Epstein-Barr virus (EBV) immortalizes B cells and is associated with human malignancies including Burkitt's lymphoma, nasopharyngeal carcinoma, Hodgkin's disease, and lymphoproliferative disease in immunosuppressed patients. Two major cell-signalling pathways are constitutively activated by EBV during immortalization. The EBV-latency membrane protein LMP-1 has effects on B cells similar to those that occur after activation of CD40, a membrane protein that is a member of the tumor necrosis factor receptor (TNFR) superfamily. LMP-1 functions as a constitutively activated TNFR. The cytoplasmic carboxyl terminus of LMP-1 binds to the TNFR-associated factors TRAF1, TRAF2, TRAF3, and TRADD, leading to activation of the transcription factor NF-kB. The EBV-encoded nuclear proteins EBNA2, EBNA3A, and EBNA3C each interact with the DNA binding factor, RBP-J. EBNA-LP has recently been shown to cooperate with EBNA2 by binding to the EBNA2 activation domain and hence indirectly targets RBP-J/Su(H).
EBNA2 binds to the transcriptional repression domain of RBP-J/Su(H), and relief of repression combined with the effects of the EBNA2 transcriptional activation domain induces expression of repressed genes. Interaction of EBNA3A and EBNA3C with RBP-J/Su(H) prevents DNA binding by RBP-J/Su(H), and the interaction of the EBNA3 proteins and EBNA2 is mutually exclusive. These properties suggest that the EBNA3 proteins may modulate the effects of EBNA2 in a regulatory partnership. Drosophila also encodes a proteins with a function analogous to the EBNA3s. The Drosophila Hairless protein interacts with the Drosophila CSL protein Su(H) and prevents it from binding to DNA (20).
The Epstein-Barr virus-immortalizing protein EBNA2 activates both cellular and viral gene expression by targeting RBP-J/Su(H) and mimicking NotchIC.