NOVEL PATTERNS OF THE EPSTEIN-BARR NUCLEAR ANTIGEN (EBNA-1) V-VAL SUBTYPE IN EBV-ASSOCIATED NASOPHARYNGEAL CARCINOMA FROM VIETNAM
Thuan LD1, Kha ND2, Minh NT3, Thuy LHA1,*
*Corresponding Author: Thuy Le Huyen Ai, Ph.D., Associate Professor, Department of Pharmaceutical and Medical Biotechnology, Faculty of Biotechnology, Room 304, 97 Vo Van Tan Street, Ward 6, District 3, Ho Chi Minh City Open University, Ho Chi Minh City, Vietnam. Tel: +84-905-784-471. E-mail: thuy.lha@ ou.edu.vn
page: 61

DISCUSSION

In the current study, we characterized the variations of the C-terminal domain of EBNA-1 sequences in a total of 44 EBNA-1-positive samples collected from Vietnamese nasopharyngeal cancer patients. To the best of our knowledge, this is the largest study of EBNA-1 sequence identification on EBV infection in Vietnamese cases on the high incidence and mortality rate of NPC in the world. In general, four EBNA-1 subtypes were designed as V-Val, P-Ala, P-Thr and V-Leu. These findings were similar to the research of Sun et al. [9] and showed that four subtypes of EBNA-1, except for V-Pro, were observed. It was related it to the geographically-associated EBNA-1 subtype distribution. Of these, V-Val, accounting for 79.55%, was the predominant subtype in Vietnam, an Asian country, which is similar to that of previous studies in Asian countries, such as Hong Kong; Chinese population but different from Western countries [9,15,16,20,23]. The V-Val subtype was reported as the isolate-induced higher transcriptional activity than those of the B95-8 subtype [13]. Additionally, in the current study, the nucleotide variations were analyzed between the nucleotide regions from 109408 to 109731, encoding the amino acid region from 487 to 594. As a result, most of the substitutions were located on the function domain of EBNA-1 protein, including the dimerization domain, DNA binding domain and transactivation domain, subsequently affecting the function of EBNA-1 related to the viral replication, transcription, or enhancement of oncogenic potential EBV [9,13]. Moreover, the substitution of the amino acid at position 524 (Thr→Ile), led to the subsequent loss of a phosphorylation site in the V-Val subtype [16]. Taken together, the variations of amino acids in V-Val subtypes might be easier maintained at the stage of latent infection. Given the amino changes at the C-terminal domain of EBNA-1, a total of five patterns were observed. Of these, four of five patterns, named as pattern 2, 3, 4 and 5, were identified as the novel patterns of the V-Val subtype of Vietnamese NPC patients. Notably, a mix of pattern 4 and novel pattern 5 of the V-Val EBNA-1 subtypes, shown in Figure 5(D), were observed. This observation was defined if double signals of base pairs occurred at nucleotide sequence residue 109423. Overall, four novel patterns were identified. However, whether these variations of the novel V-Val patterns could affect the function of the EBNA-1 protein is uncertain and needs to be further investigated. Conclusions. In summary, four EBNA-1 subtypes, including V-Val, P-Ala, P-Thr and V-Leu, were identified in 44 of 58 clinical nasopharyngeal biopsy samples, accounting for 75.86%, based on the amino acid at position 487. Of these, the V-Val subtype, accounting for 79.55%, was the preferential subtype in biopsies of NPC. The profile of V-Val subtypes were completely analyzed by sequencing, aligned and compared to the B95-8 prototype sequence (accession #V10555). As a result, five patterns of V-Val subtypes, containing seven consensus changes, including five amino acid changes at positions 487, 499, 502, 524 and 594 and two silent changes at residues 520 and 553, were observed. Notably, four of five patterns, including patterns 2, 3, 4 and 5, were identified as the novel patterns of the V-Val subtype, showed the different changes of amino acid at positions 492, 528, 529, 553, 585 and 588, by comparison with previous studies of V-Val EBNA-1.



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