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fredag 24 oktober 2014

EBOV-interaktomitutkimus vahvisti DNA topoisomeraasin TOP1:n cofaktoriosan EBOLreplikaatiossa

22 lokakuuta 2014 

 LC-MS/MS analysis identified 65 candidate proteins that co-precipitated as the EBOL interactome. Of these, the researchers chose nuclear protein DNA topoisomerase 1 (TOP1) for further investigation because previous studies had implicated this enzyme in RNA viral replication. TOP1 first unwinds the nucleic acid helical structure to allow transcription and replication by cleaving phosphodiester bridges, and it then repairs the cut ends. To begin, Takahashi and co-authors used Western blotting to confirm that TOP1 co-precipitated with EBOL. They also revealed cellular location with immunofluorescence—demonstrating that, following treatment with Venus-EBOL, TOP1 co-localized in the cytoplasm as well as in the nucleus.

To study the effect of TOP1 on viral replication, the team infected cells with an EBOV mutant in the presence or absence of small interfering TOP1 RNA (siTOP1). They found that treatment with siTOP1 downregulated TOP1 and reduced viral replication. Treatment did not, however, affect in vitro infection using two other viruses, vesicular stomatitis virus (VSV) or influenza virus, suggesting the response was EBOV-specific. Furthermore, using a mini-genome assay to investigate RNA-dependent polymerase activity, the scientists found that knockdown of TOP1 reduced EBOV enzyme activity but not that of the influenza virus.
In order to understand and further confirm the interaction between EBOL and the host cell protein, Takahashi et al. next examined whether TOP1’s DNA and RNA phosphodiester bridge-cleaving action was involved in promoting viral replication. Using mutant TOP1 constructs, the researchers found that following siTOP1 downregulation of cellular EBOL polymerase, transfection with a TOP1 mutant containing the phosphodiester bridge-cleaving activity restored activity of the viral enzyme. For further confirmation of the EBOL co-factor in EBOV replication, the researchers saw that treating infected HEK293 cells with irinotecan (CPT-11) and topotecan, inhibitors of TOP1, also reduced specific polymerase activity.
The authors propose that information arising from the characterization of the EBOV interactome in host cells will aid in drug discovery for the treatment of this deadly disease.

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