No abstract

STING (stimulator of IFN genes) activates the IFN-dependent innate immune response to infection on sensing the presence of DNA in cytosol. The quantity of STING accumulating in cultured cells varies; it is relatively high in some cell lines [e.g., HEp-2, human embryonic lung fibroblasts (HEL), and HeLa] and low in others (e.g., Vero cells). In a preceding publication we reported that STING was stable in four cell lines infected with herpes simplex virus 1 and that it was actively stabilized in at least two cell lines derived from human cancers. In this report we show that STING is exported from HEp-2 cells to Vero cells along with virions, viral mRNAs, microRNAs, and the exosome marker protein CD9. The virions and exosomes copurified. The quantity of STING and CD9 exported from one cell line to another was inoculum-size-dependent and reflected the levels of STING and CD9 accumulating in the cells in which the virus inoculum was made. The export of STING, an innate immune sensor, and of viral mRNAs whose major role may be in silencing viral genes in latently infected neurons, suggests that the virus has evolved mechanisms that curtail rather than foster the spread of infection under certain conditions. herpes simplex viruses | exosomes | STING | microRNAs | tetraspanins

Expression of herpes simplex virus genes at the initiation of replication involves two steps that take place at ND10 nuclear bodies. These are suppression of cellular repressors that attempt to silence viral DNA and remodeling of the viral chromatin to make it accessible for transcription. In earlier studies we reported on the mechanism by which viral proteins ICP0 and U S 3 protein kinase modify and disrupt the HDAC1/CoREST/REST/LSD1 repressor complex. The remodeling step requires in addition acetylation of histones bound to DNA. In an attempt to identify the enzyme, we took note of the observation that ICP0 physically and functionally interacts with Bmal1, a partner of the CLOCK histone acetyl transferase, and key members of the bHLH-PAS family of transcriptional factors. The Bmal11 and CLOCK heterodimer is best known as a regulator of the circadian oscillation in the mammalian CLOCK system. In this article we report the following: (i) in infected cells both Bmal1 and CLOCK localize at ND10 bodies; (ii) wild-type virus stabilizes the CLOCK protein; (iii) overexpression of CLOCK partially compensates for the absence of ICP0 and enables higher yields in cells infected with a ΔICP0 mutant and this activity is not expressed by CLOCK mutants lacking histone acetyl transferase activity; and (iv) depletion of CLOCK in cells infected with wild-type virus results in significant decrease in the expression of all viral proteins tested. We conclude that ICP0 interacts with Bmal1 and by extension with CLOCK histone acetyl transferase to remodel viral chromatin.O n release from capsids at the nuclear pore, herpes simplex virus 1 (HSV1) DNA aggregates in the nucleus with histones, repressors, and complexes of proteins known as ND10 bodies. The objective of the bound histones and repressor complexes is to silence the viral DNA. Current models postulate that activation of the viral transcriptional program involves two steps. In the first, VP16, a viral tegument protein released into the cells during viral entry, interacts with the cellular proteins HCF1, Oct1, demethylases, and their partners to activate the α genes (1-3). The second step of the activation process involves the α protein ICP0. At low multiplicities of infection in the absence of ICP0, transcription of downstream β and γ genes does not ensue (4). ICP0, a multifunction protein performs two key functions to enable activation of transcription of downstream genes. Thus ICP0 acts as an ubiquitin ligase that interacts with the UbcH5a-conjugating enzyme to degrade PML and SP100, key components of the ND10 bodies (5-7). ICP0 in addition, binds to corepressor of resilencing transcriptional factor, REST (CoREST) and dislodges histone deacetylase (HDAC) 1 or 2 from the repressor complex whose key constituents are HDAC1 and -2, CoREST, REST, and the lysinedependent demethylase 1 (LSD1) (8, 9). The dislocation of the repressor complex ensues. Ultimately, at least a fraction of the components of the complex is translocated to the cytoplasm (8, 9). The suppression of silencing...

STING (stimulator of IFN genes) activates the IFN pathway in response to cytosolic DNA. Knockout of STING in mice was reported to exacerbate the pathogenicity of herpes simplex virus 1 (HSV-1). Here we report the following: (i) STING is stable in cancer-derived HEp-2 or HeLa cells infected with wild-type HSV-1 but is degraded in cells infected with mutants lacking the genes encoding functional infected cell protein 0 (ICP0), ICP4, or the US3 protein kinase (US3-PK). In HEp-2 cells, depletion of STING by shRNA results in a decrease in the yields of wild-type or ΔICP0 viruses. (ii) STING is stable throughout infection with either wild-type or ICP0 mutant viruses in human embryonic lung cells (HEL) or HEK293T cells derived from normal tissues. In these cells, depletion of STING results in higher yields of both wild-type and ΔICP0 viruses. (iii) The US3-PK is also required for stabilization of IFI16, a nuclear DNA sensor. However, the stability of IFI16 does not correlate positively or negatively with that of STING. IFI16 is stable in STING-depleted HEL cells infected with wild-type virus. In contrast to HEL cells, IFI16 was undetectable in STING-depleted HEp-2 cells, and hence the role of HSV-1 in maintaining IFI16 could not be ascertained. The results indicate that in HSV-1-infected cells the stability of IFI16 and the function and stability of STING are dependent on cell derivation, the functional integrity of ICP0, and US3-PK, an indication that in wild-type virus-infected cells both proteins are actively stabilized. In HEp-2 cells, the stability of IFI16 requires STING.innate immunity | cell transformation T he studies described in this report stem from two observations. First, a voluminous literature singles out the infected cell protein 0 (ICP0) as the major herpes simplex virus 1 (HSV-1) protein dedicated to defeating host responses to infection (1). Many of the functions of ICP0 designed to defeat host responses are executed by direct interaction between ICP0 and host proteins (2-8). In some instances, a plausible connection is apparent but no physical contact between ICP0 and the host effector protein is demonstrable (9, 10). Thus, ICP0 is associated with blocking the activation of IRF3 although a physical interaction between ICP0 and IRF3 has not been reported (10). One hypothesis that could explain such observations is that ICP0 interacts with the partners of the targeted protein rather than the target itself.Second, ICP0 accumulates during the first phase of the replicative cycle in the nucleus in which it performs multiple functions to enable efficient replication. Sometime between 5 and 9 h after exposure of cells to virus and depending on cell line, functional integrity of ICP0, and the amount of foreign DNA introduced into the cell, etc., ICP0 disappears from the nucleus and accumulates in the cytoplasm (11, 12). Several functions of ICP0 linked to physical interactions with cytoplasmic proteins have been described. Thus, ICP0 interacts with EF-1δ and enhances translation efficiency and with CIN85 t...

Herpes simplex virus 1 (HSV-1)-infected cells release extracellular vesicles (EVs) that deliver to uninfected cells viral factors and host components, such as the stimulator of interferon genes (STING), which activates type I interferon upon foreign DNA sensing. The functions of EVs released by HSV-1-infected cells have remained unknown. Here, we describe a procedure to separate the EVs from HSV-1 virions that is based on an iodixanol/sucrose gradient. STING, along with the EV markers CD63 and CD9, was found in light-density fractions, while HSV components accumulated in heavy-density fractions. HSV-1 infection stimulated the release of EVs from the cells. The EVs derived from infected cells, but not from uninfected cells, activated innate immunity in recipient cells and suppressed viral gene expression and virus replication. Moreover, only the EVs derived from infected cells stimulated the expression of a subset of M1-type markers in recipient macrophages. Conversely, EVs derived from STING-knockdown cells failed to stimulate the expression of these M1-type markers, they activated innate immune responses to a lesser extent in recipient cells, and they did not sustain the inhibition of virus replication. These data suggest that STING from the EV donor cells contributes to the antiviral responses in cells receiving EVs from HSV-1-infected cells. Perturbations in the biogenesis of EVs by silencing CD63 or blocking the activity of the neutral spingomyelinase-2 (nSMase-2) increased the HSV-1 yields. Overall, our data suggest that the EVs released from HSV-1-infected cells negatively impact the infection and could control the dissemination of the virus. Extracellular vesicles (EVs) are released by all types of cells as they constitute major mechanism of intercellular communication and have the capacity to alter the functions of recipient cells despite their limited capacity for cargo. How the EVs released by HSV-infected cells could alter the surrounding microenvironment and influence the infection currently remains unknown. The cargo of EVs reflects the physiological state of the cells in which they were produced, so the content of EVs originating from infected cells is expected to be substantially different from that of healthy cells. Our studies indicate that the EVs released by HSV-1-infected cells carry innate immune components such as STING and other host and viral factors; they can activate innate immune responses in recipient cells and inhibit HSV-1 replication. The implication of these data is that the EVs released by HSV-1-infected cells could control HSV-1 dissemination promoting its persistence in the host.