Intact Microtubules Support Adenovirus and Herpes Simplex Virus Infections

Abstract

Capsids and the enclosed DNA of adenoviruses, including the species C viruses adenovirus type 2 (Ad2) and Ad5, and herpesviruses, such as herpes simplex virus type 1 (HSV-1), are targeted to the nuclei of epithelial, endothelial, fibroblastic, and neuronal cells. Cytoplasmic transport of fluorophore-tagged Ad2 and immunologically detected HSV-1 capsids required intact microtubules and the microtubule-dependent minus-enddirected motor complex dynein-dynactin. A recent study with epithelial cells suggested that Ad5 was transported to the nucleus and expressed its genes independently of a microtubule network. To clarify the mechanisms by which Ad2 and, as an independent control, HSV-1 were targeted to the nucleus, we treated epithelial cells with nocodazole ( Many viruses, including adenoviruses (Ads) and herpesviruses, spread by intracellular transport within infected host cells, thus increasing the viral load in target organs and possibly causing severe disease (44). The 51 human Ad serotypesclassified into six species (A to F)-have distinct tropisms (19). For example, Ad type 2 (Ad2) and Ad5 (species C) and Ad3 (species B) are associated with upper-airway infections. Other serotypes are linked to epidemic keratoconjunctivitis (species D), pneumonia (species E), enteric infections (species A and F), or infections of hematopoietic cells (41). The Herpesviridae family consists of the alpha-, beta-and gammaherpesviruses. Like Ads, alphaherpesviruses, including herpes simplex virus type 1 (HSV-1), infect different cell types both in cultures and in their hosts. After infection of mucosal or damaged cutaneous epithelium, these neurotropic viruses establish latent infections, primarily in sensory ganglia, that, upon reactivation, lead to recurrent epidermal lesions (40, 55). The ability to infect a broad range of postmitotic cells has made both Ads and herpesviruses useful gene delivery vehicles (21) that are currently being evaluated in clinical trials (29,39). For their application as therapeutic vectors and to identify new potential targets for antiviral therapy, it is crucial to understand how the genomes are targeted to the nucleus.The entry mechanisms for Ads and herpesviruses have been well studied. Ads are internalized by receptor-mediated endocytosis that is dependent on F actin and leave the endosomal pathway at various sites (recently reviewed in reference 11). The species C Ads, including Ad2 and Ad5, exit from a slightly acidic compartment of pH 6 at about 10 min postentry (16, 42), whereas Ad7 (species B) has been reported to escape from acidic late endosomes and lysosomes (32). In contrast, HSV-1 delivers its capsids into the cytosol upon fusion of the viral envelope with the plasma membrane (45,46). Both viruses then target their capsids to the cell nucleus, uncoat, and inject the enclosed linear double-stranded DNA genomes through the nuclear pores into the nucleoplasm for replication (14,35,53). A number of electron microscopy studies have shown that cytoplasmic capsids of both species C Ads and alpha...

HSV trafficking and development of gene therapy vectors with applications in the nervous system

“…6,77 Upon entry into the cell, HSV-1 capsids are propelled toward the minus end of microtubules 78 through an interaction of the HSV-1 tegument protein UL34 with cellular dynein. [79][80][81] The capsid docks at nuclear pore complexes (NPC) and the viral genome is deposited into the nucleus. 82 Following nuclear entry, the tegument protein VP16, in coordination with the cellular proteins Oct-1 and HCF-111, 83 initiates transcription of the five viral immediate-early (IE) genes, ICP0, ICP4, ICP22, ICP27, and ICP47, by binding to specific promoter elements within these genes.…”

Uncoating of non-enveloped viruses

“…It engages microtubule-associated motors for movement to the nuclear envelope [69][70][71][72]. Virus docks at the cytoplasmic side of the nuclear pore complex (NPC) by binding to the nucleoporin Nup214, and undergoes final disassembly [58,73].…”

DNA-tumor virus entry—From plasma membrane to the nucleus

“…Alternatively, cytoplasmic processing of incoming capsids might make them competent for docking to the nuclear pore complex (NPC) as observed shortly after infection (64). This suggests that nuclear accumulation occurs by retention, not requiring a transport bias.…”

“…Cytoplasmic transport of DNA-tumor viruses or prototypic DNA-tumor viruses has been studied in some detail, most prominently with HSV1 (64,65) and Ad2/5 (66-69).…”