Autophagy and the effects of its inhibition on varicella-zoster virus glycoprotein biosynthesis and infectivity

EM Buckingham, JE Carpenter, W Jackson… - Journal of …, 2014 - Am Soc Microbiol
EM Buckingham, JE Carpenter, W Jackson, C Grose
Journal of virology, 2014Am Soc Microbiol
Autophagy and the effects of its inhibition or induction were investigated during the entire
infectious cycle of varicella-zoster virus (VZV), a human herpesvirus. As a baseline, we first
enumerated the number of autophagosomes per cell after VZV infection compared with the
number after induction of autophagy following serum starvation or treatment with
tunicamycin or trehalose. Punctum induction by VZV was similar in degree to punctum
induction by trehalose in uninfected cells. Treatment of infected cells with the autophagy …
Abstract
Autophagy and the effects of its inhibition or induction were investigated during the entire infectious cycle of varicella-zoster virus (VZV), a human herpesvirus. As a baseline, we first enumerated the number of autophagosomes per cell after VZV infection compared with the number after induction of autophagy following serum starvation or treatment with tunicamycin or trehalose. Punctum induction by VZV was similar in degree to punctum induction by trehalose in uninfected cells. Treatment of infected cells with the autophagy inhibitor 3-methyladenine (3-MA) markedly reduced the viral titer, as determined by assays measuring both cell-free virus and infectious foci (P < 0.0001). We next examined a virion-enriched band purified by density gradient sedimentation and observed that treatment with 3-MA decreased the amount of VZV gE, while treatment with trehalose increased the amount of gE in the same band. Because VZV gE is the most abundant glycoprotein, we selected gE as a representative viral glycoprotein. To further investigate the role of autophagy in VZV glycoprotein biosynthesis as well as confirm the results obtained with 3-MA inhibition, we transfected cells with ATG5 small interfering RNA to block autophagosome formation. VZV-induced syncytium formation was markedly reduced by ATG5 knockdown (P < 0.0001). Further, we found that both expression and glycan processing of VZV gE were decreased after ATG5 knockdown, while expression of the nonglycosylated IE62 tegument protein was unchanged. Taken together, our cumulative results not only documented abundant autophagy within VZV-infected cells throughout the infectious cycle but also demonstrated that VZV-induced autophagy facilitated VZV glycoprotein biosynthesis and processing.
American Society for Microbiology