Escape of HIV-1-Infected Dendritic Cells from TRAIL-Mediated NK Cell Cytotoxicity during NK-DC Cross-Talk—A Pivotal Role of HMGB1

Early stages of Human Immunodeficiency Virus-1 (HIV-1) infection are associated with local recruitment and activation of important effectors of innate immunity, i.e. natural killer (NK) cells and dendritic cells (DCs). Immature DCs (iDCs) capture HIV-1 through specific receptors and can disseminate the infection to lymphoid tissues following their migration, which is associated to a maturation process. This process is dependent on NK cells, whose role is to keep in check the quality and the quantity of DCs undergoing maturation. If DC maturation is inappropriate, NK cells will kill them (“editing process”) at sites of tissue inflammation, thus optimizing the adaptive immunity. In the context of a viral infection, NK-dependent killing of infected-DCs is a crucial event required for early elimination of infected target cells. Here, we report that NK-mediated editing of iDCs is impaired if DCs are infected with HIV-1. We first addressed the question of the mechanisms involved in iDC editing, and we show that cognate NK-iDC interaction triggers apoptosis via the TNF-related apoptosis-inducing ligand (TRAIL)-Death Receptor 4 (DR4) pathway and not via the perforin pathway. Nevertheless, once infected with HIV-1, DC_HIV become resistant to NK-induced TRAIL-mediated apoptosis. This resistance occurs despite normal amounts of TRAIL released by NK cells and comparable DR4 expression on DC_HIV. The escape of DC_HIV from NK killing is due to the upregulation of two anti-apoptotic molecules, the cellular-Flice like inhibitory protein (c-FLIP) and the cellular inhibitor of apoptosis 2 (c-IAP2), induced by NK-DC_HIV cognate interaction. High-mobility group box 1 (HMGB1), an alarmin and a key mediator of NK-DC cross-talk, was found to play a pivotal role in NK-dependent upregulation of c-FLIP and c-IAP2 in DC_HIV. Finally, we demonstrate that restoration of DC_HIV susceptibility to NK-induced TRAIL killing can be obtained either by silencing c-FLIP and c-IAP2 by specific siRNA, or by inhibiting HMGB1 with blocking antibodies or glycyrrhizin, arguing for a key role of HMGB1 in TRAIL resistance and DC_HIV survival. These findings provide evidence for a new strategy developed by HIV to escape immune attack, they challenge the question of the involvement of HMGB1 in the establishment of viral reservoirs in DCs, and they identify potential therapeutic targets to eliminate infected DCs.     

Living together: behavior and welfare in single and mixed species groups of capuchin (Cebus apella) and squirrel monkeys (Saimiri sciureus)

There are potential advantages of housing primates in mixed species exhibits for both the visiting public and the primates themselves. If the primates naturally associate in the wild, it may be more educational and enjoyable for the public to view. Increases in social complexity and stimulation may be enriching for the primates. However, mixed species exhibits might also create welfare problems such as stress from interspecific aggression. We present data on the behavior of single and mixed species groups of capuchin monkeys (Cebus apella) and squirrel monkeys (Saimiri sciureus) housed at the Living Links to Human Evolution Research Centre in the Royal Zoological Society of Scotland's Edinburgh Zoo. These species associate in the wild, gaining foraging benefits and decreased predation. But Cebus are also predators themselves with potential risks for the smaller Saimiri. To study their living together we took scan samples at ≥15 min intervals on single (n=109) and mixed species groups (n=152), and all occurrences of intraspecific aggression and interspecific interactions were recorded. We found no evidence of chronic stress and Saimiri actively chose to associate with Cebus. On 79% of scans, the two species simultaneously occupied the same part of their enclosure. No vertical displacement was observed. Interspecific interactions were common (>2.5/hr), and equally divided among mildly aggressive, neutral, and affiliative interactions such as play. Only one aggressive interaction involved physical contact and was non‐injurious. Aggressive interactions were mostly (65%) displacements and vocal exchanges, initiated almost equally by Cebus and Saimiri. Modifications to the enclosure were successful in reducing these mildly aggressive interactions with affiliative interactions increasing in frequency and diversity. Our data suggest that in carefully designed, large enclosures, naturally associating monkeys are able to live harmoniously and are enriched by each other. Am. J. Primatol. 72:33–47, 2010. © 2009 Wiley‐Liss, Inc.     

Changes in cholesterol levels in the plasma membrane modulate cell signaling and regulate cell adhesion and migration on fibronectin

The number and distribution of lipid molecules, including cholesterol in particular, in the plasma membrane, may play a key role in regulating several physiological processes in cells. We investigated the role of membrane cholesterol in regulating cell shape, adhesion and motility. The acute depletion of cholesterol from the plasma membrane of cells that were well spread and motile on fibronectin caused the rounding of these cells and decreased their adhesion to and motility on fibronectin. These modifications were less pronounced in cells plated on laminin, vitronectin or plastic, indicating that cholesterol-mediated changes in adhesion and motility are more specific for adhesion mediated by fibronectin-specific integrins, such as alpha5beta1. These changes were accompanied by remodeling of the actin cytoskeleton, the spatial reorganization of paxillin in the membrane, and changes to the dynamics of alpha5 integrin and paxillin-rich focal adhesions. Levels of tyrosine phosphorylation at position 576/577 of FAK and Erk1/Erk2 MAP-kinase activity levels were both lower in cholesterol-depleted than in control cells. These levels normalized only on fibronectin when cholesterol was reincorporated into the cell membrane. Thus, membrane cholesterol content has a specific effect on certain signaling pathways specifically involved in regulating cell motility on fibronectin and organization of the actin cytoskeleton.     

The anti-biofilm activity secreted by a marine Pseudoalteromonas strain

Bacterial biofilms occur on all submerged structures in marine environments. The authors previously reported that the marine bacterium Pseudoalteromonas sp. 3J6 secretes antibiofilm activity. Here, it was discovered that another Pseudoalteromonas sp. strain, D41, inhibited the development of strain 3J6 in mixed biofilms. Confocal laser scanning microscope observations revealed that the culture supernatant of strain D41 impaired biofilm formation of strain 3J6 and another marine bacterium. A microtiter plate assay of the antibiofilm activity was set up and validated with culture supernatants of Pseudoalteromonas sp. 3J6. This assay was used to determine the spectra of action of strains D41 and 3J6. Each culture supernatant impaired the biofilm development of 13 marine bacteria out of 18. However, differences in the spectra of action and the physical behaviours of the antibiofilm molecules suggest that the latter are not identical. They nevertheless share the originality of being devoid of antibacterial activity against planktonic bacteria.     

The ribonucleotide reductase R1 subunits of herpes simplex virus types 1 and 2 protect cells against TNFα- and FasL-induced apoptosis by interacting with caspase-8

We previously reported that HSV-2 R1, the R1 subunit (ICP10; UL39) of herpes simplex virus type-2 ribonucleotide reductase, protects cells against apoptosis induced by the death receptor (DR) ligands tumor necrosis factor-alpha- (TNFα) and Fas ligand (FasL) by interrupting DR-mediated signaling at, or upstream of, caspase-8 activation. Further investigation of the molecular mechanism underlying HSV-2 R1 protection showed that extracellular-regulated kinase 1/2 (ERK1/2), phosphatidylinositol 3-kinase (PI3-K)/Akt, NF-κB and JNK survival pathways do not play a major role in this antiapoptotic function. Interaction studies revealed that HSV-2 R1 interacted constitutively with caspase-8. The HSV-2 R1 deletion mutant R1(1-834)-GFP and Epstein–Barr virus (EBV) R1, which did not protect against apoptosis induced by DR ligands, did not interact with caspase-8, indicating that interaction is required for protection. HSV-2 R1 impaired caspase-8 activation induced by caspase-8 over-expression, suggesting that interaction between the two proteins prevents caspase-8 dimerization/activation. HSV-2 R1 bound to caspase-8 directly through its prodomain but did not interact with either its caspase domain or Fas-associated death domain protein (FADD). Interaction between HSV-2 R1 and caspase-8 disrupted FADD-caspase-8 binding. We further demonstrated that individually expressed HSV-1 R1 (ICP6) shares, with HSV-2 R1, the ability to bind caspase-8 and to protect cells against DR-induced apoptosis. Finally, as the long-lived Fas protein remained stable during the early period of infection, experiments with the HSV-1 UL39 deletion mutant ICP6∆ showed that HSV-1 R1 could be essential for the protection of HSV-1-infected cells against FasL.     

Regulation of apoptotic mediators reveals dynamic responses to thermal stress in the reef building coral Acropora millepora

Background

Mass coral bleaching is increasing in scale and frequency across the world''s coral reefs and is being driven primarily by increased levels of thermal stress arising from global warming. In order to understand the impacts of projected climate change upon corals reefs, it is important to elucidate the underlying cellular mechanisms that operate during coral bleaching and subsequent mortality. In this respect, increased apoptotic cell death activity is an important cellular process that is associated with the breakdown of the mutualistic symbiosis between the cnidarian host and their dinoflagellate symbionts.

Methodology/Principal Findings

The present study reports the impacts of different stressors (colchicine and heat stress) on three phases of apoptosis: (i) the potential initiation by differential expression of Bcl-2 members, (ii) the execution of apoptotic events by activation of caspase 3-like proteases and (iii) and finally, the cell disposal indicated by DNA fragmentation in the reef building coral Acropora millepora. In corals incubated with colchicine, an increase in caspase 3-like activity and DNA fragmentation was associated with a relative down-regulation of Bcl-2, suggesting that the initiation of apoptosis may be mediated by the suppression of an anti-apoptotic mechanism. In contrast, in the early steps of heat stress, the induction of caspase-dependent apoptosis was related to a relative up-regulation of Bcl-2 consecutively followed by a delayed decrease in apoptosis activity.

Conclusions/Significance

In the light of these results, we propose a model of heat stress in coral hosts whereby increasing temperatures engage activation of caspase 3-dependent apoptosis in cells designated for termination, but also the onset of a delayed protective response involving overexpression of Bcl-2 in surviving cells. This mitigating response to thermal stress could conceivably be an important regulatory mechanism for cell survival in corals exposed to sudden environmental changes.     

Chimpanzees (Pan troglodytes) fail a what-where-when task but find rewards by using a location-based association strategy

Recollecting the what-where-when of an episode, or episodic-like memory, has been established in corvids and rodents. In humans, a linkage between remembering the past and imagining the future has been recognised. While chimpanzees can plan for the future, their episodic-like memory has hardly been investigated. We tested chimpanzees (Pan troglodytes) with an adapted food-catching paradigm. They observed the baiting of two locations amongst four and chose one after a given delay (15 min, 1 h or 5 h). We used two combinations of food types, a preferred and a less preferred food that disappeared at different rates. The subjects had to base their choices on the time elapsed since baiting, and on their memory of which food was where. They could recover either their preferred food or the one that remained present. All animals failed to obtain the preferred or present foods above chance levels. They were like-wise unsuccessful at choosing baited cups above chance levels. The subjects, thus, failed to use any feature of the baiting events to guide their choices. Nonetheless, their choices were not random, but the result of a developed location-based association strategy. Choices in the second half of the study correlated with the rewards obtained at each location in the first half of the study, independent from the choices made for each location in the first half of the study. This simple location-based strategy yielded a fair amount of food. The animals' failure to remember the what-where-when in the presented set-up may be due to the complexity of the task, rather than an inability to form episodic-like memories, as they even failed to remember what was where after 15 minutes.     

Can Monkeys Make Investments Based on Maximized Pay-off?

Animals can maximize benefits but it is not known if they adjust their investment according to expected pay-offs. We investigated whether monkeys can use different investment strategies in an exchange task. We tested eight capuchin monkeys (Cebus apella) and thirteen macaques (Macaca fascicularis, Macaca tonkeana) in an experiment where they could adapt their investment to the food amounts proposed by two different experimenters. One, the doubling partner, returned a reward that was twice the amount given by the subject, whereas the other, the fixed partner, always returned a constant amount regardless of the amount given. To maximize pay-offs, subjects should invest a maximal amount with the first partner and a minimal amount with the second. When tested with the fixed partner only, one third of monkeys learned to remove a maximal amount of food for immediate consumption before investing a minimal one. With both partners, most subjects failed to maximize pay-offs by using different decision rules with each partner' quality. A single Tonkean macaque succeeded in investing a maximal amount to one experimenter and a minimal amount to the other. The fact that only one of over 21 subjects learned to maximize benefits in adapting investment according to experimenters' quality indicates that such a task is difficult for monkeys, albeit not impossible.     

Rain forest expansion mediated by successional processes in vegetation thickets in the Western Ghats of India

Aim The objective of this study was to document succession from grassland thickets to rain forest, and to provide evidence for their potential as restoration tools. Location The Linganamakki region (State of Karnataka) of the Central Western Ghats of India. Method We selected thirty vegetation thickets ranging from 4 to 439 m² in area in the vicinity of rain forest. The area of each small thicket was estimated as an oval using its maximum length and its maximum width. When the shape was irregular (mostly in large thickets) the limits of the thicket were mapped and the area calculated from the map. Plant species were identified, the number of individuals was estimated and their heights measured. Results There was a progression in the thickets from early to late successional species. Small thickets were characterized by ecotone species and savanna trees such as Catunaregam dumetorum. Savanna trees served as a nucleus for thicket formation. Colonizing species were mostly bird‐dispersed. As succession proceeded in larger thickets, the proportion of evergreen, late‐successional rain forest trees increased. The species composition of the large thickets differed depending on the species composition of reproductive adults in the nearby forested areas. The species within small thickets were also found in the large thickets. The nestedness in species composition suggested that species turnover was deterministic based on thicket size. Human disturbance (leaf and wood collection by the local populations) affected the species composition and the species–area relationship of thickets. Main conclusions Vegetation thickets are nodal centres for rain forest colonization within grasslands. They expand and replace savanna. Early successional bird‐dispersed species established around savanna trees followed by late‐successional rain forest trees dispersed from the nearby forest by birds. Restoration programmes that reproduce natural successional processes such as those observed in thickets will be more successful and less expensive than the methods currently being employed, where trees are individually planted in grassland. Wood harvesting is the only factor that prevents thicket growth and coalescence and hampers forest expansion.