2005 Fiscal Year Final Research Report Summary
Study of host regulation by insect viruses
| Project/Area Number |
15580044
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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 |
Applied entomology
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| Research Institution | RIKEN (The Institute of Physical and Chemical Research) |
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Principal Investigator |
KANG WonKyung RIKEN, Discovery Research Institute, Molecular Entomology Laboratory, Senior Research Scientist, 松本分子昆虫学研究室, 先任研究員 (30291917)
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| Project Period (FY) |
2003 – 2005
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| Keywords | Bombyx mori nucleopolyhedrovirus / Host regulation / Nuclear export / Ubiquitin ligase / Foci formation / BRO / IE2 / ORF8 |
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| Research Abstract |
Baculoviruses that infect insects are known to control the host for their efficient and successful infection, but the mechanisms are still not fully understood. This study aims to understand the mechanism of host regulation by baculoviruses. In this study, we characterized three genes of Bambyx mori nucleopolyhedrovirus (BmNPV). First, we analyzed the localization of BmNPV IE2 that has been shown to contain ubiquitin ligase E3 activity. The production of BmNPV IE2 decreases and the nuclear foci formed by IE2 disappear as the infection progresses. Using a proteasome inhibitor and a defective mutant in E3 activity, we showed that IE2 was ubiquitinated and then degraded by the proteasome pathway. Our results suggest that the E3 activity of BmNPV IE2 might regulate the protein level and cellular localization of IE2 during infection. Secondly, we examined the localization of BmNPV ORF8 protein since it has been reported to localize to specific nuclear sites where BmNPV replication occurs. Using gfp-fused orf8, we showed that IE1 and hr facilitate the localization of BmNPV ORF8 to specific nuclear sites. Finally, we revealed that BmNPV BRO proteins shuttle between the nucleus and cytoplasm using inhibitors. Mutations on the leucine-rich region of BRO proteins resulted in nuclear accumulation of transiently expressed proteins, suggesting that this region functions as a CRM1-dependent nuclear export signal (NES). On the contrary, mutant BRO-D with an altered NES did not show nuclear accumulation in infected cells, although protein production seemed to be reduced. RT-PCR analysis showed that the lower level of protein production was due to a reduction in RNA synthesis. Together, our results strongly suggest that these genes play important roles in BmNPV replication. To more completely understand the molecular mechanisms, further investigations including search for interacting host factors are currently underway.
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