Cross-species comparative analysis of Dicer proteins during Sindbis virus infection.

Erika Girardi,Sébastien Pfeffer,Bill Claydon,Jean-Luc Imler,Carine Meignin,Béatrice Chane-Woon-Ming,Mathieu Lefèvre,Simona Paro

doi:10.1038/srep10693

Abstract

In plants and invertebrates RNA silencing is a major defense mechanism against virus infections. The first event in RNA silencing is dicing of long double stranded RNAs into small interfering RNAs (siRNAs). The Dicer proteins involved in this process are phylogenetically conserved and have the same domain organization. Accordingly, the production of viral derived siRNAs has also been observed in the mouse, but only in restricted cell types. To gain insight on this restriction, we compare the dicing activity of human Dicer and fly Dicer-2 in the context of Sindbis virus (SINV) infection. Expression of human Dicer in flies inefficiently rescues the production of viral siRNAs but confers some protection against SINV. Conversely, expression of Dicer-2 in human cells allows the production of viral 21 nt small RNAs. However, this does not confer resistance to viral infection, but on the contrary results in stronger accumulation of viral RNA. We further show that Dicer-2 expression in human cells perturbs interferon (IFN) signaling pathways and antagonizes protein kinase R (PKR)-mediated antiviral immunity. Overall, our data suggest that a functional incompatibility between the Dicer and IFN pathways explains the predominance of the IFN response in mammalian somatic cells.

Highlights

In plants and invertebrates RNA silencing is a major defense mechanism against virus infections
The unique Dicer interacts with two double-stranded RNA binding protein (dsRBP) partners, TRBP (TAR RNA binding protein) and PACT, which facilitate the positioning and loading of miRNAs into RISC20. Both proteins have been previously identified as regulators of protein kinase R (PKR), a double-stranded RNA (dsRNA)-activated eIF2α kinase encoded by an IFN-stimulated genes (ISGs) and involved in the shut-down of translation in virus-infected cells[21,22]
We looked whether RFP::hDicer could complement Dicer-2 function, using the white inverted repeat reporter for activity of the small interfering RNAs (siRNAs) pathway[12]

Summary

Introduction

In plants and invertebrates RNA silencing is a major defense mechanism against virus infections. The unique Dicer (hDicer) interacts with two dsRBP partners, TRBP (TAR RNA binding protein) and PACT (protein activator of the interferon-induced protein kinase), which facilitate the positioning and loading of miRNAs into RISC20. Both proteins have been previously identified as regulators of protein kinase R (PKR), a dsRNA-activated eIF2α kinase encoded by an ISG and involved in the shut-down of translation in virus-infected cells[21,22]. It remains unclear whether RNAi is a relevant component of innate antiviral immunity in differentiated mammalian cells[26,27,28] and why the structurally similar proteins Dicer-2 and hDicer have different properties in vivo

Methods

Results

Conclusion