Activated mouse Notch1 transactivates Epstein-Barr virus nuclear antigen 2-regulated viral promoters

Epstein-Barr virus nuclear antigen 2 (EBNA2) is essential for B-cell immort alization by EBV, most probably by its ability to transactivate a number of cellular and viral genes, EBNA2-responsive elements (EBNA2REs) have been i dentified in several EBNA2-regulated viral promoters, each of them carrying at least one RBP-J kappa recognition site, RBP-J kappa recruits EBNA2 to t he EBNA2RE and, once complexed to EBNA2, is converted from a repressor into an activator, An activated form of the cellular receptor Notch also intera cts with RBP-J kappa, providing a link between EBNA2 and Notch signalling. To determine whether activated Notch is able to transactivate EBNA2-respons ive viral promoters, we performed cotransfection experiments with activated mouse Notch1 (mNotch1-IC) and luciferase constructs of the BamHI C, LMP1, and LMP2A promoters. We present here evidence that mNotch1-IC transactivate s viral promoters known to be regulated by EBNA2, As shown for EBNA2, mutat ions or deletions of the RBP-J kappa sites diminish or eliminate mNotch1-IC -mediated transactivation of the promoters, pointing to an essential role f or Notch-RBP-J kappa interaction, In addition to RBP-J kappa, other cellula r factors may bind within the EBNA2REs of viral promoters. While some facto rs appear to play an important role in both EBNA2- and mNotch1-IC-mediated transactivation, others are only important for the activity of either EBNA2 or mNotch1-IC. We could observe specific mNotch 1-IC-responsive regions, t hereby throwing more light upon which cofactors interact with EBNA2 and mNo tch1-IC, thus enabling them to become functionally transactivators in vivo.