(Na, Zr) and (Ca, Zr) Phosphate-Molybdates and Phosphate-Tungstates: I-Synthesis, Sintering and Characterization.

Submicron-grade powders of Na1-xZr2(PO4)3-x(XO4)x compounds (hereafter referred to as NZP) and Ca1-xZr2(PO4)3-x(XO4)x compounds (hereafter, CZP), X = Mo, W (0 ≤ x ≤ 0.5) were obtained by sol-gel synthesis. The compounds obtained were studied by X-ray diffraction phase analysis and electron microscopy. An increase in the W or Mo contents was shown to result in an increase in the unit cell volume of the NZP and CZP crystal lattices and in a decrease in the coherent scattering region sizes. Thermal expansion behavior at high temperatures of synthesized NZP and CZP compounds has been investigated. The dependencies of the parameters a and c on the heating temperature, as well as the temperature dependence of the crystal lattice unit cell volume V in the range from the room temperature up to 800 °C, were obtained. The dependencies of the average thermal expansion coefficient (αav) and of the volume coefficient (ß) on the W and Mo contents in the compositions of NZP and CZP compounds were studied. Ceramics Na1-xZr2(PO4)3-x(XO4)x with relatively high density (more than 97.5%) were produced by spark plasma sintering (SPS). The increase in the W or Mo contents in the ceramics leads to an increase in the relative density of NZP and to a decrease of the optimum sintering temperature. The mean grain size in the NZP ceramics decreases with increasing W or Mo contents. The study of strength characteristics has revealed that the hardness of the NZP ceramics is greater than 5 GPa, and that the minimum fracture toughness factor was 1 MPa·m1/2.

(Na, Zr) and (Ca, Zr) Phosphate-Molybdates and Phosphate-Tungstates: II-Radiation Test and Hydrolytic Stability.

This paper introduces the results of hydrolytic stability tests and radiation resistance tests of phosphate molybdates and phosphate tungstates Na1-xZr2(PO4)3-x(XO4)x, X = Mo, W (0 ≤ x ≤ 0.5). The ceramics characterized by relatively high density (more than 97.5%) were produced by spark plasma sintering (SPS) of submicron powders obtained by sol-gel synthesis. The study focused on hydrolytic resistance of the ceramics in static mode at room temperature. After 28 days of testing in distilled water, the normalized leaching rate was determined. It was found that the ceramics demonstrated high hydrolytic resistance in static mode: the normalized leaching rates for Mo- and W-containing ceramics were 31·10-6 and 3.36·10-6 g·cm-2·day-1, respectively. The ceramics demonstrated high resistance to irradiation with 167 MeV Xe+26 multiple-charged ions at fluences ranging from 1·1012 to 6·1013 cm-2. The Mo-containing Na0.5Zr2(PO4)2.5(XO4)0.5 ceramics were shown to have higher radiation resistance than phosphate tungstates. Radiation was shown to trigger an increase in leaching rates for W and Mo in the crystal structure of NZP ceramics.

A potential mechanism of "cross-talk" between the p55 tumor necrosis factor receptor and Fas/APO1: proteins binding to the death domains of the two receptors also bind to each other.

The p55 tumor necrosis factor (TNF) receptor and Fas/APO1 induce cell death via distinct regions in their intracellular domains. Three cytoplasmic proteins that bind to these receptor regions have been identified recently. One, MORT1 (also called FADD), binds to Fas/APO1 but not to p55-R; another, TRADD, binds to the p55 TNF receptor but not to Fas/APO1; and the third, RIP, binds weakly to both receptors. The regions within these proteins that are involved in binding to the receptors and the receptor regions to which they bind share a common sequence motif, that of the "death domain." This study shows that the death domain motifs in MORT1, TRADD, and RIP bind effectively to each other, a mode of binding that may allow "cross-talk" between the functional expression of the p55 TNF receptor and Fas/APO1.

New functional material: spark plasma sintered Si/SiO2 nanoparticles - fabrication and properties.

A bulk nanostructured material based on oxidized silicon nanopowder was fabricated using a spark plasma sintering technique. Structural investigations revealed that this material has the composition of ∼14 nm core Si granules inside an SiO2 shell. Photoluminescence measurements have shown that the emission spectra lie in the energy range of 0.6-1.1 eV, which is not typical of the emissions of the Si/SiO2 nanostructures reported in numerous papers. This result can be explained by the formation of energy states in the bandgap and the participation of these states in both electronic transport and photoluminescence emission. Annealing of the sample leads to a decrease in defect density, which in turn leads to quenching of the 0.6-1.1 eV photoluminescence. In this case ∼1.13 eV inter-band transitions in the Si core start to play a dominant role in radiative recombination. Thus, the possibility of controlling the photoluminescence emission over a broad wavelength range was demonstrated.

Death-inducing functions of ligands of the tumor necrosis factor family: a Sanhedrin verdict.

Members of the tumor necrosis factor ligand family can kill cells in a rather straightforward manner. They induce their receptors to recruit and activate caspases, enzymes that are critically involved in the death process, and this activation is further amplified by intracellular mitochondria-associated mechanisms. The potentially hazardous expression of the ligands occurs widely in the body; it is antigen-restricted only in the lymphocytes. Yet, in addition to control modes affecting ligand expression, there are numerous inhibitory mechanisms that act within target cells, to make doubly sure of avoiding an undue 'death verdict', while allowing the cells to exhibit other, noncytocidal effects of the ligands.

The yeast two-hybrid screening technique and its use in the study of protein-protein interactions in apoptosis.

The yeast two-hybrid technique provides a general approach for cloning cDNAs merely by exploiting the ability of their encoded proteins to bind to a protein of interest. The technique therefore offered a useful access to the analysis of the mechanisms of cell death at the initial stage of their study, when only a few of the proteins involved and very little about their mode of action were known. Conversely, the knowledge of cell death mechanisms gained by this technique provided a useful insight into both the potential and the limitations of this technique.

A protein related to a proteasomal subunit binds to the intracellular domain of the p55 TNF receptor upstream to its 'death domain'.

A novel protein that binds specifically to the intracellular domain of the p55 tumor necrosis factor (TNF) receptor was cloned by two-hybrid screening of a HeLa cell cDNA library. Data bank searches revealed high sequence similarity of the protein (55.11) to yeast, nematode and plant proteins, whose functions are yet unknown. Significant similarity was also found between 55.11 and SEN3, the yeast equivalent of the p112 subunit of the 26S proteasome. Deletion analysis showed that the protein binds to the p55 receptor upstream to the region involved in induction of cell death.

Involvement of MACH, a novel MORT1/FADD-interacting protease, in Fas/APO-1- and TNF receptor-induced cell death.

Fas/APO-1 and p55 tumor necrosis factor (TNF) receptor (p55-R) activate cellular mechanisms that result in cell death. Upon activation of these receptors, Fas/APO-1 binds a protein called MORT1 (or FADD) and p55-R binds a protein called TRADD. MORT1 and TRADD can also bind to each other. We have cloned a novel protein, MACH, that binds to MORT1. This protein exists in multiple isoforms, some of which contain a region that has proteolytic activity and shows marked sequence homology to proteases of the ICE/CED-3 family. Cellular expression of the proteolytic MACH isoforms results in cell death. Expression of MACH isoforms that contain an incomplete ICE/CED-3 region provides effective protection against the cytotoxicity induced by Fas/APO-1 or p55-R triggering. These findings suggest that MACH is the most upstream enzymatic component in the Fas/APO-1- and p55-R-induced cell death signaling cascades.

MAP3K-related kinase involved in NF-kappaB induction by TNF, CD95 and IL-1.

Several members of the tumour-necrosis/nerve-growth factor (TNF/NGF) receptor family activate the transcription factor NF-kappaB through a common adaptor protein, Traf2 (refs 1-5), whereas the interleukin 1 type-I receptor activates NF-kappaB independently of Traf2 (ref. 4). We have now cloned a new protein kinase, NIK, which binds to Traf2 and stimulates NF-kappaB activity. This kinase shares sequence similarity with several MAPKK kinases. Expression in cells of kinase-deficient NIK mutants fails to stimulate NF-kappaB and blocks its induction by TNF, by either of the two TNF receptors or by the receptor CD95 (Fas/Apo-1), and by TRADD, RIP and MORT1/FADD, which are adaptor proteins that bind to these receptors. It also blocked NF-kappaB induction by interleukin-1. Our findings indicate that NIK participates in an NF-kappaB-inducing signalling cascade common to receptors of the TNF/NGF family and to the interleukin-1 type-I receptor.

Controlled evaluation of copper-silver ionization in eradicating Legionella pneumophila from a hospital water distribution system.

A controlled evaluation was made of the efficacy of copper-silver ionization in eradicating Legionella pneumophila from a hospital water supply. Copper-silver ionization units were installed on the hot water recirculation line of one building with water fixtures positive for Legionella species. Another building with the same water supply served as a control. Legionella species persisted within the system when copper and silver concentrations were < 0.3 and < 0.03 ppm, respectively. When copper and silver concentrations were > 0.4 and > 0.04 ppm, respectively, there was a significant decrease in Legionella species colonization, but the percentage of water fixtures positive for organisms was unchanged in the control building. When the ionization unit was inactivated, water fixtures continued to be free of Legionella species for 2 additional months. Copper-silver ionization can eradicate L. pneumophila in a water distribution system. The advantages of copper-silver ionization include relatively low cost, straightforward installation, easy maintenance, nontoxic by-products and the presence of a disinfecting residual.

A novel protein that interacts with the death domain of Fas/APO1 contains a sequence motif related to the death domain.

Signaling for cell death by Fas/APO1 occurs via a distinct region in its intracellular domain. This region contains a conserved sequence motif, the death domain motif, that is also found in the intracellular domains of the p55 tumor necrosis factor receptor and the low affinity nerve growth factor receptor, as well as in the regulatory domain of the ankyrins. A novel protein that specifically binds to the death domain of Fas/APO1 but not to Fas/APO1 molecules with a loss of function point mutation occurring in lprcg mice was cloned by a two-hybrid screen of a HeLa cells' cDNA library. The cloned protein itself contains a death domain motif, and this region binds to the death domain of Fas/APO1, while the region upstream to the death domain prompts self-association of the protein. Induced expression of the protein results in ligand-independent triggering of cytotoxicity, suggesting that it is involved in cell death induction by Fas/APO1.

Tumor necrosis factor receptor and Fas signaling mechanisms.

Four members of the tumor necrosis factor (TNF) ligand family, TNF-alpha, LT-alpha, LT-beta, and LIGHT, interact with four receptors of the TNF/nerve growth factor family, the p55 TNF receptor (CD120a), the p75 TNF receptor (CD120b), the lymphotoxin beta receptor (LT beta R), and herpes virus entry mediator (HVEM) to control a wide range of innate and adaptive immune response functions. Of these, the most thoroughly studied are cell death induction and regulation of the inflammatory process. Fas/Apo1 (CD95), a receptor of the TNF receptor family activated by a distinct ligand, induces death in cells through mechanisms shared with CD120a. The last four years have seen a proliferation in knowledge of the proteins participating in the signaling by the TNF system and CD95. The downstream signaling molecules identified so far--caspases, phospholipases, the three known mitogen activated protein (MAP) kinase pathways, and the NF-kappa B activation cascade--mediate the effects of other inducers as well. However, the molecules that initiate these signaling events, including the death domain- and TNF receptor associated factor (TRAF) domain-containing adapter proteins and the signaling enzymes associated with them, are largely unique to the TNF/nerve growth factor receptor family.

Exploring cell death mechanisms by analyzing signaling cascades of the TNF/NGF receptor family.

The ability of ligands of the tumor necrosis factor (TNF) family to induce death of cells independently of new protein synthesis provides a unique approach to molecular analysis of programmed cell death mechanisms. Sequential analysis of the protein-protein interactions by which these receptors signal, allows identification of specific molecules that participate in the cell death process and unequivocal definition of cause-effect relationships between them. Several receptors of this family, with structurally unrelated intracellular domains, have the ability to trigger cell death. some intracellular proteins that bind to the receptors and participate in the induction of their effects have been identified. Association of the Fas/APO1-interacting protein MORT1/FADD with the p55 TNF receptor-interacting protein TRADD, and the association of both MORT1/FADD and TRADD with a third protein, RIP, provide potential cross-talk mechanisms between Fas/APO1 and the p55 TNF receptor. TRAF2, a cytoplasmic protein that binds to the p75 TNF receptor, as well as to several other receptors of the TNF/NGF family, also binds to TRADD, thus further extending the range of receptors of this family that can share common signaling mechanisms. The N-terminal part of MORT1/FADD binds to a protease of the CED3/ICE family, MACH alpha. Activation of MACH alpha by the TNF/NGF receptors appears to be the most upstream enzymatic activity in the cascade of signaling for cell death.

Intermittent use of copper-silver ionization for Legionella control in water distribution systems: a potential option in buildings housing individuals at low risk of infection.

One copper-silver ionization system was sequentially installed onto the hot-water recirculation lines of two hospital buildings colonized with Legionella pneumophila, serogroup 1. A third building with the same water supply and also colonized with Legionella served as a control. Four weeks after activation of the system, distal site positivity for Legionella in the first test building dropped to zero. After operating for 16 weeks, the system was disconnected and installed onto the second test building. Twelve weeks of disinfection reduced the distal site positivity for Legionella in the second test building to zero. Legionella recolonization did not occur in the first test building for 6-12 weeks and in the second test building for 8-12 weeks after inactivation of the system. The control building remained Legionella-positive throughout the experimental period. A significantly higher copper concentration was found in the biofilm taken from a sampling device than in that from water. This is likely to be the reason that the copper-silver ionization system had the residual effect of preventing early recolonization. Our study raises the possibility that one copper-silver unit could be rotated among several buildings to maintain a Legionella-free environment. Such an approach may be cost-effective for buildings housing individuals at low risk for contracting legionnaires' disease.

Self-association of the "death domains" of the p55 tumor necrosis factor (TNF) receptor and Fas/APO1 prompts signaling for TNF and Fas/APO1 effects.

Signaling by the p55 tumor necrosis factor (TNF) receptor and by the structurally related receptor Fas/APO1 is initiated by receptor clustering. Data presented here and in other recent studies (Wallach, D., Boldin, M., Varfolomeev, E. E., Bigda, Y., Camonis, H.J. and Mett, I. (1994) Cytokine 6, 556; Song, H.Y., Dunbar, J.D., and Bonner, D.B. (1994) J. Biol. Chem. 269, 22492-22495) indicate that part of that region within the intracellular domains of the two receptors that is involved in signaling for cell death, as well as for some other effects (the "death domain", specifically self-associates. We demonstrate also the expected functional consequence of this association; a mere increase in p55 TNF receptor expression, or the expression just of its intracellular domain, is shown to trigger signaling for cytotoxicity as well as for interleukin 8 gene induction, while expression of the intracellular domain of Fas/APO1 potentiates the cytotoxicity of co-expressed p55 TNF receptor. These findings indicate that the p55 TNF and Fas/APO1 receptors play active roles in their own clustering and suggest the existence of cellular mechanisms that restrict the self-association of these receptors, thus preventing constitutive signaling.