Characterization of the human granulocyte-macrophage colony-stimulating factor gene promoter: an AP1 complex and an Sp1-related complex transactivate the promoter activity that is suppressed by a YY1 complex

Different Chronic Stress Paradigms Converge on Endogenous TDP43 Cleavage and Aggregation

The TAR-DNA binding protein (TDP43) is a nuclear protein whose cytoplasmic inclusions are hallmarks of Amyotrophic Lateral Sclerosis (ALS). Acute stress in cells causes TDP43 mobilization to the cytoplasm and its aggregation through different routes. Although acute stress elicits a strong phenotype, is far from recapitulating the years-long aggregation process. We applied different chronic stress protocols and described TDP43 aggregation in a human neuroblastoma cell line by combining solubility assays, thioflavin-based microscopy and flow cytometry. This approach allowed us to detect, for the first time to our knowledge in vitro, the formation of 25 kDa C-terminal fragment of TDP43, a pathogenic hallmark of ALS. Our results indicate that chronic stress, compared to the more common acute stress paradigm, better recapitulates the cell biology of TDP43 proteinopathies. Moreover, we optimized a protocol for the detection of bona fide prions in living cells, suggesting that TDP43 may form amyloids as a stress response.

The many postures of noncanonical Wnt signaling in development and diseases

Wnt signaling regulates many aspects of vertebrate development. Its dysregulation causes developmental defects and diseases including cancer. The signaling can be categorized in two pathways: canonical and noncanonical. Canonical pathway plays a key role in regulating proliferation and differentiation of cells whilst noncanonical Wnt signaling mainly controls cellular polarity and motility. During development, noncanonical Wnt signaling is required for tissue formation. Recent studies have shown that noncanonical Wnt signaling is involved in adult tissue development and cancer progression. In this review, we try to describe and discuss the mechanisms behind the biological effects of noncanonical Wnt signaling, diseases caused by its dysregulation, and implications in adult tissue development biology.

Inactivation of NF-κB p65 (RelA) in Liver Improves Insulin Sensitivity and Inhibits cAMP/PKA Pathway

The transcription factor nuclear factor-κB (NF-κB) mediates inflammation and stress signals in cells. To test NF-κB in the control of hepatic insulin sensitivity, we inactivated NF-κB in the livers of C57BL/6 mice through deletion of the p65 gene, which was achieved by crossing floxed-p65 and Alb-cre mice to generate L-p65-knockout (KO) mice. KO mice did not exhibit any alterations in growth, reproduction, and body weight while on a chow diet. However, the mice on a high-fat diet (HFD) exhibited an improvement in systemic insulin sensitivity. Hepatic insulin sensitivity was enhanced as indicated by increased pyruvate tolerance, Akt phosphorylation, and decreased gene expression in hepatic gluconeogenesis. In the liver, a decrease in intracellular cAMP was observed with decreased CREB phosphorylation. Cyclic nucleotide phosphodiesterase-3B (PDE3B), a cAMP-degrading enzyme, was increased in mRNA and protein as a result of the absence of NF-κB activity. NF-κB was found to inhibit PDE3B transcription through three DNA-binding sites in the gene promoter in response to tumor necrosis factor-α. Body composition, food intake, energy expenditure, and systemic and hepatic inflammation were not significantly altered in KO mice on HFD. These data suggest that NF-κB inhibits hepatic insulin sensitivity by upregulating cAMP through suppression of PDE3B gene transcription.

Intrinsic disorder of human Yin Yang 1 protein

YY1 (Yin Yang 1) is a zinc finger protein with an essential role in various biological functions via DNA- and protein-protein interactions with numerous partners. YY1 is involved in the regulation of a broad spectrum of cellular processes such as embryogenesis, proliferation, tumorigenesis, and snRNA transcription. The more than 100 reported targets of the YY1 protein suggest that it contains intrinsically disordered regions that are involved in such diverse interactions. Here, we present a study of the structural properties of human YY1 using several biochemical and biophysical techniques (fluorescence, circular dichroism, gel filtration chromatography, proteolytic susceptibility) together with various bioinformatics approaches. To facilitate our exploration of the YY1 structure, the full-length protein as well as an N-terminal fragment (residues 1-295) and the C-terminal DNA binding domain were used. We found the N-terminus to be a non-compact fragment of YY1 with little residual secondary structure and lacking a well-defined tertiary structure. The results of our study indicate that YY1 belongs to the family of intrinsically disordered proteins (IDPs), which exist natively in a partially unfolded conformation.

YY1TargetDB: an integral information resource for Yin Yang 1 target loci

Yin Yang 1 (YY1), a ubiquitously expressed transcription factor, plays a critical role in regulating cell development, differentiation, cellular proliferation and tumorigenesis. Previous studies identified many YY1-regulated target genes in both human and mouse. Emerging global mapping by Chromatin ImmnoPrecipitation (ChIP)-based high-throughput experiments indicate that YY1 binds to a vast number of loci genome-wide. However, the information is widely scattered in many disparate poorly cross-indexed literatures; a large portion was only published recently by the ENCODE consortium with limited annotation. A centralized database, which annotates and organizes YY1-binding loci and target motifs in a systematic way with easy access, will be valuable resources for the research community. We therefore implemented a web-based YY1 Target loci Database (YY1TargetDB). This database contains YY1-binding loci (binding peaks) from ChIP-seq and ChIP-on-chip experiments, computationally predicated YY1 and cofactor motifs within each locus. It also collects the experimentally verified YY1-binding motifs from individual researchers. The current version of YY1TargetDB contains 92 314 binding loci identified by ChIP-based experiments; 157 200 YY1-binding motifs in which 42 are experimentally verified and 157 158 are computationally predicted; and 130 759 binding motifs for 47 cofactors.

Database URL:http://www.myogenesisdb.org/YY1TargetDB

Roles Each of Snail, Yin Yang 1 and RKIP in the Regulation of Tumor Cells Chemo-immuno-resistance to Apoptosis

The current anti-cancer therapeutic armamentarium consists of surgery, chemotherapy, radiation, hormonal therapy, immunotherapy, and combinations thereof. Initial treatments usually result in objective clinical responses with prolongation of overall survival (OS) and progression-free survival (PFS) in a large subset of the treated patients. However, at the onset, there is a subset of patients who does not respond and another subset that initially responded but experiences relapses and recurrences. These latter subsets of patients develop a state of cross-resistance to a variety of unrelated therapies. Therefore, there is an urgent need to first unravel the underlying mechanisms of resistance and associated gene products that regulate the cross-resistance. Such gene products are potential therapeutic targets as well as potential prognostic/diagnostic biomarkers. In this context, we have identified three interrelated gene products involved in resistance, namely, Snail, YY1, and RKIP that are components of the dysregulated NF-κB/Snail/YY1/RKIP loop in many cancers. In this review, we will discuss the roles each of Snail, YY1 and RKIP in the regulation of tumor cell resistance to chemo and immunotherapies. Since these same gene products have also been shown to be involved in the regulation of the EMT phenotype and metastasis, we suggest that targeting any of these three gene products can simultaneously inhibit tumor cell resistance and metastasis.

Dual role of NO donors in the reversal of tumor cell resistance and EMT: Downregulation of the NF-κB/Snail/YY1/RKIP circuitry

Several studies have implicated the role of Nitric Oxide (NO) in the regulation of tumor cell behavior and have shown that NO either promotes or inhibits tumorigenesis. These conflicting findings have been resolved, in part, by the levels of NO used such that low levels promote tumor growth and high levels inhibit tumor growth. Our studies have focused on the use of high levels of NO provided primarily by the NO donor, DETANONOate. We have shown that treatment of resistant tumor cells with DETANONOate sensitizes them to apoptosis by both chemotherapeutic drugs and cytotoxic immunotherapeutic ligands. The underlying mechanisms by which NO sensitizes tumor cells to apoptosis were shown to be regulated, in part, by NO-mediated inhibition of the NF-κB survival/anti-apoptotic pathways and downstream of NF-κB by inhibition of the transcription factor Yin Yang 1 (YY1). In addition to NO-induced sensitization to apoptosis, we have also shown that NO induced the expression of the metastasis-suppressor/immunosurveillance cancer gene product, Raf-1 kinase inhibitor protein (RKIP). Overexpression of RKIP mimics NO in tumor cells-induced sensitization to apoptosis. The induction of RKIP by NO was the result of the inhibition of the RKIP repressor, Snail, downstream of NF-κB. These findings established the presence of a dysregulated NF-κB/Snail/YY1/ RKIP circuitry in resistance and that treatment with NO modifies this loop in tumor cells in favor of the inhibition of tumor cell survival and the response to cytotoxic drugs. Noteworthy, the NF-κB/Snail/YY1/RKIP loop consists of gene products that regulate the epithelial to mesenchymal transition (EMT) and, thus, tumor metastasis. Hence, we have found that treatment of metastatic cancer cell lines with DETANONOate inhibited the EMT phenotype, through both the inhibition of the metastasis-inducers, NF-κB and Snail and the induction of the metastasis-suppressor, RKIP. Altogether, the above findings establish, for the first time, the dual role of high levels of NO in the sensitization of tumor cells to apoptotic stimuli as well as inhibition of EMT. Hence, NO donors may be considered as novel potential therapeutic agents with dual roles in the treatment of patients with refractory cancer and in the prevention of the initiation of the metastatic cascade via EMT.

Systems biology evaluation of immune responses induced by human host defence peptide LL-37 in mononuclear cells

The immune system is very complex, it involves the integrated regulation and expression of hundreds of proteins. To understand in greater detail how the human host defence immunomodulatory peptide LL-37 interacts with innate immunity, a systems approach was pursued. Polychromatic flow cytometry was employed to demonstrate that within human peripheral blood mononuclear cells, CD14+ monocytes, myeloid and plasmocytoid dendritic cells and T- and B-lymphocytes, all responded to LL-37, with the differential production of intracellular cytokines. Microarray analyses with CD14+ monocytes indicated the differential expression of 475 genes in response to stimulation with LL-37. To understand this complex response, bioinformatic interrogation, using InnateDB, of the gene ontology, signalling pathways and transcription factor binding sites was undertaken. Activation of the IkappaBalpha/NFkappaB, mitogen-activated protein kinases p38, ERK1/2 and JNK, and PI3K signalling pathways in response to LL-37 was demonstrated by pathway and ontology over-representation analyses, and confirmed experimentally by inhibitor studies. Computational analysis of the predicted transcription factor binding sites upstream of the genes that were regulated by LL-37 predicted the involvement of several transcription factors including NFkappaB and five novel factors, AP-1, AP-2, SP-1, E2F1, and EGR, which were experimentally confirmed to respond to LL-37 by performing transcription factor array studies on nuclear extracts from LL-37 treated mononuclear cells. These data are discussed as reflecting the integration of several responsive signalling pathways through the involvement of transcription factor complexes in gene expression activated by LL-37 in human mononuclear cells.

Fyn is a novel target of (-)-epigallocatechin gallate in the inhibition of JB6 Cl41 cell transformation

The cancer preventive action of (-)-epigallocatechin gallate (EGCG), found in green tea, is strongly supported by epidemiology and laboratory research data. However, the mechanism by which EGCG inhibits carcinogenesis and cell transformation is not clear. In this study, we report that EGCG suppressed epidermal growth factor (EGF)-induced cell transformation in JB6 cells. We also found that EGCG inhibited EGF-induced Fyn kinase activity and phosphorylation in vitro and in vivo. Fyn was implicated in the process because EGF-induced JB6 cell transformation was inhibited by small interfering RNA (siRNA)-Fyn-JB6 cells. With an in vitro protein-binding assay, we found that EGCG directly bound with the GST-Fyn-SH2 domain but not the GST-Fyn-SH3 domain. The K(d) value for EGCG binding to the Fyn SH2 domain was 0.367 +/- 0.122 microM and B(max) was 1.35 +/- 0.128 nmol/mg. Compared with control JB6 Cl41 cells, EGF-induced phosphorylation of p38 MAP kinase (p38 MAPK) (Thr180/Tyr182), ATF-2 (Thr71) and signal transducer and activator of transcription 1 (STAT1) (Thr727) was decreased in siRNA-Fyn-JB6 cells. EGCG could inhibit the phosphorylation of p38 MAPK, ATF-2, and STAT1. The DNA binding ability of AP-1, STAT1, and ATF-2 was also decreased in siRNA-Fyn-JB6 cells. Overall, these results demonstrated that EGCG interacted with Fyn and inhibited Fyn kinase activity and thereby regulated EGF-induced cell transformation. Inhibition of Fyn kinase activity is a novel and important mechanism that may be involved in EGCG-induced inhibition of cell transformation.

Promoter sequence variants of LIGHT are associated with female vascular dementia

LIGHT (homologous to L ymphotoxins, exhibits I nducible expression, and competes with herpes simplex virus G lycoprotein D for H erpes virus entry mediator, a receptor expressed by T lymphocytes) is implicated in the inflammation by disrupted T cell homeostasis, primarily at a transcriptional level. We investigated the association of LIGHT promoter with ischemic stroke and vascular dementia induced by such inflammation. We determined transcription factor binding sites altered by promoter SNPs using transcription factor prediction programs. Six common haplotypes composed of the selected SNPs (C-770T, G-607T, G-543A, and A-399G) were used for the assay of reporter activity. The most frequent haplotype construct, CGGA, induced the highest luciferase activity. The haplotype TTGA showed the lowest expression with 0.39-fold activity (P < 0.001) of CGGA. The substitution from C to T at the locus of C-770T (TGGA) decreased the reporter activity by 47% (P < 0.001). The SNPs and haplotypes were further investigated to see their association with ischemic stroke and vascular dementia in 455 controls and 478 patients. Significant association with vascular dementia was shown in the allele T of C-770T (odds ratio [OR] = 1.54; P < 0.05) and the haplotype TTGA (OR = 10.59; P < 0.05) in females. We concluded that the allele T of C-770T and the haplotype TTGA of the promoter SNPs in LIGHT gene might decrease the expression of LIGHT and subsequently increase the susceptibility to vascular dementia in females.

Action of transcription factors in the control of transferrin receptor expression in human brain endothelium

Brain endothelium has a distinctive phenotype, including high expression of transferrin receptor, p-glycoprotein, claudin-5 and occludin. Dermal endothelium expresses lower levels of the transferrin receptor and it is absent from lung endothelium. All three endothelia were screened for transcription factors that bind the transferrin receptor promoter and show different patterns of binding between the endothelia. The transcription factor YY1 has distinct DNA-binding activities in brain endothelium and non-brain endothelium. The target-sites on the transferrin receptor promotor for YY1 lie in close proximity to those of the transcription initiation complex containing TFIID, so the two transcription factors potentially compete or interfere. Notably, the DNA-binding activity of TFIID was the converse of YY1, in different endothelia. YY1 knockdown reduced transferrin receptor expression in brain endothelium, but not in dermal endothelium, implying that YY1 is involved in tissue-specific regulation of the transferrin receptor. Moreover a distinct YY1 variant is present in brain endothelium and it associates with Sp3. A model is presented, in which expression from the transferrin receptor gene in endothelium requires the activity of both TFIID and Sp3, but whether the gene is transcribed in different endothelia, is related to the balance between activating and suppressive forms of YY1.

Involvement of the TNF-α autocrine–paracrine loop, via NF-κB and YY1, in the regulation of tumor cell resistance to Fas-induced apoptosis

Many tumors are resistant to Fas ligand (FasL)-induced apoptosis. This study examined the role of tumor-derived TNF-alpha, via an autocrine/paracrine loop, in the regulation of tumor-cell resistance to FasL-induced apoptosis. We have reported that Fas expression and sensitivity to FasL is negatively regulated by the transcription repressor factor Yin Yang 1 (YY1). Thus, we hypothesized that tumor-derived TNF-alpha induces the activation of NF-kappaB and the transcription repressor YY1, both of which negatively regulate Fas expression and sensitivity to FasL-induced apoptosis. This hypothesis was tested in PC-3 prostate cancer cells which synthesize and secrete TNF-alpha and express constitutively active NF-kappaB and YY1. Treatment of PC-3 cells with TNF-alpha (10 units) resulted in increased NF-kappaB and YY1 DNA-binding activity, upregulation of YY1 expression, downregulation of surface and total Fas expression and enhanced resistance of PC-3 to apoptosis induced by the FasL agonist antibody CH-11. In contrast, blocking the binding of secreted TNF-alpha on PC-3 cells with soluble recombinant sTNF-RI resulted in significant inhibition of constitutive NF-kappaB and YY1 DNA-binding activity, downregulation of YY1 expression, upregulation of Fas expression and sensitization of tumor cells to CH-11-induced apoptosis. The regulation of YY1 expression and activity by NF-kappaB was demonstrated by the use of the NF-kappaB inhibitor Bay 11-7085 and by the use of a GFP reporter system whereby deletion of the YY1-tandem binding site in the promoter significantly enhanced GFP expression. The direct role of YY1 expression in the regulation of PC-3 resistance to CH-11-induced apoptosis was shown in cells transfected with siRNA YY1 whereby such cells exhibited upregulation of Fas expression and were sensitized to CH-11-induced apoptosis. These findings demonstrate that the TNF-alpha autocrine-paracrine loop is involved in the constitutive activation of the transcription factors NF-kappaB and YY1 in the tumor cells and this loop leads to inhibition of Fas expression and resistance to FasL-induced apoptosis. Further, these findings identify new targets such as TNF-alpha, NF-kappaB and YY1, whose inhibition can reverse tumor cell resistance to FasL-mediated apoptosis.

Wnt signalling in lung development and diseases

There are several signalling pathways involved in lung organogenesis including Notch, TGFbeta/BMP, Sonic hedgehog (Shh), FGF, EGF, and Wnt. Despite the widely acknowledged significance of Wnt signalling in embryonic lung development, the role of different Wnt pathways in lung pathologies has been slow to emerge. In this review, we will present a synopsis of current Wnt research with particular attention paid to the role of Wnt signals in lung development and in pulmonary diseases.

Interleukin-17 augments tumor necrosis factor-alpha-induced granulocyte and granulocyte/macrophage colony-stimulating factor release from human colonic myofibroblasts

BACKGROUND

Interleukin (IL)-17 is a newly identified T-cell-specific cytokine. In this study, we investigated the effects of IL-17 on colony-stimulating factor (CSF) release in human colonic subepithelial myofibroblasts (SEMFs).

METHODS

CSF release and mRNA expression were determined by enzyme-linked immunosorbent assay (ELISA) and Northern blotting, respectively. Nuclear factor (NF)-kappaB- and activating protein (AP-1)-DNA binding activities were evaluated by electrophoretic gel mobility shift assays (EMSAs).

RESULTS

Unstimulated cells secreted a small amount of granulocyte G- and granulocyte/macrophage (GM)-CSF, and a considerable amount of M-CSF. IL-17 weakly enhanced G-CSF release, but did not affect GM- and M-CSF release. IL-17 selectively enhanced tumor necrosis factor (TNF)-alpha-induced G- and GM-CSF release. The combination of IL-17 plus TNF-alpha induced a marked increase in NF-kappaB- and AP-1-DNA binding activities. The adenovirus-mediated transfer of a stable form of IkappaBalpha and/or a dominant negative mutant of c-Jun markedly inhibited the IL-17 plus TNF-alpha-induced G- and GM-CSF mRNA expression. Furthermore, a stability study showed that IL-17 plus TNF-alpha markedly enhanced the stability of G- and GM-CSF mRNA.

CONCLUSIONS

IL-17 augments TNF-alpha-induced G- and GM-CSF release via transcriptional and posttranscriptional mechanisms.

Eicosapentaenoic acid prevents lipopolysaccharide-stimulated DNA binding of activator protein-1 and c-Jun N-terminal kinase activity

Activator protein-1 (AP-1) is a transcription factor that plays an important role in regulating the expression of proinflammatory cytokines including tumor necrosis factor-alpha (TNF-alpha). Many studies have shown that fish oil supplementation inhibits TNF-alpha production in mice and humans; however, the mechanisms remain unclear. In this study, the effects of eicosapentaenoic acid (EPA), a major n-3 fatty acid in fish oil, on lipopolysaccharide (LPS)-stimulated activation of AP-1 were investigated in human monocytic THP-1 cells. The results demonstrated that AP-1 DNA binding activity stimulated by LPS was suppressed by preincubating cells with EPA. Lipopolysaccharide-stimulated increase of c-Jun and c-Fos protein levels was also attenuated by EPA pretreatment. In addition, EPA pretreatment decreased LPS-induced c-Jun phosphorylation and c-Jun N-terminal kinase (JNK) activation. The results suggest that suppression of TNF-alpha expression by EPA may be partly mediated by its inhibitory effect on AP-1 activation.

Genetic variation in the multifunctional transcription factor Yy1 and type 1 diabetes mellitus in the BB rat

Spontaneous diabetes in B(io)B(reeding) rats is complex, polygenic, and recessively inherited. Several crossing studies have demonstrated that beside the class II genes of the major histocompatibility complex (MHC, Iddm1) additional non-MHC genes are involved in diabetes development. One of them, Iddm4, was initially mapped on chromosome 6q32. To study the physiologic importance of Iddm4 a congenic BB.SHR rat strain (BB.6S) was established. The BB.6S is characterised by a drastic reduction of diabetes frequency (86 vs. 14%) indicating existence of diabetes protective genes of SHR on the exchanged chromosomal segment. One of the possible diabetes susceptibility candidate genes located within this exchanged region is the multifunctional transcription factor Yin yang 1 (Yy1). Yy1 was therefore sequenced in BB/OK and SHR rats. No genetic variation in exons between BB/OK and SHR was found. However, three single nucleotide polymorphisms (SNPs) were detected in intron 4. To determine the "wild type" allele, intron 4 of several diabetes-resistant inbred rat strains (DA, LEW, BN, and WOKW) and wild rats was sequenced. In addition, a congenic BB/OK strain was established by introgressing the same segment of chromosome 6 (D6Rat184-D6Rat3) of wild rats onto BB/OK background (BB.6W). The sequence analysis showed the SNP pattern of SHR (A/C/C) in all inbred rat strains studied whereas both unrelated wild rats showed the pattern of BB/OK rats (T/G/A). The congenic BB.6W rats developed diabetes in the same extent than BB/OK rats. This finding may support the assumption that the SNP pattern of BB/OK and wild rats favours and that of SHR suppresses diabetes development. Because of strong synteny between rat chromosome 6q32 and human 14q32, Yy1 may be also of interest in human type 1 diabetics showing significant linkage to markers on chromosome 14q32.

Molecular Cloning and Functional Characterization of the Transcription Factor YY2

YY1 is a ubiquitous zinc finger transcription factor that binds to and regulates promoters and enhancers of many cellular and viral genes. Here we report the isolation of a human cDNA encoding a DNA sequence-specific binding protein with significant homology to the transcription factor YY1. A sequence analysis of this novel protein, YY2, revealed an overall 65% identity in the DNA sequence and a 56% identity in protein sequence compared with human YY1. The most pronounced similarity between YY1 and YY2 exists within the zinc finger regions of the two proteins, and consistent with this observation, YY2 can bind to and regulate some promoters known to be controlled by YY1. Similar to YY1, YY2 contains both transcriptional activation and repression functions. The finding of a protein with structure and function similar to YY1 provides a new opportunity to explore additional mechanisms by which YY1-responsive genes can be regulated and suggests that gene regulation by YY1 is far more complicated than previously assumed.

Nuclear factor-kappaB does not mediate the inhibitory effects of dexamethasone on granulocyte-macrophage colony-stimulating factor expression

Human granulocyte-macrophage colony-stimulating factor (GM-CSF) reporter constructs containing up to 3.3 kb of upstream promoter sequence were transiently transfected into both Jurkat and HUT78 human T-cell lines. In Jurkat cells, stimulation with phorbol 12-myristate 13-acetate (PMA) plus phytohemaglutinin (PHA) produced robust increases in reporter activity, whereas HUT78 cells showed low levels of reporter induction attributable to constitutive nuclear factor (NF)-kappaB activity. Following mutation of either the proximal NF-kappaB site (-85/-76) or the activator protein1 (AP-1) motif within the conserved lymphokine element 0 (CLE0) site (-54/-31), reporter activity was markedly reduced in both cell lines. Despite this dependence on NF-kappaB and CLE0/AP-1, GM-CSF reporter activity was unaffected by dexamethasone in either cell line. Similarly, an NF-kappaB-dependent reporter was also not repressed by dexamethasone, yet GM-CSF release from HUT78 T cells was inhibited. These data therefore confirm a critical role for both NF-kappaB and CLE0 sites in GM-CSF promoter activation and indicate that NF-kappaB may not mediate glucocorticoid-dependent repression of GM-CSF in these cells.

Identification of a minimal promoter sequence for the human N-acetyltransferase Type I gene that binds AP-1 (activator protein 1) and YY-1 (Yin and Yang 1)

Human N -acetyltransferase Type I (NAT1) catalyses the acetylation of many aromatic amine and hydrazine compounds and it has been implicated in the catabolism of folic acid. The enzyme is widely expressed in the body, although there are considerable differences in the level of activity between tissues. A search of the mRNA databases revealed the presence of several NAT1 transcripts in human tissue that appear to be derived from different promoters. Because little is known about NAT1 gene regulation, the present study was undertaken to characterize one of the putative promoter sequences of the NAT1 gene located just upstream of the coding region. We show with reverse-transcriptase PCR that mRNA transcribed from this promoter (Promoter I) is present in a variety of human cell-lines, but not in quiescent peripheral blood mononuclear cells. Using deletion mutant constructs, we identified a 20 bp sequence located 245 bases upstream of the translation start site which was sufficient for basal NAT1 expression. It comprised an AP-1 (activator protein 1)-binding site, flanked on either side by a TCATT motif. Mutational analysis showed that the AP-1 site and the 3' TCATT sequence were necessary for gene expression, whereas the 5' TCATT appeared to attenuate promoter activity. Electromobility shift assays revealed two specific bands made up by complexes of c-Fos/Fra, c-Jun, YY-1 (Yin and Yang 1) and possibly Oct-1. PMA treatment enhanced expression from the NAT1 promoter via the AP-1-binding site. Furthermore, in peripheral blood mononuclear cells, PMA increased endogenous NAT1 activity and induced mRNA expression from Promoter I, suggesting that it is functional in vivo.

Glucocorticoid inhibition of granulocyte macrophage-colony-stimulating factor from T cells is independent of control by nuclear factor-kappaB and conserved lymphokine element 0

Release of granulocyte macrophage-colony-stimulating factor (GM-CSF) from T cells is important in the differentiation, maturation, and survival of inflammatory cells. Here the induction of GM-CSF expression from T cells was dependent on transcription and translation and was prevented by dexamethasone. In primary human CD3(+) T cells, up to 3.3 kb of human GM-CSF promoter was strongly activated by PMA + PHA. Mutations in either the -85/-76 nuclear factor (NF)-kappaB site or the activator protein-1 region in the -54/-31 conserved lymphokine element 0 (CLE0) site substantially reduced promoter activity. Both GM-CSF promoter and NF-kappaB-dependent constructs were unresponsive to dexamethasone whereas the release of GM-CSF was potently repressed. Analysis of GM-CSF mRNA and protein expression at various time points and the effect of adding dexamethasone after the stimulus revealed the existence of potent mechanisms of inhibition acting at a translational level. The expression of tristetraproline and HuR, proteins that bind the AU-rich element in the GM-CSF 3'-untranslated region was unaffected by dexamethasone and overall AU-rich element binding activity was unaltered. Taken together our data support an important role for the NF-kappaB and CLE0 sites in the transcriptional control of GM-CSF expression in primary human T cells and suggest that post-transcriptional/translational mechanisms are key mediators of glucocorticoid-dependent repression.

p38 Mitogen-activated protein kinase regulation of JB6 Cl41 cell transformation promoted by epidermal growth factor

The relationship between cell transformation and p38 MAP kinase, a major mitogen-activated protein (MAP) kinase pathway converting signals of various extracellular stimuli into expression of specific target genes through activation of transcription factors, still remains unclear. The aim of the present study was to investigate the role of the p38 MAP kinase pathway in epidermal growth factor (EGF)-induced cell transformation in JB6 cells. Our data show that a dominant negative mutant of p38 MAP (DN-p38) kinase inhibits EGF-promoted JB6 Cl41 cell transformation and that SB202190, an inhibitor of p38 MAP kinase, also inhibits JB6 Cl41 cell transformation in a dose-dependent manner. Moreover, our results show that DN-p38 MAP kinase inhibits the phosphorylation of EGF-stimulated activating transcription factor-2 (ATF-2) and signal transducer and activator of transcription 1 (STAT1). Additionally, DN-p38 MAP kinase inhibits EGF-induced phosphorylation of c-Myc (Thr58/Ser62). Gel shift assays indicate that DN-p38 MAP kinase inhibits EGF-induced activator protein-1 (AP-1) DNA binding in a dose-dependent manner. These results show that p38 MAP kinase plays a key role in the regulation of EGF-induced cell transformation in JB6 cells through regulation of phosphorylation of p38 MAP kinase and activation of its target genes in phosphorylation, c-Myc cell transformation-related genes, and AP-1 binding ability.

Role of c-jun N-terminal kinase in the induced release of GM-CSF, RANTES and IL-8 from human airway smooth muscle cells

1. Human airway smooth muscle cells (HASMC) contribute to airway inflammation in asthma by virtue of their capacity to produce several inflammatory mediators including IL-8, GM-CSF and RANTES. The intracellular signal pathway underlying the production of these cytokines in HASMC is not entirely elucidated. 2. We examined the role of the mitogen-activated protein kinase (MAPK) c-jun N-terminal kinase (JNK) in TNFalpha- and IL-1beta-induced GM-CSF, RANTES and IL-8 production in HASMC by using a novel specific inhibitor for JNK (SP600125). 3. Confluent HASMC were treated with TNFalpha or IL-1beta (10 ng ml(-1)) for 24 h in the presence or absence of SP600125 (1-100 micro M). JNK activity was determined by a kinase assay. Phosphorylation of JNK, p38 MAPK and ERK was examined by Western blotting. Culture supernatants were assayed for GM-CSF, RANTES and IL-8 content by ELISA. 4. Maximum TNFalpha- or IL-1beta-induced phosphorylation of JNK in HASMC occurred after 15 min and returned to baseline levels after 4 h. SP600125 inhibited TNFalpha- and IL-1beta-induced JNK activity in HASMC as shown by the reduced phosphorylation of its substrate c-jun. Furthermore, GM-CSF, RANTES and to a lesser extent IL-8 release from HASMC treated with TNFalpha and IL-1beta was inhibited dosedependently by SP600125. 5. JNK activation is involved in TNFalpha- and IL-1beta-induced GM-CSF, RANTES and IL-8 production from HASMC. JNK may therefore represent a critical pathway for cytokine production in HASMC.

Transcription factor YY1 functions as a PcG protein in vivo

Polycomb group (PcG) proteins function as high molecular weight complexes that maintain transcriptional repression patterns during embryogenesis. The vertebrate DNA binding protein and transcriptional repressor, YY1, shows sequence homology with the Drosophila PcG protein, pleiohomeotic (PHO). YY1 might therefore be a vertebrate PcG protein. We used Drosophila embryo and larval/imaginal disc transcriptional repression systems to determine whether YY1 repressed transcription in a manner consistent with PcG function in vivo. YY1 repressed transcription in Drosophila, and this repression was stable on a PcG-responsive promoter, but not on a PcG-non-responsive promoter. PcG mutants ablated YY1 repression, and YY1 could substitute for PHO in repressing transcription in wing imaginal discs. YY1 functionally compensated for loss of PHO in pho mutant flies and partially corrected mutant phenotypes. Taken together, these results indicate that YY1 functions as a PcG protein. Finally, we found that YY1, as well as Polycomb, required the co-repressor protein CtBP for repression in vivo. These results provide a mechanism for recruitment of vertebrate PcG complexes to DNA and demonstrate new functions for YY1.

Molecular cloning of rat transcription factor YY1

YY1 is a ubiquitously expressed multifunctional transcription factor that is involved in both positive and negative regulation of gene expression as well as initiation of transcription. Here, we isolated cDNA encoding a full-length open reading frame (ORF) of rat YY1. Rat YY1 is composed of 411 amino acid residues and its amino acid sequence is 97.6% identical to that of mouse YY1 and 97.8% identical to that of human YY1. The transactivating abilities of wild-type rat YY1 and four truncated mutant forms of YY1 were examined by transient reporter assays. When residues 114-193, which sequence includes a portion of the activation region and most of the Gly/Lys-rich region, were lacking, transactivation activity decreased somewhat, but the further deletion in the activation region (of residues 56-113) did not cause further decrease of the activity. On the other hand, N-terminus of the activation region (1-78/100-106) did not have transactivation activity by itself as well as synergistic activity with an erythroid specific transcription factor GATA-1.

T cell-specific expression of the murine CD3delta promoter

T cell-specific expression of human and mouse CD3delta is known to be governed by an enhancer element immediately downstream from the gene. Here we demonstrate by transgenic and in vitro studies that the murine CD3delta (mCD3delta) promoter prefers to be expressed in cells of the T lineage. Deletion analyses of a promoter segment (-401/+48 bp) followed by transient transfections indicate that upstream elements between -149 and -112 bp contribute to full expression of the gene. Furthermore, a core promoter region -37/+29 appears to contribute to a T cell specificity. Using substitution mutant scanning, four positive and one negative regulatory elements were found within the mCD3delta core promoter. The first two positive elements comprise two classical initiator-like sites, which recruit TFII-I, whereas a third contains a functional Ets binding site. Immediately adjacent to the observed transcription start site is a negative element that utilizes the transcription regulator YY1. The last positive regulatory element contains a potentially functional CREB binding site and the minor transcriptional start site. Because NERF-2, Elf-1, and Ets-1 are expressed preferentially in lymphocytes and because, in addition, YY1 represses the promoter activity strongly in non-T cells, we conclude that the combination of these transcription factors contributes to the T cell-specific expression pattern of mouse CD3delta.

Multiple regulatory domains of IRF-5 control activation, cellular localization, and induction of chemokines that mediate recruitment of T lymphocytes

Transcription factors of the interferon regulatory factor (IRF) family have been identified as critical mediators of early inflammatory gene transcription in infected cells. We recently determined that, besides IRF-3 and IRF-7, IRF-5 serves as a direct transducer of virus-mediated signaling. In contrast to that mediated by the other two IRFs, IRF-5-mediated activation is virus specific. We show that, in addition to Newcastle disease virus (NDV) infection, vesicular stomatitis virus (VSV) and herpes simplex virus type 1 (HSV-1) infection activates IRF-5, leading to the induction of IFNA gene subtypes that are distinct from subtypes induced by NDV. The IRF-5-mediated stimulation of inflammatory genes is not limited to IFNA since in BJAB/IRF-5-expressing cells IRF-5 stimulates transcription of RANTES, macrophage inflammatory protein 1 beta, monocyte chemotactic protein 1, interleukin-8, and I-309 genes in a virus-specific manner. By transient- transfection assay, we identified constitutive-activation (amino acids [aa] 410 to 489) and autoinhibitory (aa 490 to 539) domains in the IRF-5 polypeptide. We identified functional nuclear localization signals (NLS) in the amino and carboxyl termini of IRF-5 and showed that both of these NLS are sufficient for nuclear translocation and retention in infected cells. Furthermore, we demonstrated that serine residues 477 and 480 play critical roles in the response to NDV infection. Mutation of these residues from serine to alanine dramatically decreased phosphorylation and resulted in a substantial loss of IRF-5 transactivation in infected cells. Thus, this study defines the regulatory phosphorylation sites that control the activity of IRF-5 in NDV-infected cells and provides further insight into the structure and function of IRF-5. It also shows that the range of IRF-5 immunoregulatory target genes includes members of the cytokine and chemokine superfamilies.

A functional promoter polymorphism in the macrophage migration inhibitory factor (MIF) gene associated with disease severity in rheumatoid arthritis

The macrophage migration inhibitory factor (MIF) is a potent pro-inflammatory cytokine and regulates the anti-inflammator effects of glucocorticoids. An important role for MIF within the cytokine cascade is to act in concert with endogenous glucocorticoids to control the set-point and magnitude of the inflammatory response. Elevated expression of MIF in the circulation and in the synovial joint has been documented in rheumatoid arthritis. MIF also has been linked to the development of joint damage and disease pathology in experimental animal models. We describe herein a novel CATT-tetranucleotide repeat polymorphism at position -794 of the human Mif gene and show that it functionally affects the activity of the MIF promoter in gene reporter assays. We describe four genotypes which comprise 5, 6, 7, or 8-CATT repeat units and show that the 5-CATT allele has the lowest level of basal and stimulated MIF promoter activity in vitro. The presence of the low expressing, 5-CATT repeat allele correlated with low disease severity in a cohort of rheumatoid arthritis patients.

Induction of the transcriptional repressor Yin Yang-1 by vascular cell injury. Autocrine/paracrine role of endogenous fibroblast growth factor-2

Yin Yang-1 (YY1) is a multifunctional transcription factor that can repress the expression of many growth factor, hormone, and cytokine genes implicated in atherogenesis. YY1 expression is activated in rat vascular smooth muscle cells shortly after injury. YY1 DNA binding activity paralleled elevated protein levels in the nucleus. Smooth muscle cell injury triggered the rapid extracellular release of immunoreactive fibroblast growth factor-2 (FGF-2). YY1 induction after injury was blocked by neutralizing antibodies directed against FGF-2. This growth factor increased YY1 mRNA and protein expression and stimulated YY1 binding and transcriptional activity. Overexpression of YY1 inhibited smooth muscle cell replication. Immunohistochemical analysis demonstrated YY1 staining in medial smooth muscle cells, coincident with FGF-2 expression. Proliferating cell nuclear antigen staining, in contrast, was confined mainly to the atherosclerotic intima. This is the first demonstration that YY1 is induced by either injury or FGF-2, is differentially expressed in normal and diseased human arteries, and that its overexpression inhibits vascular smooth muscle but not endothelial cell replication.

Nitric oxide inhibits the transcription repressor Yin-Yang 1 binding activity at the silencer region of the Fas promoter: a pivotal role for nitric oxide in the up-regulation of Fas gene expression in human tumor cells

NO has been increasingly implicated in control of the transcriptional machinery and serves as an intracellular second messenger to modify gene expression. We have demonstrated that NO up-regulated Fas receptor expression in ovarian carcinoma cell lines, albeit the mechanism involved is not known. Thus, we hypothesized that NO, directly or indirectly, may modify the transcriptional machinery that is responsible for the increased expression of the Fas gene. We examined the effect of NO on Fas gene expression using a Fas promoter-driven luciferase reporter system. Transient transfection of AD10 cells with pGL-3-FasP demonstrated that the IFN-gamma-dependent NO generation increases the trans-activation of the Fas promoter, and this increase was blocked by the NOS inhibitor (N(G)-monomethyl-L-arginine), but could be restored by the addition of the NO donor S-nitroso-N-acetylpenicillamine. Systematic deletion of the Fas promoter revealed that the functional region responsible for the NO-mediated effect was located at the silencer region, suggesting that NO may be responsible for the disruption of a repressor mechanism. We demonstrate that NO up-regulates the expression of the Fas receptor on AD10 cells via the specific inactivation of the transcription repressor yin-yang 1 DNA binding activity to the silencer region of the Fas promoter. These findings reveal a new mechanism of NO-mediated gene regulation by interfering with a repressor transcription factor at the silencer region of the Fas promoter.

Characterization of Inherited Differences in Transcription of the Human Integrin alpha 2 Gene

Inherited, single-base substitutions are found at only two positions, C(-)52T and C(-)92G, within the proximal 5'-regulatory region (within -1096 to +48) of the human integrin alpha(2) gene. We recently reported that the T(-)52 substitution results in decreased binding of transcription factor Sp1 to adjacent binding sites, decreased transcription of the alpha(2) gene, and reduced densities of platelet alpha(2)beta(1). In this study, we identify an additional Sp1-binding site at position -107 to -99 and show that the adjacent dimorphic sequence C(-)92G also influences the rate of gene transcription. In the erythroleukemia cell line Dami, transfected promoter-luciferase constructs bearing the G(-)92 sequence exhibit roughly a 3-fold decrease in activity relative to the C(-)92 constructs. In transfected CHRF-288-11 megakaryocytic cells, the corresponding activity decreases by 5-fold. DNase I footprinting of the promoter region with Dami nuclear extracts showed a protected segment at -107 to -99 that can be deprotected by coincubation with molar excess of a consensus Sp1 oligonucleotide. Gel mobility shift assays and supershift assays with specific antibodies indicate that Sp1 binds to this region of the alpha(2) gene promoter. Mutation of the Sp1 binding element within -107 to -99 in constructs containing either C(-)92 or G(-)92 abolishes basal promoter activity and eliminates the binding of Sp1. The G(-)92 sequence has a gene frequency of 0.15 in a typical Caucasian population, and the presence of this allele correlates with reduced densities of platelet alpha(2)beta(1). The combined substitution G(-)92/T(-)52 has an additive influence on gene transcription, resulting in an 8-fold decrease in transfected Dami cells or a 20-fold decrease in transfected CHRF-288-11 cells. In summary, the natural dimorphism C(-)92G within the proximal 5'-regulatory region of the human integrin alpha(2) gene contributes to the regulation of integrin alpha(2)beta(1) expression on megakaryocytes and blood platelets and must thereby modulate collagen-related platelet function in vivo.

Function and regulation of AP-1 subunits in skin physiology and pathology

The mouse skin has become the model of choice to study the regulation and function of AP-1 subunits in many physiological and pathological processes in vivo and in vitro. Genetically modified mice, in vitro reconstituted skin equivalents and epidermal cell lines were established, in which AP-1-regulated genetic programs of cell proliferation, differentiation and tumorigenesis can be analysed. Since the epidermis, as our interface with the environment, is subjected to radiation and injury, signal transduction pathways and critical AP-1 members regulating the mammalian stress response could be identified. Regulated expression of important components of the cytokine network, cell surface receptors and proteases, which orchestrate the process of wound healing has been found to rely on AP-1 activity. Here we review our current knowledge on the function of AP-1 subunits and AP-1 target genes in these fascinating fields of skin physiology and pathology.

Cold shock domain factors activate the granulocyte-macrophage colony-stimulating factor promoter in stimulated Jurkat T cells

Cold shock domain (CSD) family members have been shown to play roles in either transcriptional activation or repression of many genes in various cell types. We have previously shown that CSD proteins dbpAv and dbpB (also known as YB-1) act to repress granulocyte-macrophage colony-stimulating factor transcription in human embryonic lung (HEL) fibroblasts via binding to single-stranded DNA regions across the promoter. Here we show that the same CSD factors are involved in granulocyte-macrophage colony-stimulating factor transcriptional activation in Jurkat T cells. Unlike the mechanisms of CSD repression in HEL fibroblasts, CSD-mediated activation in Jurkat T cells is not mediated through DNA binding but presumably through protein-protein interactions via the C terminus of the CSD protein with transcription factors such as RelA/NF-kappaB p65. We demonstrate that Jurkat T cells lack truncated CSD factor subtypes present in HEL fibroblasts, which raises the possibility that the cellular content of CSD proteins may determine their final role as activators or repressors of transcription.

Allele-dependent transcriptional regulation of the human integrin alpha2 gene

Genetically controlled variation in alpha2beta1 expression by human blood platelets was previously described. Sixty-two haplotype sequences corresponding to the proximal 5' regulatory region (-1096 to +1) of the alpha2 gene were compared, and a dimorphic sequence -52C>T was identified that is located precisely between 2 tandem Sp1/Sp3 binding elements previously shown to be absolutely required for transcriptional activity of this gene in epithelial cell lines and the erythroleukemic cell line K562. The gene frequency of -52T in a random Caucasian population is approximately 0.35, and the expression of -52T correlates directly with reduced densities of platelet alpha2beta1. In mobility shift analyses, the -52T substitution attenuates complex formation with both Sp1 and Sp3. When transfected into the erythroleukemia cell line Dami, promoter-luciferase constructs bearing the -52T sequence exhibit a 5-fold decrease in activity relative to the -52C construct. In transfected CHRF-288-11 megakaryocytic cells, the corresponding activity decreases by 10-fold. The -52T sequence appears to be in linkage disequilibrium with the previously defined allele A3 (807C; HPA-5b), known to be associated with diminished expression of platelet alpha2beta1. In summary, a natural dimorphism has been identified within the proximal 5' regulatory region of the human integrin alpha2 gene that is responsible for decreased expression levels of the integrin alpha2beta1 on blood platelets through a mechanism that is probably mediated by the nuclear regulatory proteins Sp1 and Sp3.

c-Jun and JunB antagonistically control cytokine-regulated mesenchymal-epidermal interaction in skin

Interactions between mesenchymal and epithelial cells are responsible for organogenesis and tissue homeostasis. This mutual cross-talk involves cell surface proteins and soluble factors, which are mostly the result of regulated transcription. To elucidate dimer-specific functions of the AP-1 family of transcription factors, we reconstituted skin by combining primary human keratinocytes and mouse wild-type, c-jun(-/-), and junB(-/-) fibroblasts. We have discovered an antagonistic function of these AP-1 subunits in the fibroblast-mediated paracrine control of keratinocyte proliferation and differentiation, and traced this effect to the IL-1-dependent regulation of KGF and GM-CSF. These data suggest that the relative activation state of these AP-1 subunits in a non-cell-autonomous, transregulatory fashion directs regeneration of the epidermis and maintenance of tissue homeostasis in skin.

Molecular regulation of granulocyte macrophage colony-stimulating factor in human lung epithelial cells by interleukin (IL)-1beta, IL-4, and IL-13 involves both transcriptional and post-transcriptional mechanisms

Interleukin (IL)-1beta stimulates the release of granulocyte macrophage colony-stimulating factor (GM-CSF) from lung epithelial cells. To investigate the molecular mechanisms underlying GM-CSF regulation, we studied GM-CSF production, messenger RNA (mRNA) expression levels, and GM-CSF promoter activity in A549 human alveolar carcinoma cells stimulated with IL-1beta. Coincubation with IL-4 or IL-13 dose-dependently inhibited IL-1beta-induced GM-CSF release. Time-course studies of intracellular and extracellular protein release and mRNA expression indicated tight coupling of protein and mRNA synthesis within 6 h after stimulation. IL-4 and IL-13 both inhibited expression of GM-CSF mRNA and protein by 2 h after stimulation. Stable transfection of A549 cells, with GM-CSF promoter/ enhancer constructs containing up to 3.3 kb upstream of the transcription start site, revealed maximal activation by IL-1beta and phorbol 12-myristate 13-acetate (PMA) with a reporter containing the proximal promoter (-627 to +35). This excludes sequences further upstream from a major regulatory role in GM-CSF promoter activation by IL-1beta or PMA in these cells. IL-4 and IL-13 downregulated promoter activation but had no effect on GM-CSF mRNA half-life. However, IL-1beta activation of all constructs was far less pronounced than in Jurkat T cells, suggesting a requirement for additional mechanisms, possibly post-transcriptional, to potentiate the observed transcriptional induction.

Cellular delivery of functional peptides to block cytokine gene expression

Advances in molecular and cellular biology have identified the cellular mediators that regulate many disease processes and have facilitated the development of new therapeutic agents that control these events. However, the size, complexity, and cellular inaccessibility of these therapeutic agents make their cellular delivery difficult. Here, we describe an efficient cellular delivery system that exploits the membrane-translocating ability of signal peptides to import functional peptides into cells. Molecular conjugates consisting of the signal import peptide (IP) and nuclear localization sequence (NLS) of the transcription factor NF-kappaB were synthesized. Electrophoretic mobility shift and enzyme-linked immunosorbent assays were used to assess the inhibitory effects of these synthetic peptides on agonist-induced NF-kappaB nuclear translocation and transcriptional activation. Our results indicated that the peptides were effective in inhibiting both the nuclear translocation and transcriptional activation of NF-kappaB. However, their effects required the presence of the IP moiety for efficient cellular entry of the NLS. Structural analysis of IP showed that the hydrophobic domain, and to a lesser extent the N-terminal domain, was responsible for the membrane translocating activity of IP.

Involvement of the Sp1 site in ras-mediated downregulation of the RECK metastasis suppressor gene

We have isolated and characterized the 5'-flanking region of the mouse RECK gene aiming to understand the mechanism of oncogene-mediated suppression of RECK gene expression. The upstream 52-base region was found to contain a promoter activity which is, to some extent, suppressed by the ras oncogene. This region contains two Sp1-binding motifs, one cEBPb-binding motif, and one CAAT box. Although both of the Sp1 sites were found to associate with Sp1 as well as Sp3 proteins, ras responsiveness seems to be mediated only by the downstream Sp1 site. Our data indicate that the Sp1 motif in certain contexts can serve as a negative target for the Ras signal.

Dependence of NF-kappaB activation and free radical generation on silica-induced TNF-alpha production in macrophages

Tumor necrosis factor alpha (TNFalpha) plays an important role in the pathogenesis of silicosis and other chronic inflammatory lung diseases. The present study investigates the role nuclear transcription factor kappaB (NF-kappaB) and oxygen free radicals in silica-induced TNFalpha production in primary alveolar macrophages and RAW 264.7 cells. Using electrophoretic mobility shift assay (EMSA) and enzyme-linked immunoadsorbent assay (ELISA), we have demonstrated that silica can induce NF-kappaB activation and TNFalpha expression in a dose-dependent manner. Transient transfection assays with a plasmid construct containing NF-kappaB binding sites linked to a reporter gene further show that silica is able to induce the transcriptional activation of NF-kappaB-dependent gene. Inhibition of NF-kappaB activation by SN50, a specific NF-kappaB blocker, abolishes silica-induced TNFalpha production. Pretreatment of the cells with catalase (H2O2 scavenger) or deferoxamine (*OH scavenger) effectively inhibits NF-kappaB and TNFalpha activation, whereas superoxide dismutase (O2 scavenger) has an opposite effect. These results indicate that silica-mediated free radical generation and NF-kappaB activation play important roles in silica-induced TNFalpha gene expression.

Regulation of a cell type-specific silencer in the human interleukin-3 gene promoter by the transcription factor YY1 and an AP2 sequence-recognizing factor

Negative regulation of cytokine gene transcription is an important mechanism in maintaining homeostasis of immune function. In this study, we characterized a silencer element in the human interleukin-3 gene promoter that is responsible for the cell-specific expression of interleukin-3. This silencer activity was proposed to be mediated by an unidentified nuclear inhibitory protein (NIP). In this study, we have identified two nuclear factors that are responsible for the silencer activity in T cells. The NIP element forms four specific DNA-protein complexes (designated as complexes A-D) with the Jurkat nuclear proteins. Complex A contains a nuclear protein that shares DNA-binding specificity with the transcription factor AP2 (designated as an AP2 sequence-recognizing factor (ASRF)). Formation of this ASRF complex is required for the NIP silencer function, as mutation of the ASRF-binding site abrogated the silencer activity. Complex B contains the nuclear factor YY1 (Yin-Yang 1), whose function is to down-regulate ASRF activity in the silencer. YY1 activity is supported by data from mutation and cotransfection analyses. Complexes C and D are formed by nonspecific binding proteins and do not express any regulatory activity in the NIP element. These data indicate that a cell type-specific silencer activity might be determined by a unique profile of ubiquitous transcription factors.

Role of transcription factor NF-kappaB in asbestos-induced TNFalpha response from macrophages

Asbestos exposure in humans is associated with inflammatory, fibrotic, and malignant diseases in the lung. Increasing evidence supports the hypothesis that the production of proinflammatory cytokines such as tumor necrosis factor-alpha (TNFalpha) is an important mediator of the pathologic responses of asbestosis. In this study, we examine the role of nuclear transcription factor-kappaB (NF-kappaB) and free oxygen radicals in asbestos-induced TNFalpha gene and protein expression in lung macrophages. Exposure of the cells to crocidolite asbestos caused a parallel increase in TNFalpha production and NF-kappaB activation, as analyzed by enzyme-linked immunosorbent assay and electrophoretic mobility shift assay. Inhibition of NF-kappaB by SN50, an inhibitor of NF-kappaB nuclear translocation, or by sequence-specific oligonucleotides directed against the NF-kappaB binding site of TNFalpha promoter attenuated the asbestos effect on TNFalpha production. Gene transfection assays using an expression plasmid containing a luciferase reporter gene and a TNFalpha-derived NF-kappaB gene promoter further indicated the dependence of NF-kappaB activation on asbestos-induced gene expression. The effects of asbestos on NF-kappaB and TNFalpha activation were inhibited by oxygen radical scavengers and were enhanced by antioxidant enzyme inhibitors. These results indicate that asbestos-induced TNFalpha gene expression is mediated through a process that involves NF-kappaB activation and free radical reactions.

Induction of TNFalpha in macrophages by vanadate is dependent on activation of transcription factor NF-kappaB and free radical reactions

Vanadium-induced TNFalpha production is believed to play an important role in respiratory disease associated with air pollution and occupational exposure. While vanadium is able to induce TNFalpha in macrophages or airway epithelial cells, the underlying mechanism is not well defined. In the present study, mechanisms of vanadate-induced TNFalpha production were analyzed in the murine Raw264.7 cells. Vanadate induces a significant amount of TNFalpha at both the protein and mRNA levels, and the induction is vanadate dose-dependent. The mechanism analysis was focused on transcriptional regulation of TNFalpha gene by vanadate. Transient transfection studies show that the TNFalpha gene promoter was activated by vanadate and this activation was associated with an increase in DNA binding activity of the nuclear factor-kappaB (NF-kappaB). Mutation of the NF-kappaB binding site in the gene promoter led to a loss of the promoter responsiveness to vanadate, indicating requirement of NF-kappaB. This is supported by evidence that inhibition of NF-kappaB activation by SN50, a specific NF-kappaB inhibitor, resulted in a decrease in the TNFalpha production. A role of reactive oxygen species (ROS) was explored in vanadate activity. The result shows that vanadate-induced TNFalpha production is elevated by NADPH, which enhances vanadate-mediated generation of ROS, but is inhibited by an antioxidant, N-acetyl-L-cysteine (NAC). Modification of TNFalpha production is associated with an enhancement or a repression of NF-kappaB activity by NADPH or NAC, respectively. Taken together, these results indicate that: (a) activation of the TNFalpha gene promoter contributes to the vanadate-induced TNFalpha production; (b) NF-kappaB is required for the vanadate-induced promoter activity of TNFalpha gene; (c) free radical reactions are involved in the vanadate-induced TNFalpha production and NF-kappaB activation.

Binding of YY1 and Oct1 to a novel element that downregulates expression of IL-5 in human T cells

BACKGROUND

IL-5 controls development of eosinophilia and has been shown to be involved in the pathogenesis of allergic diseases. In both atopic and nonatopic asthma, elevated IL-5 has been detected in peripheral blood and the airways. IL-5 is produced mainly by activated T cells, and its expression is regulated at the transcriptional level.

OBJECTIVE

This study focuses on the functional analysis of the human IL-5 (hIL-5) promoter and characterization of cis -regulatory elements and transcription factors involved in the suppression of IL-5 transcription in T cells.

METHODS

Methods used in this study include DNase I footprint assays, electrophoretic mobility shift assays, and functional analysis by mammalian cell transfection involving deletion analysis and site-directed mutagenesis.

RESULTS

We identified 5 protein binding regions (BRs) located within the proximal hIL-5 promoter. Functional analysis indicates that the BRs are involved in control of hIL-5 promoter activity. Two of these regions, BR3 and BR4 located at positions -102 to -73, have not previously been described as regulators of IL-5 expression in T cells. We show that the BR3 sequence contains a novel negative regulatory element located at positions -90 to -79 of the hIL-5 promoter, which binds Oct1, octamer-like, and YY1 nuclear factors. Substitution mutations, which abolished binding of these proteins to the BR3 sequence, significantly increased hIL-5 promoter activity in activated T cells.

CONCLUSION

We suggest that Oct1, YY1, and octamer-like factors binding to the -90/-79 sequence within the proximal IL-5 promoter are involved in suppression of IL-5 transcription in T cells.

YY1 is a negative regulator of transcription of three sterol regulatory element-binding protein-responsive genes

Ying Yang 1 (YY1) is shown to bind to the proximal promoters of the genes encoding 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) synthase, farnesyl diphosphate (FPP) synthase, and the low density lipoprotein (LDL) receptor. To investigate the potential effect of YY1 on the expression of SREBP-responsive genes, HepG2 cells were transiently transfected with luciferase reporter constructs under the control of promoters derived from either HMG-CoA synthase, FPP synthase, or the LDL receptor genes. The luciferase activity of each construct increased when HepG2 cells were incubated in lipid-depleted media or when the cells were cotransfected with a plasmid encoding mature sterol regulatory element-binding protein (SREBP)-1a. In each case, the increase in luciferase activity was attenuated by coexpression of wild-type YY1 but not by coexpression of mutant YY1 proteins that are known to be defective in either DNA binding or in modulating transcription of other known YY1-responsive genes. In contrast, incubation of cells in lipid-depleted media resulted in induction of an HMG-CoA reductase promoter-luciferase construct by a process that was unaffected by coexpression of wild-type YY1. Electromobility shift assays were used to demonstrate that the proximal promoters of the HMG-CoA synthase, FPP synthase, and the LDL receptor contain YY1 binding sites and that YY1 displaced nuclear factor Y from the promoter of the HMG-CoA synthase gene. We conclude that YY1 inhibits the transcription of specific SREBP-dependent genes and that, in the case of the HMG-CoA synthase gene, this involves displacement of nuclear factor Y from the promoter. We hypothesize that YY1 plays a regulatory role in the transcriptional regulation of specific SREBP-responsive genes.

Critical role of glass fiber length in TNF-alpha production and transcription factor activation in macrophages

Recent studies have demonstrated that dielectrophoresis is an efficient method for the separation of fibers according to fiber length. This method allows the investigation of fiber-cell interactions with fiber samples of the same composition but of different lengths. In the present study, we analyzed the effects of length on the interaction between glass fibers and macrophages by focusing on production of the inflammatory cytokine tumor necrosis factor (TNF)-alpha in a mouse macrophage cell line (RAW 264.7). The underlying molecular mechanisms controlling TNF-alpha production were investigated at the gene transcription level. The results show that glass fibers induced TNF-alpha production in macrophages and that this induction was associated with activation of the gene promoter. Activation of the transcription factor nuclear factor (NF)-kappaB was responsible for this induced promoter activity. The inhibition of both TNF-alpha production and NF-kappaB activation by N-acetyl-L-cysteine, an antioxidant, indicates that generation of oxidants may contribute to the induction of this cytokine and activation of this transcription factor by glass fibers. Long fibers (17 micrometer) were significantly more potent than short fibers (7 micrometer) in inducing NF-kappaB activation, the gene promoter activity, and the production of TNF-alpha. This fiber length-dependent difference in the stimulatory potency correlated with the fact that macrophages were able to completely engulf short glass fibers, whereas phagocytosis of long glass fibers was incomplete. These results suggest that fiber length plays a critical role in the potential pathogenicity of glass fibers.

Identification of two repressor elements in the mouse alpha 2(I) collagen promoter

We recently identified three areas of Sp1 binding located between -568 and -453 of the 5' flanking region of the murine alpha2(I) collagen promoter which are necessary for optimal activity. We now identify two additional regions of Sp1 binding located at -371 to -351 (region 4) and at -690 to -613 (region 5), which when mutated increased promoter activity in transfected rat hepatic stellate cells indicating they contain negative regulatory elements. AP-2 bound to region 4 while YY1 bound most strongly to region 5. AP-2 decreased Sp1 binding to region 4 and had a dual effect on Sp1 binding to region 5 decreasing and increasing Sp1 binding at low and high concentrations of AP-2, respectively. YY1 enhanced Sp1 binding to both regions. AP-2 inhibited or enhanced the stimulatory effect of a transfected Sp1 expression vector on the alpha2(I) collagen promoter in Drosophila cells at low or high AP-2 expression, respectively. YY1 enhanced or inhibited the activation of the promoter by low or high Sp1 expression, respectively. This study identifies two negative regulatory elements in the murine alpha2(I) collagen promoter and shows that AP-2 and YY1 interact with Sp1 at these sites and can inhibit the activating action of Sp1.

An upstream negative regulatory element in human granulocyte-macrophage colony-stimulating factor promoter is recognised by AP1 family members

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a cytokine involved in haematopoiesis and host defence. Production of GM-CSF has been detected in tumour cells including the U87MG astrocytoma cell line. Previous studies have been focused on the regulatory role of the proximal region of the GM-CSF promoter. Our studies on the distal region of the promoter in U87MG cells identify a negative cis element (-1377/-1298) which contains a AP1-like site able to bind c-jun and c-fos transcription factors, according to the results of DNA/protein binding assays. Mutagenesis of the AP1-like site eliminates AP1 binding and the negative effect on promoter activity.

The transcription factor Sp1 regulates the myeloid-specific expression of the human hematopoietic cell kinase (HCK) gene through binding to two adjacent GC boxes within the HCK promoter-proximal region

The human hemopoietic cell kinase (HCK) is a member of the src family of protein tyrosine kinases specifically expressed in myeloid cells and to a minor extent in B-lymphoid cells. HCK expression is up-regulated at the transcriptional level during myeloid differentiation of hematopoietic cells. To elucidate the molecular basis of the differential HCK gene expression, the genomic region containing the HCK promoter was isolated and functionally characterized. A DNA fragment containing 101 base pairs of the 5'-flanking sequence showed strong promoter activity in the macrophage cell line RAW264 but was inactive in the non-monocytic cell lines HUT-78 and NIH-3T3. Site-directed mutagenesis of the proximal promoter region showed that two GC-rich sequence elements are essential for transcriptional activity in myeloid cells. Electrophoretic mobility shift analysis using nuclear extracts obtained from RAW264 cells and from the promonocytic cell line U-937 revealed the formation of at least three distinct protein-DNA complexes at each of these sites, one of which was found to contain the transcription factor Sp1. Expression of a reporter gene linked to the -101 HCK promoter region was up-regulated by Sp1, but not by other members of the Sp1 family of transcription factors, in Drosophila Schneider cells. A synergistic effect on HCK promoter activity was observed at high concentrations of Sp1. Our results show that Sp1 plays an essential role in the regulation of the differential gene expression of the HCK gene.