| Objective:Epstein-Barr virus(EBV)is a human herpesvirus associated with numerous human cancers,including Burkitt's lymphoma(BL),Hodgkin's disease(HD),nasopharyngeal carcinoma(NPC),gastric carcinoma(GC),and breast carcinoma.In previous studies,over 90% of the human population had EBV infection.It is said that the distribution of EBV associated cancers has the character of regional.This raises the possibility that particular EBV strains may contribute to the development of specific EBV-associated malignancies.In this study,nasopharyngeal carcinoma(NPC)patients and healthy donors in Southern China were chosen to explore the relationship between EBV genotypes and NPC.Mehods:(1)polymerase chain reaction(PCR)and DNA sequencing were chosen for the EBNA3 C polymorphism study in EBV positive NPC,GC and TW.After sequencing,the sequences were compared with EBV prototype B95-8 by DNAStar 5.0.(2)All sequences were aligned and categorized by their consensus changes.One sequence was chosen to represent the samples which have identical sequences.Alignments between representative sequences were performed using Meg Align in DNA Star software(DNASTAR,Inc,version 5.0),and the phylogenetic tree was drawn using Clastal W method.(3)To analyze the variations of EBNA3 C and to investigate the association between the gene variations with function influence.(4)The results were compared with our previous studies about NPC in Northern China.Results:EBNA2 gene was successfully amplified from 32 NPCs and 39 TWs from Guangzhou.Based on the phylogenetic tree,all isolates can be divided into 3 subtypes,named E2-A,E2-C and B95-8 respectively according to the common mutations in each pattern.(1)E2-A sequences were found in most isolates(38/71,52.1%),and NPC1 was the present sequence.5 consensus nucleotide sequence changes were identified from this subtype compared with prototype B95-8,including 2 missense mutation aa476(Glu?Gly/Trp)and aa486(Ile?Thr),3 nonsense mutation aa378(Ger ?Tyr),aa411(Val ?Ile)?aa451(Pro?His).Additional sporadic mutations were observed at 6 residues,331(Pro ?Leu),383(cct ?cca),390(ggt ?gga),411(Val ?Ile),438(Ile?Leu)and 484(Pro ?His).(2)The second common subtype was E2-C(represented by NPC3).In this subtype,there was one common nucleotide substitution(AA370,cct?cca)and two AA deletions(AA357 and 358).Additional sporadic mutations were observed at 3 residues,including 378(Ger ?Tyr),411(Val ?Ile)and 451(Pro ?His).Interestingly,we found that E2-C sequence was identical with GD1 strain,a representative EBV type isolated from NPC in Southern China.(3)The least common subtype B95-8 like(represented by TA56)only had one mutation at residue 370(cct?cca).(4)The distribution of EBNA-2 subtypes between the NPCs and TWs was significantly different(P<0.01).The proportion of the E2-A in NPCs(71.9%,22/32)was significantly higher than that in TWs(38.5%,15/39).The proportion of the B95-8 like subtype in TWs(25.6%,10/39)was significantly higher than in NPCs(0%,0/32).Conclusion:(1)subtype E2-A was the predominant subtype in Southern China,and was more prevalent in China.(2)The distribution of EBNA-2 subtypes between NPCs and TWs was significantly different(P<0.01),suggesting E2-A subtype was more related with the onset of NPC and B95-8 like subtype may be more relevant to TW.(3)EBNA-2 gene variations are tumor specific polymorphisms rather than geographically restricted. |
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