Cloning and characterization of murine glial cell-derived neurotrophic factor inducible transcription factor (MGIF)

Klf10 Regulates the Emergence of Glial Phenotypes During Hypothalamic Development

Glial cells play a pivotal role in the Central Nervous System (CNS), constituting most brain cells. Gliogenesis, crucial in CNS development, occurs after neurogenesis. In the hypothalamus, glial progenitors first generate oligodendrocytes and later astrocytes. However, the precise molecular mechanisms governing the emergence of glial lineages in the developing hypothalamus remain incompletely understood. This study reveals the pivotal role of the transcription factor KLF10 in regulating the emergence of both astrocyte and oligodendrocyte lineages during embryonic hypothalamic development. Through transcriptomic and bioinformatic analyses, we identified novel KLF10 putative target genes, which play important roles in the differentiation of neurons, astrocytes, and oligodendrocytes. Notably, in the absence of KLF10, there is an increase in the oligodendrocyte population, while the astrocyte population decreases in the embryonic hypothalamus. Strikingly, this decline in the number of astrocytes persists into adulthood, indicating that the absence of KLF10 leads to an extended period of oligodendrocyte emergence while delaying the appearance of astrocytes. Our findings also unveil a novel signaling pathway for Klf10 gene expression regulation. We demonstrate that Klf10 is a target of CREB and that its expression is upregulated via the BDNF-p38-CREB pathway. Thus, we postulate that KLF10 is an integral part of the hypothalamic developmental program that ensures the correct timing for glial phenotypes' generation. Importantly, we propose that the Klf10-/- mouse model represents a valuable tool for investigating the impact of reduced astrocyte and microglia populations in the homeostasis of the adult hypothalamus.

New Insights into the Role of KLF10 in Tissue Fibrosis

Fibrosis, characterized by excessive extracellular matrix accumulation, disrupts normal tissue architecture, causes organ dysfunction, and contributes to numerous chronic diseases. This review focuses on Krüppel-like factor 10 (KLF10), a transcription factor significantly induced by transforming growth factor-β (TGF-β), and its role in fibrosis pathogenesis and progression across various tissues. KLF10, initially identified as TGF-β-inducible early gene-1 (TIEG1), is involved in key biological processes including cell proliferation, differentiation, apoptosis, and immune responses. Our analysis investigated KLF10 gene and protein structures, interaction partners, and context-dependent functions in fibrotic diseases. This review highlights recent findings that underscore KLF10 interaction with pivotal signaling pathways, such as TGF-β, and the modulation of gene expression in fibrotic tissues. We examined the dual role of KLF10 in promoting and inhibiting fibrosis depending on tissue type and fibrotic context. This review also discusses the therapeutic potential of targeting KLF10 in fibrotic diseases, based on its regulatory role in key pathogenic mechanisms. By consolidating current research, this review aims to enhance the understanding of the multifaceted role of KLF10 in fibrosis and stimulate further research into its potential as a therapeutic target in combating fibrotic diseases.

The Distinct Roles of Transcriptional Factor KLF11 in Normal Cell Growth Regulation and Cancer as a Mediator of TGF-β Signaling Pathway

KLF11 (Krüppel-like factor 11) belongs to the family of Sp1/Krüppel-like zinc finger transcription factors that play important roles in a variety of cell types and tissues. KLF11 was initially described as a transforming growth factor-beta (TGF-β) inducible immediate early gene (TIEG). KLF11 promotes the effects of TGF-β on cell growth control by influencing the TGFβ–Smads signaling pathway and regulating the transcription of genes that induce either apoptosis or cell cycle arrest. In carcinogenesis, KLF11 can show diverse effects. Its function as a tumor suppressor gene can be suppressed by phosphorylation of its binding domains via oncogenic pathways. However, KLF 11 can itself also show tumor-promoting effects and seems to have a crucial role in the epithelial–mesenchymal transition process. Here, we review the current knowledge about the function of KLF11 in cell growth regulation. We focus on its transcriptional regulatory function and its influence on the TGF-β signaling pathway. We further discuss its possible role in mediating crosstalk between various signaling pathways in normal cell growth and in carcinogenesis.

Impaired epidermal Langerhans cell maturation in TGFβ-inducible early gene 1 (TIEG1) knockout mice

TGF-β-inducible early gene 1 (TIEG1), also known as Krüppel-like factor 10 (Klf10), represents a major downstream transcription factor of transforming growth factor-β1 (TGF-β1) signaling. Epidermal Langerhans cells (LCs), a unique subpopulation of dendritic cells (DC), essentially mediates immune surveillance and tolerance. TGF-β1 plays a pivotal role in LC maintenance and function after birth, although the underpinning mechanisms remain elusive. Here, we hypothesized that TIEG1 might be involved in TGF-β1-mediated LC homeostasis and function. Utilizing TIEG1 null mice, we discovered that TIEG1 deficiency did not alter LC homeostasis at the steady state and LC repopulation at inflamed-state, as well as their antigen-uptake capacity, but significantly impaired their maturation ability, which was opposite to the fact that loss of TGF-β1 induced spontaneous LC maturation. Moreover, the ablation of TIEG1 enhanced skin contact hypersensitivity response. Our results suggested that TIEG1 is not a key molecule involved in TGF-β1-mediated homeostasis, while TIEG1-related signaling pathways regulate LC maturation and their function.

Krüppel-like factors in mammalian stem cells and development

Krüppel-like factors (KLFs) are a family of zinc-finger transcription factors that are found in many species. Recent studies have shown that KLFs play a fundamental role in regulating diverse biological processes such as cell proliferation, differentiation, development and regeneration. Of note, several KLFs are also crucial for maintaining pluripotency and, hence, have been linked to reprogramming and regenerative medicine approaches. Here, we review the crucial functions of KLFs in mammalian embryogenesis, stem cell biology and regeneration, as revealed by studies of animal models. We also highlight how KLFs have been implicated in human diseases and outline potential avenues for future research.

Klf10 regulates odontoblast differentiation and mineralization via promoting expression of dentin matrix protein 1 and dentin sialophosphoprotein genes

Klf10, a member of the Krüppel-like family of transcription factors, is critical for osteoblast differentiation, bone formation and mineralization. However, whether Klf10 is involved in odontoblastic differentiation and tooth development has not been determined. In this study, we investigate the expression patterns of Klf10 during murine tooth development in vivo and its role in odontoblastic differentiation in vitro. Klf10 protein was expressed in the enamel organ and the underlying mesenchyme, ameloblasts and odontoblasts at early and later stages of murine molar formation. Furthermore, the expression of Klf10, Dmp1, Dspp and Runx2 was significantly elevated during the process of mouse dental papilla mesenchymal differentiation and mineralization. The overexpression of Klf10 induced dental papilla mesenchymal cell differentiation and mineralization as detected by alkaline phosphatase staining and alizarin red S assay. Klf10 additionally up-regulated the expression of odontoblastic differentiation marker genes Dmp1, Dspp and Runx2 in mouse dental papilla mesenchymal cells. The molecular mechanism of Klf10 in controlling Dmp1 and Dspp expression is thus to activate their regulatory regions in a dosage-dependent manner. Our results suggest that Klf10 is involved in tooth development and promotes odontoblastic differentiation via the up-regulation of Dmp1 and Dspp transcription.

TGFβ2 regulates hypothalamic Trh expression through the TGFβ inducible early gene-1 (TIEG1) during fetal development

The hypothalamus regulates the homeostasis of the organism by controlling hormone secretion from the pituitary. The molecular mechanisms that regulate the differentiation of the hypothalamic thyrotropin-releasing hormone (TRH) phenotype are poorly understood. We have previously shown that Klf10 or TGFβ inducible early gene-1 (TIEG1) is enriched in fetal hypothalamic TRH neurons. Here, we show that expression of TGFβ isoforms (1-3) and both TGFβ receptors (TβRI and II) occurs in the hypothalamus concomitantly with the establishment of TRH neurons during late embryonic development. TGFβ2 induces Trh expression via a TIEG1 dependent mechanism. TIEG1 regulates Trh expression through an evolutionary conserved GC rich sequence on the Trh promoter. Finally, in mice deficient in TIEG1, Trh expression is lower than in wild type animals at embryonic day 17. These results indicate that TGFβ signaling, through the upregulation of TIEG1, plays an important role in the establishment of Trh expression in the embryonic hypothalamus.

KLF10, transforming growth factor-β-inducible early gene 1, acts as a tumor suppressor

Krüppel-like factor 10 (KLF10) has been suggested to be a putative tumor suppressor. In the present study, we generated KLF10 deficient mice to explore this hypothesis in vivo. KLF10 deficient mice exhibited increased predisposition to skin tumorigenesis and markedly accelerated papilloma development after DMBA/TPA treatment. On the other hand, KLF10 deficient keratinocytes showed increased proliferation and apoptosis. In colony formation assays after oncogenic H-Ras transfection, KLF10 deficient mouse embryonic fibroblasts (MEFs) yielded more colonies than wild-type MEFs. Furthermore, KLF10 dose-dependently activated p21(WAF1/CIP1) transcription, which was independent of p53 and Sp1 binding sites in p21(WAF1/CIP1) promoter. This study demonstrates that KLF10 is a tumor suppressor and that it targets p21(WAF1/CIP1) transcription.

Adolescent social defeat increases adult amphetamine conditioned place preference and alters D2 dopamine receptor expression

Components of the brain's dopaminergic system, such as dopamine receptors, undergo final maturation in adolescence. Exposure to social stress during human adolescence contributes to substance abuse behaviors. We utilized a rat model of adolescent social stress to investigate the neural mechanisms underlying this correlation. Rats exposed to repeated social defeat in adolescence (P35-P39) exhibited increased conditioned place preference (CPP) for amphetamine (1 mg/kg) in adulthood (P70). In contrast, rats experiencing foot-shock during the same developmental period exhibited amphetamine CPP levels similar to non-stressed controls. Our previous experiments suggested adolescent defeat alters dopamine activity in the mesocorticolimbic system. Furthermore, dopamine receptors have been implicated in the expression of amphetamine CPP. Therefore, we hypothesized that alteration to dopamine receptor expression in the mesocorticolimbic system may be associated with to heightened amphetamine CPP of adult rats exposed to adolescence defeat. We measured D1 and D2 dopamine receptor protein content in the medial prefrontal cortex, nucleus accumbens (NAc), and dorsal striatum following either adolescent social defeat or foot-shock stress and then adult amphetamine CPP. In controls, amphetamine CPP training reduced D2 receptor protein content in the NAc core. However, this down-regulation of NAc core D2 receptors was blocked by exposure to social defeat but not foot-shock stress in adolescence. These results suggest social defeat stress in adolescence alters the manner in which later amphetamine exposure down-regulates D2 receptors. Furthermore, persistent alterations to adult D2 receptor expression and amphetamine responses may depend on the type of stress experienced in adolescence.

Klf10 and Klf11 as mediators of TGF-beta superfamily signaling

Klf10 and Klf11 belong to the family of Sp1/Krüppel-like zinc finger transcription factors that play important roles in a variety of cell types and tissues. Although Klf10 and Klf11 were initially introduced as transforming growth factor-beta (TGF-beta)-inducible genes, several studies have described their upregulation by a plethora of growth factors, cytokines and hormones. Here, we review the current knowledge of the inductive cues for Klf10 and Klf11 and focus on their transcriptional regulation by members of the TGF-beta superfamily. We further summarize their involvement in the regulation of the TGF-beta signaling pathway and discuss their possible role as molecules mediating crosstalk between various signaling pathways. Finally, we provide an overview of the pro-apoptotic and anti-proliferative functions of Klf10 and Klf11.

Mammalian Krüppel-like factors in health and diseases

The Krüppel-like factor (KLF) family of transcription factors regulates diverse biological processes that include proliferation, differentiation, growth, development, survival, and responses to external stress. Seventeen mammalian KLFs have been identified, and numerous studies have been published that describe their basic biology and contribution to human diseases. KLF proteins have received much attention because of their involvement in the development and homeostasis of numerous organ systems. KLFs are critical regulators of physiological systems that include the cardiovascular, digestive, respiratory, hematological, and immune systems and are involved in disorders such as obesity, cardiovascular disease, cancer, and inflammatory conditions. Furthermore, KLFs play an important role in reprogramming somatic cells into induced pluripotent stem (iPS) cells and maintaining the pluripotent state of embryonic stem cells. As research on KLF proteins progresses, additional KLF functions and associations with disease are likely to be discovered. Here, we review the current knowledge of KLF proteins and describe common attributes of their biochemical and physiological functions and their pathophysiological roles.

Tieg1/Klf10 is upregulated by NGF and attenuates cell cycle progression in the pheochromocytoma cell line PC12

The transcription factor Tieg1/Klf10 belongs to a family of Sp1/Klf proteins that have been shown to play important roles during development and maintenance of various tissues and cell types. Upregulation of Tieg1/Klf10 has been reported for TGF-beta, BMP2, BMP4, ActivinA and GDNF as members of the TGF-beta superfamily. Moreover, estrogen, the cytostatic drugs homoharringtonine and velcade as well as nitric oxide are also able to trigger Tieg1/Klf10 transcription. Recent studies suggest a role for members of the neurotrophin family in regulating Tieg1/Klf10 transcriptional upregulation. Using semi-quantitative RT-PCR and immunoblotting, we present data describing that nerve growth factor (NGF) regulates the expression of Tieg1/Klf10 in the pheochromocytoma cell line PC12 in a TrkA-dependent manner. Moreover, we provide evidence for the existence of NGF-responsive elements in the 5'-regulatory region of Tieg1/Klf10 that contain binding sites for the transcription factors Sp1 and CREB. After treatment with NGF PC12 cells exit the cell cycle and start to differentiate towards a neuron-like phenotype indicated by neurite outgrowth. Using flow cytometry and differentiation assays we demonstrate that Tieg1/Klf10 reduces cell cycle progression in PC12 cells but fails to promote their terminal differentiation. Together, our results identify Tieg1/Klf10 as a new NGF target gene and substantiate its anti-proliferative function in the NGF signaling pathway in PC12 cells.

Dynamic transcriptional changes of TIEG1 and TIEG2 during mouse tissue development

TGF-beta-inducible early-response gene (TIEG) is a family of primary response genes induced by TGF-beta, which are well recognized in regulating cellular proliferation and apoptosis. However, their expression profile has never been investigated during embryogenesis in different organs. In this study, we aimed to investigate the transcriptional level of both TIEG1 and TIEG2 during development in various mice organs, including the brain cortex, cerebellum and stem, brain striatum, muscle, heart, liver, kidney, and lung. Quantitative real-time PCR was used to profile the change of transcriptional level of the two TIEG members in the mice tissues at six developmental stages. Taken together, the expression of TIEG1 and TIEG2 was specific in different organs yet varied with different developmental time points. Their dynamic changes were moderately consistent in most organs including the brain cortex, striatum, liver, kidney, and lung. However, their mRNA expression in both the heart and muscle was significantly different at all developmental stages, which might propose a compensation of functions in the TIEG family. Nevertheless, our data indicate that both the TIEG genes are essential in regulating the normal organ development and functioning in murine model, as their expressions were ubiquitous and tissue specific at various developmental stages.

Levetiracetam attenuates hippocampal expression of synaptic plasticity-related immediate early and late response genes in amygdala-kindled rats

BACKGROUND

The amygdala-kindled rat is a model for human temporal lobe epilepsy and activity-dependent synaptic plasticity. Hippocampal RNA isolated from amygdala-kindled rats at different kindling stages was analyzed to identify kindling-induced genes. Furthermore, effects of the anti-epileptic drug levetiracetam on kindling-induced gene expression were examined.

RESULTS

Cyclooxygenase-2 (Cox-2), Protocadherin-8 (Pcdh8) and TGF-beta-inducible early response gene-1 (TIEG1) were identified and verified as differentially expressed transcripts in the hippocampus of kindled rats by in situ hybridization and quantitative RT-PCR. In addition, we identified a panel of 16 additional transcripts which included Arc, Egr3/Pilot, Homer1a, Ania-3, MMP9, Narp, c-fos, NGF, BDNF, NT-3, Synaptopodin, Pim1 kinase, TNF-alpha, RGS2, Egr2/krox-20 and beta-A activin that were differentially expressed in the hippocampus of amygdala-kindled rats. The list consists of many synaptic plasticity-related immediate early genes (IEGs) as well as some late response genes encoding transcription factors, neurotrophic factors and proteins that are known to regulate synaptic remodelling. In the hippocampus, induction of IEG expression was dependent on the afterdischarge (AD) duration. Levetiracetam, 40 mg/kg, suppressed the development of kindling measured as severity of seizures and AD duration. In addition, single animal profiling also showed that levetiracetam attenuated the observed kindling-induced IEG expression; an effect that paralleled the anti-epileptic effect of the drug on AD duration.

CONCLUSIONS

The present study provides mRNA expression data that suggest that levetiracetam attenuates expression of genes known to regulate synaptic remodelling. In the kindled rat, levetiracetam does so by shortening the AD duration thereby reducing the seizure-induced changes in mRNA expression in the hippocampus.

Functional role of KLF10 in multiple disease processes

Since the discovery by this laboratory of the zinc finger transcription factor, KLF10, a member of the Krüppel-like family of transcription factors, there have been multiple publications regarding its functions and its immediate family members, in numerous cell types. KLF10 has been shown to be rapidly induced by TGFbeta1, 2, 3, E(2), epidermal growth factor, and bone morphogenetic protein-2. TGFbeta inducible early gene-1 activates the TGFbeta-Smad signaling pathway via repression of Smad 7 expression and activation of Smad 2 expression and activity. Overall, KLF10 has been implicated in cell differentiation, as a target gene for a variety of signaling pathways, and in serving as a potential marker for human diseases such as breast cancer, cardiac hypertrophy, and osteoporosis. Like other KLF members, KLF10 is expressed in specific cell types in numerous tissues and is known to be involved in repressing cell proliferation and inflammation as well as inducing apoptosis similar to that of TGFbeta. KLF10 binds to Sp-1-GC rich DNA sequences and can activate or repress the transcription of a number of genes. Overall, KLF10 has been shown to play a major role in the TGFbeta inhibition of cell proliferation and inflammation and induction of apoptosis, and its overexpression in human osteoblasts and pancreatic carcinoma cells mimics the actions of TGFbeta.

Role of zinc in ALS

The causes of amyotrophic lateral sclerosis (ALS) are poorly understood. A small proportion, about 2%, is associated with a mutation in the superoxide dismutase (SOD1) gene, and mice expressing this mutant gene exhibit a progressive, ALS-like neurodegenerative disease. Studies of these animals, as well as of human post mortem tissue, reveal the presence of multiple pathological processes, including oxidative stress, glutamate excitotoxicity, neuroinflammation, mitochondrial degeneration, alterations in neurofilaments and neurotubules, mitochondrial damage, aggregation of proteins, abnormalities in growth factors, and apoptosis. We propose that alterations in the disposition of zinc ions may be important in the initiation and development of ALS. SOD1 binds zinc, and many of the mutant forms of this enzyme associated with ALS show altered zinc binding. Alterations in the expression of metallothioneins (MTs), which regulate cellular levels of zinc, have been reported in mutant SOD1 mice, and deletion of MTs in these animals accelerates disease progression. Zinc plays a key role in all the pathological processes associated with ALS. Our zinc hypothesis also may help explain evidence for environmental factors in some cases of ALS, such as in the Chamorro tribe in Guam and in the Gulf War.

Activation of the GDNF-inducible transcription factor (GIF) gene promoter by glucocorticoid and progesterone

Steroid hormones, especially glucocorticoids, exert physiologic effects on dopaminergic neurotransmission and have been implicated in several dopamine-mediated neuropsychiatric conditions. D(2) dopamine receptor gene expression is regulated by the zinc finger-type nuclear protein GDNF-inducible transcription factor (GIF). In this study, we sought to investigate if steroids could regulate transcription of the GIF gene itself. Transient co-transfection of the D(2) expressing neuroblastoma cell line NB41A3 with GIF promoter-luciferase constructs along with expression vectors for steroid hormone receptors showed that activation of glucocorticoid receptors but not estrogen receptors up-regulates transcription from the GIF promoter 5.0-fold. Progesterone receptors, which share the same consensus DNA recognition sequence as glucocorticoid receptors, also activated the GIF promoter. Serial 5'-deletion mutants of the GIF gene upstream region localized the glucocorticoid-responsive segment between nucleotides -128 and -66 relative to the transcription start site. This region contains a putative glucocorticoid-responsive element/progesterone-responsive element (GRE/PRE). Additionally, this fragment of the GIF gene 5'-upstream region activated the heterologous herpes simplex virus thymidine kinase (TK) promoter, which is known to be glucocorticoid and progesterone responsive. Furthermore, glucocorticoid receptor activation up-regulated endogenous GIF gene mRNA expression in NB41A3 cells. These observations demonstrate a molecular basis for glucocorticoid and progesterone-induced up-regulation of GIF gene transcription and provide a mechanism for the modulation of dopamine-mediated behaviors by these hormones.

Down-regulation of stathmin is required for TGF-beta inducible early gene 1 induced growth inhibition of pancreatic cancer cells

Transforming growth factor-beta (TGF-beta) inducible early gene 1 (TIEG1) is known to induce apoptosis in TGF-beta sensitive pancreatic cancer cells, yet its effect on TGF-beta resistant cancer cells remains unclear. In this study, TIEG1 was found to induce apoptosis in TGF-beta resistant cancer cells and concurrently enhanced gemcitabine chemosensitivity. Down-regulation of stathmin was noted to associate with TIEG1 expression, whilst ectopic overexpression of stathmin prevented TIEG1 mediated growth inhibition of tumor cells. Small interfering RNAs targeting stathmin inhibited pancreatic cancer cell growth. These suggest that stathmin is a downstream target of TIEG1.

Role of TIEG1 in biological processes and disease states

A novel TGFbeta Inducible Early Gene-1 (TIEG1) was discovered in human osteoblast (OB) cells by our laboratory. Over the past decade, a handful of laboratories have revealed a multitude of organismic, cellular, and molecular functions of this gene. TIEG1 is now classified as a member of the 3 zinc finger family of Krüppel-like transcription factors (KLF10). Other closely related factors [TIEG2 (KLF11) and TIEG3/TIEG2b] have been reported and are briefly compared. As described in this review, TIEG1 is shown to play a role in regulating estrogen and TGFbeta actions, the latter through the Smad signaling pathway. In both cases, TIEG1 acts as an inducer or repressor of gene transcription to enhance the TGFbeta/Smad pathway, as well at other signaling pathways, to regulate cell proliferation, differentiation, and apoptosis. This review outlines TIEG1's molecular functions and roles in skeletal disease (osteopenia/osteoporosis), heart disease (hypertrophic cardiomyopathy), and cancer (breast and prostate).

GDNF signaling in embryonic midbrain neurons in vitro

The glial cell line-derived neurotrophic factor (GDNF) exerts trophic actions on a number of cell types, including mesencephalic dopaminergic (mDA) neurons. Using rat mesencephalic primary cultures enriched in mDA neurons, we show that protracted GDNF stimulation increases their survival and neurite outgrowth. It modulates the expression of genes essential for DA function (tyrosine hydroxylase, TH and dopamine transporter, dat) and of DA high affinity uptake. To identify genes involved in GDNF signaling pathways, we have used DNA microarray on mDA cultures stimulated with GDNF for 3 h. Here we show that GDNF signaling sequentially activates the genes encoding for the transcription factors EGR1 and TIEG. In addition, it increases the expression of cav1, which encodes for the major component of caveolae. GDNF also modulates the expression of the genes encoding for the Calcineurin subunits ppp3R1 and ppp3CB, and inhibits calcium-calmodulin-dependent protein kinase II beta isoform (CaMKIIbeta) gene expression. These proteins are involved in neuronal differentiation and synaptic plasticity. Moreover, GDNF stimulation down regulates the expression of the glycogen synthase kinase 3beta (gsk3beta) gene, involved in neuronal apoptosis. Using inhibitors of specific intracellular signal transduction pathways we show that changes of egr1, tieg, cav1, CaMkIIbeta and gsk3beta genes expression are extracellular-signal regulated kinases 1/2 (ERK)-dependent, while the cAMP-dependent protein kinase (PKA) pathway influences the up-regulation of ppp3R1 and ppp3CB gene expression. These results demonstrate that GDNF stimulation results in the transcriptional modulation of genes involved in neuronal plasticity and survival and in mDA function, mediated in part by ERK and PKA signaling.

Differential Repression by Freud-1/CC2D1A at a Polymorphic Site in the Dopamine-D2 Receptor Gene

Freud-1/CC2D1A is a transcriptional repressor of the serotonin-1A receptor gene and was recently genetically linked to non-syndromic mental retardation. To identify new Freud-1 gene targets, data base mining for Freud-1 recognition sequences was done. A highly homologous intronic element (D2-DRE) was identified in the human dopamine-D2 receptor (DRD2) gene, and the role of Freud-1 in regulating the gene at this site was assessed. Recombinant Freud-1 bound specifically to the D2-DRE, and a major protein-D2-DRE complex was identified in nuclear extracts that was supershifted using Freud-1-specific antibodies. Endogenous Freud-1 binding to the D2-DRE in cells was detected using chromatin immunoprecipitation. The D2-DRE conferred strong repressor activity in transcriptional reporter assays that was dependent on the Freud-1 recognition sequence. In three different human cell lines, the level of Freud-1 protein was inversely related to DRD2 expression. Knockdown of endogenous Freud-1 using small interfering RNA resulted in an up-regulation of DRD2 RNA and binding sites, demonstrating a crucial role for Freud-1 in DRD2 regulation. A previously uncharacterized single nucleotide A/G polymorphism (rs2734836) was located adjacent to the D2-DRE and conferred allele-specific Freud-1 binding and repression, with the major G-allele having reduced activity. These studies demonstrate a key role for Freud-1 to regulate DRD2 expression and provide the first mechanistic insights into its transcriptional regulation. Allele-specific regulation of DRD2 expression by Freud-1 may possibly associate with psychiatric disorders or mental retardation.

Identification and analysis of cabut orthologs in invertebrates and vertebrates

Cabut (cbt) is a Drosophila melanogaster gene involved in epidermal dorsal closure (DC). Its expression is dependent on the Jun N-terminal kinase (JNK) cascade, and it functions downstream of Jun regulating dpp expression in the leading edge cells. The Cbt protein contains three C(2)H(2)-type zinc fingers and a serine-rich domain, suggesting that it functions as a transcription factor. We have identified single cbt orthologs in other Drosophila species, as well as in other insects and invertebrate organisms like ascidians and echinoderms, but not in nematodes. Gene structure and protein sequence are highly conserved among Drosophilidae, but are more diverged in the other species of invertebrates analyzed. According to this, we demonstrate that cbt expression is detected in the embryonic lateral epidermis in several Drosophila species, as it occurs in D. melanogaster, thus suggesting that the cbt orthologs may have a conserved role in these species during DC. We have also analyzed the genomes of several vertebrate species, finding that the cbt orthologous genes in these organisms encode proteins that belong to the TIEG family of Sp1-like/Krüppel-like transcription factors. Phylogenetic analysis of the invertebrate and vertebrate proteins identified indicates that they mainly follow the expected phylogeny of the species, and that the cbt gene was duplicated during vertebrate evolution. Because we were not able to identify cbt orthologous genes neither in yeast nor in plants, our results suggest that this gene has been probably conserved throughout metazoans and that it may play a fundamental role in animal biology.

Human TIEG2/KLF11 induces oligodendroglial cell death by downregulation of Bcl-XL expression

TGF-beta-induced apoptosis is essential for embryonic development and mainteanance of adult tissues. Impairment of the apoptotic pathway, regulated by TGF-beta, plays a center role in tumorigenesis and manifestations of different diseases. TIEG2/KLF11 is a recently identified human TGF-beta-inducible zinc finger protein belonging to the family of Sp1/KLF-like transcription factors. In human and murine tissues it has been shown that TIEG1 and TIEG2 induce apoptosis and inhibit cell growth. Since TGF-beta and Tieg1 are able to induce apoptosis in the oligodendroglial cell line OLI-neu, we analysed the ability of TIEG2 to mimic the effects observed after treatment with TGF-beta and overexpression of Tieg1. Herein we report that TIEG2 induces Caspase3-dependent apoptosis in murine OLI-neu cells. Furthermore, we could demonstrate that TIEG2 decreases the levels of the anti-apoptotic protein Bcl-X(L) and inhibits transcription driven by the Bcl-X(L) promoter. These data suggest that TIEG2 serves as a downstream mediator of TGF-beta, bridging TGF-beta-dependent signaling to the intracellular pathway of apoptosis.

Functional domains of the TGF-β-inducible transcription factor Tieg3 and detection of two putative nuclear localization signals within the zinc finger DNA-binding domain

The recently identified TGF-beta-inducible early gene 3 (Tieg3) belongs to the gene family of Sp1/Klf-like transcription factors and is upregulated immediately after TGF-beta treatment. To explore the molecular mechanisms of Tieg3-mediated transcriptional control, GAL4-based luciferase assays were performed in order to determine regulatory domains within the Tieg3 protein. Using EGFP-fusion proteins, we monitored the intracellular localization and mapped putative nuclear localization signals (NLS). We provide evidence that the amino-terminus of Tieg3 is essential to repress the transcription and that the loss of the mSin3A interacting domain (SID) disrupts the repressive effects of Tieg3 in the oligodendroglial cell line OLI-neu. Herein we also demonstrate that the zinc finger containing DNA-binding domain (DBD) alone is able to activate the transcription of a reporter gene. Sequence analysis of the zinc finger region revealed no similarities to known activation domains. Analysis of the subcellular localization disclosed Tieg3 as a nuclear protein. Further, we identified the DBD as being essential for the nuclear localization of Tieg3. We detected two closely located putative bipartite NLS within the second and third zinc finger, which are conserved among the members of the Tieg family of proteins. Together these results may help to increase the understanding of Tieg3-mediated transcriptional control and to characterize this TGF-beta-induced Sp1/Klf-like transcription factor.

The family feud: turning off Sp1 by Sp1-like KLF proteins

Sp1 is one of the best characterized transcriptional activators. The biological importance of Sp1 is underscored by the fact that several hundreds of genes are thought to be regulated by this protein. However, during the last 5 years, a more extended family of Sp1-like transcription factors has been identified and characterized by the presence of a conserved DNA-binding domain comprising three Krüppel-like zinc fingers. Each distinct family member differs in its ability to regulate transcription, and, as a consequence, to influence cellular processes. Specific activation and repression domains located within the N-terminal regions of these proteins are responsible for these differences by facilitating interactions with various co-activators and co-repressors. The present review primarily focuses on discussing the structural, biochemical and biological functions of the repressor members of this family of transcription factors. The existence of these transcriptional repressors provides a tightly regulated mechanism for silencing a large number of genes that are already known to be activated by Sp1.

Brain, aging and neurodegeneration: role of zinc ion availability

Actual fields of research in neurobiology are not only aimed at understanding the different aspects of brain aging but also at developing strategies useful to preserve brain compensatory capacity and to prevent the onset of neurodegenerative diseases. Consistent with this trend much attention has been addressed to zinc metabolism. In fact, zinc acts as a neuromodulator at excitatory synapses and has a considerable role in the stress response and in the functionality of zinc-dependent enzymes contributing to maintaining brain compensatory capacity. In particular, the mechanisms that modulate the free zinc pool are pivotal for safeguarding brain health and performance. Alterations in zinc homeostasis have been reported in Parkinson's and Alzheimer's disease as well as in transient forebrain ischemia, seizures and traumatic brain injury, but little is known regarding aged brain. There is much evidence that that age-related changes, frequently associated to a decline in brain functions and impaired cognitive performances, could be related to dysfunctions affecting the intracellular zinc ion availability. A general agreement emerges from studies of humans' and rodents' old brains about an increased expression of metallothionein (MT) isoforms I and II, but dyshomogenous results are reported for MT-III, and it is still uncertain whether these proteins maintain in aging the protective role, as it occurs in adult/young age. At the same time, there is considerable evidence that amyloid-beta deposition in Alzheimer's disease is induced by zinc, but the pathological significance and the causes of this phenomenon are still an open question. The scientific debate on the role of zinc and of some zinc-binding proteins in aging and neurodegenerative disorders, as well as on the beneficial effect of zinc supplementation in aged brain and neurodegeneration, is extensively discussed in this review.

Regulation of Fgf10 gene expression in the prostate: identification of transforming growth factor-beta1 and promoter elements

Fibroblast growth factor 10 (FGF10) is a mesenchymal paracrine-acting factor that plays a key role in the organogenesis of the prostate, and Fgf10 transcripts exhibit a highly restricted expression pattern within prostatic mesenchyme. To study the regulation of Fgf10 we have used organ rudiments grown in vitro as well as a primary stromal cell system derived from the ventral mesenchymal pad (VMP), a condensed area of mesenchyme known to induce prostatic organogenesis. Characterization of VMP cells (VMPCs) showed that they retained expression of AR as well as transcripts for FGF10 and TGFbeta1, -2, and -3. We propose that VMPCs are a good model of specialized mesenchyme involved in prostatic organogenesis and are distinct from general urogenital sinus mesenchyme/stroma. Treatment of VMPCs with TGFbeta1 resulted in a rapid and transient decrease in Fgf10 transcript levels, which were reduced 9-fold at 3 h. TGFbeta1 also inhibited Fgf10 expression in VMP organ rudiments grown in vitro. To further analyze Fgf10 regulation, 6 kb of mouse genomic sequence 5' to the translation start site was characterized by promoter analysis. Deletion analysis of the Fgf10 promoter in VMPCs identified a region of the promoter that mediated a significant proportion of promoter activity as well as mediating promoter down-regulation by TGFbeta1. This element was located between nucleotides -182 and -172 and contained a consensus Sp1 binding site. Taken together, our data suggest that TGFbeta1 is a regulator of Fgf10 expression in prostatic mesenchyme and that a proximal element within the Fgf10 promoter plays an important role in its regulation and expression.

Gene structure and evolution of Tieg3, a new member of the Tieg family of proteins

TGF beta-inducible immediate early gene, Tieg, belongs to the superfamily of Sp1-like transcription factors containing three C(2)H(2)-zinc finger DNA binding motifs close to the C-terminus. So far, Tieg1 and Tieg2 have been identified in human and mouse. We identified Tieg3, a new member of the Tieg protein family by screening a mouse cDNA library. Tieg3 has almost all the known features of the Tieg protein family: it shares a highly conserved C(2)H(2) zinc finger DNA binding domain and is 96% identical to Tieg2 and 86% to Tieg1, respectively. In addition, the three repression domains at the N-terminus, R1, R2 and R3 are conserved in all the Tiegs. Similar to Tieg1 and Tieg2, Tieg3 mRNA is up-regulated in response to TGF beta 1 treatment and can perform the Sp1 sites mediated repression of transcription. A 4 kilobase (kb) long transcript of mouse Tieg3 can be detected using Northern-blot analysis. The gene of mouse Tieg3 contains four exons. Due to the amino acid sequence similarity, mouse Tieg2 is regarded as an orthologue of human Tieg2. However, the mouse Tieg3 gene is localized in a conserved segment on mouse chromosome 12 corresponding to human Tieg2 on chromosome 2 with the same gene order. An interesting explanation for this apparent contradiction might be a homologous recombination leading to loci exchange between the mouse Tieg3 and Tieg2.

Diazepam-induced adaptive plasticity revealed by α1 GABAA receptor-specific expression profiling

Benzodiazepines are in wide clinical use for their sedative and tranquilizing actions, the former being mediated via alpha1-containing GABAA receptors. The signal transduction pathways elicited beyond the receptor are only poorly understood. Changes of transcript levels in cerebral cortex induced by acute diazepam administration were therefore compared by microarray analysis between wild-type and point mutated alpha1(H101R) mice, in which the alpha1 GABAA receptor subunit had been rendered insensitive to diazepam. In wild-type animals, diazepam reduced the expression levels of the alpha subunit of the calcium/calmodulin-dependent protein kinase II, as well as brain-derived neurotrophic factor, MAP kinase phosphatase, transcription factor GIF, c-fos and nerve growth factor induced gene-A. None of these transcripts was changed in the alpha1(H101R) mice after treatment with diazepam. Thus, the sedative action of diazepam is correlated with a selective down-regulation of transcripts involved in the regulation of neuronal plasticity and neurotrophic responses. Most transcript changes were transient except for the decrease of the CaMKIIalpha transcript which persisted even 40 h after the single dose of diazepam. This long-term alteration is likely to contribute to the resetting of the neuronal responsiveness, which may be involved in rebound phenomena and, under chronic treatment, in the development of tolerance and dependence.

Cell-specific pituitary gene expression profiles after treatment with leukemia inhibitory factor reveal novel modulators for proopiomelanocortin expression

Leukemia inhibitory factor (LIF) mediates the hypothalamo-pituitary-adrenal stress response. Transgenic mice overexpressing LIF in the developing pituitary have altered pituitary differentiation with expansion of corticotropes, maintenance of Rathke's cleft cysts, and suppression of all other pituitary cell types. Affymetrix GeneChips were used to identify modulators of LIF effects in corticotrope (AtT-20) and somatolactotrope (GH(3)) cells. In addition to genes known to respond to LIF in corticotrope cells [e.g. suppressor of cytokine signaling-3 (SOCS-3), signal transducer and activator of transcription-3, SH2 domain-containing tyrosine phosphatase-1, and proopiomelanocortin (POMC)], corticotrope-specific changes were also observed for genes involved in glycolysis and gluconeogenesis, transcription factors, signaling molecules, and expressed sequence tags. Two transcription factors identified, CCAAT/enhancer-binding protein beta (C/EBPbeta) and glial cell-derived neurotrophic factor (GDNF)-inducible factor (GIF), dose-dependently induced expression of the rat POMC promoter when overexpressed in AtT-20 cells. LIF further induced POMC transcription with C/EBPbeta, but not with GIF. C/EBPbeta also induced expression of the SOCS-3 promoter that was further enhanced by cotreatment with LIF. However, GIF did not affect SOCS-3 expression. These results indicate that C/EBPbeta and GIF are downstream effectors of LIF corticotrope action. LIF also stimulates the expression of inhibitors of its actions, such as SOCS-3 and SH2 domain-containing tyrosine phosphatase-1. alpha(2)-HS-glycoprotein (AHSG)/fetuin, a secreted protein that antagonizes bone TGFbeta/bone morphogenic protein signaling, was induced by LIF in a signal transducer and activator of transcription-3-dependent fashion. Pretreatment with AHSG/fetuin blocked LIF-induced expression of the POMC promoter independently of SOCS-3. Thus, using GeneChips, C/EBPbeta and GIF have been identified as novel mediators and AHSG/fetuin as an inhibitor of LIF action in corticotropes.

Identification and characterization of a consensus DNA binding element for the zinc finger transcription factor TIEG/EGRalpha

TGFbeta-Inducible Early Gene (TIEG) and the alternatively-transcribed Early Growth Response Gene alpha (EGRalpha) share a Cys(2)His(2) three-zinc finger region with high homology to Sp1 within its zinc finger region. Three-zinc finger transcription factors bind to GC-rich sequences, with small variations in consensus sequence between subfamilies. In this work, a consensus sequence was identified for TIEG/EGRalpha by expressing and purifying the zinc finger region of the protein, and using this to select a binding site from a random oligonucleotide library by iterative cycles of nitrocellulose filter binding and PCR. A fusion of the TIEG/EGRalpha with the VP16 activation domain supported transcription from this site when cloned in front of a heterologous promoter. Mutational analysis of the binding site identified a GT-rich core (5'-GGTGTG-3') that was necessary for binding, with mutations outside of this region causing only a small to moderate decrease in binding.

GDNF elicits distinct immediate-early gene responses in cultured cortical and mesencephalic neurons

Glial cell line-derived neurotrophic factor (GDNF) has been recognized as a survival-promoting molecule for several neuronal populations in the central nervous system (CNS), including midbrain dopaminergic neurons and cortical neurons. Whereas it is well established that GDNF affects dopaminergic cell survival through a receptor complex composed of the tyrosine kinase, Ret, and the glycosylphosphatidylinositol (GPI)-anchored protein, GFRalpha-1, c-Ret is basically undetectable in cortical neurons. In the present study, we have compared GDNF signaling in cortical and mesencephalic neurons by using GDNF-induced expression of the immediate-early genes, c-fos and mgif, as a readout. We found that stimulation of embryonic day (E)17 cortical cultures for 3 hr with GDNF at concentrations ranging from 10 to 80 ng/ml did not result in detectable c-fos expression. In contrast, c-fos expression occurred in E14 mesencephalic cultures exposed to both low and high GDNF concentrations. Vice versa, cortical neurons responded to high GDNF concentrations (80 ng/ml) with an increase in mRNA encoding mGIF, while a similar mGIF response was absent in mesencephalic cultures. Cleavage of GFRalpha receptor subunits from their GPI anchors by phosphatidylinositol-specific phospholipase C (PIPLC) abolished GDNF-induced c-fos expression in mesencephalic cultures, but did not interfere with the effects of GDNF on cortical mgif expression. Together, these findings point to distinct differences in the GDNF recognition and/or signal transduction machinery of cortical and mesencephalic neurons.

Transcriptional regulation of Smad2 is required for enhancement of TGF?/Smad signaling by TGF? inducible early gene

TGFbeta inducible early gene (TIEG) is a novel Krüppel-like transcriptional repressor that was recently shown to increase the activity of the TGFbeta/Smad signal transduction pathway by relieving negative feedback through repression of the inhibitory Smad7. Interestingly, while Smad7 is required for maximal enhancement of TGFbeta/Smad signaling, we observe that TIEG is still capable of increasing Smad pathway activity in the absence of Smad7. Furthermore, while Smad7 is known to block both TGFbeta and bone morphogenetic protein (BMP) signaling, we observe that TIEG specifically enhances only the TGFbeta pathway. Similarly, while both TIEG and the related Krüppel-like factor, FKLF2, repress Smad7 transcription, only TIEG is capable of enhancing Smad signaling. In order to identify additional regulatory targets of TIEG important for this enhancement of the Smad pathway activity, we performed microarray analysis and identified Smad2 as a TIEG target gene. We now show evidence that TIEG increases transcription of the Smad2 gene but not the Smad3 or Smad4 genes. Furthermore, while the TGFbeta/Smad pathway remains intact in Smad2 null cells, TIEG enhancement of Smad signaling is dramatically reduced. Thus we propose a new model whereby TIEG enhances Smad signaling by a dual mechanism involving both the repression of the inhibitory Smad7 as well as the activation of Smad2.

Modulation of transforming growth factor beta (TGFbeta)/Smad transcriptional responses through targeted degradation of TGFbeta-inducible early gene-1 by human seven in absentia homologue

Transforming growth factor beta (TGFbeta)-inducible early gene-1 (TIEG1) is a Krüppel-like transcription factor that is rapidly induced upon TGFbeta treatment. TIEG1 promotes TGFbeta/Smad signaling by down-regulating negative feedback through the inhibitory Smad7. In this report, we describe the identification of an E3 ubiquitin ligase, Seven in Absentia homologue-1 (SIAH1), as a TIEG1-interacting protein. We show that TIEG1 and SIAH1 interact through an amino-terminal domain of TIEG1. Co-expression of SIAH1 results in proteasomal degradation of TIEG1 but not of the related factor TIEG2. Importantly, co-expression of SIAH1 completely reverses repression of Smad7 promoter activity by TIEG1. Furthermore, overexpression of a dominant negative SIAH1 stabilizes TIEG1 and synergizes with TIEG1 to enhance TGFbeta/Smad-dependent transcriptional activation. These findings suggest a novel mechanism whereby the ability of TGFbeta to modulate gene transcription may be regulated by proteasomal degradation of the downstream effector TIEG1 through the SIAH pathway. In this manner, turnover of TIEG1 may serve to limit the duration and/or magnitude of TGFbeta responses.

TGFbeta inducible early gene enhances TGFbeta/Smad-dependent transcriptional responses

TGFbeta inducible early gene (TIEG) encodes a three zinc-finger Krüppel-like transcription factor whose overexpression has been shown to mimic the effects of TGFbeta in human osteosarcoma and pancreatic carcinoma cells. In order to investigate a potential role of TIEG in the TGFbeta signal transduction pathway, we studied its impact on a Smad binding element (SBE) reporter which is known to be regulated by TGFbeta through the R-Smad proteins. We demonstrate that TIEG overexpression enhances TGFbeta induction of SBE reporter activity. TIEG overexpression also enhances induction of the endogenous TGFbeta regulated genes p21 and PAI-1. The ability of TIEG to enhance TGFbeta actions is Smad dependent since TIEG has no effect on SBE transcription in the absence of Smad4 expression or when an inhibitory Smad protein, Smad7, is overexpressed. Furthermore, TIEG overexpression enhances TGFbeta induced Smad2 phosphorylation. Lastly, TIEG appears to function by binding to and thereby repressing a specific element in the proximal promoter of the inhibitory Smad7 gene. In conclusion, these results describe a novel mechanism for the potentiation of TGFbeta/Smad signaling via repression of the inhibitory Smad7 gene by TIEG.

Developmental expression of the zinc finger transcription factor DRRF (dopamine receptor regulating factor)

Dopamine receptor regulating factor (DRRF) is a novel transcription factor with unique anatomical distribution and functional properties, suggesting its importance in regulating dopaminergic neurotransmission. To gain insight into the in vivo function of this factor during embryogenesis, we studied its distribution at embryonic days E8-E16 in the mouse using in situ hybridization. DRRF mRNA is expressed uniquely during development at all time points tested with high levels observed at E12, E14 and E16 in various tissues. DRRF expression is also found in particular brain regions, such as the neopallial cortex, olfactory lobe and corpus striatum. This pattern of DRRF distribution during embryogenesis overlaps with that found in the adult brain, and with the expression profile of dopamine receptors both in the adult and during development.

Dopamine receptor regulating factor, DRRF: a zinc finger transcription factor

Dopamine receptor genes are under complex transcription control, determining their unique regional distribution in the brain. We describe here a zinc finger type transcription factor, designated dopamine receptor regulating factor (DRRF), which binds to GC and GT boxes in the D1A and D2 dopamine receptor promoters and effectively displaces Sp1 and Sp3 from these sequences. Consequently, DRRF can modulate the activity of these dopamine receptor promoters. Highest DRRF mRNA levels are found in brain with a specific regional distribution including olfactory bulb and tubercle, nucleus accumbens, striatum, hippocampus, amygdala, and frontal cortex. Many of these brain regions also express abundant levels of various dopamine receptors. In vivo, DRRF itself can be regulated by manipulations of dopaminergic transmission. Mice treated with drugs that increase extracellular striatal dopamine levels (cocaine), block dopamine receptors (haloperidol), or destroy dopamine terminals (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) show significant alterations in DRRF mRNA. The latter observations provide a basis for dopamine receptor regulation after these manipulations. We conclude that DRRF is important for modulating dopaminergic transmission in the brain.

Overexpression of a nuclear protein, TIEG, mimics transforming growth factor-beta action in human osteoblast cells

Although transforming growth factor-beta (TGF-beta) is a growth factor with many known regulatory activities in many different cell types, its intracellular signaling pathway is still not fully understood. A TGF-beta-inducible early gene (TIEG) was discovered and shown by this laboratory to be a 3-zinc finger transcription factor family member; its expression is rapidly induced in cells treated with TGF-beta. To ascertain whether TIEG plays a major role in the TGF-beta pathway, human osteosarcoma MG-63 cells were stably transfected either with an expression vector containing a TIEG cDNA or with the vector alone. Clones that contain only the vector express normal levels of TIEG mRNA and protein and display the same patterns of gene expression and levels of cell proliferation as the nontransfected, non-TGF-beta-treated parental cells. However, transfected cells that overexpress TIEG mRNA and protein (TIEG-6 and TIEG-7) display changes that mimic those of MG-63 cells treated with TGF-beta, i.e. increased alkaline phosphatase activity, decreased levels of osteocalcin mRNA and protein, and decreased cell proliferation. The degree of these changes correlated with the level of TIEG expressed in the cell lines. TGF-beta treatment of the overexpressed cells showed no added effects. These findings and other published reports support a primary role of TIEG as a transcription factor in the TGF-beta signaling pathway.

TIEG proteins join the Smads as TGF-beta-regulated transcription factors that control pancreatic cell growth

The control of epithelial cell proliferation, differentiation, and apoptosis requires a balance between signaling and transcriptional regulation. Recent developments in pancreatic cell research have revealed that transforming growth factor-beta (TGF-beta) signaling is important for the regulation of each of these phenomena. More importantly, perturbations in this pathway are associated with pancreatic cancer. A chief example of these alterations is the mutation in the TGF-beta-regulated transcription factor Smad4/DPC4 that is found in a large percentage of pancreatic tumors. Surprisingly, studies on transcription factors have remained an underrepresented area of pancreatic research. However, the discovery of Smad4/DPC4 as a transcription factor fueled further studies aimed at characterizing transcription factors involved in normal and neoplastic pancreatic cell growth. Our laboratory recently described the existence of a novel family of zinc finger transcription factors, TGF-beta-inducible early-response gene (TIEG)1 and TIEG2, from the exocrine pancreas that, similarly to Smads, participate in the TGF-beta response and inhibit epithelial cell proliferation. This review therefore focuses on describing the structure and function of these two families of transcription factor proteins that are becoming key players in the regulation of pancreatic cell growth.

AP-2beta represses D(1A) dopamine receptor gene transcription in neuro2a cells

Expression of the D(1A) dopamine receptor in brain is restricted to specific neuronal populations. To investigate the mechanism of this selective expression, we localized a silencer upstream of the human D(1A) gene and identified its binding transcription factor in the D(1A)-negative neural cell line Neuro2a. Using deletion CAT analysis, we narrowed this silencer to the region between nucleotides -561 and -532 relative to the CAP site. This 30-bp region, designated D1AS1, contains a sequence homologous to the AP-2 binding site and binds to a factor that also interacts with the AP-2 consensus sequence. In gel supershift assays, this factor is recognized by anti-AP-2beta antibody. Co-transfection of Neuro2a cells with an AP-2beta expression vector repressed the basal CAT activity of D(1A) promoter-reporter plasmids in a D1AS1-dependent manner. RT-PCR analysis indicated that, among AP-2 family members, Neuro2a cells express only AP-2beta. Furthermore, co-transfection of these cells with decoy oligonucleotides corresponding to the D1AS1 sequence de-repressed the D(1A) gene promoter. Unlike in Neuro2a cells, AP-2beta could not repress the D(1A) promoter in the D(1A)-positive neural cell line, NS20Y. In addition, the expression of AP-2beta in different brain regions does not inversely correlate with that of D(1A) dopamine receptor. These observations taken together indicate that AP-2beta is a repressive transcription factor that acts on the D1AS1 silencer of the D(1A) dopamine receptor gene via some cell-specific mechanism(s) in Neuro2a.

In vivo regulation of glial cell line-derived neurotrophic factor-inducible transcription factor by kainic acid

A putative transcription factor induced in vitro by glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-beta was recently cloned and characterized [Yajima S. et al. (1997) J. Neurosci. 17, 8657-8666]. The messenger RNA of this protein, termed murine GDNF-inducible transcription factor (mGIF, hereafter referred to as GIF), is localized within cortical and hippocampal regions of brain, suggesting that GIF might be regulated by perturbations of these brain regions. In an effort to learn more about the role of GIF in vivo, we examined GIF messenger RNA in the brains of rats treated with the glutamatergic agonist kainic acid. This treatment is known to induce seizures and alter the messenger RNA expression of several growth factors, including GDNF, in several brain regions. Rats were given intraperitoneal saline (1 ml/kg) or kainic acid (15 mg/kg) and were killed at various time-points for in situ hybridization of brain sections with a GIF messenger RNA riboprobe. In saline-treated rats, GIF messenger RNA was present at low levels in cerebral cortex, hippocampus and hippocampal remnants such as the taenia tecta. Kainic acid treatment induced robust increases in GIF messenger RNA in several brain regions, including cerebral cortex, hippocampus, caudate-putamen, nucleus accumbens, and several nuclei of the amygdala and hypothalamus. Most brain regions showed the greatest increase in GIF messenger RNA 4-6 h after kainic acid administration and a return towards normal levels at 48 h. The CA3 region of hippocampus, however, showed a more rapid increase in GIF messenger RNA that was also evident 48 h after kainic acid administration. These results demonstrate that GIF messenger RNA can be regulated in vivo, and that this novel factor warrants further study as a central mediator of GDNF and perhaps other neurotrophic factors.

Three conserved transcriptional repressor domains are a defining feature of the TIEG subfamily of Sp1-like zinc finger proteins

Sp1-like transcription factors are characterized by three highly homologous C-terminal zinc finger motifs that bind GC-rich sequences. These proteins behave as either activators or repressors and have begun to be classified into different subfamilies based upon the presence of conserved motifs outside the zinc finger domain. This classification predicts that different Sp1-like subfamilies share certain functional properties. TIEG1 and TIEG2 constitute a new subfamily of transforming growth factor-beta-inducible Sp1-like proteins whose zinc finger motifs also bind GC-rich sequences. However, regions outside of the DNA-binding domain that differ in structure from other Sp1-like family members remain poorly characterized. Here, we have used extensive mutagenesis and GAL4-based transcriptional assays to identify three repression domains within TIEG1 and TIEG2 that we call R1, R2, and R3. R1 is 10 amino acids, R2 is 12 amino acids, and R3 is approximately 80 amino acids long. None of these domains share homology with previously described transcriptional regulatory motifs, but they share strong sequence homology and are functionally conserved between TIEG1 and TIEG2. Together, these data demonstrate that TIEG proteins are capable of repressing transcription, define domains critical for this function, and further support the idea that different subfamilies of Sp1-like proteins have evolved to mediate distinct transcriptional functions.

A zinc-finger transcription factor induced by TGF-beta promotes apoptotic cell death in epithelial Mv1Lu cells

Transforming growth factor-beta (TGF-beta) superfamily members constitute a group of multifunctional factors that are able to stimulate apoptotic cell death in a variety of cells. In this report, we show that a zinc-finger transcription factor (TIEG) is an immediate early gene transcriptionally induced by TGF-beta in the epithelial Mv1Lu cell line. We also demonstrate that, mimicking TGF-beta effects, ectopic overexpression of TIEG is sufficient to trigger the apoptotic cell program in these cells, which is preceded by a decrease of Bcl-2 protein levels. Finally, apoptotic events elicited by TIEG overexpression can be effectively prevented by ectopic co-expression of Bcl-2. On the basis of these results we suggest that induction of TIEG expression has a role in the pro-apoptotic properties of TGF-beta.

A tale of three fingers: the family of mammalian Sp/XKLF transcription factors

One of the most common regulatory elements is the GC box and the related GT/CACC box, which are widely distributed in promoters, enhancers and locus control regions of housekeeping as well as tissue-specific genes. For long it was generally thought that Sp1 is the major factor acting through these motifs. Recent discoveries have shown that Sp1 is only one of many transcription factors binding and acting through these elements. Sp1 simply represents the first identified and cloned protein of a family of transcription factors characterised by a highly conserved DNA-binding domain consisting of three zinc fingers. Currently this new family of transcription factors has at least 16 different mammalian members. Here, we will summarise and discuss recent advances that have been directed towards understanding the biological role of these proteins.

Sp1 and its likes: biochemical and functional predictions for a growing family of zinc finger transcription factors

The discovery and functional characterization of Sp1 as a GC-rich binding zinc finger protein provided a useful paradigm for understanding mechanisms mediating transcriptional activation in eukaryotic cells. This early paradigm suggested that promoters carrying GC-rich sequences are activated by Sp1 through its interaction with proteins from the basal transcriptional machinery to upregulate gene expression. Since the time of this seminal work, studies from several laboratories have led to the discovery of many Sp1-like transcription factors containing highly homologous DNA binding motifs that bind to similar sequences. Consequently, this knowledge poses many important questions regarding whether these related proteins have similar or antagonistic biochemical and functional properties to Sp1. The goal of this article is to use available database information and recent experimental evidence to describe the current repertoire of Sp1-like zinc finger transcription factors in mammalian cells. Furthermore, we discuss structural and functional studies that reveal that these proteins may share a role in morphogenetic pathways. Altogether, this information is aimed at better understanding how this growing family of transcription factors work to regulate gene expression and morphogenesis.

Molecular cloning and characterization of TIEG2 reveals a new subfamily of transforming growth factor-beta-inducible Sp1-like zinc finger-encoding genes involved in the regulation of cell growth

Sp1-like zinc finger transcription factors are involved in the regulation of cell growth and differentiation. Recent evidence demonstrating that mammalian cells express novel, yet uncharacterized, Sp1-like proteins has stimulated a search for new members of this family. We and others have recently reported that the transforming growth factor (TGF)-beta-regulated gene TIEG encodes a new Sp1-like protein that inhibits cell growth in cultured cells. Here we report the identification, nuclear localization, DNA binding activity, transcriptional repression activity, and growth inhibitory effects of TIEG2, a novel TGF-beta-inducible gene related to TIEG. TIEG2 is ubiquitously expressed in human tissues, with an enrichment in pancreas and muscle. TIEG2 shares 91% homology with TIEG1 within the zinc finger region and 44% homology within the N terminus. Biochemical characterization reveals that TIEG2 is a nuclear protein, which, as predicted from the primary structure, specifically binds to an Sp1-like DNA sequence in vitro and can repress a promoter containing Sp1-like binding sites in transfected Chinese hamster ovary epithelial cells. Furthermore, functional studies using [3H]thymidine uptake and MTS (3-(4, 3-dimethyltiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-su lfophenyl)-2 H-tetrazolium) assays demonstrate that the overexpression of TIEG2 in Chinese hamster ovary cells inhibits cell proliferation. Thus, TIEG2, together with TIEG1, defines a new subfamily of TGF-beta-inducible Sp1-like proteins involved in the regulation of cell growth.