Dengue virus requires the presence of an unidentified cellular receptor on the surface of the host cell. By using a recently published affinity chromatography approach, an 84-kDa molecule, identified as heat shock protein 90 (HSP90) by matrix-assisted laser desorption ionization-time of flight mass spectrometry, was isolated from neuroblastoma and U937 cells. Based on the ability of HSP90 (84 kDa) to interact with HSP70 (74 kDa) on the surface of monocytes during lipopolysaccharide (LPS) signaling and evidence that LPS inhibits dengue virus infection, the presence of HSP70 was demonstrated in affinity chromatography eluates and by pull-down experiments. Infection inhibition assays support the conclusion that HSP90 and HSP70 participate in dengue virus entry as a receptor complex in human cell lines as well as in monocytes/macrophages. Additionally, our results indicate that both HSPs are associated with membrane microdomains (lipid rafts) in response to dengue virus infection. Moreover, methyl-␤-cyclodextrin, a raft-disrupting drug, inhibits dengue virus infection, supporting the idea that cholesterol-rich membrane fractions are important in dengue virus entry.Dengue (DEN) virus, the most important arthropod-borne human pathogen, represents a serious public health threat. DEN virus is transmitted to humans by the bite of the domestic mosquito, Aedes aegypti, and circulates in nature as four distinct serological types (DEN-1 to -4). DEN virus has been recognized in over 100 countries, and 2.5 billion people live in areas where DEN virus is endemic (16). The clinical manifestations of DEN virus infection range in severity from a simple self-limited febrile illness known as dengue fever to a hemorrhagic fever (DHF) and potentially fatal hemorrhagic shock syndrome. Each year, more than 50 million cases of dengue fever and several hundred thousand cases of DHF occur. During the past 8 years the incidence of dengue has grown in areas of endemicity, particularly in the American region. A specific treatment or vaccine is not yet available.DEN virus is an enveloped virus that belongs to the Flaviviridae family. Mature virions are icosahedral, 50 nm in diameter, and contain a single-strand and positive-polarity RNA as genome of about 10.7 kb (21). The DEN virus genome encodes three structural proteins (envelope glycoprotein, E; membrane, M; and capsid, C) and seven nonstructural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, and NS5). E protein is the major structural protein exposed on the surface of the particle, and it arrays in homodimers, parallel to viral surface. Recently, the structure of DEN virus E protein has been determined by X-ray crystallography (24). Each monomer consists of three domains: the structurally central amino-terminal domain I that organizes the structure; the dimerization domain II that contains the hydrophobic fusion peptide essential for virus-cell fusion; and finally the carboxy-terminal immunoglobulin (Ig)-like domain III, which has been proposed to function as the binding site for cellular re...

Several cellular molecules and components, specifically, cholesterol and lipid rafts have been described as necessary elements for dengue virus entry and signaling in several human cells. Thus, changes in lipid rafts formation and cholesterol levels were evaluated. Here we report that the amount of total cholesterol and lipid rafts formation increase early after infection of Huh-7 cells. This augment correlates with an increase in the amount of low density lipoprotein receptor (LDLr) on the surface of infected cells and also with a lower phosphorylation level of the 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR). None of the changes were observed in Huh 7 cells infected with VSV used as a control. These results suggest that dengue virus infection increases intracellular cholesterol levels at early times post infection by triggering the modulation of LDL particles uptake and the increase in the enzymatic activity of HMG-CoA reductase.

Dietary supplementation with the n-3 polyunsaturated fatty acids (n-3 PUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) to rats preconditions the liver against ischemia-reperfusion (IR) injury, with reduction of the enhanced nuclear factor-κB (NF-κB) functionality occurring in the early phase of IR injury, and recovery of IR-induced pro-inflammatory cytokine response. The aim of the present study was to test the hypothesis that liver preconditioning by n-3 PUFA is exerted through peroxisone proliferator-activated receptor α (PPAR-α) activation and interference with NF-κB activation. For this purpose we evaluated the formation of PPAR-α/NF-κBp65 complexes in relation to changes in PPAR-α activation, IκB-α phosphorylation and serum levels and expression of interleukin (IL)-1β and tumor necrosis factor (TNF)-α in a model of hepatic IR-injury (1 h of ischemia and 20 h of reperfusion) or sham laparotomy (controls) in male Sprague Dawley rats. Animals were previously supplemented for 7 days with encapsulated fish oil (General Nutrition Corp., Pittsburg, PA) or isovolumetric amounts of saline (controls). Normalization of IR-altered parameters of liver injury (serum transaminases and liver morphology) was achieved by dietary n-3 PUFA supplementation. EPA and DHA suppression of the early IR-induced NF-κB activation was paralleled by generation of PPAR-α/NF-κBp65 complexes, in concomitance with normalization of the IR-induced IκB-α phosphorylation. PPAR-α activation by n-3 PUFA was evidenced by enhancement in the expression of the PPAR-α-regulated Acyl-CoA oxidase (Acox) and Carnitine-Palmitoyl-CoA transferase I (CPT-I) genes. Consistent with these findings, normalization of IR-induced expression and serum levels of NF-κB-controlled cytokines IL-lβ and TNF-α was observed at 20 h of reperfusion. Taken together, these findings point to an antagonistic effect of PPAR-α on NF-κB-controlled transcription of pro-inflammatory mediators. This effect is associated with the formation of PPAR-α/NF-κBp65 complexes and enhanced cytosolic IκB-α stability, as major preconditioning mechanisms induced by n-3 PUFA supplementation against IR liver injury.

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Infection with a broad diversity of viruses often activates host cell signaling pathways including the mitogen-activated protein kinase pathway. The present study established that dengue virus infection of human macrophages activates Jun NH(2)-terminal kinase (JNK) and the p38 MAPKs pathways. The activation was observed at early times after infection and occurs when either infectious or UV-inactivated dengue virus was used. The role of these activated kinases in dengue virus infection was evaluated using specific inhibitors. Inhibition of JNK and p38 kinases did result in a significant reduction in viral protein synthesis and in viral yield. Additionally, lipid rafts disruption induced a strong inhibition of JNK activation. These results suggest that, at early stages after dengue virus infection, MAPKs are activated and that activation of JNK and p38 is required for dengue virus infection.

The 39 untranslated region (39UTR) of the dengue virus (DENV) genome contain several sequences required for translation, replication and cyclization processes. This region also binds cellular proteins such as La, polypyrimidine tract-binding protein (PTB), Y box-binding protein 1, poly(A)-binding protein and the translation initiation factor eEF-1a. PTB is a cellular protein that interacts with the regulatory sequences of positive-strand RNA viruses such as several picornaviruses and hepatitis C virus. In the present report, it was demonstrated that PTB translocates from the nucleus to the cytoplasm during DENV infection. At 48 h post-infection, PTB, as well as the DENV proteins NS1 and NS3, were found to co-localize with the endoplasmic reticulum marker calnexin. Silencing of PTB expression inhibited virus translation and replication, whilst overexpression of PTB augmented these processes. Thus, these results provide evidence that, during infection, PTB moves from the nucleus to the cytoplasm and plays an important role in the DENV replicative cycle. INTRODUCTIONDengue virus (DENV), a member of the family Flaviviridae, is the causative agent of dengue fever, dengue haemorrhagic fever and dengue shock syndrome. The single-stranded, positive-polarity RNA genome of approximately 11 kb contains a type I cap at the 59 end and lacks a poly(A) tail at the 39 end. The single open reading frame (ORF) encodes a polyprotein that generates three structural proteins -envelope (E), membrane and capsid (C) -and seven non-structural proteins -NS1, NS2A, NS2B, NS3, NS4A, NS4B and NS5. Flanking the ORF, the viral RNA contains two untranslated regions (UTRs) involved in various functions such as initiation and regulation of virus translation, replication and assembly (Lindenbach & Rice, 2001;Proutski et al., 1999). The 39UTR of DENV and other mosquito-borne flaviviruses contains a conserved stemloop structure within the last~96 nt (Brinton & Dispoto, 1988;Brinton et al., 1986;Grange et al., 1985;Mohan & Padmanabhan, 1991). Additionally, there are two pairs of conserved sequences (59CS1, 39CS1, 59UAR and 39UAR) that together induce DENV cyclization (Alvarez et al., 2005a, b; Hahn et al., 1987). These motifs are essential for negativestrand RNA synthesis of DENV (Ackermann & Padmanabhan, 2001; Alvarez et al., 2005a, b;Villordo & Gamarnik, 2009;You & Padmanabhan, 1999) and other flaviviruses (Bredenbeek et al., 2003;Corver et al., 2003;Jones et al., 2005;Khromykh et al., 2001;Lo et al., 2003;Nomaguchi et al., 2004). On the other hand, sequences present within a large stem-loop structure located at the 59 end as well as a conserved oligo(U) track function as the promoter for viral polymerase activity (Lodeiro et al., 2009). Moreover, an RNA secondary structure present in the coding region of DENV type 2 (DENV-2) directs translation, start-codon selection and replication of the viral genome (Clyde & Harris, 2006;Clyde et al., 2008). Although it has been shown that the cyclization process does not require the presence of cellular or v...

The untranslated regions (UTRs) of the positive and negative strand RNAs of several viruses are major binding sites for cellular and viral proteins. Human La autoantigen is one of the cellular proteins that interacts with various positive strand RNA viral genomes including that of dengue virus (DEN) within the 5'- and 3'-UTRs of positive (+) and the 3'-UTR of negative strand (-) RNA, and with the nonstructural proteins NS3 and NS5, that form DEN replicase complex. Since DEN replicates in human and mosquito cells, some functional interactions have to be conserved in both hosts. In the present report, we demonstrate that mosquito La protein interacts with the 3'-UTRs of (+) and (-) polarity viral RNAs. The localization of La protein, examined by confocal microscopy, indicates that La protein is redistributed in DEN-infected cells. Furthermore, the presence of La protein in an in vitro replication system inhibited RNA synthesis in a dose-dependent manner, suggesting that La protein plays an important role in dengue virus replicative cycle.