Epstein-Barr virus nuclear antigen 3A protein regulates CDKN2B transcription via interaction with MIZ-1

The Epstein-Barr virus (EBV) nuclear antigen 3 family of protein is critical for the EBV-induced primary B-cell growth transformation process. Using a yeast two-hybrid screen we identified 22 novel cellular partners of the EBNA3s. Most importantly, among the newly identified partners, five are known to play direct and important roles in transcriptional regulation. Of these, the Myc-interacting zinc finger protein-1 (MIZ-1) is a transcription factor initially characterized as a binding partner of MYC. MIZ-1 activates the transcription of a number of target genes including the cell cycle inhibitor CDKN2B. Focusing on the EBNA3A/MIZ-1 interaction we demonstrate that binding occurs in EBV-infected cells expressing both proteins at endogenous physiological levels and that in the presence of EBNA3A, a significant fraction of MIZ-1 translocates from the cytoplasm to the nucleus. Moreover, we show that a trimeric complex composed of a MIZ-1 recognition DNA element, MIZ-1 and EBNA3A can be formed, and that interaction of MIZ-1 with nucleophosmin (NPM), one of its coactivator, is prevented by EBNA3A. Finally, we show that, in the presence of EBNA3A, expression of the MIZ-1 target gene, CDKN2B, is downregulated and repressive H3K27 marks are established on its promoter region suggesting that EBNA3A directly counteracts the growth inhibitory action of MIZ-1.

Sustained autophagy contributes to measles virus infectivity

The interplay between autophagy and intracellular pathogens is intricate as autophagy is an essential cellular response to fight against infections, whereas numerous microbes have developed strategies to escape this process or even exploit it to their own benefit. The fine tuned timing and/or selective molecular pathways involved in the induction of autophagy upon infections could be the cornerstone allowing cells to either control intracellular pathogens, or be invaded by them. We report here that measles virus infection induces successive autophagy signallings in permissive cells, via distinct and uncoupled molecular pathways. Immediately upon infection, attenuated measles virus induces a first transient wave of autophagy, via a pathway involving its cellular receptor CD46 and the scaffold protein GOPC. Soon after infection, a new autophagy signalling is initiated which requires viral replication and the expression of the non-structural measles virus protein C. Strikingly, this second autophagy signalling can be sustained overtime within infected cells, independently of the expression of C, but via a third autophagy input resulting from cell-cell fusion and the formation of syncytia. Whereas this sustained autophagy signalling leads to the autophagy degradation of cellular contents, viral proteins escape from degradation. Furthermore, this autophagy flux is ultimately exploited by measles virus to limit the death of infected cells and to improve viral particle formation. Whereas CD150 dependent virulent strains of measles virus are unable to induce the early CD46/GOPC dependent autophagy wave, they induce and exploit the late and sustained autophagy. Overall, our work describes distinct molecular pathways for an induction of self-beneficial sustained autophagy by measles virus.

Autophagy is an evolutionarily conserved lysosomal dependent degradative pathway for recycling of long-lived proteins and damaged organelles. Autophagy is also an essential cellular response to fight infection by destroying infectious pathogens trapped within autophagosomes and plays a key role in the induction of both innate and adaptive immune responses. Numerous viruses have evolved strategies to counteract autophagy in order to escape from degradation or/and to inhibit immune signals. The kinetic and molecular pathways involved in the induction of autophagy upon infections might determine if cells would be able to control pathogens or would be invaded by them. We showed that measles virus (MeV) infection induces successive autophagy signallings in cells via distinct molecular pathways. A first autophagy wave is induced by the engagement of the MeV cellular receptor CD46 and the scaffold protein GOPC. A second wave is initiated after viral replication by the expression of the non-structural MeV protein C and is sustained overtime within infected cells thanks to the formation of syncytia. This sustained autophagy is exploited by MeV to limit the death of infected cells and to improve viral particle formation. We describe new molecular pathways by which MeV hijacks autophagy to promote its infectivity.

Comparative analysis of virus-host interactomes with a mammalian high-throughput protein complementation assay based on Gaussia princeps luciferase

Comparative interactomics is a strategy for inferring potential interactions among orthologous proteins or "interologs". Herein we focus, in contrast to standard homology-based inference, on the divergence of protein interaction profiles among closely related organisms, showing that the approach can correlate specific traits to phenotypic differences. As a model, this new comparative interactomic approach was applied at a large scale to human papillomaviruses (HPVs) proteins. The oncogenic potential of HPVs is mainly determined by the E6 and E7 early proteins. We have mapped and overlapped the virus-host protein interaction networks of E6 and E7 proteins from 11 distinct HPV genotypes, selected for their different tropisms and pathologies. We generated robust and comprehensive datasets by combining two orthogonal protein interaction assays: yeast two-hybrid (Y2H), and our recently described "high-throughput Gaussia princeps protein complementation assay" (HT-GPCA). HT-GPCA detects protein interaction by measuring the interaction-mediated reconstitution of activity of a split G. princeps luciferase. Hierarchical clustering of interaction profiles recapitulated HPV phylogeny and was used to correlate specific virus-host interaction profiles with pathological traits, reflecting the distinct carcinogenic potentials of different HPVs. This comparative interactomics constitutes a reliable and powerful strategy to decipher molecular relationships in virtually any combination of microorganism-host interactions.

Epstein-Barr virus protein EB2 stimulates cytoplasmic mRNA accumulation by counteracting the deleterious effects of SRp20 on viral mRNAs

The Epstein-Barr Virus (EBV) protein EB2 (also called Mta, SM and BMLF1), is an essential nuclear protein produced during the replicative cycle of EBV. EB2 is required for the efficient cytoplasmic accumulation of viral mRNAs derived from intronless genes. EB2 is an RNA-binding protein whose expression has been shown to influence RNA stability, splicing, nuclear export and translation. Using a yeast two-hybrid screen, we have identified three SR proteins, SF2/ASF, 9G8 and SRp20, as cellular partners of EB2. Then, by using siRNA to deplete cells of specific SR proteins, we found that SRp20 plays an essential role in the processing of several model mRNAs: the Renilla luciferase reporter mRNA, the human β-globin cDNA transcript and two EBV late mRNAs. These four mRNAs were previously found to be highly dependent on EB2 for their efficient cytoplasmic accumulation. Here, we show that SRp20 depletion results in an increase in the accumulation of these mRNAs, which correlates with an absence of additive effect of EB2, suggesting that EB2 functions by antagonizing SRp20. Moreover, by using RNA-immunoprecipitation assays we found that EB2 enhances the association of SRp20 with the β-globin transcript suggesting that EB2 acts by stabilizing SRp20's labile interactions with the RNA.

Autophagy and RNA virus interactomes reveal IRGM as a common target

Several intracellular pathogens have the ability to avoid or exploit the otherwise destructive process of autophagy. RNA viruses are constantly confronted with cellular autophagy, and several of them hijack autophagy during the infectious cycle to improve their own replication. Nevertheless, our knowledge of viral molecular strategies used to manipulate autophagy remains limited. Our study allowed the identification of molecular interactions between 44 autophagy-associated proteins and 83 viral proteins belonging to five different RNA virus families. This interactome revealed that the autophagy network machinery is highly targeted by RNA viruses. Interestingly, whereas some autophagy-associated proteins are targeted by only one RNA virus family, others are recurrent targets of several families. Among them, we found IRGM as the most targeted autophagy-associated protein. Downregulation of IRGM expression prevents autophagy induction by measles virus, HCV and HIV-1, and compromises viral replication. Our work combined interactomic and analytical approaches to identify potential pathogen virulence factors targeting autophagy.

Virus-human cell interactomes

Using global approaches and high-throughput technologies in virology brings a new vision of the infections physiology and allows the identification of cellular factors, mandatory for viral life cycle, that could be targeted by original therapeutic agents. It opens perspectives for the treatment of viral infections by acting on cellular pathways that the virus must use for its own replication. Combining these new molecules with classical antiviral drugs and immunomodulators diversifies and enlarges the antiviral arsenal and contributes to fight drug resistance. Our laboratory and others are constructing virus-human interactomes to propose a comprehensive analysis of viral infection at the cellular level. Studying these infection maps, where the viral infection can be visualized as perturbation of the human protein-protein interaction network, and identifying the biological functions that are impaired by these perturbations may lead to discovery of new therapeutic targets. These virus-human interaction maps are constructed in a stringent yeast two-hybrid system by screening human cDNA libraries with viral proteins as bait and integrating interactions mined from literature and public databases.

Flavivirus NS3 and NS5 proteins interaction network: a high-throughput yeast two-hybrid screen

Background

The genus Flavivirus encompasses more than 50 distinct species of arthropod-borne viruses, including several major human pathogens, such as West Nile virus, yellow fever virus, Japanese encephalitis virus and the four serotypes of dengue viruses (DENV type 1-4). Each year, flaviviruses cause more than 100 million infections worldwide, some of which lead to life-threatening conditions such as encephalitis or haemorrhagic fever. Among the viral proteins, NS3 and NS5 proteins constitute the major enzymatic components of the viral replication complex and are essential to the flavivirus life cycle.

Results

We report here the results of a high-throughput yeast two-hybrid screen to identify the interactions between human host proteins and the flavivirus NS3 and NS5 proteins. Using our screen results and literature curation, we performed a global analysis of the NS3 and NS5 cellular targets based on functional annotation with the Gene Ontology features. We finally created the first flavivirus NS3 and NS5 proteins interaction network and analysed the topological features of this network. Our proteome mapping screen identified 108 human proteins interacting with NS3 or NS5 proteins or both. The global analysis of the cellular targets revealed the enrichment of host proteins involved in RNA binding, transcription regulation, vesicular transport or innate immune response regulation.

Conclusions

We proposed that the selective disruption of these newly identified host/virus interactions could represent a novel and attractive therapeutic strategy in treating flavivirus infections. Our virus-host interaction map provides a basis to unravel fundamental processes about flavivirus subversion of the host replication machinery and/or immune defence strategy.

Innate immunity modulation in virus entry

Entry into a cell submits viruses to detection by pattern recognition receptors (PRRs) leading to an early innate anti-viral response. Several viruses evolved strategies to avoid or subvert PRR recognition at the step of virus entry to promote infection. Whereas viruses mostly escape from soluble PRR detection, endocytic/phagocytic PRRs, such as the mannose receptor or DC-SIGN, are commonly used for virus entry. Moreover, virion-incorporated proteins may also offer viruses a way to dampen anti-viral innate immunity upon virus entry, and entering viruses might usurp autophagy to improve their own infectivity.

[Autophagy and pathogens: «Bon appétit Messieurs!»]

Autophagy is a highly conserved, self-degradative pathway for clearance and recycling of cytoplasmic contents. This ubiquitous cell intrinsic process can be used as a defence mechanism against intracellular pathogens. Indeed autophagy is increased upon pathogen detection, and experimental extinction in vitro and in vivo of this cellular process has been demonstrated as a crucial role to control intracellular pathogens. Co-evolution between host-cells and pathogens has selected numerous micoorganisms able to avoid or usurp autophagy to their own benefit. Understanding mechanisms underlying the anti-microbial properties of autophagy as well as those used by certain pathogens to escape this cellular process might be crucial to manipulate this cellular function in order to prevent or treat infectious diseases.

PhEVER: a database for the global exploration of virus-host evolutionary relationships

Fast viral adaptation and the implication of this rapid evolution in the emergence of several new infectious diseases have turned this issue into a major challenge for various research domains. Indeed, viruses are involved in the development of a wide range of pathologies and understanding how viruses and host cells interact in the context of adaptation remains an open question. In order to provide insights into the complex interactions between viruses and their host organisms and namely in the acquisition of novel functions through exchanges of genetic material, we developed the PhEVER database. This database aims at providing accurate evolutionary and phylogenetic information to analyse the nature of virus-virus and virus-host lateral gene transfers. PhEVER (http://pbil.univ-lyon1.fr/databases/phever) is a unique database of homologous families both (i) between sequences from different viruses and (ii) between viral sequences and sequences from cellular organisms. PhEVER integrates extensive data from up-to-date completely sequenced genomes (2426 non-redundant viral genomes, 1007 non-redundant prokaryotic genomes, 43 eukaryotic genomes ranging from plants to vertebrates) and offers a clustering of proteins into homologous families containing at least one viral sequences, as well as alignments and phylogenies for each of these families. Public access to PhEVER is available through its webpage and through all dedicated ACNUC retrieval systems.

System-level comparison of protein-protein interactions between viruses and the human type I interferon system network

Innate immunity has evolved complex molecular pathways to protect organisms from viral infections. One pivotal line of cellular defense is the induction of the antiviral effect of interferon. To circumvent this primary response and achieve their own replication, viruses have developed complex molecular strategies. Here, we provide a systems-level study of the human type I interferon system subversion by the viral proteome, by reconstructing the underlying protein-protein interaction network. At this network level, viruses establish a massive and a gradual attack, from receptors to transcription factors, by interacting preferentially with highly connected and central proteins as well as interferon-induced proteins. We also demonstrate that viruses significantly target 22% of the proteins directly interacting with the type I interferon system network, suggesting the relevance of our network-based method to identify new candidates involved in the regulation of the antiviral response. Finally, based on the comparative analysis of interactome profiles across four viral families, we provide evidence of common and differential targeting strategies.

[The virtual infected cell: a systems biology rational for antiviral drug discovery]

Infection caused by pathogens kills millions of people every year. Comprehensive understanding of molecular pathogen-host interactions, i.e. the infectome, is one of the key steps towards the development of novel diagnostic, therapeutic and preventive strategies. In this quest, progress in high-throughput << omics >> technologies applied to pathogens, i.e. infectomics, opens new perspectives toward systemic understanding of perturbations induced during infection. Deciphering the pathogen-host system also relies on the analytical and predictive power of molecular systems biology and by developing in silico models taking into account the whole picture of the molecules and their interactions. In this context, we have reconstructed a prototype of the human virtual infected cell based on 30 years of intensive research in the field of molecular virology. This model contains more than one hundred viral infectomes, including major human pathogens (HCV, HBV, HIV, HHV, HPV) and has led to the generation of novel systems-level hypotheses that could be suitable for the development of innovative antiviral strategies based on the control of cellular functions.

Cellular receptors, differentiation and endocytosis requirements are key factors for type I IFN response by human epithelial, conventional and plasmacytoid dendritic infected cells by measles virus

While the antiviral response during measles virus (MeV) infection is documented, the contribution of the hosting cell type to the type I interferon (IFN-alpha/beta) response is still not clearly established. Here, we report that a signature heterogeneity of the IFN-alpha/beta response according to the cell type. The MeV tropism dictated by the expression of appropriate cellular receptor appeared to be crucial for epithelial cells. For conventional DCs (cDCs), the maturation state played a prominent role. In response to both wild type MeV isolates and laboratory/vaccine strains, immature cDCs produced higher levels of IFN-alpha than mature cDCs, despite the reduced expression levels of both CD46 and CD150 receptors by the former ones. While in epithelial cells and cDCs the MeV transcription was required to activate the IFN-alpha/beta response, plasmacytoid DCs (pDCs) rapidly produced large amounts of IFN-alpha mostly independently of the viral infection cycle. This argues for a significant contribution of pDCs in response to MeV infection and/or vaccination.

Pathogen recognition by the cell surface receptor CD46 induces autophagy

Autophagy is a degradative mechanism involved in cell protection against invading pathogens. Although the autophagic process is well characterized, the molecular pathways leading to its activation upon pathogen binding remain poorly understood. Our recent work demonstrates that the cell surface pathogen receptor CD46 induces autophagy upon pathogen recognition. The molecular pathway linking CD46 to the autophagosome machinery relies on the scaffold protein GOPC and on the autophagosome formation complex Beclin 1/VPS34. The CD46-dependent autophagy is critical to an early control of infection.

Autophagy induction by the pathogen receptor CD46

Autophagy is a highly regulated self-degradative mechanism required at a basal level for intracellular clearance and recycling of cytoplasmic contents. Upon intracellular pathogen invasion, autophagy can be induced as an innate immune mechanism to control infection. Nevertheless, pathogens have developed strategies to avoid or hijack autophagy for their own benefit. The molecular pathways inducing autophagy in response to infection remain poorly documented. We report here that the engagement of CD46, a ubiquitous human surface receptor able to bind several different pathogens, is sufficient to induce autophagy. CD46-Cyt-1, one of the two C-terminal splice variants of CD46, is linked to the autophagosome formation complex VPS34/Beclin1 via its interaction with the scaffold protein GOPC. Measles virus and group A Streptococcus, two CD46-binding pathogens, induce autophagy through a CD46-Cyt-1/GOPC pathway. Thus, upon microorganism recognition, a cell surface pathogen receptor can directly trigger autophagy, a critical step to control infection.

ViralORFeome: an integrated database to generate a versatile collection of viral ORFs

Large collections of protein-encoding open reading frames (ORFs) established in a versatile recombination-based cloning system have been instrumental to study protein functions in high-throughput assays. Such ‘ORFeome’ resources have been developed for several organisms but in virology, plasmid collections covering a significant fraction of the virosphere are still needed. In this perspective, we present ViralORFeome 1.0 (http://www.viralorfeome.com), an open-access database and management system that provides an integrated set of bioinformatic tools to clone viral ORFs in the Gateway® system. ViralORFeome provides a convenient interface to navigate through virus genome sequences, to design ORF-specific cloning primers, to validate the sequence of generated constructs and to browse established collections of virus ORFs. Most importantly, ViralORFeome has been designed to manage all possible variants or mutants of a given ORF so that the cloning procedure can be applied to any emerging virus strain. A subset of plasmid constructs generated with ViralORFeome platform has been tested with success for heterologous protein expression in different expression systems at proteome scale. ViralORFeome should provide our community with a framework to establish a large collection of virus ORF clones, an instrumental resource to determine functions, activities and binding partners of viral proteins.

pISTil: a pipeline for yeast two-hybrid Interaction Sequence Tags identification and analysis

BACKGROUND

High-throughput screening of protein-protein interactions opens new systems biology perspectives for the comprehensive understanding of cell physiology in normal and pathological conditions. In this context, yeast two-hybrid system appears as a promising approach to efficiently reconstruct protein interaction networks at the proteome-wide scale. This protein interaction screening method generates a large amount of raw sequence data, i.e. the ISTs (Interaction Sequence Tags), which urgently need appropriate tools for their systematic and standardised analysis.

FINDINGS

We develop pISTil, a bioinformatics pipeline combined with a user-friendly web-interface: (i) to establish a standardised system to analyse and to annotate ISTs generated by two-hybrid technologies with high performance and flexibility and (ii) to provide high-quality protein-protein interaction datasets for systems-level approach. This pipeline has been validated on a large dataset comprising more than 11.000 ISTs. As a case study, a detailed analysis of ISTs obtained from yeast two-hybrid screens of Hepatitis C Virus proteins against human cDNA libraries is also provided.

CONCLUSION

We have developed pISTil, an open source pipeline made of a collection of several applications governed by a Perl script. The pISTil pipeline is intended to laboratories, with IT-expertise in system administration, scripting and database management, willing to automatically process large amount of ISTs data for accurate reconstruction of protein interaction networks in a systems biology perspective. pISTil is publicly available for download at http://sourceforge.net/projects/pistil.

VirHostNet: a knowledge base for the management and the analysis of proteome-wide virus-host interaction networks

Infectious diseases caused by viral agents kill millions of people every year. The improvement of prevention and treatment of viral infections and their associated diseases remains one of the main public health challenges. Towards this goal, deciphering virus-host molecular interactions opens new perspectives to understand the biology of infection and for the design of new antiviral strategies. Indeed, modelling of an infection network between viral and cellular proteins will provide a conceptual and analytic framework to efficiently formulate new biological hypothesis at the proteome scale and to rationalize drug discovery. Therefore, we present the first release of VirHostNet (Virus-Host Network), a public knowledge base specialized in the management and analysis of integrated virus-virus, virus-host and host-host interaction networks coupled to their functional annotations. VirHostNet integrates an extensive and original literature-curated dataset of virus-virus and virus-host interactions (2671 non-redundant interactions) representing more than 180 distinct viral species and one of the largest human interactome (10,672 proteins and 68,252 non-redundant interactions) reconstructed from publicly available data. The VirHostNet Web interface provides appropriate tools that allow efficient query and visualization of this infected cellular network. Public access to the VirHostNet knowledge-based system is available at http://pbildb1.univ-lyon1.fr/virhostnet.

Langerhans cell histiocytosis reveals a new IL-17A-dependent pathway of dendritic cell fusion

IL-17A is a T cell-specific cytokine that is involved in chronic inflammations, such as Mycobacterium infection, Crohn's disease, rheumatoid arthritis and multiple sclerosis. Mouse models have explained the molecular basis of IL-17A production and have shown that IL-17A has a positive effect not only on granuloma formation and neurodegeneration through unknown mechanisms, but also on bone resorption through Receptor activator of NF-kappaB ligand (RANKL) induction in osteoblasts. Langerhans cell histiocytosis (LCH) is a rare disease of unknown etiology, lacking an animal model, that cumulates symptoms that are found separately in various IL-17A-related diseases, such as aggressive chronic granuloma formation, bone resorption and soft tissue lesions with occasional neurodegeneration. We examined IL-17A in the context of LCH and found that there were high serum levels of IL-17A during active LCH and unexpected IL-17A synthesis by dendritic cells (DCs), the major cell type in LCH lesions. We also found an IL-17A-dependent pathway for DC fusion, which was highly potentiated by IFN-gamma and led to giant cells expressing three major tissue-destructive enzymes: tartrate resistant acidic phosphatase and matrix metalloproteinases 9 and 12. IFN-gamma expression has been previously documented in LCH and observed in IL-17A-related diseases. Notably, serum IL-17A-dependent fusion activity correlates with LCH activity. Thus, IL-17A and IL-17A-stimulated DCs represent targets that may have clinical value in the treatment of LCH and other IL-17A-related inflammatory disorders.

Cell-cell fusion induced by measles virus amplifies the type I interferon response

Measles virus (MeV) infection is characterized by the formation of multinuclear giant cells (MGC). We report that beta interferon (IFN-beta) production is amplified in vitro by the formation of virus-induced MGC derived from human epithelial cells or mature conventional dendritic cells. Both fusion and IFN-beta response amplification were inhibited in a dose-dependent way by a fusion-inhibitory peptide after MeV infection of epithelial cells. This effect was observed at both low and high multiplicities of infection. While in the absence of virus replication, the cell-cell fusion mediated by MeV H/F glycoproteins did not activate any IFN-alpha/beta production, an amplified IFN-beta response was observed when H/F-induced MGC were infected with a nonfusogenic recombinant chimerical virus. Time lapse microscopy studies revealed that MeV-infected MGC from epithelial cells have a highly dynamic behavior and an unexpected long life span. Following cell-cell fusion, both of the RIG-I and IFN-beta gene deficiencies were trans complemented to induce IFN-beta production. Production of IFN-beta and IFN-alpha was also observed in MeV-infected immature dendritic cells (iDC) and mature dendritic cells (mDC). In contrast to iDC, MeV infection of mDC induced MGC, which produced enhanced amounts of IFN-alpha/beta. The amplification of IFN-beta production was associated with a sustained nuclear localization of IFN regulatory factor 3 (IRF-3) in MeV-induced MGC derived from both epithelial cells and mDC, while the IRF-7 up-regulation was poorly sensitive to the fusion process. Therefore, MeV-induced cell-cell fusion amplifies IFN-alpha/beta production in infected cells, and this indicates that MGC contribute to the antiviral immune response.

Murine dendritic cell transdifferentiation into osteoclasts is differentially regulated by innate and adaptive cytokines

Dendritic cells (DC) are the mononuclear cells that initiate adaptive immune responses. Osteoclasts (OC) are the multinucleated giant cells that resorb bone. As previously described for human conventional DC (cDC), we demonstrate that murine cDC, either in vitro generated from Fms-like tyrosine kinase 3 (Flt3)+ bone marrow progenitors or ex vivo purified from spleen, are able to develop into OC in response to M-CSF and receptor activator of NF-kappaB ligand (RANKL) in vitro. This transdifferentiation is driven by the immune environment that controls cDC maturation, cell fusion, tartrate-resistant acid phosphatase (TRAP) and bone resorption activities. Only immature cDC have the capacity to become OC since mature cDC or plasmacytoid DC do not. Additions of the pro-inflammatory cytokines, such as IL-1beta and TNF-alpha, or human rheumatoid synovial fluid, increase murine cDC transdifferentiation into OC, whereas IFN-alpha inhibits it. The adaptive cytokine, IFN-gamma, inhibits cDC fusion while IL-4 increases it. IL-2, IFN-gamma and IL-4 inhibit TRAP and bone resorption activities contrary to IL-10, which enhances both activities. A putative new "immune multinucleated giant cell" unable to resorb bone, which is formed owing to IL-4, is underlined. The future analysis of cDC transdifferentiation into OC in murine models of inflammatory arthritis will give us the quantitative importance of this phenomenon in vivo.

Cutting Edge: Abortive Proliferation of CD46-Induced Tr1-Like Cells due to a Defective Akt/Survivin Signaling Pathway

T regulatory cell 1 (Tr1) are low proliferating peripherally induced suppressive T cells. Engaging CD3 and CD46 on human CD4+ T cells induces a Tr1-like phenotype. In this study, we report that human Tr1-like cells do not sustain proliferation over time. The weak proliferation of these cells results first from their inability to sustain expression of various cell cycle-associated proteins, to efficiently degrade the inhibitor of cell cycle progression p27/Kip1 and, as a consequence, in their accumulation in the G0-G1 phase. Also, the reduced proliferation of Tr1-like cells results from their increased sensitivity to death as they divide, through a mechanism that is neither Fas-mediated nor Bcl2/Bcl-xL related. Both properties, impaired cell cycle and death sensitivity, are explained by a specific defective activation of Akt that impairs the expression of Survivin. Thus, our results show that CD3/CD46-induced Tr1-like cells die through a process of abortive proliferation.

High expression of antioxidant proteins in dendritic cells: possible implications in atherosclerosis

Dendritic cells (DCs) display the unique ability to activate naive T cells and to initiate primary T cell responses revealed in DC-T cell alloreactions. DCs frequently operate under stress conditions. Oxidative stress enhances the production of inflammatory cytokines by DCs. We performed a proteomic analysis to see which major changes occur, at the protein expression level, during DC differentiation and maturation. Comparative two-dimensional gel analysis of the monocyte, immature DC, and mature DC stages was performed. Manganese superoxide dismutase (Mn-SOD) reached 0.7% of the gel-displayed proteins at the mature DC stage. This important amount of Mn-SOD is a primary antioxidant defense system against superoxide radicals, but its product, H(2)O(2), is also deleterious for cells. Peroxiredoxin (Prx) enzymes play an important role in eliminating such peroxide. Prx1 expression level continuously increased during DC differentiation and maturation, whereas Prx6 continuously decreased, and Prx2 peaked at the immature DC stage. As a consequence, DCs were more resistant than monocytes to apoptosis induced by high amounts of oxidized low density lipoproteins containing toxic organic peroxides and hydrogen peroxide. Furthermore DC-stimulated T cells produced high levels of receptor activator of nuclear factor kappaB ligand, a chemotactic and survival factor for monocytes and DCs. This study provides insights into the original ability of DCs to express very high levels of antioxidant enzymes such as Mn-SOD and Prx1, to detoxify oxidized low density lipoproteins, and to induce high levels of receptor activator of nuclear factor kappaB ligand by the T cells they activate and further emphasizes the role that DCs might play in atherosclerosis, a pathology recognized as a chronic inflammatory disorder.