Characterization of the porcine reproductive and respiratory syndrome virus glycoprotein 5 (GP5) in stably expressing cells.

Porcine reproductive and respiratory syndrome virus (PRRSV) induces apoptosis in cultured cells and in infected tissues of pig, and the GP5 protein was reported to be responsible. To study the role of apoptosis during PRRSV infection, we established a subline of HeLa cells stably expressing the PRRSV GP5 protein under an inducible promoter to prevent cell death that may result from GP5 expression. The expression of GP5 was confirmed upon induction by immunofluorescence, Western blot, and immunoprecipitation. No reduction in cell numbers was observed in the GP5-expressing cells, and neither DNA fragmentation nor strand-breaks were detected in these cells. To examine if bystander cells underwent apoptosis, Marc-145 or HeLa cells were co-cultivated with GP5-expressing cells, and the apoptotic characteristics were examined in the bystanders. Neither DNA laddering, strand-breaks, nor reduction in cell numbers was observed in the co-cultivated cells. Gene expression profiles were examined for both GP5-expressing cells and bystanders by apoptosis-specific macroarrays and gene chip-based microarrays, but no genes related to apoptosis were specifically regulated. Our data suggest that the previously reported GP5-induced apoptosis may be an atypical observation. The GP5-expressing cells were immunoreactive with sera from pigs infected with the North American and European types of PRRSV, which implicates a potential usefulness of these cells as a diagnostic reagent for PRRSV.