Epstein-Barr virus immediate-early protein BRLF1 induces the lytic form ofviral replication through a mechanism involving phosphatidylinositol-3 kinase activation

Expression of the Epstein-Barr virus (EBV) immediate-early (IE) protein BRL F1 induces the lytic form of viral replication in most EBV-positive cell li nes. BRLF1 is a transcriptional activator that binds directly to a GC-rich motif present in some EBV lytic gene promoters. However, BRLF1 activates tr anscription of the other IE protein, BZLF1, through an indirect mechanism w hich we previously showed to require activation of the stress mitogen-activ ated protein kinases. Here we demonstrate that BRLF1 activates phosphatidyl inositol-3 (PI3) kinase signaling in host cells. We show that the specific PI3 kinase inhibitor, LY294002, completely abrogates the ability of a BRLF1 adenovirus vector to induce the lytic form of EBV infection, while not aff ecting lytic infection induced by a BZLF1 adenovirus vector. Furthermore, w e demonstrate that the requirement for PI3 kinase activation in BRLF1-induc ed transcriptional activation is promoter dependent. BRLF1 activation of th e SM early promoter (which occurs through a direct binding mechanism) does not require PI3 kinase activation, whereas activation of the IE BZLF1 and e arly BMRF1 promoters requires PI3 kinase activation. Thus, there are clearl y two separate mechanisms by which BRLF1 induces transcriptional activation .