Comparative Proteomic Analysis of Wild-Type and SAP Domain Mutant Foot-and-Mouth Disease Virus-Infected Porcine Cells Identifies the Ubiquitin-Activating Enzyme UBE1 Required for Virus Replication

Leader protein (Lpro)
of foot-and-mouth disease virus
(FMDV) manipulates the activities of several host proteins to promote
viral replication and pathogenicity. Lpro has a conserved
protein domain SAP that is suggested to subvert interferon (IFN) production
to block antiviral responses. However, apart from blocking IFN production,
the roles of the SAP domain during FMDV infection in host cells remain
unknown. Therefore, we identified host proteins associated with the
SAP domain of Lpro by a high-throughput quantitative proteomic
approach [isobaric tags for relative and absolute quantitation (iTRAQ)
in conjunction with liquid chromatography/electrospray ionization
tandem mass spectrometry]. Comparison of the differentially regulated
proteins in rA/FMDVΔmSAP- versus rA/FMDV-infected SK6 cells
revealed 45 down-regulated and 32 up-regulated proteins that were
mostly associated with metabolic, ribosome, spliceosome, and ubiquitin-proteasome
pathways. The results also imply that the SAP domain has a function
similar to SAF-A/B besides its potential protein inhibitor of activated
signal transducer and activator of transcription (PIAS) function.
One of the identified proteins UBE1 was further analyzed and displayed
a novel role for the SAP domain of Lpro. Overexpression
of UBE1 enhanced the replication of FMDV, and knockdown of UBE1 decreased
FMDV replication. This shows that FMDV manipulates UBE1 for increased
viral replication, and the SAP domain was involved in this process.