Two genes encoding the latent membrane protein 1 (LMP1) of the Epstein-Barr virus (EBV) were isolated from a single case of Hodgkin's disease (HD) and were tested for their biological activities. The LMP1 gene from the Reed-Sternberg cells contained point mutations relative to the prototype LMP1 gene, leading to amino-acid exchanges. The LMP1 gene from passenger lymphocytes showed identical point mutations, but also had an in-frame insertion of 132 base pairs within the 33-bp repeat region. This insert encoding 44 amino acids contained the sequence PSQQS, corresponding to the potential TRAF-binding motif PXQXT/S. When compared to the B95.8 gene, both HD-derived LMP1 genes showed an increase in the transformation of Rat-1 rodent fibroblasts. The transforming ability of the LMP1 gene with the insertion was greater than that of the other HD-derived LMP1, and was comparable with the highly transforming LMP1-Cao gene derived from a nasopharyngeal carcinoma. The HD-derived genes stimulated expression of the cell-surface markers, CD40 and CD54, similarly to the LMP1-B95.8 gene, while the LMP1-Cao gene had a significantly reduced ability to induce these proteins. In contrast, the LMP1-Cao transactivated an NF-kappaB-response element more efficiently than did the HD-derived genes. Transfer of the 132-bp insert alone into the B95.8 gene did not increase its transforming activity to the LMP1-Cao level, indicating that additional mutations in the LMP1 gene are necessary for modulating this function.
