RESUMO
A unique feature of ascovirus infection is cleavage of host cells into virus containing vesicles. It has been suggested that the virus induces apoptosis, either by expression of a caspase or other means, which is then diverted toward vesicle formation. There is little known about the mechanism of vesicle formation. Recent genome sequences of three ascoviruses indicated the presence of several putative open reading frames coding for proteins that could be involved in lipid metabolism. These proteins may play a role in rearrangement of membranes in infected host cells leading to formation of vesicles. Here, we analyzed a lipase-like gene (ORF19) from Heliothis virescens ascovirus (HvAV-3e) expressed from 8 h after infection and essential for virus replication and cell cleavage. In addition, ORF19 knock down by RNA interference inhibited virus replication indicating that the gene is indispensable for HvAV-3e replication. However, under enzymatic assays tested, we did not detect any lipase or esterase activity from ORF19.
Assuntos
Ascoviridae/enzimologia , Ascoviridae/fisiologia , Lepidópteros/virologia , Lipase/fisiologia , Proteínas Virais/fisiologia , Replicação Viral , Animais , Ascoviridae/genética , Linhagem Celular , Técnicas de Silenciamento de Genes , Lipase/genética , Interferência de RNA , Proteínas Virais/genéticaRESUMO
Ascoviruses (AVs) are double-stranded DNA viruses causing a fatal disease in lepidopteran host larvae. A unique feature of AV infection is cleavage of host cells into membrane bound vesicles containing the virions. A recent study showed that a caspase from Spodoptera frugiperda AV (SfAV) is directly involved in initiation of apoptosis and eventually cell cleavage. Results shown here indicate that Heliothis virescens AV does not induce apoptosis in host cells. HvAV codes for a caspase-like protein but no apoptosis was observed when the gene was expressed in vitro. RNAi studies indicated that the gene is essential for virus replication.
Assuntos
Apoptose/fisiologia , Ascoviridae/enzimologia , Caspases/genética , Genes Essenciais , Mariposas/virologia , Replicação Viral , Sequência de Aminoácidos , Animais , Ascoviridae/genética , Ascoviridae/patogenicidade , Ascoviridae/fisiologia , Caspases/metabolismo , Linhagem Celular , Inativação Gênica , Dados de Sequência Molecular , Interferência de RNA , Alinhamento de Sequência , Spodoptera , Proteínas Virais/genética , Proteínas Virais/metabolismo , Replicação Viral/fisiologiaRESUMO
The Spodoptera frugiperda ascovirus, a DNA virus that attacks lepidopterans, codes for an executioner caspase synthesized by 9 h after infection of Sf21 cells. This caspase alone induces apoptosis in insect cells and, during viral replication in vivo, contributes to a novel cell cleavage process in which developing apoptotic bodies are rescued by the virus and differentiate to form large vesicles in which virions assemble. These viral vesicles disseminate to the blood, where they are acquired during egg-laying by parasitic wasps that transmit the virus. No other viruses encode caspases or form such modified apoptotic bodies, suggesting this caspase plays a direct role in cell partitioning that facilitates viral reproduction and transmission.
