Varicella-Zoster Virus Infectious Cycle: ER Stress, Autophagic Flux, and Amphisome-Mediated Trafficking

Abstract

Varicella-zoster virus (VZV) induces abundant autophagy. Of the nine human herpesviruses, the VZV genome is the smallest (~124 kbp), lacking any known inhibitors of autophagy, such as the herpes simplex virus ICP34.5 neurovirulence gene. Therefore, this review assesses the evidence for VZV-induced cellular stress, endoplasmic-reticulum-associated degradation (ERAD), and autophagic flux during the VZV infectious cycle. Even though VZV is difficult to propagate in cell culture, the biosynthesis of the both N- and O-linked viral glycoproteins was found to be abundant. In turn, this biosynthesis provided evidence of endoplasmic reticulum (ER) stress, including a greatly enlarged ER and a greatly diminished production of cellular glycoproteins. Other signs of ER stress following VZV infection included detection of the alternatively spliced higher-molecular-weight form of XBP1 as well as CHOP. VZV infection in cultured cells leads to abundant autophagosome production, as was visualized by the detection of the microtubule-associated protein 1 light chain 3-II (LC3-II). The degree of autophagy induced by VZV infection is comparable to that induced in uninfected cells by serum starvation. The inhibition of autophagic flux by chemicals such as 3-methyladenine or ATG5 siRNA, followed by diminished virus spread and titers, has been observed. Since the latter observation pointed to the virus assembly/trafficking compartments, we purified VZ virions by ultracentrifugation and examined the virion fraction for components of the autophagy pathway. We detected LC3-II protein (an autophagy marker) as well as Rab11 protein, a component of the endosomal pathway. We also observed that the virion-containing vesicles were single-walled; thus, they are not autophagosomes. These results suggested that some VZ virions after secondary envelopment were transported to the outer cell membrane in a vesicle derived from both the autophagy and endosomal pathways, such as an amphisome. Thus, these results demonstrate that herpesvirus trafficking pathways can converge with the autophagy pathway.

Varicella-Zoster Virus ORF9p Binding to Cellular Adaptor Protein Complex 1 Is Important for Viral Infectivity

“…It was postulated that after secondary envelopment, VZV particles are redirected to the late secretory pathway, where they are partially degraded before reaching the cell surface (52). More recently, the transport vesicles containing VZV virions were shown to be single walled and positive for both Rab11 (endocytic pathway) and LC3B (autophagic pathway), and exocytosis of VZV particles was shown to rely, at least partially, on a convergence between the autophagy and endosomal pathways (64,65). Interestingly, vesicles resembling lysosomes and autophagosomes, some of them being in the close vicinity of transport vesicles, were frequently observed in VZV-ORF9-L231A-V5-infected cells, while they were rarer in WT-infected cells.…”

In vitro methods for testing antiviral drugs

“…Despite a general understanding that poliovirus spreads through cellular lysis, it was recently found that it may also be transferred between cells by an autophagy-dependent mechanism, called autophagosome-mediated exit without lysis (Bird and Kirkegaard, 2015b;Bird et al, 2014;Lai et al, 2016;Richards and Jackson, 2012). Similar mechanisms have been described for varicellazoster virus and human cytomegalovirus (Grose et al, 2016;Meier and Grose, 2017). Poxviruses encode several proteins that block the apoptotic cellular response to the presence of their dsDNA in the cytoplasm.…”

The beneficial effects of varicella zoster virus

“…VZV genome is approximately 125 kbp in size and is the smallest among herpes viruses. VZV genome, which has 74 open reading frame (ORF) proteins, consists of a linear double-stranded DNA molecule [45][46][47][48]. The genome consists of 2 main coding areas: the unique long segment and the unique short segment, each of which is lanked by internal repeat and terminal repeat sequences [46][47][48].…”

“…VZV genome, which has 74 open reading frame (ORF) proteins, consists of a linear double-stranded DNA molecule [45][46][47][48]. The genome consists of 2 main coding areas: the unique long segment and the unique short segment, each of which is lanked by internal repeat and terminal repeat sequences [46][47][48]. The virion is composed of an icosahedral nucleocaspid; that harbors the DNA genome; surrounded by a tegument layer which is covered by an envelope derived from the host cell or a plasma membrane with incorporated viral glycoproteins as shown in igure 1 [45][46][47][48].…”