We provide evidence for a unique pathway engaged by the type II IFN receptor, involving mTORC2/AKT-mediated downstream regulation of mTORC1 and effectors. These events are required for formation of the eukaryotic translation initiation factor 4F complex (eIF4F) and initiation of mRNA translation of type II interferon-stimulated genes. Our studies establish that Rictor is essential for the generation of type II IFN-dependent antiviral and antiproliferative responses and that it controls the generation of type II IFN-suppressive effects on normal and malignant hematopoiesis. Together, our findings establish a central role for mTORC2 in IFN␥ signaling and type II IFN responses.IFNs are cytokines that exhibit antiviral, immunomodulatory, growth-inhibitory, and cytotoxic properties (1-12). The critical roles of these cytokines in the innate immune system have provoked clinical interest and extensive studies to explore their therapeutic potential. These studies, spanning several decades, have definitively established their utility in the treatment of viral syndromes, many malignancies, and some autoimmune disorders (1-12).IFN␥, the sole type II IFN, binds to the IFNGR1 and IFNGR2 subunits of the type II IFN receptor with high affinity and activates the Janus kinases Jak1 and Jak2, leading to engagement of Jak-Stat pathways and transcriptional activation of IFN␥-regulated genes (13-16). Activation of the Jak-Stat pathway is critical for the IFN␥ transcriptional control of IFN-stimulated genes (ISGs) 3 and, subsequently, for the generation of IFN␥-induced biological responses (13-16). Beyond the classical JakStat pathways, several other signaling pathways have been shown to be activated by the type II IFN receptor, and their function appears to be critical for IFN␥ responses. These include PKC (17), MAP kinase (18,19), and Mnk kinase cascades (20). There is evidence that the AKT/mTOR pathway is engaged in IFN␥ signaling, controlling the initiation of mRNA translation for ISGs (21,22). However, the precise contribution of different mTOR complexes in this process and the sequence of events leading to ISG mRNA translation remain to be determined.The mTOR kinase forms the catalytic core of two known complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) (24 -35). mTORC1 is a protein complex consisting of mTOR, mammalian lethal with Sec 13 protein 8/G-protein ␤-protein subunit like (mLST8/G␤L), rapamycin-sensitive companion of mTOR (Raptor), Akt/PKB substrate 40 kDa (Pras40), and DEP domain-containing mTOR-interacting protein (Deptor) (24, 25). mTORC1 is known as a key regulator of pathways involved in the initiation of mRNA translation and is inhibited by allosteric inhibitors such as rapamycin, everolimus, temsirolimus, and other rapalogs (24,25). mTORC2 is comprised of mTOR, mLST8, rapamycin-insensitive companion of mTOR (Rictor), mammalian stress-activated protein kinase interacting protein 1 (Sin1), protein observed with rictor 1/2 (protor 1/2), and deptor (26 -32). Although the two mTOR complexes have different...

Edited by Charles E. SamuelThe precise signaling mechanisms by which type II IFN receptors control expression of unique genes to induce biological responses remain to be established. We provide evidence that Sin1, a known element of the mammalian target of rapamycin complex 2 (mTORC2), is required for IFN␥-induced phosphorylation and activation of AKT and that such activation mediates downstream regulation of mTORC1 and its effectors. These events play important roles in the assembly of the eukaryotic translation initiation factor 4F (eIF4F) and mRNA translation of IFN-stimulated genes. Interestingly, IFN␥-induced tyrosine phosphorylation of STAT1 is reduced in cells with targeted disruption of Sin1, leading to decreased transcription of several IFN␥-inducible genes in an mTORC2-independent manner. Additionally, our studies establish that Sin1 is essential for generation of type II IFN-dependent antiviral effects and antiproliferative responses in normal and malignant hematopoiesis. Together, our findings establish an important role for Sin1 in both transcription and translation of IFN-stimulated genes and type II IFN-mediated biological responses, involving both mTORC2-dependent and -independent functions.Interferons (IFNs) are pleiotropic cytokines that possess antiviral, immunomodulatory, growth-inhibitory, and cytotoxic properties (1-13). IFNs were among the earliest biologic therapeutic agents used to treat viral infections, certain solid tumors, hematologic cancers, and some autoimmune disorders (1-13). IFN␥, the only type II IFN, signals through a multimeric receptor complex, IFNGR, consisting of two different chains: the IFN␥ receptor binding subunit (IFNGR1) and a transmembrane accessory factor (IFNGR2) (14,15). Engagement of IFN␥ with IFNGR leads to activation of the Janus kinases, JAK1 and JAK2, leading to tyrosine phosphorylation and activation of STAT1 (14 -18). Upon activation, STAT1 homodimers bind DNA at IFN␥-activated site elements, leading to transcription of IFN-stimulated genes (ISGs) 6 (15-18). There is evidence for different signaling pathways that are activated by IFNGR. These include protein kinase C (PKC), MAPK, Mnk kinase, PI3K/AKT, and mammalian target of rapamycin complex 1 (mTORC1) and mTORC2 signaling cascades (19 -29). mTOR pathways promote mRNA translation in an mTOR/4E-BP1-dependent manner (25,(27)(28)(29)(30)(31)(32)(33). In previous studies, our group showed that AKT/mTOR pathways are engaged in IFN␥ signaling and control initiation of mRNA translation of ISGs (25,27,28,30). The 289-kDa mTOR kinase contains binding sites for multiple proteins regulating its activity or mediating its signals and consists of at least two independent multiprotein complexes: mTORC1 and mTORC2 (34 -38). mTORC1 is formed by mTOR, mLST8/G␤L (mammalian lethal with Sec13 protein 8/G-protein ␤-protein subunit-like), Raptor (rapamycin-sensitive companion of mTOR), Pras40 (Akt/PKB substrate 40 kDa), and Deptor (DEP domain-containing mTOR-interacting protein) and is sensitive to allosteric inhibitors, such ...