Gamma Interferon Activation Site Research Articles

GAS-Luc2 Reporter Cell Lines for Immune Checkpoint Drug Screening in Solid Tumors.

Recent studies highlight the integral role of the interferon gamma receptor (IFNγR) pathway in T cell-mediated cytotoxicity against solid but not liquid tumors. IFNγ not only directly facilitates tumor cell death by T cells but also indirectly promotes cytotoxicity via myeloid phagocytosis in the tumor microenvironment. Meanwhile, full human ex vivo immune checkpoint drug screening remains challenging. We hypothesized that an engineered gamma interferon activation site response element luciferase reporter (GAS-Luc2) can be utilized for immune checkpoint drug screening in diverse ex vivo T cell-solid tumor cell co-culture systems. We comprehensively profiled cell surface proteins in ATCC's extensive collection of human tumor and immune cell lines, identifying those with endogenously high expression of established and novel immune checkpoint molecules and binding ligands. We then engineered three GAS-Luc2 reporter tumor cell lines expressing immune checkpoints PD-L1, CD155, or B7-H3/CD276. Luciferase expression was suppressed upon relevant immune checkpoint-ligand engagement. In the presence of an immune checkpoint inhibitor, T cells released IFNγ, activating the JAK-STAT pathway in GAS-Luc2 cells, and generating a quantifiable bioluminescent signal for inhibitor evaluation. These reporter lines also detected paracrine IFNγ signaling for immune checkpoint-targeted ADCC drug screening. Further development into an artificial antigen-presenting cell line (aAPC) significantly enhanced T cell signaling for superior performance in these ex vivo immune checkpoint drug screening platforms.

Abstract 75: Luciferase reporter cell lines allow simultaneous incorporation of tumor cells, innate immune cells, and adaptive immune cells for in-depth immune checkpoint studies

Abstract Despite the considerable success of immune checkpoint therapies targeting T cells, a sizable proportion of patients experience resistance or relapse due to the immunosuppressive nature of the tumor microenvironment. Myeloid cells, a major component that suppresses effector lymphocytes, have emerged as an alternative and promising therapeutic target. However, there is a deep lack of widely accessible immunological models capable of representing the intricate three-way interaction between tumor cells, T cells, and myeloid cells. To address this need, we conducted a comprehensive protein profiling of human tumor and immune cell lines available at ATCC for various established and novel immune checkpoint molecules. Cell lines with high endogenous expression of the immune checkpoint proteins, such as programmed death-ligand 1 and 2 (PD-L1 and PD-L2), cluster of differentiation 155 (CD155), B7 homolog 3 (B7-H3), sialic acid-binding Ig-like lectin 10 (Siglec-10), or signal-regulatory protein alpha (SIRPα), were selected and constructed into luciferase reporter cell lines. For tumor reporter cell lines, a gamma interferon activation site (GAS) response element was placed upstream of the luciferase gene in the lentiviral vector, enabling the activation of the JAK-STAT signaling pathway within tumor cells to induce luciferase expression. In myeloid reporter cell lines, a nuclear factor kappa B (NF-κB) response element replaced GAS to monitor the activation of the NF-κB signaling pathway. In the presence of corresponding immune checkpoint inhibitors that enhance T cell-mediated anti-tumor activity, these reporter cell lines produce a bioluminescent signal based on luciferase expression. This signal can be easily detected and quantified to assess the efficacy of the inhibitor. Our data revealed that bioluminescence intensity in the tumor and myeloid reporter cell lines increased by >100-fold in a dose-dependent manner in response to interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) stimulation, respectively, and by >50-fold in response to the conditioned media collected from activated primary T cells. Furthermore, in co-culture assays involving various combinations of immune cell and tumor cell types with corresponding immune checkpoint inhibitors, these reporter cell lines demonstrated a significant increase in bioluminescence intensity. In conclusion, these newly established luciferase reporter cell lines offer an excellent ex vivo model for cancer immunotherapy. These cell lines naturally express immune checkpoint proteins, enabling the sensitive and reproducible monitoring of combinatorial responses from various immune cell types. Citation Format: Hyeyoun Chang, Alicia C. Walker, John G. Foulke, Luping Chen, Fang Tian, Zhizhan Gu. Luciferase reporter cell lines allow simultaneous incorporation of tumor cells, innate immune cells, and adaptive immune cells for in-depth immune checkpoint studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 75.

Abstract 6643: Immune checkpoint reporter cell lines based on the protein profiling of ATCC cell lines for cancer immunotherapy drug screening

Abstract The success of immune checkpoint inhibitors in the treatment of various types of cancers and their continued growth in the market have driven burgeoning interests in developing more drugs in this category. However, the intrinsic complexity of the immunological models and the variable drug responses among different cancer types have become the most prominent challenges. To facilitate large scale research projects and drug discovery of immune checkpoint inhibitors, we conducted a comprehensive protein profiling of ATCC’s vast portfolio of human tumor and immune cell lines for several established and novel immune checkpoint molecules. Based on this protein profiling data, we generated immune checkpoint reporter cancer cell lines with high expression of endogenous immune checkpoint molecule ligands (PD-L1, CD155, and B7-H3). The reporter system contains a gamma interferon activation site (GAS)-response element upstream of the luciferase gene, preventing luciferase expression when the immune checkpoint molecule ligand binds to its corresponding receptor that suppresses T cell-mediated antitumor activity. In the presence of a relevant immune checkpoint inhibitor, a luciferase expression-based bioluminescent signal is produced, which can be readily detected and quantitated to evaluate the efficacy, potency, and dynamics of the inhibitor. Our data showed that the bioluminescence in the reporter cancer cells increased approximately 100-250 folds in a dose-dependent manner in response to interferon gamma stimulation, which mimics the signaling from activated CD8+ cytotoxic T cells. The bioluminescence increased approximately 50-100 folds in response to CD8+ primary T cell-conditioned media stimulation. In particular, we observed up to 5-fold increase in luciferase signal from our PD-L1 reporter cell line in response to co-culture with CD8+ primary T cells in the presence of an anti-PD-L1 blocking antibody in a dose-dependent manner. The luciferase expression and endogenous immune checkpoint molecule ligand expression were well maintained after the cell lines had reached >30 population doubling level. These results highlight the robustness and responsiveness of the reporter system for the assessment of T cell-mediated immune responses triggered by checkpoint inhibitors. These immune checkpoint reporter cancer cell lines yield exceptional in vitro and ex vivo assay sensitivity and reproducibility, while simplify the complex immunological model by providing physiologically relevant expression of immune checkpoint molecule ligands, in comparison to similar assays with an artificial checkpoint ligand overexpression system. Citation Format: Hyeyoun Chang, Kevin Tyo, John Foulke, Luping Chen, Zhizhan Gu, Fang Tian. Immune checkpoint reporter cell lines based on the protein profiling of ATCC cell lines for cancer immunotherapy drug screening. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6643.

Prolactin regulates RANKL expression via signal transducer and activator of transcription 5a signaling in mammary epithelial cells of dairy cows.

Receptor of activated nuclear factor kappa B ligand (RANKL) is regulated by prolactin in the mammary gland. However, the intrinsic molecular mechanism is not well understood. Herein, mammary epithelial cells (MECs) of dairy cows were isolated to characterize the molecular mechanism of prolactin in vitro. We demonstrated that prolactin stimulation increased the expression of RANKL in MECs. Moreover, the expression of RANKL induced by prolactin was inhibited by the prolactin receptor or signal transducer and activator of transcription 5A (STAT5a) knockdown. Furthermore, prolactin markedly increased RANKL-Luciferase reporter activity in MECs. We identified a putative gamma-interferon activated site (GAS) in the region between residues -883 to -239 bp of the RANKL promoter. Subsequently, we found that the mutated GAS sequence failed to respond to prolactin stimulation. In addition, STAT5a knockdown markedly decreased prolactin-stimulated RANKL promoter activity. Western blot results revealed that RANKL overexpression markedly decreased the STAT5a phosphorylation level in MECs. These findings indicate that prolactin could regulate RANKL promoter activity via STAT5a, contributing to increased RANKL expression in MECs. RANKL may have a negative regulatory effect on STAT5a activity.

Mutation of Signal Transducer and Activator of Transcription 5 (STAT5) Binding Sites Decreases Milk Allergen αS1-Casein Content in Goat Mammary Epithelial Cells.

αS1-Casein (encoded by the CSN1S1 gene) is associated with food allergy more than other milk protein components. Milk allergy caused by αS1-casein is derived from cow milk, goat milk and other ruminant milk. However, little is known about the transcription regulation of αS1-casein synthesis in dairy goats. This study aimed to investigate the regulatory roles of signal transducer and activator of transcription 5 (STAT5) on αS1-casein in goat mammary epithelial cells (GMEC). Deletion analysis showed that the core promoter region of CSN1S1 was located at −110 to −18 bp upstream of transcription start site, which contained two putative STAT5 binding sites (gamma-interferon activation site, GAS). Overexpression of STAT5a gene upregulated the mRNA level and the promoter activity of the CSN1S1 gene, and STAT5 inhibitor decreased phosphorylated STAT5 in the nucleus and CSN1S1 transcription activity. Further, GAS site-directed mutagenesis and chromatin immunoprecipitation (ChIP) assays revealed that GAS1 and GAS2 sites in the CSN1S1 promoter core region were binding sites of STAT5. Taken together, STAT5 directly regulates CSN1S1 transcription by GAS1 and GAS2 sites in GMEC, and the mutation of STAT5 binding sites could downregulate CSN1S1 expression and decrease αS1-casein synthesis, which provide the novel strategy for reducing the allergic potential of goat milk and improving milk quality in ruminants.

A myxovirus resistance like protein involved in CgIFNLP mediated immune response of oyster Crassostrea gigas

The myxovirus resistance (Mx) proteins belong to interferon (IFN)-induced dynamin GTPase and play a pivotal role in the inhibition of replication of numerous viruses. In the present study, an Mx homologue (designated as CgMx1) was identified from oyster Crassostrea gigas. The open reading frame (ORF) of CgMx1 cDNA was of 1689 bp encoding a peptide of 562 amino acid residues. There was an N-terminal dynamin GTPase domain in the predicted peptide, which consisted of a tripartite GTP-binding motif (GDXXSGKS, DLPG and T/NKXD). The deduced amino acid sequence of CgMx1 shared 30–39% similarity with other Mx family members. And CgMx1 was clustered with Mx from H. discus, and then assigned into the invertebrate branch of the phylogenetic tree. The mRNA transcripts of CgMx1 were constitutively distributed in all the tested tissues, with the highest level in haemocytes (1342.45-fold of labial palps, p < 0.05). The mRNA expression of CgMx1 in haemocytes was significantly up-regulated to the highest level at 6 h (13.14-fold, p < 0.001) after poly (I:C) treatment and at 24 h (66.28-fold, p < 0.001) after recombinant IFN-like protein (rCgIFNLP) stimulation, respectively. CgMx1 protein was found to distribute in both the cytoplasm and nucleus of haemocytes. In the oysters with CgIFNLP and signal transducer and activator of transcription (CgSTAT) silenced by RNAi, the mRNA expression of CgMx1 decreased significantly in the haemocytes at 12 h after poly (I:C) stimulation, which was 0.02-fold and 0.04-fold of that in EGFP-RNAi oysters (p < 0.001), respectively. Meanwhile, EMSA assay revealed that CgSTAT was able to transactivate CgMx1 promoter through directly binding to its interferon-stimulated response element (ISRE) and gamma interferon activation site (GAS). The above results indicated that CgMx1 participated in the immune response of C. gigas through the signal pathway mediated by CgIFNLP and CgSTAT.

Elucidating the Role of Ezh2 in Tolerogenic Function of NOD Bone Marrow-Derived Dendritic Cells Expressing Constitutively Active Stat5b.

Tolerogenic dendritic cells (toDCs) are crucial to controlling the development of autoreactive T cell responses and the prevention of autoimmunity. We have reported that NOD.CD11cStat5b-CA transgenic mice expressing a constitutively active (CA) form of Stat5b under the control of a CD11c promoter are protected from diabetes and that Stat5b-CA-expressing DCs are tolerogenic and halt ongoing diabetes in NOD mice. However, the molecular mechanisms by which Stat5b-CA modulates DC tolerogenic function are not fully understood. Here, we used bone marrow-derived DCs (BMDCs) from NOD.CD11cStat5b-CA transgenic mice (Stat5b-CA.BMDCs) and found that Stat5b-CA.BMDCs displayed high levels of MHC class II, CD80, CD86, PD-L1, and PD-L2 and produced elevated amounts of TGFβ but low amounts of TNFα and IL-23. Stat5b-CA.BMDCs upregulated Irf4 and downregulated Irf8 genes and protein expression and promoted CD11c+CD11b+ DC2 subset differentiation. Interestingly, we found that the histone methyltransferase Ezh2 and Stat5b-CA bound gamma-interferon activated site (GAS) sequences in the Irf8 enhancer IRF8 transcription, whereas Stat5b but not Ezh2 bound GAS sequences in the Irf4 promoter to enhance IRF4 transcription. Injection of Stat5b-CA.BMDCs into prediabetic NOD mice halted progression of islet inflammation and protected against diabetes. Importantly, inhibition of Ezh2 in tolerogenic Stat5b-CA.BMDCs reduced their ability to prevent diabetes development in NOD recipient mice. Taken together, our data suggest that the active form of Stat5b induces tolerogenic DC function by modulating IRF4 and IRF8 expression through recruitment of Ezh2 and highlight the fundamental role of Ezh2 in Stat5b-mediated induction of tolerogenic DC function.

Nobiletin Inhibits CD36-Dependent Tumor Angiogenesis, Migration, Invasion, and Sphere Formation Through the Cd36/Stat3/Nf-Κb Signaling Axis.

Targeted cancer therapy with natural compounds is more effective than nontargeted therapy. Nobiletin is a flavonoid derived from citrus peel that has anticancer activity. Cluster of differentiation 36 (CD36) is a member of the class B scavenger receptor family that is involved in importing fatty acids into cells. CD36 plays a role in tumor angiogenesis by binding to its ligand, thrombospondin-1 (TSP-1), and then interacting with transforming growth factor beta 1 (TGFβ1). CD36 is implicated in tumor metastasis through its roles in fatty acid metabolism. This study investigated the molecular mechanisms underlying nobiletin’s anticancer activity by characterizing its interactions with CD36 as the target molecule. We hypothesize that the anti-angiogenic activity of nobiletin involving its regulation of CD36 via signal transducer and activator of transcription 3 (STAT3) rather than through TSP-1. Gene analysis identified a Gamma interferon activation site (GAS) element in the CD36 gene promoter that acts as a STAT3 binding site, an interaction that was confirmed by ChIP assay. STAT3 interacts with nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), suggesting that nobiletin also acts through the CD36/ (STAT3)/NF-κB signaling axis. Nobiletin inhibited CD36-dependent breast cancer cell migration and invasion as well as CD36-mediated tumor sphere formation. Taken together, these results suggest that nobiletin inhibits cancer stem cells in multiple ways.

Potential role of 8-oxoguanine DNA glycosylase 1 as a STAT1 coactivator in endotoxin-induced inflammatory response

Human 8-oxoguanine DNA glycosylase 1 (OGG1) is the major DNA repair enzyme that plays a key role in excision of oxidative damaged DNA bases such as 8-oxoguainine (8-oxoG). Recent studies suggest another function of OGG1, namely that it may be involved in the endotoxin- or oxidative stress-induced inflammatory response. In this study, we investigated the role of OGG1 in the inflammatory response. OGG1 expression is increased in the organs of endotoxin-induced or myelin oligodendrocyte glycoprotein (MOG)-immunized mice and immune cells, resulting in induction of the expression of pro-inflammatory mediators at the transcriptional levels. Biochemical studies showed that signal transducer and activator of transcription 1 (STAT1) plays a key role in endotoxin-induced OGG1 expression and inflammatory response. STAT1 regulates the transcriptional activity of OGG1 through recruiting and binding to the gamma-interferon activation site (GAS) motif of the OGG1 promoter region, and chromatin remodeling by acetylation and dimethylation of lysine-14 and -4 residues of histone H3. In addition, OGG1 acts as a STAT1 coactivator and has transcriptional activity in the presence of endotoxin. The data presented here identifies a novel mechanism, and may provide new therapeutic strategies for the treatment of endotoxin-mediated inflammatory diseases.

Structural and functional characterization of the Senegalese sole (Solea senegalensis) Mx promoter

Mx proteins are one of the most studied interferon-stimulated genes (ISGs). The antiviral activity against different fish viruses has been demonstrated for diverse fish Mx proteins, including the Senegalese sole (Solea senegalensis) Mx protein (SsMx). The aim of the current study is to characterize the structure and functional activity of the SsMx promoter. Several polyclonal cell populations expressing the luciferase reporter gene under the control of the SsMx promoter have been used to determine the ability of this promoter to drive the expression of the luciferase gene after poly I:C stimulation. In addition, the implication of each interferon-stimulated response element (ISRE) in the activation of the promoter has also been analysed. The genomic structure of the Senegalese sole and Japanese flounder Mx promoters (containing three ISREs) differs from the rest of the fish Mx promoters described to date. The ISRE1, the one closest to the start codon, is the main ISRE involved in the SsMx promoter activity, whereas ISRE2 and ISRE3 show a minor additive effect on this activity. Another feature differing SsMx promoter from the rest of the fish Mx promoters is the presence of a 24-bp GC island close to the ATG codon, including one Sp1 binding site, which may constitute the transcriptional start site. Furthermore, the SsMx promoter contains a gamma interferon activation site (GAS) element.

TOX3 (TNRC9) Over Expression in Bladder Cancer Cells Decreases Cellular Proliferation and Triggers an Interferon-Like Response

Background: Human TOX3 (TOX high mobility group box family member 3) regulates Ca2+ dependent transcription in neurons and has been associated with breast cancer susceptibility. Aim of the study was to investigate the expression of TOX3 in bladder cancer tissue samples and to identify genes and pathways altered upon TOX3 dysregulation using a cell line model. Methods: We performed microarray transcript profiling of biopsies and validated the data with RT-qPCR. We used cell line models for over expression and siRNA mediated knockdown of TOX3. Pathway analysis was applied for target gene identification and immunoprecipitation studies were used for DNA binding studies. Results: Microarray transcript profiling of 89 bladder biopsies showed a significant up-regulation of TOX3 (p<10-4) in non-muscle invasive (Ta-T1) bladder tumors compared to muscle-invasive (T2-T4) bladder tumors and normal urothelium. Microarray expression profiling of human bladder cancer cells over expressing TOX3 followed by Pathway analysis showed that TOX3 over expression mainly affected the Interferon Signaling Pathway. TOX3 up regulation induced the expression of several genes with a gamma interferon activation site (GAS), e.g. STAT1. In vitro functional studies showed that TOX3 was able to bind to the GAS-sequence located at the STAT1 promoter. siRNA mediated knockdown of TOX3 in RT4 bladder cancer cells decreased STAT1 expression suggesting a direct impact of TOX3 on STAT1. Immunoprecipitation of TOX3 over expressing cell extracts with an artificial “GAS”- DNA element resulted in an enrichment of the GAS containing DNA-sequence, providing evidence for a potential interaction of TOX3 with the GAS-sequence of STAT1. Conclusions: These results provide evidence for an alternative activation of the downstream interferon targets, independent of the initial interferon-receptor interaction, and consequently a biological role for TOX3.

Chromium(VI) Stimulates Fyn to Initiate Innate Immune Gene Induction in Human Airway Epithelial Cells

Mechanisms for pathogenic metal signaling in airway injury or disease promotion are poorly understood. It is widely believed that one mechanism for pathogenic and possible carcinogenic effects of inhaled chromium (Cr(VI)) is inhibition of inducible gene transactivation. However, we recently reported that Cr(VI) inhibition of Sp1-dependent transactivation required signal transducer and activator of transcription 1 (STAT1)-dependent expression of an inhibitory protein in airway epithelium. Thus, Cr(VI) exposures can induce genes, and we hypothesized that this induction resulted from Cr(VI) signaling through an innate immune-like STAT1-dependent pathway initiated by Fyn. Exposure of human airway epithelial (BEAS-2B) cells to Cr(VI) selectively transactivated the STAT-responsive interferon-stimulated response element (ISRE) and induced ISRE-driven transactivation of interferon regulatory factor 7 (IRF7), without affecting the gamma interferon-activated site (GAS)-driven IRF1 expression. Cr(VI)-induced IRF7 was absent or greatly reduced in cells that lacked STAT1, were treated with the Src family kinase inhibitor, PP2, or lacked Fyn. Expressing Fyn, but not Src, in mouse embryonic fibroblasts cells null for Src, Yes, and Fyn restored Cr(VI)-stimulated STAT1 tyrosine phosphorylation and IRF7 expression. Finally, shRNA knockdown of Fyn in BEAS-2B cells prevented Cr(VI)-activated STAT1 transactivation of IRF7. These data support a novel mechanism through which Cr(VI) stimulates Fyn to initiate interferon-like signaling for STAT1-dependent gene transactivation.

Plasticity of Drosophila Stat DNA binding shows an evolutionary basis for Stat transcription factor preferences

In vertebrates, seven signal transducer and activator of transcription (STAT) proteins bind to palindromic sites separated by spacers of two or three nucleotides (STAT1), four nucleotides (STAT6) or three nucleotides (STAT2 to STAT5a/b). This diversity of binding sites provides specificity to counter semiredundancy and was thought to be a recent evolutionary acquisition. Here, we examine the natural DNA-binding sites of the single Drosophila Stat and show that this is not the case. Rather, Drosophila Stat92E is able to bind to and activate target gene expression through both 3n and 4n spaced sites. Our experiments indicate that Stat92E has a higher binding affinity for 3n sites than for 4n sites and suggest that the levels of target gene expression can be modulated by insertion and/or deletion of single bases. Our results indicate that the ancestral STAT protein had the capacity to bind to 3n and 4n sites and that specific STAT binding preferences evolved with the radiation of the vertebrate STAT family.

Signal Transducer and Activator of Transcription 3α and Specificity Protein 1 Interact to Upregulate Intercellular Adhesion Molecule-1 in Ischemic–Reperfused Myocardium and Vascular Endothelium

Intercellular adhesion molecule-1 (ICAM-1) is upregulated rapidly on endothelial cells during ischemia-reperfusion (I-R) and mediates tissue leukocyte accumulation. The ICAM-1 proximal promoter contains a signal transducer and activator of transcription (Stat) binding motif (gamma-interferon activation site [GAS] sequence), which flanks a specificity protein 1 (Sp1) binding site. We examined the roles of Stat and Sp1 in the regulation of ICAM-1 after myocardial I-R. Open-chest anesthetized rats underwent coronary artery occlusion for 35 minutes and reperfusion for 0 to 240 minutes. Stat became activated within 15 minutes after reperfusion, primarily in vascular endothelial cells; the activated Stat protein was identified as Stat3 (alpha-isoform). After phosphorylation on serine 727 (p-S727), Stat3alpha was found in association with the transcriptional regulator Sp1, and the complex bound to an ICAM-1-GAS probe. ICAM-1 expression increased after I-R and lagged shortly behind Stat3alpha activation. In cultured human umbilical vein endothelial (HUVE) cells, activation of Stat3alpha after hypoxia-reoxygenation (H-R) was dependent on the small GTPase Rac1. Transfection of a dominant-negative Stat3 (Y705F) adenovirus or a GAS decoy oligonucleotide reduced ICAM-1 mRNA expression after H-R. Using a reporter gene transfected into HUVE cells, mutation of the GAS element in the ICAM-1 promoter resulted in reduced transcriptional activity after H-R. Sp1 coimmunoprecipitated with p-S727 Stat3 during H-R, and Sp1 or Stat3alpha interfering RNA markedly reduced ICAM-1 mRNA expression. The Sp1-Stat3 complex appears to play an important role in the upregulation of ICAM-1 transcription after reoxygenation or reperfusion.

Characterization of the Elements and Proteins Responsible for Interferon-Stimulated Gene Induction by Human Cytomegalovirus

Human cytomegalovirus (HCMV) infection of human fibroblast cells activates a large number of interferon-stimulated genes (ISGs) in a viral envelope-cell membrane fusion-dependent mechanism. In this study, we identified two interferon response elements, the interferon-stimulated response element (ISRE) and the gamma interferon-activated site (GAS), which act as HCMV response sites (VRS). Gel mobility shift assays showed that cellular proteins form specific and identical complexes with ISRE and GAS elements, and the binding of these complexes to ISRE and GAS is stimulated by HCMV infection. Point mutations in the consensus sequences of ISRE and GAS completely abolished their activities in response to HCMV-mediated transactivation, as well as their abilities to interact with HCMV-activated VRS-binding proteins. Interferon regulatory factor 3 does not appear to be present in the VRS-binding complexes or to be involved directly in HCMV-mediated ISG activation. Using ProteinChip technology, four potential proteins were identified, ranging from 20 to 42 kDa, in the VRS-binding complexes. The data suggest that HCMV infection activates VRS-binding proteins, which then bind to the VRS and stimulate ISG expression.

Two Gamma Interferon-Activated Site-Like Elements in the Human Cytomegalovirus Major Immediate-Early Promoter/Enhancer Are Important for Viral Replication

Human cytomegalovirus (HCMV) infection directly initiates a signal transduction pathway that leads to activation of a large number of cellular interferon-stimulated genes (ISGs). Our previous studies demonstrated that two interferon response elements, the interferon-stimulated response element and gamma interferon-activated site (GAS), in the ISG promoters serve as HCMV response sites (VRS). Interestingly, two GAS-like VRS elements (VRS1) were also present in the HCMV major immediate-early promoter-enhancer (MIEP/E). In this study, the importance of these VRS elements in viral replication was investigated. We demonstrate that the expression of the major IE genes, IE1 and IE2, is interferon inducible. To understand the biological significance of this signal transduction pathway in HCMV major IE expression, the two VRS1 in the MIEP/E were mutated. Mutant HCMVs in which the VRS elements were deleted or that contained point mutations grew dramatically more slowly than wild-type virus at a low multiplicity of infection (MOI). Insertion of wild-type VRS1 into the mutant viral genome rescued the slow growth phenotype. Furthermore, the expression levels of major IE RNAs and proteins were greatly reduced during infection with the VRS mutants at a low MOI. HCMV microarray analysis indicated that infection of host cells with the VRS mutant virus resulted in a global reduction in the expression of viral genes. Collectively, these data demonstrate that the two VRS elements in the MIEP/E are necessary for efficient viral gene expression and replication. This study suggests that although the HCMV-initiated signal transduction pathway results in induction of cellular antiviral genes, it also functions to stimulate viral major IE gene expression. This might be a new viral strategy in which the pathway is used to regulate gene expression and play a role in reactivation.

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.

Association of FAS (TNFRSF6)-670 gene polymorphism with villous atrophy in coeliac disease.

To investigate the association of FAS gene polymorphism with coeliac disease (CD) development. FAS-G670A gene polymorphism, located in a gamma interferon activation site, was studied in 146 unrelated CD patients and 203 healthy ethnically matched controls. The restriction fragment length polymorphism (RFLP) method was used to identify FAS-G670A gene polymorphism. No significant difference was found in genotype frequency between CD cases and controls. In controls, however, the frequency of the GG genotype was significantly higher in women (26.5%) than in men (12.8%) (OR= 2.44, 95% CI 1.15-5.20, P=0.020) and it was also higher in men with CD than controls (OR=2.60, 95% CI 0.96-7.05, P=0.061). The GG genotype frequency was significantly higher in patients with most severe villous atrophy (Marsh IIIc lesions) (OR=3.74, 95% CI 1.19-11.82, P=0.025). A significantly less proportion of men suffered from Marsh IIIc lesions than women (OR=0.20, 95% CI 0.06-0.68, P=0.01). The risk of having severe villous atrophy increased with the additive effect of the G allele in women (P=0.027 for trend, age and gender adjusted). FAS-G670A gene polymorphism is associated with the severity of villous atrophy in CD. Female gender is also associated with the severity of villous atrophy.

Cloning and functional characterization of the 5′-regulatory region of the human CD86 gene

The induction of CD86 expression by IFN-γ on the surface of various antigen presenting cells has been previously reported. In order to understand the mechanisms by which the expression of the CD86 gene is regulated by IFN-γ at the transcriptional level, we have cloned and characterized the 5′-flanking region of the human CD86 gene. To functionally analyze the upstream regulatory region of the CD86 gene, a series of luciferase reporter gene constructs were prepared and used for transfection of cells from the monocytic line U937 and Raji B cell line. Under basal conditions, functional activity of these constructs was detected in Raji cells, which show high constitutive expression of the CD86 molecule, but not in U937 cells, which show low expression of CD86 in non-activated state. Induction of CD86 expression by stimulation of U937 cells with IFN-γ revealed the presence of two functional GAS (gamma-interferon activation site) elements. Gel mobility shift assays showed that these two GAS elements specifically bind an IFN-γ-induced transcriptional complex. The DNA-protein complex was supershifted by antibody to Stat1 α (signal transducer and activator of transcription), but not by antibodies to Stat 2, Stat 3 and Sp1, indicating that GAS elements interact with Stat1 α. Point mutations in the GAS elements prevented the formation of DNA-protein complex and significantly reduced the responsiveness of the reporter gene to IFN-γ. These findings suggest that two functional GAS elements within the human CD86 promoter play an important role in the induction of CD86 gene by binding to IFN-γ-induced Stat1 α.

Constitutive activation of LIL-Stat in adult T-cell leukemia cells

The activation status of a recently identified STAT (signal transducers and activators of transcription) factor, LIL-Stat (lipopolysaccharide [LPS]/IL-1–inducible Stat) in adult T-cell leukemia (ATL) cells was investigated by electrophoretic mobility shift assays using nuclear extracts of leukemic cells from 7 patients with ATL and a GAS (gamma interferon activation site)-like element termed LILRE (LPS/IL-1–responsive element), which is found in the human prointerleukin 1β (IL1B) gene. Spontaneous DNA binding of LIL-Stat was observed in all ATL cells examined. However, in normal human peripheral lymphocytes, DNA binding of LIL-Stat was detected only after stimulation with IL-1. These results demonstrated that LIL-Stat is constitutively activated in ATL cells. Furthermore, our transient transfection studies using LILRE chloramphenicol acetyltransferase (CAT) reporters argue that LIL-Stat in ATL cells functions as a transcriptional activator through binding to the LILRE in theIL1B gene.