Vesicular trafficking permits evasion of cGAS/STING surveillance during initial human papillomavirus infection.

Brittany L Uhlorn,Shuaizhi Li,Samuel K Campos,Robert Jackson,Shauna M Bratton,Koenraad Van Doorslaer,Paul Francis Lambert

doi:10.1371/journal.ppat.1009028

Abstract

Oncogenic human papillomaviruses (HPVs) replicate in differentiating epithelium, causing 5% of cancers worldwide. Like most other DNA viruses, HPV infection initiates after trafficking viral genome (vDNA) to host cell nuclei. Cells possess innate surveillance pathways to detect microbial components or physiological stresses often associated with microbial infections. One of these pathways, cGAS/STING, induces IRF3-dependent antiviral interferon (IFN) responses upon detection of cytosolic DNA. Virion-associated vDNA can activate cGAS/STING during initial viral entry and uncoating/trafficking, and thus cGAS/STING is an obstacle to many DNA viruses. HPV has a unique vesicular trafficking pathway compared to many other DNA viruses. As the capsid uncoats within acidic endosomal compartments, minor capsid protein L2 protrudes across vesicular membranes to facilitate transport of vDNA to the Golgi. L2/vDNA resides within the Golgi lumen until G2/M, whereupon vesicular L2/vDNA traffics along spindle microtubules, tethering to chromosomes to access daughter cell nuclei. L2/vDNA-containing vesicles likely remain intact until G1, following nuclear envelope reformation. We hypothesize that this unique vesicular trafficking protects HPV from cGAS/STING surveillance. Here, we investigate cGAS/STING responses to HPV infection. DNA transfection resulted in acute cGAS/STING activation and downstream IFN responses. In contrast, HPV infection elicited minimal cGAS/STING and IFN responses. To determine the role of vesicular trafficking in cGAS/STING evasion, we forced premature viral penetration of vesicular membranes with membrane-perturbing cationic lipids. Such treatment renders a non-infectious trafficking-defective mutant HPV infectious, yet susceptible to cGAS/STING detection. Overall, HPV evades cGAS/STING by its unique subcellular trafficking, a property that may contribute to establishment of infection.

Highlights

Human papillomaviruses (HPVs) are circular, double-stranded DNA viruses that infect and replicate in differentiating epithelium
We hypothesize that HPV evades cGAS/STING detection via its unique vesicular trafficking mechanism
We show that HPV is a stealthy virus, capable of infecting keratinocytes with minimal activation of the cGAS/STING pathway

Summary

Introduction

Human papillomaviruses (HPVs) are circular, double-stranded DNA viruses that infect and replicate in differentiating epithelium. The HPV lifecycle and viral gene expression is dependent on differentiating epithelium [2,3,4]. HPV must traffic its circular dsDNA viral genome (vDNA) to the nucleus of basal keratinocytes, the only actively dividing cells within differentiating epithelium. Infected basal keratinocytes maintain vDNA episomes and serve as a reservoir for infected suprabasal cells that support the productive amplification of vDNA and assembly of progeny virions in upper epithelial layers [5,6]. Persistently infected basal keratinocytes support sustained production of progeny virions to ensure efficient transmission within hosts. Unraveling the mechanisms that underlie HPV persistence is important to understand both HPV lifecycle and cancer

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