Differential viral propagation and induction of apoptosis by grouper iridovirus (GIV) in cell lines from three non-host species

Abstract

Grouper iridovirus (GIV), belonging to the Ranavirus genus of the Iridoviridae family, was demonstrated to differentially express viral genes and induce apoptosis in three non-host fish cell lines rainbow trout monocyte/macrophage (RTS11), chinook salmon embryonic (CHSE-214) and fathead minnow Epithelioma papulosum cyprinid (EPC). These cells were challenged with GIV and virus entry into all three cell lines was confirmed by the expression of viral immediate early genes. The expression of the late major capsid protein gene was detected in CHSE-214 and EPC, but not in RTS11, suggesting an earlier termination in the viral replication cycle in RTS11. Approximately 12h after infection with GIV, cell death was prominent in all three non-host cell lines. Death was later confirmed to be apoptosis by the presence of chromosomal DNA fragmentation and phosphatidylserine externalization. To determine whether apoptosis was protein related or gene expression related, the three cell lines were challenged with heat-inactivated GIV and UV-treated GIV (GIV(UV)). The heat inactivation abolished apoptosis in all three cell lines, but each cell line responded differently to GIV(UV). Relative to GIV, GIV(UV) caused no apoptosis in CHSE-214, decreased apoptosis in RTS11, and increased apoptosis in EPC. These results suggest that early GIV gene expression was needed for apoptosis in CHSE-214 but impeded apoptosis in EPC. At the cellular level, only EPC is a permissive host as EPC was the only cell line of the three capable of producing a moderate increase in virus titer. The three non-host cell lines present a good system for potentially identifying different components of GIV-induced apoptotic pathways in future studies.