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Bovine herpes virus 1 (BHV-1) and Herpes simplex virus 1 (HSV-1) are crucial etiological viral agent of clinical diseases. HSV-1 and BHV-1 establish latent infection in sensory neurons. Periodically, reactivation from latency occurs resulting in virus excretion and transmission. Stress increases corticosteroid levels and the incidence of HSV-1 and BHV-1 reactivation from latency. The synthetic corticosteroid, dexamethasone (DEX) mimics stress and induces BHV-1 and HSV-1 reactivation. However, molecular mechanisms by which corticosteroid mediates viral reactivation are not well understood. My dissertation has focused on elucidating events that induce BHV- 1 or HSV-1 reactivation during the early stages of stress-induced escape from latency. The studies presented here revealed that during reactivation from latency, two BHV-1 regulatory proteins, BHV-1 infected cell protein 0 (bICP0) and viral protein 16 (VP16) were detected in trigeminal ganglionic (TG) sensory neurons that express the glucocorticoid receptor (GR). For these studies, reactivation from latency was initiated in latently infected calves with a single IV injection of DEX. These studies suggested that activation of the GR by DEX induces lytic viral gene expression. Furthermore, I discovered that DEX mediated activation of the GR directly stimulated the BHV-1 immediate early transcription unit 1(IEtu1) promoter that directs expression of bICP0 and bICP4. The GR was bound to IEtu1 sequences that contain two near perfect glucocorticoids response elements (GREs). Additionally, we have shown that Host Cell Factor 1 (HCF-1) is required for GR-mediated IEtu1 promoter activation.
The serum and glucocorticoid-related protein kinases (SGK1) is another stressinduced cellular factor. Expression of the serine/threonine protein kinase is strongly induced by glucocorticoids and other growth factors. Inhibiting SGK protein kinase activity significantly reduced BHV-1 and HSV-1 replication in cultured cells. The inhibitor also reduced the steady state levels of certain BHV-1 proteins.
Collectively, these studies revealed that the stress induced cellular factor, GR, stimulated BHV-1 IEtu1 promoter and productive infection in concert with HCF-1. We also provided evidence that another stress induced cellular factor, SGK-1, may regulate BHV-1 and HSV-1 replication during stress induced reactivation from latency. The studies suggest that multiple cellular factors play important roles during the early stages of stress-induced escape from latency.