A unique palindromic element mediates gamma interferon induction of mig gene expression

Overview of the Mechanisms that May Contribute to the Non-Redundant Activities of Interferon-Inducible CXC Chemokine Receptor 3 Ligands

The inflammatory chemokines CXCL9, CXCL10, and CXCL11 are predominantly induced by interferon (IFN)-γ and share an exclusive chemokine receptor named CXC chemokine receptor 3 (CXCR3). With a prototype function of directing temporal and spatial migration of activated T cells and natural killer cells, and inhibitory effects on angiogenesis, these CXCR3 ligands have been implicated in infection, acute inflammation, autoinflammation and autoimmunity, as well as in cancer. Intense former research efforts led to recent and ongoing clinical trials using CXCR3 and CXCR3 ligand targeting molecules. Scientific evidence has claimed mutual redundancy, ligand dominance, collaboration or even antagonism, depending on the (patho)physiological context. Most research on their in vivo activity, however, illustrates that CXCL9, CXCL10, and CXCL11 each contribute to the activation and trafficking of CXCR3 expressing cells in a non-redundant manner. When looking into detail, one can unravel a multistep machinery behind final CXCR3 ligand functions. Not only can specific cell types secrete individual CXCR3 interacting chemokines in response to certain stimuli, but also the receptor and glycosaminoglycan interactions, major associated intracellular pathways and susceptibility to processing by particular enzymes, among others, seem ligand-specific. Here, we overview major aspects of the molecular properties and regulatory mechanisms of IFN-induced CXCR3 ligands, and propose that their in vivo non-redundancy is a reflection of the unprecedented degree of versatility that seems inherent to the IFN-related CXCR3 chemokine system.

Suppression of IP-10/CXCL10 gene expression in LPS- and/or IFN-γ-stimulated macrophages by parasite-secreted products

T helper (Th)2 polarized immune responses are characteristically dominant in helminth infections. The gene expression of interferon (IFN)-γ-inducible protein 10 (IP-10/CXCL10), which promotes Th1 responses, in mouse macrophages stimulated with lipopolysaccharide (LPS) and/or IFN-γ was suppressed by excretory/secretory (ES) products of Spirometra erinaceieuropaei plerocercoids. ES products suppressed LPS- and/or IFN-γ-induced transcriptional activities of a luciferase reporter gene under the control of a 243-bp fragment of the IP-10 gene promoter/enhancer, which contains an IFN-stimulated response element (ISRE) and two κB elements. Consistent with this result, ES products inhibited ISRE-dependent heterologous promoter activities and LPS- or IFN-γ-induced ISRE-binding activity. ES products also suppressed LPS-induced IFN-β gene expression. Furthermore, ES products suppressed nuclear factor (NF)-κB RelA (p65)-dependent transcriptional activity, whereas ES products had no effect on the κB-binding activity. These results suggest that ES products suppress the IP-10 gene expression by inhibiting the ISRE- and RelA-dependent transcriptional activities in mouse macrophages.

Increase of circulating CXCL9 and CXCL11 associated with euthyroid or subclinically hypothyroid autoimmune thyroiditis

CONTEXT

Recently, CXCL9 and CXCL11 have been shown to be involved in autoimmune thyroid disorders; however, no data are present about CXCL9 and CXCL11 circulating levels in thyroid autoimmunity.

OBJECTIVE

Our objective was to evaluate circulating CXCL9 and CXCL11 in autoimmune thyroiditis (AIT). DESIGN AND PATIENTS OR OTHER PARTICIPANTS: Serum CXCL9 and CXCL11 have been measured in 141 consecutive patients with newly diagnosed AIT (AIT-p), 70 euthyroid controls, and 35 patients with nontoxic multinodular thyroid. The three groups were similar in gender distribution and age; among the AIT-p, 26% had subclinical hypothyroidism.

RESULTS

Serum CXCL9 and CXCL11 levels were significantly (P < 0.0001 for both) higher in AIT-p (143 ± 164 and 121 ± 63 pg/ml, respectively) than in controls (68 ± 37 and 65 ± 19 pg/ml, respectively) or patients with multinodular thyroid (87 ± 43 and 71 ± 20 pg/ml, respectively). Among AIT-p, CXCL9 and CXCL11 levels were significantly higher in patients older than 50 yr or those with a hypoechoic ultrasonographic pattern or with hypothyroidism. In a multiple linear regression model including age, thyroid volume, hypoechogenicity, hypervascularity, TSH, anti-thyroglobulin, and anti-thyroid peroxidase, only age and TSH were significantly (P < 0.05) related to serum CXCL9 or CXCL11 levels. In a multiple linear regression model of CXCL9 vs. age, TSH, and CXCL11, TSH (P = 0.032) and CXCL11 (P = 0.001) were significantly and independently related to CXCL9.

CONCLUSIONS

We first show that circulating CXCL9 and CXCL11 are increased in patients with thyroiditis and hypothyroidism and are related to each other. These results underline the importance of a Th1 immune attack in the initiation of AIT.

CXCR3 ligands: redundant, collaborative and antagonistic functions

CXCR3 is a chemokine receptor that is rapidly induced on naïve T cells following activation, and preferentially remains highly expressed on type-1 helper (Th1)-type CD4(+) T cells, effector CD8(+) T cells and innate-type lymphocytes, such as natural killer (NK) and NKT cells. CXCR3 is activated by three interferon (IFN)-γ-inducible ligands CXCL9 (monokine induced by gamma-interferon), CXCL10 (interferon-induced protein-10) and CXCL11 (interferon-inducible T-cell alpha chemoattractant). Although some studies have revealed that these ligands have redundant functions in vivo, other studies have demonstrated that the three CXCR3 ligands can also collaborate and even compete with each other. Differential regulation of the three ligands at specific times in defined anatomically restricted locations in vivo likely participates in the fine control of T-cell trafficking over the course of an immune response. Among the differences in regulation, CXCL10 is induced by a variety of innate stimuli that induce IFN-α/β as well as the adaptive immune cell cytokine IFN-γ, whereas CXCL9 induction is restricted to IFN-γ. In this review, we will discuss how the balance, timing and pattern of CXCR3 ligand expression appears to regulate the generation of effector T cells in the lymphoid compartment and subsequent migration into peripheral sites of Th1-type inflammation in which the CXCR3 ligands also then regulate the interactions and migratory behavior of effector T cells in an inflamed peripheral tissue.

Resveratrol down-regulates interferon-γ-inducible inflammatory genes in macrophages: molecular mechanism via decreased STAT-1 activation

Resveratrol (trans-3,4',5-trihydroxystilbene) is one of nonflavonoid polyphenolic phytoalexins found in various plant species, a number of which are components of human diet including grapes and red wines. Resveratrol has exerted several beneficial effects with anti-inflammation, cardioprotection and cancer chemoprevention. However, its mechanisms of action are not completely understood. In this study, we investigated effects of resveratrol on inflammatory gene expression in interferon (IFN)-γ alone-stimulated macrophages and proposed a molecular basis underlying the action. Resveratrol inhibited IFN-γ-induced production of nitric oxide (NO), IFN-γ-inducible protein-10 (IP-10), or the monokine induced by IFN-γ (MIG) in RAW 264.7 macrophages and also that of NO in primary macrophages derived from bone marrows of C3H/HeJ (toll-like receptor-4(-/-)) mice. Moreover, resveratrol diminished IFN-γ-induced protein levels of inducible NO synthase (iNOS), attenuated mRNA levels of iNOS, IP-10 or MIG as well as inhibited IFN-γ-induced promoter activity of iNOS gene, indicating that the phytoalexin could down-regulate inflammatory genes at the transcription level. To understand a mechanism of the action, we tested resveratrol could affect the signal transducers and activation of transcription-1 (STAT-1), a pivotal transcription factor in IFN-γ-induced expression of inflammatory genes. Resveratrol inhibited IFN-γ-induced transcriptional activity of STAT-1 in macrophages and also IFN-γ-induced Tyr(701) or Ser(727) phosphorylation of STAT-1. We then focused on protein kinases upstream STAT-1 phosphorylation. Resveratrol inhibited IFN-γ-induced activation of Janus kinase-2 (JAK-2) and also the extracellular signal-regulated kinase, in which JAK-2 was more sensitive. Taken together, this study proposes a new mechanism of resveratrol, blocking JAK/STAT-1 pathway that controls inflammatory responses in IFN-γ-activated macrophages.

alpha-Viniferin suppresses the signal transducer and activation of transcription-1 (STAT-1)-inducible inflammatory genes in interferon-gamma-stimulated macrophages

alpha-Viniferin, an oligostilbene of trimeric resveratrol, has been reported to have anti-inflammatory potential in carrageenin-induced paw edema or adjuvant-induced arthritis in animal models. However, little is known about the molecular basis. In this study, alpha-viniferin at 3 - 10 microM dose-dependently inhibited interferon (IFN)-gamma-induced Ser(727) phosphorylation of the signal transducer and activation of transcription-1 (STAT-1), a pivotal transcription factor controlling IFN-gamma-targeted genes, in RAW 264.7 macrophages, and also IFN-gamma-induced activation of the extracellular signal-regulated kinase (ERK)-1, a protein kinase upstream of the Ser(727) phosphorylation of STAT-1. However, alpha-viniferin, only at a higher concentration of 10 microM, inhibited Janus kinase 2-mediated Tyr(701) phosphorylation of STAT-1 in the cells. To understand STAT-1-dependent inflammatory responses, we quantified nitric oxide (NO) or chemokines. alpha-Viniferin at 3 - 10 muM dose-dependently inhibited IFN-gamma-induced production of NO, IFN-gamma-inducible protein-10 (IP-10), or the monokine induced by IFN-gamma (MIG) in RAW 264.7 cells and also that of NO in primary macrophages-derived from C57BL/6 mice. Furthermore, alpha-viniferin diminished IFN-gamma-induced protein levels of inducible NO synthase (iNOS), attenuated mRNA levels of iNOS, IP-10, or MIG as well as inhibited promoter activity of the iNOS gene. In conclusion, this study proposes an anti-inflammatory mechanism of alpha-viniferin, down-regulating STAT-1-inducible inflammatory genes via inhibiting ERK-mediated STAT-1 activation in IFN-gamma-stimulated macrophages.

The cell-specific induction of CXC chemokine ligand 9 mediated by IFN-gamma in microglia of the central nervous system is determined by the myeloid transcription factor PU.1

The IFN-gamma-inducible chemokines CXCL9 and CXCL10 are implicated in the pathogenesis of T cell-mediated immunity in the CNS. However, in various CNS immune pathologies the cellular localization of these chemokines differs, with CXCL9 produced by macrophage/microglia whereas CXCL10 is produced by both macrophage/microglia and astrocytes. In this study, we determined the mechanism for the microglial cell-restricted expression of the Cxcl9 gene induced by IFN-gamma. In cultured glial cells, the induction of the CXCL9 (in microglia) and CXCL10 (in microglia and astrocytes) mRNAs by IFN-gamma was not inhibited by cycloheximide. Of various transcription factors involved with IFN-gamma-mediated gene regulation, PU.1 was identified as a constitutively expressed NF in microglia but not in astrocytes. STAT1 and PU.1 bound constitutively to the Cxcl9 gene promoter in microglia, and this increased significantly following IFN-gamma treatment with IFN regulatory factor-8 identified as an additional late binding factor. However, in astrocytes, STAT1 alone bound to the Cxcl9 gene promoter. STAT1 was critical for IFN-gamma induction of both the Cxcl9 and Cxcl10 genes in microglia and in microglia and astrocytes, respectively. The small interfering RNA-mediated knockdown of PU.1 in microglia markedly impaired IFN-gamma-induced CXCL9 but not STAT1 or IFN regulatory factor-8. Cells of the D1A astrocyte line showed partial reprogramming to a myeloid-like phenotype posttransduction with PU.1 and, in addition to the expression of CD11b, acquired the ability to produce CXCL9 in response to IFN-gamma. Thus, PU.1 not only is crucial for the induction of CXCL9 by IFN-gamma in microglia but also is a key determinant factor for the cell-specific expression of this chemokine by these myeloid cells.

The benzoxathiolone LYR-71 down-regulates interferon-gamma-inducible pro-inflammatory genes by uncoupling tyrosine phosphorylation of STAT-1 in macrophages

BACKGROUND AND PURPOSE

Benzoxathiolone derivatives have shown anti-inflammatory and immunomodulatory potential in acne and psoriatic disorders. However, little is known about the molecular basis for these pharmacological effects. In this study, we decided to investigate the anti-inflammatory actions of a benzoxathiolone derivative LYR-71, 6-methyl-2-propylimino-6,7-dihydro-5H-benzo[1,3]oxathiol-4-one, in interferon (IFN)-gamma-activated macrophages.

EXPERIMENTAL APPROACH

RAW 264.7 macrophages or primary macrophages, derived from bone marrow of C3H/HeJ mice, were stimulated with IFN-gamma in the presence of LYR-71. Nitric oxide (NO) or chemokine production was measured by Griess reaction or enzyme-linked immunosorbent assay. RAW 264.7 cells were used to examine the molecular mechanisms of LYR-71 in modulating IFN-gamma-induced inflammatory responses.

KEY RESULTS

LYR-71 down-regulated IFN-gamma-induced transcription of inducible NO synthase, IFN-gamma-inducible protein-10 and the monokine induced by IFN-gamma genes in macrophages. This effect was mediated by uncoupling tyrosine phosphorylation of the signal transducer and activator of transcription (STAT)-1 in response to IFN-gamma. LYR-71 directly inhibited the in vitro catalytic activity of Janus kinase (JAK)-2. Further, the inhibitory actions of LYR-71 on IFN-gamma-induced STAT-1 phosphorylation and NO production were consistently abolished in the presence of peroxyvanadate, implying another target dependent on protein tyrosine phosphatase.

CONCLUSIONS AND IMPLICATIONS

Taken together, LYR-71 could restrain IFN-gamma-induced inflammatory responses through uncoupling the tyrosine phosphorylation of STAT-1, an activation index of JAK-STAT-1 signalling, in macrophages. These results may provide a molecular mechanism underlying anti-inflammatory actions shown by benzoxathiolone derivatives.

Role of the Jak/STAT pathway in the regulation of interleukin-8 transcription by oxidized phospholipids in vitro and in atherosclerosis in vivo

Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (Ox-PAPC) and its component phospholipid, 1-palmitoyl-2-epoxyisoprostane-sn-glycero-3-phosphorylcholine, induce endothelial cells (EC) to synthesize chemotactic factors, such as interleukin 8 (IL-8). Previously, we demonstrated a role for c-Src kinase activation in Ox-PAPC-induced IL-8 transcription. In this study, we have examined the mechanism regulating IL-8 transcription by Ox-PAPC downstream of c-Src. Our findings demonstrate an important role for JAK2 in the regulation of IL-8 transcription by Ox-PAPC. Treatment of human aortic EC with Ox-PAPC and 1-palmitoyl-2-epoxyisoprostane-sn-glycero-3-phosphorylcholine induced a rapid yet sustained activation of JAK2; activation of JAK2 by Ox-PAPC was dependent on c-Src kinase activity. Furthermore, pretreatment with selective JAK2 inhibitors significantly reduced Ox-PAPC-induced IL-8 transcription. In previous studies, we also demonstrated activation of STAT3 by Ox-PAPC. Here we provide evidence that STAT3 activation by Ox-PAPC is dependent on JAK2 activation and that STAT3 activation regulates IL-8 transcription by Ox-PAPC in human EC. Transfection with small interfering RNA against STAT3 significantly reduced Ox-PAPC-induced IL-8 transcription. Using chromatin immunoprecipitation assays, we demonstrated binding of activated STAT3 to the sequence flanking the consensus gamma-interferon activation sequence (GAS) in the IL-8 promoter; site-directed mutagenesis of GAS inhibited IL-8 transcription by Ox-PAPC. Finally, these studies demonstrate a role for STAT3 activation in atherosclerosis in vivo. We found increased staining for activated STAT3 in the inflammatory regions of human atherosclerotic lesions and reduced fatty streak formation in EC-specific STAT3 knock-out mice on the atherogenic diet. Taken together, these data demonstrate an important role for the JAK2/STAT3 pathway in Ox-PAPC-induced IL-8 transcription in vitro and in atherosclerosis in vivo.

Cytokine and chemokine networks: pathways to antiviral defense

The complex interplays between cytokines and chemokines are emerging as key communication signals in the shaping of innate and adaptive immune responses against foreign pathogens, including viruses. In particular, the virus-induced expression of cytokine and chemokine profiles drives the recruitment and activation of immune effector cells to sites of tissue infection. Under the conditions of infection with murine cytomegalovirus (MCMV), a herpesvirus with pathogenic potential, early immune functions are essential in the control of virus replication and virus-induced pathology. The coordinated MCMV-induced cytokine and chemokine responses promote effective natural killer (NK) cell recruitment and function, and ultimately MCMV clearance. The studies highlighted in this chapter illustrate in vivo pathways mediated by innate cytokines in regulating chemokine responses that are vital for localized antiviral defenses.

Proximal genomic localization of STAT1 binding and regulated transcriptional activity

BACKGROUND

Signal transducer and activator of transcription (STAT) proteins are key regulators of gene expression in response to the interferon (IFN) family of anti-viral and anti-microbial cytokines. We have examined the genomic relationship between STAT1 binding and regulated transcription using multiple tiling microarray and chromatin immunoprecipitation microarray (ChIP-chip) experiments from public repositories.

RESULTS

In response to IFN-gamma, STAT1 bound proximally to regions of the genome that exhibit regulated transcriptional activity. This finding was consistent between different tiling microarray platforms, and between different measures of transcriptional activity, including differential binding of RNA polymerase II, and differential mRNA transcription. Re-analysis of tiling microarray data from a recent study of IFN-gamma-induced STAT1 ChIP-chip and mRNA expression revealed that STAT1 binding is tightly associated with localized mRNA transcription in response to IFN-gamma. Close relationships were also apparent between STAT1 binding, STAT2 binding, and mRNA transcription in response to IFN-alpha. Furthermore, we found that sites of STAT1 binding within the Encyclopedia of DNA Elements (ENCODE) region are precisely correlated with sites of either enhanced or diminished binding by the RNA polymerase II complex.

CONCLUSION

Together, our results indicate that STAT1 binds proximally to regions of the genome that exhibit regulated transcriptional activity. This finding establishes a generalized basis for the positioning of STAT1 binding sites within the genome, and supports a role for STAT1 in the direct recruitment of the RNA polymerase II complex to the promoters of IFN-gamma-responsive genes.

Sulindac, a nonsteroidal anti-inflammatory drug, selectively inhibits interferon-gamma-induced expression of the chemokine CXCL9 gene in mouse macrophages

Sulindac, a non-steroidal anti-inflammatory drug, has been shown to exert an anti-tumor effect on several types of cancer. To determine the effect of sulindac on intracellular signaling pathways in host immune cells such as macrophages, we investigated the effect of the drug on interferon gamma (IFNgamma)-induced expression of signal transducer and activator of transcription 1 (STAT1) and other genes in mouse macrophage-like cell line RAW264.7 cells. Sulindac, but not aspirin or sodium salicylate, inhibited IFNgamma-induced expression of the CXC ligand 9 (CXCL9) mRNA, a chemokine for activated T cells, whereas the interferon-induced expression of CXCL10 or IFN regulatory factor-1 was not affected by sulindac. Luciferase reporter assay demonstrated that sulindac inhibited IFNgamma-induced promoter activity of the CXCL9 gene. Surprisingly, sulindac had no inhibitory effect on IFNgamma-induced STAT1 activation; however, constitutive nuclear factor kappaB activity was suppressed by the drug. These results indicate that sulindac selectively inhibited IFNgamma-inducible gene expression without inhibiting STAT1 activation.

Stat1 and SUMO modification

Many proteins are known to undergo small ubiquitin-related modifier (SUMO) modification by an E1-, E2-, and E3-dependent ligation process. Recognition that protein inhibitor of activated signal transducers and activators of transcription (STATs) (PIAS) proteins are SUMO E3 ligases raised the possibility that STATs may also be regulated by SUMO modification. Consistent with this possibility, a SUMO-ylation consensus site (PsiKxE; Psi indicates hydrophobic residue, and x indicates any residue) was identified in Stat1 (ie, (702)IKTE(705)), but not in other STATs. Biochemical analysis confirmed that Stat1 K(703) could be SUMO modified in vitro. Mutation of this critical lysine (ie, Stat1(K703R)) yielded a protein that, when expressed in Stat1(-/-) mouse embryonic fibroblasts (MEFs), exhibited enhanced DNA binding and nuclear retention. This was associated with modest changes in transcriptional and antiviral activity. However, mutation of the second critical residue in the SUMO consensus site, E(705) (ie, Stat1(E705A)), yielded a protein with wild-type DNA binding, nuclear retention, and transcriptional and antiviral activity. Similar observations were made when these mutants were expressed in primary Stat1(-/-) macrophages. These observations suggest that although Stat1 can uniquely be SUMO-ylated in vitro, this modification is unlikely to play an important role in regulating Stat1 activity in vivo.

CXCR3 and its ligands in a murine model of obliterative bronchiolitis: regulation and function

Lung transplantation remains the only effective therapy for patients with end-stage lung disease, but survival is limited by the development of obliterative bronchiolitis (OB). The chemokine receptor CXCR3 and two of its ligands, CXCL9 and CXCL10, have been identified as important mediators of OB. However, the relative contribution of CXCL9 and CXCL10 to the development of OB and the mechanism of regulation of these chemokines has not been well defined. In this study, we demonstrate that CXCL9 and CXCL10 are up-regulated in unique patterns following tracheal transplantation in mice. In these experiments, CXCL9 expression peaked 7 days posttransplant, while CXCL10 expression peaked at 1 day and then again 7 days posttransplant. Expression of CXCL10 was also up-regulated in a novel murine model of lung ischemia, and in bronchoalveolar lavage fluid taken from human lungs 24 h after lung transplantation. In further analysis, we found that 3 h after transplantation CXCL10 is donor tissue derived and not dependent on IFN-gamma or STAT1, while 24 h after transplantation CXCL10 is from recipient tissue and regulated by IFN-gamma and STAT1. Expression of both CXCL9 and CXCL10 7 days posttransplant is regulated by IFN-gamma and STAT1. Finally, we demonstrate that deletion of CXCR3 in recipients reduces airway obliteration. However, deletion of either CXCL9 or CXCL10 did not affect airway obliteration. These data show that in this murine model of obliterative bronchiolitis, these chemokines are differentially regulated following transplantation, and that deletion of either chemokine alone does not affect the development of airway obliteration.

A mechanism of transcriptional regulation of the CSF-1 gene by interferon-gamma

Interferon (IFN)-gamma exerts multiple functions including antiviral, anti-proliferative and immunomodulatory activities, which are mediated through the JAK-STAT pathway. We observed that IFN-gamma significantly increases the production of colony stimulating factor-1 (CSF-1) by a human lung carcinoma cell line, A549. To gain insight into this mechanism, we determined the unknown nucleotide sequences of 5'-flanking region of human CSF-1 gene. About 60 bases upstream of the transcription start site of the CSF-1 gene contains a possible gamma interferon activated site (GAS), TTCCCATAA. The promoter assay and the electrophoretic mobility gel shift assay revealed that IFN-gamma stimulates transcription of the CSF-1 gene through this sequence, which binds STAT1.

Calling in the troops: regulation of inflammatory cell trafficking through innate cytokine/chemokine networks

The recruitment of immune effector cells to localized sites of infection is crucial for the effective delivery of innate immune mechanisms. Under the conditions of infections with murine cytomegalovirus (MCMV), a herpesvirus with pathogenic potential, early immune functions are essential in the control of virus replication and virus-induced pathology. Our studies have demonstrated that the chemokine macrophage inflammatory protein-1alpha (MIP-1alpha) is critical for natural killer (NK) cell inflammation and delivery of interferon (IFN)-gamma to mediate downstream protective responses against MCMV infection in liver. Moreover, IFN-alpha/beta-dependent mechanisms promote MIP-1alpha production and subsequently the accumulation of NK cells in liver. Taken together, the studies highlighted in this review define a unique in vivo pathway mediated by innate cytokines in regulating chemokine responses that are essential in the promotion of NK cell inflammation for localized antiviral defense. In addition, the downstream consequences of these events in enhancing endogenous adaptive immune responses will also be discussed. Overall, the innate cytokine/chemokine networks that are described emphasize the emerging importance of chemokine functions for protective immune responses during infection with viruses.

Leptin signaling in the hypothalamus during chronic central leptin infusion

Using a rat model of chronic central leptin infusion in which neuropeptide Y neurons develop leptin resistance, we examined whether leptin signal transduction mechanism in the hypothalamus is altered during central leptin infusion. Adult male rats were infused chronically into the lateral cerebroventricle with leptin (160 ng/h) or vehicle via Alzet pumps for 16 d. In the leptin-infused group, the initial decrease in food intake was followed by a recovery to their preleptin levels by d 16, although food intake remained significantly lower than in artificial cerebrospinal fluid controls; and body weight gradually decreased reaching a nadir at d 11 and remained stabilized at lower level thereafter. Phosphorylated leptin receptor and phosphorylated signal transducer and activator of transcription-3 (p-STAT3) remained elevated in association with a sustained elevation in DNA-binding activity of STAT3 in the hypothalamus throughout 16-d period of leptin infusion. However, phosphorylated Janus kinase-2 was increased during the early part of leptin infusion but remained unaltered on d 16. Although hypothalamic suppressors of cytokine signaling-3 (SOCS3) mRNA levels were increased throughout leptin infusion, SOCS3 protein levels were increased only on d 16. This study demonstrates a sustained elevation in hypothalamic leptin receptor signaling through Janus kinase-STAT pathway despite an increased expression of SOCS3 during chronic central leptin infusion. We propose that an alteration in leptin signaling in the hypothalamus through pathways other than STAT3 and/or a defect in downstream of STAT3 signaling may be involved in food intake recovery seen after an initial decrease during chronic central leptin infusion.

Src kinases mediate STAT growth pathways in squamous cell carcinoma of the head and neck

Signal transducer and activator of transcription (STAT) proteins are constitutively activated in many malignancies, including squamous cell carcinoma of the head and neck (SCCHN). Previously, we reported that phosphorylation of the epidermal growth factor receptor (EGFR) is linked to activation of STATs 3 and 5 in SCCHN cells. The present study was undertaken to determine the role of Src family kinases in STAT activation and SCCHN growth. The Src family kinases c-Src, c-Yes, Fyn, and Lyn were expressed and activated by transforming growth factor-alpha stimulation in all four SCCHN cell lines examined but not in corresponding normal epithelial cells. In nine SCCHN cell lines tested, Src phosphotyrosine expression levels were highly correlated with activation levels of STATs 3 and 5. Co-immunoprecipitation analysis demonstrated interaction between c-Src and STATs 3 or 5 and EGFR in SCCHN cells, but no heterodimerization was detected between STAT3 and STAT5. SCCHN cells treated with either of two Src-specific inhibitors or transfected with a dominant-negative c-Src construct demonstrated decreased activation of STATs 3 and 5 and reduced growth rates in vitro. These results demonstrate a role for Src kinases in mediating activation of STATs 3 and 5 in concert with the EGFR in SCCHN cells. Strategies to target Src activation may contribute to the treatment of cancers that demonstrate increased levels of EGFR and STATs, including SCCHN.

T-cell-dependent antitumor effects produced by CD40 ligand expressed on mouse lung carcinoma cells are linked with the maturation of dendritic cells and secretion of a variety of cytokines

CD40/CD40 ligand (CD40L) interaction plays an essential role in cell-mediated immune responses. We examined whether expression of CD40L in murine lung carcinoma (A11) cells could produce antitumor effects. The proliferation rate in vitro of A11 cells transfected with the murine CD40L gene (A11/CD40L) was not different from that of parent cells; however, half of the immunocompetent mice inoculated with A11/CD40L cells did not form tumors and the growth of A11/CD40L tumors developed in the rest of mice was significantly retarded compared with that of parent tumors. Protective immunity was also induced in the mice that had rejected A11/CD40L cells. In T-cell-defective nude mice, these antitumor effects were not observed. Bone-marrow-derived dendritic cells (DCs), when cultured with A11/CD40L cells, formed clusters with the tumors and showed upregulated CD86 expression. Expression of the interleukin-23 (IL-23) p19, IL-12p35, IL-18, interferon-gamma (IFN-gamma) and Mig (monokine induced by IFN-gamma) genes was induced in the DCs that were cultured with A11/CD40L but not with A11 cells, and P40, the subunit of both IL-12 and IL-23, was secreted from the cocultured DCs. These data directly showed that the expression of CD40L in tumors facilitated the interaction between DCs and the tumors, enhanced the maturation of DCs, induced secretion of cytokines, and consequently produced T-cell-dependent systemic immunity.

Microarray analysis identifies interferon beta-regulated genes in multiple sclerosis

The molecular mechanisms for the interferon beta (IFNbeta) treatment of multiple sclerosis (MS) remain to be characterized. Using cDNA microarray technology, we have compared the gene expression profile of T and non-T cells derived from relapsing-remitting MS before and after treatment with IFNbeta-1b. IFNbeta treatment significantly altered expression of 21 genes out of 1263 at 3 and 6 months after treatment. These genes included nine with IFN-responsive promoter elements. Whereas there was no change in Th1 or Th2 marker genes, some of the changes were unexpected but coincided with the beneficial effect of IFNbeta in MS.

The transcriptional coactivator CREB-binding protein cooperates with STAT1 and NF-kappa B for synergistic transcriptional activation of the CXC ligand 9/monokine induced by interferon-gamma gene

Signal transducers and activators of transcription 1 (STAT1) and NF-kappaB cooperatively regulate the expression of many inflammatory genes. In the present study, we demonstrate that the transcriptional coactivator CREB-binding protein (CBP) mediated the STAT1/NF-kappaB synergy for transcription of the gene for CXC ligand 9 (CXCL9), an interferon-gamma (IFN-gamma)-inducible chemokine. Reporter gene analysis showed that expression of CBP potentiated IFN-gamma and tumor necrosis factor (TNFalpha)-induced promoter activity and that the CBP-mediated synergy depended upon STAT1- and NF-kappaB-binding sites in the promoter. Experiments with CBP mutants indicated that the N-terminal and C-terminal regions were necessary for the transcriptional synergy, although the histone acetyltransferase activity of CBP was dispensable. A co-immunoprecipitation assay demonstrated that STAT1 and NF-kappaB RelA (p65) simultaneously associated with CBP in vivo. Furthermore, chromatin immunoprecipitation revealed that, although costimulation with IFN-gamma and TNFalpha did not cooperatively enhance the levels of acetylated histones, it did result in increased recruitment of STAT1, CBP, and RNA polymerase II at the promoter region of the CXCL 9 gene. Together, these results demonstrate that the STAT1/NF-kappaB-dependent transcriptional synergy could result from the enhanced recruitment of RNA polymerase II complex to the promoter via simultaneous interaction of CBP with STAT1 and NF-kappaB.

NF-kappa B activation mediates the cross-talk between extracellular matrix and interferon-gamma (IFN-gamma) leading to enhanced monokine induced by IFN-gamma (MIG) expression in macrophages

In intact tissue, the extracellular matrix (ECM) provides support and helps maintain homeostasis but is considered biologically inert. In the setting of inflammation, not only is the ECM the target of inflammation, but its breakdown products modulate the magnitude and quality of an immune response. Fragments of the ECM component hyaluronan (HA) induce macrophage expression of chemokines, cytokines, and growth factors as well greatly enhance IFN-gamma-induced MIG expression. In this report, we demonstrate that the synergistic induction of MIG by HA and IFN-gamma occurs at the level of transcription via NF-kappaB. Using electrophoretic mobility shift assays and reporter assays, we have identified two NF-kappaB sites proximal to the IFN-gamma-responsive element-1 (gammaRE-1) that mediate this effect. Interestingly, our experiments also revealed a critical role for NF-kappaB in mediating IFN-gamma-induced MIG expression independent of HA. These data emphasize the ability of "degraded self" to activate/modify immune responses through the NF-kappaB pathway.

Differential function of STAT5 isoforms in head and neck cancer growth control

Up-regulation of the epidermal growth factor receptor (EGFR) is critical for the loss of growth control in a variety of human cancers, including squamous cell carcinoma of the head and neck (SCCHN). Stimulation of EGFR results in activation of mitogenic signaling pathways including Signal Transducers and Activators of Transcription (STATs). Stat5 activation has been primarily demonstrated in hematopoietic malignancies. Gene disruption studies suggest potentially distinct functions of the Stat5 isoforms, Stat5a and Stat5b, which are encoded by two genes closely linked on human chromosome 17. To determine the function of Stat5 in SCCHN growth control, we studied the expression and constitutive activation of Stat5a and Stat5b in normal and transformed human squamous epithelial cells. Increased constitutive activation of Stat5 was detected in transformed compared with normal squamous cells. Blockade of TGF-alpha or EGFR, abrogated Stat5 activation. Targeting of Stat5b using antisense oligonucleotides inhibited SCCHN growth. In addition, SCCHN cells stably transfected with dominant negative mutant Stat5b failed to proliferate in vitro. In contrast, targeting of Stat5a using either antisense or dominant negative strategies had no effect on cell growth. These results suggest that TGF-alpha/EGFR-mediated autocrine growth of transformed epithelial cells is dependent on activation of Stat5b but not Stat5a.

Transcription of the interferon gamma (IFN-gamma )-inducible chemokine Mig in IFN-gamma-deficient mice

MuMig or Mig (murine monokine induced by interferon gamma) is a CXC chemokine whose induction is thought to be strictly dependent on interferon gamma (IFN-gamma). Here we have studied the expression of this chemokine gene in various organs of mice infected with vaccinia virus. We have employed animals deficient in either IFN-gamma (IFN-gamma(-/-)), or receptors for IFN-alpha/beta, IFN-gamma, or both IFN-alpha/beta and IFN-gamma (DR(-/-)) to dissect out the role of interferons in the induction of Mig during the host response to virus infection. Our data show that Mig mRNA and protein are expressed in organs of vaccinia virus-infected IFN-gamma(-/-) mice, albeit at lower levels compared with infected, wild-type animals. In the DR(-/-) mice and in IFN-gamma(-/-) mice treated with a neutralizing antibody to IFN-alpha/beta, Mig mRNA transcripts were completely absent. Our data indicate that, in vaccinia virus-infected IFN-gamma(-/-) mice, Mig mRNA expression is mediated through the interaction between IFN-gamma responsive element 1 (gammaRE-1) and IFN-alpha/beta-induced STAT-1 complex referred to as IFN-gamma response factor 2 (gammaRF-2). Further, our findings support the view that gammaRF-2 is the IFN-alpha/beta induced STAT-1 complex, IFN-alpha-activated factor. We have found that, in the absence of IFN-gamma, IFN-alpha/beta are able to induce Mig in response to a viral infection in vivo.

DNA binding specificity of different STAT proteins. Comparison of in vitro specificity with natural target sites

STAT transcription factors are expressed in many cell types and bind to similar sequences. However, different STAT gene knock-outs show very distinct phenotypes. To determine whether differences between the binding specificities of STAT proteins account for these effects, we compared the sequences bound by STAT1, STAT5A, STAT5B, and STAT6. One sequence set was selected from random oligonucleotides by recombinant STAT1, STAT5A, or STAT6. For another set including many weak binding sites, we quantified the relative affinities to STAT1, STAT5A, STAT5B, and STAT6. We compared the results to the binding sites in natural STAT target genes identified by others. The experiments confirmed the similar specificity of different STAT proteins. Detailed analysis indicated that STAT5A specificity is more similar to that of STAT6 than that of STAT1, as expected from the evolutionary relationships. The preference of STAT6 for sites in which the half-palindromes (TTC) are separated by four nucleotides (N(4)) was confirmed, but analysis of weak binding sites showed that STAT6 binds fairly well to N(3) sites. As previously reported, STAT1 and STAT5 prefer N(3) sites; however, STAT5A, but not STAT1, weakly binds N(4) sites. None of the STATs bound to half-palindromes. There were no specificity differences between STAT5A and STAT5B.

Peroxisome proliferator-activated receptor-gamma activators inhibit IFN-gamma-induced expression of the T cell-active CXC chemokines IP-10, Mig, and I-TAC in human endothelial cells

Peroxisome proliferator-activated receptor-gamma (PPARgamma), a member of the nuclear hormone receptor superfamily originally shown to play an important role in adipocyte differentiation and glucose homeostasis, is now known to regulate inflammatory responses. Given the importance of endothelial cell (EC)-derived chemokines in regulating leukocyte function and trafficking, we studied the effects of PPARgamma ligands on the expression of chemokines induced in ECs by the Th1 cytokine IFN-gamma. Treatment of ECs with PPARgamma activators significantly inhibited IFN-gamma-induced mRNA and protein expression of the CXC chemokines IFN-inducible protein of 10 kDa (IP-10), monokine induced by IFN-gamma (Mig), and IFN-inducible T-cell alpha-chemoattractant (I-TAC), whereas expression of the CC chemokine monocyte chemoattractant protein-1 was not altered. PPARgamma activators decreased IFN-inducible protein of 10 kDa promoter activity and inhibited protein binding to the two NF-kappaB sites but not to the IFN-stimulated response element ISRE site. Furthermore, PPARgamma ligands inhibited the release of chemotactic activity for CXC chemokine receptor 3 (CXCR3)-transfected lymphocytes from IFN-gamma-stimulated ECs. These data suggest that anti-diabetic PPARgamma activators might attenuate the recruitment of activated T cells at sites of Th1-mediated inflammation.

Profiling of genes which are differentially expressed in mouse liver in response to adenoviral vectors and delivered genes

The effects of transgene delivery by adenoviral vectors were studied by probing a 588 gene, mouse cDNA array with mRNA derived from infected liver. The liver tissues were obtained from naive mice and mice infected with replication-deficient adenovirus, adenovirus expressing transforming growth factor beta1 (TGFbeta1), and adenovirus expressing connective tissue growth factor (CTGF). Expression of 98 genes was detected in the array analysis. The increased expression of the transcripts for Stat1, gamma interferon-induced monokine (MIG) and interferon regulatory factor 1 (IRF1) clearly demonstrated the immune response induced by infection with a first generation, replication-incompetent adenovirus. In vivo expression of TGFbeta1 led to a down-regulation of genes involved in the immune response. The increased expression of u-PAR1, laminin receptor and BMP-1 confirms the importance of CTGF and TGFbeta1 in angiogenesis, and tissue repair. Expression of the serine protease inhibitors, Spi 2.4 and Spi 2, is also increased in response to AdTGFbeta1 and AdCTGF.

IP-10 is critical for effector T cell trafficking and host survival in Toxoplasma gondii infection

The generation of an adaptive immune response against intracellular pathogens requires the recruitment of effector T cells to sites of infection. Here we show that the chemokine IP-10, a specific chemoattractant for activated T cells, controls this process in mice naturally infected with Toxoplasma gondii. Neutralization of IP-10 in infected mice inhibited the massive influx of T cells into tissues and impaired antigen-specific T cell effector functions. This resulted in >1000-fold increase in tissue parasite burden and a marked increase in mortality compared to control antibody-treated mice. These observations suggest that IP-10 may play a broader role in the localization and function of effector T cells at sites of Th1 inflammation.

Variegation of retroviral vector gene expression in myeloid cells

We have comparatively evaluated the efficiency of a series of retroviral vectors transducing the gp91-phox gene, whose defects are responsible for impaired production of superoxide anion (O2-) by phagocytic cells and lead to the X-linked form of chronic granulomatous disease (X-CGD). These vectors included four constructs based on the MoMuLV backbone and expressing gp91-phox from the viral long terminal repeat (LTR) or from internal promoters, and one construct based on the myelotropic FMEV vector. Expression of the therapeutic gene from the MoMuLV LTR was unsatisfactory after transduction of the PLB985 X-CGD knockout cell line and of primary CD34+ hematopoietic progenitors from X-CGD patients. The presence of either constitutive or inducible internal promoters did not result in important improvements in the efficiency of O2- production and lowered the titers of the viral preparations. In contrast, sustained levels of superoxide generation were obtained upon transduction with the FMEV vector. To analyze the efficiency of transgene expression at the single cell level, over 150 cellular clones were generated from bulk cultures of PLB985 X-CGD cells transduced with this vector, each one representative of an individual transduction event. These clones revealed a markedly heterogeneous pattern of gp91-phox expression, ranging from complete silencing to full restoration of superoxide production. Within each clone, expression of the therapeutic gene correlated with the number of expressing cells rather than with the average levels of expression from each cell, indicating that at the single cell level, the proviral promoter is regulated by a binary, on/off mechanism. Moreover, both transduced bulk and clonal cell populations displayed a tendency to a progressive extinction of expression over time, with a mechanism involving LTR methylation. The design of novel retroviral vectors escaping silencing is highly desirable for efficient gene therapy.

Salicylate-enhanced activation of transcription factors induced by interferon-gamma

Salicylate enhanced the interferon-gamma-dependent activation of two transcription factors in a murine macrophage cell line: signal transducer and activator of transcription (STAT)1 and interferon-gamma-responsive factor 1. Salicylate alone did not activate these transcription factors. This enhancement was reflected by increased DNA-binding activities and was the consequence of prolonged tyrosine phosphorylation of these transcription factors following interferon-gamma treatment. However, salicylate did not directly inhibit protein-tyrosine phosphatase activity in nuclear extracts of interferon-gamma-treated cells. The enhanced activation of STAT1 resulted in increased induction of mRNA encoding interferon regulatory factor-1. These results not only demonstrate that aspirin and its metabolite salicylate may have pro-inflammatory as well as anti-inflammatory effects but also raise the possibility that new cellular targets may be identified for modulating the Janus kinase-STAT signalling pathway.

Systemic interferon-alpha (IFN-alpha) treatment leads to Stat3 inactivation in melanoma precursor lesions

BACKGROUND

In the setting of familial melanoma, the presence of atypical nevi, which are the precursors of melanoma, is associated with a nearly 100% risk of developing primary melanoma by age 70. In patients with sporadic melanoma, it is estimated that 40-60% of melanomas develop in contiguous association with atypical nevi. Currently, the only way to prevent atypical nevi from progressing to melanoma is to monitor and excise them as soon as they exhibit changes in their clinical features. Activation of the transcription factor, Stat3, has been linked to abnormal cell growth and transformation as well as to interferon alpha (IFN-alpha)-mediated growth suppression in vitro.

MATERIALS AND METHODS

To determine whether IFN-alpha, used for adjuvant therapy of high-risk, resected melanoma, induces changes in Stat3 in atypical nevi, patients with a clinical history of melanoma who have multiple atypical nevi were treated for 3 months with low-dose IFN-alpha. Thereupon, the new technology of microscopic spectral imaging and biochemical assays such as electrophoretic mobility shift assays (EMSAs) and immunoblot analysis were used for the study of atypical nevi, obtained before and after IFN-alpha treatment.

RESULTS

The results of the investigations provided evidence that, as a result of systemic IFN-alpha treatment, Stat1 and Stat3, which are constitutively activated in melanoma precursor lesions, lose their ability to bind DNA, and as shown in the case of Stat3, become dephosphorylated.

CONCLUSIONS

Unlike primary and metastatic melanomas, melanoma precursor lesions cannot be established as cell cultures. Thus, the only way to explore pathways and treatment regimens that might help prevent progression to melanoma is within the context of a melanoma precursor lesion study conducted prospectively. The findings presented here suggest that down-regulation of the transcription factors Stat1 and Stat3 by systemic IFN-alpha treatment may represent a potential pathway to prevent the activation of gene(s) whose expression may be required for atypical nevus cells to progress to melanoma.

Hyaluronan fragments synergize with interferon-gamma to induce the C-X-C chemokines mig and interferon-inducible protein-10 in mouse macrophages

Hallmarks of chronic inflammation and tissue fibrosis are increased influx of activated inflammatory cells, mediator release, and increased turnover and production of the extracellular matrix (ECM). Recent evidence has suggested that fragments of the ECM component hyaluronan play a role in chronic inflammation by inducing macrophage expression of chemokines. Interferon-gamma (IFN-gamma), an important regulator of macrophage functions, has been shown to induce the C-X-C chemokines Mig and IP-10. These chemokines affect T-cell recruitment and inhibit angiogenesis. The purpose of this investigation was to determine the effect of hyaluronan (HA) on IFN-gamma-induced Mig and IP-10 expression in mouse macrophages. We found a marked synergy between HA and IFN-gamma on Mig and IP-10 mRNA and protein expression in mouse macrophages. This was most significant with Mig, which was not induced by HA alone. The synergy was specific for HA, was not dependent on new protein synthesis, was not mediated by tumor necrosis factor-alpha, was selective for Mig and IP-10, and occurred at the level of gene transcription. These data suggest that the ECM component HA may influence chronic inflammatory states by working in concert with IFN-gamma to alter macrophage chemokine expression.

STAT6 is required for the anti-inflammatory activity of interleukin-4 in mouse peritoneal macrophages

Interleukin-4 (IL-4) is an anti-inflammatory cytokine which inhibits many inducible macrophage functions. The present study demonstrates that the ability of IL-4 to inhibit interferon gamma (IFNgamma)-dependent gene transcription is dependent upon STAT6. IL-4 suppressed IFNgamma-induced expression of the MIG (monokine induced by IFNgamma) gene, a C-X-C chemokine, in mouse macrophages. IFNgamma-induced expression of MIG mRNA was abolished in peritoneal macrophages from Stat1-/- mice, and the suppression of MIG mRNA by IL-4 was abolished in macrophages from Stat6-/- mice. Transient transfection assays using a reporter gene containing the MIG gene promoter or the IFNgamma-responsive element (gammaRE) from the MIG gene revealed that the IFNgamma-dependent transcription was suppressed by IL-4, although IL-4 alone had no transactivating function. IFNgamma and IL-4 activated STAT1 and STAT6, respectively, and both proteins were able to bind the gammaRE motif. Furthermore, STAT6 was associated with the co-activator CREB-binding protein in RAW264.7 cells. These observations indicate that STAT6 is necessary for the IL-4-mediated suppression of IFNgamma-induced, STAT1-dependent transcription and suggest that STAT6 may directly suppress the STAT1-dependent transcription by competing with STAT1 for occupancy of the gammaRE motif and/or by competing with limiting quantities of the transcriptional coactivator.

Characterization of the Role of the Human Granulocyte-Macrophage Colony-Stimulating Factor Receptor α Subunit in the Activation of JAK2 and STAT5

The high-affinity human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor (GMR) consists of an alpha (GMRα) and a common beta (βc) subunit. The intracellular domain of βc has been extensively characterized and has been shown to be critical for the activation of both the JAK/STAT and MAP kinase pathways. The function of the intracellular domain of GMRα, however, is not as well characterized. To determine the role of this domain in GMR signaling, an extensive structure-function analysis was performed. Truncation mutants α362, α371, and α375 were generated, as well as the site-directed mutants αVQVQ and αVVVV. Although α375β, αVQNQβ, and αVVVVβ stimulated proliferation in response to human GM-CSF, the truncation mutants α362β and α371β were incapable of transducing a proliferative signal. In addition, both α371 and αVVVV were expressed at markedly reduced levels, indicating the importance of residues 372 to 374 for proper protein expression. More importantly, we show that GMRα plays a direct role in the activation of the JAK/STAT pathway, and electrophoretic mobility shift assays (EMSA) indicate that both GMRα and βc play a role in determining the STAT5 DNA binding complex activated by the GMR. Thus, the intracellular domain of the human GMRα is important for activation of the JAK/STAT pathway and protein stabilization.

© 1998 by The American Society of Hematology.

Characterization of the Role of the Human Granulocyte-Macrophage Colony-Stimulating Factor Receptor α Subunit in the Activation of JAK2 and STAT5

The high-affinity human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor (GMR) consists of an alpha (GMRα) and a common beta (βc) subunit. The intracellular domain of βc has been extensively characterized and has been shown to be critical for the activation of both the JAK/STAT and MAP kinase pathways. The function of the intracellular domain of GMRα, however, is not as well characterized. To determine the role of this domain in GMR signaling, an extensive structure-function analysis was performed. Truncation mutants α362, α371, and α375 were generated, as well as the site-directed mutants αVQVQ and αVVVV. Although α375β, αVQNQβ, and αVVVVβ stimulated proliferation in response to human GM-CSF, the truncation mutants α362β and α371β were incapable of transducing a proliferative signal. In addition, both α371 and αVVVV were expressed at markedly reduced levels, indicating the importance of residues 372 to 374 for proper protein expression. More importantly, we show that GMRα plays a direct role in the activation of the JAK/STAT pathway, and electrophoretic mobility shift assays (EMSA) indicate that both GMRα and βc play a role in determining the STAT5 DNA binding complex activated by the GMR. Thus, the intracellular domain of the human GMRα is important for activation of the JAK/STAT pathway and protein stabilization.

© 1998 by The American Society of Hematology.

Chemokines and chemotaxis of leukocytes in infectious meningitis

Chemokines constitute a constantly growing family of small inflammatory cytokines. They have been implied in many different diseases of the CNS including trauma, stroke and inflammation, e.g., multiple sclerosis. In this review we focus on the role of chemokines in infectious meningitis of bacterial or viral origin. In experimental bacterial meningitis induced by Listeria monocytogeneses both CXC and CC chemokines namely MIP-1alpha, MIP-1beta and MIP-2 are produced intrathecally by meningeal macrophages and leukocytes which infiltrate into the CNS. In patients with bacterial meningitis, IL-8, GROalpha, MCP-1, MIP-1alpha and MIP-1beta are detectable in the CSF. These chemokines contribute to CSF mediated chemotaxis on neutrophils and PBMC in vitro. In viral meningitis IL-8, IP-10 and MCP-1 are identified in the CSF to be responsible for chemotactic activity on neutrophils, PBMC and activated T cells. Taken collectively these data indicate that the recruitment of leukocytes in infectious meningitis involves the intrathecal production of chemokines.

Synergy between interferon-gamma and tumor necrosis factor-alpha in transcriptional activation is mediated by cooperation between signal transducer and activator of transcription 1 and nuclear factor kappaB

Interferon-gamma (IFNgamma) and tumor necrosis factor-alpha (TNFalpha) cooperate to induce the expression of many gene products during inflammation. The present report demonstrates that a portion of this cooperativity is mediated by synergism between two distinct transcription factors: signal transducer and activator of transcription 1 (STAT1) and nuclear factor kappaB (NF-kappaB). IFNgamma and TNFalpha synergistically induce expression of mRNAs encoding interferon regulatory factor-1 (IRF-1), intercellular adhesion molecule-1, Mig (monokine induced by gamma-interferon), and RANTES (regulated on activation normal T cell expressed and secreted) in normal but not STAT1-deficient mouse fibroblasts, indicating a requirement for STAT1. Transient transfection assays in fibroblasts using site-directed mutants of a 1.3-kilobase pair sequence of the IRF-1 gene promoter revealed that the synergy was dependent upon two sequence elements; a STAT binding element and a kappaB motif. Artificial constructs containing a single copy of both a STAT binding element and a kappaB motif linked to the herpes virus thymidine kinase promoter were able to mediate synergistic response to IFNgamma and TNFalpha; such response varied with both the relative spacing and the specific sequence of the regions between these two sites. Cooperatively responsive sequence constructs bound both STAT1alpha and NF-kappaB in nuclear extracts prepared from IFNgamma- and/or TNFalpha-stimulated fibroblasts, although binding of individual factors was not cooperative. Thus, the frequently observed synergy between IFNgamma and TNFalpha in promoting inflammatory response depends in part upon cooperation between STAT1alpha and NF-kappaB, which is most likely mediated by their independent interaction with one or more components of the basal transcription complex.

GAS elements: a few nucleotides with a major impact on cytokine-induced gene expression

Gamma interferon activation site (GAS) elements are short stretches of DNA, originally defined as a requirement for the rapid transcriptional induction of genes in response to interferon-gamma (IFN-gamma). The protein complex binding to GAS sequences in IFN-gamma-treated cells, the gamma interferon activation factor (GAF), is a dimer of Stat1, the prototype of a family of cytokine-responsive transcription factors, the signal transducers and activators of transcription. To date, seven different Stats are known (excluding alternatively spliced or processed forms), six of which recognize the same small palindromic consensus sequence TTCN2-4 GAA that defines a GAS element. Because one or several Stats take part in nuclear signaling in response to most cytokines or growth factors, the GAS sequence has changed from being viewed as a specific site for IFN-activated GAF to becoming the general nuclear end of the Jak-Stat signaling pathways. This review focuses on the identification and definition of GAS elements, their interaction with Stat transcription factors, and their contribution to the specificity of cytokine-induced gene expression.

Cellular responses to interferon-gamma

Interferons are cytokines that play a complex and central role in the resistance of mammalian hosts to pathogens. Type I interferon (IFN-alpha and IFN-beta) is secreted by virus-infected cells. Immune, type II, or gamma-interferon (IFN-gamma) is secreted by thymus-derived (T) cells under certain conditions of activation and by natural killer (NK) cells. Although originally defined as an agent with direct antiviral activity, the properties of IFN-gamma include regulation of several aspects of the immune response, stimulation of bactericidal activity of phagocytes, stimulation of antigen presentation through class I and class II major histocompatibility complex (MHC) molecules, orchestration of leukocyte-endothelium interactions, effects on cell proliferation and apoptosis, as well as the stimulation and repression of a variety of genes whose functional significance remains obscure. The implementation of such a variety of effects by a single cytokine is achieved by complex patterns of cell-specific gene regulation: Several IFN-gamma-regulated genes are themselves components of transcription factors. The IFN-gamma response is itself regulated by interaction with responses to other cytokines including IFN-alpha/beta, TNF-alpha, and IL-4. Over 200 genes are now known to be regulated by IFN-gamma and they are listed in a World Wide Web document that accompanies this review. However, much of the cellular response to IFN-gamma can be described in terms of a set of integrated molecular programs underlying well-defined physiological systems, for example the induction of efficient antigen processing for MHC-mediated antigen presentation, which play clearly defined roles in pathogen resistance. A promising approach to the complexity of the IFN-gamma response is to extend the analysis of the less understood IFN-gamma-regulated genes in terms of molecular programs functional in pathogen resistance.

Interferon-gamma induction of the human leukocyte antigen-E gene is mediated through binding of a complex containing STAT1alpha to a distinct interferon-gamma-responsive element

Expression of the human major histocompatibility complex (MHC) class I genes has been shown previously to increase at the transcriptional level following exposure to interferon-gamma (IFN-gamma). In this report we have examined the molecular mechanisms involved in the IFN-gamma-induced transcription of the human MHC class I gene, HLA-E. Functional analysis of CAT reporter gene constructs under the control of the HLA-E promoter transfected into U937 cells revealed the presence of a distinct IFN-gamma-responsive element, termed the interferon response region (IRR), that was necessary and sufficient to mediate the response to IFN-gamma. This cis-acting regulatory sequence contains an imperfect inverted repeat; the 5'-half of the IRR resembles the IFN-gamma activation site (GAS), and the 3'-half of the IRR resembles the interferon-stimulated response element (ISRE). Gel mobility shift assays demonstrated that the IRR bound a single, specific, IFN-gamma-induced complex (IRR-AC), which was formed rapidly following treatment with IFN-gamma and was independent of protein synthesis. Competition experiments with GAS and ISRE sequences from other IFN-inducible genes showed that GAS sequences competed for the IRR-AC, whereas ISRE sequences did not compete. Mutational analysis demonstrated that point mutations in either the 5'-half or 3'-half of the IRR prevented binding of the complex and abrogated or markedly reduced the IFN-gamma responsiveness of reporter gene constructs. Supershift analysis revealed that the IRR-AC contains a factor that was recognized by antibodies specific for the protein STAT1alpha (signal transducer and activator of transcription). Taken together, these findings suggest that the mechanism of IFN-gamma-induced transcription of the HLA-E gene is distinct from that of other MHC class I genes.

Growth hormone induction of hepatic serine protease inhibitor 2.1 transcription is mediated by a Stat5-related factor binding synergistically to two gamma-activated sites

A growth hormone (GH)-inducible nuclear factor (GHINF) from rat liver has been purified to near homogeneity. On SDS-polyacrylamide gel electrophoresis and UV-cross-linking, a major band of mass approximately 93 kDa and a minor band of approximately 70 kDa are detected in the purified fraction. DNase I footprinting using purified GHINF yields a protected region of -149/-115 on the rat serine protease inhibitor 2.1 (Spi 2.1) promoter encompassed within the growth hormone response element (GHRE). Mutational analysis demonstrated that GHINF binds synergistically to two gamma-interferon-activated sites (GAS) within the GHRE, with the 3' element being the pivotal binding domain. Functional assays show that both GAS elements are necessary for full GH response. GHINF has no immunoreactivity with either a C-terminal Stat1 antibody or an N-terminal Stat3 antibody, while cross-reacting with a C-terminal Stat5 monoclonal antibody. GHINF will bind to two GAS elements from the Stat5 binding region of the beta-casein gene. These studies indicate that GHINF is a Stat5-related factor binding synergistically to two GAS elements to activate Spi 2.1 transcription.

An interferon-gamma activation sequence mediates the transcriptional regulation of the IgG Fc receptor type IC gene by interferon-gamma

Expression of the IgG Fc receptor type I (Fc gamma RI) on myeloid cells is dramatically increased by treatment with interferon-gamma (IFN-gamma). We observed that Fc gamma RI transcript levels in monoblast-like U937 cells were elevated within 3 hr and peaked 12 hr after exposure to IFN-gamma. Treatment of U937 with IFN-gamma for 9 hr in the presence of cycloheximide led to super-induction of Fc gamma RI expression. Nuclear run-on analysis revealed that the rate of Fc gamma RI transcription was increased by IFN-gamma. Genomic sequence upstream of the Fc gamma RIC gene was cloned and subjected to primer extension analysis, which demonstrated a single transcription initiation site without a TATA box. Transient transfections of CAT reporter gene constructs containing various Fc gamma RIC promoter sequences into U937 cells revealed that a 20-bp region surrounding the transcription start site (-7 to +13) was capable of mediating transcription initiation and that an IFN-gamma responsive element (GIRE) was present within 74 bp upstream of the transcription initiation site. A 17-bp sequence between positions -51 and -35 conferred IFN-gamma responsiveness on a heterologous promoter. Double-stranded GIRE sequence, but not a scrambled sequence, was specifically bound by nuclear proteins from IFN-gamma treated U937 cells. Gel shift experiments further showed that the STAT1 alpha protein bound to the Fc gamma RIC GIRE in response to IFN-gamma treatment of U937 cells. The Fc gamma RIC GIRE is homologous to the IFN-gamma activation sequence (GAS) of the guanylate binding protein and to X box elements of class II MHC genes. Our results demonstrate that transcriptional regulation of the Fc gamma RIC gene by IFN-gamma involves the binding of STAT1 alpha to a 17-bp GAS homology in the proximal promoter.

Involvement of two regulatory elements in interferon-gamma-regulated expression of human indoleamine 2,3-dioxygenase gene

Interferon (IFN)-gamma-induced expression of indoleamine 2,3-dioxygenase (IDO) gene is implicated in the antimicrobial and antiproliferative effects of IFN-gamma in cell cultures. Earlier studies identified a 96 base pair (bp) regulatory region upstream of the IDO gene that conferred IFN-gamma response to the chloroamphenicol acetyltransferase (CAT) gene linked to herpesvirus thymidine kinase promoter. The IFN-gamma-responsive region was further narrowed to a 67 bp fragment by 3' deletion. This 67 bp fragment contains several sequence elements of potential interest, including a 14 bp sequence homologous to the ISRE sequence found in IFN-alpha-inducible genes and two palindromic sequences (PE I and PE II) homologous to the GAS sequence identified in IFN-gamma-inducible genes. Site-directed mutagenesis studies showed that IFN-gamma-induced expression of IDO-CAT constructs involved cooperation between two elements: the ISRE homolog and the PE II (but not PE I). Either element alone with its flanking sequence was inadequate in conferring an IFN-gamma response to CAT reporter gene. Two IFN-gamma-regulated protein factors interacting with these two elements were identified. The factor binding to the ISRE region was induced with a slower kinetics, required new protein synthesis, and reacted with antibodies to IRF-1. The factor interacting with the PE II region appeared rapidly after treatment with IFN-gamma independently of new protein synthesis, and its binding to DNA probe was blocked by antibodies to p91 factor, reported to bind to GAS element.(ABSTRACT TRUNCATED AT 250 WORDS)