IFN-β-inducing, unusual viral RNA species produced by paramyxovirus infection accumulated into distinct cytoplasmic structures in an RNA-type-dependent manner

Asuka Yoshida, Ryoko Kawabata, Tomoyuki Honda, Keizo Tomonaga, Takemasa Sakaguchi, Takashi Irie

The interferon (IFN) system is one of the most important defensive responses of mammals against viruses, and is rapidly evoked when the pathogen-associated molecular patterns (PAMPs) of viruses are sensed. Non-self, virus-derived RNA species have been identified as the PAMPs of RNA viruses. In the present study, we compared different types of IFN-β-inducing and -non-inducing viruses in the context of Sendai virus infection. We found that some types of unusual viral RNA species were produced by infections with IFN-β-inducing viruses and accumulated into distinct cytoplasmic structures in an RNA-type-dependent manner. One of these structures was similar to the so-called antiviral stress granules (avSGs) formed by an infection with IFN-inducing viruses whose C proteins were knocked-out or mutated. Non-encapsidated, unusual viral RNA harboring the 5'-terminal region of the viral genome as well as RIG-I and typical SG markers accumulated in these granules. Another was a non-SG-like inclusion formed by an infection with the Cantell strain; a copyback-type DI genome, but not an authentic viral genome, specifically accumulated in the inclusion, whereas RIG-I and SG markers did not. The induction of IFN-β was closely associated with the production of these unusual RNAs as well as the formation of the cytoplasmic structures.