Open reading frame 5 of porcine reproductive and respiratory syndrome virus as a cause of virus-induced apoptosis

Abstract

The gene product of open reading frame 5 (p25) of porcine reproductive and respiratory syndrome (PRRS) virus has been expressed by coinfection of culture cells with vaccinia virus expressing the T7 RNA polymerase and a recombinant vaccinia virus encoding the open reading frame 5 gene under the T7 promoter and the encephalomyocarditis virus internal ribosome entry site. In spite of the reported efficiency of the expression system, very poor accumulation of p25 protein was observed and a strong cytotoxicity was produced in the doubly infected cells. This cell toxicity was shown to occur by induction of apoptosis, as indicated by nucleosome ladder formation, chromatin condensation, and rRNA degradation. Apoptosis induction was also observed after infection of cultured cells with an adapted PRRS virus strain and after infection of swine macrophage cells with a PRRS virus field strain. Contrary to the observations made for other cases of virus-induced apoptosis, we could not prevent p25 protein-induced apoptosis by using a cell line permanently expressing Bcl-2 protein.

Differential host cell gene expression regulated by the porcine reproductive and respiratory syndrome virus GP4 and GP5 glycoproteins

“…Interestingly, no pro-apoptotic genes were identified in HeLa-GP5 cells. This observation is contradictory to the previous report (Suárez et al, 1996) but is consistent with our recent finding that the GP5 expressing cells did not show any detectable level of cytotoxicity or cell death (Lee et al, 2004). Zhang et al (1999) have shown that PRRSV infection induced the expression of IFN-inducible gene Mx1 and an ubiquitin-specific protease in porcine alveolar macrophages.…”

“…Marc-145 cells were chosen to establish a cell line stably expressing the GP4 protein since they are cells susceptible to infection by PRRSV. For GP5 expression, we used the tetracycline-dependent inducible gene expression system (Tet-on/Tet-off) to avoid a possible cell death that may result from GP5 expression since the PRRSV GP5 protein was reported to induce cytotoxicity in African green monkey kidney cells (Suárez et al, 1996). HeLa-Tet-off cells, that were previously transformed with the regulatory plasmid pTet-off and therefore expressing the tetracycline transactivator (tTA), were chosen for additional transformation with the ORF5 gene.…”

“…GP5 exists as a heterodimer with the M protein in the virion (Mardassi et al, 1996), and heterodimerization has been shown to be essential for virus infectivity in LDV (Faaberg et al, 1995) and EAV (Snijder et al, 2003). The GP5 protein is reported to cause apoptosis (Suárez et al, 1996) and is able to induce neutralizing monoclonal antibodies in mice (Weiland et al, 1999;Ostrowski et al, 2002).…”

Reduction of porcine reproductive and respiratory syndrome virus (PRRSV) infection in swine alveolar macrophages by porcine circovirus 2 (PCV2)-induced interferon-alpha

“…As seen in a previous study (Chiou et al, 2000) and the present study, PRRSV-infected AMs had a low but constant infectious rate between 5 and 10%, markedly reduced cell viability, and significantly increased apoptosis and TNF-a production. Currently, available data suggest that the low PRRSV infectious rate but prominent cell injury in AMs might well be the result of a non-viral indirect mechanism due to the bystander effect of the released PRRSV open reading frame 5 gene product (Suarez et al, 1996) or TNF-a (Choi and Chae, 2002) from the infected cells. In the present study, significantly elevated TNF-a production occurred in all PCV2 and/or PRRSV-infected groups, particularly in the PRRSV-A group.…”

Apoptosis in astrovirus-infected CaCo-2 cells

“…The viral gene product that is responsible for inducing apoptosis in RNA viruses has been characterized in several cases such as porcine reproductive and respiratory syndrome virus (Fernandez et al, 2002;Suarez et al, 1996), murine coronavirus , infectious bursal disease virus (Fernandez-Arias et al, 1997), HIV (Muthumani et al, 2002;Stewart et al, 2000), poliovirus (Barco et al, 2000;Goldstaub et al, 2000), influenza virus (Schultz-Cherry et al, 2001), Langat flavivirus (Prikhod'ko et al, 2002) or enterovirus 71 (Kuo et al, 2002). For other RNA virus such as Sindbis virus (Jan and Griffin, 1999) or reovirus (Connolly and Dermody, 2002), induction of apoptosis does not require virus replication.…”