Unusually high frequency of a 69-bp deletion within the carboxy terminus of the LMP-1 oncogene of Epstein–Barr virus detected in Burkitt’s lymphoma of Turkish children

Abstract

Burkitt’s lymphoma (BL) in Turkish children is commonly associated with Epstein–Barr virus (EBV) infection. The C-terminus of the latent membrane protein 1 (LMP-1) of EBV is essential for transformation and the 30-bp deletion detected in this region has been implicated to be associated with a more aggressive malignant phenotype. To understand the molecular mechanisms underlying EBV pathogenesis in BL of Turkish children, we analyzed 30-bp deletion and 33-bp variable repeat regions of the LMP-1 gene from paraffin-embedded tumor tissues of 30 BL patients (mean age 5.9 years). Primer pairs spanning the 30-bp deletion and 33-bp repeat regions were designed for amplification by polymerase chain reaction (PCR). The PCR-amplified products were analyzed by gel electrophoresis, Southern blot hybridization, and DNA sequencing. Twenty-eight (93%) of 30 BL biopsy samples were EBV positive as determined by PCR. Variable copy numbers (ranging from 4.5 to 7) of the 33-bp repeat of LMP-1 gene were detected in these EBV-containing tumor samples. To determine the frequency of the 30-bp deletion of the LMP-1 gene, we sequenced the amplimers encompassing this region. Analyses of DNA sequence of 28 Turkish BLs have disclosed four patterns: the first (32% (9/28)) is identical to B95–8 with no deletion, the second (11% (3/28)) is identical to Asian NPC CAO strain with 30-bp deletion, the third (46% (13/28)) is prevalent in Turkish BLs with a longer deletion (69 bp), and the fourth (11% (3/28)) consists of a mixture of 30-bp and 69-bp deletion. The occurrence of high frequency of the 69-bp deletion appears to have no correlation with the disease site. Mutations found in the CAO strain were also detected in the Turkish BL clustering at the amino acids 322, 334, 338 and 342; whereas mutations specific for Turkish BL were clustered at amino acids 326, 352 and 361. To assess the EBV genotype with the changes in C-terminus of LMP-1 gene, we performed genotyping by PCR to differentiate type A and B strain. All 28 patients were infected by type A EBV. Such a high frequency of the larger size (69 bp) deletion has never been reported. Ascertaining the role of this deletion in BL pathogenesis will require further study.