SUMMARY Inhibitor-of-Apoptosis (IAP) proteins contribute to tumor progression, but the requirements of this pathway are not understood. Here, we show that intermolecular cooperation between XIAP and survivin stimulates tumor cell invasion and promotes metastasis. This pathway is independent of IAP inhibition of cell death. Instead, a survivin-XIAP complex activates NFκB, which in turn leads to increased fibronectin gene expression, signaling by β1 integrin(s), and activation of cell motility kinases, FAK and Src. Therefore, IAPs are direct metastasis genes, and their antagonists could provide anti-metastatic therapies in cancer patients.

SUMMARY We provide evidence that the Unc-51-like kinase 1 (ULK1) is activated during engagement of the Type I IFN receptor (IFNR). Our studies demonstrate that the function of ULK1 is required for gene transcription mediated via IFN-stimulated response elements (ISRE) and IFNγ activation site (GAS) elements and controls expression of key IFN-stimulated genes (ISGs). We identify ULK1 as an upstream regulator of p38α MAPK and establish that the regulatory effects of ULK1 on ISG expression are mediated possibly by engagement of the p38 MAPK pathway. Importantly, we demonstrate that ULK1 is essential for antiproliferative responses and Type I IFN-induced antineoplastic effects against malignant erythroid precursors from patients with myeloproliferative neoplasms. Together, these data reveal a role for ULK1 as a key mediator of Type I IFNR-generated signals that control gene transcription and induction of antineoplastic responses.

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...

Interferons (IFNs) are released by cells on exposure to various stimuli, including viruses, double-stranded RNA, and other cytokines and various polypeptides. These IFNs play important physiological and pathophysiological roles in humans. Many clinical studies have established activity for these cytokines in the treatment of several malignancies, viral syndromes, and autoimmune disorders. In this review, the regulatory effects of type I and II IFN receptors on the translation-initiation process mediated by mechanistic target of rapamycin (mTOR) and mitogen-activated protein kinase (MAPK) pathways and the known mechanisms of control of mRNA translation of IFN-stimulated genes are summarized and discussed.

Type I interferons (IFNs) induce expression of multiple genes that control innate immune responses to invoke both antiviral and antineoplastic activities. Transcription of these interferon-stimulated genes (ISGs) occurs upon activation of the canonical Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathways. Phosphorylation and acetylation are both events crucial to tightly regulate expression of ISGs. Here, using mouse embryonic fibroblasts and an array of biochemical methods including immunoblotting and kinase assays, we show that sirtuin 2 (SIRT2), a member of the NAD-dependent protein deacetylase family, is involved in type I IFN signaling. We found that SIRT2 deacetylates cyclin-dependent kinase 9 (CDK9) in a type I IFN-dependent manner and that the CDK9 deacetylation is essential for STAT1 phosphorylation at Ser-727. We also found that SIRT2 is subsequently required for the transcription of ISGs and for IFN-driven antiproliferative responses in both normal and malignant cells. These findings establish the existence of a previously unreported signaling pathway whose function is essential for the control of JAK-STAT signaling and the regulation of IFN responses. Our findings suggest that targeting sirtuin activities may offer an avenue in the development of therapies for managing immune-related diseases and cancer. cro ARTICLE

Background:The mechanisms by which IFNs generate antineoplastic responses remain to be defined. Results: Type I IFN treatment results in activation of the Mnk/eIF4E pathway in Jak2V617F-transformed cells, and this activation is required for the antineoplastic effect. Conclusion: Mnk kinases are essential for the antineoplastic effects of IFN. Significance: This study provides evidence for a key mechanism mediating the effects of IFNs in malignant MPN precursors.

We provide evidence that S6 kinase 1 (S6K1) Aly/REF-like target (SKAR) is engaged in IFN-α signaling and plays a key role in the generation of IFN responses. Our data demonstrate that IFN-α induces phosphorylation of SKAR, which is mediated by either the p90 ribosomal protein S6 kinase (RSK) or p70 S6 kinase (S6K1), in a cell type-specific manner. This type I IFN-inducible phosphorylation of SKAR results in enhanced interaction with the eukaryotic initiation factor (eIF)4G and recruitment of activated RSK1 to 5′ cap mRNA. Our studies also establish that SKAR is present in cap-binding CBP80 immune complexes and that this interaction is mediated by eIF4G. We demonstrate that inducible protein expression of key IFN-α-regulated protein products such as ISG15 and p21 WAF1/CIP1 requires SKAR activity. Importantly, our studies define a requirement for SKAR in the generation of IFN-α-dependent inhibitory effects on malignant hematopoietic progenitors from patients with chronic myeloid leukemia or myeloproliferative neoplasms. Taken altogether, these findings establish critical and essential roles for SKAR in the regulation of mRNA translation of IFN-sensitive genes and induction of IFN-α biological responses.

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