title: Selective cleavage by trypsin of the capsid protein VP1 of type 3 poliovirus results in improved sorting of cell bound virions.
abstract: A large proportion of host cell-bound virions of poliovirus type 1 strain Mahoney (PV1/M) is known to elute to the culture medium during incubation at 37 degrees C, and only a fraction of the virions remaining cell-associated will successfully uncoat and contribute to the new replication cycle. We found that while the proportion of inoculum type 3 poliovirus strain Saukett (PV3/S) bound to GMK cells was of the same order as that of PV1/M, the bound PV3/S virions uncoated much less efficiently, as judged by velocity sedimentation analysis of virion disintegration. Rather, the majority of the cell-associated PV3/S viruses remained apparently unaffected for several hours within an unidentified intracellular compartment. Incubation of PV3/S with intestinal trypsin is known to result in selective cleavage of the capsid protein VP1 and striking antigenic changes. Trypsin treatment of stock PV3/S preparations did not affect the infectivity titre or modify single-cycle progeny virus yields significantly. However, the fate of the cell-bound inoculum virus was profoundly altered. Trypsin-treated PV3/S virions (PV3/S-Try) attached to GMK cells less tightly than the untreated PV3/S virus or PV1/M, and a relatively larger proportion of the cell-bound virus eluted to the medium during subsequent incubation at 36 degrees C. However, the fraction of virions remaining cell-associated rapidly disintegrated suggesting efficient uncoating. In accordance with these observations, one step growth curves of PV3/S-Try in all cell lines tested showed lowered eclipse phase titres compared to those obtained with the untreated PV3/S inocula. Similar effects were also demonstrated for type 3 poliovirus strain Sabin while trypsin-sensitive strains of the other two serotypes of poliovirus remained unaffected in this sense. The putative biological significance of the altered sorting of cell-bound PV3/S-Try virions is not known. It might be related to the observations that sensitivity of type 3 poliovirus strains to trypsin is conserved in spite of the fact that the target site of trypsin action is flanked by highly variable motives in an immunodominant antigenic site.
authors.affiliation: Enterovirus Laboratory, National Public Health Institute, Helsinki, Finland.
authors.forename: L
authors.initials: L
authors.lastname: Piirainen
authors.forename: A
authors.initials: A
authors.lastname: Airaksinen
authors.forename: T
authors.initials: T
authors.lastname: Hovi
authors.forename: M
authors.initials: M
authors.lastname: Roivainen
mesh_terms: D000818:Animals; D002213:Capsid / Q000378:metabolism*; D036022:Capsid Proteins; D002460:Cell Line; D002462:Cell Membrane / Q000821:virology; D002522:Chlorocebus aethiops; D006367:HeLa Cells; D006801:Humans; D017955:Poliovirus / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D014357:Trypsin; D014407:Tumor Cells, Cultured; D014709:Vero Cells; D014771:Virion / Q000502:physiology; D014779:Virus Replication
chemical_list: D036022:Capsid Proteins; C442540:VP1 protein, Poliovirus; D014357:Trypsin