Study of Epstein-Barr virus nuclear antigen (EBNA-1) variations: V-val type preferentially exists in biopsies of nasopharyngeal carcinoma from Vietnamese patients

Background: Epstein-barr virus nuclear antigen 1 (EBNA1) plays a crucial role in Nasopharyngeal carcinoma (NPC), the most common cancer of head and neck cancer in Asian countries with high incidents. Sequence variations are of high frequency within the functionally important domains of EBNA-1, which have been classified into five subtypes: Phenotype (P)-ala, P-thr, V-val, V-leu and V-pro and are related to geographical location.  This study aimed to evaluate the variations of EBNA-1 in NPC biopsy samples from Vietnamese patients.  Materials and Methods: In this descriptive analytical study, 20 NPC biopsy samples, which were positively confirmed to NPC, were collected from Cho Ray Hospital. Nested PCR – nucleotide sequencing was applied to analyze the carboxy-terminal region of EBNA-1. Phylogenetic analysis was performed using the Molecular Evolutionary Genetics Analysis, version 5.0, by Neighbor-Joining algorithm. Results: The variants of EBNA-1 have been described based on the amino acid signature at codon 487, including V-val (75.0%), P-ala (10%), P-thr (5%), V-leu (5%). Additionally, the phylogenetic results confirmed that the V-val subtype, detected in this current study of the Vietnamese population, was in accordance with previous studies that V-val is almost an exclusive variation in Asian region, especially with Chinese populations and preferentially exists in biopsies of nasopharyngeal carcinoma.  Conclusion: In this initial study, the sub-strains of EBV within V-val subtype of EBNA-1 was preferential in biopsies of NPC patients. The finding provided the initial data for the potential contribution of EBNA-1 polymorphisms to etiology of NPC in Vietnamese population.