Stress triggers expression of bovine herpesvirus 1 infected cell protein 4 (bICP4) RNA during early stages of reactivation from latency in pharyngeal tonsil

Authors: TOOMER, GABRIELA - Oklahoma State University; Workman, Aspen; HARRISON, KELLY - Oklahoma State University; STAYTON, ERIN - Oklahoma State University; HOYT, PETER - Illinois Institute Of Technology; JONES, CLINTON - Oklahoma State University

Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2022
Publication Date: 11/23/2022
Citation: Toomer, G., Workman, A.M., Harrison, K.S., Stayton, E., Hoyt, P.R., Jones, C. 2022. Stress triggers expression of bovine herpesvirus 1 infected cell protein 4 (bICP4) RNA during early stages of reactivation from latency in pharyngeal tonsil. Journal of Virology. 96(23). Article e0101022. https://doi.org/10.1128/jvi.01010-22.
DOI: https://doi.org/10.1128/jvi.01010-22

Interpretive Summary: Bovine herpesvirus 1 (BoHV-1) is a major pathogen of cattle that can cause respiratory and reproductive disorders. Following the initial infection, BHV-1 establishes a lifelong latent infection (dormancy) in sensory neurons of the trigeminal ganglia (TG) as well as cells within the pharyngeal tonsil (PT). Stressful stimuli can trigger reactivation from the latent state, causing recurrent disease, virus shedding, and spread to susceptible cattle. The latency-reactivation cycle is crucial for virus transmission and complicates disease control; however, the molecular signals that regulate latency and reactivation are not well understood. In particular, very little is known about reactivation from the PT. In the present study, we used a single injection of dexamethasone (DEX, a synthetic corticosteroid that mimics stress) to initiate BoHV-1 reactivation in latently infected cattle. We collected PT from cattle at 30, 90 and 180 minutes after DEX treatment and used RNA-sequencing to characterize both host and viral gene expression during the early stages of reactivation from latency. Viral gene expression was rapidly induced in the PT and host transcription factors were identified that are predicted to stimulate viral gene expression and thus reactivation. These findings help us better understand the virus-host interaction during the latency-reactivation cycle and could provide potential targets for novel disease control strategies to block viral reactivation and transmission.

Technical Abstract: Bovine herpesvirus 1 (BoHV-1), an important pathogen of cattle, establishes lifelong latency in sensory neurons within trigeminal ganglia (TG) after acute infection. The BoHV-1 latency-reactivation cycle, like other alphaherpesvirinae subfamily members, is essential for viral persistence and transmission. Notably, cells within pharyngeal tonsil (PT) also support a quiescent or latent BoHV-1 infection. The synthetic corticosteroid dexamethasone, which mimics the effects of stress, consistently induces BoHV-1 reactivation from latency allowing early stages of viral reactivation to be examined in the natural host. Based on previous studies, we hypothesized that stress-induced cellular factors trigger expression of key viral transcriptional regulatory genes. To explore this hypothesis, RNA-sequencing studies compared viral gene expression in PT during early stages of dexamethasone-induced reactivation from latency. Strikingly, RNA encoding infected cell protein 4 (bICP4), which is translated into an essential viral transcriptional regulatory protein, was detected 30 min after dexamethasone treatment. Ninety minutes after dexamethasone treatment bICP4 and, to a lesser extent, bICP0 RNA were detected in PT. All lytic cycle viral transcripts were detected within 3 h after dexamethasone treatment. Surprisingly, the latency related (LR) gene, the only viral gene abundantly expressed in latently infected TG neurons, was not detected in PT during latency. In TG neurons, bICP0 and the viral tegument protein VP16 are expressed before bICP4 during reactivation, suggesting distinct viral regulatory genes mediate reactivation from latency in PT versus TG neurons. Finally, these studies confirm PT is a biologically relevant site for BoHV-1 latency, reactivation from latency, and virus transmission.