Extended budded virus formation and induction of apoptosis by an AcMNPV FP-25/p35 double mutant in Trichoplusia ni cells

Ail Autographa californica nucleopolyhedrovirus (AcMNPV) mutant (AcdefrT) isolated front virus-infected Trichophlusia ni (TN-368) cells produced plasma membrane blebbing and caspase-3-like activity late in infection. It also synthesized less polyhedra, but displayed enhanced budded virus formation in TN-368 cells. This phenotype resulted from dual mutations in p35 and FP-25. In this study we showed that enhanced budded virus production occurs because the hourly rate of release of virus from AcdefrT-infected cells is higher than that for AcMNPV and it continues for longer. This may be the trigger for the induction of apoptosis late in AcdefrT-infected TN-368 cells. However, laddering of host DNA was absent in TN-368 cells infected with AcdefrT, but was observed in Spodoptera frugiperda cells. Very late polyhedrin protein production and occlusion body formation was reduced in AcdefrT-infected TN-368 cells, but chitinase and capsid late gene expression remained unchanged. The AcdefrT was rescued with a copy of a baculovirus iap3, to replace the absent p35. This modification abolished most plasma membrane blebbing in Acdeft-T-infected TN-368 cells, but did not affect enhanced budded virus production. These data Suggest that inhibitors of apoptosis are required in T ni cells, particularly when the production of budded virus is enhanced. (c) 2008 Elsevier B.V. All rights reserved.