Infectious Bursal Disease Virus hijacks endosomal membranes as the scaffolding structure for viral replication

GIMENEZ, MARÍA CECILIA; ZANETTI, FLAVIA ADRIANA; TEREBIZNIK, MAURICIO R.; COLOMBO, MARÍA ISABEL; DELGUI, LAURA RUTH

JOURNAL OF VIROLOGY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2018

0022-538X

Abstract.Birnaviruses are unconventional members of the double-stranded RNA (dsRNA) viruses group that are characterized by the lack of a transcriptionally active inner core. Instead, the birnaviral particles organize their genome in ribonucleoprotein complexes (RNPs) composed by dsRNA segments, the dsRNA-binding VP3 protein, and the viral encoded RNA-dependent RNA-polymerase (RdRp). This and other structural features suggests that birnaviruses may follow a completely different replication program from that followed by members of the Reoviridae family, supporting the hypothesis that birnaviruses are the evolutionary link between single-stranded positive RNA (+ssRNA) and dsRNA viruses. Here, we demonstrated that the Infectious Bursal Disease Virus (IBDV), a prototypical member of the Birnaviridae family, hijacks endosomal membranes of infected cells through the interaction of viral protein, VP3, with the phospholipids on the cytosolic leaflet of these compartments for replication. Employing a mutagenesis approach, we demonstrated that VP3 domain PATCH 2 (P2) mediates the association of VP3 with the endosomal membranes. To determine the role of VP3 P2 in the context of virus replication cycle, we used avian cells stably overexpressing VP3 P2 for IBDV infection. Importantly, the intra- and extra-cellular virus yields, as well as the intracellular levels of VP2 viral capsid protein, significantly diminished in VP3 P2 stably overexpressing cells. Altogether, our results indicate that the association of VP3 with endosomes has a relevant role in IBDV replication cycle. This report provides direct experimental evidence for membranous compartments such as endosomes being required by a dsRNA virus for its replication. The results also support the previously proposed role of birnaviruses as an evolutionary link between +ssRNA and dsRNA viruses.IMPORTANCE Infectious Bursal Disease (IBD, also called Gumboro disease) is an acute, highly contagious immunosuppressive disease that affects young chickens and spreads worldwide. The etiological agent of IBD is the Infectious Bursal Disease Virus (IBDV). This virus destroys the central immune organ (bursa of Fabricius), resulting in immunosuppression and reduced responses of chickens to vaccines, which increases their susceptibility to other pathogens.IBDV is a member of Birnaviridae family, which comprises unconventional members of dsRNA viruses, whose replication strategy has been scarcely studied. In this report we show that IBDV hijacks the endosomes of the infected cells for establishing viral replication complexes via the association of the ribonucleoprotein complex component VP3,with the phospholipids in the cytosolic leaflet of endosomal membranes. We show that this interaction is mediated by VP3 PATCH2 domain and demonstrated its relevant role in the context of viral infection.