Expression of Murine CD80 by Herpes Simplex Virus 1 in Place of Latency-Associated Transcript (LAT) Can Compensate for Latency Reactivation and Anti-apoptotic Functions of LAT

Abstract

High rates of wild-type (WT) herpes simplex virus 1 (HSV-1) latency reactivation depend on the anti-apoptotic activities of latency-associated transcript (LAT). Replacing LAT with the baculovirus inhibitor of apoptosis protein (cpIAP) or cellular FLIP (FLICE-like inhibitory protein) gene restored the WT latency reactivation phenotype to that of a LAT-minus [LAT(−)] virus, while similar recombinant viruses expressing interleukin-4 (IL-4) or interferon gamma (IFN-γ) did not. However, HSV-1 recombinant virus expressing cpIAP did not restore all LAT functions. Recently, we reported that a similar recombinant virus expressing CD80 in place of LAT had higher latency reactivation than a LAT-null virus. The present study was designed to determine if this CD80-expressing recombinant virus can restore all LAT functions as observed with WT virus. Our results suggest that overexpression of CD80 fully rescues LAT function in latency reactivation, apoptosis, and immune exhaustion, suggesting that LAT and CD80 have multiple overlapping functions. IMPORTANCE Recurring ocular infections caused by HSV-1 can cause corneal scarring and blindness. A major function of the HSV-1 latency-associated transcript (LAT) is to establish high levels of latency and reactivation, thus contributing to the development of eye disease. Here, we show that the host CD80 T cell costimulatory molecule functions similarly to LAT and can restore the ability of LAT to establish latency, reactivation, and immune exhaustion as well as induce the expression of caspase 3, caspase 8, caspase 9, and Bcl2. Our results suggest that, in contrast to several other previously tested genes, CD80-expressing virus can completely compensate for all known and tested LAT functions.

Increased phagocytosis in the presence of enhanced M2-like macrophage responses correlates with increased primary and latent HSV-1 infection

“…Mice were sacrificed on day 28 PI and individual TG were removed and cultured in tissue culture media as described [ 19 , 20 , 59 ]. Aliquots of media were removed from each culture daily and plated on indicator cells (RS cells) to detect reactivated virus.…”

“…TG from individual mice were collected on day 28 PI, immersed in RNA later, RNA Stabilization Reagent (Thermo Fisher Scientific, Waltham, MA, USA), and stored at −80°C until processing. Total RNA was extracted as described [ 19 , 20 , 59 ]. Levels of LAT RNA from latent TG were determined using a custom-made LAT primers and probe as follows: forward primer, 5′-GGGTGGGCTCGTGTTACAG-3′; reverse primer, 5′-GGACGGGTAAGTAACAGAGTCT CTA-3′; and probe, 5′-FAM-ACACCAGCCCGTTCTTT-3′ (amplicon length = 81 bp).…”

Immune Response to Herpes Simplex Virus Infection and Vaccine Development

“…Despite the potentiation of apoptosis reported above, it is established that inhibition of apoptosis is critical for the reactivation of latency by HSV [ 80 ], and this mechanism is mediated by the action of the latency-associated transcript (LAT), which is the only HSV transcript expressed significantly during latency. Another recent study showed that CD80 can compensate for the functions of the LAT, such as the establishment of latency, reactivation and immune exhaustion in cells infected with the LAT-null virus [ 81 ]. This is significant because this is the first time that such overlapping functionalities between LAT and CD80 have been reported.…”

“…Although CD80 rescues the functions of LAT, it has distinct functions as CD80 exacerbated eye disease in mice compared to wild-type HSV. Furthermore, CD80 potentiated the expression of the anti-apoptotic Bcl-2 gene thus modulating apoptosis in the infected cells [ 81 ]. Another HSV-1 protein that has implications in regulating cellular apoptosis—ICP22 has been shown to function via a mechanism like that used by the cellular J-protein/HSP40 family chaperone [ 82 ].…”

Multifaceted Roles of ICP22/ORF63 Proteins in the Life Cycle of Human Herpesviruses

“…HSV-1 evades clearance by the host immune system through a variety of mechanisms to establish lifelong latent infection ( Kurt-Jones et al, 2017 ; Lin and Zheng, 2019 ; Tognarelli et al, 2019 ; Zhu and Zheng, 2020 ). For example, HSV-1 LAT plays a vital role in generating dysfunctional T-cell responses in the TG of ocular infected HSV-1 mice and helps the virus resist host cell apoptosis by inhibiting the type I IFN signaling pathway, thus contributing to the establishment and activation of latent HSV-1 infection ( Perng et al, 2000 ; Branco and Fraser, 2005 ; Allen et al, 2011 ; Tormanen et al, 2019 ; Jaggi et al, 2020 ). LAT-containing neurons are occasionally surrounded by CD8 + T cells ( Theil et al, 2003 ; Verjans et al, 2007 ) that are primed in the periphery ( Held et al, 2011 ) and LAT functions in part to protect neurons against granzyme B–induced apoptosis ( Allen et al, 2011 ; Jiang et al, 2011 ).…”