BICP0 Negatively Regulates TRAF6-Mediated NF-κB and Interferon Activation by Promoting K48-Linked Polyubiquitination of TRAF6.

Chong Cao,Ran An,Yueyang Yu,Haiyue Dai,Mingchun Gao,Zhehui Qu,Junwei Wang

doi:10.3389/fmicb.2019.03040

Abstract

The infected cell protein 0 (BICP0) is an immediate early protein encoded by BHV-1, and its RING finger domain, which endows BICP0 with intrinsic E3 ubiquitin ligase activity, is common in all ICP0 proteins. Tumor necrosis factor receptor-associated factor 6 (TRAF6) is one of the TRAF family members and is ubiquitously expressed in mammalian tissues. TRAF6 forms the MyD88-TRAF6-IRF7 complex and activates interferon induction in the TLR (Toll-like receptors) and the RLR (RIG-I-like receptor) pathway. Previous studies showed that BICP0 reduced IFN-β promoter activity by interacting with IRF7. In this study, we found that BICP0 promoted the K48-ubiquitination and degradation of TRAF6 through the ubiquitin proteasome system. The interaction between BICP0 and TRAF6 is a prerequisite for ubiquitination modification, and the 346-PAERQY-351 of BICP0 is indispensable. The motif mutation experiments showed that the tyrosine 351 of BICP0 is the key amino acid involved. Further studies demonstrated that BICP0 suppressed the NF-κB pathway via the interference of TRAF6. Moreover, degradation of TRAF6 protein influenced the K63-linked ubiquitination of IRF7 and activation of interferon promoter. Collectively, these findings indicate that the BICP0 protein suppresses the inflammation signaling and IFN production by K48-linked polyubiquitination of TRAF6 and may further clarify the immune evasion function of BICP0.

Highlights

Bovine herpesvirus 1 (BHV-1) is an enveloped virus belonging to the alphaherpesvirus subfamily, and is a significant bovine pathogen that leads to abortions, genital disorders, pneumonia, conjunctivitis, and “shipping fever,” which is an upper respiratory infection (Tikoo et al, 1995)
The results indicate that the presence of Tumor necrosis factor receptorassociated factor 6 (TRAF6) protein is significantly reduced in RE-BICP0-FLAG infected Madin Darby bovine kidney (MDBK) cells in a dose-dependent manner, and that there is no reduction in TRAF6 protein in the control baculovirus-infected MDBK cells (Figure 2A)
It is known that the ubiquitin proteasome system (UPS) and the autophagic lysosomal pathway (ALP) are the two major pathways for protein degradation; as such, we aimed to investigate if BICP0 causes the decrease of TRAF6 through the proteasome pathway or through lysosomal proteolysis

Summary

Introduction

Bovine herpesvirus 1 (BHV-1) is an enveloped virus belonging to the alphaherpesvirus subfamily, and is a significant bovine pathogen that leads to abortions, genital disorders, pneumonia, conjunctivitis, and “shipping fever,” which is an upper respiratory infection (Tikoo et al, 1995). Immunosuppression caused by BHV-1 infection triggers bovine respiratory disease complex (BRDC). The Infected Cell Protein 0 encoded by bovine herpesvirus-1 (BICP0) is important for the regulation of lytic and latent viral. BICP0 Negatively Regulates TRAF6 Activation infections (Saira et al, 2008). Like the related proteins expressed by other alphaherpesvirus that infect mammalian species, BICP0 has a C3HC4 zinc RING finger domain in the amino-terminus, which is crucial for activating viral transcription and productive infection (Parkinson and Everett, 2000; Saira et al, 2008; Boutell and Everett, 2013). The RING finger domain of BICP0 is essential for E3 ubiquitin ligase activity and leads to the ubiquitination and the subsequent degradation of a number of immune defense proteins. BICP0 reduces the ability of the IFNβ promoter in a manner correlated with IRF3 degradation, IRF7 interaction, and PML-NB dissolution, which has become a strategy used to destroy inherent innate antiviral defenses (Gaudreault and Jones, 2011)

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