title: The Culicoides sonorensis inhibitor of apoptosis 1 protein protects mammalian cells from apoptosis induced by infection with African horse sickness virus and bluetongue virus.
abstract: African horse sickness virus (AHSV) and bluetongue virus (BTV) are arboviruses of the genus Orbivirus that are transmitted to their vertebrate hosts by Culicoides biting midges. These orbiviruses exhibit lytic infection (apoptosis) in mammalian cells, but cause persistent infection with no cytopathic effects in Culicoides sonorensis cells. Although regulation of apoptosis could thus be integral for establishing persistent virus infection in midge cells, nothing is known about the presence and function of apoptosis pathways in Culicoides midges and their derived cell lines. Here, we report the cloning and functional characterization of an inhibitor of apoptosis protein (IAP), designated CsIAP1, from C. sonorensis cells. The CsIAP1 protein contains two baculoviral IAP repeat (BIR) domains and a RING domain. Silencing of the Cs iap1 gene in C. sonorensis cells caused apoptosis, indicating that CsIAP1 plays a role in cell survival. Stable expression of the CsIAP1 protein in BSR mammalian cells suppressed apoptosis induced by AHSV-4 and BTV-10 infection, and biochemical data indicated that CsIAP1 is an inhibitor of mammalian caspase-9, an initiator caspase in the intrinsic apoptotic pathway. Mutagenesis studies indicated that the BIR2 and RING domains are required for the anti-apoptotic activity of CsIAP1. The results suggest that the mechanism by which CsIAP1 suppresses apoptosis in insect cells may involve inhibition of a Culicoides caspase-9 homologue through a mechanism that requires both the BIR2 and RING domains. This study provides the first evidence that the CsIAP1 protein is a key negative regulator of apoptosis in C. sonorensis cells.
authors.affiliation: Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria 0002, South Africa.
authors.forename: Elaine
authors.initials: E
authors.lastname: Vermaak
authors.affiliation: Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria 0002, South Africa; Transboundary Animal Diseases, Onderstepoort Veterinary Institute, Agricultural Research Council, Pretoria 0110, South Africa.
authors.forename: Francois F
authors.initials: FF
authors.lastname: Maree
authors.affiliation: Department of Microbiology and Plant Pathology, University of Pretoria, Pretoria 0002, South Africa. Electronic address: jacques.theron@up.ac.za.
authors.forename: Jacques
authors.initials: J
authors.lastname: Theron
mesh_terms: D000356:African Horse Sickness Virus / Q000235:genetics / Q000254:growth & development; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D001820:Bluetongue virus / Q000235:genetics / Q000254:growth & development; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D002519:Ceratopogonidae / Q000235:genetics* / Q000378:metabolism / Q000821:virology; D005786:Gene Expression Regulation; D054884:Host-Pathogen Interactions; D051034:Inhibitor of Apoptosis Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D019476:Insect Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D007303:Insect Vectors / Q000235:genetics* / Q000378:metabolism / Q000821:virology; D000072417:Protein Domains; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D012756:Sheep; D015398:Signal Transduction
chemical_list: D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins; D034741:RNA, Small Interfering; D053453:Caspase 9
keywords: African horse sickness virus; Apoptosis; Bluetongue virus; Culicoides sonorensis; Inhibitor of apoptosis; Orbivirus