ABSTRACT
DC-SIGN is a member of the C-type lectin family. Mainly expressed by myeloid DCs, it is involved in the capture and internalization of pathogens, including human CMV. Several transcripts have been identified, some of which code for putative soluble proteins. However, little is known about the regulation and the functional properties of such putative sDC-SIGN variants. To better understand how sDC-SIGN could be involved in CMV infection, we set out to characterize biochemical and functional properties of rDC-SIGN as well as naturally occurring sDC-SIGN. We first developed a specific, quantitative ELISA and then used it to detect the presence sDC-SIGN in in vitro-generated DC culture supernatants as cell-free secreted tetramers. Next, in correlation with their inflammatory status, we demonstrated the presence of sDC-SIGN in several human body fluids, including serum, joint fluids, and BALs. CMV infection of human tissues was also shown to promote sDC-SIGN release. Based on the analysis of the cytokine/chemokine content of sDC-SIGN culture supernatants, we identified IFN-γ and CXCL8/IL-8 as inducers of sDC-SIGN production by MoDC. Finally, we demonstrated that sDC-SIGN was able to interact with CMV gB under native conditions, leading to a significant increase in MoDC CMV infection. Overall, our results confirm that sDC-SIGN, like its well-known, counterpart mDC-SIGN, may play a pivotal role in CMV-mediated pathogenesis.
Subject(s)
Cell Adhesion Molecules/metabolism , Cytomegalovirus Infections/immunology , Dendritic Cells/metabolism , Dendritic Cells/virology , Inflammation/immunology , Myeloid Cells/cytology , Signal Transduction , Body Fluids/drug effects , Body Fluids/metabolism , Cloning, Molecular , Cytomegalovirus/drug effects , Cytomegalovirus/physiology , Cytomegalovirus Infections/virology , Dendritic Cells/drug effects , Dendritic Cells/enzymology , Enzyme-Linked Immunosorbent Assay , Exosomes/drug effects , Exosomes/metabolism , Female , HEK293 Cells , Humans , Interferon-gamma/pharmacology , Interleukin-8/pharmacology , Lectins, C-Type , Matrix Metalloproteinases/metabolism , Mucous Membrane/drug effects , Mucous Membrane/metabolism , Mucous Membrane/pathology , Mucous Membrane/virology , Protein Isoforms/metabolism , Protein Multimerization/drug effects , Protein Processing, Post-Translational/drug effects , Receptors, Cell Surface , Reproducibility of Results , Signal Transduction/drug effects , Solubility/drug effects , Titrimetry , Up-Regulation/drug effectsABSTRACT
Syncytin is a fusogenic protein involved in the formation of the placental syncytiotrophoblast layer. This protein is encoded by the envelope gene of the ERVWE1 proviral locus belonging to the human endogenous retrovirus W (HERV-W) family. The HERV-W infectious ancestor entered the primate lineage 25 to 40 million years ago. Although the syncytin fusion property has been clearly demonstrated, little is known about this cellular protein maturation process with respect to classical infectious retrovirus envelope proteins. Here we show that the cellular syncytin protein is synthesized as a glycosylated gPr73 precursor cleaved into two mature proteins, a gp50 surface subunit (SU) and a gp24 transmembrane subunit (TM). These SU and TM subunits are found associated as homotrimers. The intracytoplasmic tail is critical to the fusogenic phenotype, although its cleavage requirements seem to have diverged from those of classical retroviral maturation.