HSV-1 ICP22 Is a Selective Viral Repressor of Cellular RNA Polymerase II-Mediated Transcription Elongation.

Nur Firdaus Isa,Nadiah C Aziz,Olivier Bensaude,Shona Murphy

doi:10.3390/vaccines9101054

Abstract

The Herpes Simplex Virus (HSV-1) immediate-early protein ICP22 interacts with cellular proteins to inhibit host cell gene expression and promote viral gene expression. ICP22 inhibits phosphorylation of Ser2 of the RNA polymerase II (pol II) carboxyl-terminal domain (CTD) and productive elongation of pol II. Here we show that ICP22 affects elongation of pol II through both the early-elongation checkpoint and the poly(A)-associated elongation checkpoint of a protein-coding gene model. Coimmunoprecipitation assays using tagged ICP22 expressed in human cells and pulldown assays with recombinant ICP22 in vitro coupled with mass spectrometry identify transcription elongation factors, including P-TEFb, additional CTD kinases and the FACT complex as interacting cellular factors. Using a photoreactive amino acid incorporated into ICP22, we found that L191, Y230 and C225 crosslink to both subunits of the FACT complex in cells. Our findings indicate that ICP22 interacts with critical elongation regulators to inhibit transcription elongation of cellular genes, which may be vital for HSV-1 pathogenesis. We also show that the HSV viral activator, VP16, has a region of structural similarity to the ICP22 region that interacts with elongation factors, suggesting a model where VP16 competes with ICP22 to deliver elongation factors to viral genes.

Highlights

Suppression of host gene expression during HSV-1 productive infection may dampen host immune responses and increase the cellular resources available for viral gene expression and requires interaction between viral and host factors
We have investigated the ability of the core conserved region (CCR) of ICP22 to induce loss of polymerase II (pol II) carboxyl-terminal domain (CTD) Ser2 phosphorylation, a mark indicative of transcription elongation, by monitoring the effect of ectopic expression of Myc-ICP22CCR on Ser2P in a time-course experiment (Figure 1A)
To understand how ICP22 affects the control of transcription elongation on host genes, we carried out pol II and Ser2P pol II CTD chromatin immunoprecipitation (ChIP)-quantitative PCR (qPCR) on a model cellular gene, KPNB1 (Figure 1B) at 7 hpt of Myc-ICP22CCR as this time point should provide a snapshot of the repressive action of ICP22 on actively-transcribing pol II

Summary

Introduction

Suppression of host gene expression during HSV-1 productive infection may dampen host immune responses and increase the cellular resources available for viral gene expression and requires interaction between viral and host factors. Expression of HSV1 ICP22, one of five immediate early genes, is initiated by the viral tegument transcription activation protein VP16 in the absence of de novo viral protein synthesis [1,2]. Deletion of ICP22 from HSV-1 causes a significant decrease in viral replication and the establishment of latency [3,4]. While ICP22 helps to promote the expression of HSV-1 late viral genes in productive infection, this protein has the opposite effect on the host gene and early viral gene expression [5,6,7,8]. The first 160 residues of the N-terminal region and the

Methods

Results

Conclusion