Direct association of STAT3 with the IFNAR-1 chain of the human type I interferon receptor

Tyrosine kinase 2 inhibitors: Synthesis and applications in the treatment of autoimmune diseases

Janus kinase (JAK), a class of non-receptor tyrosine kinases, are essential in modulating the cytokine signaling cascade of cytokines associated with immune responses. Despite their potential in the treatment of autoimmune diseases, JAK inhibitors are associated with safety concerns, regarding cytokine suppression and significant side effects. Tyrosine kinase 2 (TYK2), a prominent member of the JAK family, is central to the signaling of interleukins (ILs) and interferons (IFNs), such as IL-12, IL-23 and IFNs. Targeted TYK2 inhibitors that specifically target the Janus Homology 1 (JH1) and pseudokinase (JH2) domains show enhanced specificity. JH1 acts as an ATP-competitive inhibitor, while JH2 acts as an allosteric regulator, contributing to reduced systemic side effects and improved therapeutic outcomes in clinical settings. This review summarizes the recent advances on the synthetic strategies of TYK2 inhibitors and their applications in the treatment of autoimmune diseases.

Langat virus inhibits the gp130/JAK/STAT signaling by reducing the gp130 protein level

The tick-borne encephalitis virus (TBEV) serocomplex includes several medically important flavivirus members endemic to Europe, Asia, and North America, which can induce severe neuroinvasive or viscerotropic diseases with unclear mechanisms of pathogenesis. Langat virus (LGTV) shares a high sequence identity with TBEV but exhibits lower pathogenic potential in humans and serves as a model for virus-host interactions. In this study, we demonstrated that LGTV infection inhibits the activation of gp130/JAK/STAT (Janus kinases (JAK) and signal transducer and activator of transcription (STAT)) signaling, which plays a pivotal role in numerous biological processes. Our data show that the LGTV-infected cells had significantly lower phosphorylated STAT3 (pSTAT3) protein upon oncostatin M (OSM) stimulation than the mock-infected control. LGTV infection blocked the nuclear translocation of STAT3 without a significant effect on total STAT3 protein level. LGTV inhibited JAK1 activation and reduced gp130 protein expression in infected cells, with the viral NS5 protein mediating this effect. TBEV infection also reduces gp130 level. On the other hand, pretreatment of Vero cells with OSM significantly reduces LGTV replication, and STAT1/STAT2 knockdown had little effect on OSM-mediated antiviral effect, which suggests it is independent of STAT1/STAT2 and, instead, it is potentially mediated by STAT3 signlaing. These findings shed light on the LGTV and TBEV-cell interactions, offering insights for the future development of antiviral therapeutics and improved vaccines.

Noncoding RNAs as regulators of STAT3 pathway in gastrointestinal cancers: Roles in cancer progression and therapeutic response

Gastrointestinal (GI) tumors (cancers of the esophagus, gastric, liver, pancreas, colon, and rectum) contribute to a large number of deaths worldwide. STAT3 is an oncogenic transcription factor that promotes the transcription of genes associated with proliferation, antiapoptosis, survival, and metastasis. STAT3 is overactivated in many human malignancies including GI tumors which accelerates tumor progression, metastasis, and drug resistance. Research in recent years demonstrated that noncoding RNAs (ncRNAs) play a major role in the regulation of many signaling pathways including the STAT3 pathway. The major types of endogenous ncRNAs that are being extensively studied in oncology are microRNAs, long noncoding RNAs, and circular RNAs. These ncRNAs can either be tumor-promoters or tumor-suppressors and each one of them imparts their activity via different mechanisms. The STAT3 pathway is also tightly modulated by ncRNAs. In this article, we have elaborated on the tumor-promoting role of STAT3 signaling in GI tumors. Subsequently, we have comprehensively discussed the oncogenic as well as tumor suppressor functions and mechanism of action of ncRNAs that are known to modulate STAT3 signaling in GI cancers.

The STAT3-Regulated Autophagy Pathway in Glioblastoma

Glioblastoma (GBM) is the most common primary brain malignancy in adults with a dismal prognosis. Despite advances in genomic analysis and surgical technique and the development of targeted therapeutics, most treatment options are ineffective and mainly palliative. Autophagy is a form of cellular self-digestion with the goal of recycling intracellular components to maintain cell metabolism. Here, we describe some recent findings that suggest GBM tumors are more sensitive to the excessive overactivation of autophagy leading to autophagy-dependent cell death. GBM cancer stem cells (GSCs) are a subset of the GBM tumor population that play critical roles in tumor formation and progression, metastasis, and relapse, and they are inherently resistant to most therapeutic strategies. Evidence suggests that GSCs are able to adapt to a tumor microenvironment of hypoxia, acidosis, and lack of nutrients. These findings have suggested that autophagy may promote and maintain the stem-like state of GSCs as well as their resistance to cancer treatment. However, autophagy is a double-edged sword and may have anti-tumor properties under certain conditions. The role of the STAT3 transcription factor in autophagy is also described. These findings provide the basis for future research aimed at targeting the autophagy-dependent pathway to overcome the inherent therapeutic resistance of GBM in general and to specifically target the highly therapy-resistant GSC population through autophagy regulation.

STAT3 regulates inflammatory cytokine production downstream of TNFR1 by inducing expression of TNFAIP3/A20

Tumour Necrosis Factor (TNF) potently induces a transient inflammatory response that must be downregulated once any invasive stimulus has resolved. Yet, how TNF‐induced inflammation is shut down in normal cells is incompletely understood. The present study shows that STAT3 was activated in mouse embryo fibroblasts (MEFs) by treatment with TNF or an agonist antibody to TNFR1. STAT3 activation was inhibited by pharmacological inhibition of the Jak2 tyrosine kinase that associates with TNFR1. To identify STAT3 target genes, global transcriptome analysis by RNA sequencing was performed in wild‐type MEFs and MEFs from STAT3 knockout (STAT3^KO) mice that were stimulated with TNF, and the results were validated at the protein level by using multiplex cytokine assays and immunoblotting. After TNF stimulation, STAT3^KO MEFs showed greater gene and protein induction of the inflammatory chemokines Ccl2, Cxcl1 and Cxcl10 than WT MEFs. These observations show that, by activating STAT3, TNF selectively modulates expression of a cohort of chemokines that promote inflammation. The greater induction by TNF of chemokines in STAT3^KO than WT MEFs suggested that TNF induced an inhibitory protein in WT MEFs. Consistent with this possibility, STAT3 activation by TNFR1 increased the expression of Tnfaip3/A20, a ubiquitin modifying enzyme that inhibits inflammation, in WT MEFs but not in STAT3^KO MEFs. Moreover, enforced expression of Tnfaip3/A20 in STAT3^KO MEFs suppressed proinflammatory chemokine expression induced by TNF. Our observations identify Tnfaip3/A20 as a new downstream target for STAT3 which limits the induction of Ccl2, Cxcl1 and Cxcl10 and inflammation induced by TNF.

Type I interferon therapies of multiple sclerosis and hepatitis C virus infection

Interferons type I (IFN-I), activated following a bacterial or viral infection, play a major role in the induction and regulation of the immune system. The immune response results in viral RNA and binds to receptors such as RIG-I-like receptors (RLRs) or Toll-like receptors, leading to the IFN-I signaling cascade. Thanks to its cellular function, IFN-I is widely used in therapies for such diseases as multiple sclerosis (MS) and hepatitis C disease (HCD).

MS is a neurological, autoimmune, chronic inflammatory disease of the central nervous system (CNS). During MS, nerve cell demyelination is observed due to the myelin heaths and oligodendrocyte damage. As a result, neuronal signal and neuron communication are attenuated. The mechanism of MS is still unknown. MS therapy applies interferon-β (IFN-β). IFN-β therapy has been used since the last century, but the therapeutic mechanism of IFN-β has not been completely understood. MS can lead to four syndromes: clinically isolated syndrome (CIS), relapsing-remitting MS (RRMS), primary progressive MS (PPMS), and secondary progressive MS (SPMS).

HCD occurs as a result of infection with the hepatitis C virus (HCV), belonging to the Flaviviridae family. HCV is a blood-borne virus with a positive single-stranded RNA. A vaccine for HCV is not available yet. HCD can lead to liver damage or cancer. In HCD interferon-α therapy (IFN-α) is applied. As with MS, the mechanism of IFN-α therapy is not completely known.

Flaming the fight against cancer cells: the role of microRNA-93

There have been attempts to develop novel anti-tumor drugs in cancer therapy. Although satisfying results have been observed at a consequence of application of chemotherapeutic agents, the cancer cells are capable of making resistance into these agents. This has forced scientists into genetic manipulation as genetic alterations are responsible for generation of a high number of cancer cells. MicroRNAs (miRs) are endogenous, short non-coding RNAs that affect target genes at the post-transcriptional level. Increasing evidence reveals the potential role of miRs in regulation of biological processes including angiogenesis, metabolism, cell proliferation, cell division, and cell differentiation. Abnormal expression of miRs is associated with development of a number of pathologic events, particularly cancer. MiR-93 plays a significant role in both physiological and pathological mechanisms. At the present review, we show how this miR dually affects the proliferation and invasion of cancer cells. Besides, we elucidate the oncogenesis or oncosuppressor function of miR-93.

Interleukin-22 Inhibits Respiratory Syncytial Virus Production by Blocking Virus-Mediated Subversion of Cellular Autophagy

Respiratory syncytial virus (RSV) infection can cause severe bronchiolitis in infants requiring hospitalization, whereas the elderly and immunocompromised are prone to RSV-induced pneumonia. RSV primarily infects lung epithelial cells. Given that no vaccine against RSV is currently available, we tested the ability of the epithelial-barrier protective cytokine interleukin-22 (IL-22) to control RSV production. When used in a therapeutic modality, IL-22 efficiently blunted RSV production from infected human airway and alveolar epithelial cells and IL-22 administration drastically reduced virus titer in the lungs of infected newborn mice. RSV infection resulted in increased expression of LC3B, a key component of the cellular autophagic machinery, and knockdown of LC3B ablated virus production. RSV subverted LC3B with evidence of co-localization and caused a significant reduction in autophagic flux, both reversed by IL-22 treatment. Our findings inform a previously unrecognized anti-viral effect of IL-22 that can be harnessed to prevent RSV-induced severe respiratory disease.

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RSV infection of lung epithelial cells subverts the cellular autophagic machinery

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RSV infection inhibits autophagic flux in infected cells

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IL-22 inhibits RSV production from human lung epithelial cells and in neonatal mice

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IL-22 blocks RSV-LC3B co-localization and restores cellular autophagic flux

Rs11655237 polymorphism of LINC00673 affects the prognosis of cervical cancer by interfering with the interaction between LINC00673 and microRNA-1231

Single-nucleotide polymorphism (SNP) in long noncoding RNAs (lncRNAs) is known to disrupt the binding between lncRNAs and microRNAs. In this paper, we aimed to explore the role of LINC00673 rs11655237 SNP in the survival of cervical cancer (CC). Real-time polymerase chain reaction and western-blot analysis were used to detect expressions of LINC00673 and microRNA-1231 (miR-1231) in CC patients with different rs11655237 SNP genotypes. And the expression of LINC00673, miR-1231, and IFNAR1 was measured in mice and cells treated with exosomes carrying GG, GA, and AA rs11655237 genotypes. Compared with patients carrying the rs11655237 A allele of LINC00673 rs11655237 SNP, patients carrying the G allele showed higher overall survival and higher miR-1231 expression. In addition, the expression of miR-1231 was the highest in patients carrying the GG genotype and the lowest in patients carrying the AA genotype. Furthermore, the exosomes carrying GG, GA, and AA genotypes of LINC00673 rs11655237 SNP reduced tumor growth in mice, while the inhibitory effect of rs11655237 A allele was much stronger than that of the rs11655237 G allele. Additionally, exosome treatment upregulated the expression of LINC000673 and IFNAR1 while downregulating the expression of miR-1231. Interestingly, the A allele of rs11655237 generated a binding site for miR-1231 and subsequently affected the expression of IFNAR1, a target gene of miR-1231 containing a miR-1231 binding site in its 3'-untranslated region. Cells transfected with exosomes carrying GG, GA, and AA genotypes of LINC00673 rs11655237 SNP achieved higher LINC000673 and IFNAR1 expression along with lower miR-1231 expression. Therefore, rs11655237 can be used as a prognostic biomarker for CC.

Type I interferon limits mast cell-mediated anaphylaxis by controlling secretory granule homeostasis

Type I interferon (IFN-I) is a family of multifunctional cytokines that modulate the innate and adaptive immunity and are used to treat mastocytosis. Although IFN-I is known to suppress mast cell function, including histamine release, the mechanisms behind its effects on mast cells have been poorly understood. We here investigated IFN-I’s action on mast cells using interferon-α/β receptor subunit 1 (Ifnar1)-deficient mice, which lack a functional IFN-I receptor complex, and revealed that IFN-I in the steady state is critical for mast cell homeostasis, the disruption of which is centrally involved in systemic anaphylaxis. Ifnar1-deficient mice showed exacerbated systemic anaphylaxis after sensitization, which was associated with increased histamine in the circulation, even though the mast cell numbers and high affinity immunoglobulin E receptor (FcεRI) expression levels were similar between Ifnar1-deficient and wild-type (WT) mice. Ifnar1-deficient mast cells showed increased secretory granule synthesis and exocytosis, which probably involved the increased transcription of Tfeb. Signal transducer and activator of transcription 1(Stat1) and Stat2 were unexpectedly insufficient to mediate these IFN-I functions, and instead, Stat3 played a critical role in a redundant manner with Stat1. Our findings revealed a novel regulation mechanism of mast cell homeostasis, in which IFN-I controls lysosome-related organelle biogenesis.

This study reveals a novel role for type I interferon in mast cell homeostasis; spontaneous type I interferon signaling regulates the biogenesis of secretory granules and maturation of mast cells via STAT1 and STAT3, and limits the onset of systemic anaphylaxis.

Exploring the tissue tropism of pseudorabies virus based on miRNA level analysis

Background

Pseudorabies virus (PRV, or suid herpesvirus, SuHV-1), a member of the herpesvirus family, has an extremely broad host range and threatens the pig industry in China. PRV can evade host innate immunity and infect the kidney, lung, brain and other tissues. At the same time, many studies have reported that microRNA (miRNA) can affect the replication of viruses by regulating gene expression levels.

Results

Here, to identify changes in miRNA expression and post-transcriptional regulation associated with PRV infection in the lung, spleen, and olfactory bulb, we sequenced small RNAs in tissues of rats infected or uninfected with PRV strain XJ (PRV-XJ). Sixty-one, 199 and 29 differentially-expressed miRNAs were identified in the lung, spleen, and olfactory bulb, respectively, of infected compared with uninfected rats. Among the miRNAs differentially-expressed in PRV-infected rats, 36, 171, and 15 miRNAs showed tissue-selective expression in the olfactory bulb, lung and spleen, respectively. All differentially-expressed miRNAs were analyzed for their GO functional annotations and KEGG pathway associations .

Conclusions

In PRV-XJ-infected rats, miRNAs were differentially expressed in the lung, spleen and olfactory bulb. These miRNAs were involved in regulating various pathways of the nervous, respiratory and immune systems, and may affect the tissue tropism of the virus and play pivotal roles in viral infection and proliferation.

miR-93-5p/IFNAR1 axis promotes gastric cancer metastasis through activating the STAT3 signaling pathway

Aberrant expression of microRNAs (miRNAs) plays an important role in gastric cancer (GC) development. miR-93-5p has shown opposing functions in different types of cancers, but the exact expression pattern and molecular mechanism of miR-93-5p in GC development remain to be elucidated. Here, we reported that miR-93-5p expression was increased in GC tissues compared with the adjacent normal tissues and that its overexpression was correlated with distant metastasis and poor survival in GC patients. miR-93-5p knockdown inhibited the migration, invasion and proliferation of GC cells in vitro and in vivo, while its overexpression displayed an opposite result. Using an mRNA microarray, we found that miR-93-5p significantly downregulated IFNAR1 expression in GC cells, which was further identified as a direct target of miR-93-5p. IFNAR1 knockdown promoted GC cell migration and invasion, but its restoration could rescue GC cell migration and invasion induced by miR-93-5p overexpression. Moreover, miR-93-5p-IFNAR1 axis increased MMP9 expression via STAT3 pathway in GC cells. Taken together, we reveal that miR-93-5p overexpression is associated with the poor survival of GC patients and miR-93-5p-IFNAR1 axis promotes GC metastasis through activation of STAT3 pathway.

Unphosphorylated STAT3 regulates the antiproliferative, antiviral, and gene-inducing actions of type I interferons

Type I interferon (IFNα/β) induces antiviral and antiproliferative responses in cells through the induction of IFN-stimulated genes (ISGs). Although the roles of IFN-activated STAT1 and STAT2 in the IFN response are well described, the function of STAT3 is poorly characterized. We investigated the role of STAT3 in the biological response to IFNα/β in mouse embryonic fibroblasts (MEFs) with a germ line deletion of STAT3. These STAT3 knockout (STAT3-KO) MEFs were reconstituted with STAT3 or the F705-STAT3 mutant (unphosphorylated STAT3) where the canonical Y705 tyrosine phosphorylation site was mutated. We show that both STAT3 and unphosphorylated STAT3 expression enhance the sensitivity of MEFs to the antiviral, antiproliferative and gene-inducing actions of IFN. By chromatin immunoprecipitation assays, unphosphorylated STAT3 appears to bind, albeit weakly, to select gene promoters to enhance their expression. These results suggest that unphosphorylated STAT3 plays an important role in the IFN response pathway.

The anti-proliferative effects of type I IFN involve STAT6-mediated regulation of SP1 and BCL6

Type I IFN-induced STAT6 has been shown to have anti-proliferative effects in Daudi and B cells. IFN-sensitive (DS) and IFN-resistant (DR) subclones of Daudi cells were used to study the role of STAT6 in the anti-proliferative activities. Type I IFN significantly increased STAT6 mRNA and protein expression in DS but not DR cells. STAT6 knockdown significantly reduced the sensitivity to IFN in both cell lines. The molecular targets and functional importance of IFN-activated STAT6 were performed by chromatin immunoprecipitation-on-chip (ChIP-on-chip) experiments in type I IFN-treated Daudi cells. Two target genes (Sp1 and BCL6) were selected from the ChIP-on-chip data. IFN-induced STAT6 activation led to Sp1 upregulation and BCL6 downregulation in DS cells, with only minimal effects in DR cells. siRNA inhibition of STAT6 expression resulted in decreased Sp1 and BCL6 mRNA and protein levels in both DS and DR cells. IFN treatment did not increase Sp1 and BCL6 expression in a STAT2-deficient RST2 cell line, and this effect was mitigated by plasmid overexpression of STAT2, indicating that STAT2 is important for STAT6 activation. These results suggest that STAT6 plays an important role in regulating Sp1 and BCL6 through STAT2 to exert the anti-proliferative effects of type I IFN.

The Type I IFN-Induced miRNA, miR-21

The interferon (IFN) family of cytokines not only has antiviral properties at various steps in the viral replication cycle, but also anticancer activity through multiple pathways that include inhibiting cell proliferation, regulating cellular responses to inducers of apoptosis and modulating angiogenesis and the immune system. IFNs are known to induce their biological activity through the induction of protein encoding IFN-stimulated genes. However, recent studies have established that IFNs also induce the expression of microRNAs (miRNAs), which are small endogenous non-coding RNAs that suppress gene expression at the post-transcriptional level. MiRNAs play critical roles in tumorigenesis and have been implicated to act as either oncogenes or tumor suppressors in various human cancers. Therefore, IFN-induced miRNAs play an important role, not only in the host response to innate immune response to cancer, but also in the tumorigenic process itself. Furthermore, IFN-induced miRNAs may participate in and/or orchestrate antiviral defense in certain viral infections. In this review, we describe our recent studies on the induction of miR-21 by type I IFN, the role of the STAT3 and NFκB signaling pathways in IFN-induced miR-21 expression, the role of miR-21 in different cancers and the role of miR-21 in regulating the antiviral response.

The Role of miR-21 in Cancer

MicroRNAs (miRNAs) are small endogenous noncoding RNAs that suppress gene expression at the post-transcriptional level. In the past decade, miRNAs have been extensively studied in a number of different human cancers. MiRNAs have been identified to act both as oncogenes and as tumor suppressors. In addition, miRNAs are associated with the intrinsic resistance of cancer to various forms of therapy, and they are implicated in both tumor progression and metastasis. The characterization of the specific alterations in the patterns of miRNA expression in cancer has great potential for identifying biomarkers for early cancer detection, as well as for potential therapeutic intervention in cancer treatment. In this chapter, we describe the ever-expanding role of miR-21 and its target genes in different cancers, and provide insight into how this oncogenic miRNA regulates cancer cell proliferation, migration, and apoptosis by suppressing the expression of tumor suppressors.

Inhibition of STAT3-interacting protein 1 (STATIP1) promotes STAT3 transcriptional up-regulation and imatinib mesylate resistance in the chronic myeloid leukemia

Background

Signal transducer and activator of transcription 3 (STAT3) is an important transcriptional factor frequently associated with the proliferation and survival of a large number of distinct cancer types. However, the signaling pathways and mechanisms that regulate STAT3 activation remain to be elucidated.

Methods

In this study we took advantage of existing cellular models for chronic myeloid leukemia resistance, western blot, in vitro signaling, real time PCR, flow cytometry approaches for cell cycle and apoptosis evaluation and siRNA assay in order to investigate the possible relationship between STATIP1, STAT3 and CML resistance.

Results

Here, we report the characterization of STAT3 protein regulation by STAT3-interacting protein (STATIP1) in the leukemia cell line K562, which demonstrates constitutive BCR-ABL TK activity. K562 cells exhibit high levels of phosphorylated STAT3 accumulated in the nucleus and enhanced BCR-ABL-dependent STAT3 transcriptional activity. Moreover, we demonstrate that STATIP1 is not involved in either BCR-ABL or STAT3 signaling but that STATIP1 is involved in the down-regulation of STAT3 transcription levels; STATIP1-depleted K562 cells display increased proliferation and increased levels of the anti-apoptosis STAT3 target genes CCND1 and BCL-XL, respectively. Furthermore, we demonstrated that Lucena, an Imatinib (IM)-resistant cell line, exhibits lower STATIP1 mRNA levels and undergoes apoptosis/cell cycle arrest in response to STAT3 inhibition together with IM treatment. We provide evidence that STATIP1 siRNA could confer therapy resistance in the K562 cells. Moreover, analysis of CML patients showed an inverse expression of STAIP1 and STAT3 mRNA levels, ratifying that IM-resistant patients present low STATIP1/high STAT3 mRNA levels.

Conclusions

Our data suggest that STATIP1 may be a negative regulator of STAT3 and demonstrate its involvement in IM therapy resistance in CML.

Interferon induction and function at the mucosal surface

Interferons (IFNs) are produced in response to virus infection and induce an antiviral state in virtually all cell types. In addition to upregulating the transcription of genes that inhibit virus replication, type I (or -α/β) IFNs also act to orchestrate the adaptive immune response to virus infection. Recently a new family of antiviral cytokines, the type III (or -λ) IFNs, has been identified that activate the same antiviral pathways via a distinct receptor. Although the identical transcription factor, IFN-stimulated gene factor 3 is activated by either IFN-α/β or IFN-λ signaling, differences in the induction and action of these two cytokine families are beginning to be appreciated. In this article, we review this emerging body of literature on the differing roles these cytokines play in host defense of the mucosal surface. Although many viruses enter the body through the respiratory and gastrointestinal tracts, we have focused the discussion on influenza A virus, respiratory syncytial virus, and rotavirus, three ubiquitous human pathogens that target the epithelial lining and are associated with a major disease burden.

Constitutive activation of STAT3 signaling regulates hTERT and promotes stem cell-like traits in human breast cancer cells

Mounting clinical data suggest that high telomerase activity is tightly associated with cancer progression and poor outcomes. Constitutively activated STAT3 is found in ∼60% of human malignancies and shows a dismal prognosis. We previously reported that activated STAT3 promoted epithelial-mesenchymal transition (EMT) and cancer stem cell phenotype in human breast cancer. However, little is known how STAT3 is regulated in the cancer stem cell and by which mechanisms STAT3 contributes to poor prognosis in aggressive breast cancer. Here we demonstrate that STAT3 physically interacts with CD44 and NF-kB and activates the catalytic subunit of telomerase (hTERT) in human breast cancer stem cells. STAT3 plays a role as a signal transducing molecule between CD44 and NF-kB. In addition to functioning as a catalytic subunit of telomerase, hTERT has been reported to function as a transcription co-factor which drives EMT and cancer stem cell phenotype in human cancer. We observed that activated hTERT increases CD44 (+) subpopulation, whereas targeted knock-down of hTERT abolished cancer stem cell phenotype. Targeted STAT3 knock-down cells also down-regulated hTERT and decreased CD44 subpopulation. Finally, CD44 knock-down resulted in the abrogation of cancer stem cell phenotype and concurrent down-regulation of pSTAT3 and hTERT. Our study delineates the signaling pathway where STAT3 functions as a modulator for CD44 and hTERT, promoting a cancer stem cell phenotype. The constitutive activation of STAT3 signaling that leads to regulation of hTERT pathway may provide novel therapeutic targets for human breast cancer stem cells.

The curcumin analog EF24 targets NF-κB and miRNA-21, and has potent anticancer activity in vitro and in vivo

EF24 is a curcumin analog that has improved anticancer activity over curcumin, but its therapeutic potential and mechanism of action is unknown, which is important to address as curcumin targets multiple signaling pathways. EF24 inhibits the NF-κB but not the JAK-STAT signaling pathway in DU145 human prostate cancer cells and B16 murine melanoma cells. EF24 induces apoptosis in these cells apparently by inhibiting miR-21 expression, and also enhances the expression of several miR-21 target genes, PTEN and PDCD4. EF24 treatment significantly suppressed the growth of DU145 prostate cancer xenografts in immunocompromised mice and resulted in tumor regression. EF24 enhanced the expression of the miR-21 target PTEN in DU145 tumor tissue, but suppressed the expression of markers of proliferating cells (cyclin D1 and Ki67). In syngeneic mice injected with B16 cells, EF24 treatment inhibited the formation of lung metastasis, prolonged animal survival, inhibited miR-21 expression and increased the expression of miR-21 target genes. Expression profiling of miRNAs regulated by EF24 in vitro and in vivo showed that the antitumor activity of EF24 reflected the enhanced expression of potential tumor suppressor miRNAs as well as the suppressed expression of oncogenic miRNAs, including miR-21. Taken together, our data suggest that EF24 is a potent anticancer agent and selectively targets NF-κB signaling and miRNA expression, indicating that EF24 has significant potential as a therapeutic agent in various cancers.

Constitutive activation of signal transducer and activator of transcription 3 (STAT3) and nuclear factor κB signaling in glioblastoma cancer stem cells regulates the Notch pathway

Malignant gliomas are locally aggressive, highly vascular tumors that have a dismal prognosis, and present therapies provide little improvement in the disease course and outcome. Many types of malignancies, including glioblastoma, originate from a population of cancer stem cells (CSCs) that are able to initiate and maintain tumors. Although CSCs only represent a small fraction of cells within a tumor, their high tumor-initiating capacity and therapeutic resistance drives tumorigenesis. Therefore, it is imperative to identify pathways associated with CSCs to devise strategies to selectively target them. In this study, we describe a novel relationship between glioblastoma CSCs and the Notch pathway, which involves the constitutive activation of STAT3 and NF-κB signaling. Glioma CSCs were isolated and maintained in vitro using an adherent culture system, and the biological properties were compared with the traditional cultures of CSCs grown as multicellular spheres under nonadherent culture conditions. Interestingly, both adherent and spheroid glioma CSCs show constitutive activation of the STAT3/NF-κB signaling pathway and up-regulation of STAT3- and NF-κB-dependent genes. Gene expression profiling also identified components of the Notch pathway as being deregulated in glioma CSCs, and the deregulated expression of these genes was sensitive to treatment with STAT3 and NF-κB inhibitors. This finding is particularly important because Notch signaling appears to play a key role in CSCs in a variety of cancers and controls cell fate determination, survival, proliferation, and the maintenance of stem cells. The constitutive activation of STAT3 and NF-κB signaling pathways that leads to the regulation of Notch pathway genes in glioma CSCs identifies novel therapeutic targets for the treatment of glioma.

IL-17: a new actor in IFN-driven systemic autoimmune diseases

Systemic autoimmune diseases such as systemic lupus erythematosus are type I IFN-driven diseases with exaggerated B-cell responses and autoantibody production. Th17 cells, a T-helper-cell subset with high inflammatory capacity, was initially discovered and characterized in the context of experimental autoimmune encephalomyelitis - an animal model of multiple sclerosis. There is now emerging evidence that Th17 cells, and more generally IL-17 and IL-17-producing cells, may play a role in the pathogenesis of type I IFN-driven systemic autoimmune diseases such as lupus. Here, we review the different studies suggesting a role for IL-17 and IL-17-producing cells in systemic autoimmune diseases, both in humans and in animal models, and we consider the possible mechanisms by which these cells may contribute to disease. We also discuss the hypothesis that type I IFN and IL-17 act in concert to sustain and amplify autoimmune and inflammatory responses, making them a dangerous combination involved in the pathogenesis of systemic autoimmune diseases.

Characterizing antiviral mechanism of interleukin-32 and a circulating soluble isoform in viral infection

Interleukin-32 (IL-32) is an inflammatory cytokine, and its activity is associated with various auto-inflammatory disorders as well as infectious pathogens such as Mycobacterium tuberculosis, and viral infections. However, the precise antiviral mechanism of IL-32 remains unclear. We assessed the IL-32 level in the sera of H1N1 influenza A patients and IL-32 level was significantly elevated. Next we examined the antiviral activity of recombinant IL-32γ (rIL-32γ) with WISH cells infected by vesicular stomatitis virus (VSV) but no antiviral activity was observed. Therefore we investigated the supernatant of rIL-32-treated THP-1 cells since this cell line effectively responded to rIL-32γ. The supernatant of rIL-32-treated THP-1 cell possessed an antiviral effect and in addition, an agonistic monoclonal antibody further enhanced a specific antiviral activity of rIL-32γ. The fractionation and mass spectrometer analysis of the THP-1 cell supernatant revealed that the antiviral activity of rIL-32γ is via a THP-1 cell-produced factor, transferrin, rather than the direct effects of rIL-32γ on epithelial cells. We also characterized a secreted soluble IL-32γ protein in serum of IL-32γ transgenic mouse (TG), but not in that of IL-32α TG. The present results suggest that IL-32γ expression and its genetic variation in individual could be an important aspect of viral infections.

The interferon-gamma-induced GTPase, mGBP-2, inhibits tumor necrosis factor alpha (TNF-alpha) induction of matrix metalloproteinase-9 (MMP-9) by inhibiting NF-kappaB and Rac protein

Matrix metalloproteinase-9 (MMP-9) is important in numerous normal and pathological processes, including the angiogenic switch during tumor development and tumor metastasis. Whereas TNF-α and other cytokines up-regulate MMP-9 expression, interferons (IFNs) inhibit MMP-9 expression. We found that IFN-γ treatment or forced expression of the IFN-induced GTPase, mGBP-2, inhibit TNF-α-induced MMP-9 expression in NIH 3T3 fibroblasts, by inhibiting MMP-9 transcription. The NF-κB transcription factor is required for full induction of MMP-9 by TNF-α. Both IFN-γ and mGBP-2 inhibit the transcription of a NF-κB-dependent reporter construct, suggesting that mGBP-2 inhibits MMP-9 induction via inhibition of NF-κB-mediated transcription. Interestingly, mGBP-2 does not inhibit TNF-α-induced degradation of IκBα or p65/RelA translocation into the nucleus. However, mGBP-2 inhibits p65 binding to a κB oligonucleotide probe in gel shift assays and to the MMP-9 promoter in chromatin immunoprecipitation assays. In addition, TNF-α activation of NF-κB in NIH 3T3 cells is dependent on Rac activation, as evidenced by the inhibition of TNF-α induction of NF-κB-mediated transcription by a dominant inhibitory form of Rac1. A role for Rac in the inhibitory action of mGBP-2 on NF-κB is further shown by the findings that mGBP-2 inhibits TNF-α activation of endogenous Rac and constitutively activate Rac can restore NF-κB transcription in the presence of mGBP-2. This is a novel mechanism by which IFNs can inhibit the cytokine induction of MMP-9 expression.

PEGylated interferon beta-1a: meeting an unmet medical need in the treatment of relapsing multiple sclerosis

Multiple sclerosis is a chronic autoimmune disease of the central nervous system for which a number of disease-modifying therapies are available, including interferon beta (Avonex®, Rebif®, and Betaseron/Betaferon®), glatiramer acetate (Copaxone®), and an anti-VLA4 monoclonal antibody (Tysabri®). Despite the availability and efficacy of these protein and peptide drugs, there remains a significant number of patients who are untreated, including those with relatively mild disease who choose not to initiate therapy, those wary of injections or potential adverse events associated with therapy, and those who have stopped therapy due to perceived lack of efficacy. Since these drugs have side effects that may affect a patient's decision to initiate and to remain on treatment, there is a need to provide a therapy that is safe and efficacious but that requires a reduced dosing frequency and hence a concomitant reduction in the frequency of side effects. Here we describe the development of a PEGylated form of interferon beta-1a that is currently being tested in a multicenter, randomized, double-blind, parallel-group, placebo-controlled study in relapsing multiple sclerosis patients, with the aim of determining the safety and efficacy of 125 microg administered via the subcutaneous route every 2 or 4 weeks.

IFN induces miR-21 through a signal transducer and activator of transcription 3-dependent pathway as a suppressive negative feedback on IFN-induced apoptosis

The microRNA miR-21 is overexpressed in many human cancers, wherein accumulating evidence indicates that it functions as an oncogene. Here, we report that the cytokine IFN rapidly induces miR-21 expression in human and mouse cells. Signal transducer and activator of transcription 3 (STAT3) was implicated in this pathway based on the lack of IFN effect on miR-21 expression in prostate cancer cells with a deletion in the STAT3 gene. STAT3 ablation abrogated IFN induction of miR-21, confirming the important role of STAT3 in regulating miR-21. Chromatin immunoprecipitation analysis showed that STAT3 directly bound the miR-21 promoter in response to IFN. Experiments in mouse embryo fibroblasts with a genetic deletion of the p65 NF-κB subunit showed that IFN-induced miR-21 expression was also dependent on NF-κB. STAT3 silencing blocked both IFN-induced p65 binding to the miR-21 promoter and p65 nuclear translocation. Thus, IFN-induced miR-21 expression is coregulated by STAT3 and NF-κB at the level of the miR-21 promoter. Several cell death regulators were identified as downstream targets of miR-21, including PTEN and Akt. Functional experiments in prostate cancer cells directly showed that miR-21 plays a critical role in suppressing IFN-induced apoptosis. Our results identify miR-21 as a novel IFN target gene that functions as a key feedback regulator of IFN-induced apoptosis.

A receptor-independent, cell-based JAK activation assay for screening for JAK3-specific inhibitors

New immunosuppressive compounds with less systemic toxicity that could replace calcineurin inhibitors are urgently needed. For identification of specific inhibitors of JAK3, a potential new drug target, from large chemical libraries we developed a cell-based screening system. TEL-JAK fusion proteins composed of an oligomerization domain of TEL and kinase and/or pseudokinase domains of JAKs provided constitutive activation of JAKs without receiving a signal from the cytokine receptors. These fusion proteins also induced STAT5b phosphorylation in the absence of cytokine receptors. Both the kinase and pseudokinase domains of JAKs were required for full activation of the JAKs, and four copies of STAT5 response elements provided the greatest luciferase activity. The sensitivity and specificity of the system was evaluated using specific JAK3, JAK2, or MEK inhibitors. Thus, we generated a receptor-independent, cell-based selective screening system for specific JAK3 inhibitors, which is easily convertible to a high-throughput screening platform.

The role of constitutively activated STAT3 in B16 melanoma cells

Constitutively activated STAT3 is found frequently in a wide variety of human tumors, including melanoma. Moreover, constitutive STAT3 activation actively participates in tumor formation and progression, making STAT3 an attractive target for cancer therapy. We report here that in murine B16 melanoma cells, which have been previously shown to express constitutively active STAT3, the expression of a mutant form of STAT3 with the canonical tyrosine phosphorylation site (residue 705) mutated to phenylanaine has dominant-negative properties (STAT3-DN). STAT3-DN inhibits STAT3 tyrosine phosphorylation and STAT3-dependent DNA binding activity. Most importantly, STAT3-DN expression in B16 cells inhibits their invasiveness, as well as their melanogenesis by down-regulation of tyrosinase mRNA and protein expression as well as tyrosinase activity. These results suggest that STAT3 signaling plays a critical role in regulating melanoma behavior, and may represent a druggable target for melanoma therapy.

Interferon-beta treatment in multiple sclerosis attenuates inflammatory gene expression through inducible activity of the phosphatase SHP-1

Interferon-beta is a current treatment for multiple sclerosis (MS). Interferon-beta is thought to exert its therapeutic effects on MS by down-modulating the immune response by multiple potential pathways. Here, we document that treatment of MS patients with interferon beta-1a (Rebif) results in a significant increase in the levels and function of the protein tyrosine phosphatase SHP-1 in PBMCs. SHP-1 is a crucial negative regulator of cytokine signaling, inflammatory gene expression, and CNS demyelination as evidenced in mice deficient in SHP-1. In order to examine the functional significance of SHP-1 induction in MS PBMCs, we analyzed the activity of proinflammatory signaling molecules STAT1, STAT6, and NF-kappaB, which are known SHP-1 targets. Interferon-beta treatment in vivo resulted in decreased NF-kappaB and STAT6 activation and increased STAT1 activation. Further analysis in vitro showed that cultured PBMCs of MS patients and normal subjects had a significant SHP-1 induction following interferon-beta treatment that correlated with decreased NF-kappaB and STAT6 activation. Most importantly, experimental depletion of SHP-1 in cultured PBMCs abolished the anti-inflammatory effects of interferon-beta treatment, indicating that SHP-1 is a predominant mediator of interferon-beta activity. In conclusion, interferon-beta treatment upregulates SHP-1 expression resulting in decreased transcription factor activation and inflammatory gene expression important in MS pathogenesis.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

Signal transducer and activator of transcription-3, inflammation, and cancer: how intimate is the relationship?

Signal transducer and activator of transcription-3 (STAT-3) is one of six members of a family of transcription factors. It was discovered almost 15 years ago as an acute-phase response factor. This factor has now been associated with inflammation, cellular transformation, survival, proliferation, invasion, angiogenesis, and metastasis of cancer. Various types of carcinogens, radiation, viruses, growth factors, oncogenes, and inflammatory cytokines have been found to activate STAT-3. STAT-3 is constitutively active in most tumor cells but not in normal cells. Phosphorylation of STAT-3 at tyrosine 705 leads to its dimerization, nuclear translocation, DNA binding, and gene transcription. The phosphorylation of STAT-3 at serine 727 may regulate its activity negatively or positively. STAT-3 regulates the expression of genes that mediate survival (survivin, bcl-xl, mcl-1, cellular FLICE-like inhibitory protein), proliferation (c-fos, c-myc, cyclin D1), invasion (matrix metalloproteinase-2), and angiogenesis (vascular endothelial growth factor). STAT-3 activation has also been associated with both chemoresistance and radioresistance. STAT-3 mediates these effects through its collaboration with various other transcription factors, including nuclear factor-kappaB, hypoxia-inducible factor-1, and peroxisome proliferator activated receptor-gamma. Because of its critical role in tumorigenesis, inhibitors of this factor's activation are being sought for both prevention and therapy of cancer. This has led to identification of small peptides, oligonucleotides, and small molecules as potential STAT-3 inhibitors. Several of these small molecules are chemopreventive agents derived from plants. This review discusses the intimate relationship between STAT-3, inflammation, and cancer in more detail.

Interferon-resistant Daudi cell line with a Stat2 defect is resistant to apoptosis induced by chemotherapeutic agents

Interferon-alpha (IFNalpha) has shown promise in the treatment of various cancers. However, the development of IFN resistance is a significant drawback. Using conditions that mimic in vivo selection of IFN-resistant cells, the RST2 IFN-resistant cell line was isolated from the highly IFN-sensitive Daudi human Burkitt lymphoma cell line. The RST2 cell line was resistant to the antiviral, antiproliferative, and gene-induction actions of IFNalpha. Although STAT2 mRNA was present, STAT2 protein expression was deficient in RST2 cells. A variant STAT2 mRNA, which resulted from alternative splicing within the intron between exon 19 and 20, was expressed in several human cell lines but at relatively high levels in RST2 cells. Most importantly, the RST2 line showed an intrinsic resistance to apoptosis induced by a number of chemotherapeutic agents (camptothecin, staurosporine, and doxorubicin). Expression of STAT2 in RST2 cells not only rescued their sensitivity to the biological activities of IFNs but also restored sensitivity to apoptosis induced by these chemotherapeutic agents. The intrinsic resistance of the RST2 cells to IFN as well as chemotherapeutic agents adds a new dimension to our knowledge of the role of STAT2 as it relates to not only biological actions of IFN but also resistance to chemotherapy-induced apoptosis.

The role of TRAF2 binding to the type I interferon receptor in alternative NF kappaB activation and antiviral response

Type I interferons (IFNs) play critical roles in the host defense by modulating gene expression through the IFN-dependent activation of STAT and NFkappaB transcription factors. Previous studies established that IFN activates NFkappaB through a classical NFkappaB pathway that results in IkappaBalpha degradation and formation of p50-containing NFkappaB complexes, as well as an alternative pathway that involves NFkappaB-inducing kinase and TRAF2, which results in the formation of p52-containing NFkappaB complexes. In this study, we examined the interaction of TRAF proteins with the type I IFN receptor. We found that TRAF2 was directly coupled to the signal-transducing IFNAR1 subunit of the IFN receptor. By immunoprecipitation, overexpression of epitope-tagged IFNAR1 constructs, and glutathione S-transferase pulldown experiments, we demonstrate that TRAF2 rapidly binds to the IFNAR1 subunit of the IFN receptor upon IFN binding. The membrane proximal half of the IFNAR1 subunit was found to directly bind TRAF2. Moreover, analysis of mouse embryo fibroblasts derived from TRAF2 knock-out mice demonstrated that TRAF2 plays a critical role in the activation of the alternative NFkappaB pathway by IFN, but not the classical NFkappaB pathway, as well as in the antiviral action of IFN. Our results place TRAF2 directly in the signaling pathway transduced through the IFNAR1 subunit of the IFN receptor. These findings provide an important insight into the molecular mechanisms by which IFN generates signals to induce its biological effects.

The role of type I interferons in TLR responses

Recent advances in unravelling the complexities of the signalling pathways that constitute innate immunity have highlighted type I interferon as a key component in the response to infection. Here we focus on the emerging field of pattern-recognition receptor signalling, specifically Toll-like receptors and retinoic acid inducible gene-like helicases, from the perspective of this 50-year-old cytokine. The type I interferon gene family encompasses more than 20 subtypes, whose nature and properties have been extensively studied during its relatively long history. In this review we update and integrate available data on the mechanics of activation of the interferon genes and the role of this cytokine family in the innate immune response.

Identification of CXCL11 as a STAT3-Dependent Gene Induced by IFN

IFNs selectively regulate gene expression through several signaling pathways. The present study explored the involvement of STAT3 in the IFN-induced expression of the gene encoding the CXCL11 chemokine. The CXCL11 gene was induced in IFN-sensitive Daudi cells, but not in an IFN-resistant DRST3 subline with a defective STAT3 signaling pathway. Although the IFN-stimulated gene ISG15 was induced to a similar extent in Daudi and DRST3 cells, expression of wild-type STAT3 in DRST3 cells restored the IFN inducibility of CXCL11. Reconstitution of STAT3 knockout mouse embryonic fibroblasts with wild-type STAT3, or STAT3 with the canonical STAT3 dimerization site at Y705 mutated, restored IFN inducibility of the CXCL11 gene. These data indicate that CXCL11 gene induction by IFN is STAT3 dependent, but that phosphorylation of Y705 of STAT3 is not required. Chromatin immunoprecipitation assays demonstrated that IFN treatment of Daudi and DRST3 cells induced STAT3 binding to the CXCL11 promoter. Chromatin immunoprecipitation assays also revealed that NF-kappaB family member p65 and IFN regulatory factor (IRF)1 were bound to CXCL11 promoter upon IFN treatment of Daudi cells. In contrast, IFN induced the binding of p50 and IRF2 to the CXCL11 promoter in DRST3 cells. The profile of promoter binding was indistinguishable in IFN-sensitive Daudi cells and DRST3 cells reconstituted with wild-type STAT3. Thus, STAT3 also plays a role in the recruitment of the transcriptional activators p65 and IRF1, and the displacement of the transcriptional repressors p50 and IRF2 from the CXCL11 promoter also appears to regulate the induction of CXCL11 gene transcription.

LM. Interferon induces NF-kappa B-inducing kinase/tumor necrosis factor receptor-associated factor-dependent NF-kappa B activation to promote cell survival

Type I interferons (IFNs) play critical roles in the host defense by modulating the expression of various genes via the IFN-dependent activation of signal transducers and activators of transcription and NF-kappaB (nuclear factor kappa B) transcription factors. Previous studies established that IFNalpha/beta activates NF-kappaB to promote cell survival through a phosphatidylinositol 3-kinase (PI3K)/Akt pathway, which involves serine phosphorylation and degradation of IkappaB alpha. We now describe a second pathway by which IFNs activate NF-kappaB that is independent of IkappaB degradation. This pathway involves NF-kappaB-inducing kinase (NIK) and the tumor necrosis factor receptor-associated factor-2 (TRAF2) and results in IFNalpha/beta-induced processing of the p100/NF-kappaB2 precursor into p52. IFNalpha/beta stimulates NF-kappaB DNA binding and NF-kappaB-dependent transcription. Whereas expression of NIK and TRAF2 constructs causes NF-kappaB activation, expression of dominant negative NIK and TRAF2 constructs blocks IFN-promoted NF-kappaB activation and IFN-stimulated kappaB-dependent transcription and IFNalpha/beta-induced processing of the p100/NF-kappaB2 precursor into p52. In contrast, PI3K does not mediate IFNalpha/beta-induced p100 processing, although PI3K is involved in the pathway resulting in IkappaB alpha degradation. Moreover, whereas IFN promotes cell survival in lymphoblastoid cells, expression of dominant negative NIK and TRAF2 constructs enhances IFN-induced apoptosis. Our results for the first time place NIK and TRAF2, previously shown to function in TNF signaling, within the IFN signal transduction pathway. Thus, IFN induces NF-kappaB activation to mediate IFN-dependent cell survival signals through a "canonical" pathway of IkappaB alpha proteolysis mediated by PI3K/Akt and a "noncanonical" pathway of p100 processing mediated by NIK/TRAF.

Interferon alpha activates NF-kappaB in JAK1-deficient cells through a TYK2-dependent pathway

In addition to activating members of the STAT transcription factor family, interferon alpha/beta (IFNalpha/beta) activates the NF-kappaB transcription factor. To determine the role of the Janus tyrosine kinase (JAK)-STAT pathway in NF-kappaB activation by IFN, we examined NF-kappaB activation in JAK1-deficient mutant human fibrosarcoma cells. In wild-type fibrosarcoma cells (2fTGH), IFN activates STAT1, STAT2, and STAT3, as well as NF-kappaB complexes comprised of p50 and p65. In contrast, in JAK1-deficient cells, IFN induces NF-kappaB activation and NF-kappaB dependent gene transcription but does not activate these STAT proteins and has no effect on STAT-dependent gene transcription. Expression of a catalytically inactive TYK2 tyrosine kinase in JAK1-deficient cells, as well as in the highly IFN-sensitive Daudi lymphoblastoid cell line, abrogates NF-kappaB activation by IFN. Moreover, IFN does not promote NF-kappaB activation in TYK2-deficient mutant fibrosarcoma cells. Our results demonstrate a dichotomy between the classical JAK-STAT pathway and the NF-kappaB signaling pathway. In the IFN signaling pathway leading to STAT activation, both JAK1 and TYK2 are essential, whereas NF-kappaB activation requires only TYK2.

Interferons, interferon-like cytokines, and their receptors

Recombinant interferon-alpha (IFN-alpha) was approved by regulatory agencies in many countries in 1986. As the first biotherapeutic approved, IFN-alpha paved the way for the development of many other cytokines and growth factors. Nevertheless, understanding the functions of the multitude of human IFNs and IFN-like cytokines has just touched the surface. This review summarizes the history of the purification of human IFNs and the key aspects of our current state of knowledge of human IFN genes, proteins, and receptors. All the known IFNs and IFN-like cytokines are described [IFN-alpha, IFN-beta, IFN-epsilon, IFN-kappa, IFN-omega, IFN-delta, IFN-tau, IFN-gamma, limitin, interleukin-28A (IL-28A), IL-28B, and IL-29] as well as their receptors and signal transduction pathways. The biological activities and clinical applications of the proteins are discussed. An extensive section on the evolution of these molecules provides some new insights into the development of these proteins as major elements of innate immunity. The overall structure of the IFNs is put into perspective in relation to their receptors and functions.

Hepatitis C virus (HCV) constitutively activates STAT-3 via oxidative stress: role of STAT-3 in HCV replication

The hepatitis C virus (HCV) causes chronic hepatitis, which often results in liver cirrhosis and hepatocellular carcinoma. We have previously shown that HCV nonstructural proteins induce activation of STAT-3 via oxidative stress and Ca2+ signaling (G. Gong, G. Waris, R. Tanveer, and A. Siddiqui, Proc. Natl. Acad. Sci. USA 98:9599-9604, 2001). In this study, we focus on the signaling pathway leading to STAT-3 activation in response to oxidative stress induced by HCV translation and replication activities. Here, we demonstrate the constitutive activation of STAT-3 in HCV replicon-expressing cells. The HCV-induced STAT-3 activation was inhibited in the presence of antioxidant (pyrrolidine dithiocarbamate) and Ca2+ chelators (BAPTA-AM and TMB-8). Previous studies have shown that maximum STAT-3 transactivation requires Ser727 phosphorylation in addition to tyrosine phosphorylation. Using a series of inhibitors and dominant negative mutants, we show that HCV-induced activation of STAT-3 is mediated by oxidative stress and influenced by the activation of cellular kinases, including p38 mitogen-activated protein kinase, JNK, JAK-2, and Src. Our results also suggest a potential role of STAT-3 in HCV RNA replication. We also observed the constitutive activation of STAT-3 in the liver biopsy of an HCV-infected patient. These studies provide an insight into the mechanisms by which HCV induces intracellular events relevant to liver pathogenesis associated with the viral infection.

IFN-alpha5 mediates stronger Tyk2-stat-dependent activation and higher expression of 2',5'-oligoadenylate synthetase than IFN-alpha2 in liver cells

Interferon-alpha5 (IFN-alpha5) is the main IFN-alpha subtype expressed in the liver. Hepatitis C virus (HCV) infection is associated with low IFN-alpha5 mRNA levels, possibly reflecting an escape mechanism of the virus. In this work, we sought to compare IFN-alpha2 and IFN-alpha5 with respect to activation of early cell signaling cascades and induction of antiviral genes in the human hepatoma HepG2 and Huh7 cell lines. We found that the Tyr701 phosphorylation kinetics of Stat1 mediated by IFN stimulation was higher when cells were incubated with IFN-alpha5 than when using IFN-alpha2. Similarly, Tyr(1054/1055) phosphorylation kinetics of Tyk2 were more intense after exposure to IFN-alpha5 than when using IFN-alpha2. Concomitantly, Tyr705 phosphorylation of Stat3 was higher after stimulation with IFN-alpha5 than with IFN-alpha2. In parallel to these findings, the mRNA levels of the antiviral IFN-inducible gene 2',5'-oligoadenylate synthetase were higher in cell samples treated with IFN-alpha5 than with IFN-alpha2. These findings suggest that interaction of IFN-alpha5 and IFN-alpha2 subtypes with IFN type I receptor occurs differently, and this affects the intensity of expression of antiviral genes. In conclusion, our data show that in hepatocytic cells, IFN-alpha5 induces stronger signaling and higher expression of antiviral genes than IFN-alpha2. These data warrant clinical trials to evaluate the efficacy of IFN-alpha5 in chronic viral hepatitis.

Type I interferons and the innate immune response--more than just antiviral cytokines

The role of type I interferon (referred to as IFN in this review) in early antiviral immunity is well known. More recently IFN has been shown to be a potent regulator of adaptive immunity. It is now becoming clear that a broad range of viruses, bacteria and even parasites express ligands capable of stimulating a growing number of signalling pathways that results in, often subtype specific, induction of IFN. Of particular interest are the signalling pathways associated with the Toll-like receptors. This family of receptors, each able to induce signals in response to a variety of ligands, initiates the pro-inflammatory response. They also contain members that have the capacity to induce IFN, making use of, and perhaps promoting the evolution of its pleiotropic responses. Greater knowledge of the events that result in induction of IFN is necessary in understanding the specificity of expression of an increasingly complex and important aspect of our immune system. This may reveal to us further therapeutic opportunities, either in the use of IFN or in the manipulation of their expression. This review details the established knowledge and recent advances made in understanding how and under what circumstances the IFNs are expressed, starting with brief overviews of IFN and Toll-like receptors before following the molecular processes from induction of IFN, activation of the JAK-STAT pathway and finally the expression of interferon stimulated genes and their functions.

STAT3 induces anti-hepatitis C viral activity in liver cells

Hepatitis C virus (HCV) infection is a leading cause a of chronic liver disease worldwide. The main therapeutic regimen is the combination of interferon alpha (IFN) and the nucleoside analog, Ribavirin. IFN initiates an intracellular antiviral state by the JAK-STAT signaling pathway, including a presumed role for STAT1 and STAT2. We have previously shown that the STAT3 activation occurs during IFN treatment of human hepatoma cells, suggesting that the STAT3-mediated pathway is relevant to IFN-induced antiviral activity. In this study, we investigate the role of activated STAT3 in the induction of anti-HCV activity in human hepatoma cells. We demonstrate that the STAT3 activation is involved in efficient IFN-induced anti-HCV activity. Using an inducible, cytokine-independent, STAT3 activation system, in which the entire coding region of STAT3 is fused with the ligand-binding domain of the estrogen receptor, we demonstrate that: activated STAT3 is tightly regulated in a stably transfected cell line by an estrogen analog, 4-HT; activated STAT3 initiates efficient anti-HCV activity in a HCV subgenomic replicon cell line; and activation of STAT3 is associated with the induction of a potential antiviral gene, 1-8U. In addition, we show that the cytokine IL-6, a potent STAT3 activator, inhibits HCV subgenomic RNA replication through STAT3 activation and ERK pathway. These results strongly suggest that STAT3 activation is capable of initiating intracellular antiviral pathways.

Interaction of stress-activated protein kinase-interacting protein-1 with the interferon receptor subunit IFNAR2 in uterine endometrium

During early pregnancy in ruminants, a type I interferon (IFN-tau) signals from the conceptus to the mother to ensure the functional survival of the corpus luteum. IFN-tau operates through binding to the type I IFN receptor (IFNR). Here we have explored the possibility that IFNAR2, one of the two subunits of the receptor, might interact with hitherto unknown signal transduction factors in the uterus that link IFN action to pathways other than the well established Janus kinase-signal transducer and activator of transcription pathways. A yeast two-hybrid screen of an ovine (ov) endometrial cDNA library with the carboxyl-terminal 185 amino acids of ovIFNAR2 as bait identified stress-activated protein kinase-interacting protein 1 (ovSin1) as a protein that bound constitutively through its own carboxyl terminus to the receptor. ovSin1 is a little studied, 522-amino acid-long polypeptide (molecular weight, 59,200) that is highly conserved across vertebrates, but has identifiable orthologs in Drosophila and yeast. It appears to be expressed ubiquitously in mammals, although in low abundance, in a wide range of mammalian tissues in addition to endometrium. Sin1 mRNA occurs in at least two alternatively spliced forms, the smaller of which lacks a 108-bp internal exon. ovSin1, although not exhibiting features of a membrane-spanning protein, such as IFNAR2, is concentrated predominantly in luminal and glandular epithelial cells of the uterine endometrium. When ovSin1 and ovIFNAR2 are coexpressed, the two proteins can be coimmunoprecipitated and colocalized to the plasma membrane and to perinuclear structures. Sin1 provides a possible link among type I IFN action, stress-activated signaling pathways, and control of prostaglandin production.

Interferon induces the interaction of prothymosin-alpha with STAT3 and results in the nuclear translocation of the complex

Interferons (IFNs) play critical roles in host defense by modulating the expression of various genes via tyrosine phosphorylation of STAT transcription factors. Many cytokines including IFNs induce tyrosine phosphorylation of the STAT3 transcription factor, which regulates acute phase gene expression. Using the yeast two-hybrid interaction trap, in which a tyrosine kinase is introduced into the yeast to allow tyrosine phosphorylation of bait proteins, prothymosin-alpha (ProTalpha) was identified to interact with the amino terminal half of tyrosine-phosphorylated STAT3. ProTalpha is a small, acidic, extremely abundant, and essential protein that may play a role in chromatin remodeling, and has been implicated in regulating the growth and survival of mammalian cells. Besides the interaction of tyrosine-phosphorylated STAT3 with ProTalpha in yeast cells, IFN induced the interaction of ProTalpha with STAT3 in mammalian cells, and this interaction was dependent on the tyrosine phosphorylation of STAT3. Moreover, IFNalpha induces the translocation of STAT3 and ProTalpha from the cytoplasm to the nucleus where these proteins colocalize. Since ProTalpha has an extremely strong nuclear localization and STAT proteins apparently lack any nuclear localization signals, the association of STAT3 with ProTalpha may provide a mechanism to result in STAT localization in the nucleus.