Functional AP1 and CRE response elements in the human keratinocyte transglutaminase promoter mediating Whn suppression

cAMP-responsive element-binding protein (CREB) and cAMP co-regulate activator protein 1 (AP1)-dependent regeneration-associated gene expression and neurite growth

To regenerate damaged axons, neurons must express a cassette of regeneration-associated genes (RAGs) that increases intrinsic growth capacity and confers resistance to extrinsic inhibitory cues. Here we show that dibutyrl-cAMP or forskolin combined with constitutive-active CREB are superior to either agent alone in driving neurite growth on permissive and inhibitory substrates. Of the RAGs examined, only arginase 1 (Arg1) expression correlated with the increased neurite growth induced by the cAMP/CREB combination, both of which were AP1-dependent. This suggests that cAMP-induced AP1 activity is necessary and interacts with CREB to drive expression of RAGs relevant for regeneration and demonstrates that combining a small molecule (cAMP) with an activated transcription factor (CREB) stimulates the gene expression necessary to enhance axonal regeneration.

Transglutaminase 2: a new player in bronchopulmonary dysplasia?

Aberrant remodelling of the extracellular matrix in the developing lung may underlie arrested alveolarisation associated with bronchopulmonary dysplasia (BPD). Transglutaminases are regulators of extracellular matrix remodelling. Therefore, the expression and activity of transglutaminases were assessed in lungs from human neonates with BPD and in a rodent model of BPD. Transglutaminase expression and localisation were assessed by RT-PCR, immunoblotting, activity assay and immunohistochemical analyses of human and mouse lung tissues. Transglutaminase regulation by transforming growth factor (TGF)-β was investigated in lung cells by luciferase-based reporter assay and RT-PCR. TGF-β signalling was neutralised in vivo in an animal model of BPD, to determine whether TGF-β mediated the hyperoxia-induced changes in transglutaminase expression. Transglutaminase 2 expression was upregulated in the lungs of preterm infants with BPD and in the lungs of hyperoxia-exposed mouse pups, where lung development was arrested. Transglutaminase 2 localised to the developing alveolar septa. TGF-β was identified as a regulator of transglutaminase 2 expression in human and mouse lung epithelial cells. In vivo neutralisation of TGF-β signalling partially restored normal lung structure and normalised lung transglutaminase 2 mRNA expression. Our data point to a role for perturbed transglutaminase 2 activity in the arrested alveolarisation associated with BPD.

Open chromatin defined by DNaseI and FAIRE identifies regulatory elements that shape cell-type identity

The human body contains thousands of unique cell types, each with specialized functions. Cell identity is governed in large part by gene transcription programs, which are determined by regulatory elements encoded in DNA. To identify regulatory elements active in seven cell lines representative of diverse human cell types, we used DNase-seq and FAIRE-seq (Formaldehyde Assisted Isolation of Regulatory Elements) to map "open chromatin." Over 870,000 DNaseI or FAIRE sites, which correspond tightly to nucleosome-depleted regions, were identified across the seven cell lines, covering nearly 9% of the genome. The combination of DNaseI and FAIRE is more effective than either assay alone in identifying likely regulatory elements, as judged by coincidence with transcription factor binding locations determined in the same cells. Open chromatin common to all seven cell types tended to be at or near transcription start sites and to be coincident with CTCF binding sites, while open chromatin sites found in only one cell type were typically located away from transcription start sites and contained DNA motifs recognized by regulators of cell-type identity. We show that open chromatin regions bound by CTCF are potent insulators. We identified clusters of open regulatory elements (COREs) that were physically near each other and whose appearance was coordinated among one or more cell types. Gene expression and RNA Pol II binding data support the hypothesis that COREs control gene activity required for the maintenance of cell-type identity. This publicly available atlas of regulatory elements may prove valuable in identifying noncoding DNA sequence variants that are causally linked to human disease.

DNA plasticity is a key determinant of the energetics of binding of Jun-Fos heterodimeric transcription factor to genetic variants of TGACGTCA motif

The Jun-Fos heterodimeric transcription factor is a target of a diverse array of signaling cascades that initiate at the cell surface and converge in the nucleus and ultimately result in the expression of genes involved in a multitude of cellular processes central to health and disease. Here, using isothermal titration calorimetry in conjunction with circular dichroism, we report the effect of introducing single nucleotide variations within the TGACGTCA canonical motif on the binding of bZIP domains of Jun-Fos heterodimer to DNA. Our data reveal that the Jun-Fos heterodimer exhibits differential energetics in binding to such genetic variants in the physiologically relevant micromolar to submicromolar range with the TGACGTCA canonical motif affording the highest affinity. Although binding energetics are largely favored by enthalpic forces and accompanied by entropic penalty, neither the favorable enthalpy nor the unfavorable entropy correlates with the overall free energy of binding in agreement with the enthalpy-entropy compensation phenomenon widely observed in biological systems. However, a number of variants including the TGACGTCA canonical motif bind to the Jun-Fos heterodimer with high affinity through having overcome such enthalpy-entropy compensation barrier, arguing strongly that better understanding of the underlying invisible forces driving macromolecular interactions may be the key to future drug design. Our data also suggest that the Jun-Fos heterodimer has a preference for binding to TGACGTCA variants with higher AT content, implying that the DNA plasticity may be an important determinant of protein-DNA interactions. This notion is further corroborated by the observation that the introduction of genetic variations within the TGACGTCA motif allows it to sample a much greater conformational space. Taken together, these new findings further our understanding of the role of DNA sequence and conformation on protein-DNA interactions in thermodynamic terms.

Molecular mechanism of proinflammatory cytokine-mediated squamous metaplasia in human corneal epithelial cells

PURPOSE

The cornified envelope protein small proline-rich protein 1B (SPRR1B) is a biomarker for squamous metaplasia. Proinflammatory cytokines IL-1beta and IFN-gamma are potent inducers of ocular surface keratinization and SPRR1B expression. Here the molecular mechanisms controlling SPRR1B gene expression in response to IL-1beta and IFN-gamma are elucidated.

METHODS

A 3-kb fragment of the SPRR1B gene 5'-flanking region was amplified from human chromosome 1, sequentially deleted, and cloned into a luciferase vector. Constructs were transiently transfected into human corneal epithelial cells, and activity was assessed in response to IL-1beta, IFN-gamma, or basal medium. Functional cis-elements responding to IL-1beta and IFN-gamma were characterized by site-directed mutagenesis and gel mobility shift assay. Effects of mitogen-activated protein kinases p38, ERK, and JNK were assessed using inhibitors and dominant-negative mutants. Results were validated by real-time RT-PCR.

RESULTS

The first 620 bp of the SPRR1B 5'-flanking region regulated constitutive expression and increased promoter activity in response to IL-1beta and IFN-gamma. Corresponding cis-elements for IL-1beta and IFN-gamma were bound by cAMP response element binding protein (CREB) and zinc-finger E-box binding homeobox 1 (ZEB1), respectively. Inhibition of p38 abolished the stimulatory effects of IL-1beta and IFN-gamma on SPRR1B, whereas inhibition of JNK and ERK had no effect. Dominant-negative mutants targeting p38alpha and p38beta2 blocked cytokine-induced SPRR1B promoter activity and mRNA expression.

CONCLUSIONS

SPRR1B is upregulated by the proinflammatory cytokines IL-1beta and IFN-gamma via p38 MAPK-mediated signaling pathways that lead to the activation of transcription factors CREB and ZEB1, respectively. These results identify key intracellular signaling intermediates involved in the pathogenesis of immune-mediated ocular surface squamous metaplasia.

Transforming growth factor-B1 and matrix metalloproteinase-7 promoter variants induce risk for Helicobacter pylori-associated gastric precancerous lesions

The expression of growth factors, proteolytic enzymes, fibrogenic factors, and cytokines is altered in the Helicobacter pylori-infected gastric mucosa. Therefore, we aimed to evaluate the association of functional promoter variants of transforming growth factor (TGF)-B1 and matrix metalloproteinase (MMP)-7 genes with gastritis and gastric precancerous lesions. After upper gastrointestinal endoscopy, a total of 130 rapid urease test-positive patients with nonulcer dyspepsia were examined for H. pylori infection using modified Giemsa stain and IgG anti-CagA ELISA. All patients and 200 asymptomatic controls were genotyped for TGF-B1 (-509 C>T) and MMP-7 (-181 A>G) substitutions using PCR-RFLP. The genotype and allele frequencies of TGF-B1 and MMP-7 polymorphisms did not differ between patients and controls (p > 0.05). However, the CagA-positive patients with TGF-B1 -509 T allele had higher risk for gastric atrophy (p = 0.026, odds ratio [OR] = 2.38) and lymphoid follicle development (p = 0.028, OR = 2.29). In addition, CagA-positive patients carrying MMP-7 -181 G allele had risk for lymphoid follicle formation (p = 0.027, OR = 2.30). Thus, the present study revealed significant association of functional MMP-7 and TGF-B1 gene variants toward susceptibility to H. pylori-induced precancerous gastric lesions.

Regulation of bovine tumor necrosis factor-alpha-induced protein 6 in ovarian follicles during the ovulatory process and promoter activation in granulosa cells

To study the regulation of bovine TNFalpha-induced protein 6 (TNFAIP6) prior to ovulation, preovulatory follicles obtained after the treatment with human chorionic gonadotropin (hCG) were used. RT-PCR analyses showed that levels of TNFAIP6 mRNA were low before hCG but significantly increased after hCG treatment in follicles. Further analyses and immunohistochemistry indicated that this increase in transcript and protein levels occurred in theca and granulosa cells. To investigate molecular mechanisms involved in TNFAIP6 transactivation, the activity of bovine TNFAIP6 promoter was studied in granulosa cell cultures. Mutant studies identified the minimal region conferring full-length promoter activity, in which activator protein-1 (AP1) and cAMP response element (CRE) elements were required for promoter activity. Overexpression of dominant-negative AP1 and activating transcription factor/cAMP response element-binding protein (CREB) inhibited forskolin-inducible promoter activity. DNA binding assays demonstrated the importance of AP1 and CRE for activity and identified JunD, FosB, Fra2, CREB1, and CREB2 as being part of the AP1 complex, and FosB, Fra2, and CREB1 for the CRE complex. Chromatin immunoprecipitation assays confirmed binding of these proteins with endogenous TNFAIP6 promoter. Treatment with forskolin, prostaglandin E2, and catalytic subunit protein kinase (cPKA) stimulated, but H89, PKA inhibitor peptide, and indomethacin inhibited, TNFAIP6 promoter activity and gene expression in granulosa cells. Collectively, this study is the first to describe that the ovulatory process in cows is associated with a gonadotropin-dependent induction of TNFAIP6 in ovarian follicles and provide the molecular basis through which AP1 and CRE sites and PKA activation played important roles in the regulation of TNFAIP6 in granulosa cells.

Thematic review series: skin lipids. Peroxisome proliferator-activated receptors and liver X receptors in epidermal biology

The epidermis is a very active site of lipid metabolism, and all peroxisome proliferator-activated receptor (PPAR) and liver X receptor (LXR) isoforms are expressed in the epidermis. Activation of PPARalpha, -beta/delta, or -gamma or LXRs stimulates keratinocyte differentiation. Additionally, activation of these receptors also improves permeability barrier homeostasis by a number of mechanisms, including stimulating epidermal lipid synthesis, increasing lamellar body formation and secretion, and increasing the activity of enzymes required for the extracellular processing of lipids in the stratum corneum, leading to the formation of lamellar membranes that mediate permeability barrier function. The stimulation of keratinocyte differentiation and permeability barrier formation also occurs during fetal development, resulting in accelerated epidermal development. PPAR and LXR activation regulates keratinocyte proliferation and apoptosis, and studies have shown that these receptors play a role in cutaneous carcinogenesis. Lastly, PPAR and LXR activation is anti-inflammatory, reducing inflammation in animal models of allergic and irritant contact dermatitis. Because of their broad profile of beneficial effects on skin homeostasis, PPAR and LXR have great potential to serve as drug targets for common skin diseases such as psoriasis, atopic dermatitis, and skin cancer.

A molecular mechanism for the differential regulation of TGF-beta1 expression due to the common SNP -509C-T (c. -1347C > T)

Transforming growth factor beta1 (TGF-beta1) levels influence many cellular, immunologic and pathologic processes. Activator protein 1 (AP1) and hypoxia are key regulators of TGF-beta1 expression levels. The common TGFB1 promoter SNP c.-1347C > T (-509C-T, rs1800469) has been linked to a nearly twofold difference in plasma levels among individuals and with risk, progression, and outcome of numerous diseases. We demonstrate exclusive in vitro and in vivo recruitment of AP1 containing JunD to -1347C. This study also is the first to demonstrate hypoxia inducible factor 1 (HIF-1) binding to the TGFB1 promoter. HIF-1 was found to associate with both -1347C and -1347T and compete with AP1 for binding to -1347C. Reporter constructs demonstrate that expression differences between -1347C and -1347T are due to selective AP1 recruitment to the TGFB1 promoter. As AP1 is known to down-regulate transcription of other genes, we suggest that the molecular mechanism for the difference in TGF-beta1 plasma levels linked to -1347 is due to transcriptional suppression by AP1 binding to -1347C. These data should aid in our understanding of the association of the -1347 SNP with the pathogenesis of certain TGF-beta1-related diseases.

Transglutaminase function in epidermis

Surface epithelial cells, such as the epidermal keratinocyte, undergo a process of terminal cell differentiation that results in the construction of a multilayered epithelium. This epithelium functions to protect the organism from the environment. Transglutaminases, enzymes that catalyze the formation of isopeptide protein-protein cross-links, are key enzymes involved in the construction of this structure. This brief review will focus on the role of these enzymes in constructing the epidermal surface.

cDNA microarray analysis of rat alveolar epithelial cells following exposure to organic extract of diesel exhaust particles

Diesel exhaust particles (DEP) induce pulmonary diseases including asthma and chronic bronchitis. Comprehensive evaluation is required to know the mechanisms underlying the effects of air pollutants including DEP on lung diseases. Using a cDNA microarray, we examined changes in gene expression in SV40T2 cells, a rat alveolar type II epithelial cell line, following exposure to an organic extract of DEP. We identified candidate sensitive genes that were up- or down-regulated in response to DEP. The cDNA microarray analysis revealed that a 6-h exposure to the DEP extract (30 microg/ml) increased (>2-fold) the expression of 51 genes associated with drug metabolism, antioxidation, cell cycle/proliferation/apoptosis, coagulation/fibrinolysis, and expressed sequence tags (ESTs), and decreased (<0.5-fold) that of 20 genes. In the present study, heme oxygenase (HO)-1, an antioxidative enzyme, showed the maximum increase in gene expression; and type II transglutaminase (TGM-2), a regulator of coagulation, showed the most prominent decrease among the genes. We confirmed the change in the HO-1 protein level by Western blot analysis and that in the enzyme activity of TGM-2. The organic extract of DEP increased the expression of HO-1 protein and decreased the enzyme activity of TGM-2. Furthermore, these effects of DEP on either HO-1 or TGM-2 were reduced by N-acetyl-l-cysteine (NAC), thus suggesting that oxidative stress caused by this organic fraction of DEP may have induced these cellular responses. Therefore, an increase in HO-1 and a decrease in TGM-2 might be good markers of the biological response to organic compounds of airborne particulate substances.

The Effect of LXR Activators on AP-1 Proteins in Keratinocytes

Oxysterols, via activation of liver X receptor (LXR), regulate keratinocyte differentiation by stimulating transglutaminase cross-linking of several constituent proteins leading to the formation of the cornified envelope. We previously reported that oxysterols increase the expression of one of these cross-linked proteins, involucrin, and that this effect can be abolished by mutations of the distal activator protein (AP)-1 response element in the involucrin promoter. Furthermore, oxysterols increase AP-1 binding in an electrophoretic gel mobility shift assay and increase the expression of an AP-1 reporter. In this study, we describe the individual components of the AP-1 complex that are involved in the oxysterol-mediated AP-1 activation and stimulation of keratinocyte differentiation. We identified Fra-1 within the AP-1 DNA binding complex by supershift analysis of nuclear extracts from oxysterol-treated, cultured keratinocytes and confirmed that oxysterol treatment increased the levels of Fra-1 by western blot analysis. Additionally, on Western and Northern analysis, oxysterol treatment increased two other AP-1 proteins, Jun-D and c-Fos, whereas Fra-2, Jun-B, and c-Jun were not changed. Similar alterations in AP-1 proteins occurred when 25-OH-cholesterol or non-steroidal LXR agonists (GW3965, TO-901317) were used. These results indicate that oxysterols induce specific AP-1 proteins, thereby activating involucrin, one of the genes required for epidermal differentiation.

A distal region of the human TGM1 promoter is required for expression in transgenic mice and cultured keratinocytes

Background

TGM1(transglutaminase 1) is an enzyme that crosslinks the cornified envelope of mature keratinocytes. Appropriate expression of the TGM1 gene is crucial for proper keratinocyte function as inactivating mutations lead to the debilitating skin disease, lamellar ichthyosis. TGM1 is also expressed in squamous metaplasia, a consequence in some epithelia of vitamin A deficiency or toxic insult that can lead to neoplasia. An understanding of the regulation of this gene in normal and abnormal differentiation states may contribute to better disease diagnosis and treatment.

Methods

In vivo requirements for expression of the TGM1 gene were studied by fusing various lengths of promoter DNA to a reporter and injecting the DNA into mouse embryos to generate transgenic animals. Expression of the reporter was ascertained by Western blotting and immunohistochemistry. Further delineation of a transcriptionally important distal region was determined by transfections of progressively shortened or mutated promoter DNA into cultured keratinocytes.

Results

In vivo analysis of a reporter transgene driven by the TGM1 promoter revealed that 1.6 kilobases, but not 1.1 kilobases, of DNA was sufficient to confer tissue-specific and cell layer-specific expression. This same region was responsible for reporter expression in tissues undergoing squamous metaplasia as a response to vitamin A deprivation. Mutation of a distal promoter AP1 site or proximal promoter CRE site, both identified as important transcriptional elements in transfection assays, did not prevent appropriate expression. Further searching for transcriptional elements using electrophoretic mobility shift (EMSA) and transfection assays in cultured keratinocytes identified two Sp1 elements in a transcriptionally active region between -1.6 and -1.4 kilobases. While mutation of either Sp1 site or the AP1 site singly had only a small effect, mutation of all three sites eliminated nearly all the transcriptional activity.

Conclusions

A distal region of the TGM1 gene promoter, containing AP1 and Sp1 binding sites, is evolutionarily conserved and responsible for high level expression in transgenic mice and in transfected keratinocyte cultures.

Transglutaminases: crosslinking enzymes with pleiotropic functions

Blood coagulation, skin-barrier formation, hardening of the fertilization envelope, extracellular-matrix assembly and other important biological processes are dependent on the rapid generation of covalent crosslinks between proteins. These reactions--which are catalysed by transglutaminases--endow the resulting supramolecular structure with extra rigidity and resistance against proteolytic degradation. Some transglutaminases function as molecular switches in cytoskeletal scaffolding and modulate protein-protein interactions. Having knowledge of these enzymes is essential for understanding the aetiologies of diverse hereditary diseases of the blood and skin, and various autoimmune, inflammatory and degenerative conditions.

Loricrin expression in cultured human keratinocytes is controlled by a complex interplay between transcription factors of the Sp1, CREB, AP1, and AP2 families

The major protein component of the cornified cell envelope barrier structure of the epidermis is loricrin, and it is expressed late during terminal differentiation in epidermal keratinocytes. We have previously shown that an AP1 site located in the proximal promoter region (position -55) is essential for human loricrin promoter activity (Rossi, A., Jang, S-I., Ceci, R., Steinert, P. M., and Markova, N. G. (1998) J. Invest. Dermatol. 110, 34-40). In this study we show that its regulation requires complex cooperative and competitive interactions between multiple transcription factors in keratinocytes located in different compartments of the epidermis. We show that as few as 154 base pairs of 5'-upstream sequences from the cap site can direct the keratinocyte-specific expression in cultured keratinocytes. Mutation and DNA-protein analyses show that Sp1, c-Jun, an unidentified regulator, and the co-activator p300/CREB-binding protein up-regulate whereas Sp3, CREB-1/CREMalpha/ATF-1, Jun B, and an AP2-like protein (termed the keratinocyte-specific repressor-1 (KSR-1)) suppress loricrin promoter activity. We show that CREB protein can compete with c-Jun for the AP1 site and repress loricrin promoter activity. We show here that the protein kinase A pathway can activate loricrin expression by manipulation of the Sp1, Sp3, and KSR-1 levels in the nucleus. Thus, in undifferentiated cells, loricrin expression is suppressed by Jun B, Sp3, and KSR-1 proteins. But in advanced differentiated cells, levels of Sp3, KSR-1, and CREB proteins are lower; the unidentified regulator protein can bind; Sp1 and c-Jun are increased; and then p300/CBP is recruited. Together, these events allow loricrin transcription to proceed. Indeed, the synergistic effects of the Sp1, c-Jun, and p300 factors indicate that p300/CBP might act as bridge to form an active transcription complex.

Regulation of human profilaggrin promoter activity in cultured epithelial cells by retinoic acid and glucocorticoids

Vitamin A and other retinoids profoundly inhibit both morphological and biochemical aspects of epidermal differentiation in vitro. Profilaggrin, like most other markers of keratinocyte differentiation, is negatively regulated by retinoic acid in vitro, both at the level of mRNA synthesis and by inhibiting the activity of endoproteases that convert profilaggrin to filaggrin. Profilaggrin is an abundant component of keratohyalin granules and forms the precursor of filaggrin, the keratin associated protein of the stratum corneum. In this report, we identify a region of the human profilaggrin promoter that is involved in the transcriptional regulation of expression by retinoic acid (RA). A series of promoter deletions linked to the chloramphenicol acetyl transferase (CAT) reporter gene were prepared and analyzed by transfection into Hela cells and keratinocytes. We also cotransfected vectors expressing retinoic acid receptor and cultured the transfected cells in the presence and absence of ligand. The region responsive to retinoic acid was localized to a 53 bp sequence between -1109 and -1056 (relative to the mRNA start site at +1) that contains a cluster of five retinoic acid response elements with variable spacing and orientation. In vitro gel shift analysis demonstrated that nuclear retinoid receptors do not bind directly to the identified sequence, suggesting that the mode of regulation by RA may be indirect or that binding requires another cofactor in addition to retinoid receptors. Whereas in keratin genes retinoic acid and glucocorticoid responsive sequences frequently coincide, the glucocorticoid response element in the profilaggrin promoter was located downstream of the RARE cluster between -965 and -951. These studies demonstrate that RA and glucocorticoids regulate profilaggrin expression at least in part by transcriptional mechanisms, via a region of the promoter that contains both retinoid and glucocorticoid responsive elements.

The nude gene and the skin

The nude mutation has been known for a long time. Nevertheless, the gene responsible for the defect has been identified only recently. It encodes a transcriptional activator of the family of forkhead proteins mainly expressed in thymic epithelium and distinct keratinocyte populations in the epidermis and hair follicles. The present review focuses on the molecular and functional characterization of the nude gene and its product and gives an overview as to its role in skin biology and the first identified target genes in the skin. In addition, evolutionary aspects are highlighted stressing the importance of such investigations for a comprehensive understanding of the nude gene product and the regulation of its expression. Furthermore, these studies give a hint as to when the nude gene has occurred first and how it has developed in molecular and functional terms since then.