Epstein-Barr Nuclear Antigen 1 (EBNA1) is the only viral latent protein continuously expressed in all Epstein-Barr Virus (EBV)-associated tumors, including nasopharyngeal carcinoma (NPC), Hodgkin’s lymphoma and different B-cell and epithelial cell malignancies. EBNA1 maintains and replicates EBV genome by binding to the viral origin of replication, oriP, for EBV latent infection. Its DNA-binding and dimerization domain (DBD) is responsible for formation of EBNA1 homodimer and binding to the dyad symmetry (DS) element in oriP. To gain insight into EBNA1 functions, we searched for cell proteins that are essential to EBNA1 functions and found a human E3 ubiquitin ligase RNF216 interacted with EBNA1-DBD. Furthermore, we demonstrated that RNF216 facilitated EBNA1 DNA binding activity in vit...[ Read more ]

Epstein-Barr Nuclear Antigen 1 (EBNA1) is the only viral latent protein continuously expressed in all Epstein-Barr Virus (EBV)-associated tumors, including nasopharyngeal carcinoma (NPC), Hodgkin’s lymphoma and different B-cell and epithelial cell malignancies. EBNA1 maintains and replicates EBV genome by binding to the viral origin of replication, oriP, for EBV latent infection. Its DNA-binding and dimerization domain (DBD) is responsible for formation of EBNA1 homodimer and binding to the dyad symmetry (DS) element in oriP. To gain insight into EBNA1 functions, we searched for cell proteins that are essential to EBNA1 functions and found a human E3 ubiquitin ligase RNF216 interacted with EBNA1-DBD. Furthermore, we demonstrated that RNF216 facilitated EBNA1 DNA binding activity in vitro, enhanced EBV oriP-dependent DNA replication and transcriptional activation, and observed that expression of EBNA1 protected tumor necrosis factor (TNF) receptor-associated factor 3 (TRAF3) from RNF216-mediated K48-linked polyubiquitination and proteasomal degradation by displacing TRAF3 from RNF216. We further demonstrated that EBNA1 attenuated inhibitory effect of RNF216 on TRAF3 in regulation of type I interferon (IFN) in MAVS signaling.

Latent membrane protein 1 (LMP1) provides EBV-induced oncogenesis and tumorigenesis by constitutive NF-κB activation in type II latency. Intracellular LMP1 level is well-monitored through exosomal trafficking pathway. Here, we demonstrated that both ubiquitinations of LMP1 and its adaptor proteins TRAF2 and TRAF3 were blocked by RNF216. LMP1 extensively localized in Golgi and its exosomal release was blocked by RNF216, indicating an alternative ubiquitin-ESCRT-dependent sorting of LMP1. Furthermore, RNF216 controlled intracellular LMP1 level by enhancing LMP1 stability, and thus promoted LMP1-mediated NF-κB activation.

Thus, these findings provide new insights how two EBV latent proteins EBNA1 and LMP1 exploit human RNF216 by promoting EBV replication and altering cellular signaling to facilitate EBV latent infection.