Cathepsin L and Cathepsin B Mediate Reovirus Disassembly in Murine Fibroblast Cells

Abstract

After attachment to receptors, reovirus virions are internalized by endocytosis and exposed to aciddependent 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(tBu)-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.

The Nipah Virus Fusion Protein Is Cleaved within the Endosomal Compartment

“…Endosomal cathepsins, metalloproteases, and secretases mediate cleavage or limited proteolysis of a variety of cellular proteins, leading either to degradation or activation of the respective proteins (31)(32)(33)(34)(35)(36)(37)(38). Furthermore, proteases of the endosomal compartment are known to be involved in the proteolytic processing of a few viral proteins such as the outer capsid proteins of reoviruses (39). However, the NiV F protein is the first viral surface glycoprotein for which it is now shown that site-specific cleavage within endosomes takes place and is required for biological activation.…”

Cleavage of the papillomavirus minor capsid protein, L2, at a furin consensus site is necessary for infection

“…Reoviruses and Ebola virus use the lysosomal cathepsin proteases to initiate their uncoating processes (24,25). For most substrates, cathepsins act as relatively nonspecific, processive proteases (26), and for these viruses the cathepsins mediate a stepwise proteolysis of the viral structural proteins.…”

Common host genes are activated in mouse brain by Japanese encephalitis and rabies viruses

“…Cathepsin S, a lysosomal cysteine protease, is involved in the processing of MHC class II-associated invariant chain in interferon-c-stimulated microglia (Gresser et al, 2001). Recently, cathepsins were shown to be involved in virus disassembly as well (Ebert et al, 2002). GARG49 is a member of the recently identified glucocorticoid-attenuated response gene (GARG) family, which also includes GARG16 and GARG39 (Smith & Herschman, 1996).…”