Angiotensin II triggers release of leukotriene C4 in vascular smooth muscle cells via the multidrug resistance-related protein 1

The multidrug resistance-related protein-1 (MRP1) is important for the management of oxidative stress in vascular cells in vivo. Substrates of MRP1 are, among others, glutathione and the leukotriene C₄ (LTC₄), an eicosanoid and mediator of inflammation. Angiotensin (Ang) II infusion results in MRP1^?/? mice compared to wild-type mice in improved endothelial function and reduced reactive oxygen species (ROS) formation. However, the interaction between Ang II, LTC₄ and MRP1 is not completely understood and has never been investigated in vitro. Ang II induced in vascular smooth muscle cells (VSMC) the release of LTC₄ and the generation of ROS. Pharmacologic inhibition of MRP1 via MK 571 significantly reduced Ang II-induced ROS release (L012-luminescence) in VSMC. The release of ROS after Ang II stimulation is inhibited, to a comparable degree, by blockade of the Cys-LT1 receptor with montelukast. Incubation of VSMC with recombined LTC₄ and Ang II caused enhanced rates of proliferation in VSMC. This effect can be rescued by either MRP1 or Cys-LT1 receptor inhibition. Accordingly, stimulation of VSMC with LTC₄ reduces intracellular levels of glutathione, but does not affect apoptosis. LTC₄ stimulation results in a significant activation of MRP1, but does not alter MRP1 expression. These findings indicate a connection between Ang II, MRP1 and LTC₄. Both, MRP1 and LTC₄, are potentially promising targets for atheroprotective therapy.     

Increase in seagrass distribution at Bourgneuf Bay (France) detected by spatial remote sensing

The changes in spatial distribution of intertidal Zostera noltii seagrass beds were studied with multispectral visible-infrared remote sensing in Bourgneuf Bay (France) over a 14-year period, between 1991 and 2005. Six SPOT satellite images acquired at low tide were calibrated using in situ spectroradiometric data and processed with the Normalized Difference Vegetation Index (NDVI). A steady and linear increase in meadow areas was observed between 1991 and 2005 with total surfaces colonized by Z. noltii increasing from 208 to 586 ha, respectively. A greater increase in the densest part of the meadow (NDVI > 0.4) was also observed: it represented only 15% of total meadow surfaces in 1991 vs. 35% in 2005. The seagrass expansion took place mainly towards the lower part of the intertidal zone, while in the upper intertidal zone the meadow appeared strictly limited by the +4 m (Lowest Astronomical Tide) bathymetric level. The influence of Z. noltii above-ground biomass variations on spectral reflectance was analyzed experimentally by spectrometry. Z. noltii displays a characteristic steep slope from 700 to 900 nm, increasing with increasing biomass. A quantitative relationship obtained experimentally between NDVI and the dry weight of leaves was used to produce a biomass distribution map. The distribution of Bourgneuf Bay intertidal seagrass beds is certainly constrained by the water turbidity and we suggest that tidal flat accretion could be a significant variable explaining the observed expansion downwards. With very limited spatial interactions, oyster aquaculture cannot be considered as a threat, while a recent increase in recreational hand fishing of Manila clams within the beds could become problematic.     

A naturally occurring human RPA subunit homolog does not support DNA replication or cell-cycle progression

Replication Protein A (RPA) is a single-stranded DNA-binding protein essential for DNA replication, repair, recombination and cell-cycle regulation. A human homolog of the RPA2 subunit, called RPA4, was previously identified and shown to be expressed in colon mucosal and placental cells; however, the function of RPA4 was not determined. To examine the function of RPA4 in human cells, we carried out knockdown and replacement studies to determine whether RPA4 can substitute for RPA2 in the cell. Unlike RPA2, exogenous RPA4 expression did not support chromosomal DNA replication and lead to cell-cycle arrest in G2/M. In addition, RPA4 localized to sites of DNA repair and reduced γ-H2AX caused by RPA2 depletion. These studies suggest that RPA4 cannot support cell proliferation but can support processes that maintain the genomic integrity of the cell.     

The SARS Coronavirus E Protein Interacts with PALS1 and Alters Tight Junction Formation and Epithelial Morphogenesis

Intercellular tight junctions define epithelial apicobasal polarity and form a physical fence which protects underlying tissues from pathogen invasions. PALS1, a tight junction-associated protein, is a member of the CRUMBS3-PALS1-PATJ polarity complex, which is crucial for the establishment and maintenance of epithelial polarity in mammals. Here we report that the carboxy-terminal domain of the SARS-CoV E small envelope protein (E) binds to human PALS1. Using coimmunoprecipitation and pull-down assays, we show that E interacts with PALS1 in mammalian cells and further demonstrate that the last four carboxy-terminal amino acids of E form a novel PDZ-binding motif that binds to PALS1 PDZ domain. PALS1 redistributes to the ERGIC/Golgi region, where E accumulates, in SARS-CoV–infected Vero E6 cells. Ectopic expression of E in MDCKII epithelial cells significantly alters cyst morphogenesis and, furthermore, delays formation of tight junctions, affects polarity, and modifies the subcellular distribution of PALS1, in a PDZ-binding motif-dependent manner. We speculate that hijacking of PALS1 by SARS-CoV E plays a determinant role in the disruption of the lung epithelium in SARS patients.     

β1A integrin is a master regulator of invadosome organization and function

Invadosomes are adhesion structures involved in tissue invasion that are characterized by an intense actin polymerization–depolymerization associated with β1 and β3 integrins and coupled to extracellular matrix (ECM) degradation activity. We induced the formation of invadosomes by expressing the constitutive active form of Src, SrcYF, in different cell types. Use of ECM surfaces micropatterned at the subcellular scale clearly showed that in mesenchymal cells, integrin signaling controls invadosome activity. Using β1^−/− or β3^−/− cells, it seemed that β1A but not β3 integrins are essential for initiation of invadosome formation. Protein kinase C activity was shown to regulate autoassembly of invadosomes into a ring-like metastructure (rosette), probably by phosphorylation of Ser785 on the β1A tail. Moreover, our study clearly showed that β1A links actin dynamics and ECM degradation in invadosomes. Finally, a new strategy based on fusion of the photosensitizer KillerRed to the β1A cytoplasmic domain allowed specific and immediate loss of function of β1A, resulting in disorganization and disassembly of invadosomes and formation of focal adhesions.     

Mitochondrial fusion proteins: Dual regulators of morphology and metabolism

Mitochondria in mammalian cells are visualized as a network or as filaments that undergo continuous changes in shape and in localization within the cells. These changes are a consequence of the activity of different processes such as mitochondrial fusion and fission, and mitochondrial remodelling. In all, these processes are referred to as mitochondrial dynamics, and relevant questions, still unexplained, are why cells require such an active dynamics, or why mitochondria move to specific cellular regions. In this review we will summarize some of the biological functions assigned to the proteins identified as participating in mitochondrial fusion, namely mitofusin 1, mitofusin 2 and OPA1. In addition to the capacity of these proteins to promote fusion, mitofusin 2 or OPA1 regulate mitochondrial metabolism and loss-of-function reduces oxygen consumption and the capacity to oxidize substrates. We propose that mitochondrial fusion proteins operate as integrators of signals so they regulate both mitochondrial fusion and metabolism.     

Pervasive and cooperative deadenylation of 3'UTRs by embryonic microRNA families

To understand how miRNA-mediated silencing impacts on embryonic mRNAs, we conducted a functional survey of abundant maternal and zygotic miRNA families in the C. elegans embryo. We show that the miR-35-42 and the miR-51-56 miRNA families define maternal and zygotic miRNA-induced silencing complexes (miRISCs), respectively, that share a large number of components. Using a cell-free C. elegans embryonic extract, we demonstrate that the miRISC directs the rapid deadenylation of reporter mRNAs with natural 3'UTRs. The deadenylated targets are translationally suppressed and remarkably stable. Sampling of the predicted miR-35-42 targets reveals that roughly half are deadenylated in a miRNA-dependent manner, but with each target displaying a distinct efficiency and pattern of deadenylation. Finally, we demonstrate that functional cooperation between distinct miRISCs within 3'UTRs is required to potentiate deadenylation. With this report, we reveal the extensive and direct impact of miRNA-mediated deadenylation on embryonic mRNAs.