The immediate-early gene Egr-1 regulates the activity of the thymidine kinase promoter at the G0-to-G1 transition of the cell cycle

Endothelial cell cycle state determines propensity for arterial-venous fate

During blood vessel development, endothelial cells become specified toward arterial or venous fates to generate a circulatory network that provides nutrients and oxygen to, and removes metabolic waste from, all tissues. Arterial-venous specification occurs in conjunction with suppression of endothelial cell cycle progression; however, the mechanistic role of cell cycle state is unknown. Herein, using Cdh5-CreERT2;R26FUCCI2aR reporter mice, we find that venous endothelial cells are enriched for the FUCCI-Negative state (early G1) and BMP signaling, while arterial endothelial cells are enriched for the FUCCI-Red state (late G1) and TGF-β signaling. Furthermore, early G1 state is essential for BMP4-induced venous gene expression, whereas late G1 state is essential for TGF-β1-induced arterial gene expression. Pharmacologically induced cell cycle arrest prevents arterial-venous specification defects in mice with endothelial hyperproliferation. Collectively, our results show that distinct endothelial cell cycle states provide distinct windows of opportunity for the molecular induction of arterial vs. venous fate.

Glial Cell AMPA Receptors in Nervous System Health, Injury and Disease

Glia form a central component of the nervous system whose varied activities sustain an environment that is optimised for healthy development and neuronal function. Alpha-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA)-type glutamate receptors (AMPAR) are a central mediator of glutamatergic excitatory synaptic transmission, yet they are also expressed in a wide range of glial cells where they influence a variety of important cellular functions. AMPAR enable glial cells to sense the activity of neighbouring axons and synapses, and as such many aspects of glial cell development and function are influenced by the activity of neural circuits. However, these AMPAR also render glia sensitive to elevations of the extracellular concentration of glutamate, which are associated with a broad range of pathological conditions. Excessive activation of AMPAR under these conditions may induce excitotoxic injury in glial cells, and trigger pathophysiological responses threatening other neural cells and amplifying ongoing disease processes. The aim of this review is to gather information on AMPAR function from across the broad diversity of glial cells, identify their contribution to pathophysiological processes, and highlight new areas of research whose progress may increase our understanding of nervous system dysfunction and disease.

Identification and characterization of doublesex in Bemisia tabaci

Bemisia tabaci (Gennadius) is an important agricultural pest with a worldwide distribution. Although B. tabaci is known to have a unique haplodiploid reproductive strategy, its sex determination mechanism is largely unknown. In this study, we cloned the full-length sequence of B. tabaci doublesex (Btdsx) and found that Btdsx has 28 splicing isoforms. We found two new splicing isoforms of transformer 2 (Bttra2), which encode two proteins. We also confirmed that both genes lack sex-specific splicing isoforms. Real-time quantitative PCR analysis showed that the expression of Btdsx and Bttra2 is higher in males than in females. RNA interference of Bttra2 affected the expression of Btdsx and vice versa. Furthermore, silencing of Bttra2 or Btdsx caused malformation of the male genitalia (anal style). It did not affect the female phenotype, but reduced the expression of vitellogenin gene in females. These results indicate that Btdsx is associated with sex determination in B. tabaci and that Btdsx and Bttra2 affect each other and are important for male genitalia formation. In addition to increasing our understanding of the roles of dsx and tra2 in the sex determination of B. tabaci, the results will be useful for studies of sex determination in other haplodiploid species.

Molecular targets and signaling pathways regulated by nuclear translocation of syndecan-1

Background

The cell-surface heparan sulfate proteoglycan syndecan-1 is important for tumor cell proliferation, migration, and cell cycle regulation in a broad spectrum of malignancies. Syndecan-1, however, also translocates to the cell nucleus, where it might regulate various molecular functions.

Results

We used a fibrosarcoma model to dissect the functions of syndecan-1 related to the nucleus and separate them from functions related to the cell-surface. Nuclear translocation of syndecan-1 hampered the proliferation of fibrosarcoma cells compared to the mutant lacking nuclear localization signal. The growth inhibitory effect of nuclear syndecan-1 was accompanied by significant accumulation of cells in the G0/G1 phase, which indicated a possible G1/S phase arrest.

We implemented multiple, unsupervised global transcriptome and proteome profiling approaches and combined them with functional assays to disclose the molecular mechanisms that governed nuclear translocation and its related functions. We identified genes and pathways related to the nuclear compartment with network enrichment analysis of the transcriptome and proteome. The TGF-β pathway was activated by nuclear syndecan-1, and three genes were significantly altered with the deletion of nuclear localization signal: EGR-1 (early growth response 1), NEK11 (never-in-mitosis gene a-related kinase 11), and DOCK8 (dedicator of cytokinesis 8). These candidate genes were coupled to growth and cell-cycle regulation. Nuclear translocation of syndecan-1 influenced the activity of several other transcription factors, including E2F, NFκβ, and OCT-1. The transcripts and proteins affected by syndecan-1 showed a striking overlap in their corresponding biological processes. These processes were dominated by protein phosphorylation and post-translation modifications, indicative of alterations in intracellular signaling. In addition, we identified molecules involved in the known functions of syndecan-1, including extracellular matrix organization and transmembrane transport.

Conclusion

Collectively, abrogation of nuclear translocation of syndecan-1 resulted in a set of changes clustering in distinct patterns, which highlighted the functional importance of nuclear syndecan-1 in hampering cell proliferation and the cell cycle. This study emphasizes the importance of the localization of syndecan-1 when considering its effects on tumor cell fate.

Electronic supplementary material

The online version of this article (10.1186/s12860-017-0150-z) contains supplementary material, which is available to authorized users.

Role of Bmznf-2, a Bombyx mori CCCH zinc finger gene, in masculinisation and differential splicing of Bmtra-2

Deciphering the regulatory factors involved in Bombyx mori sex determination has been a puzzle, challenging researchers for nearly a century now. The pre-mRNA of B. mori doublesex (Bmdsx), a master regulator gene of sexual differentiation, is differentially spliced, producing Bmdsxm and Bmdsxf transcripts in males and females respectively. The putative proteins encoded by these differential transcripts orchestrate antagonistic functions, which lead to sexual differentiation. A recent study in B. mori illustrated the role of a W-derived fem piRNA in conferring femaleness. In females, the fem piRNA was shown to suppress the activity of a Z-linked CCCH type zinc finger (znf) gene, Masculiniser (masc), which indirectly promotes the Bmdsxm type of splicing. In this study, we report a novel autosomal (Chr 25) CCCH type znf motif encoding gene Bmznf-2 as one of the potential factors in the Bmdsx sex specific differential splicing, and we also provide insights into its role in the alternative splicing of Bmtra2 by using ovary derived BmN cells. Over-expression of Bmznf-2 induced Bmdsxm type of splicing (masculinisation) with a correspondingly reduced expression of Bmdsxf type isoform in BmN cells. Further, the site-directed mutational studies targeting the tandem CCCH znf motifs revealed their indispensability in the observed phenotype of masculinisation. Additionally, the dual luciferase assays in BmN cells using 5' UTR region of the Bmznf-2 strongly implied the existence of a translational repression over this gene. From these findings, we propose Bmznf-2 to be one of the potential factors of masculinisation similar to Masc. From the growing number of Bmdsx splicing regulators, we assume that the sex determination cascade of B. mori is quite intricate in nature; hence, it has to be further investigated for its comprehensive understanding.

P2Y2 purinergic receptor activation is essential for efficient hepatocyte proliferation in response to partial hepatectomy

Extracellular nucleotides via activation of P2 purinergic receptors influence hepatocyte proliferation and liver regeneration in response to 70% partial hepatectomy (PH). Adult hepatocytes express multiple P2Y (G protein-coupled) and P2X (ligand-gated ion channels) purinergic receptor subtypes. However, the identity of key receptor subtype(s) important for efficient hepatocyte proliferation in regenerating livers remains unknown. To evaluate the impact of P2Y2 purinergic receptor-mediated signaling on hepatocyte proliferation in regenerating livers, wild-type (WT) and P2Y2 purinergic receptor knockout (P2Y2-/-) mice were subjected to 70% PH. Liver tissues were analyzed for activation of early events critical for hepatocyte priming and subsequent cell cycle progression. Our findings suggest that early activation of p42/44 ERK MAPK (5 min), early growth response-1 (Egr-1) and activator protein-1 (AP-1) DNA-binding activity (30 min), and subsequent hepatocyte proliferation (24-72 h) in response to 70% PH were impaired in P2Y2-/- mice. Interestingly, early induction of cytokines (TNF-α, IL-6) and cytokine-mediated signaling (NF-κB, STAT-3) were intact in P2Y2-/- remnant livers, uncovering the importance of cytokine-independent and nucleotide-dependent early priming events critical for subsequent hepatocyte proliferation in regenerating livers. Hepatocytes isolated from the WT and P2Y2-/- mice were treated with ATP or ATPγS for 5-120 min and 12-24 h. Extracellular ATP alone, via activation of P2Y2 purinergic receptors, was sufficient to induce ERK phosphorylation, Egr-1 protein expression, and key cyclins and cell cycle progression of hepatocytes in vitro. Collectively, these findings highlight the functional significance of P2Y2 purinergic receptor activation for efficient hepatocyte priming and proliferation in response to PH.

The serine protease inhibitor elafin maintains normal growth control by opposing the mitogenic effects of neutrophil elastase

The serine protease inhibitor, elafin, is a critical component of the epithelial barrier against neutrophil elastase (NE). Elafin is downregulated in the majority of breast cancer cell lines compared to normal human mammary epithelial cells (HMECs). Here, we evaluated the role of elafin and NE on proliferation and tumorigenesis. Elafin is induced in growth factor deprived HMECs as they enter a quiescent (G0) state, suggesting that elafin is a counterbalance against the mitogenic effects of NE in G0 HMECs. Stable knockdown of elafin compromises the ability of HMECs to maintain G0-arrest during long-term growth factor deprivation; this effect can be reversed by re-expression of wild-type elafin, but not elafin-M25G lacking protease inhibitory function. These results suggest that NE, which is largely contributed by activated neutrophils in the tumor microenvironment, may be negatively regulating the ability of elafin to arrest cells in G0. In fact when purified NE was added to elafin knockdown HMECs, these cells demonstrated greater sensitivity to the growth promoting effects of purified NE. Activation of ERK signaling, downstream of toll-like receptor 4, was essential to the mitogenic effect of NE on HMECs. These findings were next translated to patient samples, and immunohistochemical analysis of normal breast tissue revealed robust elafin expression in the mammary epithelium; however, elafin expression was dramatically downregulated in a significant proportion of human breast tumor specimens. The loss of elafin expression during breast cancer progression may promote tumor growth as a consequence of increased NE-activity. To address the role of NE in mammary tumorigenesis, we next examined if deregulated NE-activity enhances mammary tumor growth. NE knockout in the C3(1)TAg mouse model of mammary tumorigenesis suppressed proliferation and reduced the kinetics of tumor growth. Overall, the imbalance between NE and its inhibitors, such as elafin, presents an important therapeutic target in breast cancer.

MicroRNA-gene association as a prognostic biomarker in cancer exposes disease mechanisms

The transcriptional networks that regulate gene expression and modifications to this network are at the core of the cancer phenotype. MicroRNAs, a well-studied species of small non-coding RNA molecules, have been shown to have a central role in regulating gene expression as part of this transcriptional network. Further, microRNA deregulation is associated with cancer development and with tumor progression. Glioblastoma Multiform (GBM) is the most common, aggressive and malignant primary tumor of the brain and is associated with one of the worst 5-year survival rates among all human cancers. To study the transcriptional network and its modifications in GBM, we utilized gene expression, microRNA sequencing, whole genome sequencing and clinical data from hundreds of patients from different datasets. Using these data and a novel microRNA-gene association approach we introduce, we have identified unique microRNAs and their associated genes. This unique behavior is composed of the ability of the quantifiable association of the microRNA and the gene expression levels, which we show stratify patients into clinical subgroups of high statistical significance. Importantly, this stratification goes unobserved by other methods and is not affiliated by other subsets or phenotypes within the data. To investigate the robustness of the introduced approach, we demonstrate, in unrelated datasets, robustness of findings. Among the set of identified microRNA-gene associations, we closely study the example of MAF and hsa-miR-330-3p, and show how their co-behavior stratifies patients into prognosis clinical groups and how whole genome sequences tells us more about a specific genomic variation as a possible basis for patient variances. We argue that these identified associations may indicate previously unexplored specific disease control mechanisms and may be used as basis for further study and for possible therapeutic intervention.

Despite major progress and improved understanding of Glioblastoma Multiforme, the disease is still associated with poor prognosis. The identification of genomic regulatory mechanisms, their affiliation with clinical outcome and the association between specific modifications in genome sequence that can explain gain and loss of such regulatory activity, combine to suggest specific disease mechanisms and possible means of intervention in the course of the disease. We report here a method and its implementation in exposing possible regulatory mechanisms in GBM. At the core of this method is the employment of associations between micro RNAs and genes as a quantifiable metric. Identification of these associations and their affiliation with clinical features, combined with the availability of whole genome sequences, brings forward specific micro RNAs and their associated genes. Affiliation of specific genomic sequences with clinical outcome thus translates personal genomics into tumor relevant decision-making.

Phosphorylation of histone H3 at serine 10 has an essential role in arsenite-induced expression of FOS, EGR1 and IL8 mRNA in cultured human cell lines

Trivalent inorganic arsenite [iAs(III)] is known to alter the expression of a number of genes associated with transcription and cell proliferation, which was thought to be one of the possible mechanisms of arsenical carcinogenesis. However, the detailed mechanisms underlying iAs(III) induction of changes in gene expression are not fully understood. Here we examine the role of histone H3 phosphorylation at serine 10 (Ser(10) ) in gene regulation when the cells were treated with iAs(III). Among the 34 genes tested, iAs(III) induced mRNA expression of JUN, FOS, EGR1, HMOX1, HSPA1A, IL8, GADD45A, GADD45B and GADD153. Phosphorylation of histone H3 Ser(10) was induced by iAs(III) in interphase cells, and was effectively blocked by the ERKs pathway inhibitor (U0126). U0126 treatment significantly reduced constitutive mRNA expression of FOS and EGR1, and dramatically suppressed the induction of FOS, EGR1 and IL8 mRNA in iAs(III)-treated cells. The other genes, which were induced by iAs(III), were not affected by U0126 treatment. When the histone H3 nonphosphorylatable mutant of serine 10 (S10A) was overexpressed in cells, iAs(III) induction of FOS, EGR1and IL8 expression was significantly decreased as compared with wild-type cells. The other genes induced by iAs(III) were not changed in S10A cells nor by U0126 treatment. In addition, S10A cells were more resistant to iAs(III) cytotoxicity. These results indicated that the phosphorylation of histone H3 at Ser(10) through the ERKs pathway in interphase cells is an important regulatory event for iAs(III)-mediated gene expression. Aberrant gene expression seems to be an important cause of cytotoxicity and may have some relation to iAs(III) carcinogenicity.

Krox20/EGR2 deficiency accelerates cell growth and differentiation in the monocytic lineage and decreases bone mass

Krox20/EGR2, one of the 4 early growth response genes, is a highly conserved transcription factor implicated in hindbrain development, peripheral nerve myelination, tumor suppression, and monocyte/macrophage cell fate determination. Here, we established a novel role for Krox20 in postnatal skeletal metabolism. Microcomputed tomographic analysis of 4- and 8-week-old mice revealed a low bone mass phenotype (LBM) in both the distal femur and the vertebra of Krox20(+/-) mice. This was attributable to accelerated bone resorption as demonstrated in vivo by increased osteoclast number and serum C-terminal telopeptides, a marker for collagen degradation. Krox20 haploinsufficiency did not reduce bone formation in vivo, nor did it compromise osteoblast differentiation in vitro. In contrast, growth and differentiation were significantly stimulated in preosteoclast cultures derived from Krox20(+/-) splenocytes, suggesting that the LBM is attributable to Krox20 haploinsufficiency in the monocytic lineage. Furthermore, Krox20 silencing in preosteoclasts increased cFms expression and response to macrophage colony-stimulating factor, leading to a cell-autonomous stimulation of cell-cycle progression. Our data indicate that the antimitogenic role of Krox20 in preosteoclasts is the predominant mechanism underlying the LBM phenotype of Krox20-deficient mice. Stimulation of Krox20 expression in preosteoclasts may present a viable therapeutic strategy for high-turnover osteoporosis.

HGF-promoted motility in primary human melanocytes depends on CD44v6 regulated via NF-kappa B, Egr-1, and C/EBP-beta

The regulation of CD44v6, a variant of the CD44 family of glycosylated adhesion molecules, through hepatocyte growth factor (HGF) has implications for motility in primary human melanocytes. We show that exposure of primary human melanocytes to HGF results in an increase of CD44v6 expression. Immunostaining of melanocytic lesions revealed low cytoplasmic positivity of CD44v6 in some nevi but high membranous expression in primary cutaneous melanomas, and cutaneous and lymph node metastases. HGF-dependent CD44v6 regulation in melanocytes is NF-kappaB dependent because BAY 11-7082, an inhibitor of NF-kappaB activation, but not interference with the mitogen-activated protein kinase or phosphatidylinositol 3-kinase cascade, antagonized HGF-induced CD44v6 expression. NF-kappaB-mediated transcriptional regulation of CD44v6 involves the transcription factors Egr-1 and CCAAT enhancer-binding protein-beta (C/EBP-beta). In gel shift assays, the initial binding of p100/p52 NF-kappaB, C/EBP-beta, and Egr-1 to the CD44 promoter experienced reshuffling toward increased affinity of C/EBP-beta after HGF stimulation. A blocking antibody to CD44v6 decreased HGF-induced c-Met phosphorylation as well as enhanced random- and site-directed migration. Our data show that HGF-induced motility in primary human melanocytes depends on c-Met-CD44v6 interaction, and that HGF-enhanced CD44v6 expression is required for motility and transcriptional upregulation of CD44v6, presumably mediated through a complex comprising NF-kappaB/C/EBP-beta and Egr-1.

Gene expression analysis of HCT116 colon tumor-derived cells treated with the polyamine analog PG-11047

BACKGROUND

The conformationally restricted polyamine analog PG-11047 has significant growth inhibitory activity against prostate and lung cancer cell lines and is currently under evaluation in several clinical trials, both alone and in combination with other drugs, for the treatment of relapsed or refractory cancer. The objective of this study was to identify the molecular signature of genes responsive to PG-11047 treatment and the biochemical effects of this drug in the HCT116 colon cancer cell line.

MATERIALS AND METHODS

Gene expression analysis was performed using Affymetrix GeneChip human genome U133 Plus 2.0 arrays. Changes in protein expression were evaluated using 2D polyacrylamide gels followed by LCMS/MS.

RESULTS

Treatment of cells with PG-11047 at concentrations ranging from 0.1 to 10 microM caused inhibition of cell growth. The activity of PG-11047 was found to correlate with its transcriptional effects on cell cycle control, focal adhesion, adherent and gap junction genes, MAPK-, Wnt- and, TGF-beta signaling pathways, transport and DNA/RNA transcription factor genes. PG-11047 caused depletion of polyamine pools. Proteomics analysis showed that PG-11047 restricts the modification of eukaryotic translation initiation factor 5A (eIF5A), resulting in suppression of general protein synthesis in PG-11047-treated cells.

CONCLUSION

These data show that PG-11047 has a broad spectrum of anticancer activity in colon cancer cells.

Early biomarkers and potential mediators of ventilation-induced lung injury in very preterm lambs

Background

Bronchopulmonary dysplasia (BPD) is closely associated with ventilator-induced lung injury (VILI) in very preterm infants. The greatest risk of VILI may be in the immediate period after birth, when the lungs are surfactant deficient, still partially filled with liquid and not uniformly aerated. However, there have been very few studies that have examined this immediate post-birth period and identified the initial injury-related pathways that are activated. We aimed to determine if the early response genes; connective tissue growth factor (CTGF), cysteine rich-61 (CYR61) and early growth response 1 (EGR1), were rapidly induced by VILI in preterm lambs and whether ventilation with different tidal volumes caused different inflammatory cytokine and early response gene expression.

Methods

To identify early markers of VILI, preterm lambs (132 d gestational age; GA, term ~147 d) were resuscitated with an injurious ventilation strategy (V_T 20 mL/kg for 15 min) then gently ventilated (5 mL/kg) for 15, 30, 60 or 120 min (n = 4 in each). To determine if early response genes and inflammatory cytokines were differentially regulated by different ventilation strategies, separate groups of preterm lambs (125 d GA; n = 5 in each) were ventilated from birth with a V_T of 5 (VG5) or 10 mL/kg (VG10) for 135 minutes. Lung gene expression levels were compared to levels prior to ventilation in age-matched control fetuses.

Results

CTGF, CYR61 and EGR1 lung mRNA levels were increased ~25, 50 and 120-fold respectively (p < 0.05), within 30 minutes of injurious ventilation. VG5 and VG10 caused significant increases in CTGF, CYR61, EGR1, IL1-β, IL-6 and IL-8 mRNA levels compared to control levels. CTGF, CYR61, IL-6 and IL-8 expression levels were higher in VG10 than VG5 lambs; although only the IL-6 and CYR61 mRNA levels reached significance.

Conclusion

CTGF, CYR61 and EGR1 may be novel early markers of lung injury and mechanical ventilation from birth using relatively low tidal volumes may be less injurious than using higher tidal volumes.

Mycophenolic acid inhibits the autocrine PDGF-B synthesis and PDGF-BB-induced mRNA expression of Egr-1 in rat mesangial cells

BACKGROUND

Uncontrolled mesangial cell (MC) proliferation within the context of glomerular disease contributes to the development of glomerulosclerosis. Mesangial autocrine growth factor stimulation has been described as a pathogenic factor. We investigated the effects of mycophenolic acid (MPA), the active metabolite of the immunosuppressant mycophenolate mofetil (MMF), on proliferation factors of cultured rat MCs. MPA was tested on the expression of platelet-derived growth factor-B (PDGF-B) and its receptor beta (PDGFR-beta), the immediate early gene (IEG) c-fos and the early growth response gene-1 (Egr-1), and AP-1 activation.

METHODS

Growth-arrested rat MCs were stimulated with 10% fetal calf serum (FCS) or 10-25 ng/ml platelet-derived growth factor-BB (PDGF-BB) in the presence or absence of MPA (0.019-10 microM) with or without guanosine (100 microM). MC proliferation was quantified by 5-bromo-2'-deoxyuridine (BrdU) incorporation and direct cell counting. Cytotoxicity of MPA was evaluated using the MTT and LDH tests. Protein expression of PDGF-B and its receptor PDGFR-beta was quantified by western blot analysis. The effect of MPA on gene expression of PDGF-B, Egr-1 and c-fos was determined by the reverse transcriptase-polymerase chain reaction (RT-PCR). AP-1 activation was analysed by an electrophoretic mobility shift assay (EMSA).

RESULTS

Exposure of MCs to MPA caused a concentration-dependent inhibition of FCS-induced cell proliferation (cell number increase) with an IC50 of 0.44 +/- 0.03 microM and DNA synthesis with an IC50 of 0.52 +/- 0.02 microM without cell cytotoxicity in the therapeutic range. MPA decreased the PDGF-B protein expression and mRNA self-induction of PDGF-B but did not alter the protein expression of PDGFR-beta. MPA strongly inhibited the PDGF-BB-induced mRNA expression of Egr-1 decreasing to 7.6 +/- 2.5% after 30 min (P <or= 0.001) and to 4.7 +/- 3.1% after 1 h (P <or= 0.05), both being compared to the maximal expression induced by PDGF-BB. PDGF-BB-induced c-fos expression under MPA was unchanged after 30 min and decreased to 57 +/- 26% after 1 h (n.s.). MPA treatment did not affect PDGF-BB-induced AP-1 activity determined after 1 h and 2 h. The inhibitory MPA effect on PDGF-BB-induced PDGF-B expression was not significantly restored by guanosine (56 +/- 18% versus 32 +/- 17% after 2 h, n.s.), and MPA inhibition of PDGF-BB-induced Egr-1 expression was not reversed by exogenous guanosine.

CONCLUSIONS

Treatment of cultured MCs with MPA inhibits MC proliferation correlating with a downregulation of the PDGF-B gene and protein expression and a suppression of Egr-1 mRNA expression. Since exogenous guanosine was not able to reverse the inhibitory MPA effect on PDGF-B and Egr-1 expression, we conclude that the antiproliferative effect of MPA on MCs may not solely depend on dGTP depletion but on a specific interference with the autocrine PDGF-B synthesis and Egr-1 expression of MCs.

hEGR1 is induced by EGF, inhibited by gefitinib in bladder cell lines and related to EGF receptor levels in bladder tumours

The effect of EGF and gefitinib on two EGFR-positive human bladder cancer cell lines has been investigated using array-based gene expression profiling. The most prominent transcript, increased up to 6.7-fold by EGF compared with controls in RT112 cells, was human early growth response protein 1 (hEGR1). This induction was prevented by gefitinib. The hEGR1 mRNA in EGF-treated samples was reduced in the presence of gefitinib, as was hEGR1 protein in cell lysates. In the RT4 cells, hEGR1 expression was halved in the presence of EGF and gefitinib in combination. In bladder tumour samples, there was a significant correlation between hEGR1 mRNA detected by RT-PCR and EGFR detected by ligand binding, (P=0.042). The induction by EGF of the hEGR1 gene, mRNA and protein in RT112 cells, and its inhibition by gefitinib, together with the detection of hEGR1 mRNA in bladder tumours, suggests that hEGR1 may be important in the EGFR growth-signalling pathway in bladder cancer and should be further investigated for its prognostic significance and as a potential therapeutic target.

Comparative gene expression profiling reveals partially overlapping but distinct genomic actions of different antiestrogens in human breast cancer cells

Antiestrogens used for breast cancer (BC) treatment differ among each other for the ability to affect estrogen receptor (ER) activity and thereby inhibit hormone-responsive cell functions and viability. We used high-density cDNA microarrays for a comprehensive definition of the gene pathways affected by 17beta-estradiol (E2), ICI 182,780 (ICI), 4OH-tamoxifen (Tamoxifen), and raloxifene (RAL) in ER-positive ZR-75.1 cells, a suitable model to investigate estrogen and antiestrogen actions in hormone-responsive BC. The expression of 601 genes was significantly affected by E2 in these cells; in silico analysis reveals that 86 among them include one or more potential ER binding site within or near the promoter and that the binding site signatures for E2F-1, NF-Y, and NRF-1 transcription factors are significantly enriched in the promoters of genes induced by estrogen treatment, while those for CAC-binding protein and LF-A1 in those repressed by the hormone, pointing to novel transcriptional effectors of secondary responses to estrogen in BC cells. Interestingly, expression of 176 E2-regulated mRNAs was unaffected by any of the antiestrogens tested, despite the fact that under the same conditions the transcriptional and cell cycle stimulatory activities of ER were inhibited. On the other hand, of 373 antiestrogen-responsive genes identified here, 52 were unresponsive to estrogen and 25% responded specifically to only one of the compounds tested, revealing non-overlapping and clearly distinguishable effects of the different antiestrogens in BC cells. As some of these differences reflect specificities of the mechanism of action of the antiestrogens tested, we propose to exploit this gene set for characterization of novel hormonal antagonists and selective estrogen receptor modulators (SERMs) and as a tool for testing new associations of antiestrogens, more effective against BC.

Gene expression profiling during increased fetal lung expansion identifies genes likely to regulate development of the distal airways

Growth and development of the fetal lungs is critically dependent on the degree to which the lungs are expanded by liquid; increases in fetal lung expansion accelerate lung growth, whereas reductions in lung expansion cause lung growth to cease. The mechanisms mediating expansion-induced lung growth are unknown but likely include alterations in the expression of genes that regulate lung cell proliferation. Our aim was to isolate and identify genes that are up- or downregulated by increased fetal lung expansion. In chronically catheterized fetal sheep at 126 days gestational age (GA), the left lung was expanded for 36 h, while the right lung remained at a control level of expansion. Subtraction hybridization was used to isolate genes differentially expressed between the left and right lungs. Screening of ∼6,000 clones identified 1,138 and 118 cDNA fragments that were up- and downregulated by increased lung expansion, respectively. Northern blot analyses in separate groups of control fetuses and fetuses exposed to increased lung expansion were used to verify differential expression. Increased fetal lung expansion upregulated heat shock protein 47, thrombospondin-1, TROP2, tropoelastin, and tubulin-α3 in fetal lung tissue by ∼200–300%; connective tissue growth factor and cysteine-rich angiogenic inducer 61 were increased by 20–30%. Genes downregulated by increased fetal lung expansion included CCSP-related protein-1, elongation factor-1α and vitamin D3upregulated protein 1. We conclude that an increase in fetal lung expansion differentially regulates the expression of numerous genes in lung tissue, many of which have important putative roles in lung development, while the functions of others are currently unknown.

Basic calcium phosphate crystal-induced Egr-1 expression stimulates mitogenesis in human fibroblasts

Previously, we have reported that basic calcium phosphate (BCP) crystals stimulate mitogenesis and synthesis of matrix metalloproteinases in cultured human foreskin and synovial fibroblasts. However, the detailed mechanisms involved are still unclear. In the present study, using RT-PCR and Egr-1 promoter analysis we showed that BCP crystals could stimulate early growth response gene Egr-1 transcription through a PKCalpha-dependent p44/p42 MAPK pathway. Using a retrovirus gene expression system (Clontech) to overexpress Egr-1 in human fibroblast BJ-1 cells resulted in promotion of mitogenesis measured either by MTT cell proliferation analysis or by direct cell counting. The results demonstrate that Egr-1 may play a key role in mediating BCP crystal-induced synovial fibroblast mitogenesis.

Regulation of expression of the early growth response gene-1 (EGR-1) in malignant and benign cells of the prostate

BACKGROUND

Expression of the early growth response gene-1 (EGR-1) is elevated in prostate cancer and correlates with tumor progression. This study provides insight into the mechanism(s) that regulate EGR-1 expression and activity in malignant and benign prostate cells.

METHODS

Western blotting and in vitro pulse labeling were used to examine EGR-1 protein levels and half-life in malignant (PC-3) and benign (BPH-1) prostate cell lines. EGR-1 functional ability was assessed by transient transfections with an EGR-1 promoter driven luciferase plasmid and electromobility shift assays (EMSAs) to assess DNA binding of the EGR-1 protein. Protein levels of casein kinase II (CKII) were evaluated by Western blotting.

RESULTS

PC-3 cells maintain high steady-state levels of EGR-1 protein, in part due to a longer half-life of EGR-1 protein. BPH-1 cells responded to mitogenic stimuli with increased EGR-1 protein levels, and enhanced transcriptional activity. In contrast, PC-3 cells showed no response to stimuli. DNA binding of EGR-1 was higher in BPH-1 cells than in PC-3 cells. This appears to be related to the heavily phosphorylated state of EGR-1 in PC-3 cells which is correlated with increased levels of CKII found in these cells.

CONCLUSIONS

PC-3 cells maintain a long lasting, heavily phosphorylated pool of EGR-1, which binds poorly to DNA and responds poorly to mitogenic stimulus. BPH-1 cells, in contrast, maintain a more responsive, less phosphorylated EGR-1 pool. These findings suggest that EGR-1 expression and activity is differentially regulated in PC-3 and BPH-1 cell lines.

A gene for neuronal plasticity in the mammalian brain: Zif268/Egr-1/NGFI-A/Krox-24/TIS8/ZENK?

Zif268 is a transcription regulatory protein, the product of an immediate early gene. Zif268 was originally described as inducible in cell cultures; however, it was later shown to be activated by a variety of stimuli, including ongoing synaptic activity in the adult brain. Recently, mice with experimentally mutated zif268 gene have been obtained and employed in neurobiological research. In this review we present a critical overview of Zif268 expression patterns in the naive brain and following neuronal stimulation as well as functional data with Zif268 mutants. In conclusion, we suggest that Zif268 expression and function should be considered in a context of neuronal activity that is tightly linked to neuronal plasticity.

ZNF411, a novel KRAB-containing zinc-finger protein, suppresses MAP kinase signaling pathway

Cardiac differentiation involves a cascade of coordinated gene expression that regulates cell proliferation and matrix protein formation in a defined temporo-spatial manner. The zinc-finger-containing transcription factor has been implicated as a critical regulator of multiple cardiac-expressed genes as well as a regulator of inducible gene expression in response to hypertrophic stimulation. Mitogen-activated protein kinase (MAPK) signal transduction pathways are among the most widespread mechanisms of eukaryotic cell regulation. The MAPKs function inside the nucleus and target transcription factors that are prebound to DNA. Many transcription factors are probably important MAPK targets. Here, we have cloned a new zinc-finger gene named ZNF411 using degenerate primers from an early embryo heart cDNA library, which mapped to 19p13.11. The ZNF411 gene consists of 2360 nucleotides and encodes a protein of 499 amino acids with an amino-terminal KRAB domain and eleven carboxy-terminal C2H2 zinc-finger units. Northern blot analysis indicates that a 2.4 kb transcript specific for ZNF411 is expressed in heart, skeletal muscle, and placenta at adult stage and is expressed in most of the examined embryonic tissues, especially at a higher level in skeletal muscle, heart, and pancreas. ZNF411 protein distributes evenly in nuclei when overexpressed in the cells. Reporter gene assays show that ZNF411 is a transcriptional repressor and overexpression of ZNF411 in the COS-7 cells inhibits the transcriptional activities of AP-1 and SRE. These results indicate that ZNF411 is a member of the zinc-finger transcription factor family and may be involved in the heart development, and it probably works as a negative regulator in MAPK signaling pathway.

Developmental regulation of galactokinase in suckling mouse liver by the Egr-1 transcription factor

The numerous changes in metabolic pathways that accompany liver development entail associated changes in gene expression. Egr-1 is a zinc-finger transcription factor that regulates genes involved in cellular growth, differentiation, stress response, and apoptosis in many cell types. Egr-1 is induced in liver regeneration in rodents, but its role in normal hepatocyte function has not been characterized. We examined the developmental expression of Egr-1 in mouse liver and found that its expression increased during the suckling period. In screening the sequences of the genes involved in lactose assimilation, we found that the galactokinase gene Glk contains four potential Egr-1 binding sites in its proximal promoter. A minimal promoter of 155 nucleotides encompassing the four Egr-1 sites exhibited activity in hepatoma cell lines by transient transfection assays. Moreover, co-transfection of an Egr-1 expression plasmid increased promoter activity. Finally, mutations introduced into three of the four Egr-1 binding sites decreased activity, whereas mutation of the remaining site increased promoter activity. These data tie Egr-1 and galactokinase together in a developmentally regulated chain to prepare the neonate for suckling.

Antisense to the early growth response-1 gene (Egr-1) inhibits prostate tumor development in TRAMP mice

Egr-1 is a transcription factor induced by stress or injury, mitogens, and differentiation factors. Egr-1 regulates the expression of genes involved in growth control or survival. Expression of Egr-1 results in either promotion or regression of cell proliferation, depending on cell type and environment. Egr-1 acts as a tumor suppressor in many cell types and loss of Egr-1 has been proposed to contribute to cancer progression. There is strong new evidence however suggesting that Egr-1 overexpression is involved in prostate cancer progression. For example, Egr-1 expression levels are elevated in human prostate carcinomas in proportion to grade and stage. Furthermore, prostate cancer progression was significantly delayed in two models of prostate cancer mice lacking Egr-1. Our objective in the present study is to test whether inhibition of Egr-1 function would block cell proliferation and inhibit the transformed phenotype of prostate cancer cells in vitro and in vivo. We describe the development of high affinity and high specificity antisense oligonucleotides that efficiently inhibit Egr-1 expression. We show that inhibition of Egr-1 expression in mouse or human prostate cancer cells decreased proliferation and reduced the capacity of these cells to form colonies and to grow in soft agar. Conversely, stable expression of Egr-1 in normal human prostate epithelial 267B1 cells promoted transformation. In TRAMP mice, treatment with Egr-1 antisense oligonucleotides delayed the occurrence of prostate tumors. Importantly, Egr-1 antisense showed little or no toxicity when injected into animals. Finally, we identified a few genes such as cyclin D2, p19ink4d, and Fas that are directly regulated by Egr-1 in prostate cancer cells and that control cell cycle and survival.

Opposite effects of inhibitors of mitogen-activated protein kinase pathways on the egr-1 and β-globin expression in erythropoietin-responsive murine erythroleukemia cells

The effect of erythropoietin (Epo) on the expression of mitogen-activated protein kinase (MAPK) target genes egr-1 and c-fos was investigated in Epo-responsive murine erythroblastic cell line ELM-I-1. Epo induced a transient rise in egr-1 mRNA without a similar effect on c-fos expression. The induction of egr-1 correlated with a rapid ERK1/2 phosphorylation and was prevented with MEK1/2 inhibitors PD 98059 and UO126. The p38 inhibitor SB 203580 enhanced ERK1/2 phosphorylation and egr-1 mRNA levels. Longer incubations of ELM-I-1 cells with Epo revealed a second later phase of increase in egr-1 expression which was also prevented by MEK1/2 inhibitors, whereas SB 203580 had a stimulatory effect. In contrast, the beta-globin mRNA production was enhanced in the presence of PD 98059 and UO126 and reduced by SB 203580. The results suggest a regulatory role of egr-1 expression in Epo signal transduction and provide pharmacological evidence for the negative modulation of differentiation-specific gene expression by the ERK1/2 pathway in murine erythroleukemia cells.

The Cytoskeleton Differentially Localizes the Early Growth Response Gene-1 Protein in Cancer and Benign Cells of the Prostate

Prostate cancer is the most prevalent malignancy and the second leading cause of cancer mortality in men. Early growth response gene-1 (EGR-1) plays a crucial role in the development and progression of prostate cancer. The presented data show that EGR-1 differs in cellular localization in benign cells compared with malignant prostate cells and that this localization is critical for the transcriptional activation of EGR-1-dependent genes. Immunohistochemistry of human prostate cancer specimens demonstrated higher levels of EGR-1 in malignant cells located predominantly in the cytoplasm, whereas benign cells contained lower levels of EGR-1 located predominantly in the nucleus. Benign prostate cells responded to mitogens in vitro, with increased levels of EGR-1, rapid nuclear translocation, and enhanced transcriptional activity, whereas malignant prostate cells did not exhibit the same responses, and the protein remained in the cytoplasm. The central aspect of this difference is the association of EGR-1 with microtubules, which is exclusive to the benign cells of the prostate and is requisite for the nuclear translocation and transcriptional activity of EGR-1. Our in vitro data demonstrate that the differences in EGR-1 between benign and malignant prostate cells extend beyond cellular levels, which was confirmed by immunohistochemistry in human tissues. Thus, we add the novel concept that microtubules regulate EGR-1 localization in benign prostate cells but not in malignant prostate cells.

Inhibition of Egr-1 expression reverses transformation of prostate cancer cells in vitro and in vivo

Transcription factor early growth response-1 (Egr-1) is a crucial regulator of cell growth, differentiation and survival. Several observations suggest that Egr-1 is growth promoting in prostate cancer cells and that blocking its function may impede cancer progression. To test this hypothesis, we developed phosphorothioate antisense oligonucleotides that efficiently inhibit Egr-1 expression without altering the expression of other family members Egr-2, Egr-3 and Egr-4. In TRAMP mouse-derived prostate cancer cell lines, our optimal antisense oligonucleotide decreased the expression of the Egr-1 target gene transforming growth factor-beta1 whereas a control oligonucleotide had no effect, indicating that the antisense blocked Egr-1 function as a transcription factor. The antisense oligonucleotide deregulated cell cycle progression and decreased proliferation of the three TRAMP cell lines by an average of 54+/-3%. Both colony formation and growth in soft agar were inhibited by the antisense oligonucleotide. When TRAMP mice were treated systemically for 10 weeks, the incidence of palpable tumors at 32 weeks of age in untreated mice or mice injected with the control scramble oligonucleotide was 87%, whereas incidence of tumors in antisense-Egr-1-treated mice was significantly reduced to 37% (P=0.026). Thus, Egr-1 plays a functional role in the transformed phenotype and may represent a valid target for prostate cancer therapy.

Stimulation of the murine type II transforming growth factor-beta receptor promoter by the transcription factor Egr-1

Previous studies have demonstrated that differentiation of murine embryonal carcinoma (EC) cells leads to the appearance of high affinity receptors for transforming growth factor-beta (TGF-beta). Subsequently, it was demonstrated that differentiation of F9 EC cells leads to increases in the transcription of the type II TGF-beta-receptor gene (TbetaR-II) and leads to significant increases in the steady-state levels of TbetaR-II mRNA. Analysis of the human TbetaR-II promoter in F9-differentiated cells identified several cis-regulatory elements that influence the activity of the promoter, including a CRE/ATF site and a CCAAT box motif. In the work described in this report, we focused on the effect of the transcription factor Egr-1 on the murine TbetaR-II promoter. We have identified an Egr-1 response-element approximately 150 bp upstream of the major transcription start site of the murine TbetaR-II gene. We demonstrate by electrophoretic mobility shift analysis (EMSA) that this cis-regulatory element binds Egr-1, and we demonstrate that disruption of this site eliminates the response to Egr-1. As part of this analysis, we also examined the effect of Egr-1 on human TbetaR-II promoter. In contrast to a previous report, which reported that Egr-1 inhibits expression of human TbetaR-II promoter/reporter gene constructs, we did not observe an inhibitory effect of Egr-1 that was specific for the human TbetaR-II promoter. Taken together, the findings described in this report identify important differences between the human and the murine TbetaR-II promoter, and our findings identify an Egr-1 cis-regulatory element that is capable of stimulating the activity of the murine TbetaR-II promoter.

Ionizing radiation down-regulates p53 protein in primary Egr-1-/- mouse embryonic fibroblast cells causing enhanced resistance to apoptosis

In this study, we sought to investigate the mechanism of the proapoptotic function of Egr-1 in relation to p53 status in normal isogenic cell backgrounds by using primary MEF cells established from homozygous (Egr-1(-/-)) and heterozygous (Egr-1(+/-)) Egr-1 knock-out mice. Ionizing radiation caused significantly enhanced apoptosis in Egr-1(+/-) cells (22.8%; p < 0.0001) when compared with Egr-1(-/-) cells (3.5%). Radiation elevated p53 protein in Egr-1(+/-) cells in 3-6 h. However, in Egr-1(-/-) cells, the p53 protein was down-regulated 1 h after radiation and was completely degraded at the later time points. Radiation elevated the p53-CAT activity in Egr-1(+/-) cells but not in Egr-1(-/-) cells. Interestingly, transient overexpression of EGR-1 in p53(-/-) MEF cells caused marginal induction of radiation-induced apoptosis when compared with p53(+/+) MEF cells. Together, these results indicate that Egr-1 may transregulate p53, and both EGR-1 and p53 functions are essential to mediate radiation-induced apoptosis. Rb, an Egr-1 target gene, forms a trimeric complex with p53 and MDM2 to prevent MDM2-mediated p53 degradation. Low levels of Rb including hypophosphorylated forms were observed in Egr-1(-/-) MEF cells before and after radiation when compared with the levels observed in Egr-1(+/-) cells. Elevated amounts of the p53-MDM2 complex and low amounts of Rb-MDM-2 complex were observed in Egr-1(-/-) cells after radiation. Because of a reduction in Rb binding to MDM2 and an increase in MDM2 binding with p53, p53 is directly degraded by MDM2, and this leads to inactivation of the p53-mediated apoptotic pathway in Egr-1(-/-) MEF cells. Thus, the proapoptotic function of Egr-1 may involve the mediation of Rb protein that is essential to overcome the antiapoptotic function of MDM2 on p53.

Elevated Egr-1 in human atherosclerotic cells transcriptionally represses the transforming growth factor-beta type II receptor

Atherosclerotic lesions may progress due to a "failure to die" by vascular repair cells. Egr-1, a zinc finger transcription factor, is elevated more than 5-fold in human carotid lesions relative to the adjacent tunica media. Lesion cells in vitro also express 2-3-fold higher Egr-1 mRNA and protein levels but express much lower levels of the transforming growth factor-beta (TGF-beta) Type II receptor (TbetaR-2) and are functionally resistant to the antiproliferative effects of TGF-beta. Lesion cells fail to express a TbetaR-2 promoter/chloramphenicol acetyltransferase (CAT) construct but overexpress an Egr-1-inducible platelet-derived growth factor-A promoter/CAT construct. Transfection of Egr-1 cDNA represses TbetaR-2/CAT constructs but induces PDGF-A/CAT. Egr-1 transfection reduces the levels of TbetaR-2 and confers resistance to the antiproliferative effect of TGF-beta1. Egr-1 can interact directly with both the -143 Sp1 site and the positive regulatory element 2 (PRE2) (ERT/ets) region of the TbetaR-2 promoter. Thus, although activating a family of stress-responsive genes, Egr-1 also transcriptionally represses one of the major inhibitory pathways that restrains vascular repair.

Granulocyte colony-stimulating factor induces Egr-1 up-regulation through interaction of serum response element-binding proteins

Granulocyte colony-stimulating factor (G-CSF) stimulates the proliferation and maturation of myeloid progenitor cells both in vitro and in vivo. We showed that G-CSF rapidly and transiently induces expression of egr-1 in the NFS60 myeloid cell line. Transient transfections of NFS60 cells with recombinant constructs containing various deletions of the human egr-1 promoter identified the serum response element (SRE) between nucleotides (nt) -418 and -391 as a critical G-CSF-responsive sequence. The SRE (SRE-1) contains a CArG box, the binding site for the serum response factor (SRF), which is flanked at either side by an ETS protein binding site. We demonstrated that a single copy of the wild-type SRE-1 in the minimal promoter plasmid, pTE2, is sufficient to induce transcriptional activation in response to G-CSF and that both the ETS protein binding site and the CArG box are required for maximal transcriptional activation of the pTE2-SRE-1 construct. In electromobility shift assays using NFS60 nuclear extracts, we identified SRF and the ETS protein Fli-1 as proteins that bind the SRE-1. We also demonstrated through electrophoretic mobility shift assays, using an SRE-1 probe containing a CArG mutation, that Fli-1 binds the SRE-1 independently of SRF. Our data suggest that SRE-binding proteins potentially play a role in G-CSF-induced egr-1 expression in myeloid cells.

High-level expression of Egr-1 and Egr-1-inducible genes in mouse and human atherosclerosis

To understand the mRNA transcript profile in the human atherosclerotic lesion, RNA was prepared from the fibrous cap versus adjacent media of 13 patients undergoing carotid endarterectomy. cDNA expression arrays bearing 588 known genes indicated that lesions express unexpectedly high levels of the early growth response gene, Egr-1 (NGFI-A), a zinc-finger transcription factor that modulates a cluster of stress-responsive genes including PDGF and TGF-beta. Expression of Egr-1 was an average of 5-fold higher in the lesion than in the adjacent media, a result confirmed by RT-PCR, and many Egr-1-inducible genes were also strongly elevated in the lesion. Time-course analyses revealed that Egr-1 was not induced ex vivo. Immunocytochemistry indicated that Egr-1 was expressed prominently in the smooth muscle-actin positive cells, particularly in areas of macrophage infiltration, and in other cell types, including endothelial cells. Induction of atherosclerosis in LDL receptor-null mice by feeding them a high-fat diet resulted in a progressive increase in Egr-1 expression in the aorta. Thus, induction of Egr-1 by atherogenic factors may be a key step in coordinating the cellular events that result in vascular lesions.

Nitric oxide inhibits growth of glomerular mesangial cells: role of the transcription factor EGR-1

Nitric oxide inhibits growth of glomerular mesangial cells: Role of the transcription factor Egr-1.

BACKGROUND

In previous studies, we found a close link of early growth response gene-1 (Egr-1) expression to mesangial cell (MC) proliferation. Antiproliferative agents inhibited mitogen-induced Egr-1 expression. Here we investigated the effect of S-nitrosoglutathione (GSNO) on the proliferation of MCs, specifically asking how GSNO regulates the transcription factor Egr-1, which we have previously shown to be critical for the induction of MC mitogenesis.

METHODS

The proliferation of MCs was measured by thymidine incorporation and cell counting. Egr-1 mRNA and protein levels were detected by Northern and Western blots. Electrophoretic mobility shift assays (EMSAs) and chloramphenicol acetyltransferase (CAT) assays were performed to test whether GSNO modulates DNA binding and transcriptional activation of Egr-1.

RESULTS

GSNO strongly inhibited serum-induced MC proliferation (-84% at 1 mmol/L). A mild inhibition of serum-induced Egr-1 mRNA was observed at GSNO concentrations from 50 to 200 micromol/L, whereas mRNA levels increased again at concentrations above 500 micromol/L. This increased mRNA expression, however, was not translated into Egr-1 protein. Instead, Egr-1 protein induction was inhibited (-40%). EMSAs indicated that GSNO inhibited specific binding of Egr-1 to its DNA consensus sequence. Moreover, transcriptional activation by Egr-1 in CAT assays using a reporter plasmid bearing three Egr-1 binding sites was strongly suppressed by GSNO.

CONCLUSIONS

Our data identify GSNO as a potent inhibitor of MC growth with potential beneficial effects in proliferative glomerular diseases. This antimitogenic property is mediated at least in part by inhibitory effects of GSNO on Egr-1 protein levels and by reducing the ability of Egr-1 to activate transcription by impairing its DNA binding activity.

Novel Egr/NF-AT composite sites mediate activation of the CD95 (APO-1/Fas) ligand promoter in response to T cell stimulation

Expression of the CD95 (APO-1/Fas) ligand (CD95L) in activated T cells is a major cause of activation-induced T cell apoptosis. The transcription factors NF-AT and Egr-3 (a member of the immediate-early transcription factors involved in cellular growth and differentiation) have been implicated in activation of the CD95L promoter upon T cell activation. On the basis of DNase I footprinting, electrophoretic mobility shift assay, antibody supershift analysis and transfection studies, we have identified two novel Egr-binding sites 5' upstream of the previously identified Egr site. Mutation analysis of each Egr site shows that all three sites are important for full CD95L promoter activity. Strikingly, all Egr sites, including the previously identified Egr site, are adjacent to or overlap with DNA sequences homologous to NF-AT binding sites and confer T cell activation-induced, cyclosporin A-sensitive transcriptional activity. Antibody supershift analysis revealed that NF-AT and Egr proteins are the components of inducible DNA-binding complexes formed on the two novel Egr sites. Cotransfection experiments showed that Egr-1, Egr-3 and NF-AT display a cooperative and synergistic activation of transcription mediated by these three Egr/NF-AT composite regulatory elements. These findings provide further insight into the mechanisms involved in the regulation of the CD95L expression in response to T cell activation.

Phenylethanolamine N-methyltransferase gene expression. Sp1 and MAZ potential for tissue-specific expression

Phenylethanolamine N-methyltransferase (PNMT) promoter-luciferase reporter gene constructs (pGL3RP863, pGL3RP444, and pGL3RP392) transfected into COS1, RS1, PC12, NIH/3T3, or Neuro2A cells showed the highest basal luciferase activity in the Neuro2A cells. DNase I footprinting with Neuro2A cell nuclear extract identified protected PNMT promoter regions spanning the -168/-165 and -48/-45 base pair Sp1/Egr-1 binding sites. Gel mobility shift assays and transient transfection assays using site-directed mutant PNMT promoter-luciferase reporter gene constructs indicated that the elevated basal luciferase activity in the Neuro2A cells was mediated by Sp-1. Furthermore, activation of the PNMT promoter by Sp1 depends on both its binding affinity for its cognate target sequences and its intracellular concentrations. When Sp1 levels were increased through an expression plasmid, luciferase reporter gene expression rose well beyond basal wild-type levels, even with either Sp1 binding element mutated. Finally, another transcription factor expressed in the Neuro2A cells competes with Sp1 by interacting with DNA sequences 3' to the -48 base pair Sp1 site to prevent Sp1 binding and induction of the PNMT promoter. The DNA consensus sequence, Southwestern analysis, and gel mobility shift assays with antibodies identify MAZ as the competitive factor. These findings suggest that Sp1 may potentially contribute to the tissue-specific expression of the PNMT gene, with the competition between Sp1 and MAZ conferring additional tissue-specific control.

Regulation of Egr-1-dependent gene expression by the C-terminal activation domain

The present study analyzes the role of the C-terminal activation domain for Egr-1 transcriptional activity using N-terminal deletion mutants. Mutant N372 comprising the entire C-terminal activation domain and partly truncated DNA-binding and nuclear translocation domains functioned as the transdominant repressor of Egr-1-dependent gene transcription. Activity of the SV40 promoter, however, was not affected by the N372 mutant. Analysis of additional Egr-1 mutants revealed that the transdominant negative effect of N372 was dependent on truncation of the zinc finger motifs that mediate DNA binding. Reconstitution of the zinc fingers was sufficient to generate Egr-1 proteins with potent transcriptional activity. The inhibitory mutant N372 is efficiently translocated to the nucleus, but fails to bind DNA and does not displace DNA-bound wildtype Egr-1. These results provide evidence for an Egr-1-specific cofactor that interacts with the C-terminal activation domain and is essential for Egr-1 transcriptional activity.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Zif268 and Fos-like immunoreactivity in tetanus toxin-induced epilepsy: reciprocal changes in the epileptic focus and the surround

Altered gene expression for a number of molecules has been suggested as one of the underlying mechanisms of epileptogenesis. Changes in expression of the immediate early genes, zif268 and c-fos, were investigated in chronic focal epilepsy induced by tetanus toxin (TT, 20-35 ng) injected in the rat motor cortex. Most rats injected with TT and perfused on postoperative day 5, 7 or 14 had recurrent focal seizures after a latent period of 4-13 days, and showed enhanced Zif268 immunoreactivity in a cluster of neurons at the injection site, as well as reduced Zif268 immunoreactivity in a distinct cortical zone around this cluster. C-fos or Fos-related immunoreactivity was decreased over widespread areas of frontoparietal and piriform cortex in epileptic rats, except for a focus at the injection site which, in most cases, showed increases in Fos-like immunoreactivity. Some epileptic rats showed increased Zif268 immunoreactivity in neurons of the ipsilateral ventral lateral and central lateral thalamic nuclei and increased Zif268 and Fos-like immunoreactivity in the pontine nuclei. Rats perfused before onset of seizures, showed no overt changes other than a slight decrease in Zif268 and Fos-like immunoreactivity at the injection site. The reciprocal changes in Zif268 immunoreactive neurons in the epileptic focus and the immediate surround parallel changes in gene expression for a number of molecules important in epileptogenesis and suggest a state of functional disconnection of the epileptic focus from other cortical areas that may contribute to the development and maintenance of focal epilepsy.

Role of Egr-1 gene expression in B cell receptor-induced apoptosis in an immature B cell lymphoma

Ligation of B cell receptor (BCR) on BKS-2, an immature B cell lymphoma by anti-IgM antibodies (Ab) caused apoptosis. Here we report that signaling through B cell receptor in wild type BKS-2 cells down-regulated the expression of Egr-1, a zinc finger-containing transcription factor. A reduction in the level of Egr-1 mRNA could be demonstrated as early as 30 min after the ligation of BCR on BKS-2 cells. Immunocytochemical and Western blot analysis revealed that the expression of EGR-1 protein was also inhibited by anti-IgM treatment. Antisense oligonucleotides to Egr-1 caused growth inhibition and apoptosis in BKS-2 cells, suggesting that expression of Egr-1 is important for the survival of these B lymphoma cells. In contrast to wild type BKS-2 cells, the mutant 1. B5 cell line, which is refractory to B cell receptor-mediated growth-inhibitory signals, showed an increased expression of Egr-1 upon treatment with anti-IgM. These results implicate a role for Egr-1 in blocking B cell receptor-mediated apoptosis in immature B cells.

Serum- and polypeptide growth factor-inducible gene expression in mouse fibroblasts

Complex cellular processes such as proliferation, differentiation, and apoptosis are regulated in part by extracellular signaling molecules: for example, polypeptide growth factors, cytokines, and peptide hormones. Many polypeptide growth factors exert their mitogenic effects by binding to specific cell surface receptor protein tyrosine kinases. This interaction triggers numerous biochemical responses, including changes in phospholipid metabolism, the activation of a protein phosphorylation cascade, and the enhanced expression of specific immediate-early, delayed-early, or late response genes. In this review, I summarize the major findings obtained from studies investigating the effects of serum or individual polypeptide growth factors on gene expression in murine fibroblasts. Several experimental approaches, including differential hybridization screening of cDNA libraries and differential display, have been employed to identify mRNA species that are expressed at elevated levels in serum- or polypeptide growth factor-stimulated cells. These studies have demonstrated that serum- and growth factor-inducible genes encode a diverse family of proteins, including DNA-binding transcription factors, cytoskeletal and extracellular matrix proteins, metabolic enzymes, secreted chemokines, and serine-threonine kinases. Some of these gene products act as effectors of specific cell cycle functions (e.g., enzymes involved in nucleotide and DNA synthesis), others are required to successfully convert a metabolically inactive cell to a metabolically active cell that will eventually increase in size and then divide (e.g., glucose-metabolizing enzymes), and some actually function as positive or negative regulators of cell cycle progression. In conclusion, research conducted during the past 15 years on serum- and growth factor-regulated gene expression in murine fibroblasts has provided significant insight into mitogenic signal transduction and cell growth control.

Egr transcription factors in the nervous system

The Egr proteins, Egr-1, Egr-2, Egr-3 and Egr-4, are closely related members of a subclass of immediate early gene-encoded, inducible transcription factors. They share a highly homologous DNA-binding domain which recognises an identical DNA response element. In addition, they have several less-well conserved structural features in common. As immediate early proteins, the Egr transcription factors are rapidly induced by diverse extracellular stimuli within the nervous system in a discretely controlled manner. The basal expression of the Egr proteins in the developing and adult rat brain and the induction of Egr proteins by neurotransmitter analogue stimulation, physiological mimetic and brain injury paradigms is reviewed. We review evidence indicating that Egr proteins are subject to tight differential control through diverse mechanisms at several levels of regulation. These include transcriptional, translational and post-translational (including glycosylation, phosphorylation and redox) mechanisms and protein-protein interaction. Ultimately the differentially co-ordinated Egr response may lead to discrete effects on target gene expression. Some of the known target genes of Egr proteins and functions of the Egr proteins in different cell types are also highlighted. Future directions for research into the control and function of the different Egr proteins are also explored.

Regulation of inosine-5'-monophosphate dehydrogenase type II gene expression in human T cells. Role for a novel 5' palindromic octamer sequence

Expression of the gene encoding human inosine- 5'-monophosphate dehydrogenase (IMPDH) type II, an enzyme catalyzing the rate-limiting step in the generation of guanine nucleotides, is increased more than 10-fold in activated peripheral blood T lymphocytes and is required for T cell activation. We have examined the 5'-regulatory sequences that are important for the transcriptional regulation of this gene in T cells. DNase I mapping of genomic DNA identified a hypersensitive element near the transcription initiation site. Fine mapping by in vivo footprinting demonstrated five transcription factor binding sites that are occupied in both resting and activated peripheral blood T lymphocytes; these are tandem CRE motifs, a Sp1 site, an overlapping Egr-1/Sp1 site, and a novel palindromic octamer sequence (POS). The tandem CRE and POS sites are of major functional importance as judged by mutational and electrophoretic mobility shift analyses. These data provide evidence that expression of the human IMPDH type II gene is predominantly regulated by the nuclear factors ATF-2 and an as yet unidentified POS-binding protein. Additional major protein-DNA interactions do not occur within the promoter region after T lymphocyte activation, indicating a requirement for additional protein-protein interactions and/or post-translational modifications of pre-bound transcription factors to account for the observed increase in IMPDH type II gene expression.

Molecular cloning of TA16, a transcriptional repressor that may mediate glucocorticoid-induced growth arrest of leiomyosarcoma cells

The DDT1 MF2 smooth muscle tumor cell line was derived from an estrogen/androgen-induced leiomyosarcoma that arose in the ductus deferens of a Syrian hamster. The growth of this cell line is arrested at the G0/G1 phase of the cell cycle after treatment with glucocorticoids. To identify the putative gene(s) that are potentially involved in this hormone-induced cell growth arrest, we have used a differential screening technique to clone those genes whose expression is induced or up-regulated by glucocorticoids. A number of glucocorticoid response genes were thereby isolated from the leiomyosarcoma cells. One of these clones, termed TA16, was found to be markedly up-regulated by glucocorticoids in DDT1 MF2 cells, but only marginally changed in GR1 cells, a glucocorticoid-resistant variant that was selected from the wild type DDT1 MF2 cell. Isolation and sequencing of its intact cDNA indicated that the TA16 encodes a protein 485 amino acids long, and its sequence is closely homologous to a novel transcriptional repressor that presumably represses the transcription activity of some zinc finger transcriptional factors through a direct interaction. Transfection assays demonstrated that introduction of an antisense TA16 cDNA expression vector, controlled by an MMTV promoter, into the DDT1 MF2 cell significantly relieved the glucocorticoid-induced cell growth arrest. This finding suggests that TA16 might participate in the mediation of glucocorticoid-induced cell cycle arrest in leiomyosarcoma cells.

Mouse thymidine kinase stability in vivo and after in vitro translation

Using a combination of centrifugal elutriation and recultivation of synchronised cell populations we could show that murine thymidine kinase (TK) is rapidly degraded during mitosis in polyoma virus-transformed mouse fibroblasts, in parallel to the time-course for loss of cyclin A. Transformation is no prerequisite for the instability phenotype since artificial overexpression of TK under the control of a constitutive promoter in normal mouse fibroblasts also resulted in rapid turnover of TK during mitosis. The decay of TK protein could be partially mimicked in vitro with enzymatically active protein translated in a rabbit reticulocyte lysate: full length polypeptide was lost slightly more rapidly in the presence of G2/M cytosolic extracts than with G1/S preparations. In addition, an enzymatically active C-terminal truncation of 37 amino acids at Gln-196 was completely stable under the conditions tested, confining the instability domain between residues 196 to 233. These experiments also indicated the border for intact TK since translation products up to Tyr-189 or less were completely inactive. This was also confirmed by a mutant TK protein from mouse F9tk- teratocarcinoma cells which harboured a similar deletion.

Expression of the transcriptional regulator Egr-1 in experimental glomerulonephritis: requirement for mesangial cell proliferation

The early growth response gene-1 (Egr-1), a zinc finger transcriptional regulator, was induced in a rat model of mesangioproliferative glomerulonephritis (GN). Northern blot analysis revealed a maximal 14.9-fold increase in glomerular Egr-1 mRNA at day 6 of GN. By immunohistochemistry Egr-1 protein expression was demonstrated to be mainly confined to glomerular mesangial cells (MC). To test whether Egr-1 directly regulates MC proliferation, cultured MCs were stimulated with platelet-derived growth factor (PDGF) after preincubation with different Egr-1 antisense oligonucleotides (ASOs). PDGF-induced rise in 3H-thymidine uptake by 83% and almost completely abrogated increase in MC number. We conclude that Egr-1 induction is of critical importance for PDGF-induced mitogenic signaling in MCs, and inhibition of Egr-1 in vivo may offer an approach to oppose glomerular MC proliferation in glomerular inflammatory disease.

Characterization of cis-Acting Sequences and trans-Acting Signals Regulating Early Growth Response 1 and c-fos Promoters Through the Granulocyte-Macrophage Colony-Stimulating Factor Receptor in BA/F3 Cells

Human granulocyte-macrophage colony-stimulating factor (hGM-CSF ) activates a set of genes such as c-fos, jun, myc, and early growth response gene 1 (egr-1). Studies on BA/F3 cells that express hGM-CSF receptor (hGMR) showed that two different signaling pathways controlled by distinct regions within the β subunit are involved in activation of c-fos/c-jun genes and in c-myc, respectively. However, the region(s) of the β subunit responsible for activation of the egr-1 gene and other regulatory genes has not been identified. We describe here how egr-1 promoter is activated by hGMR through two regions of the β subunit, with these regions being required for activation of the c-fos promoter. Coexpression of dominant negative (dn) Ras (N17ras) or dn JAK2 almost completely suppressed the activation of egr-1 and c-fos promoters. Deletion analysis of egr-1 promoter showed two cis-acting regions responsible for activation by hGM-CSF or mouse interleukin-3 (mIL-3), one between nucleotide positions (nt) −56 and −116, and the other between nt −235 and −480, which contains tandem repeats of the serum response element (SRE) sites. Similar experiments with the c-fos promoter showed that cis-acting regions containing the SRE/AP-1 sites is sufficient for activation by hGM-CSF. Based on these observations, we propose that signaling pathways activating egr-1 and c-fos promoters are controlled by SRE elements, either through the same or overlapping pathways that involve JAK2 and Ras.

[Egr-1 transcription factor regulates the growth of glomerular mesangium cells]

BACKGROUND

The transcriptional regulator Early growth response gene-1 (Egr-1) is rapidly and transiently induced by various mitogens in cultured rat mesangial cells (MCs).

METHOD AND RESULTS

Here we show Egr-1 induction in an in vivo model of mesangioproliferative glomerulonephritis (GN). A 14.9-fold increase in Egr-1 mRNA was observed 6 days after disease induction. A concomitant increase in Egr-1 protein was demonstrated by immunocytochemistry. Egr-1 was mainly localized to the nuclei of cells in mesangial localization. To test whether Egr-1 directly regulated MC proliferation, we preincubated cultured MCs with antisense oligonucleotides directed against Egr-1. The platelet-derived growth factor (PDGF)-induced increase in Egr-1 mRNA and protein levels was inhibited by 75% and 74%, respectively. At the same time Egr-1 antisense oligonucleotides dose-dependently inhibited MC-proliferation as determined by thymidine-uptake by up to 75%. Control oligonucleotides were without effects on Egr-1 mRNA, protein or MC growth.

CONCLUSION

We conclude that Egr-1 induction is a necessary step in the mitogenic signaling cascade in glomerular MCs.

Transcription factor Egr-1 regulates glomerular mesangial cell proliferation

Increase of glomerular mesangial cells (MCs) is a prominent histopathological finding in many types of glomerulonephritis. We have shown previously that expression of the zinc-finger transcription factor, early growth response gene-1 (egr-1), is closely correlated with the proliferation of cultured MCs. To elucidate whether Egr-1 is required for MC proliferation, we inhibited serum-induced Egr-1 expression by phosphothioate-modified antisense oligonucleotides (ODNs). Uptake of antisense ODNs into MCs was demonstrated, and five different egr-1 antisense ODNs were tested for their impact on serum-induced egr-1 mRNA and protein levels and on MC growth. The most potent egr-1 antisense ODN inhibited serum-induced egr-1 mRNA by 68%, protein induction by 58%, and MC replication as measured by [3H]thymidine uptake and cell counts by 78 and 46%, respectively. The effects of antisense ODNs on MC growth correlated closely with their ability to inhibit Egr-1 protein. ODNs acted in a dose-dependent manner, the minimal effective concentration being 1 microM. Control ODNs had no significant effects. In addition, antisense ODNs against egr-1 potently inhibited endothelin-1-induced Egr-1 expression and MC growth. Heparin, a known inhibitor of MC growth, suppressed serum-induced [3H]thymidine uptake by 39% and egr-1 mRNA expression by 44%. We conclude that Egr-1 is an essential part of the mitogenic signal transduction cascade in cultured MCs.

Differential effects of n-6 and n-3 polyunsaturated fatty acids on cell growth and early gene expression in Swiss 3T3 fibroblasts

Dietary n-3 polyunsaturated fatty acids (PUFAs) have been found to reduce accelerated cell growth. To study the underlying molecular mechanisms, we evaluated the effects of the n-3 PUFAs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) compared with the n-6 PUFA arachidonic acid (AA) on cell growth and early gene mRNA accumulation in Swiss 3T3 fibroblasts. AA significantly increased cell numbers and incorporation of [3H]-thymidine compared with cells treated with EPA and DHA, which did not stimulate cell growth. In contrast to AA and parallel to its effect on cell growth, EPA and DHA did not lead to a pronounced increase in Egr-1 and c-fosmRNA levels. When they were incubated together with AA, both DHA and EPA reduced AA-induced Egr-1 and c-fosmRNA accumulation and incorporation of [3H]-thymidine. We have recently shown that AA strongly increases Egr-1 and c-fosmRNA accumulation 3T3 fibroblasts through its metabolism to prostaglandin E2 (PGE2) and its subsequent activation of protein kinase C (Danesch et al., 1994, J. Biol. Chem., 269:27258-27263). Consistent with the notion that increased PGE2 formation is required for the AA-induced early gene mRNA accumulation, EPA and DHA reduced PGE2 formation from exogenous [14C]-AA by more than 60%, but they did not decrease mRNA levels following stimulation with PGE2. We suggest that, in 3T3 fibroblasts, EPA and DHA antagonize AA-induced early gene mRNA accumulation and cell growth by reducing PGE2 formation.