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. 2015 Mar 25;10(3):e0121420.
doi: 10.1371/journal.pone.0121420. eCollection 2015.

High prevalence of the EBER variant EB-8m in endemic nasopharyngeal carcinomas

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High prevalence of the EBER variant EB-8m in endemic nasopharyngeal carcinomas

Zhi-chao Shen et al. PLoS One. .

Abstract

Epstein-Barr virus (EBV)-encoded small RNAs (EBERs) are the most highly expressed transcripts in all EBV-associated tumors and are involved in both lymphoid and epithelioid carcinogenesis. Our previous study on Chinese isolates from non-endemic area of nasopharyngeal carcinoma (NPC) identified new EBER variants (EB-8m and EB-10m) which were less common but relatively more frequent in NPC cases than healthy donors. In the present study, we determined the EBER variants in NPC cases and healthy donors from endemic and non-endemic areas of NPC within China and compared the EBER variants, in relation to the genotypes at BamHI F region (prototype F and f variant), between population groups and between two areas. According to the phylogenetic tree, four EBER variants (EB-6m, EB-8m, EB-10m and B95-8) were identified. EB-6m was dominant in all population groups except for endemic NPC group, in which EB-8m was dominant. EB-8m was more common in endemic NPC cases (82.0%, 41/50) than non-endemic NPC cases (33.7%, 32/95) (p<0.0001), and it was also more frequent in healthy donors from endemic area (32.4%, 24/74) than healthy donors from non-endemic area (1.1%, 1/92) (p<0.0001). More importantly, the EB-8m was more prevalent in NPC cases than healthy donors in both areas (p<0.0001). The f variant, which has been suggested to associate with endemic NPC, demonstrated preferential linkage with EB-8m in endemic isolates, however, the EB-8m variant seemed to be more specific to NPC isolates than f variant. These results reveal high prevalence of EBER EB-8m variant in endemic NPC cases, suggesting an association between NPC development and EBV isolates carrying EB-8m variant. Our finding identified a small healthy population group that shares the same viral strain which predominates in NPC cases. It could be interesting to carry extensive cohort studies following these individuals to evaluate the risk to develop NPC.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. EBER variations in NPC cases (A) and healthy donors (B) from NPC endemic area in China.
Numbers in the second top correspond to the nucleotide positions under which the B95-8 prototype nucleotide sequence is listed. Only nucleotides different from B95-8 are indicated. An asterisk indicates a deletion of a nucleotide. The changes in coding regions of EBER1 and EBER2 and non-coding region between EBER1 and EBER2 are separated by double lines and the positions are shown in the top. Different variants are noted to the left column, while the isolates showing identical sequences in each population group are listed by a representative isolate in the second column. The followed numbers in the parentheses denote the amount of the identical sequences from the same population group. The consensus sequence of each variant is shaded. The EBER sequences of 19 sequenced EBV genomes (B95-8, K4413-Mi, K4123-Mi, AG876, MUTU, Akata, GD1, GD2, M81, HKNPC1, C666-1 and HKNPC2 to −9) were taken from GenBank (V01555, KC440852, KC440851, DQ279927, KC207814, KC207813, AY961628, HQ020558, KF373730, JQ009376, KJ411974 and KF992564 to KF992571) [, –49].
Fig 2
Fig 2. EBER variations in NPC cases (A) and healthy donors (B) from NPC non-endemic area in China.
Numbers in the second top correspond to the nucleotide positions under which the B95-8 prototype nucleotide sequence is listed. Only nucleotides different from B95-8 are indicated. The changes in coding regions of EBER1 and EBER2 and non-coding region between EBER1 and EBER2 are separated by double lines and the positions are shown in the top. Different variants are noted to the left column, while the isolates showing identical sequences in each population group are listed by a representative isolate in the second column. The followed numbers in the parentheses denote the amount of the identical sequences from the same population group. The consensus sequence of each variant is shaded.
Fig 3
Fig 3. Phylogenetic tree based on sequences of EBER genes by neighbor-joining method.
All the 317 determined EBER sequences in our study and the 19 EBER sequences of reported EBV genomes ((B95-8, K4413-Mi, K4123-Mi, AG876, MUTU, Akata, GD1, GD2, M81, HKNPC1, C666-1 and HKNPC2 to-9) [, –49] are included in the phylogenetic tree. Isolates from endemic area are black shaded and the isolates from NPC cases are shown in italic. Population group: GDNPC and GDTW, NPC cases and healthy donors from Guangzhou, Guangdong Province, the endemic area of NPC in China; SDNPC and SDTW, NPC cases and healthy donors from Shandong Province, the non-endemic area of NPC in China. The isolates showing identical sequences in each population group are listed by a representative isolate, and the followed numbers in the parentheses denote the amount of the identical sequences from the same population group. The scale shown in the lower left shows the evolutionary distance.

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Grants and funding

This work was supported by grants from the National Natural Science Foundation of China (81171571, http://www.nsfc.gov.cn) and the Science and Technology plan project of Qingdao City, China (13-1-3-50-nsh, http://www.qdstc.gov.cn). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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