To Determine the Fate of Packaged Histones During HPV16 Viral Infection

Abstract

High-risk human papillomaviruses (HPVs) cause 5% of all human cancer worldwide. HPV infects mucosal and cutaneous epithelia and induces cellular proliferation. The HPV capsid, which is involved with the initial binding, internalization, and intracellular trafficking, is composed of 72 pentamers of major capsid protein L1 and up to 72 copies of minor capsid protein L2. HPV packages its genome with host histones to form a chromatin-like structure, and the viral genome acquires specific histone modifications from the host cell in which it was replicated and packaged into progeny virions. The L2 protein, complexed with the vDNA, traffics from endosomes to the trans-Golgi network (TGN), eventually arriving at the nucleus, in a trafficking process highly dependent on mitosis. En route to the nucleus, the packaged histones likely remain associated with vDNA, however, the specific details and fate of these packaged viral histones remain poorly characterized. We have produced epitope-tagged core histone pseudoviruses (PsVs) and utilized immunofluorescence microscopy to detect the transport of histones during HPV16 infection. We find that tagged histones associate with L1 protein and accumulate at the late endosome at 8h post-infection, similar to the behavior of tagged L2. Furthermore, both tagged histones and tagged L2 accumulate at nuclear PML bodies at late times post-infection. These data suggest that histones may remain coupled the L2/vDNA complex throughout the retrograde trafficking to the nucleus, and therefore have potential to carry epigenetic marks that may affect viral gene expression upon the next round of infection.