Abstract
The herpes simplex virus virion host shutoff (vhs) RNase destabilizes cellular and viral mRNAs and blunts host innate antiviral responses. Previous work demonstrated that cells infected with vhs mutants display enhanced activation of the host double-stranded RNA (dsRNA)-activated protein kinase R (PKR), implying that vhs limits dsRNA accumulation in infected cells. Confirming this hypothesis, we show that partially complementary transcripts of the UL23/UL24 and UL30/31 regions of the viral genome increase in abundance when vhs is inactivated, giving rise to greatly increased levels of intracellular dsRNA formed by annealing of the overlapping portions of these RNAs. Thus, vhs limits accumulation of dsRNA at least in part by reducing the levels of complementary viral transcripts. We then asked if vhs also destabilizes dsRNA after its initial formation. Here, we used a reporter system employing two mCherry expression plasmids bearing complementary 3’ UTRs to produce defined dsRNA species in uninfected cells. The dsRNAs are unstable, but are markedly stabilized by co-expressing the HSV dsRNA-binding protein US11. Strikingly, vhs delivered by super-infecting HSV virions accelerates the decay of these pre-formed dsRNAs in both the presence and absence of US11, a novel and unanticipated activity of vhs. Vhs binds the host RNA helicase eIF4A, and we find that vhs-induced dsRNA decay is attenuated by the eIF4A inhibitor hippuristanol, providing evidence that eIF4A participates in the process. Our results show that a herpesvirus host shutoff RNase destabilizes dsRNA in addition to targeting partially complementary viral mRNAs, raising the possibility that the mRNA destabilizing proteins of other viral pathogens dampen the host response to dsRNA through similar mechanisms.
Highlights
Many if not all viruses produce double-stranded RNA as an integral part of their life cycles: RNA viruses must generate complementary RNA species in order to replicate their genome, while DNA viruses produce complementary transcripts from overlapping diverging and converging transcription units
Host organisms deploy a variety of double-stranded RNA (dsRNA) receptors to trigger innate antiviral defenses
HeLa cells and telomerase-immortalized human foreskin fibroblast (HFF) cells were infected with wild-type Herpes simplex virus (HSV)-1 strain KOS37 and KOS37-derived mutants that lack functional vhs (Vhs-), US11 (US11-), or both proteins (Vhs- US11-)
Summary
Many if not all viruses produce double-stranded RNA (dsRNA) as an integral part of their life cycles: RNA viruses must generate complementary RNA species in order to replicate their genome, while DNA viruses produce complementary transcripts from overlapping diverging and converging transcription units. Host cells deploy a variety of pattern recognition (PRRs) receptors to detect dsRNA and trigger innate antiviral responses, including the type I interferon system [1]. Viruses in turn produce an array of antagonists to dampen the accumulation or recognition of dsRNA and/or interfere with downstream signaling events [2]. The host dsRNA-activated protein kinase R (PKR) is a key element of host RNA-based innate antiviral defenses [3, 4]. Following activation by binding to dsRNA or other activating ligands, PKR phosphorylates translation initiation factor eIF2α on serine 51, leading to a potent global blockade of translational initiation, severely impairing virus replication. Every mammalian virus encodes one or more PKR antagonists, which are required for efficient virus replication in cultured cells and virulence in the intact animal host [3]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have