Autophagy and the Effects of Its Inhibition on Varicella-Zoster Virus

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 infec-tion compared with the number after induction of autophagy following serum starvation or treatment with tunicamycin or treh-alose. Punctum induction by VZVwas similar in degree to punctum induction by trehalose in uninfected cells. Treatment of in-fected 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 representa-tive viral glycoprotein. To further investigate the role of autophagy in VZV glycoprotein biosynthesis as well as confirm the re-sults 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 ex-pression 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 glyco-protein biosynthesis and processing