Brent A. Hackett^a, Ari Yasunaga^a, Debasis Panda^a, Michael A. Tartell^a, Kaycie C. Hopkins^a, Scott E. Hensley^b, and Sara Cherry^a,¹

·  ^aDepartment of Microbiology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104;

·  ^bVaccine Center, Wistar Institute, Philadelphia, PA 19104

MICROBIOLOGY

Significance

Many viruses, including those of global concern, are dependent on internalization for their entry. We found that ribonuclease kappa (RNASEK) is required for infection of every virus we tested that enters cells through an acid-dependent pathway, including dengue, West Nile, Sindbis, Rift Valley Fever, and influenza viruses. Mechanistically, we found that RNASEK has no effect on virus binding to cells but, rather, is required for their uptake. RNASEK was required for diverse viruses that are dependent on clathrin-mediated endocytosis for entry, but we found that RNASEK was dispensable for general endocytic uptake. Therefore, RNASEK appears to play a unique role in viral uptake and may be a therapeutically viable target to inhibit major human viral pathogens.

Abstract

Viruses must gain entry into cells to establish infection. In general, viruses enter either at the plasma membrane or from intracellular endosomal compartments. Viruses that use endosomal pathways are dependent on the cellular factors that control this process; however, these genes have proven to be essential for endogenous cargo uptake, and thus are of limited value for therapeutic intervention. The identification of genes that are selectively required for viral uptake would make appealing drug targets, as their inhibition would block an early step in the life cycle of diverse viruses. At this time, we lack pan-antiviral therapeutics, in part because of our lack of knowledge of such cellular factors. RNAi screening has begun to reveal previously unknown genes that play roles in viral infection. We identified dRNASEK in two genome-wide RNAi screens performed in Drosophila cells against West Nile and Rift Valley Fever viruses. Here we found that ribonuclease kappa (RNASEK) is essential for the infection of human cells by divergent and unrelated positive- and negative-strand-enveloped viruses from the Flaviviridae, Togaviridae, Bunyaviridae, and Orthomyxoviridae families that all enter cells from endosomal compartments. In contrast, RNASEK was dispensable for viruses, including parainfluenza virus 5 and Coxsackie B virus, that enter at the plasma membrane. RNASEK is dispensable for attachment but is required for uptake of these acid-dependent viruses. Furthermore, this requirement appears specific, as general endocytic uptake of transferrin is unaffected in RNASEK-depleted cells. Therefore, RNASEK is a potential host cell Achilles’ heel for viral infection.

See: http://www.pnas.org/content/112/25/7797.abstract

PNAS June 23, 2015 vol. 112 no. 25 7797-7802

Fig. S1.

RNASEK promotes flavivirus infection in Drosophila cells. (A) Representative images of Drosophila DL1 cells treated with dsRNA against dRNASEK and incubated for 3 d before infection by WNV (KUN) (MOI 10) or DENV2 (S2) (MOI 5) or DENV2 (NGC) (MOI 5) for 72 h. (B and C) Cells were processed for automated microscopy and automated image analysis with (B) fold change in percentage infection shown or (C) fold change in cell number shown as mean ± SEM; n = 3; *P < 0.05.