Functional analyses of the transcription factor Sp4 reveal properties distinct from Sp1 and Sp3

The role of CEMIP in cancers and its transcriptional and post-transcriptional regulation

CEMIP is a protein known for inducing cell migration and binding to hyaluronic acid. Functioning as a hyaluronidase, CEMIP primarily facilitates the breakdown of the extracellular matrix component, hyaluronic acid, thereby regulating various signaling pathways. Recent evidence has highlighted the significant role of CEMIP in different cancers, associating it with diverse pathological states. While identified as a biomarker for several diseases, CEMIP's mechanism in cancer seems distinct. Accumulating data suggests that CEMIP expression is triggered by chemical modifications to itself and other influencing factors. Transcriptionally, chemical alterations to the CEMIP promoter and involvement of transcription factors such as AP-1, HIF, and NF-κB regulate CEMIP levels. Similarly, specific miRNAs have been found to post-transcriptionally regulate CEMIP. This review provides a comprehensive summary of CEMIP's role in various cancers and explores how both transcriptional and post-transcriptional mechanisms control its expression.

Specificity Proteins (Sp) and Cancer

The specificity protein (Sp) transcription factors (TFs) Sp1, Sp2, Sp3 and Sp4 exhibit structural and functional similarities in cancer cells and extensive studies of Sp1 show that it is a negative prognostic factor for patients with multiple tumor types. In this review, the role of Sp1, Sp3 and Sp4 in the development of cancer and their regulation of pro-oncogenic factors and pathways is reviewed. In addition, interactions with non-coding RNAs and the development of agents that target Sp transcription factors are also discussed. Studies on normal cell transformation into cancer cell lines show that this transformation process is accompanied by increased levels of Sp1 in most cell models, and in the transformation of muscle cells into rhabdomyosarcoma, both Sp1 and Sp3, but not Sp4, are increased. The pro-oncogenic functions of Sp1, Sp3 and Sp4 in cancer cell lines were studied in knockdown studies where silencing of each individual Sp TF decreased cancer growth, invasion and induced apoptosis. Silencing of an individual Sp TF was not compensated for by the other two and it was concluded that Sp1, Sp3 and Sp4 are examples of non-oncogene addicted genes. This conclusion was strengthened by the results of Sp TF interactions with non-coding microRNAs and long non-coding RNAs where Sp1 contributed to pro-oncogenic functions of Sp/non-coding RNAs. There are now many examples of anticancer agents and pharmaceuticals that induce downregulation/degradation of Sp1, Sp3 and Sp4, yet clinical applications of drugs specifically targeting Sp TFs are not being used. The application of agents targeting Sp TFs in combination therapies should be considered for their potential to enhance treatment efficacy and decrease toxic side effects.

Suppression of Krüppel-like factor 5 basal expression by CREB1 binding to far distal element

BACKGROUND

Krüppel-like factor 5 (KLF5) is a transcription factor regulating the proliferation and differentiation of epithelial cells, and its uncontrolled expression is closely associated with carcinoma progression. Sp3 binding to the minimal essential region (MER) of KLF5 gene is critical for KLF5 basal expression, but the expression control mechanism is unknown.

OBJECTIVE

This study aimed to identify a regulatory region for KLF5 basal expression and the binding protein in carcinoma cells by analyzing the promoter upstream region.

METHODS

Reporter assays determined the silencer region. The protein binding to the region was identified by database analysis and ChIP assay. The protein mediating the interaction between the region and the MER was confirmed through chromosome conformation capture (3 C) on ChIP assay. The effects of the protein on KLF5 expression were analyzed using qRT-PCR and western blot.

RESULTS

Reporter assay localized the 425-region from upstream KLF5 gene as the silencer. Database analysis and ChIP assay found CREB1 binding to the 425-region. CREB1 siRNA or mutation of CREB1-binding site in the 425-region increased luciferase activities and decreased the binding to 425-region. 3 C on ChIP assay showed that CREB1 mediated interaction of the 425-region and the MER. CREB1 overexpression decreased endogenous KLF5 expression and luciferase activity.

CONCLUSIONS

The 425-region is the silencer of KLF5 basal expression, and CREB1 binding suppresses the expression.

The androgen receptor inhibits transcription of GPER1 by preventing Sp1 and Sp3 from binding to the promoters in prostate cancer cells

G-1, a GPER1 agonist, was shown to inhibit the growth of castration-resistant mouse xenografts but not their parental androgen-dependent tumors. It is currently unknown how the androgen receptor (AR) represses GPER1 expression. Here, we found that two GPER1 mRNA variants (GPER1v2 and GPER1v4) were transcriptionally repressed, not via transcript destabilization, by the androgen-activated AR. Although no AR binding was found in all active promoters near GPER1, data from promoter assays suggested that both variants' promoters were inhibited by androgen treatment. Site-directed mutagenesis on Sp1/Sp3 binding sites revealed their role in supporting the basal expression of GPER1. Knockdown of Sp1 and Sp3 together but not separately repressed GPER1 expression whereas overexpression of both Sp1 and Sp3 together was required to alleviate AR repression of GPER1. Based on the chromatin immunoprecipitation data, Sp3 was found to bind to the promoters prior to the binding of Sp1 and RNA polymerase II. However, the binding of all three transcription factors was inhibited by DHT treatment. Concordantly, DHT treatment induced nuclear interactions between AR and Sp1 or Sp3. Taken together, these results indicate that AR represses transcription of GPER1 by binding to Sp1 and Sp3 independently to prevent their transactivation of the GPER1 promoters.

Over-representation of potential SP4 target genes within schizophrenia-risk genes

Reduction of Sp4 expression causes age-dependent hippocampal vacuolization and many other intermediate phenotypes of schizophrenia in Sp4 hypomorphic mice. Recent human genetic studies from both the Schizophrenia Exome Sequencing Meta-Analysis (SCHEMA) and the Genome-Wide Association Study (GWAS) validated SP4 as a schizophrenia-risk gene over the exome-wide or the genome-wide significance. Truncation of the human SP4 gene has an odds ratio of 9.37 (3.38-29.7) for schizophrenia. Despite successful identification of many schizophrenia-risk genes, it is unknown whether and how these risk genes may interact with each other in the development of schizophrenia. By taking advantage of the specific localization of the GC-boxes bound by SP4 transcription factors, I analyzed the relative abundance of these GC-boxes in the proximal promoter regions of schizophrenia-risk genes. I found that the GC-box containing genes are significantly over-represented within schizophrenia-risk genes, suggesting that SP4 is not only a high-risk gene for schizophrenia, but may also act as a hub of network in the regulation of many other schizophrenia-risk genes via these GC-boxes in the pathogenesis of schizophrenia.

Robust hematopoietic specification requires the ubiquitous Sp1 and Sp3 transcription factors

Background

Both tissue-specific and ubiquitously expressed transcription factors, such as Sp-family members, are required for correct development. However, the molecular details of how ubiquitous factors are involved in programming tissue-specific chromatin and thus participate in developmental processes are still unclear. We previously showed that embryonic stem cells lacking Sp1 DNA-binding activity (Sp1^ΔDBD/ΔDBD cells) are able to differentiate into early blood progenitors despite the inability of Sp1 to bind chromatin without its DNA-binding domain. However, gene expression during differentiation becomes progressively deregulated, and terminal differentiation is severely compromised.

Results

Here, we studied the cooperation of Sp1 with its closest paralogue Sp3 in hematopoietic development and demonstrate that Sp1 and Sp3 binding sites largely overlap. The complete absence of either Sp1 or Sp3 or the presence of the Sp1 DNA-binding mutant has only a minor effect on the pattern of distal accessible chromatin sites and their transcription factor binding motif content, suggesting that these mutations do not affect tissue-specific chromatin programming. Sp3 cooperates with Sp1^ΔDBD/ΔDBD to enable hematopoiesis, but is unable to do so in the complete absence of Sp1. Using single-cell gene expression analysis, we show that the lack of Sp1 DNA binding leads to a distortion of cell fate decision timing, indicating that stable chromatin binding of Sp1 is required to maintain robust differentiation trajectories.

Conclusions

Our findings highlight the essential contribution of ubiquitous factors such as Sp1 to blood cell development. In contrast to tissue-specific transcription factors which are required to direct specific cell fates, loss of Sp1 leads to a widespread deregulation in timing and coordination of differentiation trajectories during hematopoietic specification.

Electronic supplementary material

The online version of this article (10.1186/s13072-019-0282-9) contains supplementary material, which is available to authorized users.

Transcription factor Sp2 potentiates binding of the TALE homeoproteins Pbx1:Prep1 and the histone-fold domain protein Nf-y to composite genomic sites

Different transcription factors operate together at promoters and enhancers to regulate gene expression. Transcription factors either bind directly to their target DNA or are tethered to it by other proteins. The transcription factor Sp2 serves as a paradigm for indirect genomic binding. It does not require its DNA-binding domain for genomic DNA binding and occupies target promoters independently of whether they contain a cognate DNA-binding motif. Hence, Sp2 is strikingly different from its closely related paralogs Sp1 and Sp3, but how Sp2 recognizes its targets is unknown. Here, we sought to gain more detailed insights into the genomic targeting mechanism of Sp2. ChIP-exo sequencing in mouse embryonic fibroblasts revealed genomic binding of Sp2 to a composite motif where a recognition sequence for TALE homeoproteins and a recognition sequence for the trimeric histone-fold domain protein nuclear transcription factor Y (Nf-y) are separated by 11 bp. We identified a complex consisting of the TALE homeobox protein Prep1, its partner PBX homeobox 1 (Pbx1), and Nf-y as the major partners in Sp2-promoter interactions. We found that the Pbx1:Prep1 complex together with Nf-y recruits Sp2 to co-occupied regulatory elements. In turn, Sp2 potentiates binding of Pbx1:Prep1 and Nf-y. We also found that the Sp-box, a short sequence motif close to the Sp2 N terminus, is crucial for Sp2's cofactor function. Our findings reveal a mechanism by which the DNA binding-independent activity of Sp2 potentiates genomic loading of Pbx1:Prep1 and Nf-y to composite motifs present in many promoters of highly expressed genes.

SIRT3 deregulation is linked to mitochondrial dysfunction in Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the elderly. Despite decades of study, effective treatments for AD are lacking. Mitochondrial dysfunction has been closely linked to the pathogenesis of AD, but the relationship between mitochondrial pathology and neuronal damage is poorly understood. Sirtuins (SIRT, silent mating type information regulation 2 homolog in yeast) are NAD-dependent histone deacetylases involved in aging and longevity. The objective of this study was to investigate the relationship between SIRT3 and mitochondrial function and neuronal activity in AD. SIRT3 mRNA and protein levels were significantly decreased in AD cerebral cortex, and Ac-p53 K320 was significantly increased in AD mitochondria. SIRT3 prevented p53-induced mitochondrial dysfunction and neuronal damage in a deacetylase activity-dependent manner. Notably, mitochondrially targeted p53 (mito-p53) directly reduced mitochondria DNA-encoded ND2 and ND4 gene expression resulting in increased reactive oxygen species (ROS) and reduced mitochondrial oxygen consumption. ND2 and ND4 gene expressions were significantly decreased in patients with AD. p53-ChIP analysis verified the presence of p53-binding elements in the human mitochondrial genome and increased p53 occupancy of mitochondrial DNA in AD. SIRT3 overexpression restored the expression of ND2 and ND4 and improved mitochondrial oxygen consumption by repressing mito-p53 activity. Our results indicate that SIRT3 dysfunction leads to p53-mediated mitochondrial and neuronal damage in AD. Therapeutic modulation of SIRT3 activity may ameliorate mitochondrial pathology and neurodegeneration in AD.

SP1 reduces autophagic flux through activating p62 in gastric cancer cells

Gastric cancer is the most common type of gastrointestinal cancer, causing mortality worldwide. However, the underlying molecular mechanism in gastric cancer progression remains unclear. The autophagic flux was determined in gastric cancer cells overexpressing or inhibiting Sp1 transcription factor (SP1) using western blotting, reverse transcription‑polymerase chain reaction and immunofluorescence staining. Luciferase and ChIP assays were performed to detect the potential underlying mechanism of SP1 in gastric cancer cells. Lastly, immunohistochemistry was also performed on SP1 and p62 expression levels in human gastric cancer specimens. It was demonstrated that SP1 diminished autophagic flux via activating p62 in gastric cancer. Moreover, SP1 deficiency increased the rate of autophagy of gastric cancer cells. Notably, it was observed that SP1 enhanced the expression levels of p62 by directly binding to the promoter of p62. Analysis of gastric cancer specimen staining established that p62 expression levels were increased in SP1‑positve gastric tissues. The present study provided evidence for a novel mechanism regulating autophagy in gastric cancer cells.

Minor lipid metabolic perturbations in the liver of Atlantic salmon (Salmo salar L.) caused by suboptimal dietary content of nutrients from fish oil

The present study was conducted to evaluate the effects on Atlantic salmon hepatic lipid metabolism when fed diets with increasing substitution of fish oil (FO) with a vegetable oil (VO) blend. Four diets with VOs replacing 100, 90, 79 and 65 % of the FO were fed for 5 months. The levels of eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) in the experimental diets ranged from 1.3 to 7.4 % of fatty acids (FAs), while cholesterol levels ranged from 0.6 to 1.2 g kg(-1). In hepatocytes added [1-(14)C] α-linolenic acid (ALA, 18:3n-3), more ALA was desaturated and elongated to EPA and DHA in cells from fish fed 100 % VO, while in fish fed 65 % VO, ALA was elongated to eicosatrienoic acid (ETE; 20:3n-3), indicating reduced Δ6 desaturation activity. Despite increased desaturation activity and activation of the transcription factor Sp1 in fish fed 100 % VO, liver phospholipids contained less EPA and DHA compared with the 65 % VO group. The cholesterol levels in the liver of the 100 % VO group exceeded the levels in fish fed the 65 % VO diet, showing an inverse relationship between cholesterol intake and liver cholesterol content. For the phytosterols, levels in liver were generally low. The area as a proxy of volume of lipid droplets was significantly higher in salmon fed 100 % VO compared with salmon fed 65 % VO. In conclusion, the current study suggests that suboptimal dietary levels of cholesterol in combination with low levels of EPA and DHA (1.3 % of FAs) can result in minor metabolic perturbations in the liver of Atlantic salmon.

Sp1 and Sp3 Are the Transcription Activators of Human ek1 Promoter in TSA-Treated Human Colon Carcinoma Cells

BACKGROUND

Ethanolamine kinase (EK) catalyzes the phosphorylation of ethanolamine, the first step in the CDP-ethanolamine pathway for the biosynthesis of phosphatidylethanolamine (PE). Human EK exists as EK1, EK2α and EK2β isoforms, encoded by two separate genes, named ek1 and ek2. EK activity is stimulated by carcinogens and oncogenes, suggesting the involvement of EK in carcinogenesis. Currently, little is known about EK transcriptional regulation by endogenous or exogenous signals, and the ek gene promoter has never been studied.

METHODOLOGY/PRINCIPAL FINDINGS

In this report, we mapped the important regulatory regions in the human ek1 promoter. 5' deletion analysis and site-directed mutagenesis identified a Sp site at position (-40/-31) that was essential for the basal transcription of this gene. Treatment of HCT116 cells with trichostatin A (TSA), a histone deacetylase inhibitor, significantly upregulated the ek1 promoter activity through the Sp(-40/-31) site and increased the endogenous expression of ek1. Chromatin immunoprecipitation assay revealed that TSA increased the binding of Sp1, Sp3 and RNA polymerase II to the ek1 promoter in HCT116 cells. The effect of TSA on ek1 promoter activity was cell-line specific as TSA treatment did not affect ek1 promoter activity in HepG2 cells.

CONCLUSION/SIGNIFICANCE

In conclusion, we showed that Sp1 and Sp3 are not only essential for the basal transcription of the ek1 gene, their accessibility to the target site on the ek1 promoter is regulated by histone protein modification in a cell line dependent manner.

Differential effects of Sp cellular transcription factors on viral promoter activation by varicella-zoster virus (VZV) IE62 protein

The immediate early (IE) 62 protein is the major varicella-zoster virus (VZV) regulatory factor. Analysis of the VZV genome revealed 40 predicted GC-rich boxes within 36 promoters. We examined effects of ectopic expression of Sp1-Sp4 on IE62- mediated transactivation of three viral promoters. Ectopic expression of Sp3 and Sp4 enhanced IE62 activation of ORF3 and gI promoters while Sp3 reduced IE62 activation of ORF28/29 promoter and VZV DNA replication. Sp2 reduced IE62 transactivation of gI while Sp1 had no significant influence on IE62 activation with any of these viral promoters. Electrophoretic mobility shift assays (EMSA) confirmed binding of Sp1 and Sp3 but not Sp2 and Sp4 to the gI promoter. Sp1-4 bound to IE62 and amino acids 238-258 of IE62 were important for the interaction with Sp3 and Sp4 as well as Sp1. This work shows that Sp family members have differential effects on IE62-mediated transactivation in a promoter-dependent manner.

O-GlcNAc modification of Sp3 and Sp4 transcription factors negatively regulates their transcriptional activities

The addition of O-linked N-acetylglucosamine (O-GlcNAc) on serine or threonine modifies a myriad of proteins and regulates their function, stability and localization. O-GlcNAc modification is common among chromosome-associated proteins, such as transcription factors, suggesting its extensive involvement in gene expression regulation. In this study, we demonstrate the O-GlcNAc status of the Sp family members of transcription factors and the functional impact on their transcriptional activities. We highlight the presence of O-GlcNAc residues in Sp3 and Sp4, but not Sp2, as demonstrated by their enrichment in GlcNAc positive protein fractions and by detection of O-GlcNAc residues on Sp3 and Sp4 co-expressed in Escherichia coli together with O-GlcNAc transferase (OGT) using an O-GlcNAc-specific antibody. Deletion mutants of Sp3 and Sp4 indicate that the majority of O-GlcNAc sites reside in their N-terminal transactivation domain. Overall, using reporter gene assays and co-immunoprecipitations, we demonstrate a functional inhibitory role of O-GlcNAc modifications in Sp3 and Sp4 transcription factors. Thereby, our study strengthens the current notion that O-GlcNAc modification is an important regulator of protein interactome.

The cell- and tissue-specific transcription mechanism of the TATA-less syntaxin 1A gene

Syntaxin 1A (Stx1a) plays an important role in regulation of neuronal synaptic function. To clarify the mechanism of basic transcriptional regulation and neuron-specific transcription of Stx1a we cloned the Stx1a gene from rat, in which knowledge of the expression profile was accumulated, and elucidated that Stx1a consisting of 10 exons, possesses multiple transcription initiation sites and a 204-bp core promoter region (CPR) essential for transcription in PC12 cells. The TATA-less, conserved, GC-rich CPR has 2 specific protein (SP) sites that bind SP1 and are responsible for 65% of promoter activity. The endogenous CPR, including 23 CpG sites, is not methylated in PC12 cells, which express Stx1a and fetal rat skin keratinocyte (FRSK) cells, which do not, although an exogenous methylated CPR suppresses reporter activity in both lines. Trichostatin A (TSA) and class I histone deacetylase (HDAC) inhibitors, but not 5-azacytidine, induce Stx1a in FRSK cells. Acetylated histone H3 only associates to the CPR in FRSK cells after TSA addition, whereas the high acetylated histone H3-CPR association in PC12 cells was unchanged following treatment. HDAC inhibitor induction of Stx1a was negated by mithramycin A and deletion/mutation of 2 SP sites. HDAC1, HDAC2, and HDAC8 detach from the CPR when treated with TSA in FRSK cells and are associated with the CPR in lungs, and acetylated histone H3 associates to this region in the brain. In the first study characterizing a syntaxin promoter, we show that association of SP1 and acetylated histone H3 to CPR is important for Stx1a transcription and that HDAC1, HDAC2, and HDAC8 decide cell/tissue specificity in a suppressive manner.

The epigenetics of aging and neurodegeneration

Epigenetics is a quickly growing field encompassing mechanisms regulating gene expression that do not involve changes in the genotype. Epigenetics is of increasing relevance to neuroscience, with epigenetic mechanisms being implicated in brain development and neuronal differentiation, as well as in more dynamic processes related to cognition. Epigenetic regulation covers multiple levels of gene expression; from direct modifications of the DNA and histone tails, regulating the level of transcription, to interactions with messenger RNAs, regulating the level of translation. Importantly, epigenetic dysregulation currently garners much attention as a pivotal player in aging and age-related neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, and Huntington's disease, where it may mediate interactions between genetic and environmental risk factors, or directly interact with disease-specific pathological factors. We review current knowledge about the major epigenetic mechanisms, including DNA methylation and DNA demethylation, chromatin remodeling and non-coding RNAs, as well as the involvement of these mechanisms in normal aging and in the pathophysiology of the most common neurodegenerative diseases. Additionally, we examine the current state of epigenetics-based therapeutic strategies for these diseases, which either aim to restore the epigenetic homeostasis or skew it to a favorable direction to counter disease pathology. Finally, methodological challenges of epigenetic investigations and future perspectives are discussed.

Sp1 and the 'hallmarks of cancer'

For many years, transcription factor Sp1 was viewed as a basal transcription factor and relegated to a role in the regulation of so-called housekeeping genes. Identification of Sp1's role in recruiting the general transcription machinery in the absence of a TATA box increased its importance in gene regulation, particularly in light of recent estimates that the majority of mammalian genes lack a TATA box. In this review, we briefly consider the history of Sp1, the founding member of the Sp family of transcription factors. We review the evidence suggesting that Sp1 is highly regulated by post-translational modifications that positively and negatively affect the activity of Sp1 on a wide array of genes. Sp1 is over-expressed in many cancers and is associated with poor prognosis. Targeting Sp1 in cancer treatment has been suggested; however, our review of the literature on the role of Sp1 in the regulation of genes that contribute to the 'hallmarks of cancer' illustrates the extreme complexity of Sp1 functions. Sp1 both activates and suppresses the expression of a number of essential oncogenes and tumor suppressors, as well as genes involved in essential cellular functions, including proliferation, differentiation, the DNA damage response, apoptosis, senescence and angiogenesis. Sp1 is also implicated in inflammation and genomic instability, as well as epigenetic silencing. Given the apparently opposing effects of Sp1, a more complete understanding of the function of Sp1 in cancer is required to validate its potential as a therapeutic target.

HIV-1 transcriptional regulation in the central nervous system and implications for HIV cure research

Human immunodeficiency virus type-1 (HIV-1) invades the central nervous system (CNS) during acute infection which can result in HIV-associated neurocognitive disorders in up to 50% of patients, even in the presence of combination antiretroviral therapy (cART). Within the CNS, productive HIV-1 infection occurs in the perivascular macrophages and microglia. Astrocytes also become infected, although their infection is restricted and does not give rise to new viral particles. The major barrier to the elimination of HIV-1 is the establishment of viral reservoirs in different anatomical sites throughout the body and viral persistence during long-term treatment with cART. While the predominant viral reservoir is believed to be resting CD4(+) T cells in the blood, other anatomical compartments including the CNS, gut-associated lymphoid tissue, bone marrow, and genital tract can also harbour persistently infected cellular reservoirs of HIV-1. Viral latency is predominantly responsible for HIV-1 persistence and is most likely governed at the transcriptional level. Current clinical trials are testing transcriptional activators, in the background of cART, in an attempt to purge these viral reservoirs and reverse viral latency. These strategies aim to activate viral transcription in cells constituting the viral reservoir, so they can be recognised and cleared by the immune system, while new rounds of infection are blocked by co-administration of cART. The CNS has several unique characteristics that may result in differences in viral transcription and in the way latency is established. These include CNS-specific cell types, different transcription factors, altered immune surveillance, and reduced antiretroviral drug bioavailability. A comprehensive understanding of viral transcription and latency in the CNS is required in order to determine treatment outcomes when using transcriptional activators within the CNS.

Store-operated calcium entry promotes the degradation of the transcription factor Sp4 in resting neurons

Calcium (Ca(2+)) signaling activated in response to membrane depolarization regulates neuronal maturation, connectivity, and plasticity. Store-operated Ca(2+) entry (SOCE) occurs in response to depletion of Ca(2+) from endoplasmic reticulum (ER), mediates refilling of this Ca(2+) store, and supports Ca(2+) signaling in nonexcitable cells. We report that maximal activation of SOCE occurred in cerebellar granule neurons cultured under resting conditions and that this Ca(2+) influx promoted the degradation of transcription factor Sp4, a regulator of neuronal morphogenesis and function. Lowering the concentration of extracellular potassium, a condition that reduces neuronal excitability, stimulated depletion of intracellular Ca(2+) stores, resulted in the relocalization of the ER Ca(2+) sensor STIM1 into punctate clusters consistent with multimerization and accumulation at junctions between the ER and plasma membrane, and induced a Ca(2+) influx with characteristics of SOCE. Compounds that block SOCE prevented the ubiquitylation and degradation of Sp4 in neurons exposed to a low concentration of extracellular potassium. Knockdown of STIM1 blocked degradation of Sp4, whereas expression of constitutively active STIM1 decreased Sp4 abundance under depolarizing conditions. Our findings indicated that, in neurons, SOCE is induced by hyperpolarization, and suggested that this Ca(2+) influx pathway is a distinct mechanism for regulating neuronal gene expression.

Increased expression of colonic Wnt9A through Sp1-mediated transcriptional effects involving arylsulfatase B, chondroitin 4-sulfate, and galectin-3

In cultured human colonic epithelial cells and mouse colonic tissue, exposure to the common food additive carrageenan leads to inflammation, activation of Wnt signaling, increased Wnt9A expression, and decline in the activity of the enzyme arylsulfatase B (ARSB; N-acetylgalactosamine-4-sulfatase). In this study, the novel transcriptional mechanism by which carrageenan and decline in ARSB increase Wnt9A expression in NCM460 and HT-29 human colonic epithelial cells and in mouse colon is presented. Increased expression of Wnt9A has been associated with multiple malignancies, including colon carcinoma, and with ectodermal and mesoendodermal morphogenesis. When ARSB activity was reduced by siRNA or by exposure to carrageenan (1 μg/ml for 24 h), degradation of chondroitin 4-sulfate (C4S) was inhibited, leading to accumulation of more highly sulfated C4S, which binds less galectin-3, a β-galactoside-binding protein. Nuclear galectin-3 increased and mediated increased binding of Sp1 to the Sp1 consensus sequence in the Wnt9A promoter, shown by oligonucleotide-binding assay and by chromatin immunoprecipitation assay. When galectin-3 was silenced, the increases in Sp1 binding to the Wnt9A promoter and in Wnt9A expression, which followed carrageenan or ARSB silencing, were inhibited. Mithramycin A, a specific inhibitor of Sp1 oligonucleotide binding, and Sp1 siRNA blocked the carrageenan- and ARSB siRNA-induced increases in Wnt9A expression. These studies reveal how carrageenan exposure can lead to transcriptional events in colonic epithelial cells through decline in arylsulfatase B activity, with subsequent impact on C4S, galectin-3, Sp1, and Wnt9A and can exert significant effects on Wnt-initiated signaling and related vital cell processes.

Transcription of the vascular endothelial growth factor receptor-3 (VEGFR3) gene is regulated by the zinc finger proteins Sp1 and Sp3 and is under epigenetic control: transcription of vascular endothelial growth factor receptor 3

BACKGROUND

In the past, the vascular endothelial growth factor receptor-3 (VEGFR-3) has been linked to the regulation of lymphangiogenesis and the lymphatic spread of solid malignancies. The molecular mechanisms controlling VEGFR3 gene expression have, however, remained poorly understood. Here, we aimed at assessing these mechanisms through VEGFR3 gene promoter analysis and the identification of transcription factors binding to it. In addition, we focussed on epigenetic modifications underlying VEGFR3 transcription regulation.

METHODS

5' Deletion analyses for the identification of functional promoter elements, electrophoretic mobility shift assays, chromatin immunoprecipitations, methylation-specific PCRs, and Trichostatin A (TSA) and 5-Aza desoxycytidine (5-Aza dC) treatments were performed in this study.

RESULTS

Following the isolation of a 2 kb stretch of 5'-flanking DNA of VEGFR3, we identified a novel GC-rich element (GRE) spanning -101/-66 sufficient for VEGFR3 transcription and activated by Sp1 and Sp3, respectively. Histone de-acetylase inhibition by TSA led to the accumulation of acetylated histones H3/H4 at the VEGFR3 gene promoter, up-regulation of its mRNA levels, and transactivation of promoter reporter constructs in endothelial cell lines. Similarly, methylation inhibition by 5-Aza dC triggered up-regulation of VEGFR3 mRNA levels and increased promoter activity. TSA and 5-Aza-dC did not influence Sp1/Sp3 binding, but increased the transactivating capacity of both transcription factors, suggesting epigenetic modification as an underlying mechanism.

CONCLUSIONS

Here we describe the identification of regulatory elements controlling human VEGFR3 gene expression and show that histone acetylation and CpG methylation are important determinants of VEGFR3 transcription regulation. These findings may facilitate the development of intervention strategies aimed at targeting VEGFR3-based tumor lymphangiogenesis and/or lymphatic tumor spread.

Differential responses of neuronal and spermatogenic cells to the doppel cytotoxicity

Although structurally and biochemically similar to the cellular prion (PrP(C)), doppel (Dpl) is unique in its biological functions. There are no reports about any neurodegenerative diseases induced by Dpl. However the artificial expression of Dpl in the PrP-deficient mouse brain causes ataxia with Purkinje cell death. Abundant Dpl proteins have been found in testis and depletion of the Dpl gene (Prnd) causes male infertility. Therefore, we hypothesize different regulations of Prnd in the nerve and male productive systems. In this study, by electrophoretic mobility shift assays we have determined that two different sets of transcription factors are involved in regulation of the Prnd promoter in mouse neuronal N2a and GC-1 spermatogenic (spg) cells, i.e., upstream stimulatory factors (USF) in both cells, Brn-3 and Sp1 in GC-1 spg cells, and Sp3 in N2a cells, leading to the expression of Dpl in GC-1 spg but not in N2a cells. We have further defined that, in N2a cells, Dpl induces oxidative stress and apoptosis, which stimulate ataxia-telangiectasia mutated (ATM)-modulating bindings of transcription factors, p53 and p21, to Prnp promoter, resulting the PrP(C) elevation for counteraction of the Dpl cytotoxicity; in contrast, in GC-1 spg cells, phosphorylation of p21 and N-terminal truncated PrP may play roles in the control of Dpl-induced apoptosis, which may benefit the physiological function of Dpl in the male reproduction system.

Reduced expression of SP1 and SP4 transcription factors in peripheral blood mononuclear cells in first-episode psychosis

Alterations of transcription factor specificity protein 4 (SP4) and 1 (SP1) have been linked to different neuropsychiatric diseases. Reduced SP4 and SP1 protein levels in the prefrontal cortex have been associated with bipolar disorder and schizophrenia, respectively, suggesting that both factors could be involved in the pathogenesis of disorders with psychotic features. The aim of this study was to investigate whether the reduction of SP1, SP4 and SP3 protein and mRNA expression in peripheral blood mononuclear cells in the early stages of psychosis may act as a potential biomarker of these disorders. A cross-sectional study of first-episode psychosis patients (n = 14) compared to gender- and age-matched healthy controls (n = 14) was designed. Patients were recruited through the adult mental health services of Parc Sanitari Sant Joan de Déu. Protein and gene expression levels of SP1, SP4 and SP3 were assessed in peripheral blood mononuclear cells of patients with first-episode psychosis and healthy control subjects. We report that protein levels of SP1 and SP4, but not SP3, are significantly reduced in patients compared to controls. In contrast, we did not observe any differences in expression levels for SP1, SP4 or SP3 genes between patient and control groups. In patients, SP4 protein levels were significantly associated with SP1 protein levels. No association was found, however, between protein and gene expression levels for each factor. Our study shows reduced SP1 and SP4 protein levels in first-episode psychosis in lymphocytes, suggesting that these transcription factors are potential peripheral biomarkers of psychotic spectrum disorders in the early stages.

Epigenetic mechanisms of neurodegeneration in Huntington's disease

Huntington's disease (HD) is an incurable and fatal hereditary neurodegenerative disorder of mid-life onset characterized by chorea, emotional distress, and progressive cognitive decline. HD is caused by an expansion of CAG repeats coding for glutamine (Q) in exon 1 of the huntingtin gene. Recent studies suggest that epigenetic modifications may play a key role in HD pathogenesis. Alterations of the epigenetic "histone code" lead to chromatin remodeling and deregulation of neuronal gene transcription that are prominently linked to HD pathogenesis. Furthermore, specific noncoding RNAs and microRNAs are associated with neuronal damage in HD. In this review, we discuss how DNA methylation, post-translational modifications of histone, and noncoding RNA function are affected and involved in HD pathogenesis. In addition, we summarize the therapeutic effects of histone deacetylase inhibitors and DNA binding drugs on epigenetic modifications and neuropathological sequelae in HD. Our understanding of the role of these epigenetic mechanisms may lead to the identification of novel biological markers and new therapeutic targets to treat HD.

Exceptional human core promoter nucleotide compositions

The proximal promoter sequences contain basic motifs for the expression of the downstream genes. We present genome-scale computational analyses of the 120-bp immediate upstream sequences to the +1 transcription start sites (TSSs) of 10,117 human protein-coding genes, and unravel exceptional genes in respect with the core promoter nucleotide composition. Our data reveal that while in 99% of the genes the absolute purine/pyrimidine ratio ranges between 0.2 and 2.5, certain genes show exceptional skew in this balance (e.g. ratios of 82.3 in VWA3A, 61.5 in Sox5, and 24.0 in BRWD3), and consist of islands of purines or pyrimidines. Furthermore, while over 95% of the genes lack more than one short tandem repeat (STR) in their core promoters, certain gene promoters are exceptionally rich in multiple STRs (e.g. eight consecutive STRs in UBE2QL1, and six STRs in GRIA2). We found sequence bias for the majority of those promoters across species, supporting functional roles for them in gene expression. Genes downstream to those promoters were also found to be of ontologic importance (i.e. we were able to track the majority of those genes to the lower species such as Saccharomyces cerevisiae and Caenorhabditis elegans). The exceptional promoters presented in this study lack the conventional motifs for the TATA, and TATA-less promoters, hence offering novel mechanisms for gene expression. They may also provide potential mechanisms for inter-individual variations in gene expression, and complex traits/disorders.

Transcriptional regulation of human FE65, a ligand of Alzheimer's disease amyloid precursor protein, by Sp1

FE65 is a neuronal-enriched adaptor protein that binds to the Alzheimer's disease amyloid precursor protein (APP). FE65 forms a transcriptionally active complex with the APP intracellular domain (AICD). The precise gene targets for this complex are unclear but several Alzheimer's disease-linked genes have been proposed. Additionally, evidence suggests that FE65 influences APP metabolism. The mechanism by which FE65 expression is regulated is as yet unknown. To gain insight into the regulatory mechanism, we cloned a 1.6 kb fragment upstream of the human FE65 gene and found that it possesses particularly strong promoter activity in neurones. To delineate essential regions in the human FE65 promoter, a series of deletion mutants were generated. The minimal FE65 promoter was located between -100 and +5, which contains a functional Sp1 site. Overexpression of the transcription factor Sp1 potentiates the FE65 promoter activity. Conversely, suppression of the FE65 promoter was observed in cells either treated with an Sp1 inhibitor or in which Sp1 was knocked down. Furthermore, reduced levels of Sp1 resulted in downregulation of endogenous FE65 mRNA and protein. These findings reveal that Sp1 plays a crucial role in transcriptional control of the human FE65 gene.

Structural and functional characterization of the mouse tescalcin promoter

Tescalcin, an EF-hand calcium binding protein that regulates the Na(+)/H(+) exchanger 1 (NHE1), is highly expressed in various mouse tissues such as heart and brain. Despite its potentially important role in cell physiology, the mechanisms that regulate tescalcin gene (Tesc) expression are unknown. In this study, we report two new Tesc mRNA variants (V2 and V3) and characterize the mouse Tesc promoter. The V2 and V3 transcripts result from alternative splicing of intron 5. Our results show that Tesc mRNA variants are expressed in various mouse tissues. Primer extension analysis located the transcription start site at 94 nucleotides upstream of the translation start codon. The DNA nucleotide sequence of the 5'-flanking region contained a CpG island spanning the promoter region from nucleotides -372 to +814, a canonical TATA box (-38/-32), and putative transcription factor binding sites for Sp1, EGR1, ZBP-89, KLF3, MZF1, AP2, ZF5, and CDF-1. Transient transfection of the Y1 and msc-1 cell lines with a series of 5'-deleted promoter constructs indicated that the minimal promoter region was between nucleotides -130 and -40. Electrophoresis mobility shift assays, supershift assays, and mutation studies demonstrated that Sp1 and Sp3 bind to the GC-rich motifs, a CACCC box and three GC boxes, located within the Tesc proximal promoter. Nonetheless, mutations that abolished interaction of Sp1 and Sp3 with the GC-rich motifs located within the minimal promoter region did not abrogate promoter activity in Y1 cells. Mithramycin A, an inhibitor of Sp1-DNA interaction, reduced Tesc promoter activity in msc-1 cells in a dose-dependent manner. Sp3 was a weaker transactivator compared to Sp1 in Drosophila D.mel-2 cells. However, when Sp1 and Sp3 were coexpressed, they transactivated the Tesc promoter in a synergistic manner. In Y1 cells, mutation analysis of a putative ZF5 motif located within the Tesc minimal promoter indicated that this motif was critical for activity of Tesc promoter. Taken together, the data demonstrated that Sp1 and Sp3 transcription factors cooperate positively in the regulation of Tesc promoter, and that the putative ZF5 motif is critical for its activation.

Lifespan profiles of Alzheimer's disease-associated genes and products in monkeys and mice

Alzheimer's disease (AD) is characterized by plaques of amyloid-beta (Abeta) peptide, cleaved from amyloid-beta protein precursor (AbetaPP). Our hypothesis is that lifespan profiles of AD-associated mRNA and protein levels in monkeys would differ from mice and that differential lifespan expression profiles would be useful to understand human AD pathogenesis. We compared profiles of AbetaPP mRNA, AbetaPP protein, and Abeta levels in rodents and primates. We also tracked a transcriptional regulator of the AbetaPP gene, specificity protein 1 (SP1), and the beta amyloid precursor cleaving enzyme (BACE1). In mice, AbetaPP and SP1 mRNA and their protein products were elevated late in life; Abeta levels declined in old age. In monkeys, SP1, AbetaPP, and BACE1 mRNA declined in old age, while protein products and Abeta levels rose. Proteolytic processing in both species did not match production of Abeta. In primates, AbetaPP and SP1 mRNA levels coordinate, but an inverse relationship exists with corresponding protein products as well as Abeta levels. Comparison of human DNA and mRNA sequences to monkey and mouse counterparts revealed structural features that may explain differences in transcriptional and translational processing. These findings are important for selecting appropriate models for AD and other age-related diseases.

Sp proteins play a critical role in histone deacetylase inhibitor-mediated derepression of CYP46A1 gene transcription

We investigated whether the CYP46A1 gene, a neuronal-specific cytochrome P450, responsible for the majority of brain cholesterol turnover, is subject to transcriptional modulation through modifications in histone acetylation. We demonstrated that inhibition of histone deacetylase activity by trichostatin A (TSA), valproic acid and sodium butyrate caused a potent induction of both CYP46A1 promoter activity and endogenous expression. Silencing of Sp transcription factors through specific small interfering RNAs, or impairing Sp binding to the proximal promoter, by site-directed mutagenesis, led to a significant decrease in TSA-mediated induction of CYP46A1 expression/promoter activity. Electrophoretic mobility shift assay, DNA affinity precipitation assays and chromatin immunoprecipitation assays were used to determine the multiprotein complex recruited to the CYP46A1 promoter, upon TSA treatment. Our data showed that a decrease in Sp3 binding at particular responsive elements, can shift the Sp1/Sp3/Sp4 ratio, and favor the detachment of histone deacetylase (HDAC) 1 and HDAC2 and the recruitment of p300/CBP. Moreover, we observed a dynamic change in the chromatin structure upon TSA treatment, characterized by an increase in the local recruitment of euchromatic markers and RNA polymerase II. Our results show the critical participation of an epigenetic program in the control of CYP46A1 gene transcription, and suggest that brain cholesterol catabolism may be affected upon treatment with HDAC inhibitors.

Regulation of HIV-1 transcription in cells of the monocyte-macrophage lineage

Human immunodeficiency virus type 1 (HIV-1) has been shown to replicate productively in cells of the monocyte-macrophage lineage, although replication occurs to a lesser extent than in infected T cells. As cells of the monocyte-macrophage lineage become differentiated and activated and subsequently travel to a variety of end organs, they become a source of infectious virus and secreted viral proteins and cellular products that likely initiate pathological consequences in a number of organ systems. During this process, alterations in a number of signaling pathways, including the level and functional properties of many cellular transcription factors, alter the course of HIV-1 long terminal repeat (LTR)-directed gene expression. This process ultimately results in events that contribute to the pathogenesis of HIV-1 infection. First, increased transcription leads to the upregulation of infectious virus production, and the increased production of viral proteins (gp120, Tat, Nef, and Vpr), which have additional activities as extracellular proteins. Increased viral production and the presence of toxic proteins lead to enhanced deregulation of cellular functions increasing the production of toxic cellular proteins and metabolites and the resulting organ-specific pathologic consequences such as neuroAIDS. This article reviews the structural and functional features of the cis-acting elements upstream and downstream of the transcriptional start site in the retroviral LTR. It also includes a discussion of the regulation of the retroviral LTR in the monocyte-macrophage lineage during virus infection of the bone marrow, the peripheral blood, the lymphoid tissues, and end organs such as the brain. The impact of genetic variation on LTR-directed transcription during the course of retrovirus disease is also reviewed.

Sp4-dependent repression of neurotrophin-3 limits dendritic branching

Regulation of neuronal gene expression is critical to establish functional connections in the mammalian nervous system. The transcription factor Sp4 regulates dendritic patterning during cerebellar granule neuron development by limiting branching and promoting activity-dependent pruning. Here, we investigate neurotrophin-3 (NT3) as a target gene important for Sp4-dependent dendritic morphogenesis. We found that Sp4 overexpression reduced NT3 promoter activity whereas knockdown of Sp4 increased NT3 promoter activity and mRNA. Moreover, Sp4 bound to the NT3 promoter in vivo, supporting a direct role for Sp4 as a repressor of NT3 expression. Addition of exogenous NT3 promoted dendritic branching in cerebellar granule neurons. Furthermore, sequestering NT3 blocked the continued addition of dendritic branches observed upon Sp4 knockdown, but had no effect on dendrite pruning. These findings demonstrate that, during cerebellar granule neuron development, Sp4-dependent repression of neurotrophin-3 is required to limit dendritic branching and thereby promote acquisition of the mature dendritic pattern.

Transcriptional regulation of mammalian selenoprotein expression

BACKGROUND

Selenoproteins contain the twenty-first amino acid, selenocysteine, and are involved in cellular defenses against oxidative damage, important metabolic and developmental pathways, and responses to environmental challenges. Elucidating the mechanisms regulating selenoprotein expression at the transcriptional level is a key to understanding how these mechanisms are called into play to respond to the changing environment.

METHODS

This review summarizes published studies on transcriptional regulation of selenoprotein genes, focused primarily on genes whose encoded protein functions are at least partially understood. This is followed by in silico analysis of predicted regulatory elements in selenoprotein genes, including those in the aforementioned category as well as the genes whose functions are not known.

RESULTS

Our findings reveal regulatory pathways common to many selenoprotein genes, including several involved in stress-responses. In addition, tissue-specific regulatory factors are implicated in regulating many selenoprotein genes.

CONCLUSIONS

These studies provide new insights into how selenoprotein genes respond to environmental and other challenges, and the roles these proteins play in allowing cells to adapt to these changes.

GENERAL SIGNIFICANCE

Elucidating the regulatory mechanisms affecting selenoprotein expression is essential for understanding their roles in human diseases, and for developing diagnostic and potential therapeutic approaches to address dysregulation of members of this gene family.

Unique aspects of transcriptional regulation in neurons--nuances in NFkappaB and Sp1-related factors

The unique physiology and function of neurons create differences in their cellular physiology, including their regulation of gene expression. We began several years ago exploring the relationships between the NFκB transcription factor, neuronal survival, and glutamate receptor activation in telencephalic neurons. These studies led us to conclude that this population of cells is nearly incapable of activating the NFκB that is nonetheless expressed at reasonable levels. A subset of the κB cis elements are instead bound by members of the Sp1 family in neurons. Also surprising was our discovery that Sp1 itself, typically described as ubiquitous, is severely restricted in expression within forebrain neurons; Sp4 seems to be substituted during neuronal differentiation. These findings and their implications for neuronal differentiation – as well as potential dedifferentiation during degenerative processes – are discussed here.

Sp1 is required for glucose-induced transcriptional regulation of mouse vesicular glutamate transporter 2 gene

BACKGROUND & AIMS

Vesicular glutamate transporter (VGLUT) has been reported to be involved in glucose-induced insulin secretion. It has been shown that glucose stimulates the expression of VGLUT isoform 2 (VGLUT2) in beta cells via transcriptional mechanism. In this study, we identified the mouse VGLUT2 (mVGLUT2) promoter and characterized the transcriptional mechanism of glucose-stimulated mVGLUT2 expression in beta-cells.

METHODS

A promoter region of mVGLUT2 was cloned by genomic polymerase chain reaction. The mechanism of Sp1 in glucose-induced transactivation of mVGLUT2 was investigated by luciferase assay, electrophoretic mobility shift assay, chromatin immunoprecipitation assay, and Western blot analysis.

RESULTS

A promoter containing 2133 base pairs of upstream sequence of the 5'-flanking region of mVGLUT2 complementary DNA was cloned. Transient transfection of various 5'-end deletion constructs of the mVGLUT2 promoter/luciferase reporter indicated that the region between -96 to +68 base pair contains the basal promoter for mVGLUT2. Mutational analysis and electromobility shift assay showed an important role for the transcription factor Sp1 in both basal and glucose-induced mVGLUT2 transcription. The interaction between Sp1 and mVGLUT2 was confirmed by chromatin immunoprecipitation assays. Glucose stimulates the phosphorylation of Sp1 via mitogen-activated protein kinase P38 and P44/42. This leads to increased binding activity of Sp1 to the mVGLUT2 promoter and results in activation of the gene.

CONCLUSIONS

We cloned the mouse VGLUT2 promoter and showed a novel molecular mechanism of glucose-induced mVGLUT2 transcription.

Transcriptional regulation of the human CYP46A1 brain-specific expression by Sp transcription factors

Brain defective cholesterol homeostasis has been associated with neurologic diseases, such as Alzheimer's and Huntington's disease. The elimination of cholesterol from the brain involves its conversion into 24(S)-hydroxycholesterol by CYP46A1, and the efflux of this oxysterol across the blood-brain barrier. Herein, we identified the regulatory elements and factors involved the human CYP46A1 expression. Functional 5'deletion analysis mapped a region spanning from nucleotides -236/-64 that is indispensable for basal expression of this TATA-less gene. Treatment of SH-SY5Y cells with mithramycin A resulted in a significant reduction of promoter activity, suggesting a role of Sp family of transcription factors in CYP46A1 regulation. Combination of Sp1, Sp3, and Sp4 over-expression studies in Drosophila SL-2 cells, and systematic promoter mutagenesis identified Sp3 and Sp4 binding to four GC-boxes as required and sufficient for high levels of promoter activity. Moreover, Sp3 and Sp4 were demonstrated to be the major components of the protein-DNA complexes observed in primary rat cortical extracts. Our results suggest that the cell-type specific expression of Sp transcription factors - substitution of Sp1 by Sp4 in neurons - is responsible for the basal expression of the CYP46A1 gene. This study delineates for the first time the mechanisms underlying the human CYP46A1 transcription and thereby elucidates potential pathways underlying cholesterol homeostasis in the brain.

Regulation of the dual-function transcription factor Sp3 by SUMO

In eukaryotes, gene expression is controlled by a relatively small number of regulators. Post-translational modifications dramatically increase the functional possibilities of those regulators. Modification of many transcription factors and cofactors by SUMO (small ubiquitin-related modifier) correlates, in most cases, with inhibition of transcription. Recent studies suggest a model whereby SUMO conjugation to transcription factors promotes the recruitment of co-repressors through direct protein-protein interaction with the SUMO protein. HDACs (histone deacetylases) are important, but not exclusive, effectors of SUMO-mediated repression. Sp3 (specificity protein 3), a zinc-finger DNA-binding domain transcription factor, has the ability to both activate and repress transcription in a context-dependent manner. SUMOylation regulates the dual nature of Sp3 function. Current data suggest that Sp3 represses transcription in a SUMO-dependent manner but independent of HDACs. Recent studies to identify additional co-repressors associated with SUMO and further investigate regulated activity of Sp3 are providing a deeper understanding of SUMO-dependent mechanisms of transcriptional regulation.

Specificity proteins Sp1 and Sp3 interact with the rat GTP cyclohydrolase I proximal promoter to regulate transcription

The role of the proximal promoter GC-box in regulating basal and cAMP-dependent GTP Cyclohydrolase I gene transcription was investigated using a variety of cell lines and techniques. These studies show that the GC-box is composed of a triad of cis-elements that in vitro bind specificity proteins Sp1 and Sp3. Sp1 and Sp3 were found associated with the native proximal promoter in PC12 cells but were not recruited to the promoter during cAMP-dependent transcription. Studies using Drosophila SL2 cells showed that Sp3 occupies two sites within the GC-box and enhances transcription when acting alone and synergistically when combined with nuclear factor-Y (NF-Y) and CCAAT/Enhancer-Binding Protein (C/EBP)beta, cognate binding proteins for the adjacent cAMP response element (CRE) and CCAAT-box cAMP response elements. In contrast, Sp1 bound only one site within the GC-box and did not enhance transcription unless combined with NF-Y and C/EBPbeta. Studies in SL2 cells also showed that Sp1 and Sp3 do not co-occupy the GC-box, and accordingly Sp1 competes for Sp3 binding to repress Sp3-dependent transcription. In PC12 cells, complete mutation of the GC-box reduced basal but not cAMP-dependent transcription, resulting in an overall increase in the cAMP response and demonstrating that formation of this enhanceosome does not require Sp1 or Sp3. Experiments in which the GC-box was replaced with a Gal4 element and the promoter challenged with Gal4 fusion proteins support this conclusion and a role for Sp3 in maintaining high levels of basal transcription in PC12 cells. Equivalent amounts of Sp1 and Sp3 were found associated with the native proximal promoter in PC12 and Rat2 cells, which differ 10-fold in basal transcription. Similar levels of methylation of CpG dinucleotides located within the GC-box were also observed in these two cells lines. These results suggest that Sp1 and Sp3 bound to the GC-box might help to preserve an open chromatin configuration at the proximal promoter in cells which constitutively express low levels of GTP Cyclohydrolase I.

Co-localization and distribution of cerebral APP and SP1 and its relationship to amyloidogenesis

Alzheimer's disease is characterized by amyloid-beta peptide (Abeta)-loaded plaques in the brain. Abeta is a cleavage fragment of amyloid-beta protein precursor (APP) and over production of APP may lead to amyloidogenesis. The regulatory region of the APP gene contains consensus sites recognized by the transcription factor, specificity protein 1 (SP1), which has been shown to be required for the regulation of APP and Abeta. To understand the role of SP1 in APP biogenesis, herein we have characterized the relative distribution and localization of SP1, APP, and Abeta in various brain regions of rodent and primate models using immunohistochemistry. We observed that overall distribution and cellular localization of SP1, APP, and Abeta are similar and neuronal in origin. Their distribution is abundant in various layers of neocortex, but restricted to the Purkinje cell layer of the cerebellum, and the pyramidal cell layer of hippocampus. These findings suggest that overproduction of Abeta in vivo may be associated with transcriptional pathways involving SP1 and the APP gene.

IGF-1 controls GLUT3 expression in muscle via the transcriptional factor Sp1

Glucose transporter 3 (GLUT3), while first found in human fetal muscle, is predominantly expressed in brain and neural tissue. By several independent techniques we have previously shown that GLUT3 is expressed in human skeletal muscle cells. The structure of the human GLUT3 gene has not been previously reported nor has there been any evaluation of the 5'-untranslated region (UTR). To this end, we have cloned and sequenced the human GLUT3 gene. Insulin-like growth factor-1 (IGF-1) increased endogenous Glut3 protein in cultured L6 myotubes, and similarly stimulated luciferase activity in a construct of the human GLUT3 5'-UTR linked to a luciferase reporter gene. Actinomycin D, an inhibitor of mRNA synthesis, prevented IGF-1 stimulation of Glut3 protein. Transfection of L6 cells with Sp1 increased Glut3 and augmented IGF-1 stimulation of Glut3 expression. Knockdown of Glut3 expression in cultured L6 muscle cells using small interference RNA (siRNA) specific for Glut3 significantly reduced myocyte glucose uptake. DNAse footprinting and gel shift assays showed Sp1 specifically bound to the human GLUT3 5'-UTR. Substitution mutants of the human GLUT3 5'-UTR luciferase construct indicated that only one of three Sp1 site clusters was involved in IGF-1 action. These data, using both a human GLUT3 5'-UTR construct and L6 cells' endogenous promoter, suggest that IGF-1 plays a role in maintaining muscle GLUT3 expression and basal glucose uptake via the transcriptional factor Sp1.

Sp1 and Sp3 mediate NHE2 gene transcription in the intestinal epithelial cells

Our previous studies have identified a minimal Sp1-driven promoter region (nt -36/+116) directing NHE2 expression in mouse renal epithelial cells. However, this minimal promoter region was not sufficient to support active transcription of NHE2 gene in the intestinal epithelial cells, suggesting the need for additional upstream regulatory elements. In the present study, we used nontransformed rat intestinal epithelial (RIE) cells as a model to identify the minimal promoter region and transcription factors necessary for the basal transcription of rat NHE2 gene in the intestinal epithelial cells. We identified a region within the rat NHE2 gene promoter located within nt -67/-43 upstream of transcription initiation site as indispensable for the promoter function in intestinal epithelial cells. Mutations at nt -56/-51 not only abolished the DNA-protein interaction in this region, but also completely abolished NHE2 gene promoter activity in RIE cells. Supershift assays revealed that Sp1 and Sp3 interact with this promoter region, but, contrary to the minimal promoter indispensable for renal expression of NHE2, both transcription factors expressed individually in Drosophila SL2 cells activated rat NHE2 gene promoter. Moreover, Sp1 was a weaker transactivator and when coexpressed in SL2 cells it reduced Sp3-mediated NHE2 basal promoter activity. Furthermore, DNase I footprinting confirmed that nt -58/-51 is protected by nuclear protein from RIE cells. We conclude that the mechanism of basal control of rat NHE2 gene promoter activity is different in the renal and intestinal epithelium, with Sp3 being the major transcriptional activator of NHE2 gene transcription in the intestinal epithelial cells.

Glutamate receptor activation evokes calpain-mediated degradation of Sp3 and Sp4, the prominent Sp-family transcription factors in neurons

Sp-family transcription factors (Sp1, Sp3 and Sp4) contain a zinc-finger domain that binds to DNA sequences rich in G-C/T. As assayed by RT-PCR analysis of mRNA, western-blot analysis, immunofluorescence, and antibody-dependent "supershift" of DNA-binding assays, the prominent Sp-family factors in cerebral neurons were identified as Sp3 and Sp4. By contrast, glial cells were found to express Sp1 and Sp3. We previously showed that the pattern of G-C/T binding activity of Sp-family factors is rapidly and specifically altered by the calcium influx accompanying activation of glutamate receptors. Here, we demonstrate that Sp-factor activity is also lost after a cerebral ischemia/reperfusion injury in vivo. Consistent with its calcium-dependent nature, we found that glutamate's effect on Sp-family factors could be blocked by inhibitors of calpains, neutral cysteine proteases activated by calcium. Purified calpain I cleaved Sp3 and Sp4 into products that retained G-C/T-binding activity, consistent with species observed in glutamate-treated neurons. These data provide details of an impact of glutamate-receptor activation on molecular events connected to gene expression.

The promoter of the rat 5alpha-reductase type 1 gene is bidirectional and Sp1-dependent

In many androgen target tissues, testosterone is reduced to the more potent androgen, dihydrotestosterone, by steroid 5alpha-reductase. Two isoforms of 5alpha-reductase, type 1 and type 2, have been cloned. They are differentially expressed and regulated. To determine the mechanisms of regulation of 5alpha-reductase type 1 expression, we have cloned its 5'upstream region and defined its promoter. The proximal 5'upstream region of 5alpha-reductase type 1 displays all the features of a CpG island and has numerous Sp1 binding sites. By transient transfection assays, we have identified a bidirectional promoter activity in this region; this activity was highest in the negative orientation, in the direction of the methyltransferase Nsun2 (predicted) gene. Promoter activity, in either orientation, was lost in Sp1 deficient cells but was rescued following co-transfection with a Sp1 expression vector. Thus, the 5'upstream region of rat 5alpha-reductase type 1 contains a bidirectional promoter with an activity that is Sp1-dependent.

O-linked N-acetylglucosamine suppresses thermal aggregation of Sp1

We demonstrate that O-linked N-acetylglucosamine (O-GlcNAc), a ubiquitous protein modification in eukaryotes, suppresses thermal inactivation of Sp1 transcription factor. 6-Diazo-5-oxonorleucine treatment or O-GlcNAcase overexpression, which reduced O-GlcNAc levels on Sp1, deteriorated thermal stability of Sp1 and O-GlcNAc modified molecules of Sp1 resist thermal aggregation in vitro. We also showed that heat-induced elevation of heat shock protein 70 was facilitated by Sp1 but blunted under low O-GlcNAc levels, suggesting that O-GlcNAc might upregulate the expression of heat shock protein 70 through thermoprotection of Sp1, which eventually enhanced cellular thermotolerance.

KLF5 Interacts with p53 in Regulating Survivin Expression in Acute Lymphoblastic Leukemia

The Kruppel-like factor 5 (KLF5) is a transcription factor that regulates cellular signaling involved in cell proliferation and oncogenesis. Here, we report that KLF5 interacts with tumor suppressor p53 in regulating the expression of the inhibitor-of-apoptosis protein survivin, which may play a role in pathological process of cancer. The core promoter region of survivin contains multiple GT-boxes that have been characterized as KLF5 response elements. Deletion and mutation analyses as well as chromatin immunoprecipitation and electronic mobility shift assay indicated that KLF5 binds to the core survivin promoter and strongly induces its activity. Furthermore, we demonstrated that KLF5 protein is able to bind to p53 and abrogate the p53-regulated repression of survivin. Transfection of KLF5 into a KLF5-negative acute lymphoblastic leukemia cell line EU-8 enhanced survivin expression, and conversely, silencing of KLF5 by small interfering RNA in a KLF5-overexpressing acute lymphoblastic leukemia cell line EU-4 down-regulated survivin expression. The KLF5 small interfering RNA-mediated down-regulation of survivin sensitized EU-4 cells to apoptosis induced by chemotherapeutic drug doxorubicin. These findings identify a novel regulatory pathway for the expression of survivin under the control of KLF5 and p53. Deregulation of this pathway may result in overexpression of survivin in cancer, thus contributing to drug resistance.

Molecular mechanisms underlying FOXP3 induction in human T cells

FOXP3 is playing an essential role for T regulatory cells and is involved in the molecular mechanisms controlling immune tolerance. Although the biological relevance of this transcription factor is well documented, the pathways responsible for its induction are still unclear. The current study reveals structure and function of the human FOXP3 promoter, revealing essential molecular mechanisms of its induction. The FOXP3 promoter was defined by RACE, cloned, and functionally analyzed using reporter-gene constructs in primary human T cells. The analysis revealed the basal, T cell-specific promoter with a TATA and CAAT box 6000 bp upstream the translation start site. The basal promoter contains six NF-AT and AP-1 binding sites, which are positively regulating the trans activation of the FOXP3 promoter after triggering of the TCR. The chromatin region containing the FOXP3 promoter was bound by NF-ATc2 under these conditions. Furthermore, FOXP3 expression was observed following TCR engagement. Promoter activity, mRNA, and protein expression of T cells were suppressed by addition of cyclosporin A. Taken together, this study reveals the structure of the human FOXP3 promoter and provides new insights in mechanisms of addressing T regulatory cell-inducing signals useful for promoting immune tolerance. Furthermore, the study identifies essential, positive regulators of the FOXP3 gene and highlights cyclosporin A as an inhibitor of FOXP3 expression contrasting other immunosuppressants such as steroids or rapamycin.

Emerging chemotherapeutic strategies for Huntington's disease

Huntington's disease (HD) is a progressive and fatal neurological disorder caused by an expanded CAG repeat in the gene coding for the protein, huntingtin. There is no clinically proven treatment for HD. Although the exact cause of neuronal death in HD remains unknown, it has been postulated that the abnormal aggregation of the mutant huntingtin protein may cause toxic effects in neurons, leading to a cascade of pathogenic mechanisms associated with transcriptional dysfunction, oxidative stress, mitochondrial alterations, apoptosis, bioenergetic defects and subsequent excitotoxicity. Understanding how these processes interrelate has become important in identifying a pharmacotherapy in HD and in the design of clinical trials. A number of drug compounds that separately target these mechanisms have significantly improved the clinical and neuropathological phenotype of HD transgenic mice and, as such, are immediate candidates for human clinical trials in HD patients. These compounds are discussed herein.

Rapid evolution of a recently retroposed transcription factor YY2 in mammalian genomes

YY2 was originally identified due to its unusual similarity to the evolutionarily well-conserved zinc finger gene YY1. In this study, we have determined the evolutionary origin and conservation of YY2 using comparative genomic approaches. Our results indicate that YY2 is a retroposed copy of YY1 that has been inserted into another gene locus named Mbtps2 (membrane-bound transcription factor protease site 2). This retroposition is estimated to have occurred after the divergence of placental mammals from other vertebrates based on the detection of YY2 only in the placental mammals. The N- and C-terminal regions of YY2 have evolved under different selection pressures. The N-terminal region has evolved at a very fast pace with very limited functional constraints, whereas the DNA-binding, C-terminal region still maintains a sequence structure very similar to that of YY1 and is also well conserved among placental mammals. In situ hybridizations using different adult mouse tissues indicate that mouse YY2 is expressed at relatively low levels in Purkinje and granular cells of cerebellum and in neuronal cells of cerebrum, but at very high levels in testis. The expression levels of YY2 are much lower than those of YY1, but the overall spatial expression patterns are similar to those of Mbtps2, suggesting a possible shared transcriptional control between YY2 and Mbtps2. Taken together, the formation and evolution of YY2 represent a very unusual case where a transcription factor was first retroposed into another gene locus encoding a protease and survived with different selection schemes and expression patterns.

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

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

Endogenous S-nitrosoglutathione modifies 5-lipoxygenase expression in airway epithelial cells

S-Nitrosoglutathione (GSNO) is an endogenous bronchodilator with several beneficial pulmonary effects. Levels are decreased in the asthmatic airway, and GSNO inhalation has been proposed as an asthma therapy. 5-lipoxygenase (5-LO) is the rate-limiting enzyme in the synthetic pathway for cysteinyl leukotrienes (CysLTs), bronchoconstricting agents that are overproduced in asthma. Here, we have studied the effect of GSNO on the expression of 5-LO in human airway A549 cell lines and in primary normal human tracheobronchial epithelial (NHBE) cells in vitro. GSNO at concentrations of 0.5-1 microM caused a 3- to 6-fold increase in 5-LO expression. However, GSNO at>5 microM significantly inhibited both 5-LO expression and LT production. We also found that airway epithelial cells had gamma-glutamyl transpeptidase (gamma-GT) activity. The effect of 1 microM GSNO on 5-LO expression was prevented by the gamma-GT inhibitor, acivicin, suggesting a convergence of GSNO and CysLT metabolic pathway that may be relevant to asthma. Our data demonstrate that GSNO levels<or=1 microM, likely recapitulating those in the asthmatic airway, increase 5-LO expression, an effect that may increase inflammation and bronchoconstriction. However, GSNO at concentrations>5microM suppresses 5-LO expression. These data suggest that GSNO might inhibit 5-LO expression in the clinical setting.

Activation of the RNA-dependent protein kinase PKR promoter in the absence of interferon is dependent upon Sp proteins

The protein kinase regulated by RNA (PKR) is interferon (IFN)-inducible and plays important roles in many cellular processes, including virus multiplication, cell growth, and apoptosis. The TATA-less PKR promoter possesses a novel 15-bp DNA element (kinase conserved sequence (KCS)) unique to the human and mouse PKR genes that is conserved in sequence and position. We found that Sp1 and Sp3 of the Sp family of transcription factors bind at the KCS element. Their involvement was analyzed in the activation of basal and IFN-inducible PKR promoter activity. Both the small and large isoforms of Sp3 co-purified with KCS protein binding activity (KBP) by using nuclear extracts from HeLa cells not treated with IFN. Two forms of the KCS-binding protein complex were demonstrated by electrophoretic mobility shift assay analysis; one contained Sp1 and the other Sp3. In mouse cells null for all Sp3 isoforms, PKR expression was reduced to approximately 50% that of wild-type cells in the absence of IFN. The IFN-inducible expression of PKR, however, was Sp3-independent but STAT1- and JAK1-dependent. Overexpression of Sp1 in human U cells resulted in increased PKR promoter activity. In Drosophila SL2 cells lacking Sp proteins, both Sp1 and Sp3 large but not small isoforms activated PKR promoter expression, with the Sp1-mediated activation dominant. Mutational analysis of the PKR promoter region indicated a cooperative interaction between two different Sp sites, one of which is within the KCS element. These results establish that, in the absence of IFN treatment, activation of PKR basal expression is mediated by Sp1 and Sp3 proteins in a cooperative manner.

Expression of SRG3, a core component of mouse SWI/SNF chromatin-remodeling complex, is regulated by cooperative interactions between Sp1/Sp3 and Ets transcription factors

SRG3, a mouse homolog of yeast SWI3 and human BAF155, is known to be a core component of SWI/SNF chromatin-remodeling complex. We have previously shown that SRG3 plays essential roles in early mouse embryogenesis, brain development, and T-cell development. SRG3 gene expression was differentially regulated depending on the developmental stages and exhibited tissue-specific pattern. In this study, we showed that the functional interactions between Sp and Ets family transcription factors are crucial for the SRG3 expression. Sp1 and Sp3 specifically bound to the two canonical Sp-binding sites (GC boxes) at -152 and -114, and a non-canonical Sp-binding site (CCTCCT motif) at -108 in the SRG3 promoter. Using Drosophila SL2 cells, we found that various Sp or Ets family members activate the SRG3 promoter through these Sp- or Ets-binding sites, respectively, in a dose-dependent manner. Intriguingly, different combinatorial expression of Ets and Sp factors in SL2 cells resulted in either strong synergistic activation or repression of the SRG3 promoter activity. Moreover, the Sp-mediated activation of SRG3 promoter required the intact Ets-binding element. Taken together, these results suggest that diverse interactions between Sp1/Sp3 and Ets factors are crucial for the SRG3 gene expression.