Reduced Nuclear Translocation of Nuclear Factor (NF)-κB p65 in the Footpad Epidermis of Dogs Infected with Distemper Virus

Herpes simplex virus 1 E3 ubiquitin ligase ICP0 protein inhibits tumor necrosis factor alpha-induced NF-κB activation by interacting with p65/RelA and p50/NF-κB1

NF-κB plays central roles in regulation of diverse biological processes, including innate and adaptive immunity and inflammation. 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 immune modulatory 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-α)-mediated NF-κB activation. ICP0 was demonstrated to bind to the NF-κB 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-α 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-α-mediated NF-κB activation and p65 nuclear translocation and degrade p50. Notably, the RF domain of ICP0 was sufficient to interact with p50 and abolish NF-κB 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 pathway, and prevents NF-κB-dependent gene expression, which may contribute to immune evasion and pathogenesis of HSV-1.

Analyses on activation of NF-κB and effect of bortezomib in canine neoplastic lymphoid cell lines

Lymphoid malignancies, such as leukemia, and many types of lymphoma are common and severe disorders in dogs. Since shortening remission duration caused by resistance to chemotherapy often becomes clinically critical problems, development of novel and effective therapy should be required. The present study investigated the status of NF-κB and effect of its inhibitor, bortezomib, in six canine neoplastic lymphoid cell lines. NF-κB p65 and p50 were detected in the nuclear fraction of GL-1, CLBL-1 and CL-1, suggesting that NF-κB was constitutively activated in the cells. NF-κB p65 was detected in the cytoplasmic fraction of UL-1 and Ema. After incubation with bortezomib, NF-κB p50 and p65 became undetectable in the nuclear fraction of GL-1, CLBL-1 and CL-1, and CLBL-1, respectively, and p65 was clearly degraded in the cytoplasmic fraction of CLBL-1 and CL-1. Bortezomib inhibited the proliferation of all cell lines except Nody-1 in a concentration-dependent manner. The results indicated that constitutive activation of NF-κB could contribute to the proliferation of canine neoplastic lymphoid cells, and bortezomib would have suppressive effects on the NF-κB activation and the proliferation of neoplastic lymphoid cells in dogs.

Human T-cell leukemia virus type 1 bZIP factor selectively suppresses the classical pathway of NF-kappaB

Adult T-cell leukemia (ATL) is a highly aggressive T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1). The activation of NF-kappaB by Tax has been reported to play a crucial role in HTLV-1-induced transformation. The HTLV-1 bZIP factor (HBZ), which is encoded by an mRNA of the opposite polarity of the viral genomic RNA, is involved in both T cell proliferation and suppression of Tax-mediated viral gene transcription, suggesting that HBZ cooperates closely with Tax. In the present study, we observed that HBZ specifically suppressed NF-kappaB-driven transcription mediated by p65 (the classical pathway) without inhibiting the alternative NF-kappaB signaling pathway. In an immunoprecipitation assay, HBZ bound to p65 and diminished the DNA binding capacity of p65. In addition, HBZ induced p65 degradation through increasing the expression of the PDLIM2 gene, which encodes a ubiquitin E3 ligase for p65. Finally, HBZ actually repressed the transcription of some classical NF-kappaB target genes, such as IL-8, IL2RA, IRF4, VCAM-1, and VEGF. Selective suppression of the classical NF-kappaB pathway by HBZ renders the alternative NF-kappaB pathway predominant after activation of NF-kappaB by Tax or other stimuli, which might be critical for oncogenesis.