Oncogenic Herpesvirus Utilizes Stress-Induced Cell Cycle Checkpoints for Efficient Lytic Replication.

Giuseppe Balistreri,Marikki Laiho,Olli Kallioniemi,Ilkka Julkunen,Markku Varjosalo,Lauri Lyly,Karita Peltonen,Johanna Viiliäinen,Sampsa Hautaniemi,Grzegorz Sarek,Jussi Taipale,Juha Rantala,Pirita Pekkonen,Mari Teesalu,Päivi M Ojala,Denis E Kainov ,Mikko Turunen,K Ojala ,Raquel Díaz ,Oxana V Denisova

doi:10.1371/journal.ppat.1005424

Abstract

Kaposi’s sarcoma herpesvirus (KSHV) causes Kaposi’s sarcoma and certain lymphoproliferative malignancies. Latent infection is established in the majority of tumor cells, whereas lytic replication is reactivated in a small fraction of cells, which is important for both virus spread and disease progression. A siRNA screen for novel regulators of KSHV reactivation identified the E3 ubiquitin ligase MDM2 as a negative regulator of viral reactivation. Depletion of MDM2, a repressor of p53, favored efficient activation of the viral lytic transcription program and viral reactivation. During lytic replication cells activated a p53 response, accumulated DNA damage and arrested at G2-phase. Depletion of p21, a p53 target gene, restored cell cycle progression and thereby impaired the virus reactivation cascade delaying the onset of virus replication induced cytopathic effect. Herpesviruses are known to reactivate in response to different kinds of stress, and our study now highlights the molecular events in the stressed host cell that KSHV has evolved to utilize to ensure efficient viral lytic replication.

Highlights

Kaposi’s sarcoma-associated herpesvirus (KSHV) is a human tumor virus in the family of gamma2-herpesviruses
Our study highlights the key molecular host cell events that KSHV has evolved to utilize for efficient viral lytic replication: the activation of p53 and upregulation of p21, which slows down the cell cycle, but promotes viral replication and transcription of viral lytic genes
To identify novel regulators of KSHV reactivation we performed a small interfering RNA (siRNA) screen using a custom-made siRNA library targeting 615 human genes with Gene Ontology (GO) annotations related to epigenetics, chromatin remodeling/maintenance, and co-regulatory functions, and consisting of two independent siRNAs for each gene [32]

Summary

Introduction

Kaposi’s sarcoma-associated herpesvirus (KSHV) is a human tumor virus in the family of gamma2-herpesviruses. KSHV genome consists of linear double-stranded DNA (dsDNA), and like other herpesviruses, the virus displays two modes of infection in the infected cells, the latent and lytic replication phase. The latent infection (latency) provides an immunologically silent mode of persistence, whereas the lytic replication phase allows replication and production of new virions to be shed and transmitted to new cells and hosts. The KSHV-associated tumors typically show low level of virus reactivation [4,5], epidemiological studies support the importance of lytic replication in the initiation and progression of KS [6,7,8]. KSHV reactivation can be chemically induced e.g. with certain kinase agonists (TPA) and chemical inhibitors affecting histone acetylation (HDAC inhibitors) or DNA methylation (reviewed in [26])

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