Abstract
All positive strand (+RNA) viruses of eukaryotes replicate their genomes in association with membranes. The mechanisms of membrane remodeling in infected cells represent attractive targets for designing future therapeutics, but our understanding of this process is very limited. Elements of autophagy and/or the secretory pathway were proposed to be hijacked for building of picornavirus replication organelles. However, even closely related viruses differ significantly in their requirements for components of these pathways. We demonstrate here that infection with diverse picornaviruses rapidly activates import of long chain fatty acids. While in non-infected cells the imported fatty acids are channeled to lipid droplets, in infected cells the synthesis of neutral lipids is shut down and the fatty acids are utilized in highly up-regulated phosphatidylcholine synthesis. Thus the replication organelles are likely built from de novo synthesized membrane material, rather than from the remodeled pre-existing membranes. We show that activation of fatty acid import is linked to the up-regulation of cellular long chain acyl-CoA synthetase activity and identify the long chain acyl-CoA syntheatse3 (Acsl3) as a novel host factor required for polio replication. Poliovirus protein 2A is required to trigger the activation of import of fatty acids independent of its protease activity. Shift in fatty acid import preferences by infected cells results in synthesis of phosphatidylcholines different from those in uninfected cells, arguing that the viral replication organelles possess unique properties compared to the pre-existing membranes. Our data show how poliovirus can change the overall cellular membrane homeostasis by targeting one critical process. They explain earlier observations of increased phospholipid synthesis in infected cells and suggest a simple model of the structural development of the membranous scaffold of replication complexes of picorna-like viruses, that may be relevant for other (+)RNA viruses as well.
Highlights
In this study we show that PV infection results in fast upregulation of long chain fatty acids (FAs) uptake due to activation of cellular long chain acyl-Coenzyme A (CoA) synthetase activity, and we identify long chain acyl-CoA synthetase 3 (Acsl3) as a novel host factor required for polio replication
We found that in mock-infected cells the newly-imported FAs are mostly channeled to lipid droplets, while in infected cells they are immediately utilized for highly upregulated PC synthesis
Poliovirus infection increases cellular long chain FA import and prevents their targeting to lipid droplets
Summary
(+)RNA viruses of eukaryotes are a very successful group of pathogens infecting organisms from unicellular algae to humans. In spite of adaptation to diverse hosts the basic processes of genome expression and replication are highly conserved among these viruses. One such feature shared among all (+)RNA viruses is the association of RNA replication machinery with cellular membranes. It has been proposed that assembly of replication complexes on membranes may facilitate infection in several ways: increase local concentration of viral proteins; provide structural scaffold for assembly of replication machinery; hide viral dsRNA replication intermediates from the cellular innate immunity mechanisms (reviewed in [1,2]). Other members of the Picornaviridae family share the same basic genome organization and expression strategy with minor modifications [3]. Even closely related viruses vary greatly in their sensitivity to the inhibitors of
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