The mTOR Inhibitor Manassantin B Reveals A Crucial Role of mTORC2 Signaling in Epstein-Barr Virus Reactivation.

Lytic replication of Epstein-Barr virus (EBV) is not only essential for its cell-to-cell spread and host-to-host transmission, but also contributes to EBV-induced oncogenesis. Thus, blocking EBV lytic replication could be a strategy for managing EBV-associated diseases. Previously we identified a series of natural lignans isolated from the roots of Saururus chinensis (Asian lizard's tail) that efficiently blocks EBV lytic replication and virion production with low cytotoxicity. In the current study, we attempted to elucidate the molecular mechanism by which these lignans inhibit EBV lytic replication. We found that a representative compound, CSC27 (manassantin B), inhibits EBV lytic replication by suppressing the expression of EBV immediate-early gene BZLF1 via disruption of AP-1 signal transduction. Further analysis revealed that manassantin B specifically blocks mTOR complex 2 (mTORC2)-mediated phosphorylation of AKT Ser/Thr protein kinase at Ser-473 and protein kinase Cα (PKCα) at Ser-657. Using phosphoinositide 3-kinase (PI3K)-AKT-specific inhibitors for kinase mapping and shRNA-mediated gene silencing, we validated that manassantin B abrogates EBV lytic replication by inhibiting mTORC2 activity and thereby blocking the mTORC2-PKC/AKT signaling pathway. These results suggest that mTORC2 may have utility as an antiviral drug target against EBV infections and also reveal that manassantin B has potential therapeutic value for managing cancers that depend on mTORC2 signaling for survival.