Rather, we get that this regulation of 4EBP1 activity by rapamycin-resistant mTORC1 is critical for MCMV replication, as Torin1 was incapable of inhibiting MCMV growth in 4EBP1-null fibroblasts (Fig.7). of the translational repressor 4EBP1 to the 7-methylguanosine cap-binding complex. Torin1 does not impact 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. Comparable mTOR signaling events were observed during murine cytomegalovirus (MCMV) contamination, and we utilized murine fibroblasts made up of several different mutations to dissect the mechanism by which Torin1 inhibits MCMV replication. This approach exhibited 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 this inactivation of 4EBP1 by mTORC1 is critical for cytomegalovirus replication. Finally, we show that Torin1 inhibits the replication of representative users of the alpha-, beta-, and gammaherpesvirus families, demonstrating the PDGFRA potential of mTOR kinase inhibitors as broad-spectrum antiviral brokers. As intracellular parasites with limited genetic resources, viruses must rely on the host cell machinery to perform tasks essential for viral replication, even as host cell defense mechanisms inactivate many processes most commonly hijacked by viruses. As a consequence, viruses have evolved mechanisms TUG-770 TUG-770 to maintain the function of these cellular processes and to subvert them for their own ends. Viruses typically reprogram the host protein synthetic pathway to favor the translation of viral mRNAs (1,3,13). In response, the host cell has TUG-770 developed multiple defenses to inhibit the translation of viral proteins, and viruses have evolved mechanisms to antagonize this response. For example, double-stranded RNA (dsRNA) produced during viral contamination activates protein kinase R, which phosphorylates and inactivates the translation initiation factor eIF2, blocking the initiation of translation. The activation of protein kinase R is an effective antiviral mechanism, so much so that multiple viruses, including members of all three subfamilies of herpesviruses, have evolved strategies to counteract the effects of PKR on viral replication (5,17,28,33,35,36). By encoding proteins that disable the host cell control of translation, viruses maintain the capacity TUG-770 of the infected cell to translate viral proteins. Viruses also induce cellular signaling pathways that activate translation and then reprogram the activated translational apparatus to promote the synthesis of viral proteins. The mammalian target of rapamycin (mTOR) kinase is usually a metabolic sensor that regulates translation (37). The mTOR serine/threonine kinase is the catalytic subunit of two complexes, mTORC1 and mTORC2, that control cell growth, proliferation, and survival. The activation of mTORC1 signaling results in the initiation of several processes required for the efficient translation of 7-methyl guanosine (m7G)-capped mRNAs. mTORC1 phosphorylates and induces the activity of the p70 S6 kinase (4), which in turn phosphorylates ribosomal protein S6 (rpS6) to promote ribosome biogenesis. At the same time, mTORC1 phosphorylates and inactivates the translational repressor 4EBP1 (4,11,15,27). The translation of capped mRNAs requires the eIF4F complex, which is composed of eIF4E, eIF4A, and eIF4G (14,43). The eIF4F complex binds to the m7G cap of mRNAs and facilitates their association with the ribosome. Hypophosphorylated 4EBP1 binds to the mRNA cap recognition protein eIF4E, preventing the formation of the eIF4F complex and thereby blocking translation (38). The phosphorylation of 4EBP1 by mTORC1 blocks its ability to bind to eIF4E, resulting in an increased translation of capped mRNAs (4). Given its important role in the regulation of cap-dependent translation, it is not amazing that multiple viruses that rely on cap-dependent mRNA translation have evolved mechanisms to ensure that mTORC1 remains active during contamination. As a case in point, human cytomegalovirus (HCMV), a common betaherpesvirus that causes life-threatening disease in immunologically immature or compromised individuals, utilizes cap-dependent mRNA translation for its protein synthesis (3), and it induces mTOR activity, presumably to increase the translation of viral proteins (21,24,53). Furthermore, to maintain mTORC1 activity, HCMV encodes a protein, pUL38, that binds to and inhibits the tuberous sclerosis protein complex (TSC1/TSC2) (31). The TSC1 and TSC2 proteins function as a heterodimer, which limits mTORC1 activity in response to cellular stresses such as limited nutrient availability (20,45). pUL38 alone is sufficient to prevent the inhibition of mTORC1 under limiting nutrient conditions and when TSC1/TSC2 activity is usually induced by drug treatment. Under these conditions, the classical mTORC1 inhibitor rapamycin inhibits mTORC1 in the presence of the viral protein, demonstrating that pUL38 maintains the phosphorylation of mTORC1 targets by manipulating the canonical signaling pathway. HCMV contamination induces a unique set of events in the mTOR signaling pathway. While the phosphorylation of the mTORC1 effector rpS6 is usually inhibited by rapamycin during HCMV contamination, the phosphorylation of.