Induction of apoptosis in an insect cell line, IPLB-Ld652Y, infected with nucleopolyhedroviruses

Abstract

Ld652Y cells derived from the gypsy moth, Lymantria dispar, were infected with seven different nucleopolyhedroviruses (NPVs) including those from Autographa californica, Bombyx mori (BmNPV), Hyphantria cunea (HycuNPV), Spodoptera exigua (SeMNPV), L. dispar, Orgyia pseudotsugata (OpMNPV) and Spodoptera litura (SpltMNPV). The results showed that Ld652Y cells infected with BmNPV, HycuNPV, SeMNPV, OpMNPV and SpltMNPV underwent apoptosis, displaying apoptotic bodies, characteristic DNA fragmentation and increased caspase-3-like protease activity; HycuNPV induced the most severe apoptosis. In HycuNPV-infected Ld652Y cells, a considerable amount of viral DNA was synthesized although there was no detectable yield of budded virions and polyhedrin. Northern blot and immunoblot analyses revealed that HycuNPV inhibitor of apoptosis 3 (IAP3), which has been shown to function in Sf9 cells, was expressed in HycuNPV-infected Ld652Y cells at a level higher than or comparable with that in HycuNPVinfected SpIm cells, which produced a high titre of progeny virions without any apoptotic response. These results imply that the relative ease of apoptosis induction in NPV-infected Ld652Y cells is largely dependent on inherent cellular properties rather than functions of the respective NPVs, and indicate that the defect in progeny virion production is not merely due to the virus-induced apoptosis in HycuNPV-infected Ld652Y cells.

Host Range Factor 1 from Lymantria dispar Nucleopolyhedrovirus (NPV) Is an Essential Viral Factor Required for Productive Infection of NPVs in IPLB-Ld652Y Cells Derived from L. dispar

“…Slot blot analysis also showed that viral DNA in HycuNPV-infected Ld652Y cells without Z-VAD-FMK treatment decreased sharply from 24 hpi, suggesting that the decrease of viral DNA was likely due to apoptosis in HycuNPV-infected Ld652Y cells. Consistent with previous results (17) for HycuNPV-infected Ld652Y cells without Z-VAD-FMK treatment, immunoblot analysis with antisera against polyhedrin and viral structural proteins showed that there was no detectable production of virus-encoded proteins in HycuNPV-infected Ld652Y cells, irrespective of Z-VAD-FMK treatment (data not shown). These results suggested that HycuNPV replication was restricted in Ld652Y cells at a step after viral DNA replication by a mechanism other than apoptosis.…”

“…Our results demonstrated that BmNPV, HycuNPV, SeMNPV, and AcMNPV, which produced viral DNA in nonpermissive Ld652Y cells (14,17,33), were able to replicate with the aid of HRF-1, while replication of SpltMNPV, which produced no detectable viral DNA in Ld652Y cells (20), was not rescued by HRF-1. These results suggest that HRF-1 is required for an event that occurs after viral DNA replication to yield progeny virions in NPV-infected Ld652Y cells.…”

“…It was previously shown that infection of Ld652Y cells with Hyphantria cunea NPV (HycuNPV) resulted in induction of severe cellular apoptosis in which no progeny virions were produced (17). To determine if the defects in HycuNPV replication in Ld652Y cells were due to virus-induced apoptosis, Ld652Y cells were infected with HycuNPV at a multiplicity of infection (MOI) of 5 PFU/ cell.…”

Identification of a Novel Apoptosis Suppressor Gene from the Baculovirus Lymantria dispar Multicapsid Nucleopolyhedrovirus

“…Ld652Y cells are permissive for homologous L. dispar multicapsid NPV (LdMNPV) (20,(23)(24)(25) and heterologous Orgyia pseudotsugata MNPV (OpMNPV) (3), yielding high titers of progeny viruses, while they are nonpermissive for NPVs of Spodoptera exigua, Spodoptera litura, and Autographa californica (AcMNPV) (13,17,18,26). Infection of Ld652Y cells with AcMNPV results in global protein synthesis shutdown, in which viral DNA replication and viral mRNA transcription occur normally but protein synthesis is completely shut down, yielding no progeny viruses (9,10,19,21).…”

“…IPLB-Ld652Y (Ld652Y) cells derived from the gypsy moth, Lymantria dispar (8), exhibit unique responses to nucleopolyhedrovirus (NPV) infection and provide an excellent system for investigating interactions between insect cells and NPVs (13)(14)(15). Ld652Y cells are permissive for homologous L. dispar multicapsid NPV (LdMNPV) (20,(23)(24)(25) and heterologous Orgyia pseudotsugata MNPV (OpMNPV) (3), yielding high titers of progeny viruses, while they are nonpermissive for NPVs of Spodoptera exigua, Spodoptera litura, and Autographa californica (AcMNPV) (13,17,18,26).…”