The Herpes Simplex Virus Type 1 Latency-Associated Transcript Can Protect Neuron-Derived C1300 and Neuro2A Cells from Granzyme B-Induced Apoptosis and CD8 T-Cell Killing

Abstract

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) is the only HSV-1 gene transcript abundantly expressed throughout latency. LAT null mutants have a significantly reduced reactivation phenotype. LAT's antiapoptosis activity is the major LAT factor involved in supporting the wild-type reactivation phenotype. During HSV-1 latency, some ganglionic neurons are surrounded by CD8 T cells, and it has been proposed that these CD8 T cells help maintain HSV-1 latency by suppressing viral reactivations. Surprisingly, despite injection of cytotoxic lytic granules by these CD8 T cells into latently infected neurons, neither apoptosis nor neuronal cell death appears to occur. We hypothesized that protection of latently infected neurons against cytotoxic CD8 T-cell killing is due to LAT's antiapoptosis activity. Since CD8 T-cell cytotoxic lytic granule-mediated apoptosis is critically dependent on granzyme B (GrB), we examined LAT's ability to block GrB-induced apoptosis. We report here that (i) LAT can interfere with GrB-induced apoptosis in cell cultures, (ii) LAT can block GrB-induced cleavage (activation) of caspase-3 both in cell culture and in a cell-free in vitro cell extract assay, and (iii) LAT can protect C1300 and Neuro2A cells from cytotoxic CD8 T-cell killing in vitro. These findings support the hypothesis that LAT's antiapoptosis activity can protect latently infected neurons from being killed by CD8 T-cell lytic granules in vivo.Herpes simplex virus type 1 (HSV-1) is ubiquitous worldwide. Estimates of the percentage of adults that harbor latent HSV-1 range from just under 50% to over 90% (6,7,13,19,44,47,61,69). HSV-1 can infect mucosal sites, in particular the eyes, mouth, and genitals. Following primary infection at the periphery, the virus travels up axons and becomes latent in sensory neurons of the host's peripheral nervous system (PNS). HSV-1 latency is lifelong. Sporadic spontaneous reactivations of the virus from the PNS can result in return of infectious virus to the original peripheral site of infection. This reactivated virus, in the absence of clinical disease, is shed from mucosal surfaces and can be transmitted to others. Less often, viral reactivations and shedding result in recurrent pathology at the site of the original infection, such as genital lesions, cold sores in and around the mouth, and corneal disease that can lead to loss of vision. In the United States, recurrent HSV-1-induced corneal disease is the leading cause of corneal blindness due to an infectious agent (48, 59). In addition, HSV-1 causes a severe form of focal necrotizing encephalitis that affects over 2,000 people in the United States each year (20,40,67,68). Reactivations of HSV-1, rather than primary infections, are responsible for most incidences of HSV-1-induced disease and the majority of viral transmissions. Thus, understanding the molecular mechanisms of the HSV-1 latencyreactivation cycle is critical for developing methods of preventing both viral spread and HSV-1-induced disease.During neuro...

Role of activating transcription factor 3 in the synthesis of latency-associated transcript and maintenance of herpes simplex virus 1 in latent state in ganglia

“…Current consensus holds that the function of LAT and, most likely, of the miRNAs is to maintain the integrity of the neuron to maintain the virus in a silent state (38,39). In the absence of LAT, neurons harboring latent virus succumb to apoptosis (31).…”

A comparison of herpes simplex virus type 1 and varicella-zoster virus latency and reactivation

“…Due to a non-canonical splice site junction, the 1.5 kb HSV-1 LAT remains as a stable lariat in the neuronal nucleus with a half-life of 24 h (Spivack et al, 1991;Wu et al, 1996;Thomas et al, 2002;Ng et al, 2004). LAT-containing neurons are occasionally surrounded by CD8 + T-cells (Theil et al, 2003a;Verjans et al, 2007) that are primed in the periphery (Held et al, 2012) and LAT functions in part to protect neurons from granzyme B-induced apoptosis (Allen et al, 2011;Jiang et al, 2011). LAT, although dispensable to the establishment of latency, does play an active role in silencing HSV-1 lytic gene promoters during establishment of latency in part by facilitating methylation of lysine 9 on histone H3, a post-translational modification indicative of heterochromatin structures (Wang et al, 2005).…”

“…+ T-cells (Theil et al, 2003a;Verjans et al, 2007) that are primed in the periphery (Held et al, 2012) and LAT functions in part to protect neurons from granzyme B-induced apoptosis (Allen et al, 2011;Jiang et al, 2011). LAT, although dispensable to the establishment of latency, does play an active role in silencing HSV-1 lytic gene promoters during establishment of latency in part by facilitating methylation of lysine 9 on histone H3, a post-translational modification indicative of heterochromatin structures (Wang et al, 2005).…”

Interactions between Herpesvirus Entry Mediator (TNFRSF14) and Latency-Associated Transcript during Herpes Simplex Virus 1 Latency

“…HVEM mRNA levels were analyzed by qRT-PCR in two neuroblastoma lines, C1300 and Neuro2A, that stably express LAT (43,44). In both LAT(ϩ) cell lines ( Fig.…”