cDNA cloning of transcription factor E4TF1 subunits with Ets and notch motifs

GA binding protein augments autophagy via transcriptional activation of BECN1-PIK3C3 complex genes

Macroautophagy is a vesicular catabolic trafficking pathway that is thought to protect cells from diverse stressors and to promote longevity. Recent studies have revealed that transcription factors play important roles in the regulation of autophagy. In this study, we have identified GA binding protein (GABP) as a transcriptional regulator of the combinatorial expression of BECN1-PIK3C3 complex genes involved in autophagosome initiation. We performed bioinformatics analyses that demonstrated highly conserved putative GABP sites in genes that encode BECN1/Beclin 1, several BECN1 interacting proteins, and downstream autophagy proteins including the ATG12-ATG5-ATG16L1 complex. We demonstrate that GABP binds to the promoter regions of BECN1-PIK3C3 complex genes and activates their transcriptional activities. Knockdown of GABP reduced BECN1-PIK3C3 complex transcripts, BECN1-PIK3C3 complex protein levels and autophagy in cultured cells. Conversely, overexpression of GABP increased autophagy. Nutrient starvation increased GABP-dependent transcriptional activity of BECN1-PIK3C3 complex gene promoters and increased the recruitment of GABP to the BECN1 promoter. Our data reveal a novel function of GABP in the regulation of autophagy via transcriptional activation of the BECN1-PIK3C3 complex.

Expression microarray identifies the unliganded glucocorticoid receptor as a regulator of gene expression in mammary epithelial cells

Background

While glucocorticoids and the liganded glucocorticoid receptor (GR) have a well-established role in the maintenance of differentiation and suppression of apoptosis in breast tissue, the involvement of unliganded GR in cellular processes is less clear. Our previous studies implicated unliganded GR as a positive regulator of the BRCA1 tumour suppressor gene in the absence of glucocorticoid hormone, which suggested it could play a similar role in the regulation of other genes.

Methods

An shRNA vector directed against GR was used to create mouse mammary cell lines with depleted endogenous levels of this receptor in order to further characterize the role of GR in breast cells. An expression microarray screen for targets of unliganded GR was performed using our GR-depleted cell lines maintained in the absence of glucocorticoids. Candidate genes positively regulated by unliganded GR were identified, classified by Gene Ontology and Ingenuity Pathway Analysis, and validated using quantitative real-time reverse transcriptase PCR. Chromatin immunoprecipitation and dual luciferase expression assays were conducted to further investigate the mechanism through which unliganded GR regulates these genes.

Results

Expression microarray analysis revealed 260 targets negatively regulated and 343 targets positively regulated by unliganded GR. A number of the positively regulated targets were involved in pro-apoptotic networks, possibly opposing the activity of liganded GR targets. Validation and further analysis of five candidates from the microarray indicated that two of these, Hsd11b1 and Ch25h, were regulated by unliganded GR in a manner similar to Brca1 during glucocorticoid treatment. Furthermore, GR was shown to interact directly with and upregulate the Ch25h promoter in the absence, but not the presence, of hydrocortisone (HC), confirming our previously described model of gene regulation by unliganded GR.

Conclusion

This work presents the first identification of targets of unliganded GR. We propose that the balance between targets of liganded and unliganded GR signaling is responsible for controlling differentiation and apoptosis, respectively, and suggest that gene regulation by unliganded GR may represent a mechanism for reducing the risk of breast tumourigenesis by the elimination of abnormal cells.

The Ets transcription factor GABP is a component of the hippo pathway essential for growth and antioxidant defense

The transcriptional coactivator Yes-associated protein (YAP) plays an important role in organ-size control and tumorigenesis. However, how Yap gene expression is regulated remains unknown. This study shows that the Ets family member GABP binds to the Yap promoter and activates YAP transcription. The depletion of GABP downregulates YAP, resulting in a G1/S cell-cycle block and increased cell death, both of which are substantially rescued by reconstituting YAP. GABP can be inactivated by oxidative mechanisms, and acetaminophen-induced glutathione depletion inhibits GABP transcriptional activity and depletes YAP. In contrast, activating YAP by deleting Mst1/Mst2 strongly protects against acetaminophen-induced liver injury. Similar to its effects on YAP, Hippo signaling inhibits GABP transcriptional activity through several mechanisms. In human liver cancers, enhanced YAP expression is correlated with increased nuclear expression of GABP. Therefore, we conclude that GABP is an activator of Yap gene expression and a potential therapeutic target for cancers driven by YAP.

Identification of Rhit as a novel transcriptional repressor of human Mpv17-like protein with a mitigating effect on mitochondrial dysfunction, and its transcriptional regulation by FOXD3 and GABP

Mpv17-like protein (M-LP) is a protein that has been suggested to be involved in the metabolism of reactive oxygen species. To elucidate the molecular basis of M-LP expression, we recently searched for regulatory elements of M-LP and identified a novel mouse KRAB-containing protein, Rhit (regulator of heat-induced transcription), as a repressor of the transcriptional regulation of M-LP. In this study, we identified zinc-finger protein 205 as a candidate human Rhit (RhitH) and subsequently confirmed its participation in transcriptional regulation of human M-LP (M-LPH). To clarify the functions of RhitH and M-LPH, we searched for cis-regulatory elements in the promoter region of RhitH and identified two transcription factors: forkhead box D3, as a negative regulatory element, and GA-binding protein, one of the key regulators of the mitochondrial electron transport system, as a positive regulatory element. Additionally, it was demonstrated that knockdown of RhitH or overexpression of M-LPH reduces the generation of intracellular H(2)O(2) and loss of mitochondrial membrane potential caused by an inhibitor of the respiratory chain, antimycin A. These results suggest that M-LPH functions to protect cells from oxidative stress and/or initiation of the mitochondrial apoptotic cascade under stressed conditions.

Decreased expression of BRCA1 in SK-BR-3 cells is the result of aberrant activation of the GABP Beta promoter by an NRF-1-containing complex

BACKGROUND

BRCA1 has recently been identified as a potential regulator of mammary stem/progenitor cell differentiation, and this function may explain the high prevalence of breast cancer in BRCA1 mutation carriers, as well as the downregulation of BRCA1 in a large proportion of sporadic breast cancers. That is, loss of BRCA1 function results in blocked differentiation with expansion of the mammary stem/progenitor cells. Because BRCA1 also maintains genomic integrity, its loss could produce a pool of genetically unstable stem/progenitor cells that are prime targets for further transforming events. Thus, elucidating the regulatory mechanisms of BRCA1 expression is important to our understanding of normal and malignant breast differentiation.

RESULTS

Loss of BRCA1 expression in the ErbB2-amplified SK-BR-3 cell line was found to be the result of loss of activity of the ets transcription factor GABP, a previously characterized regulator of BRCA1 transcription. The expression of the non-DNA binding GABPβ subunit was shown to be deficient, while the DNA binding subunit, GABPα was rendered unstable by the absence of GABPβ. Deletion analysis of the GABPβ proximal promoter identified a potential NRF-1 binding site as being critical for expression. Supershift analysis, the binding of recombinant protein and chromatin immunoprecipitation confirmed the role of NRF-1 in regulating the expression of GABPβ. The siRNA knockdown of NRF-1 resulted in decreased GABPβ and BRCA1 expression in MCF-7 cells indicating that they form a transcriptional network. NRF-1 levels and activity did not differ between SK-BR-3 and MCF-7 cells, however the NRF-1 containing complex on the GABPβ promoter differed between the two lines and appears to be the result of altered coactivator binding.

CONCLUSIONS

Both NRF-1 and GABP have been linked to the regulation of nuclear-encoded mitochondrial proteins, and the results of this study suggest their expression is coordinated by NRF-1's activation of the GABPβ promoter. Their linkage to BRCA1, a potential breast stem cell regulator, implies a connection between the induction of mitochondrial metabolism and breast differentiation.

Profiling the thermodynamic softness of adenoviral promoters

We showed previously that anharmonic DNA dynamical features correlate with transcriptional activity in selected viral promoters, and hypothesized that areas of DNA softness may represent loci of functional significance. The nine known promoters from human adenovirus type 5 were analyzed for inherent DNA softness using the Peyrard-Bishop-Dauxois model and a statistical mechanics approach, using a transfer integral operator. We found a loosely defined pattern of softness peaks distributed both upstream and downstream of the transcriptional start sites, and that early transcriptional regions tended to be softer than late promoter regions. When reported transcription factor binding sites were superimposed on our calculated softness profiles, we observed a close correspondence in many cases, which suggests that DNA duplex breathing dynamics may play a role in protein recognition of specific nucleotide sequences and protein-DNA binding. These results suggest that genetic information is stored not only in explicit codon sequences, but also may be encoded into local dynamic and structural features, and that it may be possible to access this obscured information using DNA dynamics calculations.

GA-binding protein regulates KIS gene expression, cell migration, and cell cycle progression

The cyclin-dependent kinase inhibitor p27(Kip1) arrests cell cycle progression through G1/S phases and is regulated by phosphorylation of serine/threonine residues. Recently, we identified the serine/threonine kinase, KIS, which phosphorylates p27(Kip1) on serine 10 leading to nuclear export of p27(Kip1) and protein degradation. However, the molecular mechanisms of transcriptional activation of the human KIS gene and its biological activity are not known. We mapped the transcription initiation site approximately 116 bp 5' to the translation start site, and sequences extending to -141 were sufficient for maximal promoter activity. Mutation in either of two Ets-binding sites in this region resulted in an approximately 75-80% decrease in promoter activity. These sites form at least 3 specific complexes, which contained GA-binding protein (GABP). Knocking down GABPalpha by siRNA in vascular smooth muscle cells (VSMCs) diminished KIS gene expression and reduced cell migration. Correspondingly, in serum stimulated GABPalpha-deficient mouse embryonic fibroblasts (MEFs), KIS gene expression was also significantly reduced, which was associated with an increase in p27(Kip1) protein levels and a decreased percentage of cells in S-phase. Consistent with these findings, following vascular injury in vivo, GABPalpha-heterozygous mice demonstrated reduced KIS gene expression within arterial lesions and these lesions were significantly smaller compared to GABP+/+ mice. In summary, serum-responsive GABP binding to Ets-binding sites activates the KIS promoter, leading to KIS gene expression, cell migration, and cell cycle progression.

Nuclear respiratory factor 2 activates transcription of human mitochondrial translation initiation factor 2 gene

We studied the transcriptional regulation of the human mitochondrial translation initiation factor 2 (IF2mt) gene. The minimal promoter region for the human IF2mt gene contains binding sites for Nuclear Respiratory Factor 2 (NRF-2), which is often involved in the transcription of mitochondrial-related genes. Electrophoresis mobility shift assay (EMSA) analyses indicated that NRF-2alpha/beta binds to the IF2mt promoter. Reporter assays, where HEK293T cells were co-transfected with an NRF-2alpha/beta-expressing vector and/or an IF2mt promoter reporter vector, revealed that NRF-2 trans-activates the IF2mt promoter. NRF-2 sites were also found in the promoters of several other mitochondrial translation factors, which suggests NRF-2 may play a key role in the regulation of mitochondrial protein synthesis.

Transcriptional dysregulation in Down syndrome: predictions for altered protein complex stoichiometries and post-translational modifications, and consequences for learning/behavior genes ELK, CREB, and the estrogen and glucocorticoid receptors

The phenotype of Down syndrome, trisomy of chromosome 21, is hypothesized to be produced by the increased expression due to gene dosage of normal chromosome 21 genes. Chromosome 21 encodes a number of proteins that, based on experimental evidence or domain composition, are classed as transcription factors or their co-regulators. Other chromosome 21 proteins contribute to post-translational modification of transcription factors, including their phosphorylation, dephosphorylation and sumoylation. Several of these chromosome 21 proteins and the pathways in which they function have overlapping transcription factor specificities. Thus, altered stoichiometry in complexes and altered levels of activation of individual transcription factors may contribute to the Down syndrome phenotype by perturbation of downstream gene expression. Here we review recent data on four chromosome 21 proteins: NRIP1, GABPA, DYRK1A and SUMO3. We discuss the implications for activation of ELK, CREB, C/EBP alpha, beta estrogen and glucocorticoid receptors, and for expression of BDNF. Each of these proteins is relevant to learning, behavior and/or development and therefore perturbation of their activation may contribute to the Down syndrome phenotype.

C/EBPα functionally and physically interacts with GABP to activate the human myeloid IgA Fc receptor (FcαR, CD89) gene promoter

Human Fcα receptor (FcαR; CD89), the receptor for the crystallizable fragment (Fc) of immunoglobulin A (IgA), is expressed exclusively in myeloid cells, including granulocytes and monocytes/macrophages, and is considered to define a crucial role of these cells in immune and inflammatory responses. A 259-base pair fragment of the FCAR promoter is sufficient to direct myeloid expression of a reporter gene and contains functionally important binding sites for CCAAT/enhancer-binding protein α (C/EBPα) (CE1, CE2, and CE3) and an unidentified Ets-like nuclear protein. Here, we show that the Ets-binding site is bound by a heterodimer composed of GA-binding protein α (GABPα), an Ets-related factor, and GABPβ, a Notch-related protein. Cotransfection of GABP increased FCAR promoter activity 3.7-fold through the Ets-binding site. GABP and C/EBPα synergistically activated the FCAR promoter 280-fold. Consistent with these observations, in vitro binding analyses revealed a physical interaction between the GABPα subunit and C/EBPα. This is the first report demonstrating both physical and functional interactions between GABP and C/EBPα and will provide new insights into the molecular basis of myeloid gene expression. (Blood. 2005;106:2534-2542)

Expression of mitochondria-related genes in lymphoblastoid cells from patients with bipolar disorder

OBJECTIVES

Several studies have suggested mitochondrial abnormality in bipolar disorder. We reported the association of mitochondrial complex I subunit gene, NDUFV2 at 18p11, with bipolar disorder. A decrease in the mRNA expression of this gene was found in patients with bipolar disorder compared with controls. However, it was unclear whether only the NDUFV2 gene exhibited the decreased expression level in bipolar disorder. The aim of this study was to clarify the association of other nuclear-encoded complex I subunit genes and mitochondria-related genes with bipolar disorder.

METHODS

We quantified the mRNA expression level of five nuclear-encoded mitochondrial complex I subunit genes located at the chromosomal regions linked with bipolar disorder other than NDUFV2, three complex IV subunit genes, and four mitochondrial transcription-related genes using a real-time quantitative reverse transcription polymerase chain reaction method in the lymphoblastoid cell lines from 21 patients with bipolar disorder and 11 controls.

RESULTS

Decreased mRNA expression in patients with bipolar I disorder compared with control subjects was found in most of the complex I subunit genes. In addition, decreased expression levels of these genes correlated with that of NDUFV2. No statistically significant alterations of mRNA expression levels were found between bipolar patients and controls among two of three complex IV subunit genes and all transcription-related genes.

CONCLUSIONS

Our study suggests that the decreased expression of NDUFV2 has a considerable effect on other subunit genes in the mitochondrial respiratory chain and presents further evidence of the biological significance of NDUFV2 in bipolar disorder.

Altered mRNA expression in renal biopsy tissue from patients with IgA nephropathy

BACKGROUND

Immunoglobulin A (IgA) nephropathy (IgAN) is a renal disease characterized by glomerular deposition of IgA-dominant immune deposits that cause glomerular inflammation and sclerosis. Gene expression changes induced in renal tissues/cells as a result of the disease are largely uncharacterized.

METHODS

A sensitive differential mRNA display technique, restriction endonucleolytic analysis of differentially expressed sequences (READS) compared similarly processed normal renal tissue to renal biopsy RNA from patients with IgAN, minimal change disease, and necrotizing crescentic glomerulonephritis. A subset of genes with altered expression in IgAN as identified by the READS technology was further characterized and expression levels confirmed using real-time quantitative polymerase chain reaction (RT-PCR) analysis (TaqMan) in all RNA.

RESULTS

Initial READS analysis showed IgAN samples have lower mRNA levels relative to normal renal tissue mRNA samples based upon total RNA as measured by ribosomal RNA. One hundred seventy-five differentially expressed non-redundant fragments were found from 860 initial candidate fragments. Twenty genes were selected for additional TaqMan analysis, and 13 of 20 genes showed statistically different expression when comparing biopsies from normal individuals and IgAN patients. Expression differences were seen in these genes in biopsies of IgAN of differing clinical activities. Gene expression cluster analysis using the Ward method detailed disease- and gene-related clusters. Detailed examination of the promoter regions of the genes within two gene clusters revealed common gene transcriptional regulatory protein-binding sites.

CONCLUSION

IgAN leads to significant changes in overall mRNA transcription levels within the renal tissue, in addition to gene-specific mRNA level changes. Disease-related patterns of expression were identified and gene-specific clusters suggest common mechanisms of transcriptional alteration.

Bikunin target genes in ovarian cancer cells identified by microarray analysis

Bikunin, a Kunitz-type protease inhibitor, could potentially suppress tumor cell invasion and metastasis. Our previous study revealed that overexpression of bikunin in a human ovarian cancer cell line, HRA, resulted in a down-regulation in uPA and uPAR gene expression. For identifying the full repertoire of bikunin-regulated genes, a cDNA microarray hybridization screening was conducted using mRNA from bikunin-treated or bikunin-transfected HRA cells. A number of bikunin-regulated genes were identified, and their regulation was confirmed by Northern blot analysis. Our screen identified 11 bikunin-stimulated genes and 29 bikunin-repressed genes. The identified genes can indeed be classified into distinct subsets. These include transcriptional regulators, oncogenes/tumor suppressor genes, signaling molecules, growth/cell cycle, invasion/metastasis, cytokines, apoptosis, ion channels, extracellular matrix proteins, as well as some proteases. This screen identified suppression of several genes such as CDC-like kinase, LIM domain binding, Ets domain transcription factor, Rho GTPase-activating protein, tyrosine phosphorylation-regulated kinase, hyaluronan-binding protein, matriptase, and pregnancy-associated plasma protein-A (PAPP-A), which have previously been implicated in enhancing tumor promotion. Northern blot analysis confirmed that several genes including matriptase and PAPP-A were down-regulated by bikunin by approximately 9-fold. Further, genetic inhibition of matriptase or PAPP-A could lead to diminished invasion. These results show that bikunin alters the pattern of gene expression in HRA cells leading to a block in cell invasion.

GA-binding protein (GABP) and Sp1 are required, along with retinoid receptors, to mediate retinoic acid responsiveness of CD18 (beta 2 leukocyte integrin): a novel mechanism of transcriptional regulation in myeloid cells

CD18 (beta(2) leukocyte integrin) is transcriptionally regulated in myeloid cells, but the mechanisms that increase its expression in response to retinoic acid (RA) have not been defined. The CD18 promoter was activated by RA treatment in stably transfected U937 myeloid cells. We identified a retinoic acid response element (RARE) that lies nearly 900 nucleotides upstream of the CD18 transcriptional start site that was bound by the RA receptors, retinoic acid receptor (RAR) and retinoic X receptor (RXR). This RARE accounted for one half of the RA responsiveness of CD18. However, unexpectedly, one half of the dynamic response to RA was mediated by the 96-nucleotide CD18 minimal promoter, which lacks a recognizable RARE. Binding sites for the ets transcription factor, GA-binding protein (GABP), and Sp1 were required for full RA responsiveness of both the CD18 minimal promoter and the full-length promoter. The ets sites conferred RA responsiveness on an otherwise unresponsive heterologous promoter, and RA responsiveness was directly related to the number of ets sites. The transcriptional coactivator p300/CBP physically interacted with GABP in vivo, and p300 increased the responsiveness of the CD18 promoter to RA. These studies demonstrate a novel role for non-RAR transcription factors in mediating RA activation in myeloid cells. They support the concept that transcription factors other than RARs are required for RA-activated gene expression. We hypothesize that a multiprotein complex--an enhanceosome--that includes GABP, other transcription factors, and coactivators, dynamically regulates CD18 expression in myeloid cells.

Isolation and characterization of chicken GA-binding protein

We have purified and characterized chicken liver nuclear proteins that bind to Ets binding sites (EBSs) of ribosomal protein (r-protein) gene promoters. We employed supershift assays and antibodies to mouse GA binding protein (GABP), to show that the proteins were similar to alpha and beta subunits of GABP. Western blot analysis identified 54- and 38-kDa proteins as the alpha type, and a 46-kDa protein as the beta type. When compared with nuclear extracts (NEs) of other species, we observed that the 38-kDa protein was unique to chicken, and appears to be derived from the 54-kDa protein. The 54- and 46-kDa proteins were highly expressed in chicken tissues and were major components through higher animals, indicating that both proteins have a conserved role.

YEAF1/RYBP and YAF-2 are functionally distinct members of a cofactor family for the YY1 and E4TF1/hGABP transcription factors

The transcription factor hGABP/E4TF1 is a heterotetrameric complex composed of two DNA-binding subunits (hGABP alpha/E4TF1-60) and two transactivating subunits (hGABP beta/E4TF1-53). In order to understand the molecular mechanism of transcriptional regulation by hGABP, we searched for proteins that interact with the non-DNA-binding subunit, hGABP beta, using yeast two-hybrid screening. We identified a human cDNA encoding a protein related to YAF-2 (YY1-associated factor 2), which was previously isolated as an interacting partner of the Ying-Yang-1 (YY1) transcription factor. Reflecting this similarity, both YAF-2 and this novel protein (named YEAF1 for YY1- and E4TF1/hGABP-associated factor-1) interacted with hGABP beta and YY1 in vitro and in vivo, indicating that YEAF1 and YAF-2 constitute a cofactor family for these two structurally distinct transcription factors. By using yeast three-hybrid assay, we demonstrated that hGABP beta and YY1 formed a complex only in the presence of YEAF1, indicating that YEAF1 is a bridging factor of these two transcription factors. These cofactors are functionally different in that YAF-2 positively regulates the transcriptional activity of hGABP but YEAF1 negatively regulates this activity. Also, YAF-2 mRNA is highly expressed in skeletal muscle, whereas YEAF1 mRNA is highly expressed in placenta. We speculate that the transcriptional activity of hGABP is in part regulated by the expression levels of these tissue-specific cofactors. These results provide a novel mechanism of transcriptional regulation by functionally distinct cofactor family members.

Cell-cycle-dependent regulation of human aurora A transcription is mediated by periodic repression of E4TF1

Human aurora A is a serine-threonine kinase that controls various mitotic events. The transcription of aurora A mRNA varies throughout the cell cycle and peaks during G(2)/M. To clarify the transcriptional mechanism, we first cloned the 1.8-kb 5'-flanking region of aurora A including the first exon. Transient expression of aurora A promoter-luciferase constructs containing a series of 5'-truncated sequences or site-directed mutations identified a 7-bp sequence (CTTCCGG) from -85 to -79 as a positive regulatory element. Electromobility shift assays identified the binding of positive regulatory proteins to the CTTCCGG element. Anti-E4TF1-60 antibody generated a supershifted complex. Furthermore, coexpression of E4TF1-60 and E4TF1-53 markedly increased aurora A promoter activity. Synchronized cells transfected with the aurora A promoter-luciferase constructs revealed that the promoter activity of aurora A increased in the S phase and peaked at G(2)/M. In addition, we identified a tandem repressor element, CDE/CHR, just downstream of the CTTCCGG element, and mutation within this element led to a loss of cell cycle regulation. We conclude that the transcription of aurora A is positively regulated by E4TF1, a ubiquitously expressed ETS family protein, and that the CDE/CHR element was essential for the G(2)/M-specific transcription of aurora A.

Sp1 and Sp3 physically interact and co-operate with GABP for the activation of the utrophin promoter

The utrophin gene codes for a large cytoskeletal protein closely related to dystrophin which, in the absence of dystrophin, can functionally substitute it. Utrophin is transcribed by two independently regulated promoters about 50 kb apart. The upstream promoter is TATA-less and contains a functional GABP binding site which, in muscle, restricts the promoter activity to post-synaptic nuclei. Transient transfections analysis of mutant promoters in rhabdomyosarcoma cells showed that the upstream promoter contains three functional GC elements that are recognised by Sp1 and Sp3 factors in vitro. Co-transfections of the promoter with Sp1, Sp3 and GABP factors in Drosophila SL2 Schneider cells, which lack of endogenous Sp factors, demonstrated that both Sp1 and Sp3 are positive regulators of the utrophin promoter and that they activate transcription synergistically with GABP. Consistent with this result, we observed physical interaction of both Sp factors with the GABPalpha subunit in vitro. Functional domain interaction analysis of Sp1 and Sp3 revealed that both factors interact with GABPalpha through their DNA binding zinc finger domain. The modulation and correct interaction between Sp1, Sp3 and GABP in muscle cells may be critical for the regulation of the utrophin promoter, and provide new targets for therapies of Duchenne muscular dystrophy.

Modulation of the promoter region of prepro-hypocretin by alpha-interferon

Hypocretins 1 and 2 (also called orexins A and B, respectively) are hypothalamic neuropeptides that have recently been shown to be involved in the sleep disorder narcolepsy and possibly in the normal regulation of sleep and wake functions. These two peptides are derived from a single precursor molecule called prepro-hypocretin, also known as prepro-orexin. We have cloned a 450 bp fragment from the 5'-flanking region of the human prepro-hypocretin gene and demonstrated that this fragment has promoter activity in vitro. Deletions at the 5' end from -450 to -188 reduced the promoter activity by approximately 50%. Further deletion from the 5'-end to -69 almost completely abolished promoter activity. The 450 bp fragment contains a number of potential transcription factor binding sites, including an interferon (IFN) response element. Our studies demonstrate that alpha-IFN strongly inhibits the promoter activity of both 450 and 188 bp fragments in a dose-dependent manner. The inhibitory effect of alpha-IFN is consistent with recent studies which suggest that hypocretin 1/orexin A may be involved in modulating arousal states and with the literature indicating involvement of immune-related molecules in sleep regulation.

Regulation of the Hsp90-binding immunophilin, cyclophilin 40, is mediated by multiple sites for GA-binding protein (GABP)

Within steroid receptor heterocomplexes the large tetratricopeptide repeat-containing immunophilins, cyclophilin 40 (CyP40), FKBP51, and FKBP52, target a common interaction site in heat shock protein 90 (Hsp90) and act coordinately with Hsp90 to modulate receptor activity. The reversible nature of the interaction between the immunophilins and Hsp90 suggests that relative cellular abundance might be a key determinant of the immunophilin component within steroid receptor complexes. To investigate CyP40 gene regulation, we have isolated a 5-kilobase (kb) 5'-flanking region of the human gene and demonstrated that a approximately 50 base pair (bp) sequence adjacent to the transcription start site is essential for CyP40 basal expression. Three tandemly arranged Ets sites within this critical region were identified as binding elements for the multimeric Ets-related transcription factor, GA binding protein (GABP). Functional studies of this proximal promoter sequence, in combination with mutational analysis, confirmed these sites to be crucial for basal promoter function. Furthermore, overexpression of both GABP alpha and GABP beta subunits in Cos1 cells resulted in increased endogenous CyP40 mRNA levels. Significantly, a parallel increase in FKBP52 mRNA expression was not observed, highlighting an important difference in the mode of regulation of the CyP40 and FKBP52 genes. Our results identify GABP as a key regulator of CyP40 expression. GABP is a common target of mitogen and stress-activated pathways and may integrate these diverse extracellular signals to regulate CyP40 gene expression.

The alpha and beta subunits of the GA-binding protein form a stable heterodimer in solution. Revised model of heterotetrameric complex assembly

We have studied the assembly of GA-binding protein (GABP) in solution and established the role of DNA in the assembly of the transcriptionally active GABPalpha(2)beta(2) heterotetrameric complex. GABP binds DNA containing a single PEA3/Ets-binding site (PEA3/EBS) exclusively as the alphabeta heterodimer complex, but readily binds as the GABPalpha(2)beta(2) heterotetramer complex on DNA containing two PEA3/EBSs. Positioning of the PEA3/EBSs on the same face of the DNA helix stabilizes heterotetramer complex binding. These observations suggest that GABPalphabeta heterodimers are the predominant molecular species in solution and that DNA containing two PEA3/EBSs promotes formation of the GABPalpha(2)beta(2) heterotetrameric complex. We analyzed the assembly of GABPalpha(2)beta(2) heteromeric complexes in solution by analytical ultracentrifugation. GABPalpha exists as a monomer in solution while GABPbeta exists in a monomer-dimer equilibrium (K(d) = 1.8 +/- 0.27 microM). In equimolar mixtures of the two subunits, GABPalpha and GABPbeta formed a stable heterodimer, with no heterotetramer complex detected. Thus, GABP exists in solution as the heterodimer previously shown to be a weak transcriptional activator. Assembly of the transcriptionally active GABPalpha(2)beta(2) heterotetramer complex requires the presence of specific DNA containing at least two PEA3/EBSs.

The novel coactivator C1 (HCF) coordinates multiprotein enhancer formation and mediates transcription activation by GABP

Transcription of the herpes simplex virus 1 (HSV-1) immediate early (IE) genes is determined by multiprotein enhancer complexes. The core enhancer assembly requires the interactions of the POU-homeodomain protein Oct-1, the viral transactivator alphaTIF and the cellular factor C1 (HCF). In this context, the C1 factor interacts with each protein to assemble the stable enhancer complex. In addition, the IE enhancer cores contain adjacent binding sites for other cellular transcription factors such as Sp1 and GA-binding protein (GABP). In this study, a direct interaction of the C1 factor with GABP is demonstrated, defining the C1 factor as the critical coordinator of the enhancer complex assembly. In addition, mutations that reduce the GABP transactivation potential also impair the C1-GABP interaction, indicating that the C1 factor functions as a novel coactivator of GABP-mediated transcription. The interaction and coordinated assembly of the enhancer proteins by the C1 factor may be critical for the regulation of the HSV lytic-latent cycle.

Synergistic transcriptional activation by hGABP and select members of the activation transcription factor/cAMP response element-binding protein family

The Ets-related DNA-binding protein human GA-binding protein (hGABP) alpha interacts with the four ankyrin-type repeats of hGABPbeta to form an hGABP tetrameric complex that stimulates transcription through the adenovirus early 4 (E4) promoter. Using co-transfection assays, this study demonstrated that the hGABP complex mediated efficient activation of transcription from E4 promoter synergistically with activating transcription factor (ATF) 1 or cAMP response element-binding protein (CREB), but not ATF2/CRE-BP1. This synergy also partially occurred when hGABPalpha was used alone in place of the combination of hGABPalpha and hGABPbeta. hGABP activated an artificial promoter containing only ATF/CREB-binding sites under coexistence of ATF1 or CREB. Consistent with these results, physical interactions of hGABPalpha with ATF1 or CREB were observed in vitro. Functional domain analyses of the physical interactions revealed that the amino-terminal region of hGABPalpha bound to the DNA-binding domain of ATF1, which resulted in the formation of ternary complexes composed of ATF1, hGABPalpha, and hGABPbeta. In contrast to hGABPalpha, hGABPbeta did not significantly interact with ATF1 and CREB. Taken together, these results indicate that hGABP functionally interacts with selective members of the ATF/CREB family, and also suggest that synergy results from multiple interactions which mediate stabilization of large complexes within the regulatory elements of the promoter region, including DNA-binding and non-DNA-binding factors.

Transcriptional regulation of Fas gene expression by GA-binding protein and AP-1 in T cell antigen receptor.CD3 complex-stimulated T cells

Fas (CD95 or APO-1), a transmembrane cell surface receptor of the tumor necrosis factor receptor family, is up-regulated in activated T lymphocytes. Our present study identified an upstream enhancer element (between nucleotide positions -862 and -682) containing a GA-binding protein (GABP) site and a low affinity activating protein-1 (AP-1)-binding site. T cell activation increased the DNA binding of GABP and AP-1 to this enhancer site. The specificity of GABP and AP-1 binding was demonstrated by competition electrophoretic mobility shift assay and supershift electrophoretic mobility shift assay with antibodies against GABP and AP-1, respectively. Mutational analysis of Fas promoter revealed that both GABP- and AP-1-binding sites were required for initiating Fas gene transcription. We further show that anti-CD3 mAb, phorbol 12-myristate 13-acetate, and phorbol 12-myristate 13-acetate/ionomycin strongly activated promoters carrying multiple copies of the Fas enhancer, and mutation of either the GABP or AP-1 binding site severely reduced transcriptional activity. Taken together, these results suggest that the transcription factors GABP and AP-1 play a critical role in the induction of Fas gene expression in T cell antigen receptor.CD3-stimulated Jurkat cells.

The role of human MBF1 as a transcriptional coactivator

Multiprotein bridging factor 1 (MBF1) is a coactivator which mediates transcriptional activation by interconnecting the general transcription factor TATA element-binding protein and gene-specific activators such as the Drosophila nuclear receptor FTZ-F1 or the yeast basic leucine zipper protein GCN4. The human homolog of MBF1 (hMBF1) has been identified but its function, especially in transcription, remains unclear. Here we report the cDNA cloning and functional analysis of hMBF1. Two isoforms, which we term hMBF1alpha and hMBF1beta, have been identified. hMBF1alpha mRNA was detected in a number of tissues, whereas hMBF1beta exhibited tissue-specific expression. Both isoforms bound to TBP and Ad4BP/SF-1, a mammalian counterpart of FTZ-F1, and mediated Ad4BP/SF-1-dependent transcriptional activation. While hMBF1 was detected in the cytoplasm by immunostaining, coexpression of the nuclear protein Ad4BP/SF-1 with hMBF1 induced accumulation of hMBF1 in the nucleus, suggesting that hMBF1 is localized in the nucleus through its binding to Ad4BP/SF-1. hMBF1 also bound to ATF1, a member of the basic leucine zipper protein family, and mediated its activity as a transcriptional activator. These data establish that the coactivator MBF1 is functionally conserved in eukaryotes.

Characterization and localization to chromosome 7 of psihGABPalpha, a human processed pseudogene related to the ets transcription factor, hGABPalpha

GABP is a heteromeric transcription factor complex which consists of the ets related protein, GABPalpha, and the Notch-related protein, GABPbeta. We isolated a human genomic DNA fragment which is highly homologous and colinear with human GABPalpha cDNA, but which lacks introns. This processed pseudogene, psihGABPalpha, is expressed as RNA in U937 human myeloid cells, but a mutation at the site that corresponds to the ATG start methionine codon prevents its translation into protein. The pseudogene was localized to chromosome 7 using a somatic cell hybrid mapping panel and it is not syntenic with authentic GABPalpha, which was localized to chromosome 21. We have identified psihGABPalpha, a novel, GABPalpha-related processed pseudogene which is expressed as a RNA transcript in human myeloid cells.

Identification of a GABP alpha/beta binding site involved in the induction of oxytocin receptor gene expression in human breast cells, potentiation by c-Fos/c-Jun

Oxytocin (OT) receptors (OTRs) mediate reproductive functions, including the initiation of labor and milk ejection. OTR messenger RNA levels are highly regulated, reaching the greatest concentration in the uterus at the end of gestation, and in the mammary gland during lactation. Factors directly effecting changes in OTR gene expression in the mammary gland are not known, so the present studies were done to elucidate possible regulators by characterizing the human OTR gene promoter and 5'-flanking sequence. By analyzing expression of promoter-luciferase constructs, we localized a region between -85 and -65 that was required for both basal and serum-induced expression in a mammary tumor cell line (Hs578T) that expresses inducible, endogenous OTRs. This DNA region contains an ets family target sequence (5'-GGA-3'), and a CRE/AP-1-like motif. The specific Ets factor binding to the OTR promoter was identified, by electrophoretic mobility immunoshift assays, to be GABP alpha/beta. Co-transfection of a -85 OTR/luciferase construct with vectors expressing GABP alpha and GABP beta1 had only a modest effect on expression, but cotransfection with GABP alpha/beta- with c-Fos/c-Jun-expressing plasmids resulted in an increase of almost 10-fold in luciferase activity. Mutation of either the GABP- or CRE-like binding sites obliterated the induction. These findings are consistent with the involvement of protein kinase C activity in serum induction of the endogenous gene in Hs578T cells. We showed the requirement for GABP alpha/beta and c-Fos/c-Jun in endogenous OTR gene expression, using oligonucleotide GABP and AP-1 binding decoys to inhibit serum-induced increases in 125I-labeled OT antagonist binding to Hs578T cells. Our work is the first characterization of the proximal promoter region of the human OTR gene, and it sets the stage for studying regulation of OTR expression in breast cells.

Structures, sequence characteristics, and synteny relationships of the transcription factor E4TF1, the splicing factor U2AF35 and the cystathionine beta synthetase genes from Fugu rubripes

A cosmid containing the beta-amyloid precursor protein (APP) from Fugu rubripes has been completely sequenced. In addition to APP, the cosmid contains the E4TF1-60 transcription factor, the U2AF35 pre-mRNA splicing factor, and the cystathionine beta synthetase (CBS) gene. The human homologues of all four genes map to human chromosome 21 but are not clustered; APP and E4TF1-60 map within 21q21, whereas U2AF35 and CBS map approximately 20Mb distal in 21q22. 3. The protein sequences of the Fugu genes vary in their overall level of similarity to their mammalian homologues, but several regions of functional importance are almost identical. As expected, the intron/exon structures of the homologous pairs of genes are highly conserved, but there are significant differences in the compaction ratios. The introns of APP and E4TF1-60 are 49- and 24-fold smaller in Fugu than in human, and the intergenic distance is compressed at least 100-fold. For U2AF35 and CBS, the introns are compressed only five- to eightfold. These size differences were compared with those for a number of previously reported Fugu genes; in general, levels of compaction of Fugu genes are consistent with the isochore locations of the human homologues.

Transcriptional up-regulation of the delayed early gene HRS/SRp40 during liver regeneration. Interactions among YY1, GA-binding proteins, and mitogenic signals

Arg-Ser-rich domain-containing proteins (SR proteins), a family of splicing factors, can regulate pre-mRNA alternative splicing in a concentration dependent manner. Thus, the relative expression of various SR proteins may play an important role in alternative splicing regulation. HRS/SRp40, an SR protein and delayed early gene in liver regeneration, can mediate alternative splicing of fibronectin mRNA. Here we determined that transcription of the HRS/SRp40 gene is induced about 5-fold during liver regeneration, similar to the level of steady-state mRNA. We found that both mouse and human HRS promoters lack TATA and CAAT boxes. The mouse promoter region from -130 to -18, which contains highly conserved GA-binding protein (GABP) and YY1 binding sites, conferred high transcriptional activity. While GABPalpha/GABPbeta heterodimer transactivated the HRS promoter, YY1 functioned as a repressor. During liver regeneration, the relative amount of GABPalpha/GABPbeta heterodimer increased 3-fold, and YY1 changed little, which could partially account for the increase in HRS gene transcription. Interleukin-6, a critical mitogenic component of liver regeneration, was able to relieve the repressive activity of the YY1 site within the HRS promoter. The combined effect of small changes in the level of existing transcription factors and mitogenic signals may explain the transcriptional activation of the HRS gene during cell growth.

The cloning and characterization of a novel human diacylglycerol kinase, DGKiota

Diacylglycerol (DAG) plays a central role in both the synthesis of complex lipids and in intracellular signaling; diacylglycerol kinase (DGK) catalyzes the phosphorylation of DAG, which yields phosphatidic acid. A family of DGKs has been identified in multicellular organisms over the past few years, but the physiological function(s) of this diversity is not clear. One clue has come from the Drosophila DGK2, rdgA, since mutations in this gene cause retinal degeneration. We isolated a novel DGK, which we designated DGKiota, from human retina and brain libraries. DGKiota contains two cysteine-rich repeats, a region similar to the phosphorylation site domain of myristoylated alanine-rich C kinase substrate, a conserved catalytic domain, and four ankyrin repeats at its C terminus. By primary structure, it is most similar to human DGKzeta and Drosophila rdgA. An >12-kilobase mRNA for DGKiota was detected only in brain and retina among the tissues examined. In cells transfected with the DGKiota cDNA, we detected an approximately 130-kDa protein by immunoassay, and activity assays demonstrated that it encodes a functional DAG kinase. The protein was found to be in both the cytoplasm and nucleus with the localization controlled by PKC isoforms alpha and gamma. The gene encoding DGKiota was localized to human chromosome 7q32.3-33, which is known to be a locus for an inherited form of retinitis pigmentosa. These results have defined a novel isoform of DAG kinase, which may have important cellular functions in the retina and brain.

Cloning and Characterization of the Human Interleukin-3 (IL-3)/IL-5/ Granulocyte-Macrophage Colony-Stimulating Factor Receptor βc Gene: Regulation by Ets Family Members

High-affinity receptors for interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF) are composed of two distinct subunits, a ligand-specific  chain and a common β chain (βc). Whereas the mouse has two homologous β subunits (βc and βIL-3), in humans, only a single β chain is identified. We describe here the isolation and characterization of the gene encoding the human IL-3/IL-5/GM-CSF receptor β subunit. The gene spans about 25 kb and is divided into 14 exons, a structure very similar to that of the murine βc/βIL-3 genes. Surprisingly, we also found the remnants of a second βc chain gene directly downstream of βc. We identified a functional promoter that is active in the myeloid cell lines U937 and HL-60, but not in HeLa cells. The proximal promoter region, located from −103 to +33 bp, contains two GGAA consensus binding sites for members of the Ets family. Single mutation of those sites reduces promoter activity by 70% to 90%. The 5′ element specifically binds PU.1, whereas the 3′ element binds a yet-unidentified protein. These findings, together with the observation that cotransfection of PU.1 and other Ets family members enhances βc promoter activity in fibroblasts, reinforce the notion that GGAA elements play an important role in myeloid-specific gene regulation.

Cloning and Characterization of the Human Interleukin-3 (IL-3)/IL-5/ Granulocyte-Macrophage Colony-Stimulating Factor Receptor βc Gene: Regulation by Ets Family Members

High-affinity receptors for interleukin-3 (IL-3), IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF) are composed of two distinct subunits, a ligand-specific  chain and a common β chain (βc). Whereas the mouse has two homologous β subunits (βc and βIL-3), in humans, only a single β chain is identified. We describe here the isolation and characterization of the gene encoding the human IL-3/IL-5/GM-CSF receptor β subunit. The gene spans about 25 kb and is divided into 14 exons, a structure very similar to that of the murine βc/βIL-3 genes. Surprisingly, we also found the remnants of a second βc chain gene directly downstream of βc. We identified a functional promoter that is active in the myeloid cell lines U937 and HL-60, but not in HeLa cells. The proximal promoter region, located from −103 to +33 bp, contains two GGAA consensus binding sites for members of the Ets family. Single mutation of those sites reduces promoter activity by 70% to 90%. The 5′ element specifically binds PU.1, whereas the 3′ element binds a yet-unidentified protein. These findings, together with the observation that cotransfection of PU.1 and other Ets family members enhances βc promoter activity in fibroblasts, reinforce the notion that GGAA elements play an important role in myeloid-specific gene regulation.

Functional interactions of transcription factor human GA-binding protein subunits

The transcription factor human GA-binding protein (hGABP) is composed of two subunits, the Ets-related hGABPalpha, which binds to a specific DNA sequence, and either one of two hGABPalpha-associated subunits, hGABPbeta or hGABPgamma. The DNA-binding protein hGABPalpha cannot affect transcription by itself, but can modify hGABP-dependent transcription in vitro and in vivo in the presence of its associated subunits. In this study, co-transfection assays showed that the ratio of hGABPbeta to hGABPgamma affected transcription from a promoter containing hGABP binding sites. Biochemical analysis showed that they bind to hGABPalpha competitively, indicating that the ratio of hGABPbeta to hGABPgamma is important for hGABP complex formation. Kinetic analysis of the protein-protein interaction using the surface plasmon resonance system showed that hGABPalpha binds to hGABPbeta or hGABPgamma with similar equilibrium constants. Kinetic analysis of the DNA-hGABP interaction showed that the binding of hGABPgamma to hGABPalpha stabilized the interaction of hGABPalpha with its DNA binding site. In addition, the kinetic analysis revealed that this was due to a slower dissociation of the protein complex from the DNA. These results suggest that hGABPalpha-associated subunits influence the DNA binding stability of hGABPalpha and regulate hGABP-mediated transcription by competing with each other.

A gene encoding a novel RFX-associated transactivator is mutated in the majority of MHC class II deficiency patients

Major histocompatibility class II (MHC-II) molecules are transmembrane proteins that have a central role in development and control of the immune system. They are encoded by a multigene family and their expression is tightly regulated. MHC-II deficiency (OMIM 209920) is an autosomal recessive immunodeficiency syndrome resulting from defects in trans-acting factors essential for transcription of MHC-II genes. There are four genetic complementation groups (A, B, C and D), reflecting the existence of four MHC-II regulators. The factors defective in groups A (CIITA), C (RFX5) and D (RFXAP) have been identified. CIITA is a non-DNA-binding co-activator that controls the cell-type specificity and inducibility of MHC-II expression. RFX5 and RFXAP are two subunits of RFX, a multi-protein complex that binds the X box motif of MHC-II promoters. Mutations in the genes encoding RFX5 (RFX5) or RFXAP (RFXAP) abolish binding of RFX (refs 7,8,12). Similar to groups C and D, group B is characterized by a defect in RFX binding, and although it accounts for the majority of patients, the factor defective in group B has remained unknown. We report here the isolation of RFX by a novel single-step DNA-affinity purification approach and the identification of RFXANK, the gene encoding a third subunit of RFX. RFXANK restores MHC-II expression in cell lines from patients in group B and is mutated in these patients. RFXANK contains a protein-protein interaction region consisting of three ankyrin repeats. Its interaction with RFX5 and RFXAP is essential for binding of the RFX complex to MHC-II promoters.

Regulation of the rat thyrotropin receptor gene by the methylation-sensitive transcription factor GA-binding protein

The GA-binding protein (GABP), a transcription factor with a widespread tissue distribution, consists of two subunits, a and beta1, and acts as a potent positive regulator of various genes. The effect of GABP on transcription of the TSH receptor (TSHR) gene in rat FRTL-5 thyroid cells has now been investigated. Both deoxyribonuclease I footprint analysis and gel mobility-shift assays indicated that bacterially expressed glutathione S-transferase fusion proteins of GABP subunits bind to a region spanning nucleotides (nt) -116 to -80 of the TSHR gene. In gel mobility-shift assays, nuclear extracts of FRTL-5 cells and FRT cells yielded several specific bands with a probe comprising nt -116 to -80. Supershift assays with antibodies to GABPalpha and to GABPbeta1 showed that GABP was a component of the probe complexes formed by the nuclear extracts. Immunoblot analysis confirmed the presence of both GABP subunits in the nuclear extracts. A reporter gene construct containing the TSHR gene promoter was activated, in a dose-dependent manner, in FRTL-5 cells by cotransfection with constructs encoding both GABPalpha and GABPbeta1. Both GABP binding to and activation of the TSHR gene promoter were prevented by methylation of CpG sites at nt -93 and -85. These CpG sites were highly methylated (>82%) in FRT cells and completely demethylated in FRTL-5 cells, consistent with expression of the TSHR gene in the latter, but not the former. These results suggest that GABP regulates transcription of the TSHR gene in a methylation-dependent manner and that methylation of specific CpG sites and the methylation sensitivity of GABP contribute to the failure of FRT cells to express the endogenous TSHR gene.

The cloning and developmental regulation of murine diacylglycerol kinase zeta

Diacylglycerol kinases (DGKs) regulate the key signaling intermediates diacylglycerol (DAG) and phosphatidic acid (PA). We isolated cDNA clones of mouse diacylglycerol kinase zeta (mDGKzeta) and found that it shares 88% identity at the nucleic acid level and 95.5% identity at the amino acid level with human DGKzeta (hDGKzeta). Murine DGKzeta protein rose gradually during embryonic development, and was abundant in newborn and adult brains. By RNA whole-mount in situ hybridization, mDGKzeta was shown to be expressed in spinal ganglia and limb buds at low level in E11.5 embryos and at higher level in E12.5 embryos. In E13.5 embryos, DGKzeta mRNA was highly expressed in vibrissa follicles, in spinal ganglia, and in the interdigital regions of the developing limbs. Northern blotting showed that DGKzeta expression was limited to specific anatomical regions of the brain. Thus, the expression of DGKzeta is regulated temporally and spatially during mammalian development and correlates with the development of sensory neurons and regions undergoing apoptosis.

The GABP-responsive element of the interleukin-2 enhancer is regulated by JNK/SAPK-activating pathways in T lymphocytes

T cell activation leads via multiple intracellular signaling pathways to rapid induction of interleukin-2 (IL-2) expression, which can be mimicked by costimulation with 12-O-tetradecanoylphorbol-13-acetate (TPA) and ionomycin. We have identified a distal IL-2 enhancer regulated by the Raf-MEK-ERK signaling pathway, which can be induced by TPA/ionomycin treatment. It contains a dyad symmetry element (DSE) controlled by the Ets-like transcription factor GA-binding protein (GABP), a target of activated ERK. TPA/ionomycin treatment of T cells stimulates both mitogen-activated ERK, as well as the stress-activated mitogen-activated protein kinase family members JNK/SAPK and p38. In this study, we investigated the contribution of the stress-activated pathways to the induction of the distal IL-2 enhancer. We show that JNK- but not p38-activating pathways regulate the DSE activity. Furthermore, the JNK/SAPK signaling pathway cooperates with the Raf-MEK-ERK cascade in TPA/ionomycin-induced DSE activity. In T cells, overexpression of SPRK/MLK3, an activator of JNK/SAPK, strongly induces DSE-dependent transcription and dominant negative kinases of SEK and SAPK impair TPA/ionomycin-induced DSE activity. Blocking both ERK and JNK/SAPK pathways abolishes the DSE induction. The inducibility of the DSE is strongly dependent on the Ets-core motifs, which are bound by GABP. Both subunits of GABP are phosphorylated upon JNK activation in vivo and three different isoforms of JNK/SAPK, but not p38, in vitro. Our data suggest that GABP is targeted by signaling events from both ERK and JNK/SAPK pathways. GABP therefore is a candidate for signal integration and regulation of IL-2 transcription in T lymphocytes.

Regulation of human B19 parvovirus promoter expression by hGABP (E4TF1) transcription factor

The genetic expression of human B19 parvovirus is only dependent on one promoter in vivo and in vitro. This is the P6 promoter, which is located on the left side of the genome and is a single-stranded DNA molecule. This led us to investigate the regulation of the P6 promoter and the possible resulting variability of the nucleotide sequence. After analysis of the promoter region of 17 B19 strains, only 1.5% variability was found. More exciting was the finding of mutations that were clustered around the TATA box and defined a highly conserved region (nucleotides 113-210) in the proximal part of the P6 promoter. HeLa and UT7/Epo cell extracts were found to protect this region, which contained a core motif for Ets family proteins, with YY1 and Sp1 binding sites on either side. Gel mobility shift assays performed with nuclear proteins from HeLa and UT7/Epo cells identified DNA-binding proteins specific for these sites. By supershift analysis, we demonstrated the binding of the hGABP (also named E4TF1) protein to the Ets binding site and the fixation of Sp1 and YY1 proteins on their respective motifs. In Drosophila SL2 cells, hGABPalpha and -beta stimulated P6 promoter activity, and hGABPalpha/hGABPbeta and Sp1 exerted synergistic stimulation of this activity, an effect diminished by YY1.

Identification of redox-sensitive cysteines in GA-binding protein-alpha that regulate DNA binding and heterodimerization

The transcription factor GA-binding protein (GABP) is composed of two subunits, GABPalpha and GABPbeta. The DNA-binding subunit, GABPalpha, is a member of the Ets family of transcription factors, characterized by the conserved Ets-domain that mediates DNA binding and associates with GABPbeta, which lacks a discernible DNA binding domain, through ankyrin repeats in the NH2 terminus of GABPbeta. We previously demonstrated that GABP is subject to redox regulation in vitro and in vivo through four COOH-terminal cysteines in GABPalpha. To determine the roles of individual cysteines in GABP redox regulation, we generated a series of serine substitution mutants by site-directed mutagenesis and identified three redox-sensitive cysteine residues in GABPalpha (Cys388, Cys401, and Cys421). Sulfhydryl modification of Cys388 and Cys401 inhibits DNA binding by GABPalpha, whereas, modification of Cys421 has no effect on GABPalpha DNA binding but inhibits dimerization with GABPbeta. The positions of Cys388 and Cys401 within the known Ets-domain structure suggest two very different mechanisms for redox regulation of DNA binding. Sulfhydryl modification of Cys388 could directly interfere with DNA binding or might alter the positioning of the DNA-binding helix 3. Modification of Cys401 may inhibit DNA binding through stabilization of an inhibitory helix similar to that described in the Ets-1 protein. Thus, GABP is regulated through at least two redox-sensitive activities, DNA binding and heterodimerization.

GABP Cooperates With c-Myb and C/EBP to Activate the Neutrophil Elastase Promoter

Neutrophil elastase (NE) is a serine protease that is transcriptionally regulated during early myeloid differentiation. The murine NE (mNE) promoter contains functionally important c-Myb, C/EBP, and ets binding sites. Deletion of the ets site reduced promoter activity by 90%. Although the ets transcription factor, PU.1, bound to this ets site, it only modestly activated the mNE promoter. Here, we show that a second transcription factor from myeloid cells — GABP — binds to the mNE ets site but strongly activates the mNE promoter. GABP is a heteromeric transcription factor complex that consists of GABPα, an ets factor, and GABPβ, a Notch-related protein. GABPα bound to the mNE ets site and, in turn, recruited GABPβ to form a transcriptionally active complex. GABPα and PU.1 competed with each other for binding to the mNE ets site. GABP increased the activity of the mNE promoter sevenfold in U937 myeloid cells. GABP cooperated with c-Myb and C/EBPα to activate the mNE promoter more than 85-fold in otherwise nonpermissive, nonhematopoietic NIH 3T3 cells. Thus, GABP binds to the crucial mNE promoter ets site and powerfully activates its expression alone and in cooperation with the transcription factors c-Myb and C/EBP.

Genomic structure and chromosomal localization of the novel ETS factor, PE-2 (ERF)

The members of the ETS family of transcription factors are grouped because they share a highly conserved DNA binding domain. These factors are involved in growth factor pathways and regulate both proliferation and differentiation. To identify ETS factors that may be involved in early hematopoietic progenitor regulation, we isolated a novel member of the ETS family by reverse transcriptase-PCR of the conserved DNA binding domain using degenerate oligonucleotides. This gene directs the synthesis of a 2704-nucleotide transcript whose largest open reading frame encodes a 548-amino-acid protein. Northern blot analysis reveals ubiquitous expression in all human tissues and cell lines tested, with highest levels in the testis, ovary, pancreas, and heart. Comparison of this gene with the available databases reveals very significant homology to the ETS factor PE-1 and probable near-identity with the recently cloned factor ERF. The PE-2 gene is composed of four exons spanning over 9 kb of genomic DNA. Sequence analysis of the promoter region reveals a GC-rich sequence without a TATA motif and with putative binding motifs for CREB, c-myb, and AP-1 factors. Using mouse-human somatic hybrids and FISH analysis, the PE-2 gene is localized to human chromosome 19q13.2, a region involved in translocations and deletions in leukemias and several solid tumors, suggesting that this novel ETS factor may play a role in carcinogenesis.

Characterization of the human thrombopoietin gene promoter. A possible role of an Ets transcription factor, E4TF1/GABP

Thrombopoietin (TPO), the ligand for c-Mpl, is a cytokine that regulates megakaryocyte growth and development. We have cloned the 5'-flanking region of the human TPO gene and analyzed its promoter activity. The human TPO gene promoter lacks a TATA box and directs transcription initiation at multiple sites over a 50-nucleotide region. Transient expression in a human liver cell line (PLC) of promoter fragment-luciferase reporter gene constructs containing a series of 5'-truncated sequences or site-directed mutations identified a sequence 5'-ACTTCCG-3' from -69 to -63 as a positive cis-acting element for high level expression of TPO gene. This sequence contains a core motif (C/A)GGA(A/T) for Ets family proteins in the noncoding strand. Gel mobility shift assays performed with nuclear protein from PLC cells identified a DNA binding protein(s) specific for the element. Anti-E4TF1-60(GABPalpha) or anti-E4TF1-53/47(GABPbeta) antibodies supershifted the complex in gel shift assay. Furthermore, co-expression of E4TF1-60 and E4TF1-53/47 squelched TPO gene expression in PLC and HepG2 cells. It is concluded that Ets family transcription factor E4TF1(GABPalpha/beta), an ubiquitously expressed protein, is required for high level expression of the TPO gene in liver.

Functional domains of transcription factor hGABP beta1/E4TF1-53 required for nuclear localization and transcription activation

Transcription factor E4TF1 is the human homolog of GABP and has been renamed hGABP (human GABP). hGABP is composed of two types of subunits; hGABP beta1/E4TF1-53 and the ets-related protein hGABP alpha/E4TF1-60. Both bind together to form an (alpha)2(beta1)2 heterotetrameric complex on DNA and activate transcription at specific promoters in vitro. Tetramer formation depends on two regions of hGABP beta1; the N-terminal region containing the Notch/ankyrin-type repeats is necessary for binding to hGABP alpha and the C-terminal region is necessary for homodimerization. In this report, we constructed various deletion mutants of hGABP beta1 in order to delimit the functional regions required for nuclear localization and transcription activity. We found that hGABP beta1 localization in the nucleus is dependent on a region located between amino acids 243 and 330 and that the presence of hGABP beta1 influences the efficiency of hGABP alpha transport into the nucleus. Next, we demonstrated that the hGABP complex composed of alpha and beta1 subunits activates transcription from the adenovirus early 4 promoter in vivo. This transcription activation needs the C-terminal region of hGABP beta1 and is consistent with results obtained with the in vitro assay. Furthermore, site-directed mutagenesis analysis of the C-terminal region reveals that the alpha-helix structure and the leucine residues are important for formation of a heterotetrameric complex with hGABP alpha in vitro and for transcription activation in vivo. These results suggest that hGABP beta1 stimulates transcription as part of a heterotetrameric complex with hGABP alpha in vivo.

Redox regulation of GA-binding protein-alpha DNA binding activity

We have investigated the reduction/oxidation (redox) regulation of the heteromeric transcription factor GA-binding protein (GABP). GABP, also known as nuclear respiratory factor 2, regulates the expression of nuclear encoded mitochondrial proteins involved in oxidative phosphorylation, including cytochrome c oxidase subunits IV and Vb, as well as the expression of mitochondrial transcription factor 1. GABP is composed of two subunits, the Ets-related GABP-alpha, which mediates specific DNA binding, and GABP-beta, which forms heterodimers and heterotetramers on DNA sequences containing the PEA3/Ets motif ((C/A)GGA(A/T)(G/A)). We demonstrate here that GABP DNA binding activity and GABP-dependent gene expression in 3T3 cells are inhibited by pro-oxidant conditions. DNA binding of recombinant GABP-alpha was activated by chemical reduction (dithiothreitol) and by thioredoxin; however, GSSG inhibited GABP DNA binding activity. Treatment of GABP-alpha, but not GABP-beta1, with sulfhydryl-alkylating agents also inhibited GABP DNA binding activity. Our results suggest that GABP DNA binding activity is redox-regulated in vivo, possibly by thioredoxin-mediated reduction and by GSSG-mediated oxidation of the GABP-alpha subunit. The regulation of GABP (nuclear respiratory factor 2) DNA binding activity by cellular redox changes provides an important link between mitochondrial and nuclear gene expression and the redox state of the cell.