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...