Growth/cell cycle regulation of Sp1 phosphorylation

The Lysine Demethylase KDM7A Regulates Immediate Early Genes in Neurons

Lysine demethylase KDM7A removes histone modifications H3K9me1/2 and H3K27me1/2. KDM7A plays critical roles in gene expression and contribute to biological processes including tumorigenesis, metabolism, and embryonic development. However, the functions of KDM7A in mammalian nervous system are still poorly explored. In this study, functional roles of KDM7A are comprehensively investigated in neuronal cells by applying CUT&Tag-seq, RNA-seq and mice models. Knockdown of Kdm7a in N2A cells result in the alteration of histone modifications near transcription start sites (TSSs) and the expression changes of a large number of genes. In particular, the expression of immediate early genes (IEGs), a series of genes maintaining the function of the nervous system and associating with neurological disorders, are significantly decreased upon Kdm7a knockdown. Furthermore, in vivo knockdown of Kdm7a in dentate gyrus (DG) neuron of mice hippocampus, via Adeno-associated virus (AAV)-based stereotaxic microinjection, led to a significant decrease of the expression of c-Fos, a marker of neuron activity. Behavior assays in mice further revealed that Kdm7a knockdown in hippocampus repress neuron activity, which leading to impairment of emotion and memory. Collectively, the study reveals that KDM7A affects neuron functions by regulating IEGs, which may provide new clues for understanding epigenetic mechanisms in neurological disorders.

Transcription Factor Motifs Associated with Anterior Insula Gene Expression Underlying Mood Disorder Phenotypes

Mood disorders represent a major cause of morbidity and mortality worldwide but the brain-related molecular pathophysiology in mood disorders remains largely undefined. Because the anterior insula is reduced in volume in patients with mood disorders, RNA was extracted from the anterior insula postmortem anterior insula of mood disorder samples and compared with unaffected controls for RNA-sequencing identification of differentially expressed genes (DEGs) in (a) bipolar disorder (BD; n = 37) versus (vs.) controls (n = 33), and (b) major depressive disorder (MDD n = 30) vs. controls, and (c) low vs. high axis I comorbidity (a measure of cumulative psychiatric disease burden). Given the regulatory role of transcription factors (TFs) in gene expression via specific-DNA-binding domains (motifs), we used JASPAR TF binding database to identify TF-motifs. We found that DEGs in BD vs. controls, MDD vs. controls, and high vs. low axis I comorbidity were associated with TF-motifs that are known to regulate expression of toll-like receptor genes, cellular homeostatic-control genes, and genes involved in embryonic, cellular/organ, and brain development. Robust imaging-guided transcriptomics by using meta-analytic imaging results to guide independent postmortem dissection for RNA-sequencing was applied by targeting the gray matter volume reduction in the anterior insula in mood disorders, to guide independent postmortem identification of TF motifs regulating DEG. Our findings of TF-motifs that regulate the expression of immune, cellular homeostatic-control, and developmental genes provide novel information about the hierarchical relationship between gene regulatory networks, the TFs that control them, and proximate underlying neuroanatomical phenotypes in mood disorders.

Copy number variation (CNV) in the IGF1R gene across four cattle breeds and its association with economic traits

The insulin-like growth factor 1 receptor (IGF1R) plays a vital role in immunomodulation and muscle and bone growth. The copy number variation (CNV) is believed to the reason for many complex phenotypic variations. In this paper, we statistically analyzed the copy number and the expression profiling in different tissue types of the IGF1R gene using the 422 samples from four Chinese beef cattle breeds, and the mRNA of IGF1R was widely expressed in nine tissue types of adult cattle (heart, liver, kidney, muscle, fat, stomach, spleen, lung and testis). Results of CNV and growth traits indicated that the IGF1R CNV was significantly associated with body weight and body height of Jinnan (JN) cattle and was significantly associated with body height and hucklebone width of Qinchuan (QC) cattle, making IGF1R CNV a promising molecular marker to improve meat production in beef cattle breeding. Bioinformatics predictions show that the CNV region is highly similar to the human genome, and there are a large number of transcription factors, DNase I hypersensitive sites, and high levels of histone acetylation, suggesting that this region may play a role in transcriptional regulation, providing directions for further study of the role of bovine CNV and economic traits.

The presence of a feeder layer improves human corneal endothelial cell proliferation by altering the expression of the transcription factors Sp1 and NFI

Based on the use of tissue-cultured human corneal endothelial cells (HCECs), cell therapy is a very promising avenue in the treatment of corneal endothelial pathologies such as Fuchs' dystrophy, and post-surgical corneal edema. However, once in culture, HCECs rapidly lose their phenotypic and physiological characteristics, and are therefore unsuitable for the reconstruction of a functional endothelial monolayer. Expression of NFI, a transcription factor that can either function as an activator or a repressor of gene transcription, has never been examined in endothelial cells. The present study therefore aimed to determine the impact of a non-proliferating, lethally irradiated i3T3 feeder layer on the maintenance of HCEC's morphological characteristics, and both the expression and stability of Sp1 (a strong transcriptional activator) and NFI in such cells. The typical morphology of endothelial cells was best maintained when 8 × 103/cm2 HCECs were co-cultured in the presence of 2 × 104 cells/cm2 i3T3. HCECs were found to express both Sp1 and NFI in vitro. Also, the presence of i3T3 led to higher levels of Sp1 and NFI in HCECs, with a concomitant increase in their DNA binding levels (assessed by electrophoretic mobility shift assays (EMSA)). Specifically, i3T3 increased the expression of the NFIA, NFIB and NFIC isoforms, without a noticeable increase in their mRNAs (as revealed by gene profiling on microarray). Gene profiling analysis also identified a few feeder layer-dependent, differentially regulated genes whose protein products may contribute to improving the properties of HCECs in culture. Therefore, co-culturing HCECs with an i3T3 feeder layer clearly improves their morphological characteristics by maintaining stable levels of Sp1 and NFI in cell culture.

Analysis of differentially expressed genes and the promoters in bovine endometrium throughout estrus cycle and early pregnancy

Endometrial gene expression is primarily regulated by the ovarian steroids and pregnancy recognition factors. This study was aimed to characterize differential expression genes (DEGs) in bovine endometrium together with the analysis of their promoter region. Bovine uteri at follicular stage (FS), luteal stage (LS), and implantation stage (IS) at Day 18 of pregnancy were collected. Total RNA extracted and prepared cDNA were then subjected to high-throughput sequencing. For promoter analysis, 1 kb upstream promoter region of each DEG was analyzed. The numbers of highly expressed DEGs were 496 and 597 at FS and LS, respectively. When compared the gene expression of IS with LS, 383 and 346 DEGs showed higher and lower expression at IS, respectively. It was also observed that 20-30 transcription factors (TFs) were included in each DEGs. In addition, promoter analyses estimated 150-160 TFs for each stage. DLX4 and interferon regulatory factor 4 (IRF4) at FS, and IRF5, IRF9, STAT1, and STAT2 at IS were in common to DEGs and estimated TFs, respectively. This study highlighted potential molecular mechanisms controlling endometrial function during estrus cycle and IS, which will further guide to better understand the endometrial functions in future studies.

MiRNA Influences in Neuroblast Modulation: An Introspective Analysis

Neuroblastoma (NB) is the most common occurring solid paediatric cancer in children under the age of five years. Whether of familial or sporadic origin, chromosome abnormalities contribute to the development of NB and cause dysregulation of microRNAs (miRNAs). MiRNAs are small non-coding, single stranded RNAs that target messenger RNAs at the post-transcriptional levels by repressing translation within all facets of human physiology. Such gene 'silencing' activities by miRNAs allows the development of regulatory feedback loops affecting multiple functions within the cell, including the possible differentiation of neural stem cell (NSC) lineage selection. Neurogenesis includes stages of self-renewal and fate specification of NSCs, migration and maturation of young neurones, and functional integration of new neurones into the neural circuitry, all of which are regulated by miRNAs. The role of miRNAs and their interaction in cellular processes are recognised aspects of cancer genetics, and miRNAs are currently employed as biomarkers for prognosis and tumour characterisation in multiple cancer models. Consequently, thorough understanding of the mechanisms of how these miRNAs interplay at the transcriptomic level will definitely lead to the development of novel, bespoke and efficient therapeutic measures, with this review focusing on the influences of miRNAs on neuroblast modulations leading to neuroblastoma.

Transcriptional Regulation of Frizzled-1 in Human Osteoblasts by Sp1

The wingless pathway has a powerful influence on bone metabolism and is a therapeutic target in skeletal disorders. Wingless signaling is mediated in part through the Frizzled (FZD) receptor family. FZD transcriptional regulation is poorly understood. Herein we tested the hypothesis that Sp1 plays an important role in the transcriptional regulation of FZD1 expression in osteoblasts and osteoblast mineralization. To test this hypothesis, we conducted FZD1 promoter assays in Saos2 cells with and without Sp1 overexpression. We found that Sp1 significantly up-regulates FZD1 promoter activity in Saos2 cells. Chromatin immunoprecipitation (ChIP) and electrophoretic mobility shift (EMSA) assays identified a novel and functional Sp1 binding site at -44 to -40 from the translation start site in the FZD1 promoter. The Sp1-dependent activation of the FZD1 promoter was abolished by mithramycin A (MMA), an antibiotic affecting both Sp1 binding and Sp1 protein levels in Saos2 cells. Similarly, down-regulation of Sp1 in hFOB cells resulted in less FZD1 expression and lower alkaline phosphatase activity. Moreover, over-expression of Sp1 increased FZD1 expression and Saos2 cell mineralization while MMA decreased Sp1 and FZD1 expression and Saos2 cell mineralization. Knockdown of FZD1 prior to Sp1 overexpression partially abolished Sp1 stimulation of osteoblast differentiation markers. Taken together, our results suggest that Sp1 plays a role in human osteoblast differentiation and mineralization, which is at least partially mediated by Sp1-dependent transactivation of FZD1.

Regulation of LRRK2 promoter activity and gene expression by Sp1

Background

The dopaminergic neurodegeneration in the nigrostriatal pathway is a prominent neuropathological feature of Parkinson’s disease (PD). Mutations in various genes have been linked to familial PD, and leucine-rich repeat kinase 2 (LRRK2) gene is one of them. LRRK2 is a large complex protein, belonging to the ROCO family of proteins. Recent studies suggest that the level of LRRK2 protein is one of the contributing factors to PD pathogenesis. However, it remains elusive how LRRK2 is regulated at the transcriptional and translational level.

Results

In this study, we cloned a 1738 bp 5’-flanking region of the human LRRK2 gene. The transcriptional start site (TSS) was located to 135 bp upstream of translational start site and the fragment −118 to +133 bp had the minimum promoter activity required for transcription. There were two functional Sp1- responsive elements on the human LRRK2 gene promoter revealed by electrophoretic mobility shift assay (EMSA). Sp1 overexpression promoted LRRK2 transcription and translation in the cellular model. On the contrary, application of mithramycin A inhibited LRRK2 transcriptional and translational activities.

Conclusion

This is the first study indicating that Sp1 signaling plays an important role in the regulation of human LRRK2 gene expression. It suggests that controlling LRRK2 level by manipulating Sp1 signaling may be beneficial to attenuate PD-related neuropathology.

MicroRNA-124 regulates neuronal differentiation of mesenchymal stem cells by targeting Sp1 mRNA

MicroRNAs play an important role in neuronal development and function. miR-124 is the most abundantly expressed miRNA in the nervous system. Several different mRNA targets have been proposed for miR-124, but the precise function of endogenous miR-124 and its mRNA targets remain to be further elucidated. Specificity protein 1 (Sp1) is a transcription factor that plays key roles in many cell processes including cell cycle. However, this transcription factor is nearly absent in differentiated neurons and a remarkable suppression of Sp1 expression was shown after neurogenesis. Since miR-124 is expressed abundantly in neurons and because Sp1 levels decrease during neurogenesis, it is possible that miR-124 could regulate the expression of Sp1 during neuronal development. Therefore, the aim of the present study was to evaluate the putative targeting of Sp1 by miR-124. Overexpression of miR-124 using a plasmid coding for pri-miR-124 in HEK293 cells decreased the expression of Sp1 mRNA. The results of dual-luciferase reporter assay demonstrated that miR-124 directly targeted the 3'-untranslated regions of Sp1 mRNA. To evaluate whether Sp1 expression was regulated by miR-124 during the process of neuronal differentiation, Adipose-derived mesenchymal stem cells (A-MSCs) were differentiated into neuron-like cells. The results of qPCR analysis showed that with the gradual increase of miR-124 expression during neurogenesis, the expression of Sp1 mRNA decreased accordingly. In summary, this study demonstrated for the first time that miR-124 is able to suppress Sp1 expression, which in turn affected the neuronal differentiation of mesenchymal stem cells.

Sesamin Inhibits PDGF-Mediated Proliferation of Vascular Smooth Muscle Cells by Upregulating p21 and p27

Sesamin, an active ingredient of Asiasarum heterotropoides, is known to exhibit many bioactive functions, but the effect thereof on vascular smooth muscle cell (VSMC) proliferation remains poorly understood. Hence, we explored the antiproliferative action of sesamin on VSMCs and the underlying mechanism thereof, focusing on possible effects of sesamin on cell cycle progression. Sesamin significantly inhibited platelet-derived growth factor (PDGF)-induced VSMC proliferation (inhibition percentage at 1, 5, and 10 μM sesamin was 49.8 ± 22.0%, 74.6 ± 19.9%, and 87.8 ± 13.0%, respectively) in the absence of cytotoxicity and apoptosis, and PDGF-induced DNA synthesis; and arrested cell cycle progression in the G0/G1-to-S phase. Sesamin potently inhibited cyclin D1 and CDK4 expression, pRb phosphorylation, and expression of the proliferating cell nuclear antigen (PCNA); and upregulated p27(KIP1), p21(CIP1), and p53. The results thus indicate that the antiproliferative effect of sesamin on PDGF-stimulated VSMCs is attributable to arrest of the cell cycle in G0/G1 caused, in turn, by upregulation of p27(KIP1), p21(CIP1), and p53, and inhibition of cyclin E-CDK2 and cyclin D1-CDK4 expression.

Sp1 transcription factor: A long-standing target in cancer chemotherapy

Sp1 (specificity protein 1) is a well-known member of a family of transcription factors that also includes Sp2, Sp3 and Sp4, which are implicated in an ample variety of essential biological processes and have been proven important in cell growth, differentiation, apoptosis and carcinogenesis. Sp1 activates the transcription of many cellular genes that contain putative CG-rich Sp-binding sites in their promoters. Sp1 and Sp3 proteins bind to similar, if not the same, DNA tracts and compete for binding, thus they can enhance or repress gene expression. Evidences exist that the Sp-family of proteins regulates the expression of genes that play pivotal roles in cell proliferation and metastasis of various tumors. In patients with a variety of cancers, high levels of Sp1 protein are considered a negative prognostic factor. A plethora of compounds can interfere with the trans-activating activities of Sp1 and other Sp proteins on gene expression. Several pathways are involved in the down-regulation of Sp proteins by compounds with different mechanisms of action, which include not only the direct interference with the binding of Sp proteins to their putative DNA binding sites, but also promoting the degradation of Sp protein factors. Down-regulation of Sp transcription factors and Sp1-regulated genes is drug-dependent and it is determined by the cell context. The acknowledgment that several of those compounds are safe enough might accelerate their introduction into clinical usage in patients with tumors that over-express Sp1.

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.

Ischemia/reperfusion-induced upregulation of TIGAR in brain is mediated by SP1 and modulated by ROS and hormones involved in glucose metabolism

We previously found that TIGAR (TP53-induced glycolysis and apoptosis regulator) was upregulated in response to ischemia/reperfusion insult in a TP53-independent manner. The present study sought to investigate the regulatory mechanisms of TIGAR upregulation in animal and cellular models of stroke. The animal and cellular models of ischemia/reperfusion were produced by transient middle cerebral artery occlusion and reperfusion (tMCAO/R) and oxygen-glucose deprivation/reoxygenation (OGD/R), respectively. The expression of TIGAR protein in cortical tissues and hippocampal neuronal cell line HT22 cells or primary neurons was determined. Glucose, hormones and hydrogen peroxide (H2O2) were administered to mice via injection into the tail vein or lateral ventricle or directly added into cell culture medium. In mice subjected to tMCAO/R, the blood glucose level rapidly increased, peaking at 0.5 h and then declined. TIGAR protein was also significantly increased and then declined with a delayed time-course. The increase in TIGAR protein was blunted when blood glucose levels were controlled with insulin. However, administering glucose solution to mice or adding glucose to cell culture medium had no effect on TIGAR protein levels. In contrast adrenaline, hydrocortisone, glucagon and H2O2 significantly increased TIGAR protein expression, whereas insulin inhibited TIGAR expression. The transcription factor SP1 was induced by ischemia/reperfusion ahead of TIGAR upregulation. Inhibiting SP1 with mithramycin A or silencing SP1 with siRNA blocked the ischemia-induced TIGAR upregulation. These results suggest that ROS and hormones regulating blood glucose metabolism play a role in ischemia/reperfusion-induced TIGAR upregulation.

Functional interaction between cyclooxygenase-2 and p53 in response to an endogenous electrophile

Cyclooxygenase-2 (Cox-2) is rapidly expressed by various stimuli and plays a key role in conversion of free arachidonic acid to prostaglandins. We have previously identified 4-hydroxy-2-nonenal (HNE), a lipid peroxidation-derived electrophile, as the potent Cox-2 inducer in rat epithelial RL34 cells and revealed that the HNE-induced Cox-2 expression resulted from the stabilization of Cox-2 mRNA that is mediated by the p38 mitogen-activated protein kinase signaling pathway. In the present study, we investigated an alternative regulatory mechanism of Cox-2 expression mediated by a transcription factor p53. In addition, to characterize the causal role for Cox-2, we examined the effects of Cox-2 overexpression in RL34 cells. To examine whether the HNE-induced Cox-2 expression was mechanistically linked to the p53 expression, we analyzed changes in Cox-2 and p53 expression levels in response to HNE and observed that the Cox-2 levels were inversely correlated with the p53 levels. Down-regulation of p53 followed by the activation of a transcription factor Sp1 was suggested to be involved in the HNE-induced Cox-2 gene expression. To characterize the effect of Cox-2 expression in the cells, we established the Cox-2-overexpressing derivatives of RL34 cells by stable transfection with Cox-2 cDNA. An oligonucleotide microarray analysis revealed a dramatic down-regulation of the proteasome subunit RC1 in the Cox-2 overexpressed cells compared to the empty-vector transfected control cells. Consistent with the Cox-2-mediated down-regulation of proteasome, a moderate reduction of the proteasome activities was observed. This proteasome dysfunction mediated by the Cox-2 overproduction was associated with the enhanced accumulation of p53 and ubiquitinated proteins, leading to the enhanced sensitivity toward electrophiles. These results suggest the existence of a causal link between Cox-2 and p53, which may represent a toxic mechanism of electrophilic lipid peroxidation products.

Down-regulation of Sp1 suppresses cell proliferation, clonogenicity and the expressions of stem cell markers in nasopharyngeal carcinoma

BACKGROUND

Transcription factor Sp1 is multifaceted, with the ability to function as an oncogene or a tumor suppressor, depending on the cellular context. We previously reported that Sp1 is required for the transcriptional activation of the key oncogenes in nasopharyngeal carcinoma (NPC), including B-lymphoma mouse Moloney leukemia virus insertion region 1 (Bmi1) and centromere protein H (CENPH), but the role of Sp1 and its underlying mechanisms in NPC remained largely unexplored. The objective of this study was to investigate the cellular function of Sp1 and to verify the clinical significance of Sp1 as a potential therapeutic target in NPC.

METHODS

The levels of Sp1 in the normal primary nasopharyngeal epithelial cells (NPECs) and NPC cell lines were analyzed by Quantitative Real-time RT-PCR (qRT-PCR) and Western blot. The location and expression of Sp1 in the NPC tissues were detected by immunohistochemistry staining (IHC). The effect of Sp1 knockdown on the cell proliferation, clonogenicity, anchorage-independent growth and the stem-cell like phenotype in NPC cells were evaluated by MTT, flow cytometry, clonogenicity analysis and sphere formation assay.

RESULTS

The mRNA and protein levels of Sp1 were elevated in NPC cell lines than in the normal primary NPECs. Higher expression of Sp1 was found in NPC tissues with advanced clinical stage (P=0.00036). Either inhibition of Sp1 activity by mithramycin A, the FDA-approved chemotherapeutic anticancer drug or Sp1 silencing by two distinct siRNA against Sp1 suppressed the growth of NPC cells. Mechanism analysis revealed that Sp1 silencing may suppress cell proliferation, clonogenicity, anchorage-independent growth and the stem-cell like phenotype through inducing the expression of p27 and p21, and impairing the expressions of the critical stem cell transcription factors (SCTFs), including Bmi1, c-Myc and KLF4 in NPC cells.

CONCLUSIONS

Sp1 was enriched in advanced NPC tissues and silencing of Sp1 significantly inhibited cell proliferation, clonogenicity, anchorage-independent growth and the stem-cell like phenotype of NPC cells, suggesting Sp1 may serve as an appealing drug target for NPC.

GSTM1 and GSTT1 null polymorphisms and male infertility risk: an updated meta-analysis encompassing 6934 subjects

Published data on the association between the GST genes polymorphisms and male infertility risk are inconclusive. We investigated GST genes polymorphisms in a large sample size case-control study, and conducted a literature-based meta-analysis of 6934 individuals. Our case-control study showed the GSTM1 null genotype was significantly associated with idiopathic oligozoospermia, while the null genotype of GSTT1 was significantly associated with normozoospermia and azoospermia. Additionally, significantly elevated GSTT1 expression levels were observed in present genotype compared with null genotype. In the meta-analysis, the null genotype of GSTM1 was associated with a significantly increased risk of male infertility. Furthermore, a stratification analysis showed that the risk of GSTM1 polymorphism was associated with male infertility in both Asian and Caucasian groups. Further studies of GSTM1 and GSTT1 with their biological functions are needed to understand the role of these genes in the development of male infertility.

Phosphorylation of the leukemic oncoprotein EVI1 on serine 196 modulates DNA binding, transcriptional repression and transforming ability

The EVI1 (ecotropic viral integration site 1) gene at 3q26 codes for a transcriptional regulator with an essential role in haematopoiesis. Overexpression of EVI1 in acute myeloid leukaemia (AML) is frequently associated with 3q26 rearrangements and confers extremely poor prognosis. EVI1 mediates transcriptional regulation, signalling, and epigenetic modifications by interacting with DNA, proteins and protein complexes. To explore to what extent protein phosphorylation impacts on EVI1 functions, we analysed endogenous EVI1 protein from a high EVI1 expressing Fanconi anaemia (FA) derived AML cell line. Mass spectrometric analysis of immunoprecipitated EVI1 revealed phosphorylation at serine 196 (S196) in the sixth zinc finger of the N-terminal zinc finger domain. Mutated EVI1 with an aspartate substitution at serine 196 (S196D), which mimics serine phosphorylation of this site, exhibited reduced DNA-binding and transcriptional repression from a gene promotor selectively targeted by the N-terminal zinc finger domain. Forced expression of the S196D mutant significantly reduced EVI1 mediated transformation of Rat1 fibroblasts. While EVI1-mediated serial replating of murine haematopoietic progenitors was maintained by EVI1-S196D, this was associated with significantly higher Evi1-trancript levels compared with WT-EVI1 or EVI1-S196A, mimicking S196 non-phosphorylated EVI1. These data suggest that EVI1 function is modulated by phosphorylation of the first zinc finger domain.

CRABP2 promotes myoblast differentiation and is modulated by the transcription factors MyoD and Sp1 in C2C12 cells

Cellular retinoic acid binding protein 2 (CRABP2), a member of a family of specific carrier proteins for Vitamin A, belongs to a family of small cytosolic lipid binding proteins. Our previous study suggested that CRABP2 was involved in skeletal muscle development; however, the molecular function and regulatory mechanism of CRABP2 in myogenesis remained unclear. In this study, we found that the expression of the CRABP2 gene was upregulated during C2C12 differentiation. An over-expression assay revealed that CRABP2 promotes myogenic transformation by regulating the cell cycle during C2C12 differentiation. The region from -459 to -4 bp was identified as the core promoter and contains a TATA box, a GC box and binding sites for the transcription factors MyoD and Sp1. Over-expression, site-directed mutagenesis and EMSA assays indicated that the transcription factors MyoD and Sp1 regulate CRABP2 expression and promote myoblast differentiation in C2C12 cells.

Rescue of the transcription factors Sp1 and NFI in human skin keratinocytes through a feeder-layer-dependent suppression of the proteasome activity

Co-culturing human skin keratinocytes along with a feeder layer has proven to considerably improve their proliferative properties by delaying massive induction of terminal differentiation. Through a yet unclear mechanism, we recently reported that irradiated 3T3 (i3T3) fibroblasts used as a feeder layer increase the nuclear content of Sp1, a positive transcription factor (TF) that plays a critical role in many cellular functions including cell proliferation, into both adult skin keratinocytes and newborn skin keratinocytes. In this study, we examined the influence of i3T3 on the expression and DNA binding of NFI, another TF important for cell proliferation and cell cycle progression, and attempted to decipher the mechanism by which the feeder layer contributes at maintaining higher levels of these TFs in skin keratinocytes. Our results indicate that co-culturing both adult skin keratinocytes and newborn skin keratinocytes along with a feeder layer dramatically increases glycosylation of NFI and may prevent it from being degraded by the proteasome.

Anti-fibrotic effects via regulation of transcription factor Sp1 on hepatic stellate cells

BACKGROUND

Hepatic stellate cells (HSCs), the central cells in hepatic fibrosis, are characterized by sustaining activation, a process that consists in increased proliferation and over-expression of fibrotic genes. Transcription factor Sp1 mediates the expression of a variety of fibrotic genes expression and thereby play an important role in fibrosis. In addition, previous reports have indicated that Sp1 binding activity is greatly increased in activated HSCs. Thus, our aim was to investigate the anti-proliferative and anti-fibrotic effects of the oligonuceotide decoy of the transcription factor Sp1, ODN, a potent inhibitor of Sp1-activated transcription.

METHODS

We optimized Lipofectamin 2000 (LF2000):ODN DNA ratio for the transfection of hepatic stellate cells HSC-T6. Then we measure the effect of transfected ODN on HSC-T6 cells' proliferation and fibrotic gene expression, and study the mechanism involved.

RESULTS

At a DNA concentration of 1 μM and a ratio ODN DNA:LF2000 of 1:3, HSC-T6 cells have the maximal transfection efficiency with the lowest toxicity. Transfected ODN effectively blocks Sp1 binding to the promoter regions of cell cycle regulatory proteins cyclin D1, p27(KIP1) and fibrotic genes, including transforming growth factor (TGF)-β1, Platelet-derived growth factor (PDGF)-BB, α-SMA, α1 (I) collagen and tissue inhibitor of metalloproteinases-1 (TIMP-1). ODN inhibits HSC-T6 proliferation and fibrotic genes expression in vitro.

CONCLUSION

Sp1 is a key transcription factor that mediates proliferation and fibrotic gene synthesis of HSC-T6, inhibition of Sp1 with decoy ODN may be an effective approach to prevent the progression of hepatic fibrosis.

High-dose siRNAs upregulate mouse Eri-1 at both transcription and posttranscription levels

The eri-1 gene encodes a 3′ exonuclease that can negatively regulate RNA interference via siRNase activity. High-dose siRNAs (hd-siRNAs) can enhance Eri-1 expression, which in return degrade siRNAs and greatly reduces RNAi efficiency. Here we report that hd-siRNAs induce mouse Eri-1 (meri-1) expression through the recruitment of Sp1, Ets-1, and STAT3 to the meri-1 promoter and the formation of an Sp1-Ets-1-STAT3 complex. In addition, hd-siRNAs also abolish the 3′ untranslated region (UTR) mediated posttranscriptional repression of meri-1. Our findings demonstrate the molecular mechanism underlying the upregulation of meri-1 by hd-siRNA.

SP1 plays a pivotal role for basal activity of TIGAR promoter in liver cancer cell lines

TIGAR expression resulted in down-regulation of glycolysis, reduction of intracellular levels of reactive oxygen species, and protection from apoptosis. Despite biological importance, its promoter has not yet been characterized. In this study, we characterized that transcription factor SP1 plays a pivotal role for basal activity of TIGAR promoter. By 5'RACE, the transcription start site was identified locating at 134 bp upstream of the translation initiation site. Different portions of 5'-flanking and 5'-untranslated regions were fused to a luciferase reporter gene to create reporter plasmids, and constructs were transiently transfected into HepG2, Bel-7402, and Smmc-7721 cell lines for luciferase analysis. A minimal region -56/-4 bearing a SP1-binding site was characterized and plays a vital role. Data from electrophoretic mobility shift assay and chromatin immunoprecipitation showed that SP1 can interact with the SP1-binding site within TIGAR promoter in vitro and in vivo. Conclusively, SPl is indispensable for basal activity of TIGAR promoter.

MMP28 gene expression is regulated by Sp1 transcription factor acetylation

MMP-28 (epilysin) is a recently cloned member of the MMP (matrix metalloproteinase) family. It is highly expressed in the skin by keratinocytes, the developing and regenerating nervous system and a number of other normal human tissues, as well as a number of carcinomas. The MMP28 promoter has previously been cloned and characterized identifying a conserved GT-box that binds Sp1/Sp3 (specificity proteins 1 and 3) proteins and is essential for the basal expression of the gene. The present study demonstrates that MMP28 expression is induced by HDAC (histone deacetylase) inhibitors and that this effect is mediated through the GT-box. Transient transfection assays have shown that the induction of MMP28 expression by the HDAC inhibitior TSA (trichostatin A) is mediated via Sp1 at the GT-box. Immunoprecipitation experiments have shown that the acetylation of Sp1 and Sp3 is increased by TSA treatment; however, no effect on DNA binding was observed. Histone acetyltransferases such as p300 and P/CAF [p300/CREB (cAMP-response-element-binding protein)-binding protein-associated factor] increased induction of the MMP28 promoter by Sp1. Knockdown of HDAC1 using siRNA (small interfering RNA) also induces the MMP28 promoter. Oligonucleotide pulldown identified STRAP (serine/threonine kinase receptor-associated protein) as a further protein recruited to the MMP28 promoter and acting functionally with Sp1.

Ischemia/reperfusion reduces transcription factor Sp1-mediated cystathionine beta-synthase expression in the kidney

Cystathionine beta-synthase (CBS) is a key enzyme that catalyzes the rate-limiting step for homocysteine (Hcy) metabolism via the trans-sulfuration pathway and is also responsible for the production of H(2)S through the desulfhydration reaction. Our recent studies demonstrate that renal ischemia/reperfusion decreased the CBS activity leading to Hcy accumulation and H(2)S reduction in the kidney, which in turn contributed to kidney injury. Both Hcy and H(2)S play important roles in physiological and pathological processes. In this study we investigated the molecular mechanism by which CBS activity was regulated in the kidney. The left kidney of Sprague-Dawley rat was subjected to 45 min of ischemia followed by 6 h of reperfusion. Ischemia/reperfusion caused a significant decrease in CBS mRNA and protein levels in the kidney. As a consequence, there was a marked reduction in the CBS enzyme activity. Transfection of kidney proximal tubular cells with transcription factor (Sp1) small interfering RNA caused a marked reduction in CBS mRNA, indicating a pivotal role for Sp1 in regulating CBS expression in kidney cells. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay detected a lower Sp1 activity in kidneys subjected to ischemia/reperfusion as compared with that in a sham-operated group. ERK-mediated phosphorylation of Sp1 was responsible for a decreased transcriptional activity of Sp1 in the kidney upon ischemia/reperfusion. These results suggest that reduced kidney CBS gene expression during ischemia/reperfusion is mediated via a decrease in Sp1 transcriptional activity. Regulation of CBS-mediated Hcy and H(2)S homeostasis may offer a renal protective effect against ischemia/reperfusion injury.

A clustered set of three Sp-family genes is ancestral in the Metazoa: evidence from sequence analysis, protein domain structure, developmental expression patterns and chromosomal location

Background

The Sp-family of transcription factors are evolutionarily conserved zinc finger proteins present in many animal species. The orthology of the Sp genes in different animals is unclear and their evolutionary history is therefore controversially discussed. This is especially the case for the Sp gene buttonhead (btd) which plays a key role in head development in Drosophila melanogaster, and has been proposed to have originated by a recent gene duplication. The purpose of the presented study was to trace orthologs of btd in other insects and reconstruct the evolutionary history of the Sp genes within the metazoa.

Results

We isolated Sp genes from representatives of a holometabolous insect (Tribolium castaneum), a hemimetabolous insect (Oncopeltus fasciatus), primitively wingless hexapods (Folsomia candida and Thermobia domestica), and an amphipod crustacean (Parhyale hawaienis). We supplemented this data set with data from fully sequenced animal genomes. We performed phylogenetic sequence analysis with the result that all Sp factors fall into three monophyletic clades. These clades are also supported by protein domain structure, gene expression, and chromosomal location. We show that clear orthologs of the D. melanogaster btd gene are present even in the basal insects, and that the Sp5-related genes in the genome sequence of several deuterostomes and the basal metazoans Trichoplax adhaerens and Nematostella vectensis are also orthologs of btd.

Conclusions

All available data provide strong evidence for an ancestral cluster of three Sp-family genes as well as synteny of this Sp cluster and the Hox cluster. The ancestral Sp gene cluster already contained a Sp5/btd ortholog, which strongly suggests that btd is not the result of a recent gene duplication, but directly traces back to an ancestral gene already present in the metazoan ancestor.

The transcription factor SP1 regulates centriole function and chromosomal stability through a functional interaction with the mammalian target of rapamycin/raptor complex

Specificity protein 1 (SP1) is an essential transcription factor implicated in the regulation of genes that control multiple cellular processes, including cell cycle, apoptosis, and DNA damage. Very few nontranscriptional roles for SP1 have been reported thus far. Using confocal microscopy and centrosome fractionation, we identified SP1 as a centrosomal protein. Sp1-deficient mouse embryonic fibroblasts and cells depleted of SP1 by RNAi have increased centrosome number associated with centriole splitting, decreased microtubule nucleation, chromosome misalignment, formation of multipolar mitotic spindles and micronuclei, and increased incidence of aneuploidy. Using mass spectrometry, we identified P70S6K, an effector of the mTOR/raptor (mTORC1) kinase complex, as a novel interacting protein of SP1. We found that SP1-deficient cells have increased phosphorylation of the P70S6K effector ribosomal protein S6, suggesting that SP1 participates in the regulation of the mTORC1/P70S6K/S6 signaling pathway. We previously reported that aberrant mTORC1 activation leads to supernumerary centrosomes, a phenotype rescued by the mTORC1 inhibitor rapamycin. Similarly, treatment with rapamycin rescued the multiple centrosome phenotype of SP1-deficient cells. Taken together, these data strongly support the hypothesis that SP1 is involved in the control of centrosome number via regulation of the mTORC1 pathway, and predict that loss of SP1 function can lead to aberrant centriole splitting, deregulated mTORC1 signaling, and aneuploidy, thereby contributing to malignant transformation.

Sp1 and Sp3 mediate basal and serum-induced expression of human CENP-W

Cancer-upregulated gene 2 (CUG2), which was named since it was originally identified as a putative oncogene up-regulated in various human cancers, was recently renamed CENP-W based on the new findings that it is a component of the centromeric complex playing a crucial role in the assembly of functional kinetochore complex during mitosis. To understand the transcriptional regulation of CENP-W, we analyzed its TATA-less promoter and identified a GC-rich putative Sp1 binding site located at -46 to -36 that was critical in CENP-W expression. Competitive electrophoretic gel mobility shift assay using mutated oligos and supershift assays with Sp1 and Sp3 antibodies demonstrated that both proteins specifically bound to this promoter region. Moreover, we found that CENP-W was highly induced by serum stimulation followed by serum deprivation, with Sp1 and Sp3 transcription factors involved in this transactivation. Taken together, our results suggest that Sp1 together with Sp3 may function as the main regulator of the basal and serum-induced transcription of CENP-W.

Hepatitis B virus X protein upregulates transcriptional activation of human telomerase reverse transcriptase

It is well known that telomerase activation and virus infection are strongly associated with human hepatocellular carcinoma (HCC). Hepatitis B virus X protein (HBx) plays an important role in HCC pathogenesis. However, the mechanisms of HBx on telomerase activity are not well understood. To determine the potential roles of HBx in telomerase activity, both transfection and antisense assay were designed to examine the effects of HBx on telomerase in this report. Results showed that HBX gene increased telomerase activity and human telomerase reverse transcriptase (hTERT) expression in HBx-transfected cells and HBx-positive HCC samples. Co-transfection and luciferase reporter assay showed that HBx could stimulate hTERT promoter in a dose-dependent manner in different cells. Truncated and mutant reporter assays revealed that Sp1 binding sites mapped at -132 to +5 nt in hTERT promote were important for HBx-mediated upregulation of hTERT. Western blot did not show any change of Sp1 expression in HBx-transfected cells, but EMSA showed evidence of that HBx increased binding of Sp1 to its target DNA. These results provide new insights into the role of HBx in liver carcinogenesis.

Sp1 and Sp3 regulate transcription of the cyclin-dependent kinase 5 regulatory subunit 2 (p39) promoter in neuronal cells

Cyclin-dependent kinase 5 (cdk5) activity is critical for development and function of the nervous system. Cdk5 activity is dependent on association with the regulators p35 and p39 whose expression is highly regulated in the developing nervous system.We have identified a small 200 bp fragment of the p39 promoter that is sufficient for cell type-specific expression in neuronal cells. Mutational analysis revealed that a cluster of predicted binding sites for Sp1, AP-1/CREB/ATF and E box-binding transcription factors is essential for full activity of the p39 promoter. Electrophoretic mobility shift assays revealed that Sp1 and Sp3 bound to sequences required for p39 promoter function and chromatin immunoprecipitation assays confirmed binding of these proteins to the endogenous p39 promoter. Furthermore, depletion of either Sp1 or Sp3 by siRNA reduced expression from the p39 promoter. Our data suggest that the ubiquitously expressed transcription factors Sp1 and Sp3 regulate transcription of the cdk5 regulator p39 in neuronal cells, possibly in cooperation with tissue-specific transcription factors.

Increased hepatic UCP2 expression in rats with nonalcoholic steatohepatitis is associated with upregulation of Sp1 binding to its motif within the proximal promoter region

Uncoupling protein-2 (UCP2) is a mitochondrial inner-membrane carrier protein that is involved in the control of fatty acid metabolism. To understand the mechanism of the transcriptional regulation of ucp2 in the pathogenesis of nonalcoholic steatohepatitis (NASH), we cloned 500 bp upstream of the ucp2 exon 1 from a rat liver cDNA library and identified cis-acting regulatory elements. The transcriptional start site was identified as "C," -359 bp from the ATG codon. A reporter gene assay showed that deletion of the nucleotide sequence between -264 and -60 bp resulted in a significant decrease in promoter activity in HepG2 and H4IIE cells. Electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) revealed that the increase in promoter activity is related to an enhanced ability of Sp1 to bind to its motifs at -84 to -61 bp within the ucp2 proximal promoter. Overexpression of exogenous Sp1 in H4IIE cells also increased the promoter activity. We demonstrated that the expression of UCP2 mRNA and protein is markedly increased in rats with nonalcoholic steatohepatitis (NASH). Coincidently, levels of Sp1 binding to -84/-61 bp were also increased. Overall, our data indicate that the Sp1-binding site located at the proximal promoter is involved in the regulation of rat UCP2 expression.

Differential effects of shear stress and cyclic strain on Sp1 phosphorylation by protein kinase Czeta modulates membrane type 1-matrix metalloproteinase in endothelial cells

Membrane type 1-matrix metalloproteinase (MT1-MMP) plays a key role in extracellular matrix remodeling, endothelial cell (EC) migration, and angiogenesis. Whereas cyclic strain (CS) increases MT1-MMP expression, shear stress (SS) decreases MT1-MMP expression. The aim of this study was to determine if changes in levels of Sp1 phosphorylation induced by protein kinase Czeta (PKCzeta) in ECs exposed to SS but not CS are important for MT1-MMP expression. The results showed that SS increased Sp1 phosphorylation, which could be inhibited by pretreatment with PKCzeta inhibitors. In the presence of PKCzeta inhibitors, the SS-mediated decrease in MT1-MMP protein expression was also abolished. These data demonstrate that increased affinity of Sp1 for MT1-MMP's promoter site occurs as a consequence of PKCzeta-induced phosphorylation of Sp1 in response to SS, increasing Sp1 binding affinity for the promoter site, preventing Egr-1 binding, and consequently decreasing MT1-MMP expression.

Identification of the minimal promoter region of the mouse NKX5-3, a transcription factor implicated in eye development

Early ocular development is controlled by a complex network of transcription factors, cell cycle regulators, and diffusible signalling molecules. Together, these molecules regulate cell proliferation and apoptosis, and specify retinal fate. NKX5-3 is a homeobox transcription factor implicated in eye development. The analysis of the 5'-flanking region of the mouse Nkx5-3 gene revealed a predicted TATA-less promoter sequence between -416 and -166 of the translation start site. To functionally characterise Nkx5-3 promoter activity, serial deletions of the promoter sequence were introduced in pGL-3 basic vector and promoter activity of these 5'- and 3'-deleted constructions was tested in HeLa and CHO cells. Transactivation assays identified a region between -350 and -296 exhibiting promoter-like activity. Combined analysis by deletions and point mutations showed that this sequence, containing multiple Sp1 binding sites was necessary to promote transcriptional activity. Binding of Sp1 to this region was confirmed by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation, using an antibody specific for Sp1. Altogether, these results demonstrated that the immediate upstream region of Nkx5-3 gene possessed a strong intrinsic promoter activity in vitro, suggesting a potential role in Nkx5-3 transcription in vivo.

Phosphorylation of Sp1 in response to DNA damage by ataxia telangiectasia-mutated kinase

Sp1, a transcription factor that regulates expression of a wide array of essential genes, contains two SQ/TQ cluster domains, which are characteristic of ATM kinase substrates. ATM substrates are transducers and effectors of the DNA damage response, which involves sensing damage, checkpoint activation, DNA repair, and/or apoptosis. A role for Sp1 in the DNA damage response is supported by our findings: Activation of ATM induces Sp1 phosphorylation with kinetics similar to H2AX; inhibition of ATM activity blocks Sp1 phosphorylation; depletion of Sp1 sensitizes cells to DNA damage and increases the frequency of double strand breaks. We have identified serine 101 as a critical site phosphorylated by ATM; Sp1 with serine 101 mutated to alanine (S101A) is not significantly phosphorylated in response to damage and cannot restore increased sensitivity to DNA damage of cells depleted of Sp1. Together, these data show that Sp1 is a novel ATM substrate that plays a role in the cellular response to DNA damage.

Targeting of Sp1 transcription factor: a novel therapeutic approach for keloids, an in vitro analysis

Keloid scars are fibroproliferative disorders characterized by the accumulation of extracellular matrix (ECM) components resulting in a fibrotic condition. Several ECM promoters are regulated by Sp1. Thus, our aim was to investigate the role of Sp1 in keloid pathogenesis and investigate the antiproliferative and antifibrotic effects of Wp631 and mitoxantrone, potent inhibitors of Sp1-activated transcription. An elevated level of Sp1 was observed in tissue extracts obtained from keloid tissue. Serum stimulation elevated Sp1 levels in keloid fibroblasts (KF). Under coculture conditions Sp1 seemed to be downregulated. Wp631 and mitoxanthrone in serum growth factors resulted in a reduced expression of ECM components in KF. Both Wp631 and mitoxanthrone were also able to inhibit the proliferation of normal and keloid keratinocytes and fibroblasts significantly. As Wp631 seems to be potent in downregulating the ECM components in KF and also inhibiting the proliferation of these cells it could be explored as a possible therapeutic agent in the treatment of keloids.

Regulation of human dihydrofolate reductase activity and expression

Dihydrofolate reductase (DHFR) enzyme catalyzes tetrahydrofolate regeneration by reduction of dihydrofolate using NADPH as a cofactor. Tetrahydrofolate and its one carbon adducts are required for de novo synthesis of purines and thymidylate, as well as glycine, methionine and serine. DHFR inhibition causes disruption of purine and thymidylate biosynthesis and DNA replication, leading to cell death. Therefore, DHFR has been an attractive target for chemotherapy of many diseases including cancer. Over the following years, in order to develop better antifolates, a detailed understanding of DHFR at every level has been undertaken such as structure-functional analysis, mechanisms of action, transcriptional and translation regulation of DHFR using a wide range of technologies. Because of this wealth of information created, DHFR has been used extensively as a model system for enzyme catalysis, investigating the relations between structure in-silico structure-based drug design, transcription from TATA-less promoters, regulation of transcription through the cell cycle, and translational autoregulation. In this review, the current understanding of human DHFR in terms of structure, function and regulation is summarized.

Functional interaction of E1AF and Sp1 in glioma invasion

Transcription factor E1AF is widely known to play critical roles in tumor metastasis via directly binding to the promoters of genes involved in tumor migration and invasion. Here, we report for the first time E1AF as a novel binding partner for ubiquitously expressed Sp1 transcription factor. E1AF forms a complex with Sp1, contributes to Sp1 phosphorylation and transcriptional activity, and functions as a mediator between epidermal growth factor and Sp1 phosphorylation and activity. Sp1 functions as a carrier bringing E1AF to the promoter region, thus activating transcription of glioma-related gene for beta1,4-galactosyltransferase V (GalT V; EC 2.4.1.38). Biologically, E1AF functions as a positive invasion regulator in glioma in cooperation with Sp1 partly via up-regulation of GalT V. This report describes a new mechanism of glioma invasion involving a cooperative effort between E1AF and Sp1 transcription factors.

UCP2 and 3 deletion screening and distribution in 15 pig breeds

The uncoupling protein family is a mitochondrial anion carrier family. It plays an important role in the biological traits of animal body weight, basal metabolic rate and energy conversion. Using PCR and PCR-SSCP, we scanned the porcine uncoupling protein 2 gene (UCP2) and uncoupling protein 3 gene (UCP3) and found seven deletion sites, three in UCP2 and four in UCP3. The deletions in 15 pig breeds showed that deletion influenced weight. The genotype compounding of seven deletion sites in 15 pig breeds had significant effects on performance traits of the pig, such as body weight. We predicted the potential protein factor binding sites using the transcription factor analysis tool TFSearch version 1.3 online. Two deletions (1830 nt and 3219 nt) in UCP3 were found to change the transcriptional factor sites. The 16 bp deletion in 1830 nt added a SP1 site and a 6 bp deletion in 3219 nt removed two MZF1 sites. Seven deletion polymorphisms were covered in introns of linkage genes of UCP2 and UCP3, showing that UCPs have conservation and genetic reliability.

Hypomethylation of WNT5A, CRIP1 and S100P in prostate cancer

Oligoarray analysis of a matched pair of prostate cancer and normal cell lines derived from the same radical prostatectomy specimen identified 113 candidate hypomethylated genes that were overexpressed in the cancer cells and contained CpG islands. Hypomethylation of wingless-related MMTV integration site 5A (WNT5A), S100 calcium-binding protein P (S100P) and cysteine-rich protein 1(CRIP1) was confirmed in the cancer cells by bisulfite sequencing. Treatment of the corresponding normal prostate epithelial cells 1542-NPTX with the DNA methyltransferase inhibitor 5-Aza-2'-deoxycytidine (5-aza-CdR) induced higher levels of mRNA expression and partial loss of methylation on these genes. Primary prostate cancers were tested using methylation-specific polymerase chain reaction. WNT5A was hypomethylated in 11/17 (65%) tumors, S100P in 8/16 (50%) and CRIP1 in 13/20 (65%). Bisulfite sequencing of a section of the 5' untranslated region (UTR) of WNT5A revealed that three CpG sites (15, 24 and 35) were consistently methylated (93%) in the normal cell line and normal tissues, but not in the prostate cancer cell line and eight primary prostate cancers. Multiple putative binding sites for the transcription factors SP1 and AP-2 were found adjacent to CpG sites 15 and 24. A putative c-Myb binding site was located within the CpG site 35. Anti-c-Myb antibody co-precipitation with WNT5A was methylation-sensitive in 1542-NPTX cells. It is likely that an epigenetic mechanism regulates WNT5A expression in prostate cancer.

Phosphatidylinositol 3-kinase/protein kinase Czeta-induced phosphorylation of Sp1 and p107 repressor release have a critical role in histone deacetylase inhibitor-mediated derepression [corrected] of transcription of the luteinizing hormone receptor gene

We have demonstrated that silencing of luteinizing hormone receptor (LHR) gene transcription is mediated via a proximal Sp1 site at its promoter. Trichostatin A (TSA) induced histone acetylation and gene activation in JAR cells that prevailed in the absence of changes in Sp1/Sp3 expression, their binding activity, disassociation of the histone deacetylase/mSin3A complex from the Sp1 site, or demethylation of the promoter. This indicated a different mechanism involved in TSA-induced derepression. The present studies have revealed that phosphatidylinositol 3-kinase/protein kinase Czeta (PI3K/PKCzeta)-mediated Sp1 phosphorylation accounts for Sp1 site-dependent LHR gene activation. TSA caused marked phosphorylation of Sp1 at serine 641 in JAR and MCF-7 cells. Blockade of PI3K or PKCzeta activity by specific inhibitors, kinase-deficient mutants, or small interfering RNA abolished the effect of TSA on the LHR gene and Sp1 phosphorylation. PKCzeta was shown to associate with Sp1, and this association was enhanced by TSA. Sp1 phosphorylation at serine 641 was required for the release of the pRb homologue p107 from the LHR gene promoter, while p107 acted as a repressor of the LHR gene. Inhibition of PKCzeta activity blocked the dissociation of p107 from the LHR gene promoter and markedly reduced Sp1 phosphorylation and transcription. These results have demonstrated that phosphorylation of Sp1 by PI3K/PKCzeta is critical for TSA-activated LHR gene expression. These studies have revealed a novel mechanism of TSA action through derecruitment of a repressor from the LHR gene promoter in a PI3K/PKCzeta-induced Sp1 phosphorylation-dependent manner.

Increased chromatin association of Sp1 in interphase cells by PP2A-mediated dephosphorylations

Sp1 dephosphorylation by phosphatase 2A is related to sustained cellular proliferation and is illustrated by an enhanced electrophoretic migration shift. This event occurs concurrently with cell-cycle interphase and increases Sp1 transcriptional activity and in vitro affinity for DNA. We show here that dephosphorylated Sp1 is associated with chromatin more tightly than its phosphorylated counterparts from either resting or mitotic cells. Analysis of the expression of Sp1 point mutants and use of a phospho-specific antibody enabled identification of serine 59 as a major target of PP2A during cell-cycle interphase. Importantly, serine 59 dephosphorylation appeared to up-regulate Sp1 association with chromatin. Various studies suggested that this might occur through the control of the reciprocal O-phosphate/O-GlcNAc modification of other residues, some of which are likely to belong to the Sp1 C-terminal DNA-binding domain. In addition, we demonstrated by phosphopeptide mapping that threonine 681, which belongs to the latter region, is another target of PP2A, yet unrelated to serine 59. We propose that the coordinated dephosphorylation of several Sp1 residues, a general feature of dividing cells, is a required post-translational mechanism for Sp1-dependent transcription of genes related to cell division.

Interplay of Sps and poly(C) binding protein 1 on the mu-opioid receptor gene expression

The proximal promoter of mouse mu-opioid receptor (MOR) gene is the dominant promoter for directing MOR-1 gene expression in brain. Sp1/Sp3 (Sps) and poly(C) binding protein 1 (PCBP) bind to a cis-element of MOR proximal promoter. Functional interaction between Sps and PCBP and their individual roles on MOR proximal core promoter were investigated using SL2 cells, devoid of Sps and PCBP. Each factor contributed differentially to the promoter, with a rank order of activity Sp1>Sp3>PCBP. Functional analysis suggested the interplay of Sps and PCBP in an additive manner. The in vivo binding of individual Sps or PCBP to MOR proximal promoter was demonstrated using chromatin immunoprecipitation (ChIP). Re-ChIP assays further suggested simultaneous bindings of Sps and PCBP to the proximal promoter, indicating physiologically relevant communication between Sps and PCBP. Collectively, results documented that a functional coordination between Sps and PCBP contributed to cell-specific MOR gene expression.

Sp1 deacetylation induced by phorbol ester recruits p300 to activate 12(S)-lipoxygenase gene transcription

We previous reported that Sp1 recruits c-Jun to the promoter of the 12(S)-lipoxygenase gene in 12-myristate 13-acetate-treated cells. We now show that Sp1 that recruited HDAC1 to the Sp1/cJun complex was constitutively acetylated when cells were exposed to phorbol 12-myristate 13-acetate (PMA) (3 h). Prolonged stimulation of the cells with PMA (9 h), however, caused the dissociation of histone deacetylase 1 (HDAC1) and the deacetylation of Sp1, with the latter being able to recruit p300 that in turn caused the acetylation and dissociation of histone 3, thus enhancing the expression of 12(S)-lipoxygenase. We also overexpressed an Sp1 mutant (K703/A, lacking acetylation sites) in the cell and found that cells recruited more p300 and expressed more 12(S)-lipoxygenase. Taken together, our results indicated that Sp1 recruits HDAC1 together with c-Jun to the gene promoter, followed by deacetylation of Sp1 upon PMA treatment. p300 is then recruited to the gene promoter through the interaction with deacetylated Sp1 to acetylate histone 3, leading to the enhancement of the expression of 12(S)-lipoxygenase.

Abnormal Sp1 transcription factor expression in Alzheimer disease and tauopathies

Sp1 transcription factor expression was examined by immunohistochemistry, immunofluorescence and confocal microscopy in Alzheimer disease (AD), Pick disease (PiD), progressive supranuclear palsy (PSP), Parkinson disease (PD) and Dementia with Lewy bodies (DLB). Sp1 partly co-localizes with hyper-phosphorylated tau deposits in neurofibrillary tangles, dystrophic neurites of senile plaques and neuropil threads in AD, and in neurons, astrocytes and oligodendrocytes bearing hyper-phosphorylated tau in PiD and PSP. Sp1 is not found in alpha-synuclein inclusions in PD and DLB. These modifications are not associated with changes in the total expression levels of Sp1, as revealed with gel electrophoresis and Western blotting of brain homogenates. Furthermore, no co-immunoprecipitation of Sp1 and phospho-tau was observed in AD and PiD cases. Since Sp1 binding sites are present in the promoters of several genes involved in amyloid and tau, and Sp1 is regulated by oxidative stress, the present findings suggest that Sp1 deposition in hyper-phosphorylated tau deposits may have functional consequences in the pathology of AD and other tauopathies.

Genetic Variation and the Mitogen-Activated Protein Kinase (MAPK) Signaling Pathway

Non-synonymous single nucleotide polymorphisms (nsSNPs) are known to alter protein function, contributing to disease susceptibility. This report explores the nature of nsSNPs in the gene products of the highly conserved mitogen-activated protein kinase (MAPK) signaling pathways already implicated in cancer development. MAPK signaling pathways regulate cellular processes such as proliferation, differentiation, apoptosis, and survival mediated through interconnected signaling cascades. Using the dbSNP database, we have identified 25 nsSNPs in 17 out of 98 MAPK genes studied. Computational algorithms were used to predict whether the amino acid substitutions were evolutionarily tolerated, or affected putative functional units such as phosphorylation sites, protein motifs and domains. This study predicts that 36% of nsSNPs are likely to have functional consequences, based on evolutionary conservation analysis, and 36% based on phosphorylation prediction analysis. All such nsSNPs represent potentially functional and disease-causing/modifying alleles. More interestingly, the epistatic relationships discussed in this report represent potential synergistic/ antagonistic/additive effects of nsSNP combinations found within the same protein, or within members of the same protein complex and cascades. This strategy can effectively determine which nsSNPs potentially alter protein function, and can be utilized to study the genetic architecture and disease association of other biological protein complexes and networks.

Regulation of the ClC-2 lung epithelial chloride channel by glycosylation of SP1

Chloride channel-2 (ClC-2) is a pH- and voltage-activated chloride channel that is highly expressed in mammalian fetal airway epithelia during the period of maximal fluid secretion. A high level of luminal ClC-2 protein expression is maintained by the SP1 transcription factor until SP1 and ClC-2 decline rapidly at birth. Using fetal (preII-19) and adult (L2) rat lung Type 2 cell lines, we demonstrate that the active higher-molecular-weight 105-kD isoform of SP1 is phosphorylated and glycosylated. Exposure of either cell line to high-dose glutamine is sufficient to induce glycosylation of SP1 and to induce and maintain ClC-2. Exposure to tunicamycin to inhibit SP1 glycosylation reduces ClC-2 expression. We also demonstrate that in vivo ClC-2 expression is similarly regulated. SP1 from 6-wk-old murine lung (high ClC-2 expression) is hyperphosphorylated and hyperglycosylated compared with SP1 from 16-wk-old lung (low ClC-2 expression). Our results support the hypothesis that glycosylation of SP1 produces the 105-kD isoform of SP1 and is involved in regulating ClC-2 gene expression.