Identification of functional differences between prototype Epstein-Barr virus-encoded LMP1 and a nasopharyngeal...

The contribution of Epstein-Barr virus (EBV) strain variation to the pathogenesis of virus-associated tumours remains unknown. Given the central role of LMP1 in EBV-induced transformation, much interest has focused on the influence of LMP1 sequence variation on the signaling pathways and multiple downstream phenotypic consequences of LMP1 expression. The identification of LMP1 variants with a common 10-amino-acid deletion and additional point mutations (typified by the CAO-LMP1 isolate) in EBV strains associated with nasopharyngeal carcinoma prompted us to examine the effect of stable prototype B95.8-LMP1 and CAO-LMP1 expression on the phenotype and differentiation of SCC12F human epithelial cells. Both forms of LMP1 were able to induce expression of the antiapoptotic A20 protein and provide protection from tumour necrosis factor-alpha-induced cytotoxicity. Although B95.8-LMP1 induced growth inhibition, expression of certain cell surface molecules (CD40, CD44, and CD54), and secretion of interleukin-6 and -8 in SCC12F cells, stable CAO-LMP1 expression failed to elicit these effects. Furthermore, B95. 8-LMP1, but not CAO-LMP1, induced alterations in cell morphology and blocked epithelial cell differentiation. Both B95.8-LMP1 and CAO-LMP1 induced similar levels of nuclear factor-kappaB activation, but the ability of CAO-LMP1 to activate the AP-1 pathway was relatively impaired. These data highlight significant functional differences between the prototype B95.8-LMP1 and the CAO-LMP1 variant when stably expressed in human epithelial cells and suggest that continued analysis of LMP1 variants will help to further dissect the signaling pathways activated by LMP1 as well as provide insights into the contribution of LMP1 sequence variation to the pathogenesis of EBV-associated tumours.