title: 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 virusICP34.5neurovirulence 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 bothN- andO-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.
authors.affiliation: Virology Laboratory, Children's Hospital, University of Iowa, Iowa City, IA 52242, USA. charles-grose@uiowa.edu.
authors.forename: Charles
authors.initials: C
authors.lastname: Grose
authors.affiliation: Virology Laboratory, Children's Hospital, University of Iowa, Iowa City, IA 52242, USA. erin-buckingham@uiowa.edu.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Buckingham
authors.affiliation: Virology Laboratory, Children's Hospital, University of Iowa, Iowa City, IA 52242, USA. john-carpenter@uiowa.edu.
authors.forename: John E
authors.initials: JE
authors.lastname: Carpenter
authors.affiliation: JC Wilt Infectious Diseases Research Centre, National Microbiology Laboratory, Public Health Agency of Canada, Winnipeg, MB R3E 3L5, Canada. jeremy.kunkel@phac-aspc.gc.ca.
authors.forename: Jeremy P
authors.initials: JP
authors.lastname: Kunkel
keywords: ER-associated degradation; XBP1; autophagy; cytomegalovirus; glycoproteins; herpes simplex virus; unfolded protein response; varicella-zoster virus; xenophagy