Herpes Simplex Virus gE/gI Must Accumulate in the trans -Golgi Network at Early Times and Then Redistribute to Cell Junctions To Promote Cell-Cell Spread

Abstract

Herpes simplex virus (HSV) glycoprotein heterodimer gE/gI is necessary for virus spread in epithelial and neuronal tissues. Deletion of the relatively large gE cytoplasmic (CT) domain abrogates the ability of gE/gI to mediate HSV spread. The gE CT domain is required for the sorting of gE/gI to the trans-Golgi network (TGN) in early stages of virus infection, and there are several recognizable TGN sorting motifs grouped near the center of this domain. Late in HSV infection, gE/gI, other viral glycoproteins, and enveloped virions redistribute from the TGN to epithelial cell junctions, and the gE CT domain is also required for this process. Without the gE CT domain, newly enveloped virions are directed to apical surfaces instead of to cell junctions. We hypothesized that the gE CT domain promotes virus envelopment into TGN subdomains from which nascent enveloped virions are sorted to cell junctions, a process that enhances cell-to-cell spread. To characterize elements of the gE CT domain involved in intracellular trafficking and cell-to-cell spread, we constructed a panel of truncation mutants. Specifically, these mutants were used to address whether sorting to the TGN and redistribution to cell junctions are necessary, and sufficient, for gE/gI to promote cell-to-cell spread. gE-519, lacking 32 C-terminal residues, localized normally to the TGN early in infection and then trafficked to cell junctions at late times and mediated virus spread. By contrast, mutants gE-495 (lacking 56 C-terminal residues) and gE-470 (lacking 81 residues) accumulated in the TGN but did not traffic to cell junctions and did not mediate cell-to-cell spread. A fourth mutant, gE-448 (lacking most of the CT domain), did not localize to cell junctions and did not mediate virus spread. Therefore, the capacity of gE/gI to promote cell-cell spread requires early localization to the TGN, but this is not sufficient for virus spread. Additionally, gE CT sequences between residues 495 and 519, which contain no obvious cell sorting motifs, are required to promote gE/gI traffic to cell junctions and cell-to-cell spread.Herpes simplex virus (HSV) commonly infects mucosal and ocular epithelial tissues, causing oral and genital lesions. During primary infection in epithelial tissues, HSV enters sensory and autonomic neurons where the virus replicates and can establish latency. Periodic reactivation in neurons leads to transient replication and spread along neuronal axons, leading to the reinfection of epithelial tissues. This cycle of HSV spread in epithelial tissues, entry into neurons, spread to sensory ganglia, and return to epithelial tissues involves directed intracellular transport to specific cell surfaces and extremely rapid spread between cells (reviewed in reference 23). As evidence of the speed of this process, HSV can spread from a single infected cell to over 250 cells in the cornea within 48 h (34). HSV is largely cell associated and spreads across cell junctions and resists the effects of high concentrations of virus-neutralizing antibodie...

Function of glycoprotein E of herpes simplex virus requires coordinated assembly of three tegument proteins on its cytoplasmic tail

“…The limiting membranes of these vesicles are thought to contain gE, with its tail extended into the cytoplasm. Alterations in the tail of gE reduce the numbers of virions at cell junctions, and they instead accumulate on apical surfaces (2,6,17,35). This misrouting results in smaller plaques and reduces epithelial cell-to-cell spread in vivo and in vitro.…”

Herpes Simplex Virus Type 1 Glycoprotein E Mediates Retrograde Spread from Epithelial Cells to Neurites

“…The cell-to-cell spread defects of HSV-1 gE mutants have been reported mainly for polarized cell types (25,30,41,59). In an electron microscopy study, WT virions localized to the basolateral surface of polarized HEC-1-A and HaCaT cells, whereas gE-deleted virions localized to the apical surface (24,33).…”

“…Mutations in either the cytoplasmic tail or ectodomain of gE can produce a small plaque phenotype equivalent to that of gE-deleted viruses (25,41,44). The cytoplasmic tail of gE contains tyrosine-signaling motifs that are required to target virions to cell junctions, the sites of cell-to-cell spread (25,33,59). The gE ectodomain also promotes efficient cell-to-cell spread, possibly by interacting with an unidentified ligand at cell junctions (20,41).…”

The C Terminus of the Large Tegument Protein pUL36 Contains Multiple Capsid Binding Sites That Function Differently during Assembly and Cell Entry of Herpes Simplex Virus

“…According to the most widely accepted secondary reenvelopment model, nuclear capsids traverse the nuclear membranes by primary envelopment at the inner nuclear membrane and primary fusion with the membranes of the endoplasmic reticulum to enter the cytosol. Inner tegument proteins may bind to nuclear or cytosolic capsids, while outer tegument proteins can associate with the cytosolic tails of viral membrane proteins that are targeted to the sites of secondary envelopment containing marker proteins of the trans-Golgi network (TGN) as well as of early or late endosomes (9,11,20,34,39,43,86,93,96,97,109,112,115). Partially tegumented capsids may then travel to these cytoplasmic membranes, and interactions between inner and outer teguments could mediate secondary envelopment, giving rise to enveloped virions enclosed by a host membrane.…”