VP5, the Nonstructural Polypeptide of Infectious Bursal Disease Virus, Accumulates within the Host Plasma Membrane and Induces Cell Lysis

Infectious bursal disease virus (IBDV), the causative agent of a highly contagious disease in chickens, carries a small nonstructural protein (NS). This protein has been implicated to play a role in the induction of apoptosis. In this study, we investigate the kinetics of viral replication during a single round of viral replication and examine the mechanism of IBDV-induced apoptosis. Our results show that it is caspase dependent and activates caspases 3 and 9. Nuclear factor kappa B (NF-B) is also activated and is required for IBDV-induced apoptosis. The NF-B inhibitor MG132 completely inhibited IBDV-induced DNA fragmentation, caspase 3 activation, and NF-B activation. To study the function of the NS protein in this context, we generated the recombinant rGLS virus and an NS knockout mutant, rGLSNS⌬ virus, using reverse genetics. Comparisons of the replication kinetics and markers for virally induced apoptosis indicated that the NS knockout mutant virus induces earlier and increased DNA fragmentation, caspase activity, and NF-B activation. These results suggest that the NS protein has an antiapoptotic function at the early stage of virus infection.

Section: Discussionmentioning

confidence: 99%

Section: Infectious Bursal Disease Virus (Ibdv) Is the Causative Agenmentioning

confidence: 99%

Nonstructural Protein of Infectious Bursal Disease Virus Inhibits Apoptosis at the Early Stage of Virus Infection

Liu

Vakharia

2006

“…Examples include the human immunodeficiency virus (HIV) Vpu, influenza M2, and picornavirus 3A and 2B proteins as well as two viroporins encoded by genera within the family Reoviridae, the rotavirus NSP4 and the orbivirus NS3 proteins (6,26,60). In addition to their structural features, viroporins share the functional property of altering membrane permeability to ions and small molecules such as uridine and hygromycin B and have been implicated in virus-induced cytopathic effects and in facilitating virus release (8,9,26,41).…”

Section: Discussionmentioning

confidence: 99%

“…Viroporins are small (60 to 120 amino acids), often nonstructural, membrane-disruptive proteins with one or more hydrophobic motifs, frequently with an adjacent polybasic region. The membrane-destabilizing activity of viroporins may contribute to virus-induced cytopathic effects and to facilitating the release of both enveloped and nonenveloped viruses (6,26,41,60).…”

mentioning

confidence: 99%

Extensive Syncytium Formation Mediated by the Reovirus FAST Proteins Triggers Apoptosis-Induced Membrane Instability

Salsman

Top

Boutilier

et al. 2005

104

The fusion-associated small transmembrane (FAST) proteins of the fusogenic reoviruses are the only known examples of membrane fusion proteins encoded by nonenveloped viruses. While the involvement of the FAST proteins in mediating extensive syncytium formation in virus-infected and -transfected cells is well established, the nature of the fusion reaction and the role of cell-cell fusion in the virus replication cycle remain unclear. To address these issues, we analyzed the syncytial phenotype induced by four different FAST proteins: the avian and Nelson Bay reovirus p10, reptilian reovirus p14, and baboon reovirus p15 FAST proteins. Results indicate that FAST protein-mediated cell-cell fusion is a relatively nonleaky process, as demonstrated by the absence of significant [ 3 H]uridine release from cells undergoing fusion and by the resistance of these cells to treatment with hygromycin B, a membrane-impermeable translation inhibitor. However, diminished membrane integrity occurred subsequent to extensive syncytium formation and was associated with DNA fragmentation and chromatin condensation, indicating that extensive cell-cell fusion activates apoptotic signaling cascades. Inhibiting effector caspase activation or ablating the extent of syncytium formation, either by partial deletion of the avian reovirus p10 ectodomain or by antibody inhibition of p14-mediated cell-cell fusion, all resulted in reduced membrane permeability changes. These observations suggest that the FAST proteins do not possess intrinsic membrane-lytic activity. Rather, extensive FAST protein-induced syncytium formation triggers an apoptotic response that contributes to altered membrane integrity. We propose that the FAST proteins have evolved to serve a dual role in the replication cycle of these fusogenic nonenveloped viruses, with nonleaky cell-cell fusion initially promoting localized cell-cell transmission of the infection followed by enhanced progeny virus release from apoptotic syncytia and systemic dissemination of the infection.The reovirus fusion-associated small transmembrane (FAST) protein family is comprised of an atypical group of membrane fusion proteins encoded by nonenveloped viruses. Different FAST proteins have been isolated from four of the five recognized species in the genus Orthoreovirus, family Reoviridae (16). These fusogenic reoviruses and their corresponding FAST proteins include the p10 homologues encoded by avian reovirus (ARV) and Nelson Bay reovirus (NBV), p15 from baboon reovirus (BRV), and p14 from reptilian reovirus (RRV) (12,14,53). Unlike the membrane fusion proteins encoded by enveloped viruses, the reovirus FAST proteins are nonstructural viral proteins and therefore are not involved in virus entry (14,15,53). Rather, these proteins are expressed in virus-infected cells and trafficked through the endoplasmic reticulum-Golgi pathway to the plasma membrane (52). Accumulation of the FAST proteins at the cell surface leads to fusion of virus-infected cells with neighboring uninfected cells, in both cell cultu...

“…The major segment contains two partially overlapping open reading frames (ORFs). The first one codes for a 17-kDa polypeptide, VP5, that plays an important role in virus egress and virulence (24,44). The second one codes for the virus polyprotein (105 kDa).…”

mentioning

confidence: 99%

The Oligomerization Domain of VP3, the Scaffolding Protein of Infectious Bursal Disease Virus, Plays a Critical Role in Capsid Assembly

Maraver¹,

Oña²,

Abaitua³

et al. 2003

Self Cite

Infectious bursal disease virus (IBDV) capsids are formed by a single protein layer containing three polypeptides, pVP2, VP2, and VP3. Here, we show that the VP3 protein synthesized in insect cells, either after expression of the complete polyprotein or from a VP3 gene construct, is proteolytically degraded, leading to the accumulation of product lacking the 13 C-terminal residues. This finding led to identification of the VP3 oligomerization domain within a 24-amino-acid stretch near the C-terminal end of the polypeptide, partially overlapping the VP1 binding domain. Inactivation of the VP3 oligomerization domain, by either proteolysis or deletion of the polyprotein gene, abolishes viruslike particle formation. Formation of VP3-VP1 complexes in cells infected with a dual recombinant baculovirus simultaneously expressing the polyprotein and VP1 prevented VP3 proteolysis and led to efficient virus-like particle formation in insect cells.