Murine GBP-2: a new IFN-gamma-induced member of the GBP family of GTPases isolated from macrophages

The Large GTPase, GBP-2, Regulates Rho Family GTPases to Inhibit Migration and Invadosome Formation in Breast Cancer Cells

Simple Summary

Too many women still die of breast cancer each year. Those breast cancers that kill are those with cells that have migrated away from the primary tumor in the breast and established new tumors at other sites in the body. These tumors are not reached when the original tumor in the breast is removed. This study was designed to determine why some breast cancers move away from their primary tumor and others do not. We have identified a protein that inhibits this movement. Understanding this finding may provide us with ways to inhibit tumor cell movement in patients.

Abstract

Breast cancer is the most common cancer in women. Despite advances in early detection and treatment, it is predicted that over 43,000 women will die of breast cancer in 2021. To lower this number, more information about the molecular players in breast cancer are needed. Guanylate-Binding Protein-2 has been correlated with better prognosis in breast cancer. In this study, we asked if the expression of GBP-2 in breast cancer merely provided a biomarker for improved prognosis or whether it actually contributed to improving outcome. To answer this, the 4T1 model of murine breast cancer was used. 4T1 cells themselves are highly aggressive and highly metastatic, while 67NR cells, isolated from the same tumor, do not leave the primary site. The expression of GBP-2 was examined in the two cell lines and found to be inversely correlated with aggressiveness/metastasis. Proliferation, migration, and invadosome formation were analyzed after altering the expression levels of GBP-2. Our experiments show that GBP-2 does not alter the proliferation of these cells but inhibits migration and invadosome formation downstream of regulation of Rho GTPases. Together these data demonstrate that GBP-2 is responsible for cell autonomous activities that make breast cancer cells less aggressive.

The alpha helix of the intermediate region in hGBP-1 acts as a coupler for enhanced GMP formation

The interferon-gamma inducible large GTPase human guanylate binding protein-1 (hGBP-1) plays a key role in anti-pathogenic and anti-proliferative functions. This protein hydrolyzes GTP to both GDP and GMP (predominant product) through sequential phosphate cleavages, which makes it functionally distinct from other GTPases. Previous study on truncated variants of hGBP-1 suggested that the α-helix present in the intermediate region is essential for dimerization and thus for GMP formation. However, the role of this helix in the full-length protein in GMP formation is not clearly understood. Here, we present that substitution of the helix with a Gly-rich flexible (GGS)₃ sequence in the full-length hGBP-1 (termed as linker protein) showed a drastic decrease in GMP formation. Unlike wild-type, the linker protein is not capable of undergoing substrate-induced dimerization and thereby transition state-induced tetramerization, suggesting the importance of the helix in oligomerization. Furthermore, we examined the effect of interactions between this helix and the α2-helix of the globular domain in GMP formation through mutational studies. The L118G mutation in the α2-helix showed a significantly reduced GMP formation. These results indicate that the interactions of the α-helix with the α2-helix are essential for enhanced GMP production. We propose that these interactions help in the oligomerization-assisted proper positioning of the catalytic machinery for efficient second phosphate cleavage. These findings thus provide a better understanding into the regulation of GMP formation in a large GTPase hGBP-1.

Up-regulation of GBP2 is Associated with Neuronal Apoptosis in Rat Brain Cortex Following Traumatic Brain Injury

Guanylate binding protein 2 (GBP2) is one member of GBP family. Recently, GBP2 has been proposed to be a novel target of anti-cancer drugs. However, the role of GBP2 in the traumatic brain injury (TBI) is very limited. In this study, we sought to define GBP2's role in brain injury. GBP2 protein levels were significantly increased in the brain 3 days after injury, suggesting a functional role for GBP2 in TBI. Neuronal cells overexpressing GBP2 exhibited up-regulation of co-location of GBP2 and NeuN following TBI, suggesting that GBP2 potentiates the neuron apoptosis. To confirm the role of GBP2 in neuron apoptosis process, we employed a highly potent inhibitor of GBP2 (GBP2 RNAi). In H₂O₂-stimulated PC12 cells, in vitro blockade of GBP2 activity using GBP2 RNAi markedly attenuated the neuron apoptosis number. GBP2 RNAi also inhibited the expression levels of active caspase3 and p-Stat1. Furthermore, we found the expression of p-Stat1 in line with GBP2 and GBP2 interacted with p-Stat1 following TBI. The Jak2 inhibitor, AG490 inhibited this interaction and decreased the active caspase3 expression as well as promoted the functional recovery. Taken together, these data suggest that GBP2 RNAi has a protective effect in a rat TBI. This study demonstrates that GBP2 is an important positive regulator of TBI and is a promising therapeutic target for brain injury.

The Brain Proteome of the Ubiquitin Ligase Peli1 Knock-Out Mouse during Experimental Autoimmune Encephalomyelitis

The ubiquitin ligase Peli1 has previously been suggested as a potential treatment target in multiple sclerosis. In the multiple sclerosis disease model, experimental autoimmune encephalomyelitis, Peli1 knock-out led to less activated microglia and less inflammation in the central nervous system. Despite being important in microglia, Peli1 expression has also been detected in glial and neuronal cells. In the present study the overall brain proteomes of Peli1 knock-out mice and wild-type mice were compared prior to experimental autoimmune encephalomyelitis induction, at onset of the disease and at disease peak. Brain samples from the frontal hemisphere, peripheral from the extensive inflammatory foci, were analyzed using TMT-labeling of sample pools, and the discovered proteins were verified in individual mice using label-free proteomics. The greatest proteomic differences between Peli1 knock-out and wild-type mice were observed at the disease peak. In Peli1 knock-out a higher degree of antigen presentation, increased activity of adaptive and innate immune cells and alterations to proteins involved in iron metabolism were observed during experimental autoimmune encephalomyelitis. These results unravel global effects to the brain proteome when abrogating Peli1 expression, underlining the importance of Peli1 as a regulator of the immune response also peripheral to inflammatory foci during experimental autoimmune encephalomyelitis.

The proteomics data is available in PRIDE with accession PXD003710.

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.

Interferon-inducible guanylate binding protein (GBP2) is associated with better prognosis in breast cancer and indicates an efficient T cell response

BACKGROUND

Recently, interferon-inducible guanylate binding protein (GBP2) has been discussed as a possible control factor in tumor development, which is controlled by p53, and inhibits NF-Kappa B and Rac protein as well as expression of matrix metalloproteinase 9. However, the potential role that GBP2 plays in tumor development and prognosis has not yet been studied.

METHODS

We analyzed whether GBP2 mRNA levels are associated with metastasis-free interval in 766 patients with node negative breast carcinomas who did not receive systemic chemotherapy. Furthermore, response to anthracycline-based chemotherapy was studied in 768 breast cancer patients.

RESULTS

High expression of GBP2 in breast carcinomas was associated with better prognosis in the univariate (P < 0.001, hazard ratio 0.763, 95 % CI 0.650-0.896) as well as in the multivariate Cox analysis (P = 0.008, hazard ratio 0.731, 95 % CI 0.580-0.920) adjusted to the established clinical factors age, pT stage, grading, hormone and ERBB2 receptor status. The association was particularly strong in subgroups with high proliferation and positive estrogen receptor status but did not reach significance in carcinomas with low expression of proliferation associated genes. Besides its prognostic capacity, GBP2 also predicted pathologically complete response to anthracycline-based chemotherapy (P = 0.0037, odds ratio 1.39, 95 % CI 1.11-1.74). Interestingly, GBP2 correlated with a recently established T cell signature, indicating tumor infiltration with T cells (R = 0.607, P < 0.001).

CONCLUSION

GBP2 is associated with better prognosis in fast proliferating tumors and probably represents a marker of an efficient T cell response.

Active and passive MDMA ('ecstasy') intake induces differential transcriptional changes in the mouse brain

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') is a recreational drug widely used by adolescents and young adults. Although its rewarding effects are well established, there is controversy on its addictive potential. We aimed to compare the consequences of active and passive MDMA administration on gene expression in the mouse brain since all previous studies were based on passive MDMA administration. We used a yoked-control operant intravenous self-administration paradigm combined with microarray technology. Transcriptomic profiles of ventral striatum, frontal cortex, dorsal raphe nucleus and hippocampus were analysed in mice divided in contingent MDMA, yoked MDMA and yoked saline groups, and several changes were validated by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The comparison of contingent MDMA and yoked MDMA vs. yoked saline mice allowed the identification of differential expression in several genes, most of them with immunological and inflammatory functions, but others being involved in neuroadaptation. In the comparison of contingent MDMA vs. yoked MDMA administration, hippocampus and the dorsal raphe nucleus showed statistically significant changes. The altered expression of several genes involved in neuroadaptative changes and synapse function, which may be related to learning self-administration behaviour, could be validated in these two brain structures. In conclusion, our study shows a strong effect of MDMA administration on the expression of immunological and inflammatory genes in all the four brain regions studied. In addition, experiments on MDMA self-administration suggest that the dorsal raphe nucleus and hippocampus may be involved in active MDMA-seeking behaviour, and show specific alterations on gene expression that support the addictive potential of this drug.

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

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

The guanylate-binding proteins: emerging insights into the biochemical properties and functions of this family of large interferon-induced guanosine triphosphatase

Originally identified by their unusual ability to bind guanosine monophosphate (GMP) nucleotide agarose, the guanylate-binding proteins (GBPs) were used extensively to promote our understanding of interferon-induced gene transcription and as markers of interferon responsiveness. Structural and biochemical analyses of human GBP-1 subsequently demonstrated that the GBPs are a unique subfamily of guanosine triphosphatase (GTPases) that hydrolyze guanosine triphosphate (GTP) to both guanosine diphosphate (GDP) and GMP. As members of the larger dynamin superfamily of GTPases, GBPs exhibit such properties as nucleotide-dependent oligomerization and concentration-dependent GTPase activity. Recently, progress has been made in assigning functions to members of the GBP family. While many of these functions involve protection against intracellular pathogens, a growing number of them are not directly related to pathogen protection. It is currently unclear how the unusual properties of GBPs contribute to this growing list of functions. As future studies uncover the molecular mechanism(s) of action of the GBPs, we will gain a greater understanding of how individual GBPs can mediate what currently appears to be a divergent set of functions.

Role of GTP binding, isoprenylation, and the C-terminal α-helices in the inhibition of cell spreading by the interferon-induced GTPase, mouse guanylate-binding protein-2

Interferon-γ pre-exposure inhibits Rac activation by either integrin engagement or platelet-derived growth factor treatment. Interferon-γ does this by inducing expression of the large guanosine triphosphatase (GTPase) mouse guanylate-binding protein (mGBP-2). Inhibiting Rac results in the retardation of cell spreading. Analysis of variants of mGBP-2 containing amino acid substitutions in the guanosine triphosphate (GTP) binding domain suggests that GTP binding, and possibly dimerization, of mGBP-2 is necessary to inhibit cell spreading. However, isoprenylation is also required. Removal of the N-terminal GTP-binding globular domain from mGBP-2 yields a protein with only the extended C-terminal α-helices that lacks enzymatic activity. The ability of the C-terminal α-helices alone to inhibit cell spreading suggests that this is the domain that interacts with the downstream effectors of mGBP-2. Interestingly, mGBP-2 can inhibit cell spreading whether it is geranylgeranylated or farnesylated. This study begins to define the properties of mGBP-2 responsible for inhibiting cell spreading.

The interferon-gamma-induced murine guanylate-binding protein-2 inhibits rac activation during cell spreading on fibronectin and after platelet-derived growth factor treatment: role for phosphatidylinositol 3-kinase

Exposure of cells to certain cytokines can alter how these same cells respond to later cues from other agents, such as extracellular matrix or growth factors. Interferon (IFN)-gamma pre-exposure inhibits the spreading of fibroblasts on fibronectin. Expression of the IFN-gamma-induced GTPase murine guanylate-binding protein-2 (mGBP-2) can phenocopy this inhibition and small interfering RNA knockdown of mGBP-2 prevents IFN-gamma-mediated inhibition of cell spreading. Either IFN-gamma treatment or mGBP-2 expression inhibits Rac activation during cell spreading. Rac is required for cell spreading. mGBP-2 also inhibits the activation of Akt during cell spreading on fibronectin. mGBP-2 is incorporated into a protein complex containing the catalytic subunit of phosphatidylinositol 3-kinase (PI3-K), p110. The association of mGBP-2 with p110 seems important for the inhibition of cell spreading because S52N mGBP-2, which does not incorporate into the protein complex with p110, is unable to inhibit cell spreading. PI3-K activation during cell spreading on fibronectin was inhibited in the presence of mGBP-2. Both IFN-gamma and mGBP-2 also inhibit cell spreading initiated by platelet-derived growth factor treatment, which is also accompanied by inhibition of Rac activation by mGBP-2. This is the first report of a novel mechanism by which IFN-gamma can alter how cells respond to subsequent extracellular signals, by the induction of mGBP-2.

Allergen challenge induces Ifng dependent GTPases in the lungs as part of a Th1 transcriptome response in a murine model of allergic asthma

According to the current paradigm, allergic airway inflammation is mediated by Th2 cytokines and pro-inflammatory chemokines. Since allergic inflammation is self-limited, we hypothesized that allergen challenge simultaneously induces anti-inflammatory genes to counter-balance the effects of Th2 cytokines and chemokines. To identify these putative anti-inflammatory genes, we compared the gene expression profile in the lungs of ragweed-sensitized mice four hours after challenge with either PBS or ragweed extract (RWE) using a micro-array platform. Consistent with our hypothesis, RWE challenge concurrently upregulated Th1-associated early target genes of the Il12/Stat4 pathway, such as p47 and p65 GTPases (Iigp, Tgtp and Gbp1), Socs1, Cxcl9, Cxcl10 and Gadd45g with the Th2 genes Il4, Il5, Ccl2 and Ccl7. These Th1-associated genes remain upregulated longer than the Th2 genes. Augmentation of the local Th1 milieu by administration of Il12 or CpG prior to RWE challenge further upregulated these Th1 genes. Abolition of the Th1 response by disrupting the Ifng gene increased allergic airway inflammation and abrogated RWE challenge-induced upregulation of GTPases, Cxcl9, Cxcl10 and Socs1, but not Gadd45g. Our data demonstrate that allergen challenge induces two sets of Th1-associated genes in the lungs: 1) Ifng-dependent genes such as p47 and p65 GTPases, Socs1, Cxcl9 and Cxcl10 and 2) Ifng-independent Th1-inducing genes like Gadd45g. We propose that allergen-induced airway inflammation is regulated by simultaneous upregulation of Th1 and Th2 genes, and that persistent unopposed upregulation of Th1 genes resolves allergic inflammation.

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.

Interferon-inducible guanylate binding protein (GBP)-2: a novel p53-regulated tumor marker in esophageal squamous cell carcinomas

TP53 mutations are common in esophageal squamous cell carcinomas (SCC). To identify biological markers of possible relevance in esophageal SCC, we (i) searched for genes expressed in a p53-dependent manner in TE-1, an esophageal SCC cell line expressing the temperature-sensitive TP53 mutant V272M, and (ii) investigated the expression of one of those genes, the interferon-inducible Guanylate Binding Protein 2 (GBP-2), in esophageal SCC tissues. Clontech Human Cancer 1.2 arrays containing 1,176 human cancer gene-related sequences were used to identify differentially expressed genes in TE-1 cells at permissive (32 degrees C) and nonpermissive (37 degrees C) temperatures. The expression of GBP-2 and IRF-1, its main transcriptional regulator, was analyzed by immunohistochemistry in a retrospective series of 41 esophageal SCC cases with a clear transition zone from noncancer, apparently normal epithelium to invasive cancer. The expression of the GBP-2 gene is consistently increased in TE-1 at 32 degrees C in a p53-dependent manner, as confirmed by inhibition of p53 expression by RNA interference. Increase in GBP-2 is accompanied by an increase in protein levels of IRF-1, the main transcriptional regulator of GBP-2, and in the formation of complexes between p53 and IRF-1. GBP-2 expression is significantly higher in esophageal SCC than in adjacent normal epithelium (p<0.01), in which GBP-2 staining is limited to the basal layer. Our results suggest that p53 up-regulates GBP-2 by cooperating with IRF-1. The association of GBP-2 expression with proliferative squamous cells suggests that GBP-2 may represent a marker of interest in esophageal SCC.

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.

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.

Temporal dynamics of gene expression in the lung in a baboon model of E. coli sepsis

Background

Bacterial invasion during sepsis induces disregulated systemic responses that could lead to fatal lung failure. The purpose of this study was to relate the temporal dynamics of gene expression to the pathophysiological changes in the lung during the first and second stages of E. coli sepsis in baboons.

Results

Using human oligonucleotide microarrays, we have explored the temporal changes of gene expression in the lung of baboons challenged with sublethal doses of E. coli. Temporal expression pattern and biological significance of the differentially expressed genes were explored using clustering and pathway analysis software. Expression of selected genes was validated by real-time PCR. Cytokine levels in tissue and plasma were assayed by multiplex ELISA. Changes in lung ultrastructure were visualized by electron microscopy. We found that genes involved in primary inflammation, innate immune response, and apoptosis peaked at 2 hrs. Inflammatory and immune response genes that function in the stimulation of monocytes, natural killer and T-cells, and in the modulation of cell adhesion peaked at 8 hrs, while genes involved in wound healing and functional recovery were upregulated at 24 hrs.

Conclusion

The analysis of gene expression modulation in response to sepsis provides the baseline information that is crucial for the understanding of the pathophysiology of systemic inflammation and may facilitate the development of future approaches for sepsis therapy.

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.

Gene expression in IFN-gamma-activated murine macrophages

Macrophages are critical for natural immunity and play a central role in specific acquired immunity. The IFN-gamma activation of macrophages derived from A/J or BALB/c mice yielded two different patterns of antiviral state in murine hepatitis virus 3 infection, which were related to a down-regulation of the main virus receptor. Using cDNA hybridization to evaluate mRNA accumulation in the cells, we were able to identify several genes that are differently up- or down-regulated by IFN-gamma in A/J (267 and 266 genes, respectively, up- and down-regulated) or BALB/c (297 and 58 genes, respectively, up- and down-regulated) mouse macrophages. Macrophages from mice with different genetic backgrounds behave differently at the molecular level and comparison of the patterns of non-activated and IFN-gamma-activated A/J or BALB/c mouse macrophages revealed, for instance, an up-regulation and a down-regulation of genes coding for biological functions such as enzymatic reactions, nucleic acid synthesis and transport, protein synthesis, transport and metabolism, cytoskeleton arrangement and extracellular matrix, phagocytosis, resistance and susceptibility to infection and tumors, inflammation, and cell differentiation or activation. The present data are reported in order to facilitate future correlation of proteomic/transcriptomic findings as well as of results obtained from a classical approach for the understanding of biological phenomena. The possible implication of the role of some of the gene products relevant to macrophage biology can now be further scrutinized. In this respect, a down-regulation of the main murine hepatitis virus 3 receptor gene was detected only in IFN-gamma-activated macrophages of resistant mice.

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.

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.

Early high expression of IP-10 in F344 rats resistant to Sendai virus-induced airway injury

Weanling F344 and BN rats differ markedly in their susceptibility to Sendai virus-induced airway injury. Early gene expression that controls their differences in susceptibility remains poorly understood. In this study we combined suppressive subtractive hybridization and cDNA library array hybridization to identify genes differentially expressed in virus-susceptible BN and virus-resistant F344 rats during the first 3 days after inoculation. Differential expression of selected clones was further verified by quantitative RT-PCR. Seven virus-induced gene segments were identified. Of them, interferon-gamma-inducible protein 10 (IP-10), Mx1, and guanylate-binding protein-2 mRNA abundance in infected F344 rats was 201.5, 188.2, and 281.7% higher, respectively, than that of infected BN rats at 2 days after inoculation. In situ hybridization indicated that virus-induced IP-10 was expressed mainly in airway epithelial cells of F344 rats. Sendai virus infection can directly induce IP-10 expression in rat tracheal epithelial cells in vitro. IP-10 early high expression might contribute to the resistance to virus-induced airway disease in F344 rats by promoting Th1 responses and increasing antiviral activity.

CNS gene expression pattern associated with spontaneous experimental autoimmune encephalomyelitis

Transgenic mice with T-cell receptor (TCR) specific for myelin basic protein (MBP)-Ac1-11 peptide and homozygous for the RAG-1 mutation (T/R- mice) spontaneously develop acute progressive experimental autoimmune encephalomyelitis (Sp-EAE) mediated by CD4+ T cells. Microarray analysis of spinal cord tissue obtained from symptomatic versus non-symptomatic T/R- mice revealed strongly upregulated transcripts for genes involved in antigen presentation and processing, signal transduction, transcription regulation, metabolism, development, cell cycle, and many other processes involved in the induction of clinical and pathological signs of Sp-EAE. Several highly expressed genes were related directly to inflammation, including cytokines/receptors, chemokines/receptors, acute phase, complement molecules, and others. Many CNS-specific genes were also upregulated in sick mice. Abundance of message for the Tg TCR BV8S2 gene as well as several monocyte/macrophage-associated genes would suggest that both components play a crucial role in the pathogenesis of Sp-EAE. The profile of transcriptional changes found during the development of Sp-EAE provides the first description of the encephalitogenic process in the absence of purposeful immunization with myelin peptides and immune-enhancing adjuvants. This unique approach is the first to implicate molecules and pathways that contribute naturally to onset of paralysis and demyelination, and thus may provide unique insights and novel treatment strategies for human diseases such as multiple sclerosis.

A giant GTPase, very large inducible GTPase-1, is inducible by IFNs

The complex, partially overlapping, cellular responses to IFN type I (IFN-alpha and -beta) and IFN type II (IFN-gamma) involve several hundred genes that can be largely classified in terms of specific cellular programs functional in innate and adaptive immunity. Among these programs are previously unconsidered mechanisms of cell-autonomous resistance against various pathogens mediated by dedicated, largely novel families of GTPases. We report here the identification and characterization of a new GTPase family that contributes to the cellular response to both type I and type II IFNs. We name this family the very large inducible GTPases (VLIGs). The prototype VLIG, VLIG-1, is a strongly IFN-inducible, soluble, cytosolic and nuclear protein of 280 kDa. The open reading frame of VLIG-1 is encoded on a single very large exon, and outside the canonical GTP-binding motifs, sequence and structural prediction suggest a unique family without significant relationship to other known protein families. Within the GTPase superfamily the VLIG family is more closely related to IFN-inducible GTPases mediating cell-autonomous resistance than to other GTPase families. In addition, we provide evidence that VLIG-1 is polymorphic in mice of different genetic backgrounds and is a member of a small gene family on mouse chromosome 7 with a conserved homologue located on human chromosome 11.

Glucocorticoid-attenuated response genes induced in the lung during endotoxemia

Cytokines and other mediators whose induction in inflammatory lung disease is attenuated by glucocorticoids are potential targets for development of selective anti-inflammatory treatments. We refer to genes with these regulatory characteristics as glucocorticoid-attenuated response genes, or GARGs. Systematic identification of GARGs has not been attempted previously in vivo. Using an endotoxemia model in adrenalectomized mice, we constructed a subtracted lung library enriched in endotoxemia-induced genes and identified candidate GARGs by differential hybridization screening. Northern analysis confirmed induction in the lung during endotoxemia and attenuation by glucocorticoids of 36 genes of diverse types. The majority were genes of unknown function not previously implicated in the pulmonary response to inflammation, including a new member of a 2'-5'-oligoadenylate synthetase-like family and a novel lung inducible Neuralized-related C3HC4 RING protein. Our results suggest that a full understanding of glucocorticoid effects on lung inflammation will require elucidation of the roles of an extensive network of glucocorticoid-modulated genes.

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

A new murine member of the interferon (IFN)-inducible guanylate-binding protein (GBP) family was cloned in a search for glucocorticoid-attenuated response genes induced in the lung during endotoxemia. The full-length MuGBP-5 cDNA encodes a 590 amino acid residue protein with GTP binding motifs identical to those in human GBP-1 (HuGBP-1) and a similar isoprenylation sequence at the C-terminus. An alternatively spliced form of MuGBP-5 that lacks the second GTP binding motif and differs at the C-terminus was also identified. The MuGBP-5 gene is located on chromosome 3, near MuGBP-3 and MuGBP-2, and has a genomic organization similar to other GBP genes. To facilitate the evaluation of GBP family message expression, we constructed RNase protection assay probes for MuGBP-1, MuGBP-2, MuGBP-3, MuGBP-4/Mag-2 (macrophage activation gene-2), and MuGBP-5 and validated their use in Swiss Webster, BALB/c, and C57BL/6 mice. In BALB/c mice, all five MuGBPs were induced in multiple organs during endotoxemia, and all had a similar pattern of expression in different tissues. With minor quantitative differences, the MuGBPs also had similar patterns of response to IFN-gamma, lipopolysaccharide (LPS), interleukin-1beta (IL-1beta), and tumor necrosis factor-alpha (TNF-alpha) in RAW 264.7 and Swiss 3T3 cells. The coordinate expression of the MuGBPs suggests that they share common mechanisms of regulation.

The interferon (IFN)-induced GTPase, mGBP-2. Role in IFN-gamma-induced murine fibroblast proliferation

To investigate the function of mGBP-2, a member of the interferon (IFN)-induced guanylate-binding protein family of GTPases, NIH 3T3 fibroblasts were generated that constitutively expressed mGBP-2. mGBP-2 induced a faster growth rate, with the highest expressing clones showing approximately a 50% reduction in doubling time. mGBP-2-expressing cells also grew to higher density and exhibited partial loss of contact growth inhibition, as evidenced by the formation of foci in post-confluent cultures. In addition, mGBP-2-expressing cells showed decreased dependence on serum-derived growth factors. However, they did not lose the requirement for anchorage-dependent growth. Finally, NIH 3T3 cells expressing mGBP-2 formed tumors in athymic mice. An mGBP-2 protein carrying a point mutation (S52N) that reduced GTP binding failed to produce these phenotypes when expressed at the same levels as wild type. The additional finding that IFN-gamma treatment of NIH 3T3 cells resulted in an increase in proliferation similar to that observed for mGBP-2 in the absence of other IFN-induced proteins suggests that mGBP-2 may indeed be important for these growth changes.

Genes expressed during the IFN gamma-induced maturation of pre-B cells

Interferon-gamma (IFN gamma) exerts diverse responses in B cell development ranging from growth arrest and apoptosis to proliferation and differentiation. IFN gamma stimulates murine 70Z/3 pre-B cells to express surface immunoglobulin (Ig) and this system serves as a useful model for the pre-B to immature B cell transition in B cell development. To analyze this developmental transition, we used a PCR-based subtractive hybridization in combination with miniarray screening to identify differentially-expressed genes in IFN gamma-stimulated compared with unstimulated 70Z/3 pre-B cells. The majority (44%) of the differentially-expressed genes obtained were known IFN gamma-inducible. These included multiple isolates from each of three multi-gene families, including two guanylate-binding protein (47 and 67kDa GBP) families of GTPases and the hematopoietic IFN gamma-inducible nuclear protein family (HIN-200). These multiple isolates of genes comprised the majority of the total isolated and sequenced clones. Other known IFN gamma-induced genes in this group included Ig kappa light chain and Ly-6, as well as genes with functions in antigen processing, cellular regulation, and cytoskeletal organization. Another 36% of the genes identified were previously known, but not known to be IFN gamma-inducible (e.g. pre-B cell enhancing factor, PBEF). The remaining 20% of the IFN gamma-induced isolates did not match entries in Genbank, and thus, may represent novel genes involved in IFN gamma responses and/or in the pre-B to immature B cell transition. Overall, the majority of the individual genes isolated were either not known to be IFN gamma responsive or were not previously known.

Different subcellular localizations for the related interferon-induced GTPases, MuGBP-1 and MuGBP-2: implications for different functions?

The guanylate-binding proteins (GBPs) are a family of 65-67-kDa proteins induced by both type I and type II interferons (IFN). Members of the GBP family of GTPases are among the most abundant IFN-gamma-induced proteins. GBPs contain an unusual GTP binding site, which is consistent with GBP hydrolysis of GTP to both GDP and GMP. In addition, six of the eight known GBPs have a carboxy-terminal CaaX motif for the addition of isoprenyl lipids. Despite their abundance, however, little is known about the biologic function or cellular location of GBPs. We report here on studies to localize both a newly identified murine GBP (MuGBP-2) and its closely related family member, MuGBP-1. In both IFN-treated macrophages and fibroblasts, MuGBP-2 is found in both a granular distribution throughout the cytoplasm and localized to vesicle populations of heterogeneous sizes. The localization of MuGBP-2 to vesicles is dependent on its isoprenylation. Despite a high degree of sequence identity and the presence of an identical CaaX sequence, MuGBP-1 has a very homogeneous cytoplasmic distribution and fails to localize to intracellular vesicles. The different intracellular distribution of these two closely related family members suggests differential function(s).

Murine guanylate-binding protein: incomplete geranylgeranyl isoprenoid modification of an interferon-gamma-inducible guanosine triphosphate-binding protein

Farnesylation of Ras proteins is necessary for transforming activity. Although farnesyl transferase inhibitors show promise as anticancer agents, prenylation of the most commonly mutated Ras isoform, K-Ras4B, is difficult to prevent because K-Ras4B can be alternatively modified with geranylgeranyl (C20). Little is known of the mechanisms that produce incomplete or inappropriate prenylation. Among non-Ras proteins with CaaX motifs, murine guanylate-binding protein (mGBP1) was conspicuous for its unusually low incorporation of [(3)H]mevalonate. Possible problems in cellular isoprenoid metabolism or prenyl transferase activity were investigated, but none that caused this defect was identified, implying that the poor labeling actually represented incomplete prenylation of mGBP1 itself. Mutagenesis indicated that the last 18 residues of mGBP1 severely limited C20 incorporation but, surprisingly, were compatible with farnesyl modification. Features leading to the expression of mutant GBPs with partial isoprenoid modification were identified. The results demonstrate that it is possible to alter a protein's prenylation state in a living cell so that graded effects of isoprenoid on function can be studied. The C20-selective impairment in prenylation also identifies mGBP1 as an important model for the study of substrate/geranylgeranyl transferase I interactions.

Nucleotide-binding characteristics of human guanylate-binding protein 1 (hGBP1) and identification of the third GTP-binding motif

hGBP1 is a GTPase with antiviral activity encoded by an interferon- activated human gene. Specific binding of hGBP1 to guanine nucleotides has been established although only two classical GTP-binding motifs were found in its primary sequence. The unique position of hGBP1 amongst known GTPases is further demonstrated by the hydrolysis of GTP to GDP and GMP. Although subsequent cleavage of orthophosphates rather than pyrophosphate was demonstrated, GDP coming from bulk solution cannot serve as a substrate. The relation of guanine nucleotide binding and hydrolysis to the antiviral function of hGBP1 is unknown. Here we show similar binding affinities for all three guanine nucleotides and the ability of both products, GDP and GMP, to compete with GTP binding. Fluorimetry and isothermal titration calorimetry were applied to prove that only one nucleotide binding site is present in hGBP1. Furthermore, we identified the third canonical GTP-binding motif and verified its role in nucleotide recognition by mutational analysis. The high guanine nucleotide dissociation rates measured by stopped-flow kinetics are responsible for the weak affinities to hGBP1 when compared to other GTPases like Ras or Galpha. By means of fluorescence and NMR spectroscopy it is demonstrated that aluminium fluoride forms a complex with hGBP1 only in the GDP state, presumably mimicking the transition state of GTP hydrolysis. Tentatively, the involvement of a GAP domain in hGBP1 in GTP hydrolysis is suggested. These results will serve as a basis for the determination of the differential biological functions of the three nucleotide states and for the elucidation of the unique mechanism of nucleotide hydrolysis catalysed by hGBP1.