
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
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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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