2005 Fiscal Year Final Research Report Summary
Emergence of pandemic influenza A virus and function of NA gene in determination of host range
| Project/Area Number |
16590390
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Virology
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| Research Institution | University of Shizuoka |
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Principal Investigator |
SUZUKI Takashi University of Shizuoka, Department of Biochemistry, Associate Professor, 薬学部, 助教授 (20240947)
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| Project Period (FY) |
2004 – 2005
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| Keywords | sialidase / influenza virus / neuraminidase / low-pH stability / NA gene / pandemic influenza |
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| Research Abstract |
N2 neuraminidase (NA) genes of the 1957 and 1968 pandemic influenza virus strains possessed avian-like low-pH stability of sialidase activity, unlike most epidemic strains. We generated four reverse-genetic viruses from a genetic background of A/WSN/33 (H1N1) that included parental N2 NAs of 1968 pandemic (H3N2) and epidemic (H2N2) strains or their counterpart N2 NAs in which low-pH stability of the sialidase activity was changed by substitutions of one or two amino acid residues. We found that the transfectant viruses bearing low-pH-stable sialidase (WSN/Stable-NAs) showed 25 to 80-times greater ability to replicate in Madin-Darby canine kidney (MDCK) cells than did the transfectant viruses bearing low-pH-unstable sialidase (WSN/Unstable-NAs). Enzymatic activities of WSN/Stable-NAs were detected in endosome of MDCK cells after 90 min of virus internalization by in situ fluorescent detection with 5-bromo-4-chloro-indole-3-yl-α-N-acetylneuraminic acid and Fast Red Violet LB. Inhibition of sialidase activity of WSN/Stable-NAs on the endocytic pathway by pretreatment with 4-guanidino-2,4-dideoxy-N-acetylneuraminic acid (Zanamivir) resulted in a significant decrease in progeny viruses. In contrast, the enzymatic activities of WSN/Unstable-NAs, replication of which had no effect on pretreatment with Zanamivir, were undetectable in cells under the same condition. Hemadsorption assay on each transfectant virus-infected cells revealed that the low-pH-stability of the sialidase had no effect on the process of removing sialic acid from hemagglutinin in the Golgi regions. Moreover, high titers of viruses were recovered from the lungs of mice infected with WSN/Stable-NAs on day 3 after intranasal inoculation, but WSN/Unstable-NAs were cleared from the lungs of the mice. These results indicate that sialidase activity in late endosome/lysosome traffic enhances influenza A virus replication.
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