Abstract
Feline Calicivirus (FCV) infection results in the inhibition of host protein synthesis, known as “shut-off”. However, the precise mechanism of shut-off remains unknown. Here, we found that the FCV strain 2280 proteinase-polymerase (PP) protein can suppress luciferase reporter gene expression driven by endogenous and exogenous promoters. Furthermore, we found that the N-terminal 263 aa of PP (PPN-263) determined its shut-off activity using the expression of truncated proteins. However, the same domain of the FCV strain F9 PP protein failed to inhibit gene expression. A comparison between strains 2280 and F9 indicated that Val27, Ala96 and Ala98 were key sites for the inhibition of host gene expression by strain 2280 PPN-263, and PPN-263 exhibited the ability to shut off host gene expression as long as it contained any two of the three amino acids. Because the N-terminus of the PP protein is required for its proteinase and shut-off activities, we investigated the ability of norovirus 3C-like proteins (3CLP) from the GII.4-1987 and -2012 isolates to interfere with host gene expression. The results showed that 3CLP from both isolates was able to shut off host gene expression, but 3CLP from GII.4-2012 had a stronger inhibitory activity than that from GII.4-1987. Finally, we found that 2280 PP and 3CLP significantly repressed reporter gene transcription but did not affect mRNA translation. Our results provide new insight into the mechanism of the FCV-mediated inhibition of host gene expression.
Highlights
Caliciviridae are positive-stranded RNA viruses containing four recognized genera: Norovirus, Sapovirus, Lagovirus and Vesivirus
Our results provide new insight into the mechanism of the Feline Calicivirus (FCV)-mediated inhibition of host gene expression
To identify which FCV viral proteins could inhibit the expression of luciferase under the control of an endogenous promoter, the feline IFN-β promoter, Crandell-Reese feline kidney (CRFK) cells were cotransfected with the of an endogenous promoter, the feline IFN-β promoter, CRFK cells were cotransfected with the pIFN-β-Luc plasmid and each viral gene expression plasmid (Figure 1A)
Summary
Caliciviridae are positive-stranded RNA viruses containing four recognized genera: Norovirus, Sapovirus, Lagovirus and Vesivirus. Norovirus) and feline calicivirus (FCV) (genus Vesivirus) have been widely used as models to analyze the characteristics of the calicivirus life cycle due to their culturability [1]. FCV infection affects the oral cavity and upper respiratory tract and is a good model with many advantages, such as a mature reverse genetics system [2] and virus isolation, and culture technology. FCV possesses a linear, positive-sense, single-stranded RNA genome of 7.7 kb. The VPg protein is covalently linked to the 51 -end of both the genomic and subgenomic RNAs [3]. VPg acts as a cap substitute to recruit ribosomes and initiate translation [4,5].
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