Direct observation of cortactin protecting Arp2/3-actin filament branch junctions from GMF-mediated destabilization

How cells tightly control the formation and turnover of branched actin filament arrays to drive cell motility, endocytosis, and other cellular processes is still not well understood. Here, we investigated the mechanistic relationship between two binding partners of the Arp2/3 complex, glia maturation factor (GMF) and cortactin. Individually, GMF and cortactin have opposite effects on the stability of actin filament branches, but it is unknown how they work in concert with each other to govern branch turnover. Using TIRF microscopy, we observe that GMF's branch destabilizing activities are potently blocked by cortactin (IC50 = 1.3 nM) and that this inhibition requires direct interactions of cortactin with Arp2/3 complex. The simplest model that would explain these results is competition for binding Arp2/3 complex. However, we find that cortactin and GMF do not compete for free Arp2/3 complex in solution. Further, we use single molecule analysis to show that cortactin's on-rate (3 ×107 s-1 M-1) and off-rate (0.03 s-1) at branch junctions are minimally affected by excess GMF. Together, these results show that cortactin binds with high affinity to branch junctions, where it blocks the destabilizing effects of GMF, possibly by a mechanism that is allosteric in nature. In addition, the affinities we measure for cortactin at actin filament branch junctions (Kd = 0.9 nM) and filament sides (Kd = 206 nM) are approximately 20-fold stronger than previously reported. These observations contribute to an emerging view of molecular complexity in how Arp2/3 complex is regulated through the integration of multiple inputs.

G9a Inhibition Promotes Neuroprotection through GMFB Regulation in Alzheimer's Disease

Epigenetic alterations are a fundamental pathological hallmark of Alzheimer's disease (AD). Herein, we show the upregulation of G9a and H3K9me2 in the brains of AD patients. Interestingly, treatment with a G9a inhibitor (G9ai) in SAMP8 mice reversed the high levels of H3K9me2 and rescued cognitive decline. A transcriptional profile analysis after G9ai treatment revealed increased gene expression of glia maturation factor β (GMFB) in SAMP8 mice. Besides, a H3K9me2 ChIP-seq analysis after G9a inhibition treatment showed the enrichment of gene promoters associated with neural functions. We observed the induction of neuronal plasticity and a reduction of neuroinflammation after G9ai treatment, and more strikingly, these neuroprotective effects were reverted by the pharmacological inhibition of GMFB in mice and cell cultures; this was also validated by the RNAi approach generating the knockdown of GMFB/Y507A.10 in Caenorhabditis elegans. Importantly, we present evidence that GMFB activity is controlled by G9a-mediated lysine methylation as well as we identified that G9a directly bound GMFB and catalyzed the methylation at lysine (K) 20 and K25 in vitro. Furthermore, we found that the neurodegenerative role of G9a as a GMFB suppressor would mainly rely on methylation of the K25 position of GMFB, and thus G9a pharmacological inhibition removes this methylation promoting neuroprotective effects. Then, our findings confirm an undescribed mechanism by which G9a inhibition acts at two levels, increasing GMFB and regulating its function to promote neuroprotective effects in age-related cognitive decline.

Parkinson's Disease Dementia Patients: Expression of Glia Maturation Factor in the Brain

Parkinson's disease (PD) is the second most common progressive neurodegenerative disease characterized by the presence of dopaminergic neuronal loss and motor disorders. PD dementia (PDD) is a cognitive disorder that affects many PD patients. We have previously demonstrated the proinflammatory role of the glia maturation factor (GMF) in neuroinflammation and neurodegeneration in AD, PD, traumatic brain injury (TBI), and experimental autoimmune encephalomyelitis (EAE) in human brains and animal models. The purpose of this study was to investigate the expression of the GMF in the human PDD brain. We analyzed the expression pattern of the GMF protein in conjunction with amyloid plaques (APs) and neurofibrillary tangles (NFTs) in the substantia nigra (SN) and striatum of PDD brains using immunostaining. We detected a large number of GMF-positive glial fibrillary acidic protein (GFAP) reactive astrocytes, especially abundant in areas with degenerating dopaminergic neurons within the SN and striatum in PDD. Additionally, we observed excess levels of GMF in glial cells in the vicinity of APs, and NFTs in the SN and striatum of PDD and non-PDD patients. We found that the majority of GMF-positive immunoreactive glial cells were co-localized with GFAP-reactive astrocytes. Our findings suggest that the GMF may be involved in the pathogenesis of PDD.

Transcriptomics and Metabolomics of Reactive Oxygen Species Modulation in Near-Null Magnetic Field-Induced Arabidopsis thaliana

The geomagnetic field (GMF) is a natural component of Earth's biosphere. GMF reduction to near-null values (NNMF) induces gene expression modulation that generates biomolecular, morphological, and developmental changes. Here, we evaluate the effect of NNMF on gene expression and reactive oxygen species (ROS) production in time-course experiments on Arabidopsis thaliana. Plants exposed to NNMF in a triaxial Helmholtz coils system were sampled from 10 min to 96 h to evaluate differentially expressed genes (DEGs) of oxidative stress responses by gene microarray. In 24-96 h developing stages, H₂O₂ and polyphenols were also analyzed from roots and shoots. A total of 194 DEGs involved in oxidative reactions were selected, many of which showed a fold change ≥±2 in at least one timing point. Heatmap clustering showed DEGs both between roots/shoots and among the different time points. NNMF induced a lower H₂O₂ than GMF, in agreement with the expression of ROS-related genes. Forty-four polyphenols were identified, the content of which progressively decreased during NNMF exposition time. The comparison between polyphenols content and DEGs showed overlapping patterns. These results indicate that GMF reduction induces metabolomic and transcriptomic modulation of ROS-scavenging enzymes and H₂O₂ production in A. thaliana, which is paralleled by the regulation of antioxidant polyphenols.

MicroRNA-5195-3p alleviates high glucose‑induced injury in human ARPE-19 cells by targeting GMFB

Hyperglycemia is generally considered to be an important cause of diabetic retinopathy (DR). The aim of the present study was to investigate the role of miR-5195-3p in high glucose (HG)-induced human retinal pigment epithelial ARPE-19 cell injury. Here, we first found that the expression level of miR-5195-3p was significantly downregulated in HG-stimulated ARPE-19 cells using reverse transcription quantitative PCR. Overexpression of miR-5195-3p attenuated the impaired cell viability, increased apoptosis and pro-inflammatory cytokines secretion in ARPE-19 cells under HG condition using CCK-8 assay, flow cytometry and ELISA assay, respectively. Luciferase reporter assay showed that miR-5195-3p could specifically bind to the 3’UTR of glia maturation factor-β (GMFB). GMFB overexpression reversed, while knockdown enhanced the protective effects of miR-5195-3p overexpression against HG-induced ARPE-19 cell injury. In summary, miR-5195-3p targeting GMFB might be a potential therapeutic target for DR.

Targeted Gene Editing of Glia Maturation Factor in Microglia: a Novel Alzheimer's Disease Therapeutic Target

Alzheimer's disease (AD) is a devastating, progressive neurodegenerative disorder that leads to severe cognitive impairment in elderly patients. Chronic neuroinflammation plays an important role in the AD pathogenesis. Glia maturation factor (GMF), a proinflammatory molecule discovered in our laboratory, is significantly upregulated in various regions of AD brains. We have previously reported that GMF is predominantly expressed in the reactive glial cells surrounding the amyloid plaques (APs) in the mouse and human AD brain. Microglia are the major source of proinflammatory cytokines and chemokines including GMF. Recently clustered regularly interspaced short palindromic repeats (CRISPR) based genome editing has been recognized to study the functions of genes that are implicated in various diseases. Here, we investigated if CRISPR-Cas9-mediated GMF gene editing leads to inhibition of GMF expression and suppression of microglial activation. Confocal microscopy of murine BV2 microglial cell line transduced with an adeno-associated virus (AAV) coexpressing Staphylococcus aureus (Sa) Cas9 and a GMF-specific guide RNA (GMF-sgRNA) revealed few cells expressing SaCas9 while lacking GMF expression, thereby confirming successful GMF gene editing. To further improve GMF gene editing efficiency, we developed lentiviral vectors (LVs) expressing either Streptococcus pyogenes (Sp) Cas9 or GMF-sgRNAs. BV2 cells cotransduced with LVs expressing SpCas9 and GMF-sgRNAs revealed reduced GMF expression and the presence of indels in the exons 2 and 3 of the GMF coding sequence. Lipopolysaccharide (LPS) treatment of GMF-edited cells led to reduced microglial activation as shown by reduced p38 MAPK phosphorylation. We believe that targeted in vivo GMF gene editing has a significant potential for developing a unique and novel AD therapy.

Mast Cells Release Chemokine CCL2 in Response to Parkinsonian Toxin 1-Methyl-4-Phenyl-Pyridinium (MPP(+))

Microglial activation and release of inflammatory cytokines and chemokines are crucial events in neuroinflammation. Microglial cells interact and respond to other inflammatory cells such as T cells and mast cells as well as inflammatory mediators secreted from these cells. Recent studies have shown that neuroinflammation causes and accelerates neurodegenerative disease such as Parkinson's disease (PD) pathogenesis. 1-methyl-4-phenyl-pyridinium ion (MPP(+)), the active metabolite of neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydro pyridine activates glial cells and mediate neurodegeneration through release of inflammatory mediators. We have shown that glia maturation factor (GMF) activates glia and induces neuroinflammation and neurodegeneration and that MPP(+) activates mast cells and release proinflammatory cytokines and chemokines. The chemokine (C-C motif) ligand 2 (CCL2) levels have been shown to be elevated and play a role in PD pathogenesis. In the present study, we analyzed if MPP(+) activates mouse and human mast cells to release chemokine CCL2. Mouse bone marrow-derived mast cells (BMMCs) and human umbilical cord blood-derived cultured mast cells (hCBMCs) were incubated with MPP(+) (10 µM) for 24 h and CCL2 levels were measured in the supernatant media by ELISA. MPP(+)-significantly induced CCL2 release from BMMCs and hCBMCs. Additionally, GMF overexpression in BMMCs obtained from wild-type mice released significantly more CCL2, while BMMCs obtained from GMF-deficient mice showed less CCL2 release. Further, we show that MPP(+)-induced CCL2 release was greater in BMMCs-astrocyte co-culture conditions. Uncoupling protein 4 (UCP4) which is implicated in neurodegenerative diseases including PD was detected in BMMCs by immunocytochemistry. Our results suggest that mast cells may play role in PD pathogenesis.

GMF promotes leading-edge dynamics and collective cell migration in vivo

Lamellipodia are dynamic actin-rich cellular extensions that drive advancement of the leading edge during cell migration. Lamellipodia undergo periodic extension and retraction cycles, but the molecular mechanisms underlying these dynamics and their role in cell migration have remained obscure. We show that glia-maturation factor (GMF), which is an Arp2/3 complex inhibitor and actin filament debranching factor, regulates lamellipodial protrusion dynamics in living cells. In cultured S2R(+) cells, GMF silencing resulted in an increase in the width of lamellipodial actin filament arrays. Importantly, live-cell imaging of mutant Drosophila egg chambers revealed that the dynamics of actin-rich protrusions in migrating border cells is diminished in the absence of GMF. Consequently, velocity of border cell clusters undergoing guided migration was reduced in GMF mutant flies. Furthermore, genetic studies demonstrated that GMF cooperates with the Drosophila homolog of Aip1 (flare) in promoting disassembly of Arp2/3-nucleated actin filament networks and driving border cell migration. These data suggest that GMF functions in vivo to promote the disassembly of Arp2/3-nucleated actin filament arrays, making an important contribution to cell migration within a 3D tissue environment.

Suppression of glia maturation factor expression prevents 1-methyl-4-phenylpyridinium (MPP⁺)-induced loss of mesencephalic dopaminergic neurons

Inflammation mediated by glial activation appears to play a critical role in the pathogenesis of Parkinson disease (PD). Glia maturation factor (GMF), a proinflammatory protein predominantly localized in the central nervous system was isolated, sequenced and cloned in our laboratory. We have previously demonstrated immunomodulatory and proinflammatory functions of GMF, but its involvement in 1-methyl-4-phenylpyridinium (MPP(+)), active metabolite of classical parkinsonian toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), inducing loss of dopaminergic (DA) neurons has not been studied. Here we show that altered expression of GMF has direct consequences on the production of reactive oxygen species (ROS) and nuclear factor-kappa B (NF-κB)- mediated production of inflammatory mediators by MPP(+). We examined MPP(+)-induced DA neuronal loss in primary cultures of mouse mesencephalic neurons/glia obtained from GMF-deficient (GMF knockout (GMF-KO)) and GMF-containing wild-type (Wt) mice. We demonstrate that deficiency of GMF in GMF-KO neurons/glia led to decreased production of ROS and downregulation of NF-κB-mediated production of tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1β) as compared to Wt neurons/glia. Additionally, overexpression of GMF induced DA neurodegeneration, whereas GMF downregulation by GMF-specific shRNA protected DA neurons from MPP-induced toxicity. Subsequently, GMF deficiency ameliorates antioxidant balance, as evidenced by the decreased level of lipid peroxidation, less ROS production along with increased level of glutathione; and attenuated the DA neuronal loss via the downregulation of NF-κB-mediated inflammatory responses. In conclusion, our overall data indicate that GMF modulates oxidative stress and release of deleterious agents by MPP(+) leading to loss of DA neurons. Our study provides new insights into the potential role of GMF and identifies targets for therapeutic interventions in neurodegenerative diseases.

Actin network disassembly powers dissemination of Listeria monocytogenes

Several bacterial pathogens hijack the actin assembly machinery and display intracellular motility in the cytosol of infected cells. At the cell cortex, intracellular motility leads to bacterial dissemination through formation of plasma membrane protrusions that resolve into vacuoles in adjacent cells. Here, we uncover a crucial role for actin network disassembly in dissemination of Listeria monocytogenes. We found that defects in the disassembly machinery decreased the rate of actin tail turnover but did not affect the velocity of the bacteria in the cytosol. By contrast, defects in the disassembly machinery had a dramatic impact on bacterial dissemination. Our results suggest a model of L. monocytogenes dissemination in which the disassembly machinery, through local recycling of the actin network in protrusions, fuels continuous actin assembly at the bacterial pole and concurrently exhausts cytoskeleton components from the network distal to the bacterium, which enables membrane apposition and resolution of protrusions into vacuoles.

Augmented expression of glia maturation factor in Alzheimer's disease

We have previously demonstrated that glia maturation factor (GMF), a brain-specific protein, isolated, sequenced, and cloned in our laboratory, is a prominent mediator of inflammation in the CNS leading to the death of neurons. In the present study, we demonstrate, for the first time, a significant upregulation of the GMF protein in various regions of Alzheimer's disease (AD) brains compared with age-matched non-demented (ND) control brains. We analyzed AD and ND brain samples by quantitative enzyme-linked immunosorbent assay (ELISA) using a combination of highly specific monoclonal and polyclonal anti-GMF antibodies developed and characterized in our laboratory. For the comparison between ND controls and AD cases, we examined brain tissue from 12 ad cases (ages ranging from 78-92 years) and eight age-matched ND controls (ages ranging from 76-88 years). We observed a significant increase in GMF concentration in entorhinal cortex, parietal cortex, frontal cortex, occipital cortex, perirhinal cortex, and temporal cortex of AD patients. Our results clearly demonstrate that the GMF protein levels are significantly higher in all AD-affected brain regions than in ND controls. The immunohistochemistry analysis revealed co-localization of GMF with amyloid plaques (AP) and neurofibrillary tangles (NFTs) in AD brains. Our results imply that under conditions of neurodegeneration the expression of GMF is significantly upregulated.

GMF is a cofilin homolog that binds Arp2/3 complex to stimulate filament debranching and inhibit actin nucleation

Cell locomotion and endocytosis are powered by the rapid polymerization and turnover of branched actin filament networks nucleated by Arp2/3 complex. Although a large number of cellular factors have been identified that stimulate Arp2/3 complex-mediated actin nucleation, only a small number of studies so far have addressed which factors promote actin network debranching. Here, we investigated the function of a conserved homolog of ADF/cofilin, glia maturation factor (GMF). We found that S. cerevisiae GMF (also called Aim7) localizes in vivo to cortical actin patches and displays synthetic genetic interactions with ADF/cofilin. However, GMF lacks detectable actin binding or severing activity and instead binds tightly to Arp2/3 complex. Using in vitro evanescent wave microscopy, we demonstrated that GMF potently stimulates debranching of actin filaments produced by Arp2/3 complex. Further, GMF inhibits nucleation of new daughter filaments. Together, these data suggest that GMF binds Arp2/3 complex to both "prune" daughter filaments at the branch points and inhibit new actin assembly. These activities and its genetic interaction with ADF/cofilin support a role for GMF in promoting the remodeling and/or disassembly of branched networks. Therefore, ADF/cofilin and GMF, members of the same superfamily, appear to have evolved to interact with actin and actin-related proteins, respectively, and to make mechanistically distinct contributions to the remodeling of cortical actin structures.

Glia Maturation Factor Regulation of STAT Expression: A Novel Mechanism in Experimental Autoimmune Encephalomyelitis

Inflammatory cytokines are implemented in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. We previously demonstrated that glia maturation factor (GMF), a brain protein, isolated, sequenced and cloned in our laboratory, induce expression of proinflammatory cytokine/chemokine in the central nervous system (CNS). We found GMF-deficient (knockout) mice relatively resistant to EAE development after immunization with encephalitogenic MOG peptide 35-55. Consistent with these findings, the expression of proinflammatory cytokines in CNS of mice with EAE differed profoundly between wild type and GMF-knockout mice. In the present study we examined the expressions of six murine signal transducers and activators of transcription (STATs) genes, which are known to regulate the cytokine-dependent signal transduction pathways in autoimmune inflammation. The expressions of STATs genes were evaluated in the brains and spinal cords of wild type and GMF-knockout mice at the peak of EAE by quantitative real-time RT-PCR. Compared to GMF-knockout mice, the expressions of STAT1, STAT2, STAT3, STAT4, STAT5, and STAT6 genes were significantly (P < 0.001) upregulated in the wild type mice exhibiting EAE symptoms. The results are consistent with the diminished development of EAE in the GMF-knockout mice. A significant suppression of STATs expression in GMF-knockout mice suggests GMF as an upstream effector of JAK/STAT signaling.

A novel role of glia maturation factor: induction of granulocyte-macrophage colony-stimulating factor and pro-inflammatory cytokines

The glia maturation factor (GMF), which was discovered in our laboratory, is a highly conserved protein predominantly localized in astrocytes. GMF is an intracellular regulator of stress-related signal transduction. We now report that the overexpression of GMF in astrocytes leads to the destruction of primary oligodendrocytes by interactions between highly purified cultures of astrocytes, microglia, and oligodendrocytes. We infected astrocytes with a replication-defective adenovirus carrying the GMF cDNA. The overexpression of GMF caused the activation of p38 MAP kinase and transcription factor NF-kappaB, as well as the induction of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA and protein in astrocytes. Small interfering RNA-mediated GMF knockdown completely blocked the GMF-dependent activation of p38 mitogen-activated protein kinase (MAPK), NF-kappaB, and enhanced expression of GM-CSF by astrocytes. Inhibition of p38 MAPK or NF-kappaB by specific inhibitors prevented GM-CSF production. The cell-free conditioned medium from overexpressing GMF astrocytes contained 320 +/- 33 pg/mL of GM-CSF, which was responsible for enhanced production and secretion of TNF-alpha, IL-1beta, IL-6, and IP-10 by microglia. Presence of these inflammatory cytokines in the conditioned medium from microglia efficiently destroyed oligodendrocytes in culture. These results suggest that GMF-induced production of GM-CSF in astrocytes is depending on p38 MAPK and NF-kappaB activation. The GM-CSF-dependent expression and secretion of inflammatory cytokine/chemokine, TNF-alpha, IL-1beta, IL-6, and IP-10, is cytotoxic to oligodendrocytes, the myelin-forming cells in the central nervous system, and as well as neurons. Our results suggest a novel pathway of GMF-initiated cytotoxicity of brain cells, and implicate its involvement in inflammatory diseases such as multiple sclerosis.

Glia maturation factor-gamma is preferentially expressed in microvascular endothelial and inflammatory cells and modulates actin cytoskeleton reorganization

Actin cytoskeleton reorganization is a fundamental process for actin-based cellular functions such as cytokinesis, phagocytosis, and chemotaxis. Regulating actin cytoskeleton reorganization is therefore an attractive approach to control endothelial and inflammatory cells function and to treat cardiovascular diseases. Here, we identified glia maturation factor-gamma (GMFG) as a novel factor in actin cytoskeleton reorganization and is expressed preferentially in microvascular endothelial and inflammatory cells. During mouse embryogenesis, GMFG was expressed predominantly in blood islands of the yolk sac, where endothelial and hematopoietic cells develop simultaneously. In endothelial cells, GMFG was colocalized with F-actin in membrane ruffles and was associated with F-actin assessed by actin co-sedimentation assay. Interestingly, GMFG was phosphorylated at N-terminal serine, and its phosphorylation was enhanced by coexpression of dominant active Rac1 and Cdc42. Furthermore, a pseudophosphorylated form of GMFG (GMFG-S2E) demonstrated higher association with F-actin. Stable expression of GMFG-S2E remarkably enhanced stimulus-responsive lamellipodia and subsequent membrane ruffle formation in HeLa cells presumably through its interaction with Arp2/3 complex. Expression of GMFG enhanced actin-based cellular functions such as migration and tube-formation in endothelial cells. Moreover, we found that GMFG expression was significantly increased in a cardiac ischemia/reperfusion model where inflammation and angiogenesis take place actively. Taken together, our findings define a novel pathway in the regulation of actin-based cellular functions. Regulating GMFG function may provide a novel approach to modulate the pathophysiology of cardiovascular diseases.

GMF-knockout mice are unable to induce brain-derived neurotrophic factor after exercise

We earlier reported that overexpression of glia maturation factor (GMF) in cultured astrocytes enhances the production of brain-derived neurotrophic factor (BDNF). The current study was conducted to find out whether BDNF production is impaired in animals devoid of GMF. To this end GMF-knockout (KO) mice were subjected to exercise and the neurotrophin mRNAs were determined by real-time RT-PCR. Compared to wild-type (WT) mice, there is a decrease in exercise-induced BDNF in the KO mice. The observation was correlated with the finding that, in WT mice, exercise increases GMF expression. The results are consistent with the hypothesis that GMF is necessary for exercise-induction of BDNF, and that GMF may promote neuroprotection through BDNF production.

Glia maturation factor-beta is produced by thymoma and may promote intratumoral T-cell differentiation

AIMS

To investigate whether Glia maturation factor-beta (GMFB) is expressed in thymomas and is associated with T-cell development.

METHODS AND RESULTS

We investigated the expression of GMFB by immunohistochemistry in 86 cases of thymoma classified into five type A, 35 type AB, 11 type B1, 26 type B2, and nine type B3 thymomas according to the World Health Organization classification system. Immunoblotting and in situ hybridization (ISH) studies were also performed in selected cases. The results of the immunoblot analysis were in accordance with those of immunohistochemical scoring. The ISH study ascertained the tumour cells producing the protein. Immunohistochemically, GMFB expression was observed in one (20%) of type A, 32 (80%) of type AB, all (100%) of type B1 and B2, and eight (89%) of type B3 thymoma with statistically significant differences between type A and type AB, type B1, or type B2 thymoma, and between type B3 and type AB or type B2 thymoma. There was a significant correlation between GMFB expression and the amount of accompanying non-neoplastic T cells. GMFB promoted T-cell differentiation into CD4-/CD8+ cells when analysed by two-colour flow cytometry.

CONCLUSIONS

The present study suggests that T-cell development in thymoma may be maintained partly by GMFB produced by the tumour cells.

Gene expression versus sequence for predicting function: Glia Maturation Factor gamma is not a glia maturation factor

It is standard practice, whenever a researcher finds a new gene, to search databases for genes that have a similar sequence. It is not standard practice, whenever a researcher finds a new gene, to search for genes that have similar expression (co-expression). Failure to perform co-expression searches has lead to incorrect conclusions about the likely function of new genes, and has lead to wasted laboratory attempts to confirm functions incorrectly predicted. We present here the example of Glia Maturation Factor gamma (GMF-gamma). Despite its name, it has not been shown to participate in glia maturation. It is a gene of unknown function that is similar in sequence to GMF-beta. The sequence homology and chromosomal location led to an unsuccessful search for GMF-gamma mutations in glioma. We examined GMF-gamma expression in 1432 human cDNA libraries. Highest expression occurs in phagocytic, antigen-presenting and other hematopoietic cells. We found GMF-gamma mRNA in almost every tissue examined, with expression in nervous tissue no higher than in any other tissue. Our evidence indicates that GMF-gamma participates in phagocytosis in antigen presenting cells. Searches for genes with similar sequences should be supplemented with searches for genes with similar expression to avoid incorrect predictions.

Impaired motor performance and learning in glia maturation factor-knockout mice

Glia maturation factor (GMF) is a unique brain protein localized in astrocytes and some neuronal populations. Studies with overexpression of GMF using adenovirus vector have uncovered its regulatory role in intracellular signal transduction and downstream induction of biologically active molecules, including the neurotrophins and cytokines. The current paper deals with the behavior of mice devoid of GMF protein (knockout). GMF-null mice developed normally without gross abnormality. When tested for simple position discrimination using a T-maze and for spatial memory using a Morris water maze, the knockout mice performed as well as the wild-type, showing no defect in maze learning. However, with beam walking, GMF-knockout mice performed poorly and failed to learn. Knockout mice were also defective in learning the eyeblink classical conditioning. Histologically, the knockout mice showed a loss of neurons in the inferior olive, which is a component of the circuitry of eyeblink conditioning, and is also essential for motor performance. The structural abnormality in GMF-null mice explained their impaired ability for both motor performance and motor learning.

Expression of glia maturation factor beta after cryogenic brain injury

Glia maturation factor beta (GMFB) was identified as a growth and differentiation factor acting on neurons as well as glia. We investigated the expression of GMFB during 56 days after cryogenic brain injury, using immunohistochemistry, reverse transcriptase polymerase chain reaction (RT-PCR), Western blotting and enzyme immunoassay. Immunohistochemical analysis demonstrated that the GFAP-positive astrocytes around the lesion expressed GMFB protein, peaking 14 days after injury. Weak astrocytic expression of GMFB-immunoreactivity was seen in sham-operated animal brains. Cryogenic injury (CI) induced GMFB mRNA in the lesioned side after 7 days with a maximum at 14 days. Western blotting revealed the induction of GMFB protein starting 1 day after injury, and continuing until 14 days after injury. In the enzyme immunoassay, GMFB protein concentration peaked 14 days after injury in extracts from the injured side of the brain, whereas in serum it peaked 1 day after injury. These data indicate that the expression of GMFB increased in the astrocytes around the lesioned area after cortical cryogenic brain injury. These findings may provide new insight into GMFB function in pathological conditions following brain injury.

Decreased copper-zinc superoxide dismutase activity and increased resistance to oxidative stress in glia maturation factor-null astrocytes

Glia maturation factor (GMF) is a highly conserved protein found mainly in the nervous system. The current work was undertaken to investigate the effect of GMF expression in astrocytes on CuZn superoxide dismutase (CuZnSOD or SOD I) and on the vulnerability of the cells to H2O2 toxicity. Primary astrocyte cultures were derived from mice in which the GMF gene was completely deleted by homologous recombination (knockout). Astocytes derived from knockout animals displayed a lower level of CuZnSOD activity and protein. The reduction in CuZnSOD was restored by transfection with a GMF/adenovirus construct, and the resulting increase was blocked by the p38 MAP kinase inhibitor SB203580. There was no change in the other isoform of SOD (MnSOD or SOD II). Endogenous H2O2 was lower in the knockout cells, and the cells became more resistant to H2O2 toxicity compared to the wild type. In the GMF-null cells, concurrent with a decrease in CuZnSOD, the function of which is to convert superoxide to H2O2, there was an increase in the activity of the two enzymes that degrade H2O2: catalase and glutathione peroxidase. By regulating the redox state of the cell, GMF may be involved in a wide spectrum of cellular events ranging from survival, proliferation, differentiation, to death.

Structure and promoter activity of the human glia maturation factor-gamma gene: a TATA-less, GC-rich and bidirectional promoter

Human glia maturation factor-gamma (hGMFG) was recently identified as a gene that is homologous to glia maturation factor-beta (GMFB). In this study, we determined the organization of the 9.5-kb hGMFG gene and characterized its promoter activity. The 5'-flanking region of the first exon has putative elements for binding transcription factors Sp-1, GATA-1, AML-1a, Lyf-1 and Ets-1, but there were no TATA or CAAT boxes within a 226-bp sequence upstream from the initiation codon. Primer extension analysis and 5'RACE (rapid amplification of cDNA 5' ends) identified multiple transcription initiation sites within the region -84 to -70 nucleotides from the first ATG codon in a Kozak consensus sequence. A core promoter region was determined by transfecting a series of deletion constructs with a dual luciferase reporter system into rat astrocyte-derived ACT-57 cells. We found that 226 bp of the core promoter region exhibited bidirectional promoter activity.

Overexpression of glia maturation factor in astrocytes leads to immune activation of microglia through secretion of granulocyte-macrophage-colony stimulating factor

We infected a mixed culture of primary rat astrocytes and microglia with a replication-defective adenovirus carrying the rat glia maturation factor (GMF) cDNA. Affymetrix microarray analysis showed a big increase in the expression of several major histocompatibility complex (MHC) class II proteins along with interleukin-1beta (IL-1beta). Subsequent study using reverse transcription-polymerase chain reaction (RT-PCR) yielded the same results with the mixed culture, but not with pure astrocytes or pure microglia. We also noticed that the GMF/virus construct infected only astrocytes but not microglia. This led us to suspect that overexpression of GMF in astrocytes resulted in the secretion of an active substance that stimulated the microglia to express MHC II and IL-1beta. We identified this substance as granulocyte-macrophage-colony stimulating factor (GM-CSF). MHC II are unique to antigen-presenting cells such as microglia and monocytes. The results suggest that GMF in astrocytes can initiate a series of events, leading to immune activation in the nervous system, and implicates its involvement in autoimmune diseases such as multiple sclerosis.

Expression of glia maturation factor during retinal development in the rat

Glia maturation factor plays important roles in the development and growth of glia and neurons. We investigated the expression and localization of Glia maturation factor-beta (GMFB) and Glia maturation factor-gamma (GMFG) in the rat retina. By northern blot analysis, both GMFB and GMFG mRNAs were detected in retina as early as embryonic day (E) 18 and persisted until adult. The expression of GMFB mRNA was always much greater than that of GMFG mRNA. In situ hybridization showed that the GMFB mRNA signal was positive in the retina from E14 till adult. Immunostaining revealed that GMFB protein was present in the inner layer of retina at E14 and P1, and in Müller cells in adult. GMFG immunoreactivity was observed only in the inner limiting membrane from E14 to P1 rat retina, and was not detected in the adult retina. These results show that GMFs are synthesized and localized mainly in Müller cells in the rat retina, and suggest that they may contribute to the development and growth of glia and neurons.

Identification and isolation of a full-length clone of mouse GMFB (Gmfb), a putative intracellular kinase regulator, differentially expressed in telencephalon

We identified new transcribed sequences, using a differential display paradigm to select genes expressed in proliferating neuroblasts from mouse telencephalon at 10 days of embryonic development. In this systematic search, we isolated a 361-bp partial 3' untranslated region (3' UTR) homologous to the 3' UTR of the human gene encoding a putative intracellular kinase regulator, glia maturation factor beta (GMFB). We cloned a full-length, 4,311-bp mouse cDNA containing a 270-bp 5' UTR, a 3,615-bp 3' UTR, and an open reading frame of 426 nucleotides encoding a putative 142 amino-acid protein, identical to human GMFB, with the exception of two amino acids. This 4.3-kb transcript is present in a variety of adult tissues and is developmentally regulated as shown by Northern blot analysis. Differential expression in telencephalon was demonstrated by quantification of radioactive relative RT-PCR and confirmed by in situ hybridization. The isolation of this full-length clone of mouse Gmfb should facilitate investigation of the intracellular mechanisms involved in the development of telencephalon.

[Review of the research of glia maturation factor and cloning of human and rat glia maturation factor-gamma (GMFG) cDNA]

Glia maturation factor-beta (GMFB) is a 17-kDa protein that was initially identified as a growth and differentiation factor acting on neurons as well as glia in the vertebrate brain. We isolated human and rat glia maturation factor-gamma (GMFG) cDNA and examined the tissue distribution of GMFG in human and rat by Northern blots and Western blots. Sequence analysis of the entire cDNA revealed an open reading frame of 426 nucleotides with a deduced protein of 142 amino acid residues. The deduced amino acid sequence of its putative product is highly homologous to GMFB. Northern blot analysis indicated that a 0.9 kb mRNA is predominantly expressed in rat thymus, testis, and spleen. In comparison with GMFB, the current study demonstrated that the tissue distribution of GMFG is not the same as that of GMFB, and GMFG is predominantly in proliferative and differentiative organs.

Transfection of C6 glioma cells with glia maturation factor upregulates brain-derived neurotrophic factor and nerve growth factor: trophic effects and protection against ethanol toxicity in cerebellar granule cells

Glial cells play active roles in neuronal survival, as well as neuroprotection against toxic insult. Recent studies suggest that the brain protein glia maturation factor (GMF) is involved in intracellular signaling in glia. This study investigated whether or not GMF plays a role in the survival-promoting and neuroprotective functions of glia. C6 glioma cells were transfected in vitro with GMF utilizing an adenovirus vector. The transfected cells overexpressed GMF intracellularly, but did not secrete the protein. The conditioned medium (CM) was obtained from the GMF-transfected cells (CM-GMF) and tested on primary neuronal cultures, consisting of cerebellar granule cells (CGC). The CGC cultures were utilized because these cultures have a background level of cell death, and the survival-promoting, i.e. neurotrophic effect, of the CM could be tested. In addition, since CGC cultures are ethanol-sensitive (ethanol enhances neuronal death), the neuroprotective effect of the CM against ethanol-induced cell death was tested also. We demonstrated that the CM-GMF had an enhanced neurotrophic effect as well as an increased neuroprotective effect against ethanol-induced cell death compared to control CM obtained from untransfected C6 cells (CM-Mock) or CM obtained from cells transfected with an unrelated gene (CM-LacZ). Because neurotrophins have trophic and protective effects, we investigated whether GMF-transfection upregulated the expression of neurotrophins in C6 cells. RT-PCR verified that GMF-transfected C6 cells had increased mRNA levels for BDNF and NGF. Immunoblotting corroborated the RT-PCR results and indicated that CM-GMF contained greater concentrations of BDNF and NGF protein compared to CM-Mock and CM-LacZ. A soluble TrkB-IgG fusion protein, which selectively binds BDNF and prevents its binding to the neuronal TrkB receptor, eliminated the neurotrophic effect of CM-GMF; whereas anti-NGF antibody was ineffective in preventing this effect, suggesting that the neurotrophic effect was due to BDNF. On the other hand, both the TrkB-IgG fusion protein and anti-NGF reduced neuroprotection, suggesting that BDNF and NGF both contribute to the neuroprotective effect of CM-GMF. In conclusion, GMF upregulates the expression of BDNF and NGF in C6 cells, and these factors exert neurotrophic and neuroprotective functions on primary neurons.

Cloning of a rat glia maturation factor-gamma (rGMFG) cDNA and expression of its mRNA and protein in rat organs

We isolated a rat glia maturation factor-gamma(rGMFG) cDNA and examined the tissue distribution of GMFG in rat by Northern and Western blot analyses. Sequence analysis of the entire cDNA revealed an open reading frame of 426 nucleotides with a deduced protein of 142 amino acid residues. The deduced amino acid sequence of the putative product is highly homologous (78.9%) to rat glia maturation factor-beta (rGMFB). Northern blot analysis indicated that a 0.9-kb mRNA is predominantly expressed in rat thymus, testis, and spleen. GMFG showed a different tissue distribution from GMFB, being present predominantly in proliferative and differentiative organs.

Activation of nuclear factor-kappaB in C6 rat glioma cells after transfection with glia maturation factor

The 17-kDa endogenous brain protein glia maturation factor (GMF) was transfected into C6 rat glioma cells using a replication-defective human adenovirus vector. The cells overexpressed GMF but did not secrete the protein into the medium. Transfection with GMF led to the activation of the transcription factor nuclear factor-kappaB (NF-kappaB), as evidenced by electrophoretic mobility shift assay of the nuclear extract, using a double-stranded oligonucleotide probe containing the consensus binding sequence for NF-kappaB. The specificity of binding was demonstrated by competition with unlabeled probe and by the nonbinding of the mutant probe. Binding was detectable as early as 3 h after transfection, peaked at 6 and 12 h, and gradually declined thereafter. The observed NF-kappaB activation was reduced by cotransfection with catalase and by the presence of high concentrations of pyruvate in the medium, suggesting the involvement of H2O2. The p38 mitogen-activated protein kinase inhibitor SB-203580 also suppressed the GMF-activated NF-kappaB, suggesting the involvement of the p38 signal transduction cascade. On the other hand, the phorbol ester phorbol 12-myristate 13-acetate activated NF-kappaB whether or not GMF was overexpressed. Along with NF-kappaB activation was an enhanced expression of superoxide dismutase (SOD), which was suppressed if NF-kappaB nuclear translocation was blocked by its specific decoy DNA, implicating NF-kappaB as an upstream mediator of this antioxidant enzyme. The p38 inhibitor SB-203580 also blocked the GMF-activated SOD. As NF-kappaB and SOD are both pro-survival signals, the results suggest a cytoprotective role for endogenous GMF in glial cells.

The human glia maturation factor-gamma gene: genomic structure and mutation analysis in gliomas with chromosome 19q loss

Human glia maturation factor-gamma (hGMF-gamma) is a recently identified gene that may be involved in glial differentiation, neural regeneration, and inhibition of tumor cell proliferation. The gene maps to the long arm of chromosome 19 at band q13.2, a region that is frequently deleted in human malignant gliomas and is thus suspected to harbor a glioma tumor suppressor gene. Given the putative role of hGMF-gamma in cell differentiation and proliferation and its localization to chromosome 19q13, this gene is an interesting candidate for the chromosome 19q glioma tumor suppressor gene. To evaluate this possibility, we determined the genomic structure of human hGMF-gamma and performed mutation screening in a series of 41 gliomas with and without allelic loss of chromosome 19q. Mutations were not detected, which suggests that hGMF-gamma is not the chromosome 19q glioma suppressor gene. However, the elucidation of the genomic structure of hGMF-gamma may prove useful in future investigations of hGMF-gamma in the normal adult and developing human nervous system.