Herpes Simplex Virus 1 (HSV-1) ICP22 protein directly interacts with cyclin-dependent kinase (CDK)9 to inhibit RNA polymerase II transcription elongation.

Justyna Zaborowska,Clelia Laitem,Peter H Thomas,Sonja Baumli,Peter O'Hare,Shona Murphy,Dawn O'Reilly,Suresh Yenugu

doi:10.1371/journal.pone.0107654

Justyna Zaborowska, Clelia Laitem + Show 6 more

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https://doi.org/10.1371/journal.pone.0107654

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Abstract

The Herpes Simplex Virus 1 (HSV-1)-encoded ICP22 protein plays an important role in viral infection and affects expression of host cell genes. ICP22 is known to reduce the global level of serine (Ser)2 phosphorylation of the Tyr1Ser2Pro3Thr4Ser5Pro6Ser7 heptapeptide repeats comprising the carboxy-terminal domain (CTD) of the large subunit of RNA polymerase (pol) II. Accordingly, ICP22 is thought to associate with and inhibit the activity of the positive-transcription elongation factor b (P-TEFb) pol II CTD Ser2 kinase. We show here that ICP22 causes loss of CTD Ser2 phosphorylation from pol II engaged in transcription of protein-coding genes following ectopic expression in HeLa cells and that recombinant ICP22 interacts with the CDK9 subunit of recombinant P-TEFb. ICP22 also interacts with pol II in vitro. Residues 193 to 256 of ICP22 are sufficient for interaction with CDK9 and inhibition of pol II CTD Ser2 phosphorylation but do not interact with pol II. These results indicate that discrete regions of ICP22 interact with either CDK9 or pol II and that ICP22 interacts directly with CDK9 to inhibit expression of host cell genes.

Highlights

Herpesviruses are significant human pathogens associated with a range of mild to severe diseases
Phosphorylation of Tyr1 is reduced (Figure 1C). These results indicate that ICP22 affects the global levels of phosphorylation of the serine at position 2 and the tyrosine at position 1 of the polymerase II (pol II) carboxy-terminal domain (CTD) heptapeptide in HeLa cells
The effects on pol II and pol II CTD Ser2 phosphorylation are similar to those caused by small molecule inhibitors of CDK9, like DRB [20]. In support of this notion, ectopic expression of ICP22 inhibits pol II association with the b-actin gene beyond +1000 bp and pol II CTD Ser2 phosphorylation (Figure S3 in File S1), as we have previously shown for DRB using the same cells [20]

Summary

Introduction

Herpesviruses are significant human pathogens associated with a range of mild to severe diseases. Herpes Simplex Virus (HSV) infections are generally self-limiting in healthy individuals, they can cause inflammation of the brain and eye and pose a significant mortality risk to infants and immuno-compromised adults [1,2,3,4,5]. The HSV ICP22 protein (encoded by the US1 gene) is required for efficient viral replication, infection and latency in cell and animal models and regulates expression of some viral late genes [6,7,8,9]. ICP22 counteracts the effect of IFN-b and has been implicated in the down-regulation of cellular genes [9,10,11,12]. An N-terminal-truncated protein called US1.5 is expressed from the US1 gene [12]. US1.5 is dispensable for both efficient acute virus replication and virus-induced chaperone-enriched (VICE) domain formation [9]

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