A GT-rich sequence binding the transcription factor Sp1 is crucial for high expression of the human type VII collagen gene (COL7A1) in fibroblasts and keratinocytes

Association of Single Nucleotide Polymorphisms in the ST3GAL4 Gene with VWF Antigen and Factor VIII Activity

VWF is extensively glycosylated with biantennary core fucosylated glycans. Most N-linked and O-linked glycans on VWF are sialylated. FVIII is also glycosylated, with a glycan structure similar to that of VWF. ST3GAL sialyltransferases catalyze the transfer of sialic acids in the α2,3 linkage to termini of N- and O-glycans. This sialic acid modification is critical for VWF synthesis and activity. We analyzed genetic and phenotypic data from the Atherosclerosis Risk in Communities (ARIC) study for the association of single nucleotide polymorphisms (SNPs) in the ST3GAL4 gene with plasma VWF levels and FVIII activity in 12,117 subjects. We also analyzed ST3GAL4 SNPs found in 2,535 subjects of 26 ethnicities from the 1000 Genomes (1000G) project for ethnic diversity, SNP imputation, and ST3GAL4 haplotypes. We identified 14 and 1,714 ST3GAL4 variants in the ARIC GWAS and 1000G databases respectively, with 46% being ethnically diverse in their allele frequencies. Among the 14 ST3GAL4 SNPs found in ARIC GWAS, the intronic rs2186717, rs7928391, and rs11220465 were associated with VWF levels and with FVIII activity after adjustment for age, BMI, hypertension, diabetes, ever-smoking status, and ABO. This study illustrates the power of next-generation sequencing in the discovery of new genetic variants and a significant ethnic diversity in the ST3GAL4 gene. We discuss potential mechanisms through which these intronic SNPs regulate ST3GAL4 biosynthesis and the activity that affects VWF and FVIII.

miR-29 Regulates Type VII Collagen in Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is a complex inherited skin disorder caused by loss-of-function mutations in the COL7A1 gene. For an effective treatment of this disorder to be realized, both a thorough understanding of the regulation of COL7A1 and an understanding of the underlying nature of the complications of RDEB are needed. Currently, both posttranscriptional regulation of COL7A1 and the underlying causes of fibrosis in RDEB patients are poorly understood. Here, we describe a mechanism of regulation, to our knowledge previously unknown, by which micro RNA-29 (miR-29) regulates COL7A1 in a complex network: both directly through targeting its 3' untranslated region at two distinct seed regions and indirectly through targeting an essential transcription factor required for basal COL7A1 expression, SP1. In turn, miR-29 itself is regulated by SP1 activity and transforming growth factor-β signaling. RDEB mice express high levels of transforming growth factor-β and significantly lower miR-29 compared with wild-type cohorts. The sustained decrease in miR-29 in RDEB skin leads to an increase of miR-29 target genes expressed in the skin, including profibrotic extracellular matrix collagens. Collectively, we identify miR-29 as an important factor in both regulating COL7A1 and inhibiting transforming growth factor-β-mediated fibrosis.

Identification of Critical Elements for Regulation of Inorganic Pyrophosphatase (PPA1) in MCF7 Breast Cancer Cells

Cytosolic inorganic pyrophosphatase plays an important role in the cellular metabolism by hydrolyzing inorganic pyrophosphate (PPi) formed as a by-product of various metabolic reactions. Inorganic pyrophosphatases are known to be associated with important functions related to the growth and development of various organisms. In humans, the expression of inorganic pyrophosphatase (PPA1) is deregulated in different types of cancer and is involved in the migration and invasion of gastric cancer cells and proliferation of ovarian cancer cells. However, the transcriptional regulation of the gene encoding PPA1 is poorly understood. To gain insights into PPA1 gene regulation, a 1217 bp of its 5'-flanking region was cloned and analyzed. The 5'-deletion analysis of the promoter revealed a 266 bp proximal promoter region exhibit most of the transcriptional activity and upon sequence analysis, three putative Sp1 binding sites were found to be present in this region. Binding of Sp1 to the PPA1 promoter was confirmed by Electrophoretic mobility shift assay (EMSA) and Chromatin immunoprecipitation (ChIP) assay. Importance of these binding sites was verified by site-directed mutagenesis and overexpression of Sp1 transactivates PPA1 promoter activity, upregulates protein expression and increases chromatin accessibility. p300 binds to the PPA1 promoter and stimulates Sp1 induced promoter activity. Trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor induces PPA1 promoter activity and protein expression and HAT activity of p300 was important in regulation of PPA1 expression. These results demonstrated that PPA1 is positively regulated by Sp1 and p300 coactivates Sp1 induced PPA1 promoter activity and histone acetylation/deacetylation may contribute to a local chromatin remodeling across the PPA1 promoter. Further, knockdown of PPA1 decreased colony formation and viability of MCF7 cells.

Mesenchymal condensation-dependent accumulation of collagen VI stabilizes organ-specific cell fates during embryonic tooth formation

BACKGROUND

Mechanical compression of cells during mesenchymal condensation triggers cells to undergo odontogenic differentiation during tooth organ formation in the embryo. However, the mechanism by which cell compaction is stabilized over time to ensure correct organ-specific cell fate switching remains unknown.

RESULTS

Here, we show that mesenchymal cell compaction induces accumulation of collagen VI in the extracellular matrix (ECM), which physically stabilizes compressed mesenchymal cell shapes and ensures efficient organ-specific cell fate switching during tooth organ development. Mechanical induction of collagen VI deposition is mediated by signaling through the actin-p38MAPK-SP1 pathway, and the ECM scaffold is stabilized by lysyl oxidase in the condensing mesenchyme. Moreover, perturbation of synthesis or cross-linking of collagen VI alters the size of the condensation in vivo.

CONCLUSIONS

These findings suggest that the odontogenic differentiation process that is induced by cell compaction during mesenchymal condensation is stabilized and sustained through mechanically regulated production of collagen VI within the mesenchymal ECM.

Sp1king out cancer (....and fibrosis?)

It is becoming increasingly apparent that many of the basic mechanisms underlying cancers also underlie fibrotic diseases. For example, the Sp1 family of transcription factors plays an essential role in controlling the gene expression of proteins that promote both oncogenesis and fibrogenesis. The drug mithramycin, which prevents Sp1 binding to DNA, has been in use clinically for some cancers, but has side-effects. However, other drugs exist that affect Sp1 activity through promoting Sp1 protein degradation. Evidence has emerged that low levels of mithramycin can be combined with these drugs to result in potent antitumorigenic effects without resulting in obvious toxicity (Gao et al. Cancer Res 2011 Jun 20; Jia et al. Cancer Res 70:1111-1119, 2010). Given that Sp1 proteins also promote expression of profibrotic genes such as collagen type I and CCN2, it is possible that this combinatorial approach may be taken in the future to block not only cancer but also fibrosis.

Dominant-negative effects of COL7A1 mutations can be rescued by controlled overexpression of normal collagen VII

Dominant-negative interference by glycine substitution mutations in the COL7A1 gene causes dominant dystrophic epidermolysis bullosa (DDEB), a skin fragility disorder with mechanically induced blistering. Although qualitative and quantitative alterations of the COL7A1 gene product, collagen VII, underlie DDEB, the lack of direct correlation between mutations and the clinical phenotype has rendered DDEB less amenable to therapeutic targeting. To delineate the molecular mechanisms of DDEB, we used recombinant expression of wild-type (WT) and mutant collagen VII, which contained a naturally occurring COL7A1 mutation, G1776R, G2006D, or G2015E, for characterization of the triple helical molecules. The mutants were co-expressed with WT in equal amounts and could form heterotrimeric hybrid triple helices, as demonstrated by affinity purification and mass spectrometry. The thermal stability of the mutant molecules was strongly decreased, as evident in their sensitivity to trypsin digestion. The helix-to-coil transition, T(m), of the mutant molecules was 31-34 degrees C, and of WT collagen VII 41 degrees C. Co-expression of WT with G1776R- or G2006D-collagen VII resulted in partial intracellular retention of the collagen, and mutant collagen VII had reduced ability to support cell adhesion. Intriguingly, controlled overexpression of WT collagen VII gradually improved the thermal stability of the collective of collagen VII molecules. Co-expression in a ratio of 90% WT:10% mutant increased the T(m) to 41 degrees C for G1776R-collagen VII and to 39 degrees C for G2006D- and G2015E-collagen VII. Therefore, increasing the expression of WT collagen VII in the skin of patients with DDEB can be considered a valid therapeutic approach.

Calcineurin/NFAT-dependent regulation of 230-kDa bullous pemphigoid antigen (BPAG1) gene expression in normal human epidermal keratinocytes

BACKGROUND AND OBJECTIVE

Cyclosporin A (CsA) is utilized widely for treatment of inflammatory skin diseases, such as psoriasis vulgaris. The therapeutic effects of CsA are thought to be mediated by its immunosuppressive action on infiltrating lymphocytes in the lesional skin. CsA also inhibits epidermal keratinocyte proliferation, suggesting a direct biological action on keratinocytes. Here we tested the hypothesis that CsA can modulate the expression of the nuclear factor of activated T-cell (NFAT) in epidermal keratinocytes. We also investigated whether the keratinocyte-specific gene expression is modified by CsA through NFAT activity in association with differentiation induction.

METHODS

RT-PCR was performed using total RNAs extracted from cultured normal human epidermal keratinocytes (NHEK), normal human dermal fibroblasts (NHDF), and normal human epidermal melanocytes (NHEM) for detecting NFAT isomolecules. Transient transfections of NHEK with a 230-kDa bullous pemphigoid antigen (BPAG1) promoter/luciferase reporter gene and the luciferase assay were conducted for examining the effect of CsA on the promoter activity of the BPAG1 gene. Electrophoretic gel mobility shift assays (EMSA) with probes containing NFAT consensus sequences for analyzing the binding activities of the nuclear proteins extracted from NHEK.

RESULTS

RT-PCR revealed expression of all of the five isoforms of NFAT in the cell lines examined. The mRNA expression levels of NFAT1, NFAT2, BPAG1, and involucrin were downregulated by CsA treatment in NHEK. The luciferase assay indicated suppression of the promoter activity by CsA. EMSA with NFAT consensus probes identified in the BPAG1 promoter region demonstrated specific binding activity in the nuclear proteins of epidermal keratinocytes.

CONCLUSION

As reported previously, our results indicate that epidermal keratinocytes possess calcineurin/NFAT system, which is suppressed by CsA. In addition, the data suggest that CsA can downregulate the BPAG1 gene expression perhaps via the NFAT consensus cis-elements in the BPAG1 promoter region. Such transcriptional regulatory system might be involved in the regulation of keratinocyte differentiation and proliferation.

Nuclear receptor interaction protein, a coactivator of androgen receptors (AR), is regulated by AR and Sp1 to feed forward and activate its own gene expression through AR protein stability

Previously, we found a novel gene, nuclear receptor interaction protein (NRIP), a transcription cofactor that can enhance an AR-driven PSA promoter activity in a ligand-dependent manner in prostate cancer cells. Here, we investigated NRIP regulation. We cloned a 413-bp fragment from the transcription initiation site of the NRIP gene that had strong promoter activity, was TATA-less and GC-rich, and, based on DNA sequences, contained one androgen response element (ARE) and three Sp1-binding sites (Sp1-1, Sp1-2, Sp1-3). Transient promoter luciferase assays, chromatin immunoprecipitation and small RNA interference analyses mapped ARE and Sp1-2-binding sites involved in NRIP promoter activation, implying that NRIP is a target gene for AR or Sp1. AR associates with the NRIP promoter through ARE and indirectly through Sp1-binding site via AR–Sp1 complex formation. Thus both ARE and Sp1-binding site within the NRIP promoter can respond to androgen induction. More intriguingly, NRIP plays a feed-forward role enhancing AR-driven NRIP promoter activity via NRIP forming a complex with AR to protect AR protein from proteasome degradation. This is the first demonstration that NRIP is a novel AR-target gene and that NRIP expression feeds forward and activates its own expression through AR protein stability.

Quantitative analysis of the synthesis and secretion of type VII collagen in cultured human dermal fibroblasts with a sensitive sandwich enzyme-linked immunoassay

Type VII collagen is the major component of anchoring fibrils in the epidermal basement membrane. Its expression has been analyzed by immunostaining or Northern blotting, but rarely at the protein level. In this study, we have quantitatively examined the effects of ascorbic acid and various cytokines/growth factors on the protein synthesis and secretion of type VII collagen by human dermal fibroblasts in culture, using a developed, highly sensitive sandwich enzyme-linked immunoassay with two kinds of specific monoclonal antibodies against the non-collagenous domain-1. Ascorbic acid and its derivative induced a twofold increase in type VII collagen synthesis, and markedly increased the secretion of type VII collagen into the medium when compared with the control culture. This effect was not influenced by the presence of transforming growth factor-beta1 (TGF-beta1). The synthesis of type VII collagen was elevated by TGF-beta1, platelet-derived growth factor, tumor necrosis factor-alpha, and interleukin-1beta, but not by TGF-alpha. Thus, our data indicate that the synthesis and secretion of type VII collagen in human dermal fibroblasts are regulated by ascorbate and the enhancement of type VII collagen gene expression by cytokines/growth factors is accompanied with elevated production of type VII collagen at the protein level.

Human metallothionein gene expression is upregulated by beta-thujaplicin: possible involvement of protein kinase C and reactive oxygen species

Recently, we discovered that beta-thujaplicin (BT) induces metallothionein (MT) expression in mouse keratinocytes, both in vivo and in vitro. However, the molecular mechanisms by which BT exerts its biological effects have not been elucidated. The purpose of this study is to explore the signal transduction pathway involved in the MT mRNA induction by BT. Using a HaCaT keratinocyte cell line, Northern blotting was performed for analyzing the human MT-IIA mRNA expression levels in combination with BT and a number of protein kinase (PK) inhibitors including H7, HA1004 and a PKC-specific inhibitor chelerythrin. CAT assays with the MT-IIA gene promorter-CAT construct were conducted for examining the transcriptional regulation by BT of MT. A free radical scavenger N-acetylcysteine (NAC) was used for analyzing a role of oxidative stress for the MT gene induction by BT. BT increased MT-IIA gene transcript levels and CAT activity in a dose-dependent fashion in HaCaT cells. The increase in MT-IIA mRNA levels and CAT activity were completely suppressed by H7 but not by HA1004. In addition, chelerythrin prevented BT-inducible MT-IIA promoter activation. Furthermore, NAC suppressed BT-inducible MT-IIA promoter activation. These results demonstrate that BT is a potent activator of the MT-IIA gene promoter and that PKC activation and reactive oxygen species are implicated in BT-inducible MT-IIA gene expression. BT may be a useful tool for dissecting the signal transduction pathway mediating MT-IIA promoter activation.

Lung Krüppel-like factor (LKLF) is a transcriptional activator of the cytosolic phospholipase A2 alpha promoter

Increased expression of cPLA2 (cytosolic phospholipase A2) has been shown to be the cause of tumorigenesis of NSCLC (non-small-cell lung cancer). Our laboratory has previously demonstrated that oncogenic forms of Ras increase transcription of cPLA2 in normal lung epithelial cells and NSCLC lines through activation of the ERK (extracellular-signal-regulated kinase) and JNK (c-Jun N-terminal kinase) MAPK (mitogen-activated protein kinase) family. We have also defined a minimal region of the cPLA2 promoter that is critical for this induction. To identify potential transcription factors that bind to this region and regulate expression, a yeast one-hybrid screen was performed with a rat lung cDNA library. Multiple members of the Krüppel family were identified, with LKLF (lung Krüppel-like factor) being isolated a number of times. Overexpression of LKLF in lung epithelial cells or Drosophila SL-2 cells increased cPLA2 promoter activity. Conversely, expression of a dominant negative form of LKLF inhibited induction of cPLA2 promoter activity by oncogenic Ras in normal lung epithelial cells and NSCLC. By electrophoretic mobility-shift assay analysis, it was found that LKLF bound to a GC-rich region of the cPLA2 promoter located between -37 and -30 upstream from the transcription start site. Expression of siRNA (small interfering RNA) directed against LKLF inhibited basal expression of cPLA2 in lung epithelial cells and blocked induction by H-Ras. In NSCLC, siRNA against LKLF co-operated with siRNA against Sp1 (stimulatory protein 1) to inhibit cPLA2 promoter activity. Finally, recombinant LKLF was a substrate for ERKs. These results indicate that LKLF is an important regulator of cPLA2 expression and participates in the induction of this protein, which is critical for increased eicosanoid production associated with lung tumorigenesis.

Transcriptional Control of the Mouse Col7a1 Gene in Keratinocytes: Basal and Transforming Growth Factor-β Regulated Expression

Anchoring fibrils at the cutaneous basement membrane zone of the stratified squamous epithelia are essential to maintaining skin integrity, as absence of these structures leads to the chronic blistering disease, dystrophic epidermolysis bullosa. Type VII collagen, the major component of anchoring fibrils, is synthesized primarily by basal keratinocytes and to a lesser degree by dermal fibroblasts. To elucidate the transcriptional control elements of the type VII collagen gene (Col7a1), 3 kb of 5' flanking sequence of the mouse gene was cloned, sequenced, and fused to the chloramphenicol acetyltransferase reporter gene. Promoter deletion analyses revealed that 560 bp of Col7a1 5' flanking sequence was sufficient and necessary for basal level of transcription in cultured murine keratinocytes. Mutagenesis of DNA sequences with similarity to consensus binding sites for transcription factors, including Sp1/Sp3, AP2, AP1, and Smads, within the p-560Col7a1 promoter/chloramphenicol acetyltransferase construct, coupled with DNA binding assays, revealed the importance of these sites for basal Col7a1 expression. The effect of transforming growth factor beta, an activator of Col7a1 expression in keratinocytes and dermal fibroblasts, was examined using the same Col7a1 promoter/chloramphenicol acetyltransferase constructs. These analyses demonstrated that transforming growth factor beta1 stimulation of Col7a1 transcription is dependent on a putative interaction between Smads and AP1. Interestingly, the Smad-like binding site was essential for both basal and transforming growth factor beta1 stimulated Col7a1 transcription. Collectively, these findings attest to the complex regulation of Col7a1 transcription in epidermal keratinocytes.

Sp1 is essential for estrogen receptor alpha gene transcription

The exact molecular mechanisms regulating estrogen receptor (ER)alpha expression in breast tumors are unclear, but studies suggest that the regulation is at least partly transcriptional. We therefore undertook a detailed analysis of ERalpha promoter activity in a number of breast cancer cell lines. We find that the majority of ERalpha promoter activity lies within the first 245bp of the 5'-flanking region of the gene. Three elements essential for full ERalpha promoter transcriptional activity were identified within the -245 to -192bp region in transient transactivation assays using linker-scanner mutation analysis. These three elements include two binding sites for the Sp1 family of transcription factors as well as a non-consensus E box. We show that both Sp1 and Sp3 bind to this region using electrophoretic mobility shift assays. Exogenous expression of Sp1 or Sp3 in Sp1/3-negative Drosophila Schneider SL2 cells results in transactivation of the -245 to +212bp fragment of the ERalpha promoter. These data demonstrate that transcription of ERalpha is dependent upon the expression of members of the Sp1 family.

Cyclin A-CDK phosphorylates Sp1 and enhances Sp1-mediated transcription

Cyclin A-mediated activation of cyclin-dependent kinases (CDKs) is essential for cell cycle transversal. Cyclin A activity is regulated on several levels and cyclin A elevation in a number of cancers suggests a role in tumorigenesis. In the present study, we used a modified DNA binding site selection and PCR amplification procedure to identify DNA binding proteins that are potential substrates of cyclin A-CDK. One of the sequences identified is the Sp1 transcription factor binding site. Co-immunoprecipitation experiments show that cyclin A and Sp1 can interact physically. In vitro and in vivo phosphorylation studies indicate that cyclin A-CDK complexes can phosphorylate Sp1. The phosphorylation site is located in the N-terminal region of the protein. Cells overexpressing cyclin A have elevated levels of Sp1 DNA binding activity, suggesting that cyclin A-CDK-mediated phosphorylation augments Sp1 DNA binding properties. In co-transfection studies, cyclin A expression stimulated transcription from an Sp1-regulated promoter. Mutation of the phosphorylation site abrogated cyclin A-CDK-dependent phosphorylation, augmentation of Sp1 transactivation function and DNA binding activity.

Promoter characterization of the human and mouse epilysin (MMP-28) genes

Epilysin (MMP-28) is a recently cloned member of the matrix metalloproteinase family (Lohi et al., J. Biol. Chem. 276 (2001) 10134). It is expressed at highest levels in the skin by basal and suprabasal keratinocytes, and in testis by developing germ cells. To characterize the epilysin promoter, we isolated a 3.0 kb fragment of human genomic DNA containing 5'-flanking sequence of the epilysin gene, and a corresponding 660 bp fragment from the mouse. The 5'-flanking sequences contain no typical TATA-boxes or CCAAT sequences close to the translation initiation sites. RNase protection assay revealed that two transcription start sites are utilized in the human epilysin gene, situated 210 and 230 bp upstream from the translation start site. The promoter contains a GT-box, situated 300 bp upstream from the translation start site, with homology to the consensus binding site for transcription factors of the Sp family. This site is perfectly conserved between the human and mouse promoters. For reporter gene assays a series of constructs with fragments of increasing length of the epilysin promoter were coupled to the firefly luciferase gene. Reporter gene assays indicated that deletion or mutation of the GT-box dramatically reduces the transcriptional activity both in keratinocytes and in spermatogonia. Gel mobility shift assays showed that several nuclear proteins bind specifically to this sequence. Supershift assays with antibodies specific for members of the Sp family identified Sp1 and Sp3 as components of these protein/DNA complexes and hence as possible regulators of the epilysin gene. Our results indicate that the epilysin promoter has distinctive structural and functional features, which may control the unique expression and regulation patterns of the epilysin gene.

UVA-340 as energy source, mimicking natural sunlight, activates the transcription factor AP-1 in cultured fibroblasts: evidence for involvement of protein kinase-C

Ultraviolet radiation (UVR) is known to affect a variety of cellular functions, including gene expression. A number of signaling pathways have been suggested to mediate these effects, including the participation of activator protein-1 (AP-1), activator protein-2 (AP-2) and nuclear factor-kappa B (NF-kappa B). The divergent results from previous studies could be explained, at least in part, by the source of UVR with different spectral characteristics as well as the type of cells employed as targets. In this study we have utilized UVA-340 as an energy source with output which closely matches the spectrum of natural sunlight over the range of 295-350 nm for irradiation of cultured fibroblasts. Combination of electrophoretic mobility shift assays and Northern analyses revealed activation of AP-1 but not NF-kappa B or AP-2. Inhibition studies further suggested the participation of protein kinase-C, but not protein kinase-A, and that an inhibitor of mitogen-activated protein kinase (MEK-1/2) did not alter the AP-1 activation. Free radical quenchers, sodium azide and N-acetylcysteine, did not affect the AP-1 binding activity. Finally, UVA-340 was shown to enhance transcriptional expression of the type-VII collagen gene (COL7A1), which is endogenously expressed in dermal fibroblast in an AP-1 dependent manner. Introduction of a mutation into the AP-1 site of the COL7A1 promoter abolished this activation. Thus, our results obtained by utilizing a novel energy source, UVA-340, mimicking natural sunlight at UVB and lower UVA range indicate a role for AP-1 in mediating the enhanced gene expression by UVR. Collectively, these results suggest that AP-1 is an important mediator of UVR action in fibroblasts.

Blocking sp1 transcription factor broadly inhibits extracellular matrix gene expression in vitro and in vivo: implications for the treatment of tissue fibrosis

Fibrosis is a consequence of injury characterized by accumulation of excess collagen and other extracellular matrix components, resulting in the destruction of normal tissue architecture and loss of function. Sp1 was originally described as a ubiquitous transcription factor. It is involved in the basal expression of extracellular matrix genes and may, therefore, be important in fibrotic processes. To evaluate the effect of Sp1 blockade on the expression of extracellular matrix genes, clones of NIH 3T3 fibroblasts stably transfected with an anti-sense Sp1 expression vector. Simultaneously reduced expression of several extracellular matrix genes as compared with mock-transfected clones was noted using differential hybridization of cDNA microarrays, without significant alteration in cell growth. Transfection of human dermal fibroblasts with several extracellular matrix gene (COL1A1, COL1A2, COL3A1, COL5A2, COL7A1, TIMP-1, and decorin) promoter/reporter constructs demonstrated that anti-sense Sp1-induced reduction of extracellular matrix gene mRNA steady-state levels results from transcriptional repression, consistent with the role of Sp1 as a transcription factor. Decoy Sp1 binding oligonucleotides inhibited COL1A2 promoter activity both in cultured fibroblasts and in vivo, in the skin of transgenic mice, which have integrated a mouse COL1A2 promoter/luciferase reporter gene construct. These results indicate that targeting Sp1 efficiently blocks extracellular matrix gene expression, and suggest that such an approach may represent an interesting therapeutic alternative toward the treatment of fibrotic disorders.

Smad3/AP-1 interactions control transcriptional responses to TGF-beta in a promoter-specific manner

Smad proteins transduce signals from TGF-beta receptors and regulate transcription of target genes either directly or in combination with other sequence-specific transcription factors. AP-1 sites and their cognate transcription factors also play important roles in the gene regulatory activities of TGF-beta. In this report, we have investigated the functional interactions of the Smad and AP-1 transcription factors. We demonstrate that Smad and AP-1 complexes specifically bind to their cognate cis-elements and do not interact with each other on-DNA, whereas off-DNA interactions occur between Smad3 and both c-Jun and JunB. Using both artificial constructs specific for either the Smad or AP-1 signaling pathways or natural promoters known to be TGF-beta-responsive, we have determined that Jun family members downregulate Smad3-mediated gene transactivation whereas AP-1-dependent promoters are synergistically activated by Smad3 and Jun proteins. We propose a model where the presence of Smad- and/or AP-1-specific cis-elements within TGF-beta-responsive genes allows dynamic modulation of gene expression, in contrast to the existing model where interactions between Smad and AP-1 proteins are merely an on/off mechanism to regulate TGF-beta/Smad targets.

Identification of novel TGF-beta /Smad gene targets in dermal fibroblasts using a combined cDNA microarray/promoter transactivation approach

Despite major advances in the understanding of the intimate mechanisms of transforming growth factor-beta (TGF-beta) signaling through the Smad pathway, little progress has been made in the identification of direct target genes. In this report, using cDNA microarrays, we have focussed our attention on the characterization of extracellular matrix-related genes rapidly induced by TGF-beta in human dermal fibroblasts and attempted to identify the ones whose up-regulation by TGF-beta is Smad-mediated. For a gene to qualify as a direct Smad target, we postulated that it had to meet the following criteria: (1) rapid (30 min) and significant (at least 2-fold) elevation of steady-state mRNA levels upon TGF-beta stimulation, (2) activation of the promoter by both exogenous TGF-beta and co-transfected Smad3 expression vector, (3) up-regulation of promoter activity by TGF-beta blocked by both dominant-negative Smad3 and inhibitory Smad7 expression vectors, and (4) promoter transactivation by TGF-beta not possible in Smad3(-/-) mouse embryo fibroblasts. Using this stringent approach, we have identified COL1A2, COL3A1, COL6A1, COL6A3, and tissue inhibitor of metalloproteases-1 as definite TGF-beta/Smad3 targets. Extrapolation of this approach to other extracellular matrix-related gene promoters also identified COL1A1 and COL5A2, but not COL6A2, as novel Smad targets. Together, these results represent a significant step toward the identification of novel, early-induced Smad-dependent TGF-beta target genes in fibroblasts.

Downregulation of human type VII collagen (COL7A1) promoter activity by dexamethasone. Identification of a glucocorticoid receptor binding region

Type VII collagen is the major collagenous component of the anchoring fibrils, attachment structures that stabilize the association of the cutaneous basement membrane zone to the underlying dermis. It is expressed by both epidermal keratinocytes and dermal fibroblasts. In this study, we have examined the pharmacological control of COL7A1 gene expression by the glucocorticorticoid dexamethasone. We demonstrate that dexamethasone is a potent transcriptional inhibitor of COL7A1 promoter activity in dermal fibroblasts, and we identify a potential glucocorticoid response element in the region -318/-212 of the promoter. In addition, we have determined that dexamethasone antagonizes transforming growth factor-beta (TGF-beta) activation of the COL7A1 promoter. This effect occurred without dexamethasone interfering with TGF-beta-induced Smad-specific gene transcription. These results indicate potential deleterious effects of glucocorticosteroids on epidermal wound healing, as reduced COL7A1 expression likely leads to decreased anchoring fibril formation, which may translate into delayed or impaired reepithelialization.

Sequence of the 5'-flanking region and promoter activity of the human mucin gene MUC5B in different phenotypes of colon cancer cells

Control of gene expression in intestinal cells is poorly understood. Molecular mechanisms that regulate transcription of cellular genes are the foundation for understanding developmental and differentiation events. Mucin gene expression has been shown to be altered in many intestinal diseases and especially cancers of the gastrointestinal tract. Towards understanding the transcriptional regulation of a member of the 11p15.5 human mucin gene cluster, we have characterized 3.55 kb of the 5'-flanking region of the human mucin gene MUC5B, including the promoter, the first two exons and the first intron. We report here the promoter activity of successively 5'-truncated sections of 956 bases of this region by fusing it to the coding region of a luciferase reporter gene. The transcription start site was determined by primer-extension analysis. The region upstream of the transcription start site is characterized by the presence of a TATA box at bases -32/-26, DNA-binding elements for transcription factors c-Myc, N-Myc, Sp1 and nuclear factor kappaB as well as putative activator protein (AP)-1-, cAMP-response-element-binding protein (CREB)-, hepatocyte nuclear factor (HNF)-1-, HNF-3-, TGT3-, gut-enriched Krüppel factor (GKLF)-, thyroid transcription factor (TTF)-1- and glucocorticoid receptor element (GRE)-binding sites. Intron 1 of MUC5B was also characterized, it is 2511 nucleotides long and contains a DNA segment of 259 bp in which are clustered eight tandemly repeated GA boxes and a CACCC box that bind Sp1. AP-2alpha and GATA-1 nuclear factors were also shown to bind to their respective cognate elements in intron 1. In transfection studies the MUC5B promoter showed a cell-specific activity as it is very active in mucus-secreting LS174T cells, whereas it is inactive in Caco-2 enterocytes and HT-29 STD (standard) undifferentiated cells. Within the promoter, maximal transcription activity was found in a segment covering the first 223 bp upstream of the transcription start site. Finally, in co-transfection experiments a transactivating effect of Sp1 on to MUC5B promoter was seen in LS174T and Caco-2 cells.

Differential expression of cytokeratin after orthotopic implantation of newly established human tongue cancer cell lines of defined metastatic ability

Two human tongue squamous cell carcinoma cell lines, SQUU-A and SQUU-B, were established from the same patient. Cervical lymph node metastasis was detected in the mice orthotopically implanted with SQUU-B (86.7%, 13/15), but not in those with SQUU-A (0/13). Histologically, SQUU-B showed invasive growth and intravasation in the tongue, whereas SQUU-A simply demonstrated expansive growth without intravasation. By Western blot analysis, nonmetastatic clone SQUU-A expressed cytokeratin (CK)13/4, 14, 16/6, 18/8, and 19, whereas a high metastatic clone SQUU-B expressed CK18/8 and 19. The reverse transcription-polymerase chain reaction technique showed that CK13/4 mRNA was expressed in both cell lines, but CK14 and 16 mRNA was expressed only in SQUU-A. CK13 was immunohistochemically expressed in both SQUU-A and SQUU-B transplanted into the tongues of nude mice; CK14 and 16 were detected in SQUU-A of the tongues, but not in SQUU-B. As seen in SQUU-B cell line, SQUU-B of the cervical lymph node metastasis did not exhibit CK13, 14, or 16. These results suggest that the loss or down-regulation of CK13, 14, or 16 is related to the invasive and metastatic ability of cancer. The cytoskeletal system is thus considered to be closely related to the malignant phenotype.

Comparative mutation detection screening of the type VII collagen gene (COL7A1) using the protein truncation test, fluorescent chemical cleavage of mismatch, and conformation sensitive gel electrophoresis

Mutations in the type VII collagen gene, COL7A1, give rise to the blistering skin disease, dystrophic epidermolysis bullosa. We have developed two new mutation detection strategies for the screening of COL7A1 mutations in patients with dystrophic epidermolysis bullosa and compared them with an established protocol using conformational sensitive gel electrophoresis. The first strategy consisted of an RNA based protein truncation test that amplified the entire coding region in only four overlapping nested reverse transcriptase-polymerase chain reaction assays. These fragments were transcribed and translated in vitro and analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. We have used the protein truncation test procedure to characterize 15 truncating mutations in 13 patients with severe recessive dystrophic epidermolysis bullosa yielding a detection sensitivity of 58%. The second strategy was a DNA-based fluorescent chemical cleavage of mismatch (fl-CCM) procedure that amplified the COL7A1 gene in 21 polymerase chain reaction assays. Mismatches, formed between patient and control DNA, were identified using chemical modification and cleavage of the DNA. We have compared fl-CCM with conformational sensitive gel electrophoresis by screening a total of 50 dominant and recessive dystrophic epidermolysis bullosa patients. The detection sensitivity for fl-CCM was 81% compared with 75% for conformational sensitive gel electrophoresis (p = 0.37 chi2-test). Using a combination of the three techniques we have screened 93 dystrophic epidermolysis bullosa patients yielding an overall sensitivity of 87%, detecting 79 different mutations, 57 of which have not been reported previously. Comparing all three approaches, we believe that no single method is consistently better than the others, but that the fl-CCM procedure is a sensitive, semiautomated, high throughput system that can be recommended for COL7A1 mutation detection.

Cooperation between SMAD and NF-kappaB in growth factor regulated type VII collagen gene expression

We have previously demonstrated that transforming growth factor-beta (TGF-beta) and pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta, synergistically enhance the expression of type VII collagen gene (COL7A1) in human dermal fibroblasts in culture (Mauviel et al., 1994). Recently, we identified a SMAD-containing complex, rapidly induced by TGF-beta and binding the region [-496/-444] of the COL7A1 promoter, responsible for COL7A1 gene transactivation (Vindevoghel et al., 1998a). In this report, we demonstrate that TGF-beta and TNF-alpha response elements are distinct entities within the COL7A1 promoter. In particular, we demonstrate that the TNF-alpha effect is mediated by NF-kappaB1/RelA (p50/p65) and RelA/RelA (p65/p65) NF-kappaB complexes binding the TNF-alpha response element (TaRE) located in the region [-252/-230], with RelA acting as the transcriptional activator. Finally, we provide definitive evidence for the role of both TGF-beta and TNF-alpha response elements as enhancer sequences, functioning in the context of a heterologous promoter in an additive manner in response to TGF-beta and TNF-alpha. This study provides the first identification of a functional interaction between the two immediate-early transcription factors, SMAD and NF-kappaB, to activate the expression of an extracellular matrix-related gene, COL7A1.

SMAD3/4-dependent transcriptional activation of the human type VII collagen gene (COL7A1) promoter by transforming growth factor beta

The human type VII collagen gene (COL7A1) recently has been identified as an immediate-early response gene for transforming growth factor beta (TGF-beta)/SMAD signaling pathway. In this study, by using MDA-MB-468 SMAD4-/- breast carcinoma cells, we demonstrate that expression of SMAD4 is an absolute requirement for SMAD-mediated promoter activity. We also demonstrate that the SMAD binding sequence (SBS) representing the TGF-beta response element in the region -496/-444 of the COL7A1 promoter functions as an enhancer in the context of a heterologous promoter. Electrophoretic mobility-shift assays with nuclear extracts from COS-1 cells transfected with expression vectors for SMADs 1-5 indicate that SMAD3 forms a complex with a migration similar to that of the endogenous TGF-beta-specific complex observed in fibroblast extracts. Electrophoretic mobility-shift assays using recombinant glutathione S-transferase-SMAD fusion proteins indicate that both SMAD4 and C-terminally truncated SMAD3, but not SMAD2, can bind the COL7A1 SBS. Coexpression of SMAD3 and SMAD4 in COS-1 cells leads to the formation of two complexes: a DNA/protein complex containing SMAD3 alone and another slower-migrating complex containing both SMAD3 and SMAD4, the latter complex not being detected in fibroblasts. Maximal transactivation of COL7A1 SBS-driven promoters in either MDA-MB-468 carcinoma cells or fibroblasts requires concomitant overexpression of SMAD3 and SMAD4. These data may represent the first identification of a functional homomeric SMAD3 complex regulating a human gene.

Further characterization of the 5'-flanking promoter region of the human beta1-adrenergic receptor gene

Further characterization of the 5'-flanking promoter region of the human beta1-adrenergic receptor (AR) gene was attempted. The transcription initiation sites, determined by the primer extension and the rapid amplification of the 5'-cDNA end, are multiple in a spanning about 30 nucleotides (-289 to -261 relative to the translation start site). There exist inverted CCAAT boxes, multiple binding sites for transcription factor Sp1 and AP-2 nearby transcription initiation sites, however, this region lacks a typical TATA box. In order to localize the regulatory region for the basal transcription of the human beta1-AR gene, a variety of 5'-flanking sequence/chloramphenicol acetyltransferase reporter gene fusion constructs was prepared and transiently expressed in HeLa cells. Functional analyses reveal negatively (-3813 to -2925 and -1772 to -796) as well as positively (-2925 to -1772) regulatory regions, in addition to the region (-796 to -87) being necessary for the basic expression of the human beta1-AR gene.

Modulation of human alpha1(I) procollagen gene activity by interaction with Sp1 and Sp3 transcription factors in vitro

In previous work, we delineated a proximal region of the human alpha1(I) collagen gene (COL1A1) promoter necessary to direct its basal transcription in fibroblasts. This region has potential recognition sites for a variety of DNA-binding proteins. Here, we show that the -129/-107-bp sequence in this region of the promoter, which harbors an inverted CCAAT motif closely linked to a GC-rich direct repeat and is perfectly conserved between mouse and human, specifically bound the transcription factors Sp1, Sp3, and CTF/NF-1 in nuclear extracts from human skin and lung fibroblasts. Drosophila Schneider L2 cells lacking endogenous Sp activity were used to investigate the effect of expression of Sp or CTF/NF-1 transcription factors on COLlAl promoter activity. Expression of Sp1 caused potent trans-activation of a COL1A1 promoter (-174 to +42bp). In contrast, expression of Sp3, which binds to the same recognition sites as Sp1, and CTF/NF-1 stimulated COL1A1 promoter activity only at higher concentrations, and Sp2 did not transactivate. Expression of a 10-fold excess of Sp3, but not CTF/NF-1 or Sp2, abrogated the stimulation of COL1A1 promoter activity induced by Sp1. TGF-beta at concentrations previously shown to increase COL1A1 transcription caused a decrease in the relative amount of Sp3 in fibroblast nuclear extracts. These results suggest that both Sp1 and Sp3 bind to the proximal COL1A1 promoter and stimulate its activity; however, their interaction with each other may result in repression of Sp1-induced COL1A1 transcription. Alterations in the relative amounts or DNA-binding activities of these transcription factors in a cell- or signal-specific manner may contribute to the control of transcription from the COL1A1 promoter. The present findings, and recent observations implicating Sp1 and its homologs in regulating the expression of several collagen genes, suggest that the family of Sp1 transcription factors play a role in physiological and pathological modulation of connective tissue accumulation.

Sp3 regulates fas expression in lung epithelial cells

By transducing an apoptotic signal in immune effector cells, Fas has been directly implicated in the control of immunological activity. Expression and functional results, however, have also suggested a role for Fas in regulating cell turnover in specific epithelial populations. To characterize factors responsible for Fas expression in epithelial cells, approximately 3 kb of the 5' flanking region of the mouse Fas gene was isolated. By rapid amplification of cDNA ends and primer extension, transcriptional start sites were identified within 50 bp upstream of the translation start site. Transient transfection of promoter-luciferase constructs in a mouse lung epithelial cell line, MLE-15, localized promoter activity to the first 77 bp of upstream sequence. By using a 60 bp DNA probe (-18 to -77) in electrophoretic mobility-shift assays, three shifted complexes were found. Incubation with excess cold Sp1 oligonucleotide or an anti-Sp3 antibody inhibited complex formation. Site-directed mutagenesis of the Sp1 site resulted in 60-70% loss of promoter activity. In Drosophila SL-2 cells, promoter activity was markedly increased by co-transfection of an Sp3 expression construct. These results show that the Sp3 protein is involved in regulating Fas gene expression in lung epithelial cells.

Smad-dependent transcriptional activation of human type VII collagen gene (COL7A1) promoter by transforming growth factor-beta

We have previously shown that transforming growth factor-beta (TGF-beta) increases type VII collagen gene (COL7A1) expression in human dermal fibroblasts in culture (Mauviel, A., Lapière, J.-C., Halcin, C., Evans, C. H., and Uitto, J. (1994) J. Biol. Chem. 269, 25-28). To gain insight into the molecular mechanisms underlying the up-regulation of COL7A1 by this growth factor, we performed transient cell transfections with a series of 5'-deletion promoter/chloramphenicol acetyltransferase reporter gene constructs. We identified a 68-base pair region between nucleotides -524 and -456, relative to the transcription start site, as critical for TGF-beta response. Using electrophoresis mobility shift assays (EMSAs) with an oligonucleotide spanning the region from -524 to -444, we discovered that a TGF-beta-specific protein-DNA complex was formed as early as 11 min after TGF-beta stimulation and persisted for 1 h after addition of the growth factor. Deletion analysis of the TGF-betaresponsive region of the COL7A1 promoter by EMSA identified segment -496/-444 as the minimal fragment capable of binding the TGF-beta-induced complex. Furthermore, two distinct segments, -496/-490 and -453/-444, appeared to be necessary for TGF-beta-induced DNA binding activity, suggesting a bipartite element. Supershift experiments with a pan-Smad antibody unambiguously identified the TGF-beta-induced complex as containing a Smad member. This is the first direct identification of binding of endogenous Smad proteins to regulatory sequences of a human gene.

Multiple transcriptional elements in the avian type X collagen gene. Identification of Sp1 family proteins as regulators for high level expression in hypertrophic chondrocytes

During the cartilage-to-bone transition, participating chondrocytes eventually undergo hypertrophy and are replaced by bone and marrow. Type X collagen is synthesized by chondrocytes specifically when they become hypertrophic, and this specificity is primarily regulated at the level of transcription. Previously, we demonstrated that a proximal promoter region from nucleotide -562 to +86 contained cis-acting elements that directed high level expression of a reporter gene in a cell-specific manner (Long, F., and Linsenmayer, T. F. (1995) J. Biol. Chem. 270, 31310-31314). In the present study, we have further dissected this region by generating a series of constructs and examining their expression in hypertrophic versus nonhypertrophic chondrocytes. Several positive and negative elements have been delineated within the proximal promoter region to mediate the regulation of transcription in hypertrophic chondrocytes. Most notably, a sequence from nucleotide -139 to +5 was sufficient to direct high level expression in this cell type. Electrophoresis mobility shift assay and supershift experiments identified within this sequence two 10-base pair noncanonical binding sites for Sp1 proteins. Mutations within the Sp1 binding sites either diminished or abolished the expression driven by the sequence from -139 to +5. These results indicate that the Sp1 proteins mediate the cell-specific expression of type X collagen.