Rapamycin-Resistant mTORC1 Kinase Activity Is Required for Herpesvirus Replication

Human cytomegalovirus (HCMV) infection has been shown to activate the mTORC1 signaling pathway. However, the phosphorylation of mTORC1 targets is differentially sensitive to the mTORC1 inhibitor rapamycin, and the drug inhibits HCMV replication to a modest extent. Using Torin1, a newly developed inhibitor that targets the catalytic site of mTOR kinase, we show that HCMV replication requires both rapamycin-sensitive and rapamycin-resistant mTOR activity. The treatment of infected cells with Torin1 inhibits the phosphorylation of rapamycin-sensitive and rapamycin-resistant mTOR targets and markedly blocks the production of virus progeny. The blockade of mTOR signaling with Torin1, but not rapamycin, disrupts the assembly of the eIF4F complex and increases the association of the translational repressor 4EBP1 to the 7-methylguanosine cap-binding complex. Torin1 does not affect HCMV entry and only modestly reduces the accumulation of the immediate-early and early viral proteins that were tested despite the disruption of the eIF4F complex. In contrast, Torin1 significantly decreases the accumulation of viral DNA and the pUL99 viral late protein. Similar mTOR signaling events were observed during murine cytomegalovirus (MCMV) infection, and we utilized murine fibroblasts containing several different mutations to dissect the mechanism by which Torin1 inhibits MCMV replication. This approach demonstrated that mTORC2 and the Akt1 and Akt2 kinases are not required for the Torin1-mediated inhibition of cytomegalovirus replication. The inhibition of MCMV replication by Torin1 was rescued in cells lacking 4EBP1, demonstrating that the inactivation of 4EBP1 by mTORC1 is critical for cytomegalovirus replication. Finally, we show that Torin1 inhibits the replication of representative members of the alpha-, beta-, and gammaherpesvirus families, demonstrating the potential of mTOR kinase inhibitors as broad-spectrum antiviral agents.