Unit: Flavivirus-Host Molecular Interactions
Director: Philippe DESPRES
The structure has been established in 2002. The research programs are conducted to improve the knowledge of the viral and cellular mechanisms that contribute to the pathogenicity of flaviviruses responsible for emerging flaviviroses dengue (DEN) and West Nile (WN) fever. The analysis of the host cell responses upon flavivirus infection in mosquito vectors and mammalian hosts is of particular importance for the understanding of diseases.
Molecular basis of mosquito-dengue virus interactions (program leader: A. Delécluse)
Relationships between dengue virus and its arthropod vector, Aedes aegypti, are crucial in the maintenance and transmission of the disease. Understanding the mosquito-virus interactions will allow development of innovative control methods to prevent DEN disease transmission. Mosquito populations display variable susceptibility to flavivirus development, termed " vector competence ". Competence reflects the different barriers encountered by the virus from its entry into the mosquito midgut to the release in the saliva. Various factors including specific mosquito receptors and differential viral replication in the mosquito are critical in the competence. We are currently developing both biochemical (surface plasmon resonance) and molecular biology (2-hybrid system in yeast) approaches to identify the cellular factors responsible for vector competence to DEN virus.
DC-SIGN functions as attachment receptor for dengue virus (program leader: P. Desprès)
We have analyzed the interactions between DEN virus and human dendritic cells (DCs) at the level of virus entry. DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN) molecule, a cell surface C-type lectin, binds mosquito-cell-derived DEN viruses and allows viral replication . DC-SIGN acts as DEN virus binding lectin through interaction with the DEN envelope glycoprotein. DEN virus serotypes greatly differ in their capacity to infect DC-SIGN-expressing cells. The differential usage of DC-SIGN by DEN viruses may account for immunopathogenesis of DEN disease. (Collaboration: F. Arenzana).
The genetic determinism of susceptibility to flavivirus infection (program leader: P. Desprès)
WN virus infection in mice has been used as a model system to characterize genes involved in the genetic determinism of susceptibility to flaviviruses. The resistance/sensitivity phenotype of WN virus-infected mice was completely correlated with the occurrence of a point mutation resulting in the truncation of the 2'-5'-oligoadenylate synthetase (Oas) 1b isoform. The interferon-inducible Oas 1b gene is critical on flavivirus pathogenicity through an anti-viral effect restricting viral RNA replication at the cellular level. (Collaboration: J-L. Guénet).
The biological properties of flavivirus NS1 glycoprotein (program leader : M. Flamand)
Flavivirus NS1 is essential for virus viability. Cell-associated NS1 protein has been shown to participate in virus replication although no proper biological activity has been related to it. We demonstrated that glycoprotein NS1 is also secreted as a unique hexameric species in the culture fluids of dengue virus-infected primate cells. In vivo, we found that NS1 circulates in the blood stream of most patients during the acute phase of dengue virus infection. In mice, hexameric NS1 appears to accumulate the liver. In vitro, extracellular NS1 can be endocytosed by different target cells such as hepatocytes and endothelial cells. In both cell types, the protein resides within lysobisphosphatidic acid-rich structures reminiscent of late endosomes. Questions regarding the mode of entry of the NS1 protein, the signaling pathways that may be triggered during endocytosis and their possible contribution to the physiopathology of disease remain to be addressed. (Collaboration : M. Arborio, J. Gruenberg, I. LeBlanc, S. Kayal)
The ectodomain of the M protein contains a proapoptotic sequence (program leader : P. Desprès)
We demonstrated that intracellular transport of the ectododomain of the small membrane M protein along the compartments of the secretory pathway can trigger apoptosis in host cells of various origins. The death-promoting activity of the M ectodomain reflects the proapoptotic properties of the last 9 carboxy-terminal amino acids referred to as ApoptoM. The sequence ApopoM exerts its cytotoxicity by activating a mitochondrion-dependent apoptotic pathway. (Collaboration: S. Susin).
Vaccination strategy against West Nile virus infection (program leader : P. Desprès)
The Schwarz vaccine strain of Measles virus (MV), a live-attenuated RNA virus, is used as a replicative vector to induce protective immunity against WN disease. We demonstrated the efficacy of Schwarz MV-derived vector expressing the WN E glycoprotein in a mouse model. Immunization induced high titers of specific anti-WN virus neutralizing antibodies and protection against WN virus infection. We propose that the live-attenuated MV expressing the E glycoprotein is an effective medical vaccine against WN disease. (Collaboration: F. Tangy).
Diagnosis of flavivirus infections based on the detection of seric nonstructural NS1 antigen (program leader : M. Flamand)
We have generated a diagnostic tool designed for the detection of ongoing dengue virus infections that is now entering industrial development (in collaboration with Bio-Rad). The innovative approach consists in the capture of nonstructural glycoprotein NS1 in patients' sera during the clinical phase of infection. An antigen-capture ELISA offers many advantages compared to the other currently available methods. Indeed, specific antibodies can be detected by ELISA but not during the early phase of the disease and RT-PCR cannot be routinely used to establish an ongoing flaviviral infection. We are investigating whether NS1 antigen may constitute a reliable marker for other flaviviral infections.
Photo 1. Dengue virus-infected dendritic cell. Immature DC was infected with DEN-1 virus and viral antigens were immunostained with antibodies specific to DEN virus by indirect immunofluorescence.
Keywords: Dengue, host susceptibility, vector competence, viral pathogenicity, viral diagnostic, West Nile fever, Emerging viral diseases, flavivirology