Characterizing the use of differentiated medulloblastoma cells to examine Herpes Simplex Virus latency and reactivation

Abstract

In human infection, herpes simplex virus (HSV) navigates two distinct life cycles; lytic and latent. The latent cycle takes place in sensory neurons, and is characterized as a dormant period punctuated by stress-induced episodes of viral reactivation. Understanding the mechanisms by which HSV latency and reactivation occur has been hindered by the lack of a model that faithfully recapitulates the environment of a human sensory neuron. Systems ranging from rat neurons to human fibroblasts have been developed to host HSV latency, however few available models have been able to investigate the role of human neuron-specific factors. To address this need, human medulloblastoma tumour cell lines, which derive from neuronal precursor cells, were differentiated and examined for their ability to host the HSV latency-reactivation cycle—in a manner similar to the differentiated PC-12 cell model. ONS-76 and UW228 medulloblastoma cell lines were screened for differentiation capacity. The differentiated cells were demonstrated to possess neuronal character as several neuron-specific proteins were found to be expressed. Differentiated ONS-76 cells were not compatible with hosting HSV latency, however, infection with a viral mutant impaired for lytic cycle initiation exhibited a deviant pattern of gene expression that resembles what has been observed in reactivation. Differentiated UW228 cells were found to host a low frequency, stable infection with the HSV mutant, characterized by the absence of infectious virus and viral lytic gene expression in the presence of persisting viral DNA. This DNA could further be induced to re-enter the lytic cycle through heat shock treatment and removal of differentiating agents from cell cultures. These results depict differentiated medulloblastoma cells as a novel tool in the study of HSV latency and reactivation, as these cells derive from the central nervous system and provide a new cellular perspective through which HSV biology can be viewed.