Proteomic characterization of a novel structural protein ORF5a of porcine reproductive and respiratory syndrome virus.

Porcine reproductive and respiratory syndrome virus (PRRSV) emerged in the late 1980s in both Europe and North America is an arterivirus causing great economic losses in the pig industry worldwide. Recently, a novel structural protein, ORF5a, encoded by an alternative ORF of a subgenomic mRNA encoding the major envelope glycoprotein, GP5, has been discovered in all arteriviruses, suggesting its important role in arterivirology. The present study attempted to investigate compensatory changes of cellular gene expression in natural target cells regulated by the ORF5a. We thus established sublines of PAM cells to stably express the PRRSV ORF5a protein and assessed alterations in cellular protein productions of ORF5a-expressing PAM (PAM-ORF5a) cells at different time courses by the use of proteomic analysis. A total of 36 protein spots were initially found to be differentially expressed in PAM-ORF5a cells compared with normal PAM cells by high-resolution two-dimensional gel electrophoresis (2DE). Of these spots, 16 protein spots with statistically significant alteration, including 13 up-regulated and 3 down-regulated protein spots, were picked out for subsequent protein identification by peptide mass fingerprinting after matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS). The altered cellular proteins identified in this study were grouped into the functions associated with a variety of cellular processes such as cell growth, cytoskeleton networks and cell communication, metabolism, protein biosynthesis, RNA processing, and transportation. The proteomics data will provide valuable information for better understanding the specific cellular response to the novel ORF5a protein during PRRSV replication.