Immunohistochemical demonstration of carbonic anhydrase

Summary Rabbits were immunized using human erythroxyte carbonic anhydrase B (HCA B) purified. by the modified methods of Armstrong et al. (1966) and Bernstein and Schraer (1972). The globulin fraction was isolated by ammonium sulphate precipitation. The anti-HCA B globulin was specific, when judged using the double diffusion technique of Ouchterlony and immunoelectrophoresis. No cross reaction with human erythrocyte carbonic anhydrase C was found, but cross reactions with erythrocyte carbonic anhydrase from rat, mouse and guinea pig were observed. Fluorescein isothiocyanate conjugated goat anti-rabbit globulin was used for the localization of HCA B in tissue sections and erythrocytes on slides.     

Real-time, in vivo analysis of malaria ookinete locomotion and mosquito midgut invasion

Invasion of the Anopheles mosquito midgut by the Plasmodium ookinete is a critical step in the malaria transmission cycle. We have generated a fluorescent P. berghei transgenic line that expresses GFP in the ookinete and oocyst stages, and used it to perform the first real-time analysis of midgut invasion in the living mosquito as well as in explanted intact midguts whose basolateral plasma membranes were vitally stained. These studies permitted detailed analysis of parasite motile behaviour in the midgut and cell biological analysis of the invasion process. Throughout its journey, the ookinete displays distinct modes of motility: stationary rotation, translocational spiralling and straight-segment motility. Spiralling is based on rotational motility combined with translocation steps and changes in direction, which are achieved by transient attachments of the ookinete's trailing end. As it moves from the apical to the basal side of the midgut epithelium, the ookinete uses a predominant intracellular route and appears to glide on the membrane in foldings of the basolateral domain. However, it traverses serially the cytoplasm of several midgut cells before entering and migrating through the basolateral intercellular space to access the basal lamina. The invaded cells commit apoptosis, and their expulsion from the epithelium invokes wound repair mechanisms including extensive lamellipodia crawling. A 'hood' of lamellipodial origin, provided by the invaded cell, covers the ookinete during its egress from the epithelium. The flexible ookinete undergoes shape changes and temporary constrictions associated with passage through the plasma membranes. Similar observations were made in both A. gambiae and A. stephensi, demonstrating the conservation of P. berghei interactions with these vectors.     

Internalization of Coxsackievirus A9 Is Mediated by β2-Microglobulin,Dynamin, and Arf6 but Not by Caveolin-1 or Clathrin

Coxsackievirus A9 (CAV9) is a member of the human enterovirus B species within the Enterovirus genus of the family Picornaviridae. It has been shown to utilize αV integrins, particularly αVβ6, as its receptors. The endocytic pathway by which CAV9 enters human cells after the initial attachment to the cell surface has so far been unknown. Here, we present a systematic study concerning the internalization mechanism of CAV9 to A549 human lung carcinoma cells. The small interfering RNA (siRNA) silencing of integrin β6 subunit inhibited virus proliferation, confirming that αVβ6 mediates the CAV9 infection. However, siRNAs against integrin-linked signaling molecules, such as Src, Fyn, RhoA, phosphatidylinositol 3-kinase, and Akt1, did not reduce CAV9 proliferation, suggesting that the internalization of the virus does not involve integrin-linked signaling events. CAV9 endocytosis was independent of clathrin or caveolin-1 but was restrained by dynasore, an inhibitor of dynamin. The RNA interference silencing of β2-microglobulin efficiently inhibited virus infection and caused CAV9 to accumulate on the cell surface. Furthermore, CAV9 infection was found to depend on Arf6 as both silencing of this molecule by siRNA and the expression of a dominant negative construct resulted in decreased virus infection. In conclusion, the internalization of CAV9 to A549 cells follows an endocytic pathway that is dependent on integrin αVβ6, β2-microglobulin, dynamin, and Arf6 but independent of clathrin and caveolin-1.Coxsackievirus A9 (CAV9), a member of the human enterovirus B species in the family Picornaviridae, is a significant human pathogen. It causes infections of the central nervous system, myocarditis, and respiratory diseases and may occasionally cause fatal generalized infections in newborns (6, 22, 26). The CAV9 particle is about 30 nm in diameter and consists of a naked capsid with an icosahedral symmetry, surrounding a positive-sense RNA genome of approximately 7,400 nucleotides (30). The capsid is made up of 60 copies of each of the four proteins VP1 to VP4 and interacts with cell surface integrins during the early stages of infection via arginine-glycine-aspartic acid (RGD) motif that resides in the C terminus of the VP1 protein (11). While CAV9 binds to both integrin αVβ3 and αVβ6 in vitro (53, 61), our recent data show that integrin αVβ6 is the primary receptor of the virus (29).Viruses can utilize several endocytic pathways to enter mammalian cells: macropinocytosis and clathrin-mediated, caveolin-mediated, and clathrin- and caveolin-independent routes (14, 40-41, 50). Recent studies have shown that some of these pathways differ only slightly from each other, and certain endocytic components can participate in more than just one pathway (35, 41, 55). Most of the research carried out on enterovirus endocytosis has been done with echovirus 1 (EV1), coxsackievirus B3 (CBV3), and poliovirus (PV). Recently, Karjalainen et al. showed that EV1 enters SAOS cells via tubulovesicular structures in a dynamin-independent manner that resembles fluid-phase endocytosis and macropinocytosis and that at later stages of infection is targeted to caveosomes (33). EV1 entry to CV-1 cells, on the other hand, was shown to be strictly dynamin dependent (49). PV is endocytosed to HeLa cells by a rapid clathrin- and caveolin-independent pathway, whereas in brain microvascular endothelial cells it uses slower, caveolin- and dynamin-dependent endocytosis (4, 7, 17). CBV3 enters HeLa cells by clathrin-mediated endocytosis (13) and polarized epithelial CaCo-2 cells by a process that combines features of caveolar endocytosis and macropinocytosis (16, 18). Foot-and-mouth-disease virus (FMDV), a member of the Aphthovirus genus of the family Picornaviridae, binds to several αV-integrins, including αVβ6, and is internalized through the clathrin-mediated pathway (5, 19, 31). In the light of these examples, it is evident that enterovirus internalization to human cells is a complex phenomenon wherein a virus may use different mechanisms to enter different cell types.In the CAV9 infection cycle, the steps that follow the initial attachment of the virus to the cell surface integrins are still poorly characterized. An early electron microscopic work by Hecker et al. has shown that single CAV9 particles enter monkey kidney cells in vesicles, which then occasionally fuse and form larger structures (28). Interestingly, they found that most internalized virus particles became eventually trapped in large vacuoles, presumably lysosomes, where they were confined without proceeding to capsid uncoating and RNA release. More recently, a number of cell surface molecules have been proposed to contribute to CAV9 internalization. A subunit of major histocompatibility complex class I (MHC-I) complex, β2-microglobulin (β2M), has been shown to be essential for the infection of several picornaviruses, including CAV9, and it is supposed to have a postattachment role (12, 59, 61). In addition, heat shock 70-kDa protein 5 (HSPA5 protein, also known as glucose-regulated protein 78-kDa, or GRP78) has been suggested to function as a coreceptor for the virus and to mediate CAV9 infection by its interaction with β2M on the cell surface (57). CAV9 entry has been proposed to occur through lipid microdomains, where a number of signaling events takes place (58).The aim of this study was to elucidate the internalization mechanism of CAV9 in A549 human lung carcinoma cells. We used chemical inhibitors, RNA interference (RNAi) silencing, and the expression of dominant negative constructs combined to virus infectivity assays and confocal imaging to examine which cellular molecules are involved in the entry process. The results indicate that CAV9 internalization is dependent on integrin αVβ6, β2M, dynamin 2, and Arf6 (ADP-ribosylation factor 6) but not clathrin or caveolin-1.     

Integrin alpha v beta 6 is an RGD-dependent receptor for coxsackievirus A9

Coxsackievirus A9 (CAV9), a member of the Enterovirus genus of Picornaviridae, is a common human pathogen and is one of a significant number of viruses containing a functional arginine-glycine-aspartic acid (RGD) motif in one of their capsid proteins. Previous studies identified the RGD-recognizing integrin alpha(v)beta(3) as its cellular receptor. However, integrin alpha(v)beta(6) has been shown to be an efficient receptor for another RGD-containing picornavirus, foot-and-mouth disease virus (FMDV). In view of the similarity in sequence context of the RGD motifs in CAV9 and FMDV, we investigated whether alpha(v)beta(6) can also serve as a receptor for CAV9. We found that CAV9 can bind to purified alpha(v)beta(6) and also to SW480 cells transfected with beta(6) cDNA, allowing expression of alpha(v)beta(6) on their surface, but it cannot bind to mock-transfected cells. In addition, a higher yield of CAV9 was obtained in beta(6)-expressing cells than in mock-transfected cells. There was no similar enhancement in infection with an RGD-less CAV9 mutant. We also found beta(6) on the surface of GMK cells, a cell line which CAV9 infects efficiently by an RGD-dependent mechanism. Significantly, this infection is blocked by an antibody to alpha(v)beta(6), while this antibody did not block the low level of infection by the RGD-less mutant. Thus, integrin alpha(v)beta(6) is an RGD-dependent receptor for CAV9 and may be important in natural CAV9 infections.     

Bacterial communities at a groundwater-surface water ecotone: gradual change or abrupt transition points along a contamination gradient?

Microbial communities contribute greatly to groundwater quality, but the impacts of land-use practices on bacteria in groundwaters and groundwater-dependent ecosystems remain poorly known. With 16S rRNA gene amplicon sequencing, we assessed bacterial community composition at the groundwater-surface water ecotone of boreal springs impacted by urbanization and agriculture, using spring water nitrate-N as a surrogate of contamination. We also measured the rate of a key ecosystem process, organic matter decomposition. We documented a recurrent pattern across all major bacterial phyla where diversity started to decrease at unexpectedly low nitrate-N concentrations (100–300 μg L⁻¹). At 400 NO₃⁻-N μg L⁻¹, 25 bacterial exact sequence variants showed a negative response, resulting in a distinct threshold in bacterial community composition. Chthonomonas, Acetobacterales and Hyphomicrobium were the most sensitive taxa, while only three taxa (Duganella, Undibacterium and Thermoanaerobaculaceae) were enriched due to increased contamination. Decomposition rate responded unimodally to increasing nitrate-N concentration, with a peak rate at ~400 NO₃⁻-N μg L⁻¹, parallelly with a major shift in bacterial community composition. Our results emphasize the utility of bacterial communities in the assessment of groundwater-dependent ecosystems. They also call for a careful reconsideration of threshold nitrate values for defining groundwater ecosystem health and protecting their microbial biodiversity.     

RIPK1 and Caspase-8 Ensure Chromosome Stability Independently of Their Role in Cell Death and Inflammation

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Spatial and seasonal variation in greenhouse gas and nutrient dynamics and their interactions in the sediments of a boreal eutrophic lake

Dynamics of greenhouse gases, CH₄, CO₂ and N₂O, and nutrients, NO ₂ ^– + NO ₃ ^– , NH ₄ ⁺ and P, were studied in the sediments of the eutrophic, boreal Lake Kevätön in Finland. Undisturbed sediment cores taken in the summer, autumn and winter from the deep and shallow profundal and from the littoral were incubated in laboratory microcosms under aerobic and anaerobic water flow conditions. An increase in the availability of oxygen in water overlying the sediments reduced the release of CH₄, NH ₄ ⁺ and P, increased the flux of N₂O and NO ₂ ^– + NO ₃ ^– , but did not affect CO₂ production. The littoral sediments produced CO₂ and CH₄ at high rates, but released only negligible amounts of nutrients. The deep profundal sediments, with highest carbon content, possessed the greatest release rates of CO₂, CH₄, NH ₄ ⁺ and P. The higher fluxes of these gases in summer and autumn than in winter were probably due to the supply of fresh organic matter from primary production. From the shallow profundal sediments fluxes of CH₄, NH₄ ⁺ and P were low, but, in contrast, production of N₂O was the highest among the different sampling sites. Due to the large areal extension, the littoral and shallow profundal zones had the greatest importance in the overall gas and nutrient budgets in the lake. Methane emissions, especially the ebullition of CH₄ (up to 84% of the total flux), were closely related to the sediment P and NH ₄ ⁺ release. The high production and ebullition of CH₄, enhances the internal loading of nutrients, lake eutrophication status and the impact of boreal lakes to trophospheric gas budgets.     

Fc-fusion proteins and FcRn: structural insights for longer-lasting and more effective therapeutics

Nearly 350 IgG-based therapeutics are approved for clinical use or are under development for many diseases lacking adequate treatment options. These include molecularly engineered biologicals comprising the IgG Fc-domain fused to various effector molecules (so-called Fc-fusion proteins) that confer the advantages of IgG, including binding to the neonatal Fc receptor (FcRn) to facilitate in vivo stability, and the therapeutic benefit of the specific effector functions. Advances in IgG structure-function relationships and an understanding of FcRn biology have provided therapeutic opportunities for previously unapproachable diseases. This article discusses approved Fc-fusion therapeutics, novel Fc-fusion proteins and FcRn-dependent delivery approaches in development, and how engineering of the FcRn–Fc interaction can generate longer-lasting and more effective therapeutics.