Characterization of Epstein-Barr Nuclear Antigen 1 (EBNA1) Effects on Host Cells and its Functional Interaction with the Cellular Kinase CK2

Epstein-Barr virus (EBV) immortalizes host cells as part of its latent mode of infection, and the Epstein-Barr Nuclear Antigen 1 (EBNA1) is essential for establishing EBV latency. In addition to its roles on the EBV genome, increasing evidence suggests that EBNA1 contributes to cell immortalization and survival. The aim of this thesis is to further characterize the effects of EBNA1 on cells. Firstly, I performed a 2D-DiGE proteomic screen on the nuclear proteome of nasopharyngeal carcinoma (NPC) cells with or without EBNA1 expression, and identified several new proteins whose levels were modulated by EBNA1. In addition, I found that stable EBNA1 expression resulted in an accumulation of ROS (reactive oxygen species) in NPC cells, which may be partly due to an EBNA1-induced increase in the transcript and protein levels of NOX1 and NOX2 NADPH oxidases. These findings indicate new ways that EBNA1 can alter the host cell environment and contribute to the development of NPC. EBNA1 exerts multiple effects through interactions with cellular proteins. Here, I also investigated the EBNA1 interaction with the cellular kinase CK2 (Casein Kinase 2), and showed that this interaction is critical for the ability of EBNA1 to disrupt PML (promyelocytic leukemia) nuclear bodies, that mediate tumour suppressor functions and the anti-viral response. Specifically, EBNA1 increases the association of two cellular enzymes, CK2 and USP7 (ubiquitin specific protease 7), with PML nuclear bodies, which leads to the phosphorylation and polyubiqutylation of the PML proteins resulting in their degradation. Lastly, through the characterization of the EBNA1-CK2 interaction, I discovered a novel protein binding pocket in CK2β, containing a KSSR motif, which mediates protein-protein interactions with viral and cellular proteins. The CK2β KSSR motif has the propensity to bind polyserine tracts on EBNA1 as well as on another cellular protein, ARKL1.Ph