Induction of apoptosis in frog virus 3-infected cells

Abstract

The ability of frog virus 3 (FV3), the type species of the family Iridoviridae, to induce apoptosis was examined by monitoring DNA cleavage, chromatin condensation, and cell-surface expression of phosphotidylserine (PS) in fathead minnow (FHM) and baby hamster kidney (BHK) cells. In productively infected FHM cells, DNA fragmentation was first noted at 6-7 h postinfection and was clearly seen by 17 h postinfection, while chromatin condensation was detected at 8.5 h postinfection. As with some other viruses, FV3-induced apoptosis did not require de novo viral gene expression as both heat-inactivated and UV-inactivated virus readily triggered DNA fragmentation in FHM cells. Moreover, FV3-induced apoptosis was blocked in FHM cells by the pan-caspase inhibitor Z-VAD-FMK, suggesting that virus infection triggers programmed cell death through activation of the caspase cascade. FV3 infection also triggered apoptosis in BHK cells as monitored by TUNEL and annexin V binding assays. To determine whether FV3, similar to other large DNA viruses, encoded proteins that block or delay apoptosis, mock- and FV3-infected FHM cells were osmotically shocked and assayed for DNA fragmentation 3 hours later. DNA fragmentation was clearly seen whether or not shocked cells were previously infected with FV3, indicating that infection with FV3 did not block apoptosis induced by osmotic shock in FHM cells. The above results demonstrate that iridoviruses triggered apoptosis and that the induction of programmed cell death did not require viral gene expression. However, it remains to be determined if virion attachment to target cells is sufficient to induce cell death, or if apoptosis is triggered directly or indirectly by one or more virion-associated proteins.

Innate Immune Responses and Permissiveness to Ranavirus Infection of Peritoneal Leukocytes in the FrogXenopus laevis

“…FV3 and related viruses are known to be cytolytic, causing apoptosis of infected cell lines in vitro and organ failure in vivo (2). Interestingly, during our analysis of PLs from FV3-infected animals stained by Giemsa, we noted the presence of a high number of apop- .…”

Pathogenicity in six Australian reptile species following experimental inoculation with Bohle iridovirus

“…Lesions observed here and subsequent death of the animal could be due to direct destruction of cells by the viral replication, or possibly indirect destruction by the encoded tetanus-like toxin (Eaton et al 2007), which may act at the cellular level. The high ratio of re-isolation from affected animals possibly indicates that viral replication was taking place during the disease process and this could give rise to hostmediated damage such as cytokine storm or apoptosis (Chinchar et al 2003). Cytoplasmic inclusions, as described for rainbow trout and redfin perch infected with EHNV (Reddacliff & Whittington 1996) and in infected tissues of gopher turtles, Hermann's tortoises and eastern box tortoises (Heldstab & Bestetti 1982, Westhouse et al 1996, Marschang et al 1999, Allender et al 2006, were observed in neither the BIV-exposed tortoises in this study nor the ranavirus challenge study of tortoises described by Johnson et al (2007) or the natural infection case described by De Voe et al (2004).…”

Mitochondrion-mediated apoptosis induced by Rana grylio virus infection in fish cells

“…In this study, the RGVinfected cells display characteristic morphological and biochemical hallmarks of apoptosis, such as nuclear chromatin condensation, DNA fragmentation and formation of apoptotic bodies, suggesting that RGV-induced cell death should be mediated by apoptosis. Previously, some other members in family Iridoviridae, such as epizootic hematopoietic necrosis virus (EHNV), frog virus 3 (FV3), lymphocystis disease virus (LCDV) and red sea bream iridovirus (RSIV), were also proved to induce typical apoptosis during in vitro infection [14,[22][23][24].…”

“…Apoptosis of fish cells can be also triggered by virus infection [14][15][16], but systematic studies on mitochondrial dynamics and the molecular mechanisms are very limited. In our previous studies, an iridovirus isolated from the cultured pig frog (Rana grylio), which is called Rana grylio virus (RGV), has been characterized [17], and a similar apoptotic process has been observed in RGV infected fish cells [18].…”