Identification of a novel TGF-beta-regulated gene encoding a putative zinc finger protein in human osteoblasts

The biology of the mammalian Krüppel-like family of transcription factors

Recent advances in molecular cloning have led to the identification of a large number of mammalian zinc finger-containing transcription factors that exhibit homology to the Drosophila melanogaster protein, Krüppel. Although the amino acid sequences in the zinc finger domains of these Krüppel-like factors (KLFs) are closely related to one another, the regions outside the zinc fingers of the proteins are usually unique. KLFs display seemingly different and broad biological properties with each functioning as an activator of transcription, a repressor or both. This review article provides a current phylogenetic classification of the identified KLFs to date. More importantly, the currently known biological activities of the KLFs in regulating transcription, cell proliferation, differentiation and development are summarized and compared. Further characterization of this interesting protein family should provide additional insights into the their respective regulatory role in various important biological processes.

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.

Differential display of human marrow stromal cells reveals unique mRNA expression patterns in response to dexamethasone

Human bone marrow stromal cells (hBMSC) are pluripotent cells that have the ability to differentiate into bone, cartilage, hematopoietic-supportive stroma, and adipocytes in a process modulated by dexamethasone (DEX). To characterize changes in hBMSC in response to DEX, we carried out differential display experiments using hBMSC cultured for 1 week in the presence or absence of 10(-8) M DEX. When RNA from these cells was used for differential display, numerous cDNA bands were identified that were up-regulated and down-regulated by DEX. The cDNA bands were reamplified by PCR and directly used to screen an hBMSC cDNA library. Seven clones were isolated and characterized by DNA sequencing and found to encode the following genes: transforming growth factor-beta-induced gene product ((beta)ig-h3), calphobindin II, cytosolic thyroid-binding protein, 22-kDA smooth muscle protein (SM22), and the extracellular matrix proteins osteonectin/SPARC, type III collagen, and fibronectin. To confirm that these genes were regulated by DEX, the cells were treated continuously with this hormone for periods ranging from 2 to 30 days, and steady-state mRNA levels were measured by Northern blot analysis. All genes showed some level of regulation by DEX. The most profound regulation by DEX was observed in the (beta)ig-h3 gene, which showed a relative 10-fold decrease in mRNA levels after 6 days of treatment. Interestingly, (beta)ig-h3 expression was not altered by DEX in fibroblasts from other human tissues, including thymus stromal fibroblasts, spleen stromal fibroblasts, and foreskin fibroblasts. In summary, differential display of DEX-treated hBMSC revealed unique patterns of gene expression and has provided new information about phenotypic changes that accompany the differentiation of hBMSC toward osteogenesis. J. Cell. Biochem. 76:231-243, 1999. Published 1999 Wiley-Liss, Inc.

The transforming growth factor beta(1)-inducible transcription factor TIEG1, mediates apoptosis through oxidative stress

Transforming growth factor beta(1) (TGF-beta(1))-inducible transcription factors have recently elicited interest because of their critical role in the regulation of cell proliferation, differentiation, and apoptosis. We have previously reported that the TGF-beta(1)-inducible transcription factor, TIEG1, induces apoptosis in a pancreas-derived cell line. However, the mechanisms underlying the apoptotic effects of this transcription factor remain to be defined. In this study, using the TGF-beta(1)-sensitive Hep 3B cell line, we have defined the mechanistic sequence of events that characterize TIEG1-mediated apoptosis and compared these events with the changes observed during TGF-beta(1)-induced apoptosis. Both TGF-beta(1)- and TIEG1-induced cell death were accompanied by an increase in the generation of reactive oxygen species and a loss of the mitochondrial membrane potential preceding the morphological changes of apoptosis. In contrast, increases in caspase 3-like activity and glutathione (GSH) depletion occurred later in the apoptotic process, concurrent with the morphological features of apoptosis. The antioxidant, trolox, decreased the formation of reactive oxygen species and apoptosis. These results demonstrate that similar to TGF-beta(1), TIEG1 induces apoptosis by a mechanism involving the formation of reactive oxygen species.

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.

The Sp-family of transcription factors

GC-boxes and related motifs are frequently occurring DNA-elements present in many promoters and enhancers. In contrast to other elements it was generally thought that the transcription factor Sp1 is the only factor acting through these motifs. The cloning of paralogous genes of the Sp1 factor uncovered the existence of a small protein family consisting of Sp1, Sp2, Sp3 and Sp4. All four proteins exhibit very similar structural features. They contain a highly conserved DNA-binding domain composed of three zinc fingers close the C-terminus and serine/threonine- and glutamine-rich domains in their N-terminal regions. The high degree of structural conservation between these four proteins suggested that they do exert similar functions. Molecular, genetic and biochemical analyses, however, demonstrated that Sp2, Sp3 and Sp4 are not simply functional equivalents of Sp1. Here, I will summarize and discuss recent advances which have been made towards understanding the mode of action and biological function of individual family members.

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.

Id genes are direct targets of bone morphogenetic protein induction in embryonic stem cells

Bone morphogenetic proteins (BMPs) are morphogenetic signaling molecules essential for embryonic patterning. To obtain molecular insight into the influence of BMPs on morphogenesis, we searched for new genes directly activated by BMP signaling. In vitro cultured mouse embryonic stem (ES) cells were used, cultivated in chemically defined growth medium (CDM). CDM-cultured ES cells responded very selectively to stimulation by various mesoderm inducers (BMP2/4, activin A, and basic fibroblast growth factor). BMP2/4 rapidly induced transcript levels of the homeobox genes Msx-1 and Msx-2 and the proto-oncogene JunB, whereas c-jun transcripts displayed delayed albeit prolonged increase. Using differential display cDNA cloning, six direct BMP target genes were identified. These include Id3, which showed strong mRNA induction, and the moderately induced Cyr61, DEK, and eIF4AII genes, as well as a gene encoding a GC-binding protein. Besides Id3, also the Id1 and Id2 genes were activated by BMP4 in both ES cells and a range of different cell lines. Id genes encode negative regulators of basic helix-loop-helix transcription factors. In vivo we observed local ectopic expression of Id3 and Msx-2 mRNAs in Ft/+ embryos at overlapping regions of ectopic Bmp4 misexpression. We therefore propose that the Msx and Id genes are direct target genes of embryonic BMP4 signaling in vivo.

Mammalian Krüppel-like transcription factors: more than just a pretty finger

The transcription factor SP1 contains three Krüppel-like zinc fingers. Recently, several related proteins, including erythroid, lung and gut-enriched Krüppel-like factors, have been identified. Together with SP1, these proteins form a sizeable family of transcription factors that share homology in their zinc-finger domains but differ elsewhere. Analysis of these differences is illuminating specific mechanisms by which transcription is regulated.

FKLF, a novel Krüppel-like factor that activates human embryonic and fetal beta-like globin genes

A cDNA encoding a novel Krüppel-type zinc finger protein, FKLF, was cloned from fetal globin-expressing human fetal erythroid cells. The deduced polypeptide sequence composed of 512 amino acids revealed that, like Sp1 and EKLF, FKLF has three contiguous zinc fingers at the near carboxyl-terminal end. A long amino-terminal domain is characterized by the presence of two acidic and two proline-rich regions. Reverse transcription (RT)-PCR assays using various cell lines demonstrated that the FKLF mRNA is expressed predominantly in erythroid cells. FKLF message is detectable by RT-PCR in fetal liver but not in adult bone marrow cells. As predicted from its structural features, FKLF is a transcriptional activator. In luciferase assays FKLF activated the gamma- and epsilon-globin gene promoters, and, to a much lower degree, the beta-globin promoter. Studies of HS2-gamma gene reporter constructs carrying CACCC box deletions revealed that the CACCC box sequence of the gamma gene promoter mediates the activation of the gamma gene by FKLF. Other erythroid promoters (GATA-1, glycophorin B, ferrochelatase, porphobilinogen deaminase, and 5-aminolevulinate synthase) containing CACCC elements or GC-rich potential Sp1-binding sites were activated minimally, if at all, by FKLF, indicating that FKLF is not a general activator of genes carrying the CACCC motifs. Transfection of K562 cells with FKLF cDNA enhanced the expression of the endogenous epsilon- and gamma-globin genes, suggesting an in vivo role of FKLF in fetal and embryonic globin gene expression. Our results indicate that the protein potentially encoded by the FKLF cDNA acts as a transcriptional activator of embryonic and fetal beta-like globin genes.

h-sgk serine-threonine protein kinase gene as transcriptional target of transforming growth factor beta in human intestine

BACKGROUND & AIMS

Recently, the immediate early gene h-sgk was cloned as a hypertonicity-induced gene from human hepatoma cells. The aim of this study was to localize h-sgk messenger RNA (mRNA) expression in normal and inflamed intestinal mucosa and to identify potential transcriptional regulators.

METHODS

h-sgk mRNA in small intestinal mucosa from healthy persons and patients with Crohn's disease was determined by in situ hybridization. Transcriptional regulation was studied by Northern blot analysis of total RNA isolated from cultured human Intestine 407, U937, and HepG2 cells.

RESULTS

In normal ileum, h-sgk mRNA was selectively localized to the apical villus enterocytes, whereas no staining was detected in crypt cells. In Crohn's disease, enterocytes of the crypts expressed h-sgk and abundant h-sgk positive inflammatory cells appeared in the lamina propria. Combined h-sgk in situ hybridization and immunohistochemical analysis of CD68 antigen expression identified a part of these cells as macrophages. In addition to spatial correlation of transforming growth factor (TGF)-beta1 protein and h-sgk mRNA expression, h-sgk transcription in human Intestine 407 and HepG2 cells as well as in U937 monocytes/macrophages was strongly induced by TGF-beta1 in vitro.

CONCLUSIONS

h-sgk expression in normal and inflamed intestinal mucosa may be regulated by TGF-beta1 and may contribute to the pleiotropic actions of TGF-beta1 in mucosal cell populations.

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.

TGFbeta-inducible early gene (TIEG) also codes for early growth response alpha (EGRalpha): evidence of multiple transcripts from alternate promoters

TGFbeta-inducible early gene (TIEG) and early growth response alpha (EGRalpha) are putative transcription factors based on homology to known zinc finger proteins SP1, EGR1, BTEB, and Wilm tumor. Here we report that TIEG and EGRalpha are expressed from alternative promoters of the same gene. The TIEG/EGRalpha gene spans 8 kb and contains five exons. Use of alternative first exons results in TIEG having 12 unique amino acids on its N-terminus. Computer analysis of the 5' upstream regions of either TIEG (exon 1a) or EGRalpha (exon 1b) does not identify a TATA box or initiator sequencebut shows consensus sequence similarities to binding sites for several transcription factors including SP1,JunB, and aromatic hydrocarbon/receptor-ligand complexes. Analysis of constructs containing 5'-flanking regions show that both the TIEG and the EGRalpha promoters have significant activity in human fetal osteoblast cells. Northern analysis of mRNA from various human tissues and several cell lines reveals that TIEG is the predominant transcript produced and regulated by growth factors from the TIEG/EGRalpha gene.

Identification of a novel bone morphogenetic protein-responsive gene that may function as a noncoding RNA

Bone morphogenetic proteins (BMPs)/osteogenic proteins (OPs), members of the transforming growth factor-beta superfamily, have a wide variety of effects on many cell types including osteoblasts and chondroblasts, and play critical roles in embryonic development. BMPs transduce their effects through binding to two different types of serine/threonine kinase receptors, type I and type II. Signaling by these receptors is mediated by the recently identified Smad proteins. Despite the rapid progress in understanding of the signaling mechanism downstream of BMP receptors, the target genes of BMPs are poorly understood in mammals. Here we identified a novel gene, termed BMP/OP-responsive gene (BORG), in C2C12 mouse myoblast cell line which trans-differentiates into osteoblastic cells in response to BMPs. Expression of BORG was dramatically induced in C2C12 cells by the treatment with BMP-2 or OP-1 within 2 h and peaked at 12-24 h, whereas transforming growth factor-beta had a minimal effect. BMP-dependent expression of BORG was also detected in other cell types which are known to respond to BMPs, suggesting that BORG is a common target gene of BMPs. Cloning and sequence analysis of BORG cDNA and the genomic clones revealed that, unexpectedly, the transcript of BORG lacks any extensive open reading frames and contains a cluster of multiple interspersed repetitive sequences in its middle part. The unusual structural features suggested that BORG may function as a noncoding RNA, although it is spliced and polyadenylated as authentic protein-coding mRNAs. Together with the observation that transfection of antisense oligonucleotides of BORG partially inhibited BMP-induced differentiation in C2C12 cells, it is possible that a new class of RNA molecules may have certain roles in the differentiation process induced by BMPs.

Sp family transcription factors regulate expression of rat D2 dopamine receptor gene

The rat D2 dopamine receptor gene is transcribed from a TATA-less promoter that has an initiator-like sequence and several putative Sp1 binding sites. We previously reported that a negative modulator is located between nucleotides -116 and -76 (D2Neg-B) in this gene and that Sp1 as well as another unknown factor bind to this region (Minowa et al., J. Biol. Chem. 269, 11656, 1994). In the present investigation employing the in situ filter detection method, we identified this factor as Sp3. Anti-Sp3 antiserum used in gel-shift assays also revealed that Sp3 binds to the D2Neg-B sequence. Cotransfection of Drosophila Schneider's SL2 cells with Sp3 or Sp1 expression plasmids in the presence of CAT reporter plasmids containing D2 promoter regions demonstrated that Sp1 increased CAT activity in a dose-dependent manner, whereas Sp3, either alone or in the presence of Sp1, failed to activate or repress transcription. On the other hand, using the TATA-containing reporter plasmid BCAT-2, Sp3 coexpression significantly repressed Sp1-induced trans-activation, although Sp3 alone was ineffective. Thus, the transcriptional activity of Sp3 is dependent on the promoter context, and the negative regulation of D2 gene expression appears quite complex and may not depend simply on known DNA-protein interactions involving only Sp1 and Sp3.

Hippocampal plasticity involves extensive gene induction and multiple cellular mechanisms

Long-term plasticity of the central nervous system (CNS) involves induction of a set of genes whose identity is incompletely characterized. To identify candidate plasticity-related genes (CPGs), we conducted an exhaustive screen for genes that undergo induction or downregulation in the hippocampus dentate gyrus (DG) following animal treatment with the potent glutamate analog, kainate. The screen yielded 362 upregulated CPGs and 41 downregulated transcripts (dCPGs). Of these, 66 CPGs and 5 dCPGs are known genes that encode for a variety of signal transduction proteins, transcription factors, and structural proteins. Seven novel CPGs predict the following putative functions: cpg2--a dystrophin-like cytoskeletal protein; cpg4--a heat-shock protein: cpg16--a protein kinase; cpg20--a transcription factor; cpg21--a dual-specificity MAP-kinase phosphatase; and cpg30 and cpg38--two new seven-transmembrane domain receptors. Experiments performed in vitro and with cultured hippocampal cells confirmed the ability of the cpg-21 product to inactivate the MAP-kinase. To test relevance to neural plasticity, 66 CPGs were tested for induction by stimuli producing long-term potentiation (LTP). Approximately one-fourth of the genes examined were upregulated by LTP. These results indicate that an extensive genetic response is induced in mammalian brain after glutamate receptor activation, and imply that a significant proportion of this activity is coinduced by LTP. Based on the identified CPGs, it is conceivable that multiple cellular mechanisms underlie long-term plasticity of the nervous system.

Estrogen regulation of a transforming growth factor-beta inducible early gene that inhibits deoxyribonucleic acid synthesis in human osteoblasts

This laboratory reported the identification and characterization of a unique three zinc finger, transcription factor-like, transforming growth factor-beta inducible early gene (TIEG) (see Ref. 35). TIEG expression has been shown to be tissue- and cell type specific, enhanced by specific growth factors, and to decrease with advancing stages of breast cancer. Recent studies involving TIEG overexpression in pancreatic carcinoma cells indicate that TIEG expression inhibits DNA synthesis, similar to a tumor suppressor-like gene, and plays a role in apoptosis (see Ref. 37). This paper describes the rapid, but transient, induction of TIEG steady-state messenger RNA (mRNA) levels by 17beta-estradiol (E2) in estrogen receptor (ER)-positive, human fetal osteoblastic (hFOB/ER) cells. This rapid induction is shown to be ER- and steroid dose-dependent but protein synthesis independent. An antagonism between E2 and PTH, which occurs in skeletal metabolism, is shown to concur rapidly with TIEG mRNA expression. Scanning confocal microscopy (using polarized, laser-based immunofluorescence) shows that TIEG protein is localized in the nucleus of hFOB/ER cells, with the levels rapidly increasing after E2 treatment. The rapid E2-induced increase in TIEG expression is followed by an E2-induced inhibition of DNA synthesis in the hFOB/ER cells. Antiestrogens block not only the induction of TIEG mRNA levels but also the inhibition of cell proliferation. Lastly, hFOB cells, stably transfected with a TIEG expression vector, display markedly reduced DNA synthesis/cell proliferation, compared with nontransfected cells. These results support the finding that TIEG is an early responding regulatory gene for E2 in human osteoblast cells that inhibits DNA synthesis. It is speculated that TIEG may play a role in the signaling pathway for E2 in inhibiting cell proliferation.

Transforming growth factor-beta1 coregulates mRNA expression of aryl hydrocarbon receptor and cell-cycle-regulating genes in human cancer cell lines

Transforming growth factor (TGF)-beta1 down-regulates mRNA expression of the aryl hydrocarbon receptor (AhR) and of AhR-inducible genes in A549 cells. Here, we describe a dose-dependent inhibition of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-induced cytochrome P450 (CYP) 1A1, CYP1B1 and NADPH-quinone-oxidoreductase (NMO-1) mRNA expression as well as TCDD-induced 7-ethoxyresorufin-O-deethylase (EROD) activity in MDA-MB 231 cells. The AhR mRNA expression was not affected by TGF-beta1. TGF-beta-responsiveness was investigated by examining the effect on the expression of responsive genes. While TGF-beta1 up-regulates mRNA expression of TGF-beta1 and TIEG (TGF-beta-inducible early gene) as well as luciferase activity of a responsive reporter plasmid in both cell lines, a down-regulation of c-myc and cyclin A mRNA expression was only found in A549 cells. Furthermore, TGF-beta1 inhibits only cell proliferation of A549 but not of MDA-MB 231 cells. The results show a coregulation of mRNA expression of AhR and cell-cycle regulating genes, and further indicate that the AhR may be involved in regulation of cell proliferation.

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

The potent neurotrophic factor glial cell-derived neurotrophic factor (GDNF) is a distant member of the transforming growth factor-beta (TGF-beta) superfamily of proteins. We report a transcription factor that is the first nuclear protein known to be induced by GDNF, thus designated murine GDNF inducible factor (mGIF). The cDNA was cloned in the course of investigating transcription factors that bind to Sp1 consensus sequences, using the in situ filter detection method, and it was found to encode a protein having the same C2-H2 zinc finger motif as Sp1. Sequence analysis indicated that mGIF is homologous to the human TGF-beta inducible early gene (TIEG) and human early growth response gene-alpha (EGR-alpha). mGIF is widely distributed in the adult mouse with high mRNA levels in kidney, lung, brain, liver, heart, and testis. In the adult brain, mGIF is abundantly expressed in hippocampus, cerebral cortex, cerebellum, and amygdala with lower amounts in striatum, nucleus accumbens, olfactory tubercle, thalamus, and substantia nigra. During development, mGIF mRNA also has a wide distribution, including in cerebral cortex, cerebellar primordium, kidney, intestine, liver, and lung. GDNF induces the expression of mGIF rapidly and transiently both in a neuroblastoma cell line and in primary cultures of rat embryonic cortical neurons. Co-transfection of the Drosophila SL2 cells using mGIF expression plasmid and reporter constructs having Sp1 binding sites indicated that mGIF represses transcription from a TATA-containing as well as from a TATA-less promoter. These observations suggest that the zinc finger transcription factor mGIF could be important in mediating some of the biological effects of GDNF.

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

The potent neurotrophic factor glial cell-derived neurotrophic factor (GDNF) is a distant member of the transforming growth factor-beta (TGF-beta) superfamily of proteins. We report a transcription factor that is the first nuclear protein known to be induced by GDNF, thus designated murine GDNF inducible factor (mGIF). The cDNA was cloned in the course of investigating transcription factors that bind to Sp1 consensus sequences, using the in situ filter detection method, and it was found to encode a protein having the same C2-H2 zinc finger motif as Sp1. Sequence analysis indicated that mGIF is homologous to the human TGF-beta inducible early gene (TIEG) and human early growth response gene-alpha (EGR-alpha). mGIF is widely distributed in the adult mouse with high mRNA levels in kidney, lung, brain, liver, heart, and testis. In the adult brain, mGIF is abundantly expressed in hippocampus, cerebral cortex, cerebellum, and amygdala with lower amounts in striatum, nucleus accumbens, olfactory tubercle, thalamus, and substantia nigra. During development, mGIF mRNA also has a wide distribution, including in cerebral cortex, cerebellar primordium, kidney, intestine, liver, and lung. GDNF induces the expression of mGIF rapidly and transiently both in a neuroblastoma cell line and in primary cultures of rat embryonic cortical neurons. Co-transfection of the Drosophila SL2 cells using mGIF expression plasmid and reporter constructs having Sp1 binding sites indicated that mGIF represses transcription from a TATA-containing as well as from a TATA-less promoter. These observations suggest that the zinc finger transcription factor mGIF could be important in mediating some of the biological effects of GDNF.

Two potent nuclear localization signals in the gut-enriched Krüppel-like factor define a subfamily of closely related Krüppel proteins

The gut-enriched Krüppel-like factor (GKLF) is a newly identified transcription factor that contains three C2H2 Krüppel-type zinc fingers. Previous immunocytochemical studies indicate that GKLF is exclusively localized to the nucleus. To identify the nuclear localization signal (NLS) within GKLF, cDNA constructs with various deletions in the coding region of GKLF were generated and analyzed by indirect immunofluorescence in transfected COS-1 cells. In addition, constructs fusing regions representing putative NLSs of GKLF to green fluorescent protein (GFP) were generated and examined by fluorescence microscopy in similarly transfected cells. The results indicate that GKLF contains two potent, independent NLSs: one within the zinc fingers and the other in a cluster of basic amino acids (called 5' basic region) immediately preceding the first zinc finger. In comparison, putative NLSs within the zinc fingers and the 5' basic region of a related Krüppel protein, zif268/Egr-1, are relatively less efficient in their ability to translocate GFP into the nucleus. A search in the protein sequence data base revealed that despite the existence of numerous Krüppel proteins, only two, the lung Krüppel-like factor (LKLF) and the erythroid Krüppel-like factor (EKLF), exhibit similar NLSs to those of GKLF. These findings indicate that GKLF, LKLF, and EKLF are members of a subfamily of closely related Krüppel proteins.

Overexpression of the TGFbeta-regulated zinc finger encoding gene, TIEG, induces apoptosis in pancreatic epithelial cells

Members of the TGFbeta family of peptides exert antiproliferative effects and induce apoptosis in epithelial cell populations. In the exocrine pancreas, these peptides not only regulate normal cell growth, but alterations in these pathways have been associated with neoplastic transformation. Therefore, the identification of molecules that regulate exocrine pancreatic cell proliferation and apoptotic cell death in response to TGFbeta peptides is necessary for a better understanding of normal morphogenesis as well as carcinogenesis of the pancreas. In this study, we have characterized the expression and function in exocrine pancreatic epithelial cells of the TGFbeta-inducible early gene (TIEG), a Krüppel-like zinc finger transcription factor encoding gene previously isolated from mesodermally derived osteoblastic cells. We demonstrate that this gene is expressed in both acinar and ductular epithelial cell populations from the exocrine pancreas. In addition, we show that the expression of TIEG is regulated by TGFbeta1 as an early response gene in pancreatic epithelial cell lines. Moreover, overexpression of TIEG in the TGFbeta-sensitive epithelial cell line PANC1 is sufficient to induce apoptosis. Together, these results support a role for TIEG in linking TGFbeta-mediated signaling cascades to the regulation of pancreatic epithelial cell growth.

A novel zinc finger protein is encoded by the Arabidopsis LSD1 gene and functions as a negative regulator of plant cell death

Arabidopsis Isd1 mutants are hyperresponsive to cell death initiators and fail to limit the extent of cell death. Superoxide is a necessary and sufficient signal for cell death propagation. Thus, LSD1 monitors a superoxide-dependent signal and negatively regulates a plant cell death pathway. We isolated LSD1 via its map position. The predicted LSD1 protein contains three zinc finger domains, defined by CxxCxRxxLMYxxGASxVxCxxC. These domains are present in three additional Arabidopsis genes, suggesting that LSD1 defines a zinc finger protein subclass. LSD1 is constitutively expressed, consistent with the mutant phenotype. Alternate splicing gives rise to a low abundance mRNA encoding an extra five amino-terminal amino acids. We propose that LSD1 regulates transcription, via either repression of a prodeath pathway or activation of an antideath pathway, in response to signals emanating from cells undergoing pathogen-induced hypersensitive cell death.