Related Experiment Videos
A late adenovirus factor induces eIF-4E dephosphorylation and inhibition of cell protein synthesis
Y Zhang1, D Feigenblum, R J Schneider
1Department of Biochemistry, New York University Medical Center, New York 10016.
Abstract:
Adenovirus prevents host cell protein synthesis during its late phase of replication in large part by causing the underphosphorylation of translation initiation factor eIF-4E, a component of initiation factor eIF-4F (cap-binding protein complex). Late adenovirus mRNAs are preferentially translated because they possess a reduced requirement for eIF-4F. This study continues the characterization of the mechanism by which adenovirus inhibits cellular protein synthesis. First it is shown that adenovirus blocks the addition of phosphate to eIF-4E rather than enhancing its removal, establishing that the virus impairs a signalling pathway or protein kinase activity involved in eIF-4E phosphorylation. It is then shown that shutoff of cell protein synthesis and translation of late viral mRNAs are uncoupled, in that shutoff actually occurs a short time (1 to 3 h) after late adenovirus mRNAs are already undergoing translation. Finally, by using a variety of genetic mutants stalled at different stages in the viral life cycle, it was found that dephosphorylation of eIF-4E and inhibition of cell translation are not caused by early adenovirus gene products acting at late times or by events related to viral DNA replication. Instead, it is shown that inhibition of eIF-4E phosphorylation and cell translation are mediated upon activation of the viral major late transcription unit. These and other results presented indicate that the adenovirus signal which induces eIF-4E dephosphorylation and shutoff of cell protein synthesis is linked either to an activity of one or more late viral polypeptides, to double-stranded RNA produced by opposition of the early and late viral transcription units, or to both.
Insights
Adenovirus inhibits host protein synthesis by preventing eIF-4E phosphorylation. This shutoff is linked to the activation of the viral major late transcription unit, not viral DNA replication.
Area of Science:
- Molecular Biology
- Virology
- Biochemistry
Background:
- Adenovirus replication inhibits host cell protein synthesis during its late phase.
- This inhibition is largely due to the underphosphorylation of the translation initiation factor eIF-4E.
- Late adenovirus mRNAs are preferentially translated due to a reduced dependence on the eIF-4F complex.
Purpose of the Study:
- To further characterize the mechanism by which adenovirus inhibits cellular protein synthesis.
- To determine if adenovirus blocks phosphate addition or enhances removal from eIF-4E.
- To investigate the timing and viral components responsible for eIF-4E dephosphorylation and host protein synthesis shutoff.
Main Methods:
- Investigated eIF-4E phosphorylation status in infected cells.
- Analyzed the temporal relationship between late viral mRNA translation and host shutoff.
- Utilized adenovirus genetic mutants at various life cycle stages.
Main Results:
- Adenovirus blocks phosphate addition to eIF-4E, indicating impairment of a phosphorylation signaling pathway or kinase.
- Host protein synthesis shutoff is uncoupled from late viral mRNA translation, occurring after translation begins.
- eIF-4E dephosphorylation and host translation inhibition are mediated by the activation of the viral major late transcription unit, not early gene products or viral DNA replication.
Conclusions:
- The adenovirus-induced shutoff of host protein synthesis is primarily mediated by the inhibition of eIF-4E phosphorylation.
- This inhibition is triggered by events associated with the activation of the viral major late transcription unit.
- The signal for eIF-4E dephosphorylation and host shutoff may involve late viral polypeptides, double-stranded RNA, or both.