Sp1 induced gene TIMP1 is related to immune cell infiltration in glioblastoma

Tumor immune microenvironment exerts a profound effect on the population of infiltrating immune cells. Tissue inhibitor of matrix metalloproteinase 1 (TIMP1) is frequently overexpressed in a variety of cells, particularly during inflammation and tissue injury. However, its function in cancer and immunity remains enigmatic. In this study, we find that TIMP1 is substantially up-regulated during tumorigenesis through analyzing cancer bioinformatics databases, which is further confirmed by IHC tissue microarrays of clinical samples. The TIMP1 level is significantly increased in lymphocytes infiltrating the tumors and correlated with cancer progression, particularly in GBM. Notably, we find that the transcriptional factor Sp1 binds to the promoter of TIMP1 and triggers its expression in GBM. Together, our findings suggest that the Sp1-TIMP1 axis can be a potent biomarker for evaluating immune cell infiltration at the tumor sites and therefore, the malignant progression of GBM.

Tumor Extracellular Matrix Stiffness Promptly Modulates the Phenotype and Gene Expression of Infiltrating T Lymphocytes

The immune system is a fine modulator of the tumor biology supporting or inhibiting its progression, growth, invasion and conveys the pharmacological treatment effect. Tumors, on their side, have developed escaping mechanisms from the immune system action ranging from the direct secretion of biochemical signals to an indirect reaction, in which the cellular actors of the tumor microenvironment (TME) collaborate to mechanically condition the extracellular matrix (ECM) making it inhospitable to immune cells. TME is composed of several cell lines besides cancer cells, including tumor-associated macrophages, cancer-associated fibroblasts, CD4+ and CD8+ lymphocytes, and innate immunity cells. These populations interface with each other to prepare a conservative response, capable of evading the defense mechanisms implemented by the host's immune system. The presence or absence, in particular, of cytotoxic CD8+ cells in the vicinity of the main tumor mass, is able to predict, respectively, the success or failure of drug therapy. Among various mechanisms of immunescaping, in this study, we characterized the modulation of the phenotypic profile of CD4+ and CD8+ cells in resting and activated states, in response to the mechanical pressure exerted by a three-dimensional in vitro system, able to recapitulate the rheological and stiffness properties of the tumor ECM.

Sinomenine relieves oxygen and glucose deprivation-induced microglial activation via inhibition of the SP1/miRNA-183-5p/IκB-α signaling pathway

Studies have shown that the inflammatory activation of miroglia (MG) and nuclear factor kappa B ( NF-κB ) play a dominant role in inflammatory response. Previous studies have shown that sinomenine, an anti-inflammatory agent extracted from Sinomenium acutum, can directly protect neurons against cerebral ischemia injury. However, there are no reports on its effect on ischemia/reperfusion-induced inflammatory activation of MG. In the present study, an in vitro ischemia/reperfusion model was developed with mouse BV-2 microglia cells, a model of oxygen-glucose deprivation/reperfusion (OGD/R), and the inhibitory effect of sinomenine pretreatment on inflammatory activation was confirmed through measurement of inflammatory indicators. Mechanistically, sinomenine suppressed OGD/R-induced inflammatory activation through the SP1/miRNA-183-5p/IκB-α pathway. In conclusion, this study shows that sinomenine effectively inhibits OGD/R-induced inflammatory activation in MG by suppressing the activation of transcription specificity protein 1 (SP 1). This finding is of significance for the clinical use of sinomenine in treating cerebral ischemia/reperfusion injury.

LPS depletes PHLPP levels in macrophages through the inhibition of SP1 dependent transcriptional regulation

We have previously reported that bacterial endotoxin LPS attenuates expression of PHLPP, a ser/thr phosphatase, at both transcript and protein levels in different immune cells, however the underlying molecular mechanism is unknown and is of significant interest. Here, in line with the decreased transcript levels upon LPS treatment, we observed that LPS caused significant reduction in PHLPP promoter activity. We observed that SP1, a transcription factor frequently associated with inflammation, was recruited to the PHLPP promoter region. Ectopic expression of SP1 enhanced both transcript and protein levels of PHLPP while knockdown of SP1 or pharmacological inhibition of SP1 DNA binding by mithramycin reduced PHLPP expression. Moreover, over-expression of SP1 co-activators CBP/p300 augmented SP1 driven PHLPP promoter activity. Of note, LPS treatment depleted SP1 and CBP protein levels due to which recruitment of SP1 to PHLPP promoter was reduced. Further, we found that re-introduction of SP1 restored promoter activity and transcript levels of PHLPP in LPS stimulated cells. Collectively, our data revealed the molecular mechanism underlying the regulation of PHLPP expression during LPS induced macrophage inflammatory response.

HTLV-1 induces a Th1-like state in CD4+CCR4+ T cells

Human T-lymphotropic virus type 1 (HTLV-1) is linked to multiple diseases, including the neuroinflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T cell leukemia/lymphoma. Evidence suggests that HTLV-1, via the viral protein Tax, exploits CD4+ T cell plasticity and induces transcriptional changes in infected T cells that cause suppressive CD4+CD25+CCR4+ Tregs to lose expression of the transcription factor FOXP3 and produce IFN-γ, thus promoting inflammation. We hypothesized that transformation of HTLV-1-infected CCR4+ T cells into Th1-like cells plays a key role in the pathogenesis of HAM/TSP. Here, using patient cells and cell lines, we demonstrated that Tax, in cooperation with specificity protein 1 (Sp1), boosts expression of the Th1 master regulator T box transcription factor (T-bet) and consequently promotes production of IFN-γ. Evaluation of CSF and spinal cord lesions of HAM/TSP patients revealed the presence of abundant CD4+CCR4+ T cells that coexpressed the Th1 marker CXCR3 and produced T-bet and IFN-γ. Finally, treatment of isolated PBMCs and CNS cells from HAM/TSP patients with an antibody that targets CCR4+ T cells and induces cytotoxicity in these cells reduced both viral load and IFN-γ production, which suggests that targeting CCR4+ T cells may be a viable treatment option for HAM/TSP.

Role of Penaeus monodon Kruppel-like factor (PmKLF) in infection by white spot syndrome virus

Sp1-like proteins and Kruppel-like factors (KLFs) are highly related zinc-finger proteins that have crucial roles in transcription. One expressed sequence tag (EST, HPA-N-S01-EST0038) from shrimps is homologous to Sp1. This study reports the cloning and characteristics of a KLF from shrimp, Penaeus monodon (PmKLF). The full-length PmKLF cDNA is 1702 bp, encoding a polypeptide of 360 amino acids. Sequence analysis revealed that the sequence of PmKLF is similar to that of KLF11 in humans, mice and zebrafish. RT-PCR analysis indicated that PmKLF mRNA is expressed in all examined tissues. Additionally, immunofluorescence analysis revealed that GFP-KLF fusion protein is located in the nucleus as dots in an insect cell line, Sf9. Localization of PmKLF in the nucleus is also observed in the hemolymph from white spot syndrome virus (WSSV)-infected and WSSV-uninfected Litopenaeus vannamei. Knockdown of the expression of PmKLF transcript in WSSV-infected shrimp resulted in delayed cumulative mortalities, suggesting that PmKLF is important to WSSV infection. Moreover, inhibition of PmKLF expression reduced the copy number of WSSV and ie1 expression, revealing that PmKLF affects WSSV infection via interfering with ie1 expression.

Sodium butyrate upregulates expression of NKG2D ligand MICA/B in HeLa and HepG2 cell lines and increases their susceptibility to NK lysis

Natural killer (NK) cells are important effectors in the immune response to tumors. A number of cell-surface inhibitory and activating receptors on NK cells tightly regulate their interaction with target cell ligands. In particular, the strength of an anti-tumor immune response appears to depend critically on surface levels of one activating receptor, NKG2D. Correspondingly, expression of NKG2D ligands on target cells is a requirement for effective tumor immunosurveillance and the elimination of pathogen-infected cells. Sodium butyrate, a potent repressor of histone deacetylase (HDAC), has recently been proposed as a potential agent in cancer treatment based on its ability to modify, in several cancer cell types, the expression of a variety of genes related to cell cycle regulation and apoptosis. Here we report that, in the HeLa and HepG2 tumor cell lines, sodium butyrate upregulated the expression of the MHC class I-related chain molecules A and B (MICA and MICB) at both the mRNA and protein levels, resulting in an enhanced susceptibility of cells in both lines to NK lysis. It also led to an elevated expression of heat shock protein 70 (HSP70) and transcription factor Sp1, and increased the binding of transcription factors Sp1 and heat shock transcription factor 1 (HSF1) to the MICA/B promoter, resulting in increased expression of MICA and MICB. siRNA targeting Sp1 significantly attenuate the enhancement of MICA expression by sodium butyrate. These results suggest that sodium butyrate and other HDAC inhibitors may have therapeutic potential by enhancing the immune response to cancer.

Antimicrobial activity-specific to Gram-negative bacteria and immune modulation-mediated NF-kappaB and Sp1 of a medaka beta-defensin

Defensins are a group of cationic antimicrobial peptides which play an important role in the innate immune system by exerting their antimicrobial activity against pathogens. In this study, we cloned a novel beta-defensin cDNA from medaka (Oryzias latipes) by rapid amplification of cDNA ends (RACE) technique. The full-length cDNA consists of 480 bp, and the open reading frame (ORF) of 189 bp encodes a polypeptide of 63 amino acids (aa) with a predicted molecular weight of 7.44 kDa. Its genomic organization was analyzed, and Southern blot detection confirmed that only one copy of beta-defensin exists in the medaka HNI strain. RT-PCR, Western blot and immunohistochemistry detections showed that the beta-defensin transcript and protein could be detected in eyes, liver, kidney, blood, spleen and gill, and obviously prevalent expression was found in eyes. Antimicrobial activity of the medaka beta-defensin was evaluated, and the antibacterial activity-specific to Gram-negative bacteria was revealed. Furthermore, the lipopolysaccharide (LPS), a major component of the outer membrane of Gram-negative bacteria, was demonstrated to be able to induce about 13-fold up-regulation of the beta-defensin within first 12h. In addition, promoter and promoter mutagenesis analysis were performed in the medaka beta-defensin. A proximal 100 base pair (bp) sequence (+26 to -73) and the next 1700 bp sequence (-73 to -1755) were demonstrated to be responsible for the basal promoter activity and for the transcription regulation. Three nuclear factor kappa B (NF-kappaB) cis-elements and a Sp1 cis-element were revealed by mutagenesis analysis to exist in the 5' flanking sequence, and they were confirmed to be responsible for the up-regulation of medaka beta-defensin stimulated by LPS. And, the Sp1 cis-element was further revealed to be related to the basal promoter activity, and transcriptional factor II D (TFIID) was found to be in charge of the gene transcription initiation. All the obtained data suggested that the novel medaka beta-defensin should have antimicrobial activity-specific to Gram-negative bacteria, and the antibacterial immune function should be modulated by NF-kappaB and Sp1.

Induction of IL-6 gene expression in a CF bronchial epithelial cell line by Pseudomonas aeruginosa is dependent on transcription factors belonging to the Sp1 superfamily

Cystic fibrosis (CF) is a genetic disease characterized by chronic bacterial lung infection, most commonly sustained by Pseudomonas aeruginosa. Upon infection, elevated concentrations of pro-inflammatory cytokines (i.e. IL-6 and IL1beta) and chemokines (i.e. IL-8 and GROgamma) are found in the bronchoalveolar fluid of CF patients. We report in this paper that: (a) IL-8, IL-6, IL-1beta, ICAM-1, and GRO-gamma genes are upregulated following infection of CF bronchial epithelial IB3-1 cells with P. aeruginosa; (b) Sp1 transcription factor activity is induced following infection of the cystic fibrosis IB3-1 and CuFi-1 cell lines; (c) inhibition of Sp1 activity using transcription factor decoy molecules leads to inhibition of the expression of IL-6 gene. From the theoretical point of view, our results demonstrate that Sp1 transcription factor activity is induced following infection of CF cells with P. aeruginosa, and that this effect is important in the activation of IL-6 gene transcription. From the practical point of view, our data sustain the potential use of decoy molecules targeting the transcription factor Sp1 to control a relevant molecule involved in the inflammatory process associated with the cystic fibrosis airway pathology.

17beta-estradiol induces IL-1alpha gene expression in rheumatoid fibroblast-like synovial cells through estrogen receptor alpha (ERalpha) and augmentation of transcriptional activity of Sp1 by dissociating histone deacetylase 2 from ERalpha

Rheumatoid arthritis (RA) occurs four times more frequently in women than in men, although the mechanistic basis of the gender difference is unknown. RA is characterized by the overproliferation of synoviocytes producing proinflammatory cytokines such as IL-1, implicated in the pathogenesis of the disease. In this study we examined whether 17beta-estradiol (E2) induced IL-1alpha mRNA expression in the rheumatoid fibroblast-like cell line MH7A, as well as in primary synovial cells from RA patients, and investigated the underlying molecular mechanisms. E2 induced IL-1alpha mRNA expression in both cell types in an estrogen receptor-dependent manner. In MH7A cells ERalpha but not ERbeta mediated the effects of E2. Deletion and mutation analysis revealed that a GC-rich region within the IL-1alpha gene promoter was responsible for the response to E2. EMSAs showed that Sp1 and Sp3 bound to the GC-rich region and that the transcriptional activity of Sp1 was up-regulated by the treatment with E2. Sp1 and ERalpha interacted physically regardless of the presence of E2. Physical interaction was also observed between ERalpha and histone deacetylase 2 (HDAC2), and E2 induced the dissociation of HDAC2 from ERalpha. These results suggest that E2 induces the dissociation of corepressor HDAC2 from ERalpha, which leads to the augmentation of Sp1 transcriptional activity through the GC-rich region within the IL-1alpha gene promoter.

Purification and identification of proteins that bind to the hereditary persistence of fetal hemoglobin -198 mutation in the gamma-globin gene promoter

Expression of the gamma-globin gene is silenced in adult humans. However, certain point mutations in the gamma-globin gene promoter are capable of maintaining expression of this gene during adult erythropoiesis, a condition called non-deletion hereditary persistence of fetal hemoglobin (HPFH). Among these, the British form of HPFH carrying a T-->C point mutation at position -198 of the Agamma-globin gene promoter results in 4-10% fetal hemoglobin in heterozygotes. In this study, we used nuclear extracts from murine erythroleukemia cells to purify a protein complex that binds the HPFH -198 gamma-globin gene promoter. Members of this protein complex were identified by mass spectrometry and include DNMT1, the transcriptional coactivator p52, the protein SNEV, and RAP74 (the largest subunit of the general transcription factor IIF). Sp1, which was previously considered responsible for HPFH -198 gamma-globin gene activation, was not identified. The potential role of these proteins in the reactivation and/or maintenance of gamma-globin gene expression in the adult transcriptional environment is discussed.

The Xenopus B2 factor involved in TFIIIA gene regulation is closely related to Sp1 and interacts in a complex with USF

In the Xenopus laevis oocyte there is a million fold more transcription factor IIIA (TFIIIA) and its corresponding mRNA than in a somatic cell. These high levels of TFIIIA gene expression are achieved primarily by transcriptional regulation. The TATA box along with three positive cis-elements in the control region of the TFIIIA gene located at positions -269 to -264 (E1), -235 to -220 (E2), and -669 to -636 (E3) are required for this high level of expression in oocytes. The proteins that bind E1 and E3 of the TFIIIA gene have been identified as Xenopus USF (Xl-USF) and B3 (homolog of Vg1 RBP/VERA). In this study the B2 protein was found to bind E2 in a zinc-dependent fashion and anti-human Sp1 (but not Sp2, Sp3, nor Sp4) supershifted the B2:element 2 complex. The E2 binding protein was purified by DNA affinity chromatography. Based on supershift analysis, molecular weight estimation experiments, and purified human Sp1 DNA binding affinity tests the data strongly support the idea that the B2 protein is the Xenopus ortholog of Sp1, but not Sp2, Sp3, nor Sp4. Xl-USF binds to element 1 of the TFIIIA gene which is immediately adjacent to element 2. Coimmunoprecipitation experiments using crude whole oocyte extracts revealed that Xenopus Sp1 and USF or closely related factors are present together in a high-affinity complex. This structure contributes positively to the initiation of TFIIIA gene transcription in Xenopus oocytes.

Functional analysis of the KCS-like element of the interferon-inducible RNA-specific adenosine deaminase ADAR1 promoter

The ADAR1 gene encodes an RNA-specific adenosine deaminase that alters the functional activity of both viral and cellular RNAs by posttranscriptional adenosine-to-inosine RNA editing. The interferon (IFN) responsive PI promoter of the ADAR1 gene possesses an IFN-stimulated response element (ISRE) responsible for IFN-inducibility, as well as an adjacent upstream sequence, designated kinase conserved sequence-like (KCS-l) element. The KCS-l element is similar to the 15-bp KCS element so far unique to the human and mouse RNA-dependent PKR kinase gene promoters. The KCS element of the PKR kinase (PKR) promoter is essential for both basal and IFN-inducible PKR promoter activity. We have now examined the functional properties of the KCS-l element of the ADAR1 PI promoter. Electrophoretic mobility shift assays (EMSAs) detected constitutively expressed nuclear proteins that bound selectively to the ADAR1 KCS-l element. Competition EMSA and antibody supershift assays indicated that ADAR1 KCS-l-binding proteins shared some properties with PKR KCS-binding proteins. However, transient transfection analyses performed with ADAR1 PI promoter constructs possessing deletion and substitution mutant forms of the KCS-l element revealed that the ADAR1 KCS-l element was not essential for either basal or IFN-inducible promoter activity. Substitution of the ADAR1 KCS-l element with the PKR KCS element increased both basal and inducible ADAR1 PI promoter activity. These results suggest that the KCS-l element of the ADAR1 PI promoter is not functionally equivalent to the KCS element of the PKR promoter.

Increased expression of AP2 and Sp1 transcription factors in human thyroid tumors: a role in NIS expression regulation?

BACKGROUND

Sodium/iodide symporter (NIS) is a key protein in iodide transport by thyroid cells and this activity is a prerequisite for effective radioiodide treatment of thyroid cancer. In the majority of thyroid cancers, however, iodide uptake is reduced, probably as a result of decreased NIS protein expression.

METHODS

To identify the mechanisms that negatively affect NIS expression in thyroid tumors, we performed electrophoresis mobility shift assays and immunoblot analysis of nuclear protein extracts from normal and tumoral thyroid tissues from 14 unrelated patients.

RESULTS

Two proteins closely related to the transcription factors AP2 and Sp1 were identified in the nuclear extracts. Expression of both AP2 and Sp1 in nuclear extracts from thyroid tumors was significantly higher than that observed in corresponding normal tissues.

CONCLUSION

These observations raise the possibility that NIS expression, and subsequently iodide transport, are reduced in thyroid tumors at least in part owing to alterations in the binding activity of AP2 and Sp1 transcription factors to NIS promoter.

Human cytomegalovirus hyperimmune globulin not only neutralizes HCMV infectivity, but also inhibits HCMV-induced intracellular NF-kappaB, Sp1, and PI3-K signaling pathways

Inhibition of virus-induced intracellular signaling pathways and viral infectivity are our ultimate goals in the development of effective antiviral agents to control human cytomegalovirus (HCMV) infections. The HCMV hyperimmune globulin may meet such criteria. In a human embryonic lung (HEL) fibroblast culture model, pretreatment of Towne strain HCMV with HCMV hyperimmune globulin was shown to inhibit viral infectivity successfully, as measured by a standard plaque assay. The extracellular viral titers and extracellular viral DNA, as measured by plaque assay and PCR, respectively, were also decreased. In addition, the HCMV hyperimmune globulin prevented HCMV from inducing the intracellular activation of NF-kappaB, Sp-1, and PI3-K signaling pathways. The PI3-K pathway was examined by following phosphorylation (activation) of two of its downstream kinases, Akt and p70S6K. HCMV hyperimmune globulin also prevented the production of immediate early, early, and late viral proteins. These studies show that HCMV hyperimmune globulin neutralization of HCMV prevents the earliest known events observed after viral envelope glycoproteins bind their cell membrane receptors, i.e., NF-kappaB, Sp-1 and PI3-K activation. This suggests that HCMV hyperimmune globulin not only can inhibit viral infectivity, but can also prevent the abnormal cellular signaling that may induce unwanted cellular proliferation or cytokine synthesis.

Sp1 as G1 cell cycle phase specific transcription factor in epithelial cells

Sp1 binding sites have been identified in enhancer/promoter regions of several growth and cell cycle regulated genes, and it has been shown that Sp1 is increasingly phosphorylated in G1 phase of the cell cycle. Interactions of Sp1 with proteins involved in control of cell cycle and tumor formation have been reported. Here we show that expression of Sp1 protein predominates in the G1 phase of the cell cycle in epithelial cells. This is achieved by proteasome-dependent degradation. Inhibition of endogeneous Sp1 activity by a dominant-negative Sp1 mutant was associated with a cell cycle arrest in G1 phase, a strongly reduced expression of cyclin D1, the EGF-receptor and increased levels of p27Kip1. We have thus identified Sp1 as an important regulator of the cell cycle in G1 phase.

Nuclear receptors modulate the interaction of Sp1 and GC-rich DNA via ternary complex formation

Binding sites for transcription factor Sp1 have been implicated in the transcriptional regulation of several genes by hormones or vitamins, and here we show that a GC-rich element contributes to the retinoic acid response of the interleukin 1beta promoter. To explain such observations, it has been proposed that nuclear receptors can interact with Sp1 bound to GC-rich DNA. However, evidence supporting this model has remained indirect. So far, nuclear receptors have not been detected in a complex with Sp1 and GC-rich DNA, and the expected ternary complexes in non-denaturing gels were not seen. In search for these missing links we found that nuclear receptors [retinoic acid receptor (RAR), thyroid hormone receptor (TR), vitamin D(3) receptor, peroxisome-proliferator-activated receptor and retinoic X receptor] induce an electrophoretic mobility increase of Sp1-GC-rich DNA complexes. Concomitantly, binding of Sp1 to the GC-box is enhanced. It is proposed that nuclear receptors may partially replace Sp1 in homo-oligomers at the GC-box. RARs and Sp1 can also combine into a complex with a retinoic acid-response element. The presence of RAR and Sp1 in complexes with either cognate site was revealed in supershift experiments. The C-terminus of Sp1 interacts with nuclear receptors. Both the ligand- and DNA-binding domains of the receptor are important for complex formation with Sp1 and GC-rich DNA. In spite of similar capacity to form ternary complexes, RAR but not TR up-regulated an Sp1-driven reporter in a ligand-dependent way. Thus additional factors limit the transcriptional response mediated by nuclear receptors and Sp1.

Sp1 and Sp3 function as key regulators of leukotriene C(4) synthase gene expression in the monocyte-like cell line, THP-1

The goal of this study was to examine the mechanisms of leukotriene C(4) (LTC(4)) synthase gene expression in mononuclear phagocytes. Transfection of the monocyte-like cell line THP-1 with LTC(4) synthase promoter-reporter constructs demonstrated that the first 1.3 kb of the promoter mediated a 21.1-fold increase in reporter activity. Deletion analysis revealed that the region between -92 and -23 bp, which contains a signal protein (Sp)1 consensus site at -42 to -37 bp, mediated an 11.5-fold increase in reporter activity. Using a probe from -56 to -17 bp, electrophoretic mobility shift assays (EMSAs) demonstrated that Sp1 and THP-1 and HeLa nuclear extracts bind to this region. Binding was eliminated by mutation of the Sp1 consensus site. Supershift EMSAs using anti-Sp1 and anti-Sp3 antibodies demonstrated that these Sp family members bind to the region. Transfection of the Sp-deficient Drosophila SL-2 cell line with a construct containing the -92 to -23 bp promoter region and Sp expression vectors revealed that Sp1 and Sp3 transactivate gene transcription. We conclude that the Sp1 site is a necessary element for LTC(4) synthase gene transcription. Sp1 and Sp3 function through this site to positively regulate transcription. Thus, we provide evidence that the LTC(4) synthase gene is transcriptionally regulated in mononuclear phagocytes.

Transactivation of classical and nonclassical HLA class I genes through the IFN-stimulated response element

The IFN-stimulated response element (ISRE) is an important conserved cis-acting regulatory element in the promoter of MHC class I genes, but displays considerable locus-specific nucleotide variation. In this report, the putative ISREs of classical and nonclassical HLA class I genes were investigated for their contribution to MHC class I transactivation. It is shown that IFN-gamma induced MHC class I transactivation through the ISRE of HLA-A, HLA-B, HLA-C, and HLA-F. This is congruent with the binding of IFN regulatory factor-1 to the ISREs of these loci upon IFN-gamma treatment. Sp1 was shown to bind to the CG-rich sequences in the ISRE regions of HLA-B, HLA-C, and HLA-G. The putative E box 5' of the ISRE in most HLA-B alleles was shown to bind the upstream stimulatory factors (USF) 1 and 2. The Sp1 and USF binding sites did not influence IFN-gamma-induced transactivation. However, the USF binding site played a suppressive role in the constitutive expression of HLA-B. The locus-specific transcriptional control through the ISRE could be an important mechanism in the differential regulation of classical and nonclassical MHC class I expression, which determines adequate Ag presentation upon pathogenic challenge.

Long-term increase of Sp-1 transcription factors in the hippocampus after kainic acid treatment

Systemic administration of kainic acid (KA), a glutamate receptor agonist, causes robust seizures and has been used as an excellent rodent model for human temporal lobe epilepsy. Recently, we have demonstrated that a single injection of KA increases the steady-state levels of proenkephalin (PENK) mRNA in the rat hippocampus for at least one year. However, the molecular mechanisms underlying this long-term increase in PENK mRNA levels have not been clearly defined. To determine the possible involvement of the Sp-1 transcription factors in this regulation, electrophoresis mobility-shift assays were used to study the expression of Sp-1 factors in the hippocampus after KA treatment. The results showed that there are long-lasting increases in Sp-1 DNA-binding activity. The Sp-1 DNA-binding complexes were only competed by the non-radioactive Sp-1 element and not by ENKCRE2, AP-1 or CRE elements, indicating the specificity of Sp-1 DNA-binding activity. Since the expression of Sp-1 parallels the time course of long-lasting increase in the expression of PENK mRNA and mossy fiber sprouting after KA treatment, we hypothesize that the increase in Sp-1 activity may be associated with the long-term changes in the plasticity of hippocampal function after KA-induced seizures.

Sp1 recognition sites in the proximal promoter of the human vascular endothelial growth factor gene are essential for platelet-derived growth factor-induced gene expression

Stimulation of NIH3T3 cells with platelet-derived growth factor (PDGF)-BB enhances expression of vascular endothelial growth factor (VEGF), an endothelial cell-specific mitogen and a key mediator of tumor angiogenesis. Here, we identified cis-acting VEGF promoter elements and trans-acting factors which are involved in PDGF-stimulated VEGF expression. By 5'-deletion and transient transfection analysis, a G + C-rich region at -85 to -50 of the human VEGF promoter was shown to be necessary and sufficient for both PDGF inducible and basal expression. The region contains three potential recognition sites for Sp1 transcription factors, which overlap with two Egr-1 sites. Mutations that abolish the ability of Sp1 to interact with the VEGF promoter element also abrogate expression induced by PDGF. Mutations of the potential Egr-1 binding sites did not affect PDGF responsiveness. Gel shift and antibody supershift analyses showed that Sp1 and Sp3 interact constitutively with the VEGF promoter element. Our data strongly suggest that enhanced VEGF gene expression in PDGF-induced NIH3T3 cells is mediated by Sp1 and/or Sp3 transcription factors bound to the -85 to -50 promoter region of the VEGF gene.

The transcriptional activator Sp1, a novel autoantigen

OBJECTIVE

To identify one nuclear autoantigenic protein within a complex of DNA binding proteins that bind to GC-rich sequences in Epstein-Barr virus and cellular DNA, and to describe the clinical characteristics of patients whose sera contained autoantibodies to this novel autoantigen.

METHODS

Antibodies to autoantigen Sp1 were initially measured by an electrophoretic mobility shift assay to detect DNA binding proteins. Nuclear extracts and purified Sp1 protein were used in these assays. Recognition of the autoantigen by autoimmune sera was confirmed by immunoprecipitation and immunoblotting.

RESULTS

The autoantigen was identified as Sp1. Anti-Sp1 was detected in sera from 8 (3%) of 230 patients. These sera contained antinuclear antibodies, but lacked antibodies to double-stranded DNA or to several extractable nuclear antigens. The patients whose sera contained antibodies to Sp1 were white women with fatigue, arthritis, Raynaud's phenomenon, malar rash, and photosensitivity.

CONCLUSION

Sp1 is the first described example of an RNA polymerase II transcription activator as an autoantigen. The presence of Sp1 autoantibodies is associated with undifferentiated connective tissue disease.

A novel SP-1 site in the human interleukin-1 beta promoter confers preferential transcriptional activity in keratinocytes

To investigate the mechanisms of transcriptional activation of interleukin-1beta (IL-1beta) in non-monocytic cells, we constructed a series of reporter plasmids with the bacterial chloramphenicol acetyltransferase gene linked to various parts of the human IL-1beta promoter and performed transient transfection experiments. We identified a promoter segment that activates transcription most efficiently in keratinocytes. Electrophoretic mobility shift assays (EMSA) with a 43-mer oligonucleotide derived from the functionally identified cis-acting element revealed specific complexes. By competition analysis with transcription factor consensus sequence oligonucleotides and by immunosupershift, transcription factor SP-1 or a closely related protein was shown to bind to this regulatory element. The closest match to the known SP-1 consensus sequence within the respective region is a TCCCCTCCCCT motif. Mutation of this motif almost completely, and specifically, abolished the binding of two low-mobility complexes and led to a 95% decrease of constitutive transcriptional activation of a reporter construct IL-1beta (-170/+108). Likewise, activation of this reporter construct by tumor necrosis factor-alpha depended on the SP-1 site. These observations suggest that a so-far-unrecognized SP-1 site in the human IL-1beta promoter may participate in the transcriptional regulation of this gene in keratinocytes.

Role of estrogen receptor/Sp1 complexes in estrogen-induced heat shock protein 27 gene expression

Treatment of MCF-7 human breast cancer cells with 10 nM 17 beta-estradiol (E2) resulted in a 2-fold induction of heat shock protein (Hsp) 27 mRNA levels, and this response persisted for up to 24 h. The 5'-promoter region of the gene was further investigated to identify genomic sequences associated with E2 responsiveness. An Sp1 and half-palindromic estrogen response element (ERE) separated by 10 nucleotides, GGGCGGG(N)10GGTCA, were identified at -105 to -84, and formation of the Sp1/estrogen receptor (ER) complex was investigated by in vitro assays using synthetic Hsp 27-[32P]Sp1/ERE oligonucleotides in a gel mobility shift assay and transient transfection studies using short (-108/-84) and long (-108/+23) 5'-promoter sequences linked to a thymidine kinase promoter and the bacterial chloramphenicol acetyl transferase (CAT) reporter gene (Hsp-CATs and Hsp-CATl, respectively). Incubation of nuclear extracts from MCF-7 cells with an Hsp 27-[32P]Sp1/ERE oligonucleotide results in formation of an Sp1/ER complex. The formation of this complex was inhibited by coincubation with unlabeled Sp1/ERE, ERE, and Sp1 oligonucleotides and by preincubation with ER or Sp1 antibodies (immunodepletion). In addition, the complex was supershifted by coincubation with ER antibodies. Mutation of either Sp1 or ERE sites also decreases formation of the retarded band. E2 induced CAT activity in MCF-7 cells transiently transfected with either Hsp-CATs or Hsp-CATl plasmids. It was also demonstrated that E2 did not significantly induce CAT activity in MCF-7 cells transiently transfected with Hsp-CATl-containing mutations in both the Sp1 and ERE sites. The results of this study demonstrate that an Sp1/ER complex is involved in E2-induced Hsp 27 gene expression.

Generation of monoclonal antibodies to the zinc finger domain of the eukaryotic transcription factor Sp1

Using a synthetic peptide that encompasses the zinc finger domain of the eukaryotic transcription factor Sp1, we produced a number of monoclonal antibodies that specifically reacted with the target antigen. Analysis by competitive inhibition assay of five of the monoclonal antibodies revealed that they all recognized a dominant epitope in the synthetic peptide and reacted strongly to recombinantly synthesized beta-galactosidase-Sp1 fusion polypeptide. To determine cellular distribution of Sp1-like molecules, cytoplasmic and nuclear proteins from human lung fibroblasts (HFL-1) and a human rhabdomyosarcoma cell line (A204) were immunoblotted and reacted with our antibodies. In addition to the well characterized 95 Kd and 105 Kd proteins, considered to be the authentic Sp1 polypeptide, a number of other cellular proteins reacted with these antibodies. Immunofluorescence staining of the cells with mAb to the zinc finger of Sp1 also revealed cell-specific differences in intracellular distribution of Sp1-like molecules. Both cytoplasmic and nuclear staining was readily observed in the rhabdomyosarcoma cells. In contrast, while some HFL-1 cells exhibited staining of only cytoplasm, both cytoplasmic and nuclear immunofluorescence was seen in others.