Human cytomegalovirus and Herpes Simplex type I virus can engage RNA polymerase I for transcription of immediate early genes.

Ourania N Kostopoulou,Sharan Ananthaseshan,Cecilia Söderberg-Naucler,Mikael S Lindström,Jiri Bartek,Sina Raiss,Vanessa Wilhelmi

doi:10.18632/oncotarget.22106

Abstract

Human cytomegalovirus (HCMV) utilizes RNA polymerase II to transcribe viral genes and produce viral mRNAs. It can specifically target the nucleolus to facilitate viral transcription and translation. As RNA polymerase I (Pol I)-mediated transcription is active in the nucleolus, we investigated the role of Pol I, along with relative contributions of the human Pol II and Pol III, to early phases of viral transcription in HCMV infected cells, compared with Herpes Simplex Virus-1 (HSV-1) and Murine cytomegalovirus (MCMV). Inhibition of Pol I with siRNA or the Pol I inhibitors CX-5461 or Actinomycin D (5nM) resulted in significantly decreased IE and pp65 mRNA and protein levels in human fibroblasts at early times post infection. This initially delayed replication was compensated for later during the replication process, at which stage it didn’t significantly affect virus production. Pol I inhibition also reduced HSV-1 ICP0 and gB transcripts, suggesting that some herpesviruses engage Pol I for their early transcription. In contrast, inhibition of Pol I failed to affect MCMV transcription. Collectively, our results contribute to better understanding of the functional interplay between RNA Pol I-mediated nucleolar events and the Herpes viruses, particularly HCMV whose pathogenic impact ranges from congenital malformations and potentially deadly infections among immunosuppressed patients, up to HCMV’s emerging oncomodulatory role in human tumors.

Highlights

Human cytomegalovirus (HCMV) is a beta herpesvirus that has infected 40% - 100% of the adult population worldwide [1]
Earlier studies have demonstrated that HCMV utilizes RNA polymerase II (Pol II) to transcribe viral genes and produce viral mRNAs [33]
As polymerase I (Pol I) is the specific active polymerase in the nucleolus, and inhibition of rRNA synthesis results in exit of HCMV IE72 and pp65 from the nucleolus and a strong inhibition of HCMV infection [28], we hypothesized that Pol I may play a role in early viral transcription

Summary

Introduction

Human cytomegalovirus (HCMV) is a beta herpesvirus that has infected 40% - 100% of the adult population worldwide [1]. Ganciclovir has been available for treatment and prevention of HCMV infections for almost three decades, this virus still causes concerning morbidity and mortality in stem cell and organ transplant patients and in AIDS patients. Emerging evidence suggests that HCMV is highly prevalent in breast, colon, and prostate cancer, rhabdomyosarcoma, hepatocellular cancer, salivary gland tumors, neuroblastoma and brain tumors (medulloblastoma and glioblastoma) [5,6,7,8,9,10,11,12] This virus is not considered to be oncogenic per se, but rather promotes oncomodulatory functions leading to more aggressive cancer phenotypes and may thereby promote tumor progression. In support of this statement, anti-viral treatment of patients with HCMV positive glioblastoma tumors indicate highly improved patient survival rates [13]

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