initiates tau pathology that slowly spreads throughout the medial temporal cortex and neocortices independently of Aβ, eventually leading to memory loss. Here we show that a brief exposure to extracellular recombinant human tau oligomers (oTau), but not monomers, produces an impairment of long-term potentiation (LTP) and memory, independent of the presence of high oAβ levels. The impairment is immediate as it raises as soon as 20 min after exposure to the oligomers. These effects are reproduced either by oTau extracted from AD human specimens, or naturally produced in mice overexpressing human tau. Finally, we found that oTau could also act in combination with oAβ to produce these effects, as sub-toxic doses of the two peptides combined lead to LTP and memory impairment. These findings provide a novel view of the effects of tau and Aβ on memory loss, offering new therapeutic opportunities in the therapy of AD and other neurodegenerative diseases associated with Aβ and tau pathology.

NANOG is a master transcription factor associated with the maintenance of stem cell pluripotency. Here, we demonstrate that transcription factor NANOG is expressed in cultured endothelial cells (ECs) and in a subset of tumor cell lines. Importantly, we provide evidence that WNT3A stimulation of ECs induces the transcription of NANOG which mediates the expression of vascular endothelial growth factor receptor-2, also known as fetal liver kinase-1 (FLK1). We defined ATTA as a minimal binding site for NANOG. Accordingly, a luciferase reporter assay showed that NANOG binds to and activates 4 ATTA binding sites identified in the FLK1 promoter after WNT3A stimulation. Consistent with this data, we found that, under basal conditions and in response to WNT3A stimulation, NANOG binding to these ATTA sequences markedly induced the expression of FLK1. Thus, our data indicate an essential role in angiogenesis for NANOG binding to these 4 ATTA sites. Surprisingly, NANOG depletion not only decreased FLK1 expression but also reduced cell proliferation and angiogenesis. These findings show the necessary and sufficient role of NANOG in inducing the transcription of IntroductionAngiogenesis, the sprouting of new capillaries from preexisting blood vessels, is not only required for embryonic development and wound healing but also contributes to pathologic processes, including atherosclerosis, diabetic retinopathy, and tumor progression. 1,2 In this regard, the activation of Wnt (Wingless) signaling in endothelial cells (ECs) has been shown to induce transcriptional events to regulate angiogenesis [3][4][5] ; however, the underlying mechanisms of these processes are not entirely clear. Beyond binding to the cytoplasmic domain of vascular endothelial-or E-cadherin, ␤-catenin plays a key role in the transduction of Wnt signals by serving as a coactivator for the transcription factor T-cell factor/ lymphocyte enhancer binding factor (TCF/LEF-1). 6,7 The ligation of Wnt to the Frizzled receptor induces the inhibition of glycogen synthase kinase-3␤ that results in decreased phosphorylation of ␤-catenin, thereby reduced proteolysis and degradation. [5][6][7] Stabilized ␤-catenin translocates into the nucleus to associate with transcription factors of the TCF/LEF-1 family that can transactivate genes containing TCF/LEF-1 binding sequences. [5][6][7] Recent gene expression profiling has identified a role for Wnt signaling in EC commitment 8 and in control of vasculo-angiogenic aspects of embryonic development. [9][10][11][12][13][14][15] NANOG is a divergent homeobox transcription factor expressed in germ cells and pluripotent stem cells that is critical for morphogenesis and embryonic development. [16][17][18][19] Mouse embryos lacking nanog die between days embryonic (E) 3.5 and E5.5, before any vasculature has developed. 20,21 Nanog overexpression renders mouse embryonic stem (ES) cells independent of leukemia inhibitory factor/signal transducer and activator of transcription-3 stimulation for self-renewal. [17][18][19] Analyses of the ...

Infection with the protozoan parasite Cryptosporidium parvum (CP) causes cryptosporidiosis, a widespread diarrhoeal disease. Impaired intestinal epithelial barrier function and increased permeability are most commonly associated with diarrhoeal diseases caused by enteric infections. However, studies on barrier disruption and underlying mechanisms in cryptosporidiosis are extremely limited. Epithelial tight junctions (TJs) and adherens junctions (AJs) are important in maintaining barrier integrity. Therefore, we examined the effects of CP infection on paracellular permeability and on the expression of the major TJ and AJ proteins utilising in vitro, ex vivo, and in vivo models. CP infection (0.5 × 10 oocysts/well in Transwell inserts, 24 hr) increased paracellular permeability (FITC-dextran flux) in Caco-2 cell monolayers and substantially decreased the protein levels of occludin, claudin 4, and E-cadherin. Claudin 3, zonula occludens-1 (ZO1) and α-catenin were also significantly decreased, whereas claudins 1 and 2 and β-catenin were not altered. Substantial downregulation of occludin, claudin 4, and E-cadherin was also observed in response to CP infection ex vivo in mouse enteroid-derived monolayers and in vivo in the ileal and jejunal mocosa of C57BL/6 mice. The mRNA levels of these proteins were also significantly decreased in CP-infected mouse ileum and jejunum but were unaltered in Caco-2 cells. Further, bafilomycin-A, an inhibitor of lysosomal proton pump, partially abrogated CP effects on occludin expression in Caco-2 cells, suggesting a potential role of posttranslational mechanisms, such as induction of protein degradation pathways, in mediating the effects of the parasite. Our studies suggest that disruption of barrier function via downregulation of specific key components of TJ and AJ could be a major mechanism underlying CP infection-induced diarrhoea.

Eukaryotic initiation factor 5A (eIF5A) is the only protein in nature that contains hypusine, an unusual amino acid derived from the modification of lysine by spermidine. Two genes, TIF51A and TIF51B, encode eIF5A in the yeast Saccharomyces cerevisiae. In an effort to understand the structure-function relationship of eIF5A, we have generated yeast mutants by introducing plasmid-borne tif51A into a double null strain where both TIF51A and TIF51B have been disrupted. One of the mutants, tsL102A strain (tif51A L102A tif51aDelta tif51bDelta) exhibits a strong temperature-sensitive growth phenotype. At the restrictive temperature, tsL102A strain also exhibits a cell shape change, a lack of volume change in response to temperature increase and becomes more sensitive to ethanol, a hallmark of defects in the PKC/WSC cell wall integrity pathway. In addition, a striking change in actin dynamics and a complete cell cycle arrest at G1 phase occur in tsL102A cells at restrictive temperature. The temperature-sensitivity of tsL102A strain is due to a rapid loss of mutant eIF5A with the half-life reduced from 6 h at permissive temperature to 20 min at restrictive temperature. Phenylmethyl sulfonylfluoride (PMSF), an irreversible inhibitor of serine protease, inhibited the degradation of mutant eIF5A and suppressed the temperature-sensitive growth arrest. Sorbitol, an osmotic stabilizer that complement defects in PKC/WSC pathways, stabilizes the mutant eIF5A and suppresses all the observed temperature-sensitive phenotypes.

RationaleInduced pluripotent stem (iPS) cells have emerged as a source of potentially unlimited supply of autologous endothelial cells (ECs) for vascularization. However, the regenerative function of these cells relative to adult ECs and ECs derived from embryonic stem (ES) cells is unknown. The objective was to define the differentiation characteristics and vascularization potential of Fetal liver kinase (Flk)1+ and Vascular Endothelial (VE)-cadherin+ ECs derived identically from mouse (m)ES and miPS cells. Methods and ResultsNaive mES and miPS cells cultured in type IV collagen (IV Col) in defined media for 5 days induced the formation of adherent cell populations, which demonstrated similar expression of Flk1 and VE-cadherin and the emergence of EC progenies. FACS purification resulted in 100% Flk1+ VE-cadherin+ cells from both mES and miPS cells. Emergence of Flk1+VE-cadherin+ cells entailed expression of the vascular developmental transcription factor Er71, which bound identically to Flk1, VE-cadherin, and CD31 promoters in both populations. Immunostaining with anti-VE-cadherin and anti-CD31 antibodies and microscopy demonstrated the endothelial nature of these cells. Each cell population (unlike mature ECs) organized into well-developed vascular structures in vitro and incorporated into CD31+ neovessels in matrigel plugs implanted in nude mice in vivo.ConclusionThus, iPS cell-derived Flk1+VE-cadherin+ cells expressing the Er71 are as angiogenic as mES cell-derived cells and incorporate into CD31+ neovessels. Their vessel forming capacity highlights the potential of autologous iPS cells-derived EC progeny for therapeutic angiogenesis.

Microbiota derived metabolites act as chemical messengers that elicit a profound impact on host physiology. Vitamin D receptor (VDR) is a key genetic factor for shaping the host microbiome. However, it remains unclear how microbial metabolites are altered in the absence of VDR. We investigated metabolites from mice with tissue-specific deletion of VDR in intestinal epithelial cells or myeloid cells. Conditional VDR deletion severely changed metabolites specifically produced from carbohydrate, protein, lipid, and bile acid metabolism. Eighty-four out of 765 biochemicals were significantly altered due to the Vdr status, and 530 significant changes were due to the high-fat diet intervention. The impact of diet was more prominent due to loss of VDR as indicated by the differences in metabolites generated from energy expenditure, tri-carboxylic acid cycle, tocopherol, polyamine metabolism, and bile acids. The effect of HFD was more pronounced in female mice after VDR deletion. Interestingly, the expression levels of farnesoid X receptor in liver and intestine were significantly increased after intestinal epithelial VDR deletion and were further increased by the high-fat diet. Our study highlights the gender differences, tissue specificity, and potential gut-liver-microbiome axis mediated by VDR that might trigger downstream metabolic disorders.

Vitamin D/vitamin D receptor (VDR) deficiency causes a high risk of colon cancer, but how VDR is involved in tumorigenesis through microbiota remains unknown. We provide insights into the mechanism of VDR dysfunction leading to dysbiosis and tumorigenesis, indicating a new target: microbiome and VDR for the prevention of cancer. BACKGROUND & AIMS: Vitamin D exerts regulatory roles via vitamin D receptor (VDR) in mucosal immunity, host defense, and inflammation involving host factors and microbiome. Human Vdr gene variation shapes the microbiome and VDR deletion leads to dysbiosis. Low VDR expression and diminished vitamin D/VDR signaling are observed in colon cancer. Nevertheless, how intestinal epithelial VDR is involved in tumorigenesis through gut microbiota remains unknown. We hypothesized that intestinal VDR protects mice against dysbiosis via modulating the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway in tumorigenesis. METHODS: To test our hypothesis, we used an azoxymethane/ dextran sulfate sodium-induced cancer model in intestinal VDR conditional knockout (VDR DIEC) mice, cell cultures, stem cell-derived colonoids, and human colon cancer samples. RESULTS: VDR DIEC mice have higher numbers of tumors, with the location shifted from the distal to proximal colon. Fecal microbiota analysis showed that VDR deletion leads to a bacterial profile shift from normal to susceptible carcinogenesis. We found enhanced bacterial staining in mouse and human tumors. Microbial metabolites from VDR DIEC mice showed increased secondary bile acids, consistent with observations in human CRC. We further identified that VDR protein bound to the Jak2 promoter, suggesting that VDR transcriptionally regulated Jak2. The JAK/ STAT pathway is critical in intestinal and microbial homeostasis. Fecal samples from VDR DIEC mice activate the STAT3 signaling in human and mouse organoids. Lack of VDR led to hyperfunction of Jak2 in response to intestinal dysbiosis. A JAK/STAT inhibitor abolished the microbiome-induced activation of STAT3. CONCLUSIONS: We provide insights into the mechanism of VDR dysfunction leading to dysbiosis and tumorigenesis. It indicates a new target: microbiome and VDR for the prevention of cancer.