12-O-tetradecanoyl-phorbol-13-acetate induction of the human collagenase gene is mediated by an inducible enhancer element located in the 5'-flanking region

Chromatin-embedded reporter genes: Quantification of stimulus-induced gene transcription

Receptors and ion channels expressed on the cell surface ensure proper communication between the cells and the environment. In multicellular organism, stimulus-regulated gene transcription is the basis for communication with the environment allowing individual cells to respond to stimuli such as nutrients, chemical stressors and signaling molecules released by other cells of the organism. Hormones, cytokines, and mitogens bind to receptors and ion channels and induce intracellular signaling cascades involving second messengers, kinases, phosphatases, and changes in the concentration of particular ions. Ultimately, the signaling cascades reach the nucleus. Transcription factors are activated that respond to cellular stimulation and induce changes in gene transcription. Investigating stimulus-transcription coupling combines cell biology with genetics. In this review, we discuss the molecular biology of stimulus-induced transcriptional activators and their responsiveness to extracellular and intracellular signaling molecules and to epigenetic regulators. Stimulus-induced gene expression is measured by several methods, including detection of nuclear translocation of transcription factors, phosphorylation or DNA binding. In this article, we emphasize that the most reliable method to directly measure transcriptional activation involves the use of chromatin-embedded reporter genes.

Stimulation of c-Jun/AP-1-Activity by the Cell Cycle Inhibitor p57Kip2

p57 is a member of the Cip/Kip family of cell cycle inhibitors which restrict the eukaryotic cell cycle by binding to and inhibiting cyclin/CDK complexes. They are considered as tumor suppressors and inactivating genomic mutations of p57 are associated with human overgrowth disorders. Increasing evidence suggests that p57 controls additional cellular processes beyond cell cycle control such as apoptosis, cell migration or transcription. Here we report that p57 can stimulate AP-1 promotor activity. While transactivation by c-Jun is strongly activated by p57, it did not enhance c-Fos induced transcription. This indicates that c-Jun is the target of p57 in the canonical AP-1 heterodimeric transcription factor. We could detect endogenous p57/c-Jun containing complexes in cells by co-immunoprecipitation. The strong stimulation of c-Jun activity is not the consequence of activating phosphorylation in the transactivation domain (TAD) of c-Jun, but rather due to negative interference with c-Jun repressors and positive interference with c-Jun activators. In contrast to full-length p57, the amino- and carboxy-terminal domains of p57 are insufficient for a significant activation of c-Jun induced transcription. When expressed in presence of full length p57, the p57 C-terminus abrogated and the N-terminus enhanced c-Jun activation. This indicates that the C-terminus may bind and sequester a putative activator of c-Jun, whereas the N-terminus may sequester a c-Jun repressor. Interestingly, the p57 aminoterminus is sufficient for binding to the two c-Jun repressors HDAC1 and HDAC3. These data are consistent with a model of c-Jun activation where p57 is a part of large nuclear remodeling/transcription complexes. p57 might stimulate transcription by inhibiting transcription repressor proteins like HDACs via its N-terminus and/or attracting transcription activators through its C-terminus. These data suggest that in addition to its role as a CDK inhibitor and tumor suppressor, p57 may also exert tumor promoting functions by activation of the proto-oncoprotein c-Jun.

MEF2C Interacts With c-FOS in PTH-Stimulated Mmp13 Gene Expression in Osteoblastic Cells

Parathyroid hormone (PTH) regulates the transcription of many genes in the osteoblast. One of these genes is Mmp13, which is involved in bone remodeling and early stages of endochondral bone formation. Previously, we reported that PTH induces Mmp13 transcription by regulating the dissociation of histone deacetylase 4 (HDAC4) from runt-related transcription factor 2 (Runx2), and the association of the HATs, p300, and p300/CREB binding protein (CBP)-associated factor. It is known that, in addition to Runx2, HDAC4 binds to the transcription factor, myocyte-specific enhancer factor 2c (MEF2C), and represses its activity. In this work, we investigated whether MEF2C participates in PTH-stimulated Mmp13 gene expression in osteoblastic cells and how it does so. Knockdown of Mef2c in UMR 106-01 cells repressed Mmp13 messenger RNA expression and promoter activity with or without PTH treatment. Chromatin immunoprecipitation (ChIP) assays showed that MEF2C associated with the Mmp13 promoter; this increased after 4 hours of PTH treatment. ChIP-reChIP results indicate that endogenous MEF2C associates with HDAC4 on the Mmp13 promoter; after PTH treatment, this association decreased. From gel shift, ChIP, and promoter-reporter assays, MEF2C was found to associate with the activator protein-1 (AP-1) site without directly binding to DNA and had its stimulatory effect through interaction with c-FOS. In conclusion, MEF2C is necessary for Mmp13 gene expression at the transcriptional level and participates in PTH-stimulated Mmp13 gene expression by increased binding to c-FOS at the AP-1 site in the Mmp13 promoter. The observation of MEF2C interacting with a member of the AP-1 transcription factor family provides knowledge of the functions of HDAC4, c-FOS, and MEF2C.

Gastrin stimulates MMP-1 expression in gastric epithelial cells: putative role in gastric epithelial cell migration

The pyloric antral hormone gastrin plays a role in remodeling of the gastric epithelium, but the specific targets of gastrin that mediate these effects are poorly understood. Glandular epithelial cells of the gastric corpus express matrix metalloproteinase (MMP)-1, which is a potential determinant of tissue remodeling; some of these cells express the CCK-2 receptor at which gastrin acts. We have now examined the hypothesis that gastrin stimulates expression of MMP-1 in the stomach. We determined MMP-1 transcript abundance in gastric mucosal biopsies from Helicobacter pylori negative human subjects with normal gastric mucosal histology, who had a range of serum gastrin concentrations due in part to treatment with proton pump inhibitors (PPI). The effects of gastrin were studied on gastric epithelial AGS-GR cells using Western blot and migration assays. In human subjects with increased serum gastrin due to PPI usage, MMP-1 transcript abundance was increased 2-fold; there was also increased MMP-7 transcript abundance but not MMP-3. In Western blots, gastrin increased proMMP-1 abundance, as well that of a minor band corresponding to active MMP-1, in the media of AGS-GR cells, and the response was mediated by protein kinase C and p42/44 MAP kinase. There was also increased MMP-1 enzyme activity. Gastrin-stimulated AGS-GR cell migration in both scratch wound and Boyden chamber assays was inhibited by MMP-1 immunoneutralization. We conclude that MMP-1 expression is a target of gastrin implicated in mucosal remodeling.

The role of APE/Ref-1 signaling pathway in hepatocellular carcinoma progression

Hepatocellular carcinoma (HCC) is responsible for a third of the estimated cancer-caused deaths worldwide. To deeply understand the mechanisms controlling HCC progression is of primary importance to develop new approaches for treatment. Apurinic/apyrimidinic endonuclease-1/redox effector factor 1 (APE/Ref-1) has been uncovered elevated in various types of cancer, including HCC. Additionally, HCC progression is always correlated with elevated copper (Cu). Our previous data demonstrated that Cu treatment initiated APE/Ref-1 expression and its downstream targets. Therefore, we hypothesized that APE/Ref-1 may be involved in HCC progression through mediating the effect of Cu to its signaling cascades. Following different treatments, human HCC cell line (Hep3B) and immortalized non-malignant hepatocyte cell line (THLE3) were analyzed to explore the role of APE/Ref-1 signaling pathway. Unstained human tissue microarrays (TMA) were subjected to IHC analysis to study the relationship between APE/Ref-1 expression and clinic features. APE/Ref-1 was upregulated in HCC cells consistent with the strong expression of APE/Ref-1 in HCC tissue microarray. Greater cytoplasmic accumulation of APE/Ref-1 was found in poorly differentiated and more aggressive tumors. Also we provide evidence to show that APE/Ref-1 signaling pathway stimulates cellular proliferation, enhances antiapoptosis, and facilitates metastasis through experimental knockdown of APE/Ref-1 using siRNA in Hep3B cells or overexpressing APE/Ref-1 in THLE3 cells. These results define a novel role of APE/Ref-1 in HCC progression as being an important mediating and potentiating molecule, and also provide a basis for further investigations utilizing appropriate APE/Ref-1 inhibitors in combination with chemo-drugs for HCC treatment.

Resveratrol stimulates AP-1-regulated gene transcription

SCOPE

Many intracellular functions have been attributed to resveratrol, a polyphenolic phytoalexin found in grapes and in other plants, including the regulation of transcription. Here, we have analyzed the impact of resveratrol on the activity of the transcription factor activator protein-1 (AP-1).

METHODS AND RESULTS

Using a chromosomally embedded AP-1-responsive reporter gene, we show that the AP-1 activity was significantly elevated in resveratrol-treated 293 human embryonic kidney and HepG2 hepatoma cells. The 12-O-tetradecanoylphorbol-13-acetate-responsive element, a binding site for c-Jun and c-Fos, was identified as resveratrol-responsive element. Expression of c-Jun and c-Fos, two proteins that constitute AP-1, is upregulated in resveratrol-stimulated HEK293 cells. On the transcriptional level, c-Jun and the ternary complex factor Elk-1 are essential for the activation of AP-1 in resveratrol-treated cells. In addition, mitogen-activated protein kinases and protein kinase C are required to connect resveratrol stimulation with enhanced AP-1 controlled transcription. Finally, we show that resveratrol increased the activities of the AP-1 responsive cyclin D1 and tumor necrosis factor α promoters.

CONCLUSION

Resveratrol regulates gene transcription via activation of stimulus-regulated protein kinases and the stimulus-responsive AP-1 transcription factors. The fact that resveratrol regulates AP-1 activity may explain many of the pleiotropic intracellular alterations induced by resveratrol.

Fra-1 regulation of Matrix Metallopeptidase-1 (MMP-1) in metastatic variants of MDA-MB-231 breast cancer cells

Matrix Metallopeptidase 1 (MMP-1) expression has repeatedly been correlated to tumorigenesis and metastasis.  Yet, MMP-1 regulation in a metastatic context remains largely unknown.  Here we confirm differential MMP-1 expression in mammary carcinoma cells with varied metastatic potentials. We show that MMP-1 expression is regulated by an AP-1 element in its promoter in highly metastatic MDA-MB-231 mammary carcinoma cell derivatives.  Fra-1, an AP-1 family transcription factor, differentially binds this element in highly metastatic cells compared to low metastatic cells and is required for MMP-1 expression.  Overexpression of Fra-1 also caused increased MMP-1 expression. Fra-1 mRNA levels are unchanged in the cell variants, however its protein levels are higher in the metastatic cells. While there was no change in Fra-1 protein degradation rates, protein synthesis of Fra-1 was increased in the metastatic cell variant. These results demonstrate that Fra-1 and MMP-1 levels are differentially regulated in metastatic cell variants at the level of Fra-1 protein translation. Consistent with the importance of Fra-1 for tumor growth, we found that Fra-1 overexpression was sufficient to increase cell motility and anchorage independent growth.  These results suggest that increased Fra-1 translation is critical for regulation of MMP-1 and tumor cell metastasis.

Transcription factor ATF-3 regulates allele variation phenotypes of the human SLC11A1 gene

Genetic polymorphisms in the human solute carrier family 11 member 1 (SLC11A1) gene predispose to susceptibility to infectious/inflammatory diseases and cancer. Human susceptibility to these diseases exhibits allelic association with a polymorphic regulatory Z-DNA-forming microsatellite of a (GT/AC)n repeat. The carriage of different alleles may influence chromatin remodeling and accessibility by transcription factors. Of particular importance is the binding site for the Activating Protein 1 (AP-1) elements, (ATF-3 and c-Jun), adjacent to the 5' sequence of the Z-DNA-forming polymorphism. The aim of the study was to characterize the transcriptional mechanisms controlling different alleles of SLC11A1 expression by ATF-3 and c-Jun. Allele 2, [T(GT)5AC(GT)5AC(GT)10GGCAGA(G)6], and Allele 3, [T(GT)5AC(GT)5AC(GT)9GGCAGA(G)6], were subcloned into the PGL2Basic vector. Transient transfections of THP-1 cells with the constructs, in the presence or absence of pATF-3 were preformed. Luciferase expression was determined. To document the recruitment of ATF-3 and c-Jun, to the polymorphic promoter alleles in vivo, we performed ChIP assays with transient transfected THP-1 cells treated with or without lipopolyssacharides. Our data documented that ATF-3 suppresses the transcriptional activation of Allele-3, and this suppression is enhanced in the presence of lipopolyssacharides. Our findings suggest that ATF-3 and c-Jun may influence heritable variation in SLC11A1-dependent innate resistance to infection and inflammation both within and between populations.

Transcriptional response to calcium-sensing receptor stimulation

Elevated extracellular Ca(2+) concentrations stimulate the G-protein coupled receptor calcium-sensing receptor. Here we show that this stimulation induces the expression of biologically active early growth response protein 1 (Egr-1), a zinc finger transcription factor. Expression of a dominant-negative mutant of the ternary complex factor Ets-like protein-1 (Elk-1), a key transcriptional regulator of serum response element-driven gene transcription, prevented Egr-1 expression, indicating that Elk-1 or related ternary complex factors connect the intracellular signaling cascade elicited by activation of calcium-sensing receptors with transcription of the Egr-1 gene. These data were corroborated by the fact that stimulation of calcium-sensing receptors increased the transcriptional activation potential of Elk-1. In addition, activator protein-1 (AP-1) transcriptional activity was significantly elevated after the stimulation of calcium-sensing receptors. The expression of a dominant-negative mutant of Elk-1 reduced c-Fos expression and prevented the up-regulation of AP-1 activity as a result of calcium-sensing receptor stimulation, indicating that ternary complex factors control both Egr-1- and AP-1-regulated transcription. In addition, AP-1 activity was reduced after the expression of a dominant-negative mutant of c-Jun in cells expressing an activated calcium-sensing receptor. Stimulus-transcription coupling leading to the up-regulation of Egr-1 and AP-1 controlled transcription in cells expressing calcium-sensing receptors required the protein kinases Raf and ERK, whereas the overexpression of MAPK phosphatase-1 interrupted the signaling cascade connecting calcium-sensing receptor stimulation with transcription of Egr-1 and AP-1 controlled genes. The fact that calcium-sensing receptor stimulation activates the transcription factors Egr-1, Elk-1, and AP-1 indicates that regulation of gene transcription is an integral part of calcium-sensing receptor induced signaling.

Functional characterization of the matrix metalloproteinase-1 cigarette smoke-responsive region and association with the lung health study

BACKGROUND

Prior studies have demonstrated that the distal 1.5 kb of the MMP-1 promoter is fundamental in directing the induction of the MMP-1 gene by cigarette smoke.

METHODS

To characterize the genetic variants in the MMP-1 cigarette smoke-responsive element, deep re-sequencing of this element was performed on DNA samples from participants in the Lung Health Study. Furthermore, evidence of Sp1 binding to the MMP-1 promoter was assessed using chromatin immunoprecipitation assays and the influence of cigarette smoke exposure on this interaction was evaluated in cultured human small airway epithelial cells.

RESULTS

Ten polymorphisms (four novel) were detected in the cigarette smoke-responsive element. Chromatin immunoprecipitation assays to assess the protein-DNA interactions at Sp1 sites in the MMP-1 promoter showed increased binding to the Sp1 sites in the cigarette smoke-responsive element in small airway epithelial cells treated with cigarette smoke extract. In contrast, a Sp1 site outside of the element exhibited the opposite effect. None of the polymorphisms were more prevalent in the fast decliners versus the slow decliners (fast decliners = mean -4.14% decline in FEV1% predicted per year vs. decline in FEV1% predicted per year).

CONCLUSIONS

Sequencing analyses identified four novel polymorphisms within the cigarette smoke-responsive element of the MMP-1 promoter. This study identifies functional activity within the cigarette smoke-responsive element that is influenced by cigarette smoke and examines this region of the promoter within a small patient population.

Immediate-early transcriptional response to angiotensin II in human adrenocortical cells

Angiotensin II binds to the angiotensin II receptors type 1 (AT1 receptors) in adrenocortical cells and triggers an intracellular signaling cascade leading to changes in the gene expression pattern. Here, we show that stimulation with angiotensin II induces the expression of biologically active early growth response (Egr)-1, a zinc finger transcription factor, in human H295R adrenocortical cells. Expression of a dominant-negative mutant of the ternary complex factor Elk-1, a key transcriptional regulator of serum response element-driven gene transcription, prevented Egr-1 expression in angiotensin II-stimulated H295R cells, indicating that Ets-like protein-1 (Elk-1) or related ternary complex factors connect the intracellular signaling cascade elicited by activation of AT1 receptors with transcription of the Egr-1 gene. These data were corroborated by the fact that angiotensin II stimulation increased the transcription activation potential of Elk-1. In addition, activator protein-1 transcriptional activity was significantly elevated in angiotensin II-treated H295R cells. Expression of c-Jun and c-Fos was increased as well as the transcription activation potential of c-Fos. Expression of a dominant-negative mutant of Elk-1 reduced c-Fos expression in angiotensin II-stimulated adrenocortical cells, suggesting that the serum response element within the c-Fos promoter functions as an angiotensin II-response element. Expression of a dominant-negative mutant of c-Jun reduced activator protein-1 activity in angiotensin II-stimulated adrenocortical cells and reduced the up-regulation of c-Jun after angiotensin II stimulation. Thus, c-Jun regulates its own expression in adrenocortical cells. Together, the data show that angiotensin II stimulation activates the transcription factors Egr-1, Elk-1, c-Jun, and c-Fos in adrenocortical cells, leading to stimulus-dependent changes in the gene expression pattern.

Fank1 interacts with Jab1 and regulates cell apoptosis via the AP-1 pathway

Regulation of apoptosis at various stages of differentiation plays an important role in spermatogenesis. Therefore, the identification and characterisation of highly expressed genes in the testis that are involved in apoptosis is of great value to delineate the mechanism of spermatogenesis. Here, we reported that Fank1, a novel gene highly expressed in testis, functioned as an anti-apoptotic protein that activated the activator protein 1 (AP-1) pathway. We found that Jab1 (Jun activation domain-binding protein 1), a co-activator of AP-1, specifically interacted with Fank1. Reporter analyses showed that Fank1 activated AP-1 pathway in a Jab1-dependent manner. Fank1 overexpression also increased the expression and activation of endogenous c-Jun. Further study showed that Fank1 inhibited cell apoptosis by upregulating and activating endogenous c-Jun and its downstream target, Bcl-3. This process was shown to be Jab1 dependent. Taken together, our results indicated that by interacting with Jab1, Fank1 could suppress cell apoptosis by activating the AP-1-induced anti-apoptotic pathway.

The role of manganese superoxide dismutase in skin cancer

Recent studies have shown that antioxidant enzyme expression and activity are drastically reduced in most human skin diseases, leading to propagation of oxidative stress and continuous disease progression. However, antioxidants, an endogenous defense system against reactive oxygen species (ROS), can be induced by exogenous sources, resulting in protective effects against associated oxidative injury. Many studies have shown that the induction of antioxidants is an effective strategy to combat various disease states. In one approach, a SOD mimetic was applied topically to mouse skin in the two-stage skin carcinogenesis model. This method effectively reduced oxidative injury and proliferation without interfering with apoptosis. In another approach, Protandim, a combination of 5 well-studied medicinal plants, was given via dietary administration and significantly decreased tumor incidence and multiplicity by 33% and 57%, respectively. These studies suggest that alterations in antioxidant response may be a novel approach to chemoprevention. This paper focuses on how regulation of antioxidant expression and activity can be modulated in skin disease and the potential clinical implications of antioxidant-based therapies.

Redox-control of matrix metalloproteinase-1: a critical link between free radicals, matrix remodeling and degenerative disease

Many degenerative disease processes associated with aging result from enhanced extracellular matrix (ECM) breakdown. Concomitant with aberrant matrix destruction are alterations in levels of reactive oxygen species (ROS) generating and detoxification systems. ROS function as second messengers due to their ability to react with wide range of biomolecules resulting in modification of an array of signaling networks. ROS can activate upstream kinases (MKK) responsible for MAPK activation and restrict the activity of their inhibitory phosphatases. Here we focus on the redox-sensitive signaling components that control the expression of MMP-1, which is largely responsible for maintaining ECM homeostasis. Numerous disease processes are associated with shifts in steady state ROS levels that influence overall ECM degradation. This review highlights the redox-sensitive regulatory signals that control the expression of the primary initiating protease MMP-1 and provides strong rational for the use of antioxidant based therapies for treatment of degenerative disorders associated with aberrant matrix destruction.

Wnt5a signaling is involved in the aggressiveness of prostate cancer and expression of metalloproteinase

Wnt5a is a representative ligand that activates the beta-catenin-independent pathway in Wnt signaling. Although it has been reported that abnormal activation of the Wnt/beta-catenin-dependent pathway is often observed in human prostate cancer, the involvement of the beta-catenin-independent pathway in this cancer is unclear. Abnormal expression of Wnt5a and beta-catenin was observed in 27 (28%) and 49 (50%) of 98 prostate cancer cases, respectively, by immunohistochemical analyses. Simultaneous expression of Wnt5a and beta-catenin was observed in only five cases, suggesting their exclusive expression. The positive detection of Wnt5a was correlated with high Gleason scores and biochemical relapse of prostate cancer, but that of beta-catenin was not. Knockdown and overexpression of Wnt5a in human prostate cancer cell lines reduced and stimulated, respectively, their invasion activities, and the invasion activity required Frizzled2 and Ror2 as Wnt receptors. Wnt5a activated Jun-N-terminal kinase through protein kinase D (PKD) and the inhibition of PKD suppressed Wnt5a-dependent cell migration and invasion. In addition, Wnt5a induced the expression of metalloproteinase-1 through the recruitment of JunD to its promoter region. These results suggest that Wnt5a promotes the aggressiveness of prostate cancer and that its expression is involved in relapse after prostatectomy.

Induction of MMP-1 (collagenase-1) by relaxin in fibrocartilaginous cells requires both the AP-1 and PEA-3 promoter sites

OBJECTIVES - Relaxin induces the matrix metalloproteinase MMP-1 (collagenase-1) in TMJ fibrocartilaginous cells, and this response is potentiated by beta-estradiol. We identified the MMP-1 promoter sites and transcription factors that are induced by relaxin with or without beta-estradiol in fibrocartilaginous cells. MATERIAL AND METHODS - Early passage cells were transiently transfected with the pBLCAT2 plasmid containing specific segments of the human MMP-1 promoter regulating the chloramphenicol acyl transferase (CAT) gene and co-transfected with a plasmid containing the beta-galactosidase gene. The cells were cultured in serum-free medium alone or medium containing 0.1 ng/ml relaxin, or 20 ng/ml beta-estradiol or both hormones, and lysates assayed for CAT and beta-galactosidase activity. RESULTS - Cells transfected with the -1200/-42 or -139/-42 bp MMP-1 promoter-reporter constructs showed 1.5-fold and 3-fold induction of CAT by relaxin in the absence or presence of beta-estradiol, respectively. Relaxin failed to induce CAT in the absence of the -137/-69 region of the MMP-1 promoter, which contains the AP-1-and PEA3-binding sites. Using wild type or mutated minimal AP-1 and PEA-3 promoters we found that both these promoter sites are essential for the induction of MMP-1 by relaxin. The mRNAs for transcription factors c-fos and c-jun, which together form the AP-1 heterodimer, and Ets-1 that modulates the PEA-3 site, were upregulated by relaxin or beta-estradiol plus relaxin. CONCLUSION - These studies show that both the AP-1 and PEA-3 promoter sites are necessary for the induction of MMP-1 by relaxin in fibrocartilaginous cells.

Induced Accumulation of Polyubiquitin Gene Transcripts in HeLa Cells after UV-irradiation and TPA-treatment

There are three species of ubiquitin gene transcripts in HeLa cells, termed UbA (approximately 0.7 kb), UbB (approximately 1.1 kb) and UbC (approximately 2.5 kb). In the present report, the UbC transcript was shown to accumulate up to 2.5-fold after irradiation with UV light or treatment with the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA). The kinetic analysis indicated that the induced accumulation of UbC was rapid and transient; maximal accumulation of UbC was induced at 2.5 h after UV irradiation or 3 h after TPA treatment. Inhibition of a de novo protein synthesis by cycloheximide did not repress the induction of UbC after treatment with UV light and TPA. On the other hand, induction of UbA and UbB, in most cases, was not observed. UV-inducibility of human ubiquitin conjugating enzyme, E2(17k), was also tested. E2(17k) is a protein with high sequence similarity to the product of yeast DNA repair gene, RAD6. While the RAD6 gene has been reported to be inducible by UV light, no change in E2(17k) gene transcript was observed after UV irradiation.

Lipopolysaccharide-induced expression of matrix metalloproteinases in human monocytes is suppressed by IFN-gamma via superinduction of ATF-3 and suppression of AP-1

Matrix metalloproteinases (MMPs) are induced during inflammatory responses and are important for immune regulation, angiogenesis, wound healing, and tissue remodeling. Expression of MMPs needs to be tightly controlled to avoid excessive tissue damage. In this study, we investigated the regulation of MMP expression by inflammatory factors in primary human monocytes and macrophages. IFN-gamma, which augments inflammatory cytokine production in response to macrophage-activating factors such as TLR ligands, instead broadly suppressed TLR-induced MMP expression. Inhibition of MMP expression was dependent on STAT1 and required de novo protein synthesis. IFN-gamma strongly enhanced TLR-induced expression of the transcriptional repressor activating transcription factor (ATF-3) in a STAT1-dependent manner, which correlated with recruitment of ATF-3 to the endogenous MMP-1 promoter as detected by chromatin immunoprecipitation assays. RNA interference experiments further supported a role for ATF-3 in suppression of MMP-1 expression. In addition, IFN-gamma suppressed DNA binding by AP-1 transcription factors that are known to promote MMP expression and a combination of supershift, RNA interference and overexpression experiments implicated AP-1 family member Fra-1 in the regulation of MMP-1 expression. These results define an IFN-gamma-mediated homeostatic loop that limits the potential for tissue damage associated with inflammation, and identify transcriptional factors that regulate MMP expression in myeloid cells in inflammatory settings.

Expression of the transcriptional repressor ATF3 in gonadotrophs is regulated by Egr-1, CREB, and ATF2 after gonadotropin-releasing hormone receptor stimulation

Stimulation of GnRH receptors enhances expression of activating transcription factor (ATF) 3 in a pituitary gonadotroph cell line. The signaling pathway requires elevated cytosolic Ca2+ levels and activation of ERK and c-Jun N-terminal protein kinase. The signaling cascade was blocked by overexpression of either MAPK phosphatase (MKP)-1 or MAPK phosphatase-5 that dephosphorylate nuclear ERK and c-Jun N-terminal protein kinase. In addition, ATF3 biosynthesis was impaired after lentiviral-mediated expression of a constitutively active mutant of calcineurin A. Thus, MKP-1, MKP-5, and calcineurin may function as shut-off devices for GnRH receptor signaling. Expression of dominant-negative mutants of early growth response protein (Egr)-1, cAMP response element binding protein (CREB), and ATF2 blocked the biosynthesis of ATF3, indicating that these transcription factors connect the intracellular signaling cascade elicited by activation of GnRH receptors with transcription of the ATF3 gene. This view was corroborated by chromatin immunoprecipitation experiments revealing that Egr-1 and the phosphorylated forms of CREB and ATF2 bound to the 5'-upstream region of the ATF3 gene in buserelin-stimulated gonadotrophs. Together the data indicate that the ATF3 gene is a bona fide target gene of Egr-1, CREB, and ATF2 in gonadotrophs. Moreover, we show that in gonadotrophs ATF3 bound to its own promoter under physiological conditions. The analysis of a lentiviral-transmitted ATF3 promoter/luciferase reporter gene, embedded into the chromatin of the cells, revealed that ATF3 blocked the activity of its own promoter. We additionally identified the chromogranin B gene as bona fide target gene of ATF3 in gonadotrophs.

Fra-1 regulates vimentin during Ha-RAS-induced epithelial mesenchymal transition in human colon carcinoma cells

The process of epithelial mesenchymal transition, whereby cells acquire molecular alterations and fibroblastic features, is a fundamental process of embryogenesis and cancer invasion/metastasis. The mechanisms responsible for epithelial mesenchymal transition remain elusive. Human tumors frequently establish constitutively activated RAS signaling, which contributes to the malignant phenotype. In an effort to dissect distinct RAS isoform specific functions, we previously established human colon cell lines stably overexpressing activated Harvey-RAS (Ha-RAS) and Kirsten-RAS (Ki-RAS). Using these, we observed that only oncogenic Ha-RAS overexpression resulted in morphologic and molecular changes suggestive of epithelial to mesenchymal transition. We showed that vimentin, a key molecule of epithelial mesenchymal transition, was differentially regulated between Ha-RAS and Ki-RAS leading to a Ha-RAS specific induction of a migratory phenotype and eventually epithelial to mesenchymal transition. We demonstrated that the AP-1 sites in vimentin promoter could be involved in this regulation. A potential role of FRA-1 was suggested in the regulation of vimentin during the Ha-RAS-induced epithelial to mesenchymal transition, in association with colon cell migration. Our results therefore propose that in colon cells, the induction of epithelial mesenchymal transition by oncogenic Ha-RAS could occur through the overexpression of proteins like FRA-1 and vimentin.

Natural aging, expression of fibrosis-related genes and collagen deposition in rat lung

Aging lung is characterized by morpho-structural modifications, including progressive fibrosis, that lead to an altered function. Here we provide a comprehensive description of lung collagen expression and metabolism during natural aging of rats. Peribronchial collagen increased significantly in the oldest animals (p=0.05 2- vs. 6- and 19-month-old rats), as a consequence of Collagen-I and Collagen-III (COL-I, COL-III) protein accumulation (p<0.05 in 6-, 12- and 19-month-old rats versus the youngest). No changes in fibronectin (FN) protein expression and in COL-III and transforming grow factor beta-1 (TGFbeta-1) mRNA expression were observed. Conversely the transcription activity of the COL-I gene was overexpressed in the oldest animals (p<0.05). In the aged rats, the activity of lung matrix metalloproteinases (MMP), MMP-1 and MMP-2, dropped significantly (p<0.05), whilst MMP-9 levels were slightly decreased. These changes were associated with a concomitant increase of tissue inhibitors of MMP (TIMP-1 and TIMP-2). All together, these results suggest that, during natural aging, collagen accumulation in the lung and its progressive fibrosis are mainly due to a reduced proteolytic activity of MMP, in which TIMP-1 and -2 seem to be the major regulating factors.

Cytokines

During physiological and pathological skeletal remodelling, immune cells and stromal fibroblasts near active bone-forming and bone-resorbing surfaces might modulate the functions of skeletal tissue cells. Osteoblasts, osteoclasts and their progenitor cells are the probable direct targets of these effector cells (e.g. lymphocytes and monocytes) which act through direct contact or the release of soluble ligands (e.g. interleukin 1 or tumour necrosis factor, lymphotoxins, transforming growth factors). These cytokines bind to specific cellular receptors, resulting in changes in the form and function of the target bone cells and variable activation of genes coding for extracellular matrix proteins and proteinases which are responsible for remodelling the matrix. The synthesis and release of eicosanoids such as prostaglandins (e.g. PGE2) are frequent associated events. PGE2, in turn, affects several functions of the skeletal tissue cells as well as the lymphocytes and monocytes in their environment. The mesenchymal cells may also be induced to release ligands such as colony-stimulating factors, other cellular products or hormones resulting in a system of feedback and amplification loops. The cellular responses are thus subject to multiple controls not only determined by these ligands acting on their respective receptors but also by the pathways of signal transduction and how they, in turn, are influenced by interactions with molecules within the cells.

Different domains of the transcription factor ELF3 are required in a promoter-specific manner and multiple domains control its binding to DNA

Elf3 is an epithelially restricted member of the ETS transcription factor family, which is involved in a wide range of normal cellular processes. Elf3 is also aberrantly expressed in several cancers, including breast cancer. To better understand the molecular mechanisms by which Elf3 regulates these processes, we created a large series of Elf3 mutant proteins with specific domains deleted or targeted by point mutations. The modified forms of Elf3 were used to analyze the contribution of each domain to DNA binding and the activation of gene expression. Our work demonstrates that three regions of Elf3, in addition to its DNA binding domain (ETS domain), influence Elf3 binding to DNA, including the transactivation domain that behaves as an autoinhibitory domain. Interestingly, disruption of the transactivation domain relieves the autoinhibition of Elf3 and enhances Elf3 binding to DNA. On the basis of these studies, we suggest a model for autoinhibition of Elf3 involving intramolecular interactions. Importantly, this model is consistent with our finding that the N-terminal region of Elf3, which contains the transactivation domain, interacts with its C terminus, which contains the ETS domain. In parallel studies, we demonstrate that residues flanking the N- and C-terminal sides of the ETS domain of Elf3 are crucial for its binding to DNA. Our studies also show that an AT-hook domain, as well as the serine- and aspartic acid-rich domain but not the pointed domain, is necessary for Elf3 activation of promoter activity. Unexpectedly, we determined that one of the AT-hook domains is required in a promoter-specific manner.

Bone protection by estrens occurs through non-tissue-selective activation of the androgen receptor

The use of estrogens and androgens to prevent bone loss is limited by their unwanted side effects, especially in reproductive organs and breast. Selective estrogen receptor modulators (SERMs) partially avoid such unwanted effects, but their efficacy on bone is only moderate compared with that of estradiol or androgens. Estrens have been suggested to not only prevent bone loss but also exert anabolic effects on bone while avoiding unwanted effects on reproductive organs. In this study, we compared the effects of a SERM (PSK3471) and 2 estrens (estren-alpha and estren-beta) on bone and reproductive organs to determine whether estrens are safe and act via the estrogen receptors and/or the androgen receptor (AR). Estrens and PSK3471 prevented gonadectomy-induced bone loss in male and female mice, but none showed true anabolic effects. Unlike SERMs, the estrens induced reproductive organ hypertrophy in both male and female mice and enhanced MCF-7 cell proliferation in vitro. Estrens directly activated transcription in several cell lines, albeit at much higher concentrations than estradiol or the SERM, and acted for the most part through the AR. We conclude that the estrens act mostly through the AR and, in mice, do not fulfill the preclinical efficacy or safety criteria required for the treatment or prevention of osteoporosis.

Identification in human osteoarthritic chondrocytes of proteins binding to the novel regulatory site AGRE in the human matrix metalloprotease 13 proximal promoter

OBJECTIVE

Matrix metalloprotease 13 (MMP-13) plays a major role in osteoarthritic (OA) processes. We previously identified the AG-rich element (AGRE) regulatory site (GAAAAGAAAAAG) in the proximal promoter of this gene. Electrophoretic mobility shift assays (EMSAs) done with nuclear extracts from OA chondrocytes showed the presence of 2 AGRE protein-binding complexes, the formation of which depended on the pathophysiologic state (high or low) of the cells; the low OA (L-OA) chondrocytes have low MMP-13 basal levels and high interleukin-1beta (IL-1beta) inducibility, and the high OA (H-OA) chondrocytes have high MMP-13 basal levels and low IL-1beta inducibility. In this study, we sought to determine the importance of individual AGRE bases in promoter activity and to identify AGRE binding proteins from L-OA and H-OA chondrocyte complexes.

METHODS

Promoter activity was determined following transient transfection into human OA chondrocytes. AGRE binding proteins were identified by mass spectroscopy.

RESULTS

Individual mutations of the AGRE site differentially modulated promoter activity, indicating that the intact AGRE site is required for optimal MMP-13 expression. Damage-specific DNA binding protein 1 (DDB-1) was identified in the L-OA chondrocyte-binding complex. EMSA experiments performed with the mutation of the left AGRE site (GTGCTGAAAAAG) and nuclear extracts of L-OA chondrocytes reproduced the pattern seen in the H-OA chondrocytes. Mass spectroscopy identified p130cas as one of the proteins in this complex. Supershift experiments showed the presence of p130cas and nuclear matrix transcription factor 4 (NMP-4) in the wild-type AGRE/H-OA chondrocyte complex.

CONCLUSION

These data suggest that the binding of p130(cas) and NMP-4 to the AGRE site regulates MMP-13 expression and may trigger the change in human chondrocytes from the L-OA state to the H-OA state.

Differential regulation of matrix degrading enzymes in a TNFalpha-induced model of nucleus pulposus tissue degeneration

Intervertebral disc degeneration occurs commonly and is linked to persistent back pain and the development of disc herniation. The mechanisms responsible for tissue catabolism have not yet been fully elucidated. Previously we characterized an in vitro model of TNFalpha-induced nucleus pulposus degeneration, which demonstrates decreased expression of matrix macromolecules, increased expression of matrix degrading enzymes, and the activation of aggrecanase-mediated proteoglycan degradation [Seguin, C.A., Pilliar, R.M., Roughley, P.J., and Kandel, R.A. 2005. Tumor necrosis factor-alpha modulates matrix production and catabolism in nucleus pulposus tissue. Spine 30: 1940-1948]. This study explores the intracellular pathways activated during TNFalpha-induced matrix degradation. We demonstrate that in nucleus pulposus cells, the p38 and JNK pathways regulate induction of MMP-1 and -3; p38, JNK, and NF-kappaB regulate the induction of MMP-13; and ERK regulates the up-regulation of MT1-MMP mRNA in response to TNFalpha. Induction of ADAMTS-4 and -5 mRNA occurred downstream of NF-kappaB activation. Depletion of tissue proteoglycans was mediated by ERK and NF-kappaB-dependent "aggrecanase" activity, suggesting MT1-MMP and ADAMTS-4 and -5 as effectors of TNFalpha-induced tissue catabolism.

Avian MyoD and c-Jun coordinately induce transcriptional activity of the 3,5,3'-triiodothyronine nuclear receptor c-ErbAalpha1 in proliferating myoblasts

Although physical interactions with other receptors have been reported, heterodimeric complexes of T(3) nuclear receptors (TR) with retinoid X receptors (RXRs) are considered as major regulators of T(3) target gene expression. However, despite the potent T(3) influence in proliferating myoblasts, RXR isoforms are not expressed during proliferation, raising the question of the nature of the complex involved in TRalpha transcriptional activity. We have previously established that c-Jun induces TRalpha1 transcriptional activity in proliferating myoblasts not expressing RXR. This regulation is specific to the muscle lineage, suggesting the involvement of a muscle-specific factor. In this study, we found that MyoD expression in HeLa cells stimulates TRalpha1 activity, an influence potentiated by c-Jun coexpression. Similarly, in the absence of RXR, MyoD or c-Jun overexpression in myoblasts induces TRalpha1 transcriptional activity through a direct repeat 4 or an inverted palindrome 6 thyroid hormone response element. The highest rate of activity was recorded when c-Jun and MyoD were coexpressed. Using c-Jun-negative dominants, we established that MyoD influence on TRalpha1 activity needs c-Jun functionality. Furthermore, we demonstrated that TRalpha1 and MyoD physically interact in the hinge region of the receptor and the transactivation and basic helix loop helix domains of MyoD. RXR expression (spontaneously occurring at the onset of myoblast differentiation) in proliferating myoblasts abrogates these interactions. These data suggest that in the absence of RXR, TRalpha1 transcriptional activity in myoblasts is mediated through a complex including MyoD and c-Jun.

Novel functions of intracellular IL-1ra in human dermal fibroblasts: implications in the pathogenesis of fibrosis

Intracellular IL-1 receptor antagonist (icIL-1ra) is reportedly involved in functions independent of blocking IL-1 receptor signaling. Fibroblasts derived from the involved skin of patients with systemic sclerosis (SSc) are predominantly of the myofibroblast phenotype, with higher levels of icIL-1ra compared to normal skin fibroblasts. We examined the effect of overexpression of icIL-1ra on the phenotype and function of normal fibroblasts with respect to the expression of alpha smooth muscle actin (alpha-SMA), a specific marker for myofibroblasts, and plasminogen activator inhibitor (PAI), a protein involved in fibrogenesis and expressed at higher levels in myofibroblasts, and the production of collagenase (matrix metalloproteinase-1 (MMP-1)), the major enzyme involved in the degradation of native collagen in the skin. Normal human foreskin fibroblasts overexpressing icIL-1ra showed higher levels of alpha-SMA and PAI and had lower levels of collagenase and MMP-1 mRNA induced by inflammatory cytokines. By contrast, levels of mRNA for tissue inhibitor of metalloproteinase-1 in the transfected cells were not different from the control cells. Pretreatment of the ic-IL-1ra-transfected cells with antisense oligonucleotide directed against the mRNA of icIL-1ra restored MMP-1 expression induced by stimulation with IL-1beta. Our data indicate novel functions for icIL-1ra, which might be relevant to the genesis of fibrotic diseases such as SSc.

The AP-1 transcription factor regulates postnatal mammary gland development

The AP-1 transcription factor is activated by multiple growth factors that are critical regulators of breast cell proliferation. We previously demonstrated that AP-1 blockade inhibits breast cancer cell growth in vitro. Yet a specific role of AP-1 in normal mammary gland development has not been studied. Using a bi-transgenic mouse expressing an inducible AP-1 inhibitor (Tam67), we found that the AP-1 factor regulates postnatal proliferation of mammary epithelial cells. Mammary epithelial proliferation was significantly reduced after AP-1 blockade in adult, prepubertal, pubertal, and hormone-stimulated mammary glands. In pubertal mice, mammary cell proliferation was greatly reduced, and the cells that did proliferate failed to express Tam67. We also observed structural changes such as suppressed branching and budding, reduced gland tree size, and less fat pad occupancy in developing mammary glands after AP-1 blockade. We further demonstrated that Tam67 suppressed the expression of AP-1-dependent genes (TIMP-1, vimentin, Fra-1, and fibronectin) and the AP-1-dependent growth regulatory genes (cyclin D1 and c-myc) in AP-1-blocked mammary glands. We therefore conclude that AP-1 factor is a pivotal regulator of postnatal mammary gland growth and development.

Up-regulation of tyrosine hydroxylase gene transcription by tetradecanoylphorbol acetate is mediated by the transcription factors Ets-like protein-1 (Elk-1) and Egr-1

Tyrosine hydroxylase is the rate-limiting enzyme in the biosynthesis of catecholamines. Expression of the tyrosine hydroxylase gene is regulated at the transcriptional level by extracellular signalling molecules, including epidermal growth factor (EGF), nerve growth factor (NGF) and glucocorticoids. We have analysed the stimulation of tyrosine hydroxylase gene transcription by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) in noradrenergic locus coeruleus-like CATH.a cells and observed a striking enhancement of the transcriptional activation potential of the ternary complex factor Ets-like protein-1 (Elk-1), a key transcriptional regulator of serum response element-driven gene transcription. Likewise, TPA strongly up-regulated the biosynthesis of the transcription factor Egr-1 via distal serum response elements within the Egr-1 5'-flanking region. Subsequently, enhancement of the transcriptional activation potential of Egr-1 was observed. Overexpression of Egr-1 was sufficient to activate transcription of a tyrosine hydroxylase promoter/reporter gene, corroborating the view that the tyrosine hydroxylase gene is a target gene of Egr-1. Expression of dominant-negative mutants of Elk-1 or Egr-1 impaired TPA-induced stimulation of a tyrosine hydroxylase promoter/reporter gene transcription. In contrast, dominant-negative mutants of the transcription factors activating transcription factor (ATF)-2, ATF4, cAMP response element-binding protein, c-Jun and CCAAT/enhancer binding protein (C/EBP) did not change TPA-induced tyrosine hydroxylase promoter activity, indicating that these proteins are not part of the TPA-mediated signalling cascade directed towards the tyrosine hydroxylase gene.

Inflammation-responsive transcription factors SAF-1 and c-Jun/c-Fos promote canine MMP-1 gene expression

Matrix metalloproteinase-1 (MMP-1) has been implicated in the pathogenesis of osteoarthritis (OA) due to its ability to degrade extracellular matrix component of the joint cartilage tissue that cushions the bone from frictional damage. Canine hip dysplasia, a developmental orthopedic disease which results in arthritic condition as is seen in human OA is an excellent system to study the involvement of MMP-1 in the pathogenesis of OA. To date, however, no report is available regarding canine MMP-1 promoter and the regulatory mechanism by which increased synthesis of MMP-1 protein might be regulated. To gain an insight, we have investigated the promoter region of canine MMP-1. MMP-1 synthesis in the resident cells of arthritic joints is regulated via two major cytokines, IL-1beta and TNF-alpha. By using a series of progressively deleted reporter constructs, multiple cytokine-responsive elements were identified in the proximal promoter region of canine MMP-1. These include DNA-binding elements of AP-1 and SAF-1 transcription factors. Mutation of AP-1 or SAF-1 element resulted in marked reduction in the cytokine responsiveness of MMP-1 promoter. We show that AP-1 and SAF-1 DNA-binding activities are increased in cytokine-stimulated cells as well as in osteoarthritic cartilage tissues. In correlation, immunohistochemical analysis indicated higher levels of MMP-1, SAF-1 and AP-1 proteins in osteoarthritic but not in the normal cartilage tissue. These results show that induction and activation of AP-1 and SAF-1 transcription factors are involved in the regulation of MMP-1 expression in the chondrocytes which could be used as therapeutic targets to combat pathogenesis of OA.

Stratifin-Induced Matrix Metalloproteinase-1 in Fibroblast Is Mediated by c-fos and p38 Mitogen-Activated Protein Kinase Activation

Previously, we have demonstrated that keratinocyte releasable stratifin, also known as 14-3-3 sigma protein, stimulates matrix metalloproteinase (MMP)-1 expression in dermal fibroblasts. In this study, we showed that stratifin induced fibroblast MMP-1 messenger ribonucleic acid (mRNA) and protein levels through p38 mitogen-activated protein kinase (MAPK). Our data indicated that treatment of dermal fibroblasts with stratifin resulted in rapid and transient upregulation of c-jun and c-fos mRNA levels. We also demonstrated that SB203580 (SB), a specific inhibitor of p38 MAPK activity, inhibited the activation of fibroblast MMP-1 mRNA expression by stratifin. Subsequently, western blot analysis revealed phosphorylation of p38 at 90 min after stratifin stimulation and this was decreased to approximately 50% of the maximum value by 120 min. Stratifin was demonstrated to increase MMP-1 protein levels starting at 4 h and reaching its peak at 12-24 h. Furthermore, SB significantly blocked the stratifin induction of MMP-1 protein levels (***p<0.005, n=3). Microarray analysis of stratifin-treated fibroblasts shows an increase in Elk4/Sap1 mRNA expression and this finding was confirmed by northern blot analysis. Our results indicate that stratifin markedly increase Elk4/Sap1 mRNA expression in a time-dependent fashion. In conclusion, stratifin stimulates fibroblast MMP-1 levels through the activation of c-fos and MAPK pathway.

Tadpole collagenase, the single parent of such a large family

This editorial review comments the development of the field of the matrix metalloproteinases that was initiated by the demonstration of the tadpole collagenase in 1962.

Histone deacetylase inhibitors suppress the induction of c-Jun and its target genes including COX-2

Cyclooxygenase-2 (COX-2) is considered to be a target for anticancer therapy. Histone deacetylase (HDAC) inhibitors exhibit antitumor activity, but the mechanisms of action are incompletely understood. We investigated whether HDAC inhibitors blocked AP-1-mediated activation of COX-2 transcription. Trichostatin A and suberoylanilide hydroxamic acid, two structurally related inhibitors of HDAC activity, blocked AP-1-mediated induction of COX-2 expression and prostaglandin E2 biosynthesis. Chromatin immunoprecipitation assays indicated that HDAC inhibitors suppressed c-Jun binding to the COX-2 promoter and thereby blocked transcription. The observed reduction in binding reflected reduced levels of c-Jun. HDAC inhibitors suppressed the induction of c-jun transcription by blocking the recruitment of the preinitiation complex (RNA polymerase II and TFIIB) to the c-jun promoter. HDAC3 but not HDAC1 or HDAC2 was required for AP-1-mediated stimulation of c-jun expression. Because HDAC inhibitors suppressed the induction of c-jun gene expression, resulting in reduced COX-2 transcription, it was important to determine whether other known AP-1 target genes were also modulated. Cyclin D1 and collagenase-1 are AP-1-dependent genes that have been implicated in carcinogenesis. HDAC inhibitors suppressed the induction of both cyclin D1 and collagenase-1 transcription by inhibiting the binding of c-Jun to the respective promoters. Taken together, these results suggest that HDAC inhibitors block the induction of c-jun transcription by inhibiting the recruitment of the preinitiation complex to the c-jun promoter. This led, in turn, to reduced expression of several activator protein-1-dependent genes (COX-2, cyclin D1, collagenase-1). These findings provide new insights into the mechanisms underlying the antitumor activity of HDAC inhibitors.

Transcriptional activation of the Egr-1 gene mediated by tetradecanoylphorbol acetate and extracellular signal-regulated protein kinase

Activation of extracellular signal-regulated protein kinase (ERK) triggers the biosynthesis of Egr-1, a zinc finger transcription factor. Likewise, the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) strongly upregulates Egr-1 biosynthesis. Here, we have analyzed the genetic elements involved in the regulation of Egr-1 gene transcription by ERK and TPA in human hepatoma cells. Expression experiments using mitogen-activated protein kinase phosphatase-1 or a dominant-negative mutant of the ternary complex factor Elk-1 revealed that the distal cluster of serum response elements is essential in the TPA-induced enhancement of Egr-1 promoter activity, encompassing two independent TPA-responsive elements. The CRE in the proximal Egr-1 promoter plays, if anything, only a marginal role in TPA-induced stimulus-transcription coupling of the Egr-1 gene. The fact that Egr-1 promoter/reporter gene transcription is upregulated by a constitutively active CREB mutant indicates that the CRE couples other signaling cascades via CREB to the Egr-1 gene.

Retinoic acid induced repression of AP-1 activity is mediated by protein phosphatase 2A in ovarian carcinoma cells

In previous studies we have shown that all-trans retinoic acid (atRA)-treatment of the atRA-sensitive ovarian carcinoma cell line CA-OV3 repressed AP-1 activity by about 50%, while a similar effect was not observed in the atRA-resistant ovarian carcinoma cell line, SK-OV3. These results suggested that the repression of AP-1 activity may be one of the mechanisms by which atRA inhibits the growth of atRA-sensitive CA-OV3 cells. In the present studies, we investigated further the molecular mechanism by which AP-1 activity is repressed by atRA. We show that the repression of AP-1 activity correlates with an increase in JunB protein expression and a decrease in N-terminal phosphorylation of c-Jun. The decrease in N-terminal phosphorylation of c-Jun does not appear to be modulated by JNK or ERK, since their protein expression patterns and kinase activity do not correlate with the repression of AP-1 activity following treatment with atRA. However, the activity of the protein phosphatase PP2A was found to increase 24 h following atRA treatment in CA-OV3 cells. Moreover, the catalytic subunit of PP2A was found to associate with c-Jun in vivo following atRA treatment. Since the inhibition of AP-1 activity following atRA treatment of CA-OV3 cells was abolished in the presence of specific PP2A inhibitors, it is likely that PP2A plays an important role in the atRA-induced repression of AP-1.

Analysis of Smad nucleocytoplasmic shuttling in living cells

Transforming growth factor β (TGF-β) signalling leads to phosphorylation and activation of receptor-regulated Smad2 and Smad3, which form complexes with Smad4 and accumulate in the nucleus. The Smads, however, do not seem to reside statically in the cytoplasm in the absence of signalling or in the nucleus upon TGF-β stimulation, but have been suggested to shuttle continuously between these cellular compartments in both the absence and presence of TGF-β. Here we investigate this nucleocytoplasmic shuttling in detail in living cells using fusions of Smad2 and Smad4 with enhanced GFP. We first establish that the GFPSmad fusions behave like wild-type Smads in a variety of cellular assays. We go on to demonstrate directly, using photobleaching experiments, that Smad2 and Smad4 shuttle between the cytoplasm and nucleus in both TGF-β-induced cells and in uninduced cells. In uninduced cells, GFPSmad2 is less mobile in the cytoplasm than is GFPSmad4, suggesting that it may be tethered there. In addition, we show that both GFPSmad2 and GFPSmad4 undergo a substantial decrease in mobility in the nucleus upon TGF-β stimulation, suggesting that active complexes of Smads are tethered in the nucleus, whereas unactivated Smads are more freely diffusible. We propose that regulated cytoplasmic and nuclear retention may play a role in determining the distribution of Smads between the cytoplasm and the nucleus in both uninduced cells and upon TGF-β induction.

Effect of cyclosporin A on human gingival fibroblast collagen turnover in relation to the development of gingival overgrowth: an in vitro study

In a significant number of cases (25-81%) immunosuppressant treatment with cyclosporin A (CsA) is associated with gingival overgrowth, seriously interfering with the functions of mastication and speech. In CsA-induced gingival enlargement, quantitative modifications of the extracellular matrix components occur, and collagen (COL) metabolism and matrix metalloproteinases (MMPs) have been suggested as being the main targets. Since the mechanisms at the basis of CsA-induced gingival overgrowth are not yet completely understood, our aim was to analyze the effect of CsA on COL turnover in cultured human gingival fibroblasts. Cultured human gingival fibroblasts from four healthy volunteers were incubated with CsA (800 ng/ml) or with its vehicle (VH) for variable intervals of time (24, 48, 72 h). Fibroblast morphology was studied by light and electron microscope. Collagen type I (COL-I), MMP-1, MMP-2, TIMP-1 and TGF-beta1 mRNA were determined by RT-PCR; COL-I and MMP-1 by dot blot, and MMP-2 by zymography. Our results evidenced an up-regulation of COL-I and TGF-beta1 gene expression 72 h after CsA treatment. MMP-1, MMP-2 and TIMP-1 mRNA levels are affected but not significantly. Protein analysis revealed COL-I increase at all the considered times and, 72 h after CsA treatment, reduced collagenolytic levels. Our data suggest that COL accumulation during CsA-induced gingival overgrowth may be mainly sustained by an altered COL-I degradation due to decreased MMP-1 activity. However, interindividual differences of collagenase levels after CsA treatment suggest that a genetic predisposition to develop gingival overgrowth may be relevant.