Raúl Fernández

Biologically active APRIL is secreted following intracellular processing in the Golgi apparatus by furin convertase.

Tumor necrosis factor (TNF) ligand family members are synthesized as transmembrane proteins, and cleavage of the membrane‐anchored proteins from the cell surface is frequently observed. The TNF‐related ligands APRIL and BLyS and their cognate receptors BCMA/TACI form a two ligand/two receptor system that has been shown to participate in B‐ and T‐cell stimulation. In contrast to BLyS, which is known to be cleaved from the cell surface, we found that APRIL is processed intracellularly by furin convertase. Blockage of protein transport from the endoplasmic reticulum to the Golgi apparatus by Brefeldin A treatment abrogated APRIL processing, whereas monensin, an inhibitor of post‐Golgi transport, did not interfere with cleavage of APRIL, but blocked secretion of processed APRIL. Thus, APRIL shows a unique maturation pathway among the TNF ligand family members, as it not detectable as a membrane‐anchored protein at the cell surface, but is processed in the Golgi apparatus prior to its secretion.

STAG2 and Rad21 mammalian mitotic cohesins are implicated in meiosis

STAG/SA proteins are specific cohesin complex subunits that maintain sister chromatid cohesion in mitosis and meiosis. Two members of this family, STAG1/SA1 and STAG2/SA2, ‡ are classified as mitotic cohesins, as they are found in human somatic cells and in Xenopus laevis as components of the cohesinSA1 and cohesinSA2 complexes, in which the shared subunits are Rad21/SCC1, SMC1 and SMC3 proteins. A recently reported third family member, STAG3, is germinal cell‐specific and is a subunit of the meiotic cohesin complex. To date, the meiosis‐specific cohesin complex has been considered to be responsible for sister chromatid cohesion during meiosis. We studied replacement of the mitotic by the meiotic cohesin complex during mouse germinal cell maturation, and we show that mammalian STAG2 and Rad21 are also involved in several meiosis stages. Immunofluorescence results suggest that a cohesin complex containing Rad21 and STAG2 cooperates with a STAG3‐specific complex to maintain sister chromatid cohesion during the diplotene stage of meiosis.

Bcl-2 Targets Protein Phosphatase 1α to Bad

The diverse forms of protein phosphatase 1 (PP1) in vivo result from the association of the catalytic subunit with different regulatory subunits. We recently have described that PP1α is a Ras-activated Bad phosphatase that regulates IL-2 deprivation-induced apoptosis. With the yeast two-hybrid system, GST fusion proteins, indirect immunofluorescence, and coimmunoprecipitation, we found that Bcl-2 interacts with PP1α and Bad. In contrast, Bad did not interact with 14-3-3 protein. Bcl-2 depletion decreased phosphatase activity and association of PP1α to Bad. Bcl-2 contains the RIVAF motif, analogous to the well characterized R/KXV/IXF consensus motif shared by most PP1-interacting proteins. This sequence is involved in the binding of Bcl-2 to PP1α. Disruption of Bcl-2/PP1α association strongly decreased Bcl-2 and Bad-associated phosphatase activity and formation of the trimolecular complex. These results suggest that Bcl-2 targets PP1α to Bad.

Alteration of compacted bentonite by diffusion of highly alkaline solutions

Compliance of concrete – bentonite barriers is a key issue in the performance assessment of long-term underground storage of radioactive waste. The reaction of synthetic alkaline solutions (K–Na–OH and Ca–(OH) 2 ) interacting by diffusion with a Mg-saturated compacted FEBEX-bentonite column of 2.1 cm thickness was investigated through closed-system experiments at 60 °C over 6 and 12 months. The first few millimeteres near the surface were grated to resolve mineralogical changes at sub-mm resolution determined by XRD, SEM, BET and the analysis of exchangeable cations. Alkaline cations diffused beyond the mineralogical alteration zone (2–2.5 mm), and were exchanged by Mg 2+ in the interlayer region of montmorillonite, but no K-silicates were formed. The presence of minor zeolites in the alteration assemblage was only detected by XRD on samples treated with ethylene-glycol. A cemented rim mixed with poorly ordered clay materials, mainly brucite, a chlorite-like phase and Mg-smectite was found at the interface. Montmorillonite was partially dissolved and a part of it remained shielded by the newly-formed cementation crusts. Cation diffusion through the interlayer of montmorillonite is inferred to be the dominant transport pathway in compacted bentonite equilibrated with external high pH solutions. The high pH front diffused at a much slower rate due to buffering of mineral reactions.

The alkaline reaction of FEBEX bentonite: a contribution to the study of the performance of bentonite/concrete engineered barrier system

Desde 1997, el desarrollo de dos proyectos de la Union Europea, Effects of Cement On CLAY barrier performance (ECOCLAY, 1997-2000) y ECOCLAY phase II (2000-2003), ha permitido abordar la investigacion del efecto de la pluma alcalina inducida por la lixiviacion del hormigon sobre la bentonita. Ambos materiales forman parte de un concepto de barrera compuesta de hormigon y bentonita, en el contexto del almacenamiento de residuos a una profundidad dada. El grupo de geoquimica aplicada a las arcillas de la Universidad Autonoma de Madrid (UAM) ha participado en ambos proyectos, y ha conseguido aportar experiencia y cono¬cimiento al estudio del comportamiento de la bentonita de referencia espanola (FEBEX) bajo condiciones de elevada alcalinidad. Este articulo ofrece una sintesis del trabajo desarrollado, mencionando las lecciones aprendidas sobre la reactividad alcalina de la bentonita, y su enfoque practico hacia el analisis del comportamiento de uno de los conceptos de referencia, el almacenamiento de residuos en formaciones arcillosas. Se han seleccionado las principales contribuciones cientificas a este respecto, a juicio de los autores: (1) la naturaleza particular de los productos generados en la reaccion alcalina de la bentonita FEBEX (zeolitas, arcillas magnesicas y geles de silicato aluminato calcico hidratado (CASH)); (2) la aproximacion mediante mineralogia cuantitativa al ritmo de reaccion de la montmorillonita FEBEX a pHs elevados, y (3) la validacion experimental de la reactividad alcalina de la bentonita a partir de experimentos en columna.

Formation of C-A-S-H phases from the interaction between concrete or cement and bentonite

Abstract Concrete and bentonite are being considered as engineered barriers for the deep geological disposal of high-level radioactive waste in argillaceous rocks. Three hydrothermal laboratory experiments of different scalable complexity were performed to improve our knowledge of the formation of calcium aluminate silicate hydrates (C-A-S-H) at the interface between the two materials: concretebentonite transport columns, lime mortar-bentonite transport columns and a portlandite- (bentonite and montmorillonite) batch experiment. Precipitation of C-A-S-H was observed in all experiments. Acicular and fibrous morphologies with certain laminar characteristics were observed which had smaller Ca/Si and larger Al/Si ratios with increasing temperature and lack of accessory minerals. The compositional fields of these C-A-S-H phases formed in the experiments are consistent with Al/(Si+Al) ratios of 0.2- 0.3 described in the literature. The most representative calcium silicate hydrate (C-S-H) phase from the montmorillonite-cement interface is Al-tobermorite. Structural analyses revealed a potential intercalation or association of montmorillonite and C-A-S-H phases at the pore scale.

Improvement of attenuation functions of a clayey sandstone for landfill leachate containment by bentonite addition.

Enhanced sand-clay mixtures have been prepared by using a sandstone arkosic material and have been evaluated for consideration as landfill liners. A lab-scale test was carried out under controlled conditions with different amended natural sandstones whereby leachate was passed through the compacted mixtures. The compacted samples consisted of siliceous sand (quartz-feldspar sand separated from the arkose sandstone) and clay (purified clay from arkose sandstone and two commercial bentonites) materials that were mixed in different proportions. The separation of mineral materials from a common and abundant natural source, for soil protection purposes, is proposed as an economic and environmentally efficient practice. The liner qualities were compared for their mineralogical, physicochemical and major ions transport and adsorption properties. Although all samples fulfilled hydraulic conductivity requirements, the addition of bentonite to arkose sandstone was determined to be an effective strategy to decrease the permeability of the soil and to improve the pollutants retention. The clay materials from arkose sandstone also contributed to pollutant retention by a significant improvement of the cation exchange capacity of the bulk material. However, the mixtures prepared with clay materials from the arkose, exhibited a slight increase of hydraulic conductivity. This effect has to be further evaluated.

Nature of C-(A)-S-H Phases Formed in the Reaction Bentonite/Portlandite

Reactions between bentonite/montmorillonite and portlandite have been studied in the context of the engineered barriers of a purpose built repository for the deep geological disposal of spent fuel and high-level radioactive wastes. Portlandite was selected as the representative material of cement leaching in the early alkaline stage expected in a repository when conventional Ordinary Portland Cement (OPC) is used. Eight different batch experiments were performed for a reaction time near to two months, including bentonite or montmorillonite at montmorillonite/portlandite molar ratios of 2 : 1 and 3 : 1 under hydrothermal conditions. Temperatures of reactions were maintained constant at either 60 or 120°C. Calcium silicates hydrates with limited substitution of Al for Si (C-(A)-S-H phases with Al/Si <0.3) were formed with different structures and compositions as a function of the reaction conditions. Orthorhombic 11 A-tobermorite-type phase was detected in experiments at 120°C while a more disordered monoclinic tobermorite formed at 60°C. These results are useful for the interpretation of experimental data in more complex experiments using concrete or cement pastes and bentonite, where C-(A)-S-H phases of variable compositions can precipitate, in addition to the characteristic cement hydrates and other secondary minerals carbonates.

Adsorption of phenanthrene by stevensite and sepiolite

Abstract Polycyclic aromatic hydrocarbons are increasingly widespread pollutants introduced into the environment via oil spillage and incomplete anthropogenic combustion of fossil fuels. In this work, the capacity of stevensite and sepiolite to adsorb phenanthrene (PHE) has been evaluated experimentally by batch testing. Both clay minerals are distributed widely in the Madrid Basin, are of low cost and can be applied with minimal environmental impact. In the context of few previous studies, adsorption isotherms have been developed to understand the adsorption mechanisms andwere fitted to the Freundlich and linear models with virtually the same results. Although stevensite showed greater adsorption capacity than sepiolite, the isotherms were constructed for equilibrium concentrations up to 0.8-1.0 mg/L due to the low solubility of PHE in water. When compared to other adsorbents the ability of stevensite to retain PAHs should be examined further in order to add and complement novel functions in reactive barriers.

Stevensite-based geofilter for the retention of tetracycline from water.

The antibiotic tetracycline, is considered a contaminant of emerging concern due to its presence in wastewater effluents, surface waters and groundwaters. Adsorption of tetracycline on soils and clays has been extensively studied to remove the contaminant from the water. A decreasing adsorption as the pH increases is normally reported in the pH range 3-9. However, adsorption isotherms performed on a commercial stevensite presented increasing adsorption with the increasing pH, in the pH range 2-8. This is very interesting since the pH in natural and wasterwaters are normally in the range 6-8. A laboratory design of a geofilter using a mixture of sand and stevensite was tested against an inflow solution of tetracycline 1 g/L, NaNO3 0.1 M and pH = 7 in an advective transport cell experiment. The number of tetracycline molecules exceed by >3 times the number exchangeable positions in the stevensite geofilter. Under these conditions, the TC adsorption on the geofilter reaches 590 mg/g, surpassing the retention capacity of most adsorbents found in literature. Besides, the tetracycline is completely desorbed by the inflow of a saline solution (Mg(NO3)2 0.5 M, at pH = 2) with capacity to replace the exchangeable positions, thus, recovering the geofilter and the tetracycline.