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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 IFNγ signaling and type II IFN responses.

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.

The mechanisms of generation of the antineoplastic effects of interferons (IFNs) in malignant hematopoietic cells remain to be precisely defined. We examined the activation of type I IFN-dependent signaling pathways in malignant cells transformed by Jak2V617F, a critical pathogenic mutation in myeloproliferative neoplasms (MPNs). Our studies demonstrate that during engagement of the type I IFN receptor (IFNAR), there is activation of Jak-Stat pathways and also engagement of Mnk kinases. Activation of Mnk kinases is regulated by the Mek/Erk pathway and is required for the generation of IFN-induced growth inhibitory responses, but Mnk kinase activation does not modulate IFN-regulated Jak-Stat signals. We demonstrate that for type I IFNs to exert suppressive effects in malignant hematopoietic progenitors from patients with polycythemia vera, induction of Mnk kinase activity is required, as evidenced by studies involving pharmacological inhibition of Mnk or siRNA-mediated Mnk knockdown. Altogether, these findings provide evidence for key and essential roles of the Mnk kinase pathway in the generation of the antineoplastic effects of type I IFNs in Jak2V617F-dependent MPNs.

Over the last two decades, a lot of research work has been focused on the interferon (IFN)-regulated JAK-STAT pathway and understanding the mechanisms governing the transcription of interferon stimulated genes (ISGs). Evidence suggests that the JAK-STAT pathway alone does not account in its entirety for mediating cellular responses to IFNs. There is emerging evidence that non-Stat pathways play important roles in mediating signals for the generation of IFN-responses. Various studies have underscored the importance of mitogen activated protein kinases (MAPKs), especially p38 and ERK1/2, as well as the PI 3'K/AKT pathway in transmitting signals that are of critical importance for the biological effects of IFNs. Besides regulating the transcription of ISGs in some cases, engagement of these signaling pathways by the IFN-receptor (IFNR) associated complexes also plays an important role in mediating the translation of ISGs. The mechanisms regulating mRNA translation of ISGs is an area of ongoing active research and a lot more efforts will be required to complete our understanding of the various cellular elements involved in this process. In this review we highlight the mechanisms regulating translation of ISGs. We focus on the proteins regulated by the PI 3'K/AKT pathway, their role in mediating mRNA translation of ISGs and the functional consequences of this regulation. In addition, MAPKs are known to regulate the phosphorylation of various eukaryotic initiation factors and we summarize the roles of eIF4B and eIF4E phosphorylations on the translation of ISGs. The emerging roles of microRNAs in mRNA translation of ISGs are also discussed.

Although the roles of Jak-Stat pathways in type I and II interferon (IFN)-dependent transcriptional regulation are well established, the precise mechanisms of mRNA translation for IFN-sensitive genes remain to be defined. We examined the effects of IFNs on the phosphorylation/activation of eukaryotic translation initiation factor 4B (eIF4B). Our data show that eIF4B is phosphorylated on Ser422 during treatment of sensitive cells with alpha IFN (IFN-alpha) or IFN-gamma. Such phosphorylation is regulated, in a cell type-specific manner, by either the p70 S6 kinase (S6K) or the p90 ribosomal protein S6K (RSK) and results in enhanced interaction of the protein with eIF3A (p170/eIF3A) and increased associated ATPase activity. Our data also demonstrate that IFN-inducible eIF4B activity and IFN-stimulated gene 15 protein (ISG15) or IFN-gamma-inducible chemokine CXCL-10 protein expression are diminished in S6k1/S6k2 double-knockout mouse embryonic fibroblasts. In addition, IFN-alpha-inducible ISG15 protein expression is blocked by eIF4B or eIF3A knockdown, establishing a requirement for these proteins in mRNA translation/protein expression by IFNs. Importantly, the generation of IFN-dependent growth inhibitory effects on primitive leukemic progenitors is dependent on activation of the S6K/eIF4B or RSK/eIF4B pathway. Taken together, our findings establish critical roles for S6K and RSK in the induction of IFN-dependent biological effects and define a key regulatory role for eIF4B as a common mediator and integrator of IFN-generated signals from these kinases.

Arsenic trioxide (As(2)O(3)) is a potent inducer of apoptosis of leukemic cells in vitro and in vivo, but the mechanisms that mediate such effects are not well understood. We provide evidence that the Akt kinase is phosphorylated/activated during treatment of leukemia cells with As(2)O(3), to regulate downstream engagement of mammalian target of rapamycin (mTOR) and its effectors. Using cells with targeted disruption of both the Akt1 and Akt2 genes, we found that induction of arsenic trioxide-dependent apoptosis is strongly enhanced in the absence of these kinases, suggesting that Akt1/Akt2 are activated in a negative feedback regulatory manner, to control generation of As(2)O(3) responses. Consistent with this, As(2)O(3)-dependent pro-apoptotic effects are enhanced in double knock-out cells for both isoforms of the p70 S6 kinase (S6k1/S6k2), a downstream effector of Akt and mTOR. On the other hand, As(2)O(3)-dependent induction of apoptosis is diminished in cells with targeted disruption of TSC2, a negative upstream effector of mTOR. In studies using primary hematopoietic progenitors from patients with acute myeloid leukemia, we found that pharmacological inhibition of mTOR enhances the suppressive effects of arsenic trioxide on leukemic progenitor colony formation. Moreover, short interfering RNA-mediated inhibition of expression of the negative downstream effector, translational repressor 4E-BP1, partially reverses the effects of As(2)O(3). Altogether, these data provide evidence for a key regulatory role of the Akt/mTOR pathway in the generation of the effects of As(2)O(3), and suggest that targeting this signaling cascade may provide a novel therapeutic approach to enhance the anti-leukemic properties of As(2)O(3).

Summary Peroxidases (PODs) are known to be quite stable at elevated temperatures. Moreover, partially denatured peroxidases are able to regain their catalytic activity during incubation at room temperature. In this paper, we describe the effects of some heat shock proteins on the self-reactivation of plant peroxidase preparations. Horseradish and artichoke peroxidases (HRP and ARP, respectively) were first heated (at 60 °C or 90 °C), then incubated at a slightly elevated temperature (30 °C). The heat-treatment resulted in a considerable loss of activity of both enzymes but the subsequent incubation allowed their reactivation. However, no reactivation could be detected when incubation was carried out in the presence of the molecular chaperone ClpX. Other chaperones that were tested (DnaK, DnaJ and GrpE) did not show the inhibitory effect. Electrophoretic analyses further indicated that the heat-treated horseradish peroxidase, but not the native enzyme, binds to ClpX eliminating the possibility of undesirable protein refolding that would result in aggregation.

A vector was constructed for intracellular expression of the Arabidopsis thaliana DnaJ homologue AtJ2 in the methylotrophic yeast Pichia pastoris. The vector includes DNA encoding an amino-terminal histidine-tag, to simplify protein purification. Shake-flask cultures could be induced to produce approximately 250 mg/ L of AtJ2. Purified recombinant AtJ2 was able to stimulate the ATPase activities of both the Escherichia coli and Zea mays cytoplasmic Stress70 chaperone proteins five- to ninefold. The carboxy terminus of AtJ2 is -CAQQ, a protein farnesylation motif. When transformed P. pastoris was induced to synthesize AtJ2 in the presence of [(3)H]mevalonolactone, radioactivity was incorporated into the protein, suggesting farnesylation.

There is emerging evidence that the IFN-inducible family of Slfn genes and proteins play important roles in cell cycle progression and control of cellular proliferation, but the precise functional roles of different Slfn members in the regulation of tumorigenesis remain unclear. In the present study, we undertook a systematic analysis on the expression and functional relevance of different mouse Slfn genes in malignant melanoma and renal cell carcinoma cells. Our studies demonstrate that several mouse Slfn genes are up-regulated in response to IFN treatment of mouse melanoma and renal cell carcinoma cells, including Slfn1, Slfn2, Slfn4, Slfn5, and Slfn8. Our data show that Slfn2 and Slfn3 play essential roles in the control of mouse malignant melanoma cell proliferation and/or anchorage-independent growth, suggesting key and non-overlapping roles for these genes in the control of malignant melanoma tumorigenesis. In renal cell carcinoma cells, in addition to Slfn2 and Slfn3, Slfn5 also exhibits important antineoplastic effects. Altogether, our findings indicate important functions for distinct mouse Slfn genes in the control of tumorigenesis and provide evidence for differential involvement of distinct members of this gene family in controlling tumorigenesis. They also raise the potential of future therapeutic approaches involving modulation of expression of members of this family of genes in malignant melanoma and renal cell carcinoma.

Type I Interferons (IFNs) are cytokines that exhibit important anti-tumorigenic, anti-viral and immunomodulatory functions. Yet, the precise mechanisms and sequence of events by which IFNs activate different signaling pathways required to mediate such responses remain to be fully defined. We have found that engagement of Type I IFN receptor (IFNR) activates a novel pathway, possibly involving both PI3K-AKT-dependent and independent meditators, culminating in activation of the Unc-51-like kinase 1 (ULK1). Importantly, ULK1 kinase activity seems to cooperate with the MAPKKK-MKK3/6 signaling cascade for optimal IFN-induced activation of p38 MAPK and gene transcription of key interferon stimulated genes (ISGs). Moreover, we have now identified novel interactors of ULK1 during engagement of IFNR by mass spectrometry analysis, which reveal new IFN-triggered ULK1-mediated signaling pathways. Our studies have also established that ULK1 is essential for Type I IFN-induced antiviral and antineoplastic effects against malignant erythroid precursors from patients with myeloproliferative neoplasms (MPNs). Altogether, our findings have important clinical-translational implications, as modulation of the ULK1 activity may be used as an approach to selectively enhance the activity of IFNs in normal hematopoiesis and against malignant cells. An update on our ongoing studies and the putative interactive proteins of the pathway in the interferon system will be presented and discussed.