Murine GBP-5, a new member of the murine guanylate-binding protein family, is coordinately regulated with other GBPs in vivo and in vitro

Host Restrictive Factors Are the Emerging Storm Troopers Against Enterovirus: A Mini-Review

Enterovirus infection continues to be a global health problem. The lack of specific drugs and broad-spectrum vaccines means an urgent need to develop effective strategies against enteroviruses. Host restrictive factors are a class of intrinsic host antiviral factors that have been broadly defined and investigated during HIV infections and have great significance for drug development and treatment design. In recent years, the essential role of host restrictive factors in regulating enteroviral infections has been gradually recognized and investigated. An increasing number of studies have shown that host-restrictive factors regulate multiple steps in the life cycle of enteroviruses. This mini-review discusses the restrictive factors against enteroviruses, their antiviral mechanism, and the arms race between them and enteroviruses. We also summarise the pathways that enteroviruses use to impair host antiviral signals. This mini-review characterizes the essential role of host restriction factors in enterovirus infections, which provides ideas and potential targets for antiviral drug design by regulating host restrictive factors. It also reveals potential future research on the interplay between host restrictive factors and enteroviruses.

GBP5 drives malignancy of glioblastoma via the Src/ERK1/2/MMP3 pathway

Guanylate binding proteins (GBPs), a family of interferon-inducible large GTPase, play a pivotal role in cell-autonomous immunity and tumor malignant transformation. Glioblastoma (GBM) is the most prevalent and lethal primary brain tumor in adults. Here we show that GBP5 was highly expressed in GBM cell lines and in clinical samples, especially in the mesenchymal subtype. The expression levels of GBP5 were negatively correlated with the prognosis of GBM patients. Overexpression of GBP5 promoted the proliferation, migration, and invasion of GBM cells in vitro and in vivo. In contrast, silencing GBP5 by RNA interference exhibited the opposite effects. Consequently, targeting GBP5 in GBM cells resulted in impaired tumor growth and prolonged survival time of mice with GBM tumors. We further identified that the Src/ERK1/2/MMP3 axis was essential for GBP5-promoted GBM aggressiveness. These findings suggest that GBP5 may represent a novel target for GBM intervention.

IRF8 Regulates Gram-Negative Bacteria-Mediated NLRP3 Inflammasome Activation and Cell Death

Inflammasomes are intracellular signaling complexes that are assembled in response to a variety of pathogenic or physiologic stimuli to initiate inflammatory responses. Ubiquitously present LPS in Gram-negative bacteria induces NLRP3 inflammasome activation that requires caspase-11. We have recently demonstrated that IFN regulatory factor (IRF) 8 was dispensable for caspase-11-mediated NLRP3 inflammasome activation during LPS transfection; however, its role in Gram-negative bacteria-mediated NLRP3 inflammasome activation remains unknown. In this study, we found that IRF8 promotes NLRP3 inflammasome activation in murine bone marrow-derived macrophages (BMDMs) infected with Gram-negative bacteria such as Citrobacter rodentium, Escherichia coli, or Pseudomonas aeruginosa mutant strain ΔpopB Moreover, BMDMs deficient in IRF8 showed substantially reduced caspase-11 activation and gasdermin D cleavage, which are required for NLRP3 inflammasome activation. Mechanistically, IRF8-mediated phosphorylation of IRF3 was required for Ifnb transcription, which in turn triggered the caspase-11-dependent NLRP3 inflammasome activation in the infected BMDMs. Overall, our findings suggest that IRF8 promotes NLRP3 inflammasome activation during infection with Gram-negative bacteria.

C57BL/6 and 129 inbred mouse strains differ in Gbp2 and Gbp2b expression in response to inflammatory stimuli in vivo

Background: Infections cause the production of inflammatory cytokines such as Interferon gamma (IFNγ). IFNγ in turn prompts the upregulation of a range of host defence proteins including members of the family of guanylate binding proteins (Gbps). In humans and mice alike, GBPs restrict the intracellular replication of invasive microbes and promote inflammation. To study the physiological functions of Gbp family members, the most commonly chosen in vivo models are mice harbouring loss-of-function mutations in either individual Gbp genes or the entire Gbp gene cluster on mouse chromosome 3. Individual Gbp deletion strains differ in their design, as some strains exist on a pure C57BL/6 genetic background, while other strains contain a 129-derived genetic interval encompassing the Gbp gene cluster on an otherwise C57BL/6 genetic background. Methods: To determine whether the presence of 129 alleles of paralogous Gbps could influence the phenotypes of 129-congenic Gbp-deficient strains, we studied the expression of Gbps in both C57BL/6J and 129/Sv mice following in vivo stimulation with adjuvants and after infection with either Toxoplasma gondii or Shigella flexneri. Results: We show that C57BL/6J relative to 129/Sv mice display moderately elevated expression of Gbp2, but more prominently, are also defective for Gbp2b (formerly Gbp1) mRNA induction upon immune priming. Notably, Toxoplasma infections induce robust Gbp2b protein expression in both strains of mice, suggestive of a Toxoplasma-activated mechanism driving Gbp2b protein translation. We further find that the higher expression of Gbp2b mRNA in 129/Sv mice correlates with a gene duplication event at the Gbp2b locus resulting in two copies of the Gbp2b gene on the haploid genome of the 129/Sv strain. Conclusions: Our findings demonstrate functional differences between 129 and C57BL/6 Gbp alleles which need to be considered in the design and interpretation of studies utilizing mouse models, particularly for phenotypes influenced by Gbp2 or Gbp2b expression.

Gpr137b is an orphan G-protein-coupled receptor associated with M2 macrophage polarization

Macrophages are classified mainly into two subtypes, M1 and M2, which exhibit distinct phenotypes, based on their microenvironment. Although recent studies have suggested that G-protein-coupled receptors (GPCRs) are associated with M1/M2 macrophage polarization, available information on GPCR-mediated macrophage polarization is still limited. In the present study, we identified Gpr137b as an orphan GPCR abundantly expressed in RAW264, a mouse macrophage cell line, and illuminated its role in M2 macrophage polarization. We generated Gpr137b-knockout (Gpr137b-KO) clones of RAW264 cells using the CRISPR/Cas9 genome editing system. Two independent Gpr137b-KO clones were isolated, which were demonstrated to have frameshifting 188-nucleotide deletions at a region containing the ATG start codon of Gpr137b. Consistently, qRT-PCR analysis revealed that the deleted region is not transcribed. We then treated the Gpr137b-KO and wildtype RAW264 cells with interleukin-4 (IL-4) to induce M2 macrophage polarization. Microarray analysis revealed that the IL-4-induced gene expression of representative M2 macrophage markers was significantly reduced in the Gpr137b-KO cells, and this was validated by qRT-PCR analysis. By contrast, M1 macrophage marker gene expression induced by lipopolysaccharide was unaffected by Gpr137b-KO. Collectively, the current study shows that Gpr137b is a possible regulator of M2 macrophage polarization.

Interferon-induced guanylate-binding proteins: Guardians of host defense in health and disease

The role of guanylate-binding proteins in host defense.

Guanylate-binding proteins (GBPs) have recently emerged as central orchestrators of immunity to infection, inflammation, and neoplastic diseases. Within numerous host cell types, these IFN-induced GTPases assemble into large nanomachines that execute distinct host defense activities against a wide variety of microbial pathogens. In addition, GBPs customize inflammasome responses to bacterial infection and sepsis, where they act as critical rheostats to amplify innate immunity and regulate tissue damage. Similar functions are becoming evident for metabolic inflammatory syndromes and cancer, further underscoring the importance of GBPs within infectious as well as altered homeostatic settings. A better understanding of the basic biology of these IFN-induced GTPases could thus benefit clinical approaches to a wide spectrum of important human diseases.

For when bacterial infections persist: Toll-like receptor-inducible direct antimicrobial pathways in macrophages

Macrophages are linchpins of innate immunity, responding to invading microorganisms by initiating coordinated inflammatory and antimicrobial programs. Immediate antimicrobial responses, such as NADPH-dependent reactive oxygen species (ROS), are triggered upon phagocytic receptor engagement. Macrophages also detect and respond to microbial products through pattern recognition receptors (PRRs), such as TLRs. TLR signaling influences multiple biological processes including antigen presentation, cell survival, inflammation, and direct antimicrobial responses. The latter enables macrophages to combat infectious agents that persist within the intracellular environment. In this review, we summarize our current understanding of TLR-inducible direct antimicrobial responses that macrophages employ against bacterial pathogens, with a focus on emerging evidence linking TLR signaling to reprogramming of mitochondrial functions to enable the production of direct antimicrobial agents such as ROS and itaconic acid. In addition, we describe other TLR-inducible antimicrobial pathways, including autophagy/mitophagy, modulation of nutrient availability, metal ion toxicity, reactive nitrogen species, immune GTPases (immunity-related GTPases and guanylate-binding proteins), and antimicrobial peptides. We also describe examples of mechanisms of evasion of such pathways by professional intramacrophage pathogens, with a focus on Salmonella, Mycobacteria, and Listeria. An understanding of how TLR-inducible direct antimicrobial responses are regulated, as well as how bacterial pathogens subvert such pathways, may provide new opportunities for manipulating host defence to combat infectious diseases.

Interferon-Inducible GTPases in Host Resistance, Inflammation and Disease

Cell-autonomous immunity is essential for host organisms to defend themselves against invasive microbes. In vertebrates, both the adaptive and the innate branches of the immune system operate cell-autonomous defenses as key effector mechanisms that are induced by pro-inflammatory interferons (IFNs). IFNs can activate cell-intrinsic host defenses in virtually any cell type ranging from professional phagocytes to mucosal epithelial cells. Much of this IFN-induced host resistance program is dependent on four families of IFN-inducible GTPases: the myxovirus resistance proteins, the immunity-related GTPases, the guanylate-binding proteins (GBPs), and the very large IFN-inducible GTPases. These GTPase families provide host resistance to a variety of viral, bacterial, and protozoan pathogens through the sequestration of microbial proteins, manipulation of vesicle trafficking, regulation of antimicrobial autophagy (xenophagy), execution of intracellular membranolytic pathways, and the activation of inflammasomes. This review discusses our current knowledge of the molecular function of IFN-inducible GTPases in providing host resistance, as well as their role in the pathogenesis of autoinflammatory Crohn's disease. While substantial advances were made in the recent past, few of the known functions of IFN-inducible GTPases have been explored in any depth, and new functions await discovery. This review will therefore highlight key areas of future exploration that promise to advance our understanding of the role of IFN-inducible GTPases in human diseases.

Murine Oncostatin M Acts via Leukemia Inhibitory Factor Receptor to Phosphorylate Signal Transducer and Activator of Transcription 3 (STAT3) but Not STAT1, an Effect That Protects Bone Mass

Oncostatin M (OSM) and leukemia inhibitory factor (LIF) are IL-6 family members with a wide range of biological functions. Human OSM (hOSM) and murine LIF (mLIF) act in mouse cells via a LIF receptor (LIFR)-glycoprotein 130 (gp130) heterodimer. In contrast, murine OSM (mOSM) signals mainly via an OSM receptor (OSMR)-gp130 heterodimer and binds with only very low affinity to mLIFR. hOSM and mLIF stimulate bone remodeling by both reducing osteocytic sclerostin and up-regulating the pro-osteoclastic factor receptor activator of NF-κB ligand (RANKL) in osteoblasts. In the absence of OSMR, mOSM still strongly suppressed sclerostin and stimulated bone formation but did not induce RANKL, suggesting that intracellular signaling activated by the low affinity interaction of mOSM with mLIFR is different from the downstream effects when mLIF or hOSM interacts with the same receptor. Both STAT1 and STAT3 were activated by mOSM in wild type cells or by mLIF/hOSM in wild type and Osmr^-/- cells. In contrast, in Osmr^-/- primary osteocyte-like cells stimulated with mOSM (therefore acting through mLIFR), microarray expression profiling and Western blotting analysis identified preferential phosphorylation of STAT3 and induction of its target genes but not of STAT1 and its target genes; this correlated with reduced phosphorylation of both gp130 and LIFR. In a mouse model of spontaneous osteopenia caused by hyperactivation of STAT1/3 signaling downstream of gp130 (gp130^Y757F/Y757F), STAT1 deletion rescued the osteopenic phenotype, indicating a beneficial effect of promoting STAT3 signaling over STAT1 downstream of gp130 in this low bone mass condition, and this may have therapeutic value.

Interferon-inducible guanylate-binding proteins at the interface of cell-autonomous immunity and inflammasome activation

Guanylate-binding proteins (GBPs) are essential components of cell-autonomous immunity. In response to IFN signaling, GBPs are expressed in the cytoplasm of immune and nonimmune cells, where they unleash their antimicrobial activity toward intracellular bacteria, viruses, and parasites. Recent studies have revealed that GBPs are essential for mediating activation of the caspase-1 inflammasome in response to the gram-negative bacteria Salmonella enterica serovar Typhimurium, Francisella novicida, Chlamydia muridarum, Chlamydia trachomatis, Legionella pneumophila, Vibrio cholerae, Enterobacter cloacae, and Citrobacter koseri During infection with vacuolar-restricted gram-negative bacteria, GBPs disrupt the vacuolar membrane to ensure liberation of LPS for cytoplasmic detection by caspase-11 and the noncanonical NLRP3 inflammasome. In response to certain cytosolic bacteria, GBPs liberate microbial DNA for activation of the DNA-sensing AIM2 inflammasome. GBPs also promote the recruitment of antimicrobial proteins, including NADPH oxidase subunits and autophagy-associated proteins to the Mycobacterium-containing vacuole to mediate intracellular bacterial killing. Here, we provide an overview on the emerging relationship between GBPs and activation of the inflammasome in innate immunity to microbial pathogens.

Identification of potential biomarkers for post-traumatic complications released after trauma-hemorrhage from murine Kupffer cells and its investigation in lung and liver

CONTEXT

Early diagnosis of complications after severe trauma by specific biomarkers remains difficult.

OBJECTIVE

Identify potential new biomarkers for early diagnosis of post-traumatic complications.

MATERIAL AND METHODS

Mice underwent pressure-controlled hemorrhage or sham procedure. Four hours later, genome-wide expression of isolated Kupffer cells was compared with controls using Affymetrix-Genechip-Expression-Analysis and real-time-PCR.

RESULTS

Expression analysis and real-time-PCR revealed a significant increase of gene expression of Cxcl10, Il4ra, Csf2rb2, Lcn2, and Gbp5.

CONCLUSION

Cxcl10, Il4ra, Csf2rb2, Lcn2, and Gbp5 might represent new biomarkers for early diagnosis of post-traumatic complications, if they are linked to the development of post-traumatic complications.

Amphisomal route of MHC class I cross-presentation in bacteria-infected dendritic cells

Dendritic cells (DCs) are among the first professional APCs encountered by the obligate intracellular bacterium Chlamydia during infection. Using an established mouse bone marrow-derived DC line, we show that DCs control chlamydial infection in multiple small inclusions characterized by restricted bacterial growth, impaired cytosolic export of the virulence factor chlamydial protease-like activity factor, and interaction with guanylate-binding protein 1, a host cell factor involved in the initiation of autophagy. During maturation of infected DCs, chlamydial inclusions disintegrate, likely because they lack chlamydial protease-like activity factor-mediated protection. Released cytosolic Chlamydia are taken up by autophagosomes and colocalize with cathepsin-positive amphisomal vacuoles, to which peptide transporter TAP and upregulated MHC class I (MHC I) are recruited. Chlamydial Ags are subsequently generated through routes involving preprocessing in amphisomes via cathepsins and entry into the cytosol for further processing by the proteasome. Finally, bacterial peptides are reimported into the endosomal pathway for loading onto recycling MHC I. Thus, we unravel a novel pathway of MHC I-mediated cross-presentation that is initiated with a host cellular attack physically disrupting the parasitophorous vacuole, involves autophagy to collect cytosolic organisms into autophagosomes, and concludes with complex multistep antigenic processing in separate cellular compartments.

Non-apoptotic toxicity of Pseudomonas aeruginosa toward murine cells

Although P. aeruginosa is especially dangerous in cystic fibrosis (CF), there is no consensus as to how it kills representative cell types that are of key importance in the lung. This study concerns the acute toxicity of the sequenced strain, PAO1, toward a murine macrophage cell line (RAW 264.7). Toxicity requires brief contact with the target cell, but is then delayed for more than 12 h. None of the classical toxic effectors of this organism is required and cell death occurs without phagocytosis or acute perturbation of the actin cytoskeleton. Apoptosis is not required for toxicity toward either RAW 264.7 cells or for alveolar macrophages. Transcriptional profiling shows that encounter between PAO1 and RAW 264.7 cells elicits an early inflammatory response, followed by growth arrest. As an independent strategy to understand the mechanism of toxicity, we selected variant RAW 264.7 cells that resist PAO1. Upon exposure to P. aeruginosa, they are hyper-responsive with regard to classical inflammatory cytokine production and show transient downregulation of transcripts that are required for cell growth. They do not show obvious morphologic changes. Although they do not increase interferon transcripts, when exposed to PAO1 they dramatically upregulate a subset of the responses that are characteristic of exposure to g-interferon, including several guanylate-binding proteins. The present observations provide a novel foundation for learning how to equip cells with resistance to a complex challenge.

CDK8 kinase phosphorylates transcription factor STAT1 to selectively regulate the interferon response

Gene regulation by cytokine-activated transcription factors of the signal transducer and activator of transcription (STAT) family requires serine phosphorylation within the transactivation domain (TAD). STAT1 and STAT3 TAD phosphorylation occurs upon promoter binding by an unknown kinase. Here, we show that the cyclin-dependent kinase 8 (CDK8) module of the Mediator complex phosphorylated regulatory sites within the TADs of STAT1, STAT3, and STAT5, including S727 within the STAT1 TAD in the interferon (IFN) signaling pathway. We also observed a CDK8 requirement for IFN-γ-inducible antiviral responses. Microarray analyses revealed that CDK8-mediated STAT1 phosphorylation positively or negatively regulated over 40% of IFN-γ-responsive genes, and RNA polymerase II occupancy correlated with gene expression changes. This divergent regulation occurred despite similar CDK8 occupancy at both S727 phosphorylation-dependent and -independent genes. These data identify CDK8 as a key regulator of STAT1 and antiviral responses and suggest a general role for CDK8 in STAT-mediated transcription. As such, CDK8 represents a promising target for therapeutic manipulation of cytokine responses.

Murine guanylate binding protein 2 (mGBP2) controls Toxoplasma gondii replication

IFN-γ orchestrates the host response against intracellular pathogens. Members of the guanylate binding proteins (GBP) comprise the most abundant IFN-γ-induced transcriptional response. mGBPs are GTPases that are specifically up-regulated by IFN-γ, other proinflammatory cytokines, toll-like receptor agonists, as well as in response to Listeria monocytogenes and Toxoplasma gondii infection. mGBP2 localizes at the parasitophorous vacuole (PV) of T. gondii; however, the molecular function of mGBP2 and its domains in T. gondii infection is not known. Here, we show that mGBP2 is highly expressed in several cell types, including T and B cells after stimulation. We provide evidence that the C-terminal domain is sufficient and essential for recruitment to the T. gondii PV. Functionally, mGBP2 reduces T. gondii proliferation because mGBP2-deficient cells display defects in the replication control of T. gondii. Ultimately, mGBP2-deficient mice reveal a marked immune susceptibility to T. gondii. Taken together, mGBP2 is an essential immune effector molecule mediating antiparasitic resistance.

Autophagy restricts Chlamydia trachomatis growth in human macrophages via IFNG-inducible guanylate binding proteins

Interferon γ (IFNG) is a key host response regulator of intracellular pathogen replication, including that of Chlamydia spp The antichlamydial functions of IFNG manifest in a strictly host, cell-type and chlamydial strain dependent manner. It has been recently shown that the IFNG-inducible family of immunity-related GTPases (IRG) proteins plays a key role in the defense against nonhost adapted chlamydia strains in murine epithelial cells. In humans, IFN-inducible guanylate binding proteins (hGBPs) have been shown to potentiate the antichlamydial effect of IFNG; however, how hGBPs regulate this property of IFNG is unknown. In this study, we identified hGBP1/2 as important resistance factors against C. trachomatis infection in IFNG-stimulated human macrophages. Exogenous IFNG reduced chlamydial infectivity by 50 percent in wild-type cells, whereas shRNA hGBP1/2 knockdown macrophages fully supported chlamydial growth in the presence of exogenous IFNG. hGBP1/2 were recruited to bacterial inclusions in human macrophages upon stimulation with IFNG, which triggered rerouting of the typically nonfusogenic bacterial inclusions for lysosomal degradation. Inhibition of lysosomal activity and autophagy impaired the IFNG-mediated elimination of inclusions. Thus, hGBP1/2 are critical effectors of antichlamydial IFNG responses in human macrophages. Through their capacity to remodel classically nonfusogenic chlamydial inclusions and stimulate fusion with autophagosomes, hGBP1/2 disable a major chlamydial virulence mechanism and contribute to IFNG-mediated pathogen clearance.

Proteomic characterization of the cellular response to nitrosative stress mediated by s-nitrosoglutathione reductase inhibition

The S-nitrosoglutathione-metabolizing enzyme, GSNO reductase (GSNOR), has emerged as an important regulator of protein S-nitrosylation. GSNOR ablation is protective in models of asthma and heart failure, raising the idea that GSNOR inhibitors might hold therapeutic value. Here, we investigated the effects of a small molecule inhibitor of GSNOR (GSNORi) in mouse RAW 264.7 macrophages. We found that GSNORi increased protein S-nitrosylation in cytokine-stimulated cells, and we utilized stable isotope labeling of amino acids in cell culture (SILAC) to quantify the cellular response to this "nitrosative stress". The expression of several cytokine-inducible immunomodulators, including osteopontin, cyclooxygenase-2, and nitric oxide synthase isoform 2 (NOS2), were decreased by GSNORi. In addition, selective targets of the redox-regulated transcription factor, nuclear factor (erythroid-derived 2)-like 2 (Nrf2)-including heme oxygenase 1 (HO-1) and glutamate cysteine ligase modulatory subunit-were induced by GSNORi in a NOS2- and Nrf2-dependent manner. In cytokine-stimulated cells, Nrf2 protected from GSNORi-induced glutathione depletion and cytotoxicity and HO-1 activity was required for down-regulation of NOS2. Interestingly, GSNORi also affected a marked increase in NOS2 protein stability. Collectively, these data provide the most complete description of the global effects of GSNOR inhibition and demonstrate several important mechanisms for inducible response to GSNORi-mediated nitrosative stress.

Antiviral effects of the interferon-induced protein guanylate binding protein 1 and its interaction with the hepatitis C virus NS5B protein

Interferons (IFNs) and the interferon-stimulated genes (ISGs) play a central role in antiviral responses against hepatitis C virus (HCV) infection. We have reported previously that ISGs, including guanylate binding protein 1 (GBP-1), interferon alpha inducible protein (IFI)-6-16, and IFI-27, inhibit HCV subgenomic replication. In this study we investigated the effects of these ISGs against HCV in cell culture and their direct molecular interaction with viral proteins. HCV replication and virus production were suppressed significantly by overexpression of GBP-1, IFI-6-16, or IFI-27. Knockdown of the individual ISGs enhanced HCV RNA replication markedly. A two-hybrid panel of molecular interaction of the ISGs with HCV proteins showed that GBP-1 bound HCV-NS5B directly. A protein truncation assay showed that the guanine binding domain of GBP-1 and the finger domain of NS5B were involved in the interaction. Binding of NS5B with GBP-1 inhibited its guanosine triphosphatase GTPase activity, which is essential for its antiviral effect. Taken together, interferon-induced GBP-1 showed antiviral activity against HCV replication.

CONCLUSION

Binding of the HCV-NS5B protein to GBP-1 countered the antiviral effect by inhibition of its GTPase activity. These mechanisms may contribute to resistance to innate, IFN-mediated antiviral defense and to the clinical persistence of HCV infection.

The evolutionarily dynamic IFN-inducible GTPase proteins play conserved immune functions in vertebrates and cephalochordates

Interferon (IFN)-inducible GTPases currently include four families of proteins: myxovirus resistant proteins (Mxs), guanylate-binding proteins (GBPs), immunity-related GTPase proteins (IRGs), and very large inducible GTPase proteins (VLIGs). They are all under conserved regulation by IFNs in humans and mice and play a critical role in preventing microbial infections. However, differences between vertebrates are poorly characterized, and their evolutionary origins have not been studied in detail. In this study, we performed comparative genomic analysis of the four families in 18 representative animals that yielded several unexpected results. Firstly, we found that Mx, GBP, and IRG protein families arose before the divergence of chordate subphyla, but VLIG emerged solely in vertebrates. Secondly, IRG, GBP, and VLIG families have experienced a high rate of gene gain and loss during the evolution, with the GBP family being lost entirely in two pufferfish and VLIG family lost in primates and carnivores. Thirdly, the regulation of these genes by IFNs is highly conserved throughout vertebrates although the VLIG protein sequences in fish have lost the first 870 amino acid residues. Finally, amphioxus IFN-inducible GTPase genes are all highly expressed in immune-related organs such as gill, liver, and intestine and are upregulated after challenge with PolyI:C and pathogens, although no IFNs or their receptors were detected in the current amphioxus genome database. These results suggest that IFN-inducible GTPase genes play conserved immune functions both in vertebrates and in cephalochordates.

Gene expression signatures characterizing the development of lymphocyte response during experimental Chlamydia pneumoniae infection

In this study experimental mouse model for Chlamydia pneumoniae infection was used to elucidate the nature of immune response developing during primary and secondary infection. First we examined the mononuclear cells from different lymphoid organs in BALB/c mice during C. pneumoniae infection and detected a strong lymphocyte influx into mediastinal lymph nodes (MLN). To further characterize the C. pneumoniae induced immune response the gene expression profiles of MLN derived lymphocytes was studied. To identify genes characteristic for reinfection we compared gene expression profiles during reinfection and primary infection and found 148 genes to be differentially regulated in CD19+ cells, 7 in CD4+ cells and 12 in CD8+ cells. A panel of these genes was selected to be confirmed by real-time RT-PCR. Genes related to interferon signaling like Ifit1, Ifit3, Gbp2, Irf7 and Usp18 were found to be upregulated when reinfection was compared to primary infection. In our study we were able to identify 8 genes that were differentially expressed between reinfection and primary infection in lymphocytes. These novel gene expression signatures provide new insights and clues to the nature of protective immunity established during experimental C. pneumoniae immunity.

Gene expression analysis of macrophages derived from ankylosing spondylitis patients reveals interferon-gamma dysregulation

OBJECTIVE

To determine whether macrophages, a type of cell implicated in the pathogenesis of ankylosing spondylitis (AS), exhibit a characteristic gene expression pattern.

METHODS

Macrophages were derived from the peripheral blood of 8 AS patients (median disease duration 13 years [range <1-43 years]) and 9 healthy control subjects over 7 days with the use of granulocyte-macrophage colony-stimulating factor. Cells were stimulated for 24 hours with interferon-gamma (IFN gamma; 100 units/ml), were left untreated for 24 hours, or were treated for 3 hours with lipopolysaccharide (LPS; 10 ng/ml). RNA was isolated and examined by microarray and real-time quantitative reverse transcription-polymerase chain reaction analysis.

RESULTS

Microarray analysis revealed 198 probe sets detecting the differential expression of 141 unique genes in untreated macrophages from AS patients compared with healthy controls. Clustering and principal components analysis clearly distinguished AS patients and controls. Of the differentially expressed genes, 78 (55%) were IFN-regulated, and their relative expression indicated a "reverse" IFN signature in AS patient macrophages, where IFN gamma-up-regulated genes were underexpressed and down-regulated genes were overexpressed. Treatment of macrophages with exogenous IFN gamma normalized the expression of these genes between patients and controls. In addition, the messenger RNA encoded by the IFN gamma gene was approximately 2-fold lower in AS patient macrophages at baseline (P = 0.004) and was poorly responsive to LPS (P = 0.018), as compared with healthy controls.

CONCLUSIONS

Our findings reveal consistent differences in gene expression in macrophages from AS patients, with evidence of a striking "reverse" IFN signature. Together with poor expression and responsiveness of the IFN gamma gene, these results suggest that there may be a relative defect in IFN gamma gene regulation, with autocrine consequences and implications for disease pathogenesis.

Host biomarkers and biological pathways that are associated with the expression of experimental cerebral malaria in mice

Cerebral malaria (CM) is a primary cause of malaria-associated deaths among young African children. Yet no diagnostic tools are available that could be used to predict which of the children infected with Plasmodium falciparum malaria will progress to CM. We used the Plasmodium berghei ANKA murine model of experimental cerebral malaria (ECM) and high-density oligonucleotide microarray analyses to identify host molecules that are strongly associated with the clinical symptoms of ECM. Comparative expression analyses were performed with C57BL/6 mice, which have an ECM-susceptible phenotype, and with mice that have ECM-resistant phenotypes: CD8 knockout and perforin knockout mice on the C57BL/6 background and BALB/c mice. These analyses allowed the identification of more than 200 host molecules (a majority of which had not been identified previously) with altered expression patterns in the brain that are strongly associated with the manifestation of ECM. Among these host molecules, brain samples from mice with ECM expressed significantly higher levels of p21, metallothionein, and hemoglobin alpha1 proteins by Western blot analysis than mice unaffected by ECM, suggesting the possible utility of these molecules as prognostic biomarkers of CM in humans. We suggest that the higher expression of hemoglobin alpha1 in the brain may be associated with ECM and could be a source of excess heme, a molecule that is considered to trigger the pathogenesis of CM. Our studies greatly enhance the repertoire of host molecules for use as diagnostics and novel therapeutics in CM.

Analyses of murine GBP homology clusters based on in silico, in vitro and in vivo studies

The interactions between pathogens and hosts lead to a massive upregulation of antimicrobial host effector molecules. Among these, the 65 kDa guanylate binding proteins (GBPs) are interesting candidates as intricate components of the host effector molecule repertoire. Members of the GBP family are highly conserved in vertebrates. Previous reports indicate an antiviral activity of human GBP1 (hGBP1) and murine GBP2 (mGBP2). We recently demonstrated that distinct murine GBP (mGBP) family members are highly upregulated upon Toxoplasma gondii infection and localize around the intracellular protozoa T. gondii. Moreover, we characterised five new mGBP family members within the murine 65 kDa GBP family. Here, we identified a new mGBP locus named mGbp11. Based on bacterial artificial chromosome (BAC), expressed sequence tag (EST), and RT-PCR analyses this study provides a detailed insight into the genomic localization and organization of the mGBPs. These analyses revealed a 166-kb spanning region on chromosome 3 harboring five transcribed mGBPs (mGbp1, mGbp2, mGbp3, mGbp5, and mGbp7) and one pseudogene (pseudomGbp1), as well as a 332-kb spanning region on chromosome 5 consisting of six transcribed mGBPs (mGbp4, mGbp6, mGbp8, mGbp9, mGbp10, and mGbp11), and one pseudogene (pseudomgbp2). Besides the strikingly high homology of 65% to 98% within the coding sequences, the mGBPs on chromosome 5 cluster also exhibit a highly homologous exon-intron structure whereas the mGBP on chromosome 3 reveals a more divergent exon-intron structure. This study details the comprehensive genomic organization of mGBPs and suggests that a continuously changing microbial environment has exerted evolutionary pressure on this gene family leading to multiple gene amplifications. A list of links for this article can be found in the Availability and requirements section.

Induction of guanylate binding protein 5 by gamma interferon increases susceptibility to Salmonella enterica serovar Typhimurium-induced pyroptosis in RAW 264.7 cells

The regulation of caspase-1 activation in macrophages plays a central role in host defense against bacterial pathogens. The activation of caspase-1 by the detection of bacterial products through Nod-like receptors leads to the secretion of mature interleukin-1beta (IL-1beta) and IL-18 and the induction of rapid host cell death (pyroptosis). Here, we report that pyroptosis induced by Salmonella enterica serovar Typhimurium can be positively regulated by prior gamma interferon (IFN-gamma) stimulation of RAW 264.7 cells. This increase in cell death is dependent on both caspase-1 activation and, in part, Salmonella pathogenicity island 1 (SPI-1) expression by Salmonella. Furthermore, the exogenous expression of the IFN-gamma-induced protein guanylate binding protein 5 (GBP-5) is sufficient to induce a heightened susceptibility of RAW 264.7 cells to Salmonella-induced pyroptosis, and the endogenous expression of GBP-5 is important for this phenomenon. RAW 264.7 cells with decreased expression of GBP-5 mRNA (inhibited by short hairpin RNA against GBP-5) release twofold less lactate dehydrogenase (a marker of membrane permeability) upon infection by invasive S. enterica serovar Typhimurium than do infected control cells. Importantly, 3x FLAG-tagged GBP-5 is localized to membrane ruffles, which contact invasive Salmonella, and is found on the membranes of spacious phagosomes containing Salmonella (although it is also found in the cytoplasm and on other cellular membranes), placing 3x FLAG GBP-5 at the interface of secreted SPI-1 effectors and host protein machinery. The regulation of pyroptosis by the IFN-gamma-induced protein GBP-5 may play an important role in the host defense against Salmonella enterica serovar Typhimurium and perhaps other invasive bacterial pathogens.

In silico and in vitro characterization of mGBP4 splice variants

In a systematic approach to identify interferon-gamma (IFN-gamma)-regulated host effector molecules, we found several members of the 65 kDa guanylate-binding proteins (GBPs) highly upregulated. During extensive characterization of these guanosine triphosphatases (GTPases), we identified discrepancies between the cloned and published sequences of the murine GTPase mGBP4. Two splice variants of mGBP4 could be detected. One variant led to a premature stop codon after 312 bp. The second variant resulted in a transcript with a disrupted G2 domain and was deposited as mGBP4.1 to the GenBank. Interestingly, only mGBP4, not mGBP4.1 mRNA, was highly upregulated in mice after infection with Listeria monocytogenes.

Extensive characterization of IFN-induced GTPases mGBP1 to mGBP10 involved in host defense

IFN-gamma orchestrates a potent antimicrobial host response. However, the underlying molecular basis for this immunological defense system is largely unknown. In a systematic approach to identify IFN-gamma-regulated host effector molecules, a notable number of transcripts with consensus GTP-binding motives were obtained. Further extensive transcriptome and genome analyses identified five novel family members of murine guanylate-binding proteins (mGBPs) now designated mGBP6, 7, 8, 9, and 10. Moreover, in this study, all 10 mGBP members (mGBP1-10) were extensively characterized. mGBPs are selectively up-regulated in vitro by a set of proinflammatory cytokines and TLR agonists as well as in vivo after Listeria monocytogenes and Toxoplasma gondii infection. After IFN-gamma stimulation, mGBP1, 2, 3, 6, 7, and 9 are associated with intracellular Toxoplasma parasites and, interestingly, virulent Toxoplasma interfere with mGBP recruitment. Taken together, mGBPs comprise an important set of host defense molecules.

Emerging themes in IFN-gamma-induced macrophage immunity by the p47 and p65 GTPase families

Vertebrates have evolved complex immune specificity repertoires beyond the primordial components found in lower multi-cellular organisms to combat microbial infections. The type II interferon (IFN-gamma) pathway represents one such system, bridging innate and acquired immunity and providing host protection in a cell-autonomous manner. Recent large-scale transcriptome analyses of IFN-gamma-dependent gene expression in effector cells such as macrophages have highlighted the prominence of two families of GTPases -- p47 IRGs and p65 GBPs -- that are now beginning to emerge as major determinants of antimicrobial resistance. Here we discuss the recent clarification of known family members, their cellular biochemistry and host defense functions as a means to understanding the complex innate immune response engendered in higher vertebrates such as humans and mice.

Repeated BCG treatment of mouse bladder selectively stimulates small GTPases and HLA antigens and inhibits single-spanning uroplakins

BACKGROUND

Despite being a mainstay for treating superficial bladder carcinoma and a promising agent for interstitial cystitis, the precise mechanism of Bacillus Calmette-Guerin (BCG) remains poorly understood. It is particularly unclear whether BCG is capable of altering gene expression beyond its well-recognized pro-inflammatory effects and how this relates to its therapeutic efficacy. The objective of this study was to determine differentially expressed genes in the mouse bladder following repeated intravesical BCG therapy.

METHODS

Mice were transurethrally instilled with BCG or pyrogen-free on days 1, 7, 14, and 21. Seven days after the last instillation, urothelia along with the submucosa was removed and amplified ds-DNA was prepared from control- and BCG-treated bladder mucosa and used to generate suppression subtractive hybridization (SSH). Plasmids from control- and BCG-specific differentially expressed clones and confirmed by Virtual Northern were then purified and the inserts were sequenced and annotated. Finally, chromatin immune precipitation combined with real-time polymerase chain reaction assay (ChIP/Q-PCR) was used to validate SSH-selected transcripts.

RESULTS

Repeated intravesical BCG treatment induced an up regulation of genes associated with antigen presentation (B2M, HLA-A, HLA-DQA1, HLA-DQB2, HLA-E, HLA-G, IGHG, and IGH) and representatives of two IFNgamma-induced small GTPase families: the GBPs (GBP1, GBP2, and GBP5) and the p47GTPases (IIGTP1, IIGTP2, and TGTP). Genes expressed in saline-treated bladders but down-regulated by BCG included: the single-spanning uroplakins (UPK3a and UPK2), SPRR2G, GSTM5, and RSP 19.

CONCLUSION

Here we introduced a hypothesis-generator approach to determine key genes involved in the urothelium/sumbmucosa responses to BCG therapy. Urinary bladder responds to repeated BCG treatment by up-regulating not only antigen presentation-related genes, but also GBP and p47 small GTPases, both potentially serving to mount a resistance to the replication of the Mycobacterium. It will be of tremendous future interest to determine whether these immune response cascades play a role in the anti-cancer effects exerted by BCG.

Exonization of active mouse L1s: a driver of transcriptome evolution?

Background

Long interspersed nuclear elements (LINE-1s, L1s) have been recently implicated in the regulation of mammalian transcriptomes.

Results

Here, we show that members of the three active mouse L1 subfamilies (A, G_F and T_F) contain, in addition to those on their sense strands, conserved functional splice sites on their antisense strands, which trigger multiple exonization events. The latter is particularly intriguing in the light of the strong antisense orientation bias of intronic L1s, implying that the toleration of antisense insertions results in an increased potential for exonization.

Conclusion

In a genome-wide analysis, we have uncovered evidence suggesting that the mobility of the large number of retrotransposition-competent mouse L1s (~2400 potentially active L1s in NCBIm35) has significant potential to shape the mouse transcriptome by continuously generating insertions into transcriptional units.

In silico genomic analysis of the human and murine guanylate-binding protein (GBP) gene clusters

The guanylate-binding proteins (GBPs) were among the first interferon (IFN)-stimulated genes (ISGs) discovered, but until recently, little was known about their functions and even less about the composition of the gene family. Analysis of the promoter of human GBP-1 contributed significantly toward the understanding of Jak-Stat signaling and the delineation of the IFN-gamma activation site (GAS) and IFN-stimulated response element (ISRE) promoter elements. In this study, we have examined the genomic arrangement and composition of the GBPs in both mouse and humans. There are seven GBP paralogs in humans and at least one pseudogene, all of which are located in a cluster of genes on chromosome 1. Five of the six MuGBPs and a GBP pseudogene are clustered in a syntenic region on chromosome 3. The sixth MuGBP, MuGBP-4, and three GBP pseudogenes are located on chromosome 5. As might be expected, the GBPs share similar genomic organizations of introns and exons. Five of the MuGBPs had previously been shown to be coordinately induced by IFNs, and as expected, all of the MuGBPs have GAS and ISRE elements in their promoters. Interestingly, not all of the HuGBPs have GAS and ISRE elements, suggesting that not all GBPs are IFN responsive in humans.

Unique features of different members of the human guanylate-binding protein family

Guanylate-binding proteins (GBPs) are the most abundant cellular proteins expressed in response to interferon-gamma (IFN-gamma), with seven highly homologous members in humans, termed HuGBP-1 to HuGBP-7. To date, differential features that may indicate differential functions of these proteins have not been described. Here, we investigated the expression and subcellular localization of the different HuGBPs in endothelial cells (EC). IFN-gamma, tumor necrosis factor-alpha (TNF-alpha), and interleukin-1beta (IL-1beta) induced the expression of HuGBP-1, HuGBP-2, and HuGBP-3 at similar high levels. In contrast, expression of HuGBP-4 and HuGBP-5 was robustly induced only by IFN-gamma and not by TNF-alpha and IL-1beta. Expression of HuGBP-6 and HuGBP-7 was not detected in EC under the various conditions examined. Investigating subcellular localization of the EC-expressed HuGBPs, HuGBP-1, HuGBP-3, and HuGBP-5 were exclusively detected in the cytoplasm, whereas HuGBP-2 and HuGBP-4 displayed a nucleocytoplasmic distribution. Treatment of the cells with IFN-gamma and aluminum fluoride caused rapid enrichment of HuGBP-1 and HuGBP-2 in the Golgi apparatus, as demonstrated by time-lapse microscopy and fluorescence analyses of GFP-tagged HuGBPs. HuGBP-3 and HuGBP-4 were never detected in the Golgi apparatus, whereas HuGBP-5 was constitutively enriched in this cytosolic compartment, irrespective of stimulation. These results assign a characteristic pattern of expression and subcellular localization to each of the HuGBPs, indicating for the first time that these proteins may have different cellular functions.

Identification of Japanese encephalitis virus-inducible genes in mouse brain and characterization of GARG39/IFIT2 as a microtubule-associated protein

Several mouse central nervous system genes have been identified that are differentially regulated during Japanese encephalitis virus (JEV) infection, including those which have not been reported to be induced by any other neurotropic virus. Interestingly, approximately 80 % of JEV-inducible genes identified in this study are also induced by Sindbis virus, indicating activation of common host signalling pathways by these two viruses, despite their diverse life cycles. One of these, the glucocorticoid attenuated response gene 39 (GARG39, also known as IFIT2, ISG54 and MuP54) was characterized further. It was demonstrated that GARG39 protein interacts with microtubules in vitro, co-localizes with beta-tubulin in vivo and is enriched in the mitotic spindle of non-neuronal cells undergoing mitosis. While GARG39 was known for a long time as an inflammation-inducible glucocorticoid attenuated protein, its identification as a microtubule-associated protein in this study suggests a possible role for this protein in cell proliferation, virion assembly/transport and microtubule dynamics.

The Interferon-Inducible GTPases

Mammalian cells respond to interferons (IFNs) secreted during infection by the transcriptional upregulation of as many as a thousand genes. This remarkable transition prepares cells and organisms for resistance to infection, and many IFN-regulated gene products are players in well-understood resistance programs. Oddly, however, many of the most abundantly induced proteins are GTPases whose functions are not well understood. Here we review the progress that has been made toward understanding the roles of individual GTPase families in disease resistance and the hints of common mechanisms that are now available.

Microarray analysis of IFN-gamma response genes in astrocytes

IFN-gamma (IFN-gamma) has been shown to activate astrocytes to acquire immune functions. In this study the effect of IFN-gamma on murine astrocytes was investigated via microarray analysis. The activating effect of IFN-gamma on the astrocyte transcriptome showed predominance toward pathways involved in adaptive immunity, initiation of the immune response and innate immunity. Previously unknown astrocytic genes expressed included members of the p47 GTPases and guanine nucleotide binding protein (GBP) families. Down-regulatory effects of IFN-gamma stimulation were confined to pathways involved in growth regulation, cell differentiation and cell adhesion. This data supports the notion that astrocytes are an important immunocompetant cell in the brain and indicate that astrocytes may have a significant role in various infectious diseases such as Toxoplasmic Encephalitis and neurological diseases with an immunological component such as Alzheimer's and autoimmune disorders.

Regulation of gene expression in RAW 264.7 macrophage cell line by interferon-γ

Macrophages play an important role in immune responses and in inflammatory disease states such as atherosclerosis. Interferon-gamma (IFN-gamma) is a major cytokine involved in the activation of macrophages. To elucidate the primary response of various genes and biological pathways regulated by IFN-gamma in macrophage, we analyzed the gene expression profile in RAW 264.7 macrophage cells treated with IFN-gamma for 4h. Microarray analysis revealed that about 400 genes were differentially expressed, of which about 250 genes were up-regulated and 150 were down-regulated. Functional organization of the transcriptome revealed that induced genes are involved in antimicrobial and antiviral responses, antigen presentation, chemokine and cytokine signaling, and inhibition of cell growth. We also found that expression of genes involved in cell-cycle control, DNA repair, and lipid metabolism was suppressed by IFN-gamma. We also identified induction of multiple transcription factors by IFN-gamma in RAW 264.7 cells. Functional annotation of genes regulated by IFN-gamma in RAW 264.7 cells may provide novel insights into the role of macrophages in immunity and in inflammatory disease.

Molecular and expression analysis of an interferon-gamma-inducible guanylate-binding protein from rainbow trout (Oncorhynchus mykiss)

Guanylate-binding proteins (GBPs) are some of the most abundant proteins accumulating in mammalian cells in response to interferon-gamma (IFN-gamma). GBPs have been suggested to function in antiviral activity, macrophage activation, fibroblast proliferation and inhibition of endothelial cell proliferation and invasiveness. Here we confirm that IFN-gamma-inducible GBP also exist in fish. A 2 kb GBP cDNA was cloned from head kidney of rainbow trout treated with an IFN-inducing compound. The open reading frame predicts a 635 amino acid protein (rbtGBP) of 72.7 kDa possessing a tripartite GTP binding motif and a secondary structure similar to human GBP1. Like most mammalian GBPs, rbtGBP possesses an isoprenylation motif at the C-terminal end. The overall amino acid sequence identity between rbtGBP and mammalian GBPs is only 41-47%, however. The rainbow trout macrophage cell line RTS11 showed a dose-dependent increase in rbtGBP transcripts in response to IFN-gamma after 6h of stimulation, with rbtGBP being undetectable in non-treated RTS11 cells. Moreover, polyinosinic polycytidylic acid (poly I:C) induced increased GBP transcript levels in RTS11 and RTG2 cells after 4-6 h of stimulation, and in head kidney and liver of live fish after 24 h. These studies suggest that rbtGBP is an early response gene in rainbow trout, which may have similar functions in IFN-gamma mediated responses as mammalian GBPs.

A novel inflammation-induced ubiquitin E3 ligase in alveolar type II cells

LINCR was identified as a glucocorticoid-attenuated response gene induced in the lung during endotoxemia. The LINCR protein has structural similarities to Drosophila Neuralized, which regulates the developmentally important Notch signaling pathway. Endotoxemia-induced LINCR expression in vivo was localized by in situ hybridization to alveolar epithelial type II cells, and shown to be induced by LPS and inflammatory cytokines in the T7 alveolar epithelial type II cell line. RING domain-dependent ubiquitin E3 ligase activity of LINCR was demonstrated using full-length FLAG-LINCR or a deletion mutant lacking the RING domain expressed in 293T cells, and using a GST-LINCR RING fusion protein expressed in Escherichia coli. LINCR preferentially interacted with the ubiquitin-conjugating enzyme UbcH6 and preferentially generated polyubiquitin chains linked via non-canonical lysine residues. We conclude that LINCR is a novel inflammation-induced ubiquitin E3 ligase expressed in alveolar epithelial type II cells, and discuss its potential role in the lung response to inflammation.

Review:The Guanylate-Binding Proteins (GBPs): Proinflammatory Cytokine-Induced Members of the Dynamin Superfamily with Unique GTPase Activity

The guanylate-binding proteins (GBPs) were first identified in the late 1970s, and within a short period of time, investigators were aware that GBPs possessed unique properties, in particular the ability to bind GMP agarose. Since then, much study has gone into understanding their mechanism of induction by interferons (IFNs) and other cytokines, and they have been used extensively as markers for IFN responsiveness in both cells and organisms. In time, we learned that GBPs had the unusual ability to hydrolyze GTP to both GDP and GMP. More recently, we have begun to appreciate their novel structure, one that suggests unique mechanisms of GTP binding and hydrolysis and unique forms of regulation. In addition, we have begun to unravel some of their functions and to separate these function into those functions that do and those that do not require GTPase activity.

An integrative genomics approach to the reconstruction of gene networks in segregating populations

The reconstruction of genetic networks in mammalian systems is one of the primary goals in biological research, especially as such reconstructions relate to elucidating not only common, polygenic human diseases, but living systems more generally. Here we propose a novel gene network reconstruction algorithm, derived from classic Bayesian network methods, that utilizes naturally occurring genetic variations as a source of perturbations to elucidate the network. This algorithm incorporates relative transcript abundance and genotypic data from segregating populations by employing a generalized scoring function of maximum likelihood commonly used in Bayesian network reconstruction problems. The utility of this novel algorithm is demonstrated via application to liver gene expression data from a segregating mouse population. We demonstrate that the network derived from these data using our novel network reconstruction algorithm is able to capture causal associations between genes that result in increased predictive power, compared to more classically reconstructed networks derived from the same data.

Human guanylate binding protein-1 (hGBP-1) characterizes and establishes a non-angiogenic endothelial cell activation phenotype in inflammatory diseases

Blood vessel activation in inflammatory diseases is triggered by a myriad of different factors that partially reveal opposite activities on endothelial cells (EC). For example, inflammatory cytokines (IC) inhibit EC proliferation and induce cell adhesiveness for leukocytes. In contrast, angiogenic growth factors (AGF) activate EC proliferation and inhibit cell adhesiveness for leukocytes. In consequence, IC and AGF may induce two different activation phenotypes in EC that appear in a temporally and/or spatially coordinated manner in inflammatory tissues. Human guanylate binding protein-1 (hGBP-1) is a member of the large GTPase protein family. New results demonstrate that hGBP-1 is a specific marker of IC-activated EC that allows to differentiate the IC- and AGF-activated phenotype of EC at the single cell level, both in vitro and in vivo. In addition, hGBP-1 is the key mediator of the inhibitory effects of IC on EC proliferation and invasiveness. Both the expression pattern of hGBP-1 and its activity in EC supported the hypothesis that IC- and AGF-activation induce distinct adversely related phenotypes in EC. In future, hGBP-1 may be used as a marker to monitor the IC-induced phenotype of EC in inflammation and may also be exploited as a target to modulate EC activity in inflammatory diseases and tumor angiogenesis.

IFN-inducible GTPases and immunity to intracellular pathogens

By eliciting host antimicrobial programs in nearly all nucleated cells interferons (IFNs) help orchestrate the innate immune response of mammals to a diverse array of microbial pathogens. Recent work has highlighted the complexity of this transcriptional repertoire and the emergence of several families of IFN-inducible guanosine 5' triphosphatases (GTPases)--p47, guanylate-binding protein (GBP), Mx and very large inducible GTPases (VLIG)--that subsume pathogen-specific roles. Such specificity arises from a combination of both the type and timing of inductive stimuli, target-cell population, subcellular binding partners and the infectious agent encountered. Evolution of different GTPase families to combat compartmentalized versus cytosolic pathogens reveals a hitherto unexpected level of intracellular discrimination during vertebrate host defense.

Phospholipid scramblase 1 potentiates the antiviral activity of interferon

Phospholipid scramblase 1 (PLSCR1) is an interferon (IFN)- and growth factor-inducible, calcium-binding protein that either inserts into the plasma membrane or binds DNA in the nucleus depending on its state of palmyitoylation. In certain hematopoietic cells, PLSCR1 is required for normal maturation and terminal differentiation from progenitor cells as regulated by select growth factors, where it promotes recruitment and activation of Src kinases. PLSCR1 is a substrate of Src (and Abl) kinases, and transcription of the PLSCR1 gene is regulated by the same growth factor receptor pathways in which PLSCR1 potentiates afferent signaling. The marked transcriptional upregulation of PLSCR1 by IFNs led us to explore whether PLSCR1 plays an analogous role in cellular responses to IFN, with specific focus on antiviral activities. Accordingly, human cells in which PLSCR1 expression was decreased with short interfering RNA were rendered relatively insensitive to the antiviral activity of IFNs, resulting in higher titers of vesicular stomatitis virus (VSV) and encephalomyocarditis virus. Similarly, VSV replicated to higher titers in mouse PLSCR1(-/-) embryonic fibroblasts than in identical cells transduced to express PLSCR1. PLSCR1 inhibited accumulation of primary VSV transcripts, similar to the effects of IFN against VSV. The antiviral effect of PLSCR1 correlated with increased expression of a subset of IFN-stimulated genes (ISGs), including ISG15, ISG54, p56, and guanylate binding proteins. Our results suggest that PLSCR1, which is itself an ISG-encoded protein, provides a mechanism for amplifying and enhancing the IFN response through increased expression of a select subset of potent antiviral genes.

Nuclear factor-kappaB motif and interferon-alpha-stimulated response element co-operate in the activation of guanylate-binding protein-1 expression by inflammatory cytokines in endothelial cells

The large GTPase GBP-1 (guanylate-binding protein-1) is a major IFN-gamma (interferon-gamma)-induced protein with potent anti-angiogenic activity in endothelial cells. An ISRE (IFN-alpha-stimulated response element) is necessary and sufficient for the induction of GBP-1 expression by IFN-gamma. Recently, we have shown that in vivo GBP-1 expression is strongly endothelial-cell-associated and is, in addition to IFN-gamma, also activated by interleukin-1beta and tumour necrosis factor-alpha, both in vitro and in vivo [Lubeseder-Martellato, Guenzi, Jörg, Töpolt, Naschberger, Kremmer, Zietz, Tschachler, Hutzler, Schwemmle et al. (2002) Am. J. Pathol. 161, 1749-1759; Guenzi, Töpolt, Cornali, Lubeseder-Martellato, Jörg, Matzen, Zietz, Kremmer, Nappi, Schwemmle et al. (2001) EMBO J. 20, 5568-5577]. In the present study, we identified a NF-kappaB (nuclear factor kappaB)-binding motif that, together with ISRE, is required for the induction of GBP-1 expression by interleukin-1beta and tumour necrosis factor-alpha. Deactivation of the NF-kappaB motif reduced the additive effects of combinations of these cytokines with IFN-gamma by more than 50%. Importantly, NF-kappaB p50 rather than p65 activated the GBP-1 promoter. The NF-kappaB motif and ISRE were detected in an almost identical spatial organization, as in the GBP-1 promoter, in the promoter regions of various inflammation-associated genes. Therefore both motifs may constitute a cooperative inflammatory cytokine response module that regulates GBP-1 expression. Our findings may open new perspectives for the use of NF-kappaB inhibitors to support angiogenesis in inflammatory diseases including ischaemia.

GBP-5 Splicing Variants: New Guanylate-Binding Proteins with Tumor-Associated Expression and Antigenicity

We have identified a new gene, gbp-5, with high homology to the guanylate binding proteins (GBP) belonging to the GTPase superfamily including the ras gene. gbp-5 is transcribed at least into three splicing variants (gbp-5a, -5b, and -5ta) leading to two different proteins (GBP-5a/b, GBP-5ta). GBP-5ta is C-terminally truncated by 97aa and has therefore lost its isoprenylation site. Although RT-PCR results indicated expression of GBP-5 members in selected normal tissues, western blotting using two newly generated antibodies revealed that expression of both proteins is restricted to peripheral blood monocytes with GBP-5ta at lower levels. In contrast, cutaneous T-cell lymphoma (CTCL) tumor tissues (seven of seven) were positive solely for GBP-5ta, and four of four CTCL cell lines expressed both proteins. Eight of nine melanoma cell lines expressed GBP-5a/b and four of nine additionally low levels of GBP-5ta. SEREX retesting using CTCL sera indicated a higher immunogenicity for GBP-5ta (nine of 16) than for GBP-5a/b (two of 11). Treatment of CTCL cell lines with interferon-gamma did not alter protein expression of GBP-5ta or GBP-5a/b. The restricted expression pattern of both GBP-5ta and GBP-5a/b and the pivotal role of many known members of the GTP-binding proteins in proliferation and differentiation suggest possible cancer-related functions of gbp-5.

p47 GTPases: regulators of immunity to intracellular pathogens

Activation of the innate immune system by interferon-gamma (IFN-gamma is crucial for host resistance to infection. IFN-gamma induces the expression of a wide range of mediators that undermine the ability of pathogens to survive in host cells, including a newly discovered family of 47-kDa GTPases. Elimination of different p47 GTPases in mice by gene targeting severely cripples IFN-gamma-regulated defence against Toxoplasma gondii, Listeria monocytogenes, Mycobacterium spp. and other pathogens. In this article, we review our understanding of the role of p47 GTPases in resistance to intracellular infection and discuss the present evidence concerning their mode of action.