RNase L Antiviral Activity Is Not a Critical Component of the Oas1b-Mediated Flavivirus Resistance Phenotype

Abstract

The mouse genome encodes a family of Oas proteins that synthesize 2′-5′A in response to dsRNA. 2′-5′A activates the endonuclease RNase L to cleave single-stranded viral and cellular RNAs. The inactive, full-length Oas1b protein confers flavivirus-specific disease resistance. Although similar numbers of neurons were infected in resistant and susceptible brains after an intracranial virus infection, viral components amplified only in susceptible brains at later times. A line of resistant RNase L −/− mice was used to evaluate the contribution of RNase L to the resistance phenotype in vivo . Activation of RNase L antiviral activity by flavivirus infection was indicated by increased viral RNA levels in the brains of RNase L −/− mice. Oas1a and Oas1b mRNA levels were higher in infected RNase L −/− mice, indicating that activated RNase L also have a proflaviviral affect. However, the resistance phenotype was equally robust in RNase L −/− and RNase L +/+ mice. In mice, resistance to central nervous system (CNS) disease induced by members of the genus Flavivirus is conferred by an allele of the 2′-5′ oligoadenylate synthetase 1b gene that encodes the inactive full-length protein (Oas1b-FL). The susceptibility allele encodes a C-terminally truncated protein (Oas1b-tr). We show that the efficiency of neuron infection in the brains of resistant and susceptible mice is similar after an intracranial inoculation of two flaviviruses, but amplification of viral proteins and double-stranded RNA (dsRNA) is inhibited in infected neurons in resistant mouse brains at later times. Active OAS proteins detect cytoplasmic dsRNA and synthesize short 2′-5′-linked oligoadenylates (2′-5′A) that interact with the latent endonuclease RNase L, causing it to dimerize and cleave single-stranded RNAs. To evaluate the contribution of RNase L to the resistance phenotype in vivo , we created a line of resistant RNase L −/− mice. Evidence of RNase L activation in infected RNase L +/+ mice was indicated by higher levels of viral RNA in the brains of infected RNase L −/− mice. Activation of type I interferon (IFN) signaling was detected in both resistant and susceptible brains, but Oas1a and Oas1b mRNA levels were lower in RNase L +/+ mice of both types, suggesting that activated RNase L also has a proflaviviral effect. Inhibition of virus replication was robust in resistant RNase L −/− mice, indicating that activated RNase L is not a critical factor in mediating this phenotype. IMPORTANCE The mouse genome encodes a family of Oas proteins that synthesize 2′-5′A in response to dsRNA. 2′-5′A activates the endonuclease RNase L to cleave single-stranded viral and cellular RNAs. The inactive, full-length Oas1b protein confers flavivirus-specific disease resistance. Although similar numbers of neurons were infected in resistant and susceptible brains after an intracranial virus infection, viral components amplified only in susceptible brains at later times. A line of resistant RNase L −/− mice was used to evaluate the contribution of RNase L to the resistance phenotype in vivo . Activation of RNase L antiviral activity by flavivirus infection was indicated by increased viral RNA levels in the brains of RNase L −/− mice. Oas1a and Oas1b mRNA levels were higher in infected RNase L −/− mice, indicating that activated RNase L also have a proflaviviral affect. However, the resistance phenotype was equally robust in RNase L −/− and RNase L +/+ mice.