Date Published: June 26, 2014
Publisher: Public Library of Science
Author(s): Yen-Chin Liu, Rei-Lin Kuo, Jing-Yi Lin, Peng-Nien Huang, Yi Huang, Hsuan Liu, Jamine J. Arnold, Shu-Jen Chen, Robert Yung-Liang Wang, Craig E. Cameron, Shin-Ru Shih, Mark T. Heise.
The primary role of cytoplasmic viral RNA-dependent RNA polymerase (RdRp) is viral genome replication in the cellular cytoplasm. However, picornaviral RdRp denoted 3D polymerase (3Dpol) also enters the host nucleus, where its function remains unclear. In this study, we describe a novel mechanism of viral attack in which 3Dpol enters the nucleus through the nuclear localization signal (NLS) and targets the pre-mRNA processing factor 8 (Prp8) to block pre-mRNA splicing and mRNA synthesis. The fingers domain of 3Dpol associates with the C-terminal region of Prp8, which contains the Jab1/MPN domain, and interferes in the second catalytic step, resulting in the accumulation of the lariat form of the splicing intermediate. Endogenous pre-mRNAs trapped by the Prp8-3Dpol complex in enterovirus-infected cells were identified and classed into groups associated with cell growth, proliferation, and differentiation. Our results suggest that picornaviral RdRp disrupts pre-mRNA splicing processes, that differs from viral protease shutting off cellular transcription and translation which contributes to the pathogenesis of viral infection.
RNA viruses in general replicate in the cytoplasm and interfere host cellular gene expression by utilizing proteolytic destruction of cellular targets as the primary mechanism . However, several viral proteins have been found in the nucleus and altered host gene expression . For example, our previous finding shows that picornaviral 3C protease cleaves CstF-64 and inhibits cellular polyadenylation in the nucleus . Besides the protease, the RNA-dependent RNA polymerase (RdRp) also appears in the nucleus, but the role of viral RNA polymerase in the nucleus remains unclear. This study utilized picornaviral polymerase to probe the function of RdRp in the nucleus.
Picornaviral 3Dpol plays a key role in viral genome replication in the cytoplasm. Both picornaviral 3CD and 3Dpol have also been observed in the nucleus as a result of infection, and this localization is mediated through the NLS of 3Dpol. In the nucleus, mature 3C from the precursor 3CD shuts off host cell transcription , , . Although evidence for the entry of picornaviral 3Dpol into the nucleus was first reported approximately a decade ago, the precise role of 3Dpol in the host nucleus has remained unknown. A schematic model is provided in Figure 6. Our study uncovered a novel mechanism for picornaviral 3Dpol invasion of host cells by its localization to the nucleus and association with the Prp8 protein, which is located at the center of the spliceosome. The viral 3Dpol affects the splicing function of Prp8 in the C1-complex and inhibits the second step of the splicing process, resulting in accumulation of the lariat form and a reduction on mRNA levels. The intracellular targeted RNAs that are trapped by the Prp8-3Dpol complexes are primarily responsible for cell growth, proliferation, and differentiation.