Addition of exogenous protease facilitates reovirus infection in many restrictive cells.
Virion uncoating is a critical step in the life cycle of mammalian orthoreoviruses. In cell culture, and probably in extraintestinal tissues in vivo, reovirus virions undergo partial proteolysis within endosomal or/or lysosomal compartments. This process converts the virion into a form referred to as an intermediate subvirion particle (ISVP). In natural enteric reovirus infections, proteolytic uncoating takes place extracellularly within the intestinal lumen. The resultant proteolyzed particles, unlike intact virions, have the capacity to penetrate cell membranes and thereby gain access to cytoplasmic components required for viral gene expression. We hypothesized that the capacity of reovirus outer capsid proteins to be proteolyzed is a determinant of cellular host range. To investigate this hypothesis, we asked if the addition of protease to cell culture medium would expand the range of cultured mammalian cell lines that can be productively infected by reoviruses. We identified many transformed and nontransformed cell lines, as well as primary cells, that restrict viral infection. In several of these restrictive cells, virion uncoating is inefficient or blocked. Addition of proteases to the cell culture medium generates ISVP-like particles and promotes viral growth in nearly all cell lines tested. Interestingly, we found that some cell lines that restrict reovirus uncoating still express mature cathepsin L, a lysosomal protease required for virion disassembly in murine L929 cells. This finding suggests that factors in addition to cathepsin L are required for efficient intracellular proteolysis of reovirus virions. Our results demonstrate that virion uncoating is a critical determinant of reovirus cellular host range and that many cells which otherwise support productive reovirus infection cannot efficiently mediate this essential early step in the virus life cycle.
Golden
Joseph W
JW
Department of Microbiology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Linke
Jessica
J
Schmechel
Stephen
S
Thoemke
Kara
K
Schiff
Leslie A
LA
D000818:Animals; D056668:Cathepsin L; D002403:Cathepsins / Q000378:metabolism; D002460:Cell Line; D002918:Chymotrypsin / Q000378:metabolism*; D003470:Culture Media; D003546:Cysteine Endopeptidases; D006801:Humans; D051379:Mice; D030102:Orthoreovirus, Mammalian / Q000472:pathogenicity* / Q000502:physiology; D012088:Reoviridae Infections / Q000821:virology*; D013045:Species Specificity; D014764:Viral Proteins / Q000378:metabolism; D014771:Virion / Q000378:metabolism*; D014779:Virus Replication
D003470:Culture Media; D014764:Viral Proteins; D002403:Cathepsins; D002918:Chymotrypsin; D003546:Cysteine Endopeptidases; C534281:CTSL protein, human; D056668:Cathepsin L; C534278:Ctsl protein, mouse