ICP0 dismantles microtubule networks in herpes simplex virus-infected cells.

Mingyu Liu,Edward E Schmidt,William P Halford,Cheryl A Stoddart

doi:10.1371/journal.pone.0010975

Mingyu Liu, Edward E Schmidt + Show 2 more

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https://doi.org/10.1371/journal.pone.0010975

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Abstract

Infected-cell protein 0 (ICP0) is a RING finger E3 ligase that regulates herpes simplex virus (HSV) mRNA synthesis, and strongly influences the balance between latency and replication of HSV. For 25 years, the nuclear functions of ICP0 have been the subject of intense scrutiny. To obtain new clues about ICP0's mechanism of action, we constructed HSV-1 viruses that expressed GFP-tagged ICP0. To our surprise, both GFP-tagged and wild-type ICP0 were predominantly observed in the cytoplasm of HSV-infected cells. Although ICP0 is exclusively nuclear during the immediate-early phase of HSV infection, further analysis revealed that ICP0 translocated to the cytoplasm during the early phase where it triggered a previously unrecognized process; ICP0 dismantled the microtubule network of the host cell. A RING finger mutant of ICP0 efficiently bundled microtubules, but failed to disperse microtubule bundles. Synthesis of ICP0 proved to be necessary and sufficient to disrupt microtubule networks in HSV-infected and transfected cells. Plant and animal viruses encode many proteins that reorganize microtubules. However, this is the first report of a viral E3 ligase that regulates microtubule stability. Intriguingly, several cellular E3 ligases orchestrate microtubule disassembly and reassembly during mitosis. Our results suggest that ICP0 serves a dual role in the HSV life cycle, acting first as a nuclear regulator of viral mRNA synthesis and acting later, in the cytoplasm, to dismantle the host cell's microtubule network in preparation for virion synthesis and/or egress.

Highlights

Herpes simplex virus 1 (HSV-1) is a large, dsDNA virus that is capable of alternating between two programs of gene expression that lead to a productive or silent infection
Infected-cell protein 0 (ICP0)’s presence in the cytoplasm of herpes simplex virus (HSV)-infected cells has become undeniable, and it is well established that ICP0 is incorporated into the tegument of HSV-1 virions [26,27,28,29]. It remains unclear if ICP0 mediates a specific function in the cytoplasm of HSV-1 infected cells, or if ICP0 translocates to the cytoplasm for the sole purpose of its incorporation into HSV-1 virions [26,27,28,29]
Chimeric ICP0GFP genes were introduced into the LAT-ICP0 locus of HSV-1 strain KOS by homologous recombination to yield HSV-1 02GFP, 0+GFP12, 0+GFP24, or 0+GFP105 (Fig. 1B)

Summary

Introduction

Herpes simplex virus 1 (HSV-1) is a large, dsDNA virus that is capable of alternating between two programs of gene expression that lead to a productive or silent infection. One of HSV’s immediate-early (IE) proteins, ICP0, is a positive regulator whose synthesis represents a key step by which HSV ‘‘decides’’ whether or not an infection is likely to culminate in the production of new infectious virus At MOIs below 0.1 pfu per cell, the same ICP02 viruses establish quiescent infections in 99% of the cells they infect [4,5,6]. ICP0 potentiates ICP4’s function as a transcriptional activator of HSV mRNA synthesis [7,8,9]; 2. ICP0’s E3 ubiquitin ligase activity triggers the dispersal of pro-myelocytic leukemia (PML) nuclear bodies [13,14], which may contribute to the formation of adjacent, subnuclear replication compartments [15,16]

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