2013a. Herpes Simplex Virus 1 E3 Ubiquitin Ligase ICP0 Protein Inhibits Tumor Necrosis Factor Alpha-Induced NF- B Activation by Interacting with p65/RelA and p50/NF- B1

NF-B plays central roles in regulation of diverse biological processes, including innate and adaptive immunity and inflamma-tion. HSV-1 is the archetypal member of the alphaherpesviruses, with a large genome encoding over 80 viral proteins, many of which are involved in virus-host interactions and show immunemodulatory capabilities. In this study, we demonstrated that the HSV-1 ICP0 protein, a viral E3 ubiquitin ligase, was shown to significantly suppress tumor necrosis factor alpha (TNF-)-medi-ated NF-B activation. ICP0 was demonstrated to bind to the NF-B subunits p65 and p50 by coimmunoprecipitation analysis. ICP0 bound to the Rel homology domain (RHD) of p65. Fluorescence microscopy demonstrated that ICP0 abolished nuclear translocation of p65 upon TNF- stimulation. Also, ICP0 degraded p50 via its E3 ubiquitin ligase activity. The RING finger (RF) domain mutant ICP0 (ICP0-RF) lost its ability to inhibit TNF--mediated NF-B activation and p65 nuclear translocation and degrade p50. Notably, the RF domain of ICP0 was sufficient to interact with p50 and abolish NF-B reporter gene activity. Here, it is for the first time shown that HSV-1 ICP0 interacts with p65 and p50, degrades p50 through the ubiquitin-proteasome path-way, and prevents NF-B-dependent gene expression, which may contribute to immune evasion and pathogenesis of HSV-1. The innate immune response to viruses involves activation ofpattern recognition receptors (1–3) and transcriptional in-duction of type I interferons (IFNs) and proinflammatory cyto-kines (4). The transcription factor NF-B plays a pivotal role in many cellular events, such as innate and adaptive immunity an