Analysis of bovine herpesvirus-1 proteins expressed during latency and their interaction with host cellular factors

Bovine herpesvirus type 1 (BHV-1) is an important pathogen of cattle. Like other Alphaherpesvirinae subfamily members, BHV-1 establishes latency in sensory neurons following acute infection. Reactivation from latency occurs periodically, resulting in virus shedding and spread to uninfected cattle. During latency only the latency-related (LR) gene and ORF-E are abundantly expressed in sensory neurons of trigeminal ganglia (TG). The LR gene is required for the virus' latency-reactivation cycle in cattle. It is alternatively spliced in TG during acute infection, expanding the protein coding potential of the LR gene by fusing open reading frames. Both ORF-E and the LR gene express proteins during infection of trigeminal ganglionic neurons. The central hypothesis of this work is that proteins encoded by the LR gene and ORF-E regulate specific aspects of the BHV-1 latency-reactivation cycle. The focus of my studies was to characterize these viral proteins, and identify host proteins that interact with proteins encoded by the LR gene. At 7 days post infection an abundant spliced LR transcript is expressed in TG that is translated into a novel protein, which fuses the two major LR open reading frames: ORF2 and ORF1. I characterized the interaction of the ORF2/ORF1 fusion protein with the host transcription factor CCAAT enhancer binding protein alpha (C/EBPalpha). C/EBPalpha protein expression is stimulated during productive infection and reactivation from latency. C/EBPalpha protein expression is not detected during latency suggesting it promotes productive viral replication and that its expression is extinguished during the establishment of latency. C/EBPalpha cooperates synergistically with the viral transactivators bICP0 and bTIF to activate immediate-early (IE) and late viral promoters. C/EBPalpha interacted with sequences in the IE transcription unit 1 promoter during productive infection, providing a molecular mechanism by which C/EBPalpha stimulates productive infection. Finally, I discovered that two other proteins, ORF1 and ORF-E, are produced during productive infection. Since these proteins are also expressed in trigeminal ganglionic neurons of latently infected calves, I predict these proteins regulate certain aspects of the BHV-1 latency-reactivation cycle.