Sequence variations of Epstein-Barr virus LMP2A gene in gastric carcinoma in Japan

The latent EBV gene products expressed in Epstein-Barr virus (EBV)-associated gastric carcinoma (EBVaGC), are only LMP2A, EBNA-1, BARF-0 and EBERs. To examine the correlation between LMP2A sequence variation in EBVaGC and transformation of the cells, the complete sequence of the LMP2A gene was determined in three cases of Japanese EBVaGC and compared with the prototype B95-8 strain. In addition, the sequences of exons 2,6 and 7 of LMP2A were determined in four to six EBVaGC cases. The results of sequence analysis indicated that LMP2A of EBVaGC was structurally very similar to B95-8, but contained a significant nucleotide variation. Ten nucleotide substitutions were identified in almost all cases tested, and three of these caused amino acid changes. Of these three, two amino acid substitutions were not expected to change any known functions of LMP2A. The other amino acid substitution from serine to threonine was located at codon 348 within one of the target epitopes of EBV-specific cytotoxic T-lymphocytes. The LMP2A of EBV in peripheral blood lymphocytes from six healthy individuals showed serine (4/6 cases) or threonine (2/6 cases) substitution at codon 348, while LMP2A with the threonine substitution was the major form (5/6 cases) observed in EBVaGC, indicating that EBV with the threonine substitution may confer an advantage for viral persistence in tumor cells. However, our sequencing results suggested that the LMP2A protein in EBVaGC is functionally similar to that of the B95-8 strain and is not unique to gastric carcinoma, indicating the importance of LMP2A for EBV latency.