Activation of the NF-κB pathway by the STAT3 inhibitor JSI-124 in human glioblastoma cells

Glioblastoma tumors are characterized by their invasiveness and resistance to therapies. The transcription factor signal transducer and activator of transcription 3 (STAT3) was recently identified as a master transcriptional regulator in the mesenchymal subtype of glioblastoma (GBM), which has generated an increased interest in targeting STAT3. We have evaluated more closely the mechanism of action of one particular STAT3 inhibitor, JSI-124 (cucurbitacin I). In this study, we confirmed that JSI-124 inhibits both constitutive and stimulus-induced Janus kinase 2 (JAK2) and STAT3 phosphorylation, and decreases cell proliferation while inducing apoptosis in cultured GBM cells. However, we discovered that before the inhibition of STAT3, JSI-124 activates the nuclear factor-κB (NF-κB) pathway, via NF-κB p65 phosphorylation and nuclear translocation. In addition, JSI-124 treatment induces the expression of IL-6, IL-8, and suppressor of cytokine signaling (SOCS3) mRNA, which leads to a corresponding increase in IL-6, IL-8, and SOCS3 protein expression. Moreover, the NF-κB-driven SOCS3 expression acts as a negative regulator of STAT3, abrogating any subsequent STAT3 activation and provides a mechanism of STAT3 inhibition after JSI-124 treatment. Chromatin immunoprecipitation analysis confirms that NF-κB p65 in addition to other activating cofactors are found at the promoters of IL-6, IL-8, and SOCS3 after JSI-124 treatment. Using pharmacological inhibition of NF-κB and inducible knockdown of NF-κB p65, we found that JSI-124-induced expression of IL-6, IL-8, and SOCS3 was significantly inhibited, showing an NF-κB-dependent mechanism. Our data indicate that although JSI-124 may show potential antitumor effects through inhibition of STAT3, other off-target proinflammatory pathways are activated, emphasizing that more careful and thorough preclinical investigations must be implemented to prevent potential harmful effects.

Abstract A80: Role of myeloid SOCS3 in prostate cancer progression

Suppressor Of Cytokine Signaling (SOCS) proteins, negative regulators of the JAK/STAT pathway, have been implicated in having a key protective role in tumor initiation and progression. However, the role of SOCS3 in regulating the differentiation and functions of myeloid-derived suppressor cells (MDSC) is poorly understood. Recent studies show the important role of MDSCs in promoting tumor progression as well as metastasis by regulating immune surveillance. To determine the role of myeloid SOCS3 in tumor progression, Conditional SOCS3 deletion in myeloid cells (LysMCre-SOCS3fl/fl) and SOCS3fl/fl C57BL/6 mice were used as recipients for subcutaneous transplantation of TRAMP-derived mouse prostate tumor cells. Our results indicate that tumor growth is significantly enhanced in myeloid-specific SOCS3-deficient mice, which correlates with elevated levels of Gr1+/CD11b+ cells in both spleen and tumor, and less CD8+ T-cell infiltration in tumors. Tumors from myeloid-specific SOCS3-deficient mice also express high levels of Arginase-1 and have elevated Akt signaling. In vitro, SOCS3-deficient bone-marrow-derived mononuclear cells (BDMC) exhibit heightened STAT3 activation and are subject to differentiation towards the MDSC phenotype. These findings suggest that myeloid cell SOCS3 provides protection from tumor progression by regulating MDSC differentiation.

Citation Format: Hao Yu, Yudong Liu, Etty N. Benveniste, Hongwei Qin. Role of myeloid SOCS3 in prostate cancer progression. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr A80.

Protective role of STAT3 in NMDA and glutamate-induced neuronal death: negative regulatory effect of SOCS3

The present study investigates the involvement of the IL-6 family of cytokines, activation of the transcription factor Signal Transducer and Activator of Transcription-3 (STAT3), and the role of Suppressor Of Cytokine Signaling-3 (SOCS3) in regulating excitotoxic neuronal death in vitro. Biochemical evidence demonstrates that in primary cortical neurons and SH-SY5Y neuroblastoma cells, IL-6 cytokine family members, OSM and IL-6 plus the soluble IL-6R (IL-6/R), prevent NMDA and glutamate-induced neuronal toxicity. As well, OSM and IL-6/R induce tyrosine and serine phosphorylation of STAT3 in primary cortical neurons and SH-SY5Y cells. Studies using Pyridine 6 (P6), a pan-JAK inhibitor, demonstrate that the protective effect of OSM and IL-6/R on neuronal death is mediated by the JAK/STAT3 signaling pathway. In parallel to STAT3 phosphorylation, OSM and IL-6/R induce SOCS3 expression at the mRNA and protein level. P6 treatment inhibits SOCS3 expression, indicating that STAT3 is required for OSM and IL-6/R-induced SOCS3 expression. Lentiviral delivery of SOCS3, an inhibitor of STAT3 signaling, into primary neurons and SH-SY5Y cells inhibits OSM and IL-6/R-induced phosphorylation of STAT3, and also reverses the protective effect of OSM and IL-6/R on NMDA and glutamate-induced neurotoxicity in primary cortical neurons. In addition, treatment with IL-6 cytokines increases expression of the anti-apoptotic protein Bcl-xL and induces activation of the Akt signaling pathway, which are also negatively regulated by SOCS3 expression. Thus, IL-6/R and OSM-induced SOCS3 expression may be an important factor limiting the neuroprotective effects of activated STAT3 against NMDA and glutamate-induced neurotoxicity.

AMP-activated protein kinase restricts IFN-γ signaling

Inflammation in the CNS contributes to neurologic disorders. Neuroinflammation involves the release of inflammatory molecules from glial cells, such as astrocytes and microglia, and can lead to neuronal damage if unabated. In multiple sclerosis, peripheral immune cells, including IFN-γ-producing Th1 cells, infiltrate the CNS and are important in shaping the inflammatory microenvironment, in part through cytokine-mediated interactions with glial cells. Recent evidence suggests that AMP-activated protein kinase (AMPK), a central regulator of energetic metabolism, can regulate inflammatory gene expression. In this study, we identified that IFN-γ induces biphasic AMPK signaling, suggestive of negative-feedback mechanisms. Activation of AMPK suppresses several IFN-γ-induced cytokines and chemokines in primary astrocytes and microglia. IFN-γ regulates gene expression through activation of STAT1, and deletion of AMPK results in a marked increase in basal expression of STAT1. Conversely, activation of AMPK blocks IFN-γ-induced STAT1 expression. Deletion of AMPK leads to increased basal and IFN-γ-induced expression of inflammatory molecules, including TNF-α, CXCL10, and CCL2. AMPK does not affect the phosphorylation of STAT1, but instead attenuates nuclear translocation of STAT1, DNA binding, and subsequent gene expression. In vivo, AMPK signaling during experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis, is downregulated in the brain at onset and peak of disease. Diminution of AMPK signaling in vivo correlates with increased expression of IFN-γ and CCL2 in the CNS. Overall, these findings provide the first link between AMPK and STAT1 and may provide important clues about how bioenergetics and inflammation are linked.

SOCS3 deficiency promotes M1 macrophage polarization and inflammation

Macrophages participate in both the amplification of inflammation at the time of injury and downregulation of the inflammatory response to avoid excess tissue damage. These divergent functions of macrophages are dictated by their microenvironment, especially cytokines, which promote a spectrum of macrophage phenotypes. The M1 proinflammatory phenotype is induced by LPS, IFN-γ, and GM-CSF, and IL-4, IL-13, and M-CSF induce anti-inflammatory M2 macrophages. Suppressors of cytokine signaling (SOCS) proteins function as feedback inhibitors of the JAK/STAT signaling pathway, and they can terminate innate and adaptive immune responses. In this study, we have evaluated the influence of SOCS3 on macrophage polarization and function. Macrophages obtained from LysMCre-SOCS3(fl/fl) mice, which lack SOCS3 in myeloid lineage cells, exhibit enhanced and prolonged activation of the JAK/STAT pathway compared with macrophages from SOCS3(fl/fl) mice. Furthermore, SOCS3-deficient macrophages have higher levels of the M1 genes IL-1β, IL-6, IL-12, IL-23, and inducible NO synthase owing to enhanced transcriptional activation and chromatin modifications. SOCS3-deficient M1 macrophages also have a stronger capacity to induce Th1 and Th17 cell differentiation than M1 macrophages from SOCS3(fl/fl) mice. Lastly, LPS-induced sepsis is exacerbated in LysMCre-SOCS3(fl/fl) mice and is associated with enhanced STAT1/3 activation and increased plasma levels of M1 cytokines/chemokines such as IL-1β, TNF-α, IL-6, CCL3, CCL4, and CXCL11. These findings collectively indicate that SOCS3 is involved in repressing the M1 proinflammatory phenotype, thereby deactivating inflammatory responses in macrophages.

Regulation of CCL20 expression in astrocytes by IL-6 and IL-17

Astrocytes have an important role in the regulation of inflammation within the central nervous system (CNS). In neuroinflammatory conditions such as multiple sclerosis, numerous cytokines and chemokines are elevated including IL-6, IL-17, and CCL20. IL-17 enhances IL-6 signaling and subsequent IL-6 expression in astrocytes. CCL20 is a CC motif chemokine that functions as a chemoattractant to facilitate the recruitment of CCR6-expressing cells, including Th17 cells. In this study, we examined the role of IL-6 and IL-17 on CCL20 production in primary murine astrocytes. IL-6 in combination with the IL-6 soluble receptor (sIL-6R) stimulated CCL20 expression in part through STAT3 activation, whereas IL-17 alone had no effect. However, the combination of IL-6, sIL-6R, and IL-17 led to a robust increase in CCL20 production. IL-17 increased the activation-associated phosphorylation of NF-κB, and inhibition of the NF-κB pathway significantly inhibited the enhancement of CCL20 expression by IL-17. In addition, chromatin immunoprecipitation revealed that stimulation of primary astrocytes with IL-6 plus the sIL-6R induced STAT3 binding to the CCL20 promoter. Combined stimulation with IL-6, sIL-6R, and IL-17 increased the recruitment of phosphorylated NF-κB to the CCL20 promoter, increased binding of coactivators such as p300 and CBP, and enhanced H3 and H4 histone acetylation, consistent with a transcriptionally active gene. The astrocyte-produced CCL20 increased T cell migration as determined by transwell migration assay. Collectively, these results suggest that astrocytes, in response to IL-6, sIL-6R, and IL-17, may shift chemokine production to that favoring T cell recruitment to the CNS.

ELISA methodology to quantify astrocyte production of cytokines/chemokines in vitro

Astrocytes are intimately involved in immunological and inflammatory events occurring in the central nervous system (CNS), due to their ability to secrete and respond to a large number of immunoregulatory cytokines/chemokines such as IL-1β, IL-6, IL-8, IL-10, IL-17, IL-27, TNF-α, TGF-β, IFN-γ, IFN-β, CCL2, CCL3, CCL5, CXCL10, and CXCL12. Although expression of cytokines and chemokines is limited in the normal CNS, elevated expression of these proteins, as seen in disease entities such as multiple sclerosis (MS), HIV-1 associated neurocognitive disorders (HAND), Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), contributes to the development of inflammation and neuronal demise in these diseases. As a potent source of cytokines and chemokines, astrocytes play a pivotal role in the type and extent of neuroinflammatory responses. Astrocytes can be stimulated in vitro to produce numerous cytokines/chemokines, which are secreted and detected in supernatants by a technique known as enzyme-linked immunosorbent assay (ELISA). In this chapter, we describe our experience using ELISAs to detect and quantify cytokines and chemokines secreted by stimulated murine astrocytes, specifically IL-6 and CXCL10.

Therapeutic potential of AZD1480 for the treatment of human glioblastoma

Aberrant activation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway has been implicated in glioblastoma (GBM) progression. To develop a therapeutic strategy to inhibit STAT-3 signaling, we have evaluated the effects of AZD1480, a pharmacologic inhibitor of JAK1 and JAK2. In this study, the in vitro efficacy of AZD1480 was tested in human and murine glioma cell lines. AZD1480 treatment effectively blocks constitutive and stimulus-induced JAK1, JAK2, and STAT-3 phosphorylation in both human and murine glioma cells, and leads to a decrease in cell proliferation and induction of apoptosis. Furthermore, we used human xenograft GBM samples as models for the study of JAK/STAT-3 signaling in vivo, because human GBM samples propagated as xenografts in nude mice retain both the hallmark genetic alterations and the invasive phenotype seen in vivo. In these xenograft tumors, JAK2 and STAT-3 are constitutively active, but levels vary among tumors, which is consistent with the heterogeneity of GBMs. AZD1480 inhibits constitutive and stimulus-induced phosphorylation of JAK2 and STAT-3 in these GBM xenograft tumors in vitro, downstream gene expression, and inhibits cell proliferation. Furthermore, AZD1480 suppresses STAT-3 activation in the glioma-initiating cell population in GBM tumors. In vivo, AZD1480 inhibits the growth of subcutaneous tumors and increases survival of mice bearing intracranial GBM tumors by inhibiting STAT-3 activity, indicating that pharmacologic inhibition of the JAK/STAT-3 pathway by AZD1480 should be considered for study in the treatment of patients with GBM tumors.

Loss of the promyelocytic leukemia protein in gastric cancer: implications for IP-10 expression and tumor-infiltrating lymphocytes

Gastric cancer is one of the most common causes of cancer-related mortality worldwide. Expression of the tumor suppressor, promyelocytic leukemia (PML) protein, is reduced or abolished in gastric carcinomas, in association with an increased level of lymphatic invasion, development of higher pTNM staging, and unfavorable prognosis. Herein, we investigated the relationship between the extent of tumor-infiltrating lymphocytes and the status of PML protein expression in advanced gastric carcinoma. We observed higher numbers of infiltrating T-cells in gastric carcinoma tissues in which PML expression was reduced or abolished, compared to tissues positive for PML. The extent of T-cell migration toward culture supernatants obtained from interferon-gamma (IFN-γ-stimulated gastric carcinoma cell lines was additionally affected by expression of PML in vitro. Interferon-gamma-inducible protein 10 (IP-10/CXCL10) expression was increased in gastric carcinoma tissues displaying reduced PML levels. Moreover, both Pml knockout and knockdown cells displayed enhanced IP-10 mRNA and protein expression in the presence of IFN-γ. PML knockdown increased IFN-γ-mediated Signal Transducer and Activator of Transcription-1 (STAT-1) binding to the IP-10 promoter, resulting in elevated transcription of the IP-10 gene. Conversely, PML IV protein expression suppressed IP-10 promoter activation. Based on these results, we propose that loss of PML protein expression in gastric cancer cells contributes to increased IP-10 transcription via enhancement of STAT-1 activity, which, in turn, promotes lymphocyte trafficking within tumor regions.

An NF-κB p65-cIAP2 link is necessary for mediating resistance to TNF-α induced cell death in gliomas

Malignant gliomas are diffusively infiltrative and remain among the deadliest of all cancers. NF-κB is a transcription factor that mediates cell growth, migration and invasion, angiogenesis and resistance to apoptosis. Normally, the activity of NF-κB is tightly regulated by numerous mechanisms. However, in many cancers, NF-κB is constitutively activated and may function as a tumor promoter. Herein, we show that in gliomas, NF-κB is constitutively activated and the levels of cIAP2, Bcl-2, Bcl-xL and Survivin are elevated. These genes are regulated by NF-κB and can inhibit apoptosis. To understand the potential role of NF-κB p65 in suppressing apoptosis, we generated human glioma cell lines that inducibly express shRNA molecules specific for p65. We demonstrate that in the absence of p65, TNF-α induced cIAP2 expression is significantly reduced while the levels of Bcl-2, Bcl-xL and Survivin are not affected. These data suggest that of these genes, only cIAP2 is a direct target of p65, which was confirmed using RT-PCR and chromatin immunoprecipitation (ChIP) assays. By reducing the levels of p65 and/or cIAP2 levels, we demonstrate that the levels of RIP poly-ubiquitination are reduced, and that p65-deficient glioma cells are more sensitive to the cytotoxic effects of TNF-α. Specifically, in the presence of TNF-α glioma cells lacking p65 and/or cIAP2 showed cellular proliferation defects and underwent cell death. These data suggest that NF-κB and/or cIAP2 may be therapeutically relevant targets for the treatment of malignant gliomas.

Th17 cells induce colitis and promote Th1 cell responses through IL-17 induction of innate IL-12 and IL-23 production

Both Th1 and Th17 cells have been implicated in the pathogenesis of inflammatory bowel disease and experimental colitis. However, the complex relationship between Th1 and Th17 cells and their relative contributions to the pathogenesis of inflammatory bowel disease have not been completely analyzed. Although it has been recently shown that Th17 cells can convert into Th1 cells, the underlying in vivo mechanisms and the role of Th1 cells converted from Th17 cells in the pathogenesis of colitis are still largely unknown. In this study, we report that Th17 cells from CBir1 TCR transgenic mice, which are specific for an immunodominant microbiota Ag, are more potent than Th1 cells in the induction of colitis, as Th17 cells induced severe colitis, whereas Th1 cells induced mild colitis when transferred into TCRβxδ(-/-) mice. High levels of IL-12 and IL-23 and substantial numbers of IFN-γ(+) Th1 cells emerged in the colons of Th17 cell recipients. Administration of anti-IL-17 mAb abrogated Th17 cell-induced colitis development, blocked colonic IL-12 and IL-23 production, and inhibited IFN-γ(+) Th1 cell induction. IL-17 promoted dendritic cell production of IL-12 and IL-23. Furthermore, conditioned media from colonic tissues of colitic Th17 cell recipients induced IFN-γ production by Th17 cells, which was inhibited by blockade of IL-12 and IL-23. Collectively, these data indicate that Th17 cells convert to Th1 cells through IL-17 induction of mucosal innate IL-12 and IL-23 production.

Generation of mucosal dendritic cells from bone marrow reveals a critical role of retinoic acid

It is unknown how dendritic cells (DCs) become specialized as mucosal DCs and maintain intestinal homeostasis. We report that a subset of bone marrow cells freshly isolated from C57BL/6 mice express the retinoic acid (RA)-synthesizing enzyme aldehyde dehydrogenase family 1, subfamily A2 (ALDH1a2) and are capable of providing RA to DC precursors in the bone marrow microenvironment. RA induced bone marrow-derived DCs to express CCR9 and ALDH1a2 and conferred upon them mucosal DC functions, including induction of Foxp3(+) regulatory T cells, IgA-secreting B cells, and gut-homing molecules. This response of DCs to RA was dependent on a narrow time window and stringent dose effect. RA promoted bone marrow-derived DC production of bioactive TGF-β by inhibiting suppressor of cytokine signaling 3 expression and thereby enhancing STAT3 activation. These RA effects were evident in vivo, in that mucosal DCs from vitamin A-deficient mice had reduced mucosal DC function, namely failure to induce Foxp3(+) regulatory T cells. Furthermore, MyD88 signaling enhanced RA-educated DC ALDH1a2 expression and was required for optimal TGF-β production. These data indicate that RA plays a critical role in the generation of mucosal DCs from bone marrow and in their functional activity.

IL-27 inhibits OSM-mediated TNF-alpha and iNOS gene expression in microglia

Elevated levels of Oncostatin M (OSM), an interleukin-6 family cytokine, have been observed in multiple sclerosis (MS), HIV-associated neurocognitive disorder (HAND), and glioblastoma (GBM); however, its effects within the CNS are not well understood. OSM regulates gene expression primarily by activating the JAK/STAT, NF-kappaB, and/or MAPK pathways, in a cell-type specific manner. In our studies, OSM induces the production of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) and inducible nitric oxide synthase (iNOS) from microglia in an NF-kappaB-dependent manner. This expression also partially requires the intermediate production of TNF-alpha and subsequent NF-kappaB activation via TNF-R1. We also demonstrate that OSM-induced TNF-alpha production from microglia is neurotoxic. The IL-12 family member, IL-27, suppresses OSM-mediated TNF-alpha and iNOS expression at the transcriptional level by inhibiting activation of the NF-kappaB pathway, and rescues the neurotoxicity induced by OSM-stimulated microglia. These studies are the first to demonstrate the proinflammatory effects of OSM in microglia, and also identify IL-27 as a novel inhibitor of inflammatory processes in these cells.

Suppressor of cytokine signaling 3 inhibits antiviral IFN-beta signaling to enhance HIV-1 replication in macrophages

HIV-1 replication within macrophages of the CNS often results in cognitive and motor impairment, which is known as HIV-associated dementia (HAD) in its most severe form. IFN-beta suppresses viral replication within these cells during early CNS infection, but the effect is transient. HIV-1 eventually overcomes this protective innate immune response to resume replication through an unknown mechanism, initiating the progression toward HAD. In this article, we show that Suppressor of Cytokine Signaling (SOCS)3, a molecular inhibitor of IFN signaling, may allow HIV-1 to evade innate immunity within the CNS. We found that SOCS3 is elevated in an in vivo SIV/macaque model of HAD and that the pattern of expression correlates with recurrence of viral replication and onset of CNS disease. In vitro, the HIV-1 regulatory protein transactivator of transcription induces SOCS3 in human and murine macrophages in a NF-kappaB-dependent manner. SOCS3 expression attenuates the response of macrophages to IFN-beta at proximal levels of pathway activation and downstream antiviral gene expression and consequently overcomes the inhibitory effect of IFN-beta on HIV-1 replication. These studies indicate that SOCS3 expression, induced by stimuli present in the HIV-1-infected brain, such as transactivator of transcription, inhibits antiviral IFN-beta signaling to enhance HIV-1 replication in macrophages. This consequence of SOCS3 expression in vitro, supported by a correlation with increased viral load and onset of CNS disease in vivo, suggests that SOCS3 may allow HIV-1 to evade the protective innate immune response within the CNS, allowing the recurrence of viral replication and, ultimately, promoting progression toward HAD.

IL-17 enhancement of the IL-6 signaling cascade in astrocytes

Astrocytes have important physiological roles in CNS homeostasis and serve as a bridge between the CNS and immune system. IL-17 and IL-6 are important in many CNS disorders characterized by neuroinflammation. We examined the role of IL-17 on the IL-6 signaling cascade in primary astrocytes. IL-17 functioned in a synergistic manner with IL-6 to induce IL-6 expression in astrocytes. The synergistic effect involved numerous signaling pathways including NF-kappaB, JNK MAPK, and p38 MAPK. The NF-kappaB pathway inhibitor BAY-11, JNK inhibitor JNKi II, and p38 inhibitor SB203580 suppressed the synergistic effect of IL-6 and IL-17 on IL-6 expression. IL-17 synergized with IL-6 to enhance the recruitment of activated NF-kappaB p65, c-Fos, c-Jun, and the histone acetyltransferases CREB-binding protein and p300 to the IL-6 promoter in vivo to induce IL-6 transcription. This was accompanied by enhanced acetylation of histones H3 and H4 on the IL-6 promoter. Moreover, we elucidated an important role for suppressor of cytokine signaling (SOCS) 3 in IL-17 enhancement of IL-6 signaling in astrocytes. SOCS3 small interfering RNA knockdown and SOCS3 deletion in astrocytes augmented the synergistic effect of IL-6 and IL-17 due to an enhancement of activation of the NF-kappaB and MAPK pathways. These results indicate that astrocytes can serve as a target of Th17 cells and IL-17 in the CNS, and SOCS3 participates in IL-17 functions in the CNS as a negative feedback regulator.

SOCS1 and SOCS3 in the control of CNS immunity

In the decade following their initial discovery, the suppressor of cytokine signaling (SOCS) proteins have been studied for their potential use as immunomodulators in disease. SOCS proteins, especially SOCS1 and SOCS3, are expressed by immune cells and cells of the central nervous system (CNS) and have the potential to impact immune processes within the CNS, including inflammatory cytokine and chemokine production, activation of microglia, macrophages and astrocytes, immune cell infiltration and autoimmunity. We describe CNS-relevant in vitro and in vivo studies that have examined the function of SOCS1 or SOCS3 under various neuroinflammatory or neuropathological conditions, including exposure of CNS cells to inflammatory cytokines or bacterial infection, demyelinating insults, stroke, spinal cord injury, multiple sclerosis and glioblastoma multiforme.

TGF-beta promotes Th17 cell development through inhibition of SOCS3

TGF-beta, together with IL-6 and IL-21, promotes Th17 cell development. IL-6 and IL-21 induce activation of STAT3, which is crucial for Th17 cell differentiation, as well as the expression of suppressor of cytokine signaling (SOCS)3, a major negative feedback regulator of STAT3-activating cytokines that negatively regulates Th17 cells. However, it is still largely unclear how TGF-beta regulates Th17 cell development and which TGF-beta signaling pathway is involved in Th17 cell development. In this report, we demonstrate that TGF-beta inhibits IL-6- and IL-21-induced SOCS3 expression, thus enhancing as well as prolonging STAT3 activation in naive CD4(+)CD25(-) T cells. TGF-beta inhibits IL-6-induced SOCS3 promoter activity in T cells. Also, SOCS3 small interfering RNA knockdown partially compensates for the action of TGF-beta on Th17 cell development. In mice with a dominant-negative form of TGF-beta receptor II and impaired TGF-beta signaling, IL-6-induced CD4(+) T cell expression of SOCS3 is higher whereas STAT3 activation is lower compared with wild-type B6 CD4(+) T cells. The addition of a TGF-beta receptor I kinase inhibitor that blocks Smad-dependent TGF-beta signaling greatly, but not completely, abrogates the effect of TGF-beta on Th17 cell differentiation. Our data indicate that inhibition of SOCS3 and, thus, enhancement of STAT3 activation is at least one of the mechanisms of TGF-beta promotion of Th17 cell development.

Involvement of SOCS Proteins in the Inhibitory Effect of IL-27 on Th17 Development (47.21)

Suppressor Of Cytokine Signaling (SOCS) proteins are critical feedback inhibitors of the JAK/STAT signaling pathway and have neuroprotective effects. Recently, several reports have shown that the cytokine IL-27 functions as an inhibitory regulator, and represses the development of Th17 cells associated with autoimmune brain inflammation. Stimulation with IL-27 results in the activation of members of the STAT family, predominantly STAT-1 and STAT-3. In this study, we describe that IL-27 induces SOCS-1 and SOCS-3 gene expression, which is correlated with IL-27 induced STAT-1α and STAT-3 activation in anti-CD3 and anti-CD28 activated CD4+ T cells. Furthermore, we demonstrate that IL-27 induction of SOCS-1 and SOCS-3 gene expression in CD4+ T cells occurs at the transcriptional level as assessed by promoter assays. IL-27-induced SOCS-1 and SOCS-3 expression in CD4+ T cells from WT and STAT-1 deficient mice indicate that induction of SOCS-1 occurs in a STAT-1 dependent manner, and SOCS-3 induction partially depends on STAT-1. The inhibitory effects of IL-27 on Th17 development in CD4+ T cells with specific SOCS-3 deficiency and/or SOCS-1 knockdown will be investigated in the near future. These results indicate that IL-27 induces SOCS-1 and SOCS-3 expression in CD4+ T cells by activation of STAT-1α and/or STAT-3. We propose that SOCS-1 and SOCS-3 may participate in IL-27-mediated suppression of Th17 cell production and autoimmune brain inflammation.

Molecular basis of oncostatin M-induced SOCS-3 expression in astrocytes

Under neuropathological conditions, reactive astrocytes release cytokines and chemokines, which act in an autocrine and/or paracrine fashion to modulate production of immunoregulatory factors from cells including microglia, astrocytes, and neurons. In this way, astrocytes play an important role in orchestrating immune responses within the central nervous system (CNS). Suppressor of cytokine signaling (SOCS) proteins are endogenous, negative regulators of the JAK/STAT signaling pathway and function as attenuators of the immune and inflammatory responses. As such, SOCS proteins may have critical roles in the CNS under neuroinflammatory conditions. In the inflamed CNS, expression of IL-6 cytokine family member oncostatin M (OSM) is elevated; however, its functional effects are not well understood. We demonstrate that OSM is a potent inducer of SOCS-3 in astrocytes. Analysis of the SOCS-3 promoter revealed that an AP-1 element, two IFN-gamma activation sequence (GAS) elements, and a GC-rich region are crucial for SOCS-3 gene expression. Using small interfering RNA against STAT-3, as well as a STAT-3 dominant-negative construct, we demonstrate that STAT-3 activation is critical for OSM induction of SOCS-3 expression. The ERK1/2 and JNK pathways also contribute to OSM-induced SOCS-3 gene expression. OSM stimulation led to a time-dependent recruitment of the transcription factors STAT-3, c-Fos, c-Jun, and Sp1 and the coactivators CREB-binding protein (CBP) and p300 to the endogenous SOCS-3 promoter. These data indicate that OSM-induced activation of STAT-3 and the ERK1/2 and JNK pathways are critical for astrocytic expression of SOCS-3, which provides for feedback inhibition of cytokine-induced inflammatory responses in the CNS.

Thrombospondin-1-induced apoptosis of brain microvascular endothelial cells can be mediated by TNF-R1

Thrombospondin-1 (TSP-1) treatment of dermal microvascular endothelial cells (MvEC) has been shown to upregulate Fas ligand (FasL) and to induce apoptosis by a mechanism that requires caspase-8 activity. We have examined the potential anti-angiogenic effects of TSP-1 on primary human brain MvEC. The addition of TSP-1 to primary human brain MvEC cultured as monolayers on type 1 collagen, induced cell death and apoptosis (evidenced by caspase-3 cleavage) in a dose- (5-30 nM) and time-dependent (maximal at 17 h) manner. TSP-1 treatment for 17 h induced caspase-3 cleavage that required caspase-8 activity and the tumor necrosis factor receptor 1 (TNF-R1). We did not find a requirement for Fas, or the tumor necrosis-related apoptosis-inducing ligand receptors (TRAIL-R) 1 and 2. We confirmed the findings using caspase inhibitors, blocking antibodies and small interfering RNA (siRNA). Further analysis indicated that the TSP-1 induction of caspase-3 cleavage of primary human brain MvEC adherent to collagen required the synthesis of new message and protein, and that TSP-1 induced the expression of TNFalpha mRNA and protein. Consistent with these findings, when the primary human brain MvEC were propagated on collagen gels mAb anti-TNF-R1 reversed the inhibitory effect, in part, of TSP-1 on tube formation and branching. These data identify a novel mechanism whereby TSP-1 can inhibit angiogenesis-through induction of apoptosis in a process mediated by TNF-R1.

TRAIL induces MMP-9 expression via ERK activation in human astrocytoma cells

Matrix metalloproteinase-9 (MMP-9) is an important angiogenic and prognostic factor in malignant tumors. Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is known as the death ligand, which induces preferential apoptosis of transformed tumor cells. In this study, we investigated the biological functions of TRAIL, other than its role in induction of apoptosis. We demonstrated that TRAIL induces MMP-9 expression in human astrocytoma cells, which is preceded by activation of extracellular signal-regulated protein kinase (ERK). In addition, TRAIL induces the DNA-binding activity of NF-kappaB, an important transcription factor for MMP-9 induction. The specific MEK inhibitor, U0126, significantly blocks TRAIL-mediated NF-kappaB activation and subsequent MMP-9 induction. These findings indicate that TRAIL treatment in human astrocytoma cells leads to the activation of NF-kappaB and subsequent expression of MMP-9, which are dependent on ERK activation. Collectively, these results suggest that TRAIL has alternative biological functions in addition to its role in inducing apoptosis in human malignant astrocytoma cells.

The IFN-gamma-induced transcriptional program of the CIITA gene is inhibited by statins

Statins are 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors that exert anti-inflammatory effects. IFN-gamma induction of class II MHC expression, which requires the class II transactivator (CIITA), is inhibited by statins; however, the molecular basis for suppression is undetermined. We describe that statins inhibit IFN-gamma-induced class II MHC expression by suppressing CIITA gene expression, which is dependent on the HMG-CoA reductase pathway. In addition, CIITA expression is inhibited by GGTI-298 or Clostridium difficile Toxin A, specific inhibitors of Rho family protein prenylation, indicating the involvement of small GTPases. Rac1 is involved in IFN-gamma inducible expression of CIITA, and statins inhibit IFN-gamma-induced Rac1 activation, contributing to the inhibitory effect of statins. IFN-gamma induction of the CIITA gene is regulated by the transcription factors STAT-1alpha, interferon regulatory factor (IRF)-1 and upstream stimulatory factor (USF)-1. We previously reported that statins inhibit constitutive STAT-1alpha expression. IRF-1, a STAT-1 dependent gene, is also inhibited by statins. Therefore, statin treatment results in decreased recruitment of STAT-1alpha and IRF-1 to the endogenous CIITA promoter IV (pIV). The recruitment of USF-1 to CIITA pIV is also reduced by statins, as is the recruitment of RNA polymerase II (Pol II), p300 and Brg-1. These data indicate that statins inhibit the transcriptional program of the CIITA gene.

Loss of protein inhibitors of activated STAT-3 expression in glioblastoma multiforme tumors: implications for STAT-3 activation and gene expression

PURPOSE

STATs activate transcription in response to numerous cytokines, controlling proliferation, gene expression, and apoptosis. Aberrant activation of STAT proteins, particularly STAT-3, is implicated in the pathogenesis of many cancers, including GBM, by promoting cell cycle progression, stimulating angiogenesis, and impairing tumor immune surveillance. Little is known about the endogenous STAT inhibitors, the PIAS proteins, in human malignancies. The objective of this study was to examine the expression of STAT-3 and its negative regulator, PIAS3, in human tissue samples from control and GBM brains.

EXPERIMENTAL DESIGN

Control and GBM human tissues were analyzed by immunoblotting and immunohistochemistry to determine the activation status of STAT-3 and expression of the PIAS3 protein. The functional consequence of PIAS3 inhibition by small interfering RNA or PIAS3 overexpression in GBM cells was determined by examining cell proliferation, STAT-3 transcriptional activity, and STAT-3 target gene expression. This was accomplished using [(3)H]TdR incorporation, STAT-3 dominant-negative constructs, reverse transcription-PCR, and immunoblotting.

RESULTS AND CONCLUSIONS

STAT-3 activation, as assessed by tyrosine and serine phosphorylation, was elevated in GBM tissue compared with control tissue. Interestingly, we observed expression of PIAS3 in control tissue, whereas PIAS3 protein expression in GBM tissue was greatly reduced. Inhibition of PIAS3 resulted in enhanced glioblastoma cellular proliferation. Conversely, PIAS3 overexpression inhibited STAT-3 transcriptional activity, expression of STAT-3-regulated genes, and cell proliferation. We propose that the loss of PIAS3 in GBM contributes to enhanced STAT-3 transcriptional activity and subsequent cell proliferation.