After attachment to receptors, reovirus virions are internalized by endocytosis and exposed to
acid-dependent
proteases that catalyze viral disassembly. Previous studies using the
cysteine protease inhibitor E64 and a mutant cell line that does not support reovirus disassembly suggest a requirement for specific endocytic
proteases in reovirus entry. This study identifies the endocytic
proteases that mediate reovirus disassembly in murine fibroblast cells.
Infection of both L929 cells treated with the
cathepsin L inhibitor
Z-Phe-Tyr(t-Bu)-diazomethyl
ketone and
cathepsin L-deficient mouse embryo fibroblasts resulted in inefficient proteolytic disassembly of viral outer-
capsid proteins and decreased viral yields. In contrast, both L929 cells treated with the
cathepsin B inhibitor
CA-074Me and
cathepsin B-deficient mouse embryo fibroblasts support reovirus disassembly and growth. However, removal of both
cathepsin B and
cathepsin L activity completely abrogates disassembly and growth of reovirus. Concordantly,
cathepsin L mediates reovirus disassembly more efficiently than
cathepsin B in vitro. These results demonstrate that either
cathepsin L or
cathepsin B is required for reovirus entry into murine fibroblasts and indicate that
cathepsin L is the primary mediator of reovirus disassembly. Moreover, these findings suggest that specific endocytic
proteases can determine host cell susceptibility to
infection by intracellular pathogens.