VP5, the nonstructural polypeptide of infectious bursal disease virus, accumulates within the host plasma membrane and induces cell lysis

Infectious bursal disease virus (IBDV) encodes a 17-kDa nonstructural polyp eptide known as VP5. This polypeptide is not essential for virus replicatio n in vitro but it plays an important role in in vivo dissemination and path ogenesis. We have characterized the expression of VP5 in three eukaryotic s ystems: (i) IBDV-infected chicken embryo fibroblasts; (ii) BSC-1 cells infe cted with a recombinant vaccinia virus vector; and (iii) Cos-1 cells transi ently transfected with a plasmid vector. Immunofluorescence analyses showed that upon expression VP5 accumulates within the plasma membrane. This find ing was consistent with sequence-based topology predictions, indicating tha t VP5 is a class II membrane protein with a cytoplasmic N-terminus and an e xtracellular C-terminal domain. Brefeldin A treatment of VP5-expressing cel ls prevented the accumulation of this polypeptide in the plasma membrane, t hus showing the requirement of an active exocytic pathway to reach that com partment. Expression of VP5 was shown to be highly cytotoxic. Induction of VP5 expression resulted in the alteration of cell morphology, the disruptio n of the plasma membrane, and a drastic reduction of cell viability. VP5-in duced cytotoxicity was prevented by blocking its transport to the membrane with Brefeldin A. Our findings suggest that VP5 plays an important role in the release of the IBDV progeny, (C) 2000 Academic Press.