Oxidative stress in cells infected with bovine viral diarrhoea virus: a crucial step in the induction of apoptosis.

Abstract

Bovine viral diarrhoea virus (BVDV) belongs to the genus Pestivirus of the family Flaviviridae. Both a noncytopathic (ncp) and an antigenically related cytopathic (cp) BVDV can be isolated from persistently infected animals suffering from mucosal disease. In every case studied so far, the genomic changes leading to the cp biotype correlate with the production of the NS3 nonstructural protein, which, in the ncp biotype, is present in its uncleaved form, NS23. This report shows that, in contrast to ncp BVDV, the cp biotype induces apoptosis in cultured embryonic bovine turbinate cells. Early in the process of apoptosis, cells show a rise in the intracellular level of reactive oxygen species, which is indicative of oxidative stress. This precedes two hallmarks of apoptosis, caspase activation as shown by cleavage of the caspase substrate poly(ADP-ribose) polymerase, and DNA fragmentation. Cells were protected from apoptosis only by certain antioxidants (butylated hydroxyanisole and ebselen), whereas others (N-acetylcysteine, pyrrolidine dithiocarbamate, lipoic acid, dihydrolipoic acid and tiron) turned out to be ineffective. Antioxidants that protected cells from apoptosis prevented oxidative stress but failed to block virus growth. These observations suggest that oxidative stress, which occurs early in the interaction between cp BVDV and its host cell, may be a crucial event in the sequence leading to apoptotic cell death. Hence, apoptosis is not required for the multiplication of the cp biotype of BVDV.

The bovine viral diarrhea virus (BVDV) NS3 protein, when expressed alone in mammalian cells, induces apoptosis which correlates with caspase-8 and caspase-9 activation

“…In addition, oxydative stress [40], intracellular viral RNA accumulation [44], caspase-12-associated ER stress [18], and mitochondriadependent caspase-9 activation [11] have been reported to be associated with cp BVDV-induced apoptosis. Here we show that NS3/NS3∆50 of BVDV induced apoptosis, and correlated with both caspase-8 and caspase-9 activation.…”

“…Although the NS3/ NS3∆50 protein induces caspase-8-and -9-dependent apoptosis, several lines of evidence suggest that several factors (cellular and/or viral) or activation pathways of apoptosis are likely to be involved in the BVDV-associated apoptosis process. The facts that oxidative stress is observed in cells infected with cp BVDV [40], and that caspase-12-associated ER stress, a feature that was not addressed in this study, is observed in cp BVDV-induced apoptosis are consistent with the latter statement [18]. Caspase-12, which resides within the cytoplasmic side of the ER, is believed to play a central role in the ER stress-mediated apoptosis [31] and can activate caspase-8 [7] which in turn stimulates, through Bid processing, cytochrome c release and activates caspase-9 [17].…”

“…This apoptosis process has been associated with the accumulation of large amounts of viral RNA [44], cleavage of poly(ADP-ribose) polymerase (PARP) [14], mitochondrial-dependent caspase-9 activation [11], and endoplasmic reticulum (ER) stress induction that correlates with the activation of caspase-12 [18]. It is prevented by certain anti-oxidants [40]. In this report, we demonstrate that the NS3 protein of BVDV expressed from an inducible promoter in an adenovirus vector (AdV) induces programmed cell death (apoptosis) in vitro.…”

Apoptosis in Bovine Viral Diarrhea Virus (BVDV)–Induced Mucosal Disease Lesions

“…20,31 Similarly, it has been shown that TNF-a is released by primary bovine fetal muscle cells experimentally infected with cp BVDV, and this might be involved in caspase-8 activation, albeit the effect was rather small compared with the strong stimulation of caspase-3 activity. 48 In other studies, oxidative stress, 36 endoplasmic reticulum (ER) stress, 19,27 intracellular viral RNA 42 or double-stranded (ds) RNA accumulation, 47 and mitochondria-dependent caspase-9 activation 13 have been reported to be associated with cp BVDVinduced apoptosis.…”

“…27,33 It has been previously reported that cell death associated with cp BVDV in vitro is mediated by apoptosis. 15,17,36,50 Infection of cell cultures with BVDV of the cp biotype is characterized by the predominant expression of the NS3 protein, the cleaved form of the nonstructural protein NS2-3. In contrast, in cells infected with ncp BVD viruses, the uncleaved NS2-3 precursor protein prevails.…”