Efficient Translation of Epstein-Barr Virus (EBV) DNA Polymerase Contributes to the Enhanced Lytic Replication Phenotype of M81 EBV

Abstract

Epstein-Barr virus (EBV) is linked to the development of both lymphoid and epithelial malignancies worldwide. The M81 strain of EBV, isolated from a Chinese patient with nasopharyngeal carcinoma (NPC), demonstrates spontaneous lytic replication and high-titer virus production in comparison to the prototype B95-8 EBV strain. Genetic comparisons of M81 and B95-8 EBVs were previously been performed in order to determine if the hyperlytic property of M81 is associated with sequence differences in essential lytic genes. EBV SM is an RNA-binding protein expressed during early lytic replication that is essential for virus production. We compared the functions of M81 SM and B95-8 SM and demonstrate that polymorphisms in SM do not contribute to the lytic phenotype of M81 EBV. However, the expression level of the EBV DNA polymerase protein was much higher in M81- than in B95-8-infected cells. The relative deficiency in the expression of B95-8 DNA polymerase was related to the B95-8 genome deletion, which truncates the BALF5 3' untranslated region (UTR). Similarly, the insertion of bacmid DNA into the widely used recombinant B95-8 bacmid creates an inefficient BALF5 3' UTR. We further showed that the while SM is required for and facilitates the efficient expression of both M81 and B95-8 mRNAs regardless of the 3' UTR, the BALF5 3' UTR sequence is important for BALF5 protein translation. These data indicate that the enhanced lytic replication and virus production of M81 compared to those of B95-8 are partly due to the robust translation of EBV DNA polymerase required for viral DNA replication due to a more efficient BALF5 3' UTR in M81. Epstein-Barr virus (EBV) infects more than 90% of the human population, but the incidence of EBV-associated tumors varies greatly in different parts of the world. Thus, understanding the connection between genetic polymorphisms from patient isolates of EBV, gene expression phenotypes, and disease is important and may help in developing antiviral therapy. This study examines potential causes of the enhanced lytic replicative properties of M81 EBV isolated from a nasopharyngeal carcinoma (NPC) patient and provides new evidence for the role of the BALF5 gene 3' UTR sequence in DNA polymerase protein expression during lytic replication. Variation in the gene structure of the DNA polymerase gene may therefore contribute to lytic virus reactivation and pathogenesis.

Intra-host changes in Kaposi sarcoma-associated herpesvirus genomes in Ugandan adults with Kaposi sarcoma

“…In EBV infections, intra-host selection and compartmentalization of viruses may have a role in pathogenesis of EBV-associated cancers [11][12][13]. Additionally, EBV strains isolated from nasopharyngeal carcinomas (NPC) have unique genomic [14,15] and phenotypic [16][17][18] variations compared to other strains and isolates from geographically clustered individuals without cancer [19]. NPC-associated strains were also found to have increased tropism for epithelial-versus B-cells [16,20].…”

Epstein–Barr virus co-opts TFIIH component XPB to specifically activate essential viral lytic promoters

“…Next, 250 μL of filtered supernatant was used to infect Raji cells. Virus titer was measured and quantitated in infected cells by flow cytometry (66).…”

Role of BamHI-A Rightward Frame 1 in Epstein–Barr Virus-Associated Epithelial Malignancies

“…There are some early promoters regulated by these IE proteins such as BMRF1, SM, BHLF1, and BHRF1. The genes that are currently translated at this stage are the viral DNA polymerase (BALF5) [ 34 ], DNA polymerase processivity factor (BMRF1) [ 35 ], helicase (BBLF4) [ 36 ], primase (BSLF1) [ 36 ], and others. BMRF1 and BRRF1 are transcription factors that activate the oriLyt (lytic replication origin).…”