|Zhu, Liqian - Oklahoma State University|
|Smith, Timothy - Tim|
|Jones, Clinton - Oklahoma State University|
Submitted to: Journal of Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2018
Publication Date: 4/1/2018
Citation: Workman, A.M., Zhu, L., Keel, B.N., Smith, T.P.L., Jones, C. 2018. The Wnt signaling pathway is differentially expressed during the bovine herpesvirus 1 latency-reactivation cycle: evidence that two protein kinases associated with neuronal survival (Akt3 and bone morphogenetic protein receptor 2) are expressed at higher levels during latency. Journal of Virology. 92:e01937-17. https//doi.org/10.1128/JVI.01937-17.
Interpretive Summary: Bovine herpes virus 1 (BoHV-1) is a significant viral pathogen of cattle that contributes to bovine respiratory disease complex, the most important disease in cattle. The virus causes an acute infection in the respiratory tract then establishes a life-long latency (dormancy) in neurons. Periodic reactivation from the latent state causes 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 mechanisms that regulate reactivation are unknown. A better understanding of the virus-host interaction during the latency-reactivation cycle could provide potential targets for novel disease control strategies. The present study identified cellular signaling pathways differentially regulated during stress-induced virus reactivation. Genes associated with a signaling pathway were upregulated during viral latency and then repressed during reactivation from latency. This pathway promotes neurogenesis and cell survival, important functions for maintaining a life-long latency. Additional studies in cultured cells revealed that a viral protein expressed during latency interacts with proteins of this pathway, modulating their activity. These novel findings provide insight into how cellular factors cooperate with viral gene products to regulate the BoHV-1 latency-reactivation cycle.
Technical Abstract: Sensory neurons in trigeminal ganglia (TG) of calves latently infected with bovine herpesvirus 1 (BoHV-1) abundantly express latency-related (LR) gene products, including a protein (ORF2) and two micro-RNAs. Recent studies in mouse neuroblastoma cells (Neuro-2A) demonstrated ORF2 interacts with ß-catenin and a ß-catenin coactivator, high-mobility group AT-hook 1 (HMGA1) protein, which correlates with increased ß-catenin-dependent transcription and cell survival. ß-Catenin and HMGA1 are readily detected in a subset of latently infected TG neurons but not TG neurons from uninfected calves or reactivation from latency. Consequently, we hypothesized that the Wnt/ß-catenin signaling pathway is differentially expressed during the latency and reactivation cycle and an active Wnt pathway promotes latency. RNA-sequencing studies revealed that 102 genes associated with the Wnt/ß-catenin signaling pathway were differentially expressed in TG during the latency reactivation cycle in calves. Wnt agonists were generally expressed at higher levels during latency, but these levels decreased during dexamethasone-induced reactivation. The Wnt agonist bone morphogenetic protein receptor 2 (BMPR2) was intriguing because it encodes a serine/threonine receptor kinase that promotes neuronal differentiation and inhibits cell death. Another differentially expressed gene encodes a protein kinase (Akt3), which is significant because Akt activity enhances cell survival and is linked to herpes simplex virus 1 latency and neuronal survival. Additional studies demonstrated ORF2 increased Akt3 steady-state protein levels and interacted with Akt3 in transfected Neuro-2A cells, which correlated with Akt3 activation. Conversely, expression of Wnt antagonists increased during reactivation from latency. Collectively, these studies suggest Wnt signaling cooperates with LR gene products, in particular ORF2, to promote latency.