The bovine herpesvirus-1 LR ORF2 is critical for this gene's ability to restore the high wild-type reactivation phenotype to a herpes simplex virus-1 LAT null mutant During neuronal latency of herpes simplex virus (HSV)-1, the latency-associated transcript (LAT) is the only viral gene readily detectable. LAT is required for the high-level reactivation phenotype in animal models. LAT's anti-apoptotic activity was recently demonstrated by our group and it was proposed that LAT's anti-apoptotic function is involved in enhancing the reactivation phenotype. Recently, using chimeric virus CJLAT, it was shown that the reactivation phenotype of LAT " mutant dLAT2903 can be restored to wild-type levels by inserting the bovine herpes virus (BHV)-1 latency-related (LR) gene into the LAT locus of this HSV-1 LAT deletion mutant. Although transcription of the LR gene, like LAT, inhibits apoptosis, LR appears to be multifunctional. To investigate whether the LR gene's anti-apoptotic function was responsible for restoring the high-reactivation phenotype, a mutated BHV-1 LR gene was inserted into the LAT locus of HSV-1 generating the chimeric virus CJLATmut. This mutation consists of three stop codons inserted just after the ATG of the first LR open reading frame (ORF2). In plasmids and in a BHV-1 mutant, this mutation eliminated the LR gene's anti-apoptotic activity, strongly suggesting that ORF2 encodes a protein responsible for LR's anti-apoptotic activity. Reactivation of the CJLATmut virus, in both rabbits and mice, was significantly lower than in wild-type McKrae virus (P=0?0001 and P=0?0003, respectively) and CJLAT virus, containing wild-type LR in place of LAT (P<0?0001) and was similar to LAT " dLAT2903 (P=0?8 and P=0?7, respectively). Thus, disruption of BHV-1 LR ORF2 eliminated the high-reactivation phenotype.
INTRODUCTIONOver 80 % of adults in the United States harbour latent herpes simplex virus type 1 (HSV-1). Following primary peripheral infection of the eye, HSV-1 travels along axons via antegrade transport to sensory neurons of the trigeminal ganglia (TG) where latency is established. The latent virus reactivates sporadically as a result of stress, UV exposure and other unknown stimuli. Reactivations can also occur in the absence of known stimuli, which we have operationally defined as spontaneous reactivation. Following reactivation, HSV-1 travels along axons in a retrograde direction to the initial infection site, where it can replicate and cause recurrent disease (Andreansky et al., 1998;Roizman & Whitley, 2001). Recurrent HSV-1 infection in the eye can cause corneal scarring leading to the loss of vision. As a result, HSV-1 is one of the leading infectious causes of corneal blindness in the developed world (Liesegang et al., 1989). The mechanism(s) by which the latent virus reactivates and causes disease are currently not completely understood.The only gene that is actively transcribed during HSV-1 neuronal latency is the latency-associated transcript (LAT) (Rock et al., 1987b; Stevens et al., 1987). A stab...