Entrapment of Viral Capsids in Nuclear PML Cages Is an Intrinsic Antiviral Host Defense against Varicella-Zoster Virus

Mike Reichelt,Li Wang,Armin Baiker,Nandini Sen,Ann M Arvin,Leigh Zerboni,Adel M Nour,John Perrino,Marvin Sommer,Roger Everett

doi:10.1371/journal.ppat.1001266

Abstract

The herpesviruses, like most other DNA viruses, replicate in the host cell nucleus. Subnuclear domains known as promyelocytic leukemia protein nuclear bodies (PML-NBs), or ND10 bodies, have been implicated in restricting early herpesviral gene expression. These viruses have evolved countermeasures to disperse PML-NBs, as shown in cells infected in vitro, but information about the fate of PML-NBs and their functions in herpesvirus infected cells in vivo is limited. Varicella-zoster virus (VZV) is an alphaherpesvirus with tropism for skin, lymphocytes and sensory ganglia, where it establishes latency. Here, we identify large PML-NBs that sequester newly assembled nucleocapsids (NC) in neurons and satellite cells of human dorsal root ganglia (DRG) and skin cells infected with VZV in vivo. Quantitative immuno-electron microscopy revealed that these distinctive nuclear bodies consisted of PML fibers forming spherical cages that enclosed mature and immature VZV NCs. Of six PML isoforms, only PML IV promoted the sequestration of NCs. PML IV significantly inhibited viral infection and interacted with the ORF23 capsid surface protein, which was identified as a target for PML-mediated NC sequestration. The unique PML IV C-terminal domain was required for both capsid entrapment and antiviral activity. Similar large PML-NBs, termed clastosomes, sequester aberrant polyglutamine (polyQ) proteins, such as Huntingtin (Htt), in several neurodegenerative disorders. We found that PML IV cages co-sequester HttQ72 and ORF23 protein in VZV infected cells. Our data show that PML cages contribute to the intrinsic antiviral defense by sensing and entrapping VZV nucleocapsids, thereby preventing their nuclear egress and inhibiting formation of infectious virus particles. The efficient sequestration of virion capsids in PML cages appears to be the outcome of a basic cytoprotective function of this distinctive category of PML-NBs in sensing and safely containing nuclear aggregates of aberrant proteins.

Highlights

Promyelocytic leukemia protein (PML) is a major organizing component of structures that are referred to as PML nuclear bodies (PML-NBs) or nuclear domain 10 (ND10) bodies [1,2,3]
PML cages containing virion capsids were found in VZVinfected neurons and satellite cells in human sensory ganglia and in skin cells, which are major targets during varicella-zoster virus (VZV) pathogenesis
We found that cages formed by PML isoform IV sequestered both the virion capsids of VZV, which is a neurotropic herpesvirus, and the mutant Huntington’s disease protein

Summary

Introduction

Promyelocytic leukemia protein (PML) is a major organizing component of structures that are referred to as PML nuclear bodies (PML-NBs) or nuclear domain 10 (ND10) bodies [1,2,3]. These nuclear bodies are heterogenous in size, shape and molecular composition [4,5,6], are prominent in most mammalian cell types and participate in many basic cellular functions, including transcriptional regulation [7], DNA repair [8] and apoptosis [9,10,11,12]. While little is known about the tissue or cell specific patterns of expression of individual PML isoforms, these nonconserved PML regions are of interest for their likely involvement in isoform-dependent functions within particular cell types and in the response to changing intracellular or extracellular conditions [17]

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