Analysis of the genes encoding the latency associated transcript of bovine herpesvirus type 1 (BHV-1) and herpes simplex type 1: Their anti-apoptotic activity and a novel function identified for the BHV-1 latency related gene

The Alphaherpesvirinae subfamily members establish latency in sensory neurons of the nerve ganglia. In contrast to 70–75 viral genes expressed during productive infection, only one viral gene is active during latency; the latency-related (LR) gene of BHV-1 or the latency-associated-transcript (LAT) encoded by HSV-1. The LR gene is alternatively spliced in trigeminal ganglia and the LR protein associates with cell cycle regulatory proteins. Productive infection requires certain cell cycle proteins and this can lead to apoptosis. Neurons are post-mitotic and will undergo apoptosis if cell cycle progression is initiated. Consequently, I hypothesized that the LR gene and LAT protect neurons from apoptosis thus promoting latency.; My studies focus on characterizing the LR gene and LAT with respect to inhibition of apoptosis. Furthermore, I constructed a LR-mutant virus and characterized the growth properties of this mutant in cattle. In transient transfection studies, the LR protein exhibits anti-apoptotic activity. The LR mutant, wt BHV-1 and the rescued LR mutant viruses have similar growth properties in cultured cells. In contrast, the LR mutant grows poorly in ocular tissue of acutely infected calves, exhibits reduced establishment of latency, causes an increase in neurotoxicity during acute infection, and does not reactivate from latency.; Anti-apoptotic genes have been identified for HSV-1 suggesting that this function is important for viral propagation. However, these previously identified genes are not abundantly expressed during latency. Therefore, the anti-apoptotic activity of HSV-1 LAT was also examined. A panel of HSV-1 LAT plasmid constructs were generated that contained deletions in the LAT promoter, the 5 ′ end of the 8.3Kb transcript, or portions of the stable 2kb intron. Our results demonstrate that LAT sequences that have anti-apoptotic activity also promote spontaneous reactivation. In summary, the ability of the LR gene and LAT to inhibit apoptosis is important for the latency-reactivation cycle.