Thyroid hormone-dependent epigenetic suppression of herpes simplex virus-1 gene expression and viral replication in differentiated neuroendocrine cells

Abstract

A global HSV-1 gene repression occurs during latency in sensory neurons where most viral gene transcriptions are suppressed. The molecular mechanisms of gene silencing and how stress factors trigger the reactivation are not well understood. Thyroid hormones are known to be altered due to stress, and with its nuclear receptor impart transcriptional repression or activation depending upon the hormone level. Therefore we hypothesized that triiodothyronine (T3) treatment of infected differentiated neuron like cells would reduce the ability of HSV-1 to produce viral progeny compared to untreated infected cells. Previously we identified putative thyroid hormone receptor elements (TREs) within the promoter regions of HSV-1 thymidine kinase (TK) and other key genes. Searching for a human cell line that can model neuronal HSV-1 infection, we performed HSV-1 infection experiments on differentiated human neuroendocrine cells, LNCaP. Upon androgen deprivation these cells undergo complete differentiation and exhibit neuronal-like morphology and physiology. These cells were readily infected by our HSV-1 recombinant virus, expressing GFP and maintaining many processes iconic of dendritic morphology. Our results demonstrated that differentiated LNCaP cells produced suppressive effects on HSV-1 gene expression and replication compared to its undifferentiated counterpart and T3 treatment have further decreased the viral plaque counts compared to untreated cells. Upon washout of the T3 viral plaque counts were restored, indicating an increase of viral replication. The qRT-PCR experiments using primers for TK showed reduced expression under T3 treatment. ChIP assays using a panel of antibodies for H3 lysine 9 epigenetic marks showed increased repressive marks on the promoter regions of TK. In conclusion we have demonstrated a T3 mediated quiescent infection in differentiated LNCaP cells that has potential to mimic latent infection. In this HSV-1 infection model thyroid hormone treatment caused decreased viral replication, repressed TK expression and increased repressive histone tail marks on the TK promoter.

Overexpression of thyroid hormone receptor β1 altered thyroid hormone-mediated regulation of herpes simplex virus-1 replication in differentiated cells

“…It was shown that Vero cells have very low TRβ1 expression [37]. The infection of Vero cells with A1 virus, the HSV-1 without TRβ1 transgene , did not increase the expression (Fig.…”

“…3C). In addition, infection of A1 did not show this regulatory consequence [37], indicating this T 3 -mediated replication increase resulted from the presence of TRβ1.…”

“…The expression of TRβ1 in epithelial cells such as Vero is quite low and showed no regulatory effect on HSV-1 replication [37]. TRβ1 was present in TG neurons but the concentration is undetermined [38].…”

“…TRβ1 was present in TG neurons but the concentration is undetermined [38]. Using differentiated human neuroendocrine cells LNCaP as a model for T 3 -mediated HSV-1 regulation studies indicated that T 3 /TRβ1 suppressed viral replication [37]. However, it is our observation that human cells are very prone to HSV-1 infection compared to mouse cells and the moi needs to be kept very low or the cells died after 24-48 hpi (unpublished data).…”

Occupancy of RNA Polymerase II Phosphorylated on Serine 5 (RNAP S5 P ) and RNAP S2 P on Varicella-Zoster Virus Genes 9, 51, and 66 Is Independent of Transcript Abundance and Polymerase Location within the Gene

“…Indeed, ChIP has shown that during productive herpes simplex virus 1 (HSV-1) infection, virus gene transcription is regulated, in part, by binding of virus (26) or host (27) proteins to specific DNA sequences within gene promoters or to protein components of the transcriptional apparatus (28). Importantly, ChIP analyses of HSV-1-infected neurons have shown that posttranslational modification of histone proteins is a critical factor that maintains the unique transcriptional pattern of virus genes during latency.…”