Hepatitis C Virus Exploitation of Processing Bodies

KSHV RNA-binding protein ORF57 inhibits P-body formation to promote viral multiplication by interaction with Ago2 and GW182

Cellular non-membranous RNA-granules, P-bodies (RNA processing bodies, PB) and stress granules (SG), are important components of the innate immune response to virus invasion. Mechanisms governing how a virus modulates PB formation remain elusive. Here, we report the important roles of GW182 and DDX6, but not Dicer, Ago2 and DCP1A, in PB formation, and that Kaposi's sarcoma-associated herpesvirus (KSHV) lytic infection reduces PB formation through several specific interactions with viral RNA-binding protein ORF57. The wild-type ORF57, but not its N-terminal dysfunctional mutant, inhibits PB formation by interacting with the N-terminal GW-domain of GW182 and the N-terminal domain of Ago2, two major components of PB. KSHV ORF57 also induces nuclear Ago2 speckles. Homologous HSV-1 ICP27, but not EBV EB2, shares this conserved inhibitory function with KSHV ORF57. By using time-lapse confocal microscopy of HeLa cells co-expressing GFP-tagged GW182, we demonstrated that viral ORF57 inhibits primarily the scaffolding of GW182 at the initial stage of PB formation. Consistently, KSHV-infected iSLK/Bac16 cells with reduced GW182 expression produced far fewer PB and SG, but 100-fold higher titer of infectious KSHV virions when compared to cells with normal GW182 expression. Altogether, our data provide the first evidence that a DNA virus evades host innate immunity by encoding an RNA-binding protein that promotes its replication by blocking PB formation.

Transcriptional responses of LSm14A after infection of blue eggshell layers with Newcastle disease viruses

LSm14A is a key innate immunity component of processing body (P-body) that mediates interferon-β (IFN-β) signaling by viral RNA. This is the first study to report chicken LSm14A (cLSm14A) cloning from blue eggshell layer, high tibia and frizzle chickens. The cLSm14A gene, encoding 461 amino acids, is highly homologous in the three types of chickens. The cLSm14A was extensively expressed in several tissues. The transcriptional level of cLSm14A was significantly increased in various stages of Newcastle disease virus (NDV) infection. In HEK293 cells, full length cLSm14A from blue eggshell layer was localized in the cytoplasm as dots. The results of this study indicated that cLSm14A is an important sensor that mediates innate immunity in chicken against NDV infections.