Study the Roles of Enteroviral 3D Protein and the Cellular Protein NEDD4L in the Regulation of IFN-Βeta Production

Infection of enterovirus 71 (EV71) in children may result in severe neurological syndromes, such as encephalitis and meningitis. In recent years, this virus has caused several outbreaks with severe complications and deaths across the Asia-Pacific countries. Therefore, it is crucial to investigate the pathogenesis caused by this virus. Since the regulation of type I IFNs have been correlated to virus replication which is associated to the pathogenicity, to explore the mechanisms of the regulation of type I IFN activation during EV71 infection has been pursuing in our laboratory. It has been identified that two cytoplasmic nucleic acid sensors, retinoic acid-inducible gene I (RIG-I) and melanoma- differentiation-associated gene 5 (MDA5), recognize viral RNAs and trigger the signal for type I IFN expression. Our previous research showed that MDA5, but not RIG-I, plays an important role in EV71 RNA-mediated IRF3 activation and IFN- production. Although it is thought that long double-stranded RNAs or high-ordered RNA structures which are generated during RNA virus replication could be the pathogen-associated patterns for MDA5 recognition, the features of the RNA sequences directly detected by MDA5 remain inconclusive. Because our preliminary result demonstrated that the 5’ UTR of EV71 RNA is sufficient to activate IFN- transcription, we intend to further determine the role of MDA5 in sensing the 5’ UTR for activating IFN- expression in this proposal. Furthermore, several researches have reported that enteroviruses have various mechanisms to counter host innate immunity. Our previous study also demonstrated that the expression of IFN- is reduced upon EV71 infection via the MDA5 cleavage induced by caspase activation. To further investigate how EV71 suppresses IFN- production in the infected cells, we have examined the roles of EV71 proteins and host proteins in the regulation. Our preliminary results showed that EV71 3D protein negatively regulates IFN- promoter activity. Because we have also found that EV71 3D protein binds to a key splicing factor, Prp8, and interferes with host RNA splicing, we intend to study the correlation between the splicing interference and the inhibition of IFN-β expression. Moreover, in addition to the proteins encoded by EV71, EV71 may also regulate the expression of host proteins to block the signaling pathways of IFN- activation. Our previous experiments showed that the E3 ubiquitin ligase NEDD4L, which is induced upon EV71 infection, inhibits the activation of IFN-β promoter. Therefore, the mechanism of NEDD4L in the inhibition of type I IFN activation will be elucidated in this research. In summary, the major goals of this grant proposal are to investigate the mechanisms of the regulation of host type I IFN response during EV71 infection, and to reveal the roles of the enteroviral 3D protein and the host protein NEDD4L in suppression of type I IFN expression. The information obtained from this research will facilitate the understanding for pathogenicity of EV71 and the antiviral development.

Project ID:PC10401-0625
External Project ID:MOST103-2320-B182-024-MY3