Budding site of Sendai virus in polarized epithelial cells is one of the determinants for tropism and pathogenicity in mice.
Wild-type Sendai virus fusion (F) glycoprotein requires trypsin or a trypsin-like protease for cleavage-activation in vitro and in vivo, respectively. The virus is pneumotropic in mice and buds at the apical domain of bronchial epithelial cells. On the other hand, the F protein of the protease-activation host range mutant, F1-R, is cleaved by ubiquitous proteases present in different cell lines and in various organs of mice. F1-R causes a systemic infection in mice and the mutant buds bipolarly at the apical and basolateral domains of infected epithelial cells. The enhanced cleavability of the F protein of F1-R has been shown to be a primary determinant for pantropism. Additionally, it has been postulated that bipolar budding of F1-R is required for the systemic spread of the virus and it has been attributed to mutations in the matrix (M) protein of F1-R (Tashiro et al., Virology 184, 227-234, 1991). In this study protease-activation mutants (KD series) were isolated from wild-type virus. They were revealed to bud at the apical domain, and the F protein was cleaved by ubiquitous proteases in mouse organs. The KD mutants were exclusively pneumotropic in mice following intranasal infection, whereas they caused a generalized infection when inoculated directly into the circulatory system. Comparative nucleotide sequence analysis of the F gene of the KD mutants revealed that the deduced amino acid substitutions responsible for enhanced cleavability of the F protein occurred removed from the cleavage site. Mutations were not at all found in the M gene of the KD mutants analyzed, in support of the role of the M protein of F1-R and of a revertant T-9 derived from the latter in bipolar budding. These results suggest that bipolar budding is necessary for the systemic spread of F1-R from the lungs and that apical budding by wild-type virus and the KD mutants leads to respiratory infections. Differential budding at the primary target of infection, in addition to the cleavage-activation of the F protein in mouse organs, is therefore also a determinant for tropism and pathogenicity of Sendai virus in mice.
Tashiro
M
M
Department of Virology, Jichi Medical School, Tochigi-ken, Japan.
Seto
J T
JT
Choosakul
S
S
Yamakawa
M
M
Klenk
H D
HD
Rott
R
R
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D016764:Cell Polarity; D004252:DNA Mutational Analysis; D004285:Dogs; D004848:Epithelium / Q000382:microbiology; D005814:Genes, Viral; D008168:Lung / Q000382:microbiology; D051379:Mice; D008969:Molecular Sequence Data; D009924:Organ Culture Techniques; D010222:Parainfluenza Virus 1, Human / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity*; D014357:Trypsin / Q000494:pharmacology; D014760:Viral Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015678:Viral Structural Proteins / Q000235:genetics; D014779:Virus Replication
D014760:Viral Fusion Proteins; D015678:Viral Structural Proteins; D014357:Trypsin