Abstract
The identification of host cell factors for virus entry is useful for the molecular explanation of viral tropisms and often leads to a more profound understanding of virus-induced diseases. Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease caused by SFTS virus. No countermeasures against the disease exist. In this report, we show an efficient method using virus-like particles for the functional screening of a cellular cDNA library to identify SFTS virus entry factors. Two variants encoding dendritic cell-specific ICAM-3 grabbing non-integrin related (DC-SIGNR), a calcium-dependent lectin known to enhance SFTS virus infection, were successfully identified from a human liver cDNA library. We will discuss applications for yet unidentified factor(s) for SFTS virus entry and for entry factor(s) for other viruses related to SFTS virus.
Highlights
The identification of host cell factors for virus entry is useful for the molecular explanation of viral tropisms and often leads to a more profound understanding of virus-induced diseases
We focused on the established reverse genetics of the Severe fever with thrombocytopenia syndrome (SFTS) virus for viral genome manipulation[37,38] and on a characteristic of SFTS virus that the virus shows no or weak cytotoxicity in infected cells[15,34] and investigated whether SFTS virus-based vectors, like retroviral/lentiviral www.nature.com/scientificreports vectors, could be useful for identifying SFTS virus entry factors
The reporter expression by infectious VLP (iVLP) did not continue for more than one week, we screened a liver cDNA library with iVLPs and succeeded in identifying a C-type lectin, DC-SIGNR, which has been reported as an entry-enhancing factor[13,14]
Summary
The identification of host cell factors for virus entry is useful for the molecular explanation of viral tropisms and often leads to a more profound understanding of virus-induced diseases. Calcium-dependent (C-type) lectins have been shown to enhance SFTS virus infection when expressed in cells that otherwise show little susceptibility[13,14]; this cannot fully explain the viral tropisms because most non-lymphoid cell lines do not generally express them. In 1st generation panning, cellular cDNA libraries are stably expressed in non-adherent cell lines by using a retroviral vector, which integrates genes into cellular genomes with no or low cytotoxicity and do not inhibit cell growth, and screened based on colony formation of target cells on viral particle-coated dishes. In 2nd generation panning, same as in 1st generation panning, cellular cDNA libraries are stably expressed in non-adherent cell lines by using a retroviral vector, but two additional non- or low-cytotoxic retroviral/lentiviral vectors which bear intended viral envelope proteins and whose genome encode either a membrane spanning protein or a fluorescence protein as a reporter are used for screening. We have experienced cases in which some viruses (e.g., West Nile virus) did not meet the prerequisites for either method and for which virus entry factors could not be identified by our methods (data not shown)
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