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Published on: November 12, 2015
Promyelocytic leukemia protein isoform II inhibits infection by human adenovirus type 5 through effects on HSP70 and
Zeenah Atwan1, Jordan Wright1, Andrew Woodman1
1University of Warwick, School of Life Sciences, Gibbet Hill Road, Coventry CV4 7AL, UK.
Abstract:
Promyelocytic leukemia (PML) proteins have been implicated in antiviral responses but PML and associated proteins are also suggested to support virus replication. One isoform, PML-II, is required for efficient transcription of interferon and interferon-responsive genes. We therefore investigated the PML-II contribution to human adenovirus 5 (Ad5) infection, using shRNA-mediated knockdown. HelaΔII cells showed a 2-3-fold elevation in Ad5 yield, reflecting an increase in late gene expression. This increase was found to be due in part to the reduced innate immune response consequent upon PML-II depletion. However, the effect was minor because the viral E4 Orf3 protein targets and inactivates this PML-II function. The major benefit to Ad5 in HelaΔII cells was exerted via an increase in HSP70; depletion of HSP70 completely reversed this replicative advantage. Increased Ad5 late gene expression was not due either to the previously described inhibition of inflammatory responses by HSP70 or to effects of HSP70 on major late promoter or L4 promoter activity, but might be linked to an observed increase in E1B 55K, as this protein is known to be required for efficient late gene expression. The induction of HSP70 by PML-II removal was specific for the HSPA1B gene among the HSP70 gene family and thus was not the consequence of a general stress response. Taken together, these data show that PML-II, through its various actions, has an overall negative effect on the Ad5 lifecycle.
Insights
Promyelocytic leukemia protein II (PML-II) negatively impacts adenovirus 5 (Ad5) replication. Its depletion enhances Ad5 yield by increasing HSP70, a key factor for viral gene expression.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Promyelocytic leukemia (PML) proteins play complex roles in viral infections, potentially aiding or inhibiting replication.
- PML isoform II (PML-II) is crucial for interferon-stimulated gene transcription, suggesting an antiviral role.
- The interaction between PML proteins and human adenovirus 5 (Ad5) requires further investigation.
Purpose of the Study:
- To elucidate the specific role of PML-II in Ad5 infection.
- To determine how PML-II influences Ad5 replication and viral gene expression.
Main Methods:
- Utilized shRNA-mediated knockdown to deplete PML-II in Hela cells (HelaΔII).
- Quantified Ad5 yield and analyzed late gene expression.
- Investigated the involvement of innate immune responses, viral protein E4 Orf3, heat shock protein 70 (HSP70), and specific viral promoters.
Main Results:
- PML-II depletion led to a 2-3 fold increase in Ad5 yield and enhanced late gene expression.
- Reduced innate immune response and increased HSP70 expression contributed to higher Ad5 yield.
- The viral E4 Orf3 protein partially counteracted the effect of PML-II depletion on the immune response.
- Increased HSP70 levels, specifically HSPA1B, were the primary driver of Ad5 replication advantage, potentially via an increase in E1B 55K protein.
Conclusions:
- PML-II exerts an overall negative effect on the Ad5 lifecycle.
- HSP70 induction upon PML-II depletion is a major mechanism supporting Ad5 replication.
- Ad5 has evolved mechanisms, like E4 Orf3, to counteract PML-II's antiviral functions.
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