RIG-I is a major cytoplasmic sensor of viral pathogen-associated molecular pattern (PAMP) RNA and induces type I interferon (IFN) production upon viral infection. A double-stranded RNA (dsRNA)-binding protein, PACT, plays an important role in potentiating RIG-I function. We have shown previously that arenaviral nucleoproteins (NPs) suppress type I IFN production via their RNase activity to degrade PAMP RNA. We report here that NPs of arenaviruses block the PACT-induced enhancement of RIG-I function to mediate type I IFN production and that this inhibition is dependent on the RNase function of NPs, which is different from that of a known mechanism of other viral proteins to abolish the interaction between PACT and RIG-I. To understand the biological roles of PACT and RIG-I in authentic arenavirus infection, we analyze growth kinetics of recombinant Pichinde virus (PICV), a prototypical arenavirus, in RIG-I knockout (KO) and PACT KO mouse embryonic fibroblast (MEF) cells. Wild-type (WT) PICV grew at higher titers in both KO MEF lines than in normal MEFs, suggesting the important roles of these cellular proteins in restricting virus replication. PICV carrying the NP RNase catalytically inactive mutation could not grow in normal MEFs but could replicate to some extent in both KO MEF lines. The level of virus growth was inversely correlated with the amount of type I IFNs produced. These results suggest that PACT plays an important role in potentiating RIG-I function to produce type I IFNs in order to restrict arenavirus replication and that viral NP RNase activity is essential for optimal viral replication by suppressing PACT-induced RIG-I activation.
Bibliographical noteFunding Information:
This work was supported in part by NIH NIAID grants R01 AI093580 (to H.L.) and R01 AI131586 (to Y.L. and H.L.) and by a doctoral dissertation fellowship from the University of Minnesota to J.S.
We thank C. Basler (Georgia State University) and G. Amarasinghe (Washington University) for the RIG-I and PACT expression plasmids and G. Sen (Cleveland Clinic) and M. Gale, Jr. (University of Washington), for the RIG-I KO and PACT KO MEF cells, respectively. This work was supported in part by NIH NIAID grants R01 AI093580 (to H.L.) and R01 AI131586 (to Y.L. and H.L.) and by a doctoral dissertation fellowship from the University of Minnesota to J.S.
© 2018 American Society for Microbiology.
- Lassa virus
- RNase activity
- Type I interferon