Dengue virus is responsible for the highest rates of disease and mortality among the members of the Flavivirus genus. Dengue epidemics are still occurring around the world, indicating an urgent need of prophylactic vaccines and antivirals. In recent years, a great deal has been learned about the mechanisms of dengue virus genome amplification. However, little is known about the process by which the capsid protein recruits the viral genome during encapsidation. Here, we found that the mature capsid protein in the cytoplasm of dengue virus infected cells accumulates on the surface of ER-derived organelles named lipid droplets. Mutagenesis analysis using infectious dengue virus clones has identified specific hydrophobic amino acids, located in the center of the capsid protein, as key elements for lipid droplet association. Substitutions of amino acid L50 or L54 in the capsid protein disrupted lipid droplet targeting and impaired viral particle formation. We also report that dengue virus infection increases the number of lipid droplets per cell, suggesting a link between lipid droplet metabolism and viral replication. In this regard, we found that pharmacological manipulation of the amount of lipid droplets in the cell can be a means to control dengue virus replication. In addition, we developed a novel genetic system to dissociate cis-acting RNA replication elements from the capsid coding sequence. Using this system, we found that mislocalization of a mutated capsid protein decreased viral RNA amplification. We propose that lipid droplets play multiple roles during the viral life cycle; they could sequester the viral capsid protein early during infection and provide a scaffold for genome encapsidation.

• Dengue infection triggers functional inflammasome assembly in platelets.• Platelets may contribute to increased vascular permeability in dengue virus infection by synthesis and release of IL-1b.Dengue is the most frequent hemorrhagic viral disease and re-emergent infection in the world. Although thrombocytopenia is characteristically observed in mild and severe forms of dengue, the role of platelet activation in dengue pathogenesis has not been fully elucidated. We hypothesize that platelets have major roles in inflammatory amplification and increased vascular permeability during severe forms of dengue. Here we investigate interleukin (IL)-1b synthesis, processing, and secretion in platelets during dengue virus (DV) infection and potential contribution of these events to endothelial permeability during infection. We observed increased expression of IL-1b in platelets and plateletderived microparticles from patients with dengue or after platelet exposure to DV in vitro. We demonstrated that DV infection leads to assembly of nucleotide-binding domain leucine rich repeat containing protein (NLRP3) inflammasomes, activation of caspase-1, and caspase-1-dependent IL-1b secretion. Our findings also indicate that plateletderived IL-1b is chiefly released in microparticles through mechanisms dependent on mitochondrial reactive oxygen speciestriggered NLRP3 inflammasomes. Inflammasome activation and platelet shedding of IL-1b-rich microparticles correlated with signs of increased vascular permeability. Moreover, microparticles from DV-stimulated platelets induced enhanced permeability in vitro in an IL-1-dependent manner. Our findings provide new evidence that platelets contribute to increased vascular permeability in DV infection by inflammasome-dependent release of IL-1b. (Blood. 2013;122(20):3405-3414)

Background Dengue is the most prevalent human arbovirus disease in the world. Dengue infection may cause a range of clinical manifestation from self-limiting febrile illness through life-threatening syndrome accompanied by bleeding and shock. Thrombocytopenia is frequently observed in mild and severe disease, however the mechanisms involved in DENV-induced platelet activation and thrombocytopenia are incompletely understood. Patients/ Methods Freshly-isolated platelets from patients with dengue were evaluated for markers of activation, mitochondrial alterations and activation of cell death pathways. In parallel, we determined whether DENV induced direct activation and apoptosis of platelets that were obtained from healthy subjects. Results We found that platelets from DENV-infected patients display increased activation when compared to control subjects. Moreover, platelets from DENV-infected patients exhibited classic signs of the intrinsic pathway of apoptosis that include increased surface phosphatidylserine exposure, mitochondrial depolarization and activation of caspase-9 and 3. Indeed, thrombocytopenia was shown to strongly associate with enhanced platelet activation and cell death in DENV-infected patients. Platelet activation, mitochondrial dysfunction and caspase-dependent phosphatidylserine exposure on platelets were also observed when platelets from healthy subjects were directly exposed to DENV in vitro. DENV-induced platelet activation was shown to occur through mechanisms largely dependent of DC-SIGN. Conclusions Together our results demonstrate that platelets from patients with dengue present signs of activation, mitochondrial dysfunction, and activation of apoptosis caspase cascade, which may contribute to the genesis of thrombocytopenia in patients with dengue. Our results also suggest the involvement of DC-SIGN as a critical receptor in DENV-dependent platelet activation.

One-sentence summary: This review addresses the structural rearrangements of dengue virus proteins and their functions during virus entry into the host cells, exploring (a) the cellular elements involved in virus binding to mammalian and mosquito cells, (b) the internalization routes that ultimately lead to virus entry into the cell and (c) the mechanisms by which viral genome gain access to the cytoplasm, including original insights from our recent work that supports the hypothesis that the capsid protein has a role in this process. Editor: Urs Greber ABSTRACTDengue is the most prevalent arthropod-borne viral disease, caused by dengue virus, a member of the Flaviviridae family. Its worldwide incidence is now a major health problem, with 2.5 billion people living in risk areas. In this review, we integrate the structural rearrangements of each viral protein and their functions in all the steps of virus entry into the host cells. We describe in detail the putative receptors and attachment factors in mammalian and mosquito cells, and the recognition of viral immunocomplexes via Fcγ receptor in immune cells. We also discuss that virus internalization might occur through distinct entry pathways, including clathrin-mediated or non-classical clathrin-independent endocytosis, depending on the host cell and virus serotype or strain. The implications of viral maturation in virus entry are also explored. Finally, we discuss the mechanisms of viral genome access to the cytoplasm. This includes the role of low pH-induced conformational changes in the envelope protein that mediate membrane fusion, and original insights raised by our recent work that supports the hypothesis that capsid protein would also be an active player in this process, acting on viral genome translocation into the cytoplasm.

Dengue virus (DENV) affects millions of people, causing more than 20,000 deaths annually. No effective treatment for the disease caused by DENV infection is currently available, partially due to the lack of knowledge on the basic aspects of the viral life cycle, including the molecular basis of the interaction between viral components and cellular compartments. Here, we characterized the properties of the interaction between the DENV capsid (C) protein and hepatic lipid droplets (LDs), which was recently shown to be essential for the virus replication cycle. Zeta potential analysis revealed a negative surface charge of LDs, with an average surface charge of ؊19 mV. The titration of LDs with C protein led to an increase of the surface charge, which reached a plateau at ؉13.7 mV, suggesting that the viral protein-LD interaction exposes the protein cationic surface to the aqueous environment. Atomic force microscopy (AFM)-based force spectroscopy measurements were performed by using C proteinfunctionalized AFM tips. The C protein-LD interaction was found to be strong, with a single (un)binding force of 33.6 pN. This binding was dependent on high intracellular concentrations of potassium ions but not sodium. The inhibition of Na ؉ /K ؉ -ATPase in DENV-infected cells resulted in the dissociation of C protein from LDs and a 50-fold inhibition of infectious virus production but not of RNA replication, indicating a biological relevance for the potassium-dependent interaction. Limited proteolysis of the LD surface impaired the C protein-LD interaction, and force measurements in the presence of specific antibodies indicated that perilipin 3 (TIP47) is the major DENV C protein ligand on the surface of LDs. Dengue virus (DENV) causes the most important arthropodborne human viral disease, with 2.5 billion people at risk, 100 million infections, and more than 20,000 deaths annually, primarily in tropical developing countries (20). Four genetically distinct serotypes (DENV1 to DENV4) have been identified, which are transmitted among humans through the bite of an infected mosquito of the genus Aedes. DENV belongs to the family Flaviviridae, together with other important human pathogens, such as yellow fever virus (YFV), West Nile virus (WNV), and hepatitis C virus (HCV). The clinical manifestations of DENV infection range from a mild illness to a severe and potentially life-threatening disease for which no treatment is available so far, due at least in part to the limited understanding of the molecular mechanisms that underlie the interaction between DENV and its host cells.The DENV genome is a single-stranded positive-sense RNA molecule of approximately 11 kb that is translated from a single open reading frame, generating a polyprotein associated with the endoplasmic reticulum (ER) membrane (34). The polyprotein is cleaved co-and posttranslationally by cellular and viral proteases into three structural proteins (capsid [C], premembrane [prM], and envelope [E]) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B,...