Identification of host factors for Rift Valley Fever Phlebovirus.

BACKGROUND

Rift Valley fever phlebovirus (RVFV) is a zoonotic pathogen that causes Rift Valley fever (RVF) in livestock and humans. Currently, there is no licensed human vaccine or antiviral drug to control RVF. Although multiple species of animals and humans are vulnerable to RVFV infection, host factors affecting susceptibility are not well understood.

METHODOLOGY

To identify the host factors or genes essential for RVFV replication, we conducted a CRISPR-Cas9 knock-out screen in human A549 cells. We then validated the putative genes using siRNA-mediated knockdowns and CRISPR-Cas9-mediated knockout studies, respectively. The role of a candidate gene in the virus replication cycle was assessed by measuring intracellular viral RNA accumulation, and the virus titers by plaque assay or TCID assay.

FINDINGS

We identified approximately 900 genes with potential involvement in RVFV infection and replication. Further evaluation of the effect of six genes on viral replication using siRNA-mediated knockdowns found that silencing two genes (WDR7 and LRP1) significantly impaired RVFV replication. For further analysis, we focused on the gene since the role of in RVFV replication was previously described in detail. Knock-out A549 cell lines were generated and used to dissect the effect of on RVFV and another bunyavirus, La Crosse encephalitis virus (LACV). We observed significant effects of knock-out cells on both intracellular RVFV RNA levels and viral titers. At the intracellular RNA level, affected RVFV replication at a later phase of its replication cycle (24h) when compared to LACV which was affected an earlier replication phase (12h).

CONCLUSION

In summary, we have identified as an essential host factor for the replication of two relevant bunyaviruses, RVFV and LACV. Future studies will investigate the mechanistic role by which facilitates Phlebovirus replication.