Herpes Simplex Virus Organizes Cytoplasmic Membranes To Form a Viral Assembly Center in Neuronal Cells

Abstract

Herpes simplex virus (HSV) is a neuroinvasive virus that has been used as a model organism for studying common properties of all herpesviruses. HSV induces host organelle rearrangement and forms multiple, dispersed assembly compartments in epithelial cells, which complicates the study of HSV assembly. In this study, we show that HSV forms a visually distinct unitary cytoplasmic viral assembly center (cVAC) in both cancerous and primary neuronal cells that concentrates viral structural proteins and is a major site of capsid envelopment. The HSV cVAC also concentrates host membranes that are important for viral assembly, such as Golgi- and recycling endosome-derived membranes. Lastly, we show that HSV cVAC formation and/or maintenance depends on an intact microtubule network and a viral tegument protein, pUL51. Our observations suggest that the neuronal cVAC is a uniquely useful model to study common herpesvirus assembly pathways, and cell-specific pathways for membrane reorganization. Importance Herpesvirus particles are complex and contain many different proteins that must come together in an organized and coordinated fashion. Many viruses solve this coordination problem by creating a specialized assembly factory in the host cell, and the formation of such factories provides a promising target for interfering with virus production. Herpes simplex virus 1 (HSV-1) infects several types of cells, including neurons, but has not previously been shown to form such an organized factory in the non-neuronal cells in which its assembly has been best studied. Here we show that HSV-1 forms an organized assembly factory in neuronal cells, and we identify some of the viral and host cell factors that are important for its formation.

Subcellular Organization of Viral Particles During Maturation of Nucleus-Forming Jumbo Phage

“…Assembly of viruses in eukaryotes typically occurs in defined subcellular compartments referred to as assembly factories or virus assembly centers (VACs) [1, 10]. For example, many eukaryotic viruses complete their final assembly at the plasma membrane, where high concentrations of viral proteins accumulate before being incorporated to form the mature virion.…”

“…Subcellular organization is an important trait in all domains of cellular life, allowing cells to carry out their myriad required functions faithfully and efficiently, and also plays a key role in the replication of viruses [1-4]. Upon infection of a host cell, many eukaryotic viruses manipulate host proteins and components of various organelles such as the Golgi apparatus and endoplasmic reticulum to form replication factories in which they can safely and efficiently replicate their genomes [5-9].…”

“…Upon infection of a host cell, many eukaryotic viruses manipulate host proteins and components of various organelles such as the Golgi apparatus and endoplasmic reticulum to form replication factories in which they can safely and efficiently replicate their genomes [5-9]. They also assemble mature viral particles in specific subcellular compartments [1, 10]. Despite bacteria generally lacking organelles to manipulate and the longstanding assumption that bacteriophage replication is spatially disorganized, recent work suggests that some phages reproduce by forming replication factories and display a high level of subcellular organization within their host cells [11-20].…”

“…While we are now beginning to appreciate the subcellular complexity of nucleus-forming bacteriophages and its potential effects on viral speciation, less is known about the final stages of phage particle assembly. The assembly and maturation of many eukaryotic viruses are known to occur in defined subcellular compartments [1-9]. In contrast, the major steps of tailed phage maturation, which involves separate assembly of the phage tail and capsid, followed by viral DNA packaging and finally attachment of the phage head and tail, has been observed proceeding in an apparently random manner throughout the cell, leading to a random distribution of complete phage particles filling the host cytoplasm before lysis [30-33].…”

Localization of the WD Repeat-Containing Protein 5 to the Virion Assembly Compartment Facilitates Human Cytomegalovirus Assembly

“…Previously, the vAC had been thought to represent a unique structure associated with HCMV infection that was not described in other herpesviruses (25). However, a recent study showed that herpes simplex virus 1 (HSV-1) forms juxtanuclear assembly compartments similar to the HCMV vAC in primary mouse neurons and human neuron-derived cells, but not in fibroblasts or epithelial cells (26). Although not essential for virion production, vAC formation has been shown to be necessary for efficient HCMV virion assembly and maturation.…”