Rachel Nygaard

E-mail: nyga0078@umn.edu

Thesis advisor: Leslie Schiff

Year entered: 2006

Degree received:
B.S., Biology, Central Missouri State University, Warrensburg, MO 2001

Honors and Awards:
DOVE Fellowship 2006

Thesis research:
Mammalian reoviruses naturally infect hosts via the enteric and/or respiratory routes. Productive infection depends upon host-expressed proteases to remove the outer capsid protein sigma-3 and expose the underlying membrane penetration protein, mu-1. In murine L929 cells, endosomal acid-dependent cysteine proteases cathepsin (cat) L and cat B degrade sigma-3. In other cell lines, distinct proteases (including cat S and neutrophil elastase), can mediate productive uncoating. These cell culture studies indicate that reovirus capsid processing can be achieved by a wide variety of proteases. Despite these findings, the proteases that mediate virion uncoating during natural reovirus infections have yet to be completely defined. In a murine model of enteric infection, inhibitor studies reveal a role for secreted pancreatic serine proteases in sigma-3 removal. To identify proteases that might be involved in respiratory reovirus infections, we examined the ability of several respiratory proteases to promote productive virion disassembly. Using in vitro uncoating assays, we found that endogenous respiratory proteases, including human airway trypsin-like protease (HAT), and the inflammatory proteases cat G and chymase, can facilitate sigma-3 removal and generate ISVP-like particles. Subviral particles generated with the inflammatory proteases were infectious, replicated with the same kinetics as chymotrypsin-generated ISVPS, and did not require additional proteolytic processing by cysteine or acid-dependent proteases. We also showed that ectopic expression of HAT and other human airway proteases in cell culture promoted reovirus entry. These findings further demonstrate that reovirus capsid processing can be mediated by a variety of proteases and they provide a foundation for our studies in mouse models of respiratory reovirus infection.