Polymorphism On Latent Membrane Protein Gene Of Epstein-barr Virus In Lymphomas

Background and objective: As an oncogenic gene, Epstein-Barr Virus(EBV) latent membrane protein 1(LMP1) plays important role in the tumorigenesis of EBV-related tumors. Different sequence variations have been found in LMP1 gene and much attention has been focused on the association of LMP1 variants with EBV-associated tumors. However, whether the LMP1 variants preferentially associate with particular malignancies or represent geographical polymorphism remains controversial. In China, most studies of the sequence variations of LMP1 have been limited to the nasopharyngeal carcinoma cases. The lymphoma cases have not been extensively determined and most studies only detected single gene variation of LMP1. To characterize the variations of the LMP1 gene in Qingdao area and to explore the association between LMP1 gene variations and lymphomas, the sequences of LMP1 gene from lymphoma biopsies and throat washing samples of healthy donors were analyzed.Method: PCR and DNA sequencing were used to analyze the gene sequences of LMP1 in isolates from 80 EBV positive lymphoma tissues(47 extranodal NK/T cell lymphomas, 26 Hodgkin’s lymphomas, 2 diffuse large B cell lymphomas and 5 T cell lymphomas) and 70 throat washing samples of healthy donors in Qingdao. The nucleotide and amino acid sequences of LMP1 were compared with the prototype B95-8 strain and classified according to the signature changes and the phylogenetic tree. The distribution of LMP1 variants was compared between lymphomas and healthy donors, as well as between different lymphomas.Results: ①Compared with the LMP1 sequence of B95-8 prototype, all sequences of LMP1 gene from 150 isolates demonstrated sequence variations, including point nucleotide mutations, insert, deletions and repetitive sequence changes. According to phylogenetic tree and the signature changes in coding region of LMP1, three major subtypes(China 1, China 2 and Med-) and a few recombinant strains of different subtypes, were identified. Furthermore, three major variants also carried characteristic changes in non-coding regions and repetitive sequence region. LMP1 subtypes and recombinant strains demonstrated various spectrum to Xho I(-)(loss of an Xho I site) in N-terminus of LMP1 and del-LMP1(30 bp deletion) in C-terminus of LMP1. ②The frequencies of China 1, China 2 and Med- in lymphomas were 85.0%(68/80), 6.3%(5/80) and 7.5%(6/80), respectively, and those in healthy donors were 65.7%(46/70), 5.7%(4/70) and 21.4%(15/70). Another 1(2.1%) lymphoma isolate and 5(7.2%) healthy donor isolates were recombinant strains of different subtypes. The distribution of LMP1 subtypes between lymphoma and healthy donors was significant different(P=0.014). The frequencies of Xho I(-) and del-LMP1 in lymphomas(92.5% and 85.0%) were significantly higher than those in healthy donors(74.3% and 67.1%), and the differences were significant( P=0.002, 0.010). ③There was no significant difference of the distribution of LMP1 gene variants between 47 extranodal NK/T cell lymphomas and 26 Hodgkin’s lymphomas.Conclusions: ①The variations of LMP1 are complicated and it is better to analyze the whole sequences of LMP1 to fully understand the variations of LMP1. ②China 1, Xho I(-) and del-LMP1 are the major LMP1 subtypes in lymphomas and healthy donors in Qingdao area. The higher frequencies of these three variants in lymphomas than healthy donors suggest their association with the susceptibility of lymphomas although no evidence for cell tropism of specific lymphomas is found.