Characterization of intercellular adhesion molecule-1 regulation by Epstein-Barr virus-encoded latent membrane protein-1 identifies pathways that cooperate with nuclear factor kappa B to activate transcription.

The latent membrane protein-1 (LMP1) of Epstein-Barr virus induces gene transcription, phenotypic changes, and oncogenic transformation. One cellular gene induced by LMP1 is that for intercellular adhesion molecule-1 (ICAM-1), which participates in a wide range of inflammatory and immune responses. ICAM-1 may enhance the immune recognition of cells transformed by Epstein-Barr virus, and thus combat development of malignancy. Despite growing understanding of the various signaling functions of LMP1, the molecular mechanisms by which LMP1 induces ICAM-1 are not understood. Here, we demonstrate that transcriptional activation by LMP1 is absolutely dependent upon a variant NF-kappaB motif within the tumor necrosis factor alpha (TNFalpha) response element of the ICAM-1 promoter. Although the TNFalpha response element is sufficient for TNFalpha induction of the ICAM-1 promoter, LMP1 also required the cooperation of additional upstream sequences for optimal induction. Inhibitor studies of known LMP1-induced signaling pathways ruled out the involvement of c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase, and the Janus-activating tyrosine kinase 3 (JAK3), and confirmed NF-kappaB as a critical factor for induction of ICAM-1. However, although constitutive activation of NF-kappaB efficiently induced promoter activity, it was not sufficient to induce either ICAM-1 mRNA or ICAM-1 protein. Using signaling defective LMP1 mutants and deacetylation inhibitors, we showed that the C-terminal activator region 1 of LMP1 delivers a new cooperating signal to induce ICAM-1 mRNA.