Characterizing the Role of the Cellular Protein Schlafen 11 in Flavivirus Replication
Schlafen 11 (Slfn11) is a ubiquitously expressed interferon stimulating gene (ISG) that controls synthesis of proteins by regulating tRNA abundance. Through this mechanism Slfn11 has previously been shown to impair human immunodeficiency virus 1 (HIV-1) infection and the expression of codon-biased open reading frames. Because replication of positive-sense single- stranded RNA [(+)ssRNA viruses] requires the immediate translation of the incoming viral genome whereas negative sense, single stranded [(-)ssRNA] viruses carry at infection an RNA replicase that makes multiple translation competent copies of the incoming viral genome, we reasoned that (+)ssRNA viruses will be more sensitive to the effect of Slfn11 on protein synthesis than (-)ssRNA viruses. To evaluate this hypothesis, we tested the effects of Slfn11 on the replication of a panel of ssRNA viruses in the human glioblastoma cell line A172, which naturally expresses Slfn11. Depletion of Slfn11 in this cell line significantly increased the replication of (+)ssRNA viruses from the Flavivirus family, including West Nile (WNV), dengue (DENV), and Zika virus (ZIKV) but had no significant effect on the replication of the (-)ssRNA viruses vesicular stomatitis (VSV, Rhabdoviridae family) and Rift Valley fever (RVFV, Phenuiviridae family). Mutagenesis analysis indicated that the N-terminus of Slfn11 was necessary and sufficient to restrict WNV replication. To test the mechanism of action of Slfn11, we evaluated the effect of WNV infection on the tRNA repertoire of cells expressing or not this protein using tRNA PCR array. WNV infection down-regulated a subset of host tRNAs and this modification was opposed by Slfn11. Viral protein expression analysis suggests that the changes induced by WNV on the tRNA pool led to a decrease in viral protein translation efficiency which was accompanied by production of higher viral titers. In light of these data, we propose that WNV-induced tRNA changes enhanced co-translational protein folding. Intriguingly, overexpression of Slfn11 in HEK293T, HeLa, and BHK-21 cells, all of which naturally lack the expression of this protein, did not impair infection by WNV or HIV-1, suggesting that other cellular protein(s) absent in these cells may be required for the antiviral activity of Slfn11. In summary, we have identified Slfn11 as an important restriction factor on the replication of flaviviruses.
Valdez, Federico, "Characterizing the Role of the Cellular Protein Schlafen 11 in Flavivirus Replication" (2018). ETD Collection for University of Texas, El Paso. AAI10930813.