EBNA-1 sequence variations reflect active EBV replication and disease status or quiescent latency in lymphocytes

EBV infects most of the global population, but only a small percentage of infected individuals develop EBV-associated malignancies. Host and viral factors may play a role in determining the clinical outcome. Because EBNA-1 functions as an oriP binding protein and links the episomal viral DNA to metaphase chromosomes, variation of EBNA-1 has been suggested to contribute to determining the tissue tropism of EBV and the development of various EBV-associated diseases. Five subtypes have been described, according to the amino acid at residue 487: P-ala (B95-8 prototype), P-thr (aa 487 ala to thr), V-val, V-pro and V-leu. Other studies, however, concluded that EBNA-1 sequence variation simply reflects the geographical distribution of EBV. To clarify these possibilities, we collected DNA samples from healthy individuals and patients with various EBV-associated diseases in Taiwan for PCR amplification and DNA sequencing. The results indicate that: 1) V-val EBNA-1 was detected in patients with nasopharyngeal carcinoma (NPC) and other EBV-associated malignant diseases; 2) the prototype P-ala strain was detected only in peripheral blood lymphocytes; 3) mixed populations of different subtypes of N-terminal and C-terminal sequences were observed in samples from one patient with nasopharyngeal carcinoma, one with T lymphoma and one with infectious mononucleosis sample; 4) intermediate variations between P-ala and V-val were observed in T-lymphoma, Hodgkin disease and infectious mononucleosis samples; and 5) in comparison with the major sequences identified in healthy carriers, the EBNA-1 sequences in peripheral lymphocytes from nasopharyngeal carcinoma were mixed types in 4 of 5 patients, implying increasing frequency of V-val might correlate with the progression of nasopharyngeal carcinoma.