Multiple promoter elements are required for the stimulatory effect of insulin on human collagenase-1 gene transcription. Selective effects on activator protein-1 expression may explain the quantitative difference in insulin and phorbol ester action

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.

Insulin and epidermal growth factor suppress basal glucose-6-phosphatase catalytic subunit gene transcription through overlapping but distinct mechanisms

The G6Pase (glucose-6-phosphatase catalytic subunit) catalyses the final step in the gluconeogenic and glycogenolytic pathways, the hydrolysis of glucose-6-phosphate to glucose. We show here that, in HepG2 hepatoma cells, EGF (epidermal growth factor) inhibits basal mouse G6Pase fusion gene transcription. Several studies have shown that insulin represses basal mouse G6Pase fusion gene transcription through FOXO1 (forkhead box O1), but Stoffel and colleagues have recently suggested that insulin can also regulate gene transcription through FOXA2 (forkhead box A2) [Wolfrum, Asilmaz, Luca, Friedman and Stoffel (2003) Proc. Natl. Acad. Sci. 100, 11624-11629]. A combined GR (glucocorticoid receptor)-FOXA2 binding site is located between -185 and -174 in the mouse G6Pase promoter overlapping two FOXO1 binding sites located between (-188 and -182) and (-174 and -168). Selective mutation of the FOXO1 binding sites reduced the effect of insulin, whereas mutation of the GR/FOXA2 binding site had no effect on the insulin response. In contrast, selective mutation of the FOXO1 and GR/FOXA2 binding sites both reduced the effect of EGF. The effect of these mutations was additive, since the combined mutation of both FOXO1 and GR/FOXA2 binding sites reduced the effect of EGF to a greater extent than the individual mutations. These results suggest that, in HepG2 cells, GR and/or FOXA2 are required for the inhibition of basal G6Pase gene transcription by EGF but not insulin. EGF also inhibits hepatic G6Pase gene expression in vivo, but in cultured hepatocytes EGF has the opposite effect of stimulating expression, an observation that may be explained by a switch in ErbB receptor sub-type expression following hepatocyte isolation.

The MAPK pathway and HIF-1 are involved in the induction of the human PAI-1 gene expression by insulin in the human hepatoma cell line HepG2

Enhanced levels of plasminogen activator inhibitor-1 (PAI-1) are considered to be a risk factor for pathological conditions associated with hypoxia or hyperinsulinemia. The expression of the PAI-1 gene is increased by insulin in different cells, although, the molecular mechanisms behind insulin-induced PAI-1 expression are not fully known yet. Here, we show that insulin upregulates human PAI-1 gene expression and promoter activity in HepG2 cells and that mutation of the hypoxia-responsive element (HRE)-binding hypoxia-inducible factor-1 (HIF-1) abolished the insulin effects. Mutation of E-boxes E4 and E5 abolished the insulin-dependent activation of the PAI-1 promoter only under normoxia, but did not affect it under hypoxia. Furthermore, the insulin effect was associated with activation of HIF-1alpha via mitogen-activated protein kinases (MAPKs) but not PDK1 and PKB in HepG2 cells. Furthermore, mutation of a putative FoxO1 binding site which was supposed to be involved in insulin-dependent PAI-1 gene expression influenced the insulin-dependent activation only under normoxia. Thus, insulin-dependent PAI-1 gene expression might be regulated by the action of both HIF-1 and FoxO1 transcription factors.

Administration of pioglitazone in low-density lipoprotein receptor-deficient mice inhibits lesion progression and matrix metalloproteinase expression in advanced atherosclerotic plaques

Recent clinical trials have provided evidence that pioglitazone reduces cardiovascular events in patients with type 2 diabetes. However, the underlying mechanisms are not well understood. Because it has been well established that disruption of atherosclerotic plaques is a key event involved in acute myocardial infarction, we hypothesized that pioglitazone reduces cardiovascular events by stabilizing atherosclerotic lesions. In this study, we used an animal model to test our hypothesis. Low-density lipoprotein receptor-deficient (LDLR-/-) male mice were first fed a high-fat diet for 4 months to induce the formation of aortic atherosclerotic plaques and then treated with pioglitazone for the next 3 months. Analysis of atherosclerotic plaques at the end of the study showed that treatment with pioglitazone at 20 mg/kg/day reduced the progression of atherosclerotic plaques as compared to untreated mice. Furthermore, gene array analysis, quantitative real-time polymerase chain reaction, and immunohistochemical analysis showed that pioglitazone inhibited high-fat diet-induced upregulation of matrix metalloproteinase (MMP) expression. Finally, Sirius red staining showed that atherosclerotic lesions in mice receiving pioglitazone had higher collagen contents than those in untreated mice. This study demonstrated for the first time that administration of pioglitazone in LDLR-/- mice inhibited lesion progression and MMP expression in established atherosclerotic plaques and thus delineated a potential mechanism by which pioglitazone reduces cardiovascular events in patients with type 2 diabetes.

Balance between polyoma enhancing activator 3 and activator protein 1 regulates Helicobacter pylori-stimulated matrix metalloproteinase 1 expression

Helicobacter pylori infection and elevated expression of tissue matrix metalloproteinase 1 (MMP-1) are both associated with gastric cancer. We investigated the regulation of MMP-1 expression during H. pylori infection. Real-time reverse transcription-PCR was used to examine mucosal MMP-1 mRNA levels in 55 patients with gastric cancers and 61 control patients. Increased MMP-1 mRNA levels in the gastric mucosa and epithelial cells were observed in H. pylori infections in which both the cag pathogenicity island (PAI) and outer inflammatory protein A (OipA) were expressed. The combined induction of c-fos, c-jun, and polyoma enhancing activator-3 (pea-3) by H. pylori caused maximal increase in MMP-1 expression. Activation of the MMP-1 promoter by H. pylori involved occupation of the activator protein 1 (AP-1) sites at -72 and -181 and, surprisingly, vacancy of the -88 PEA-3 site. Electrophoretic mobility shift, supershift, and chromatin immunoprecipitation assays showed increased binding of c-Fos and c-Jun to the -72 and -181 AP-1 sites during H. pylori infection. Importantly, during wild-type H. pylori infection, we detected increased PEA-3 binding to the -72AP-1 site and decreased PEA-3 binding to the -88 PEA-3 site. However, during infection with the cag PAI and oipA mutants, PEA-3 binding to the -88 site was detected. MMP-1 and pea-3 activities are increased in gastric cancers. Maximal activation of MMP-1 transcription requires the cag PAI and OipA, which regulate AP-1 and PEA-3 binding. Thus, cag PAI and OipA provide a possible link between bacterial virulence factors and important host factors related to disease pathogenesis.

Transcriptional repression of MMP-1 by p21SNFT and reduced in vitro invasiveness of hepatocarcinoma cells

p21SNFT (21 kDa small nuclear factor isolated from T cells) is a human basic leucine zipper transcription factor that can repress AP-1-mediated transcription. We show here that overexpression of p21SNFT in HepG2 cells leads to repression of matrix metalloproteinase-1 by 70-80%. p21SNFT interacted with Jun at the matrix metalloproteinase-1 promoter -88 Ets/AP-1 enhancer element, where Jun is known to activate transcription via interaction with Fos and Ets proteins. When p21SNFT/Jun dimers bound the element in the presence of Ets, DNA was protected differently than when Fos was paired with Jun. The data suggest a difference in overall conformation between p21SNFT-containing and Fos-containing complexes that may be involved in the repression of matrix metalloproteinase-1 by p21SNFT. Overexpression of p21SNFT led to a reduction in invasiveness of HepG2 cells through type I collagen and reconstituted basement membrane, an effect similar to that obtained via direct immunodepletion of matrix metalloproteinase-1. The results indicate that the mechanism of repression of matrix metalloproteinase-1 by p21SNFT may be exploited in inhibiting pathological matrix remodeling during cancer progression in vivo.

Insulin suppresses collagenase stimulatory effect of stratifin in dermal fibroblasts

A delicate balance between synthesis and degradation of extracellular matrix (ECM) by matrix metalloproteinases (MMPs) is an essential feature of tissue remodeling. We have recently demonstrated that keratinocyte releasable stratifin, also known as 14-3-3 sigma protein, plays a critical role in modulating collagenase (MMP-1) mRNA expression in human dermal fibroblasts. In this study, we further characterized the collagenase stimulatory effect of stratifin in dermal fibroblasts and evaluated its effect in the presence and absence of insulin. Our data indicate that stratifin increases the expression of collagenase mRNA more than 20-fold in dermal fibroblasts, grown in either Dulbecco's modified Eagle's medium (DMEM) plus 2% or 10% fetal bovine serum (FBS). Collagenase stimulatory effect of stratifin was completely blocked, when fibroblasts were cultured in test medium consisting of 50% keratinocyte serum-free medium (KSFM) and 50% DMEM. The collagenase suppressive effect of test medium was directly proportional to the volume of KSFM used. As this medium contained insulin, we then evaluated the collagenase stimulatory effect of stratifin in dermal fibroblasts in the presence and absence of insulin. The results revealed that stratifin significantly increased the expression of collagenase mRNA/18S (*p < 0.05, n = 3) ratio, while insulin significantly decreased the expression of collagenase mRNA/18S (*p < 0.05, n = 3) ratio. The insulin inhibitory effect on collagenase mRNA expression was time and dose dependent. The maximal inhibitory effect of insulin was seen at 36 h post treatment. In conclusion, stratifin stimulates the expression of collagenase mRNA expression in dermal fibroblasts and this effect is suppressed by insulin treatment.

P53 down-regulates matrix metalloproteinase-1 by targeting the communications between AP-1 and the basal transcription complex

We have previously reported that human matrix metalloproteinase-1 (MMP1) is a p53 target gene subject to down-regulation (Sun et al. [1999]: J Biol Chem 274:11535-11540]. In the present study, we demonstrate that the down-regulation of the human -83MMP1 promoter fragment by p53 was abolished when the -72AP-1 site was eliminated and that a GAL4-cJun-mediated but not a GAL4-Elk1-mediated induction of pFR-luci was effectively inhibited by p53 suggesting an AP-1 dependent but AP-1 binding independent mechanism. Results from gel mobility shift assays were consistent with an AP-1 binding independent mechanism. We also demonstrate that both p300 and TATA box binding proteins cooperated with the transcription factor AP-1 to induce the promoter of MMP1; however, p53 only inhibited the p300-mediated induction of the MMP1 promoter and the inhibition was -72AP-1 dependent. Furthermore, the down-regulation of the MMP1 promoter and mRNA by p53 could be reversed by p300 and by a p53 binding p300 fragment that had no coactivator activity. Taken together, these results indicate that p53 down-regulates MMP1 mainly by disrupting the communications between the transactivator AP-1 and the basal transcriptional complex, which are partially mediated by p300. Finally, by using p53 truncated mutant constructs, we demonstrate that both the N-terminal activation domain and the C-terminal oligomerization domains of p53 were required for the down-regulation of MMP1 transcription.

The proximal islet-specific glucose-6-phosphatase catalytic subunit-related protein autoantigen promoter is sufficient to initiate but not maintain transgene expression in mouse islets in vivo

We have previously reported the discovery of an islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) that is predominantly expressed in islet beta-cells. IGRP has recently been identified as a major autoantigen in a mouse model of type 1 diabetes. The analysis of IGRP-chloramphenicol acetyltransferase (CAT) fusion gene expression in transiently transfected islet-derived hamster insulinoma tumor and betaTC-3 cells revealed that the promoter region located between -306 and +3 confers high-level reporter gene expression. To determine whether this same promoter region is sufficient to confer islet beta-cell-specific gene expression in vivo, it was ligated to a beta-galactosidase reporter gene, and transgenic mice expressing the resulting fusion gene were generated. In two independent founder lines, this -306 to +3 promoter region was sufficient to drive beta-galactosidase expression in newborn mouse islets, predominantly in beta-cells, which was initiated during the expected time in development, around embryonic day 12.5. However, unlike the endogenous IGRP gene, beta-galactosidase expression was also detected in the cerebellum. Moreover, beta-galactosidase expression was almost completely absent in adult mouse islets, suggesting that cis-acting elements elsewhere in the IGRP gene are required for determining appropriate IGRP tissue-specific expression and for the maintenance of IGRP gene expression in adult mice.

Differential regulation of islet-specific glucose-6-phosphatase catalytic subunit-related protein gene transcription by Pax-6 and Pdx-1

Islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) is selectively expressed in islet beta cells and is a major autoantigen in a mouse model of type I diabetes. The analysis of IGRP-chloramphenicol acetyltransferase (CAT) fusion gene expression through transient transfection of islet-derived betaTC-3 cells revealed that a promoter region, located between -273 and -254, is essential for high IGRP-CAT fusion gene expression. The sequence of this promoter region does not match that for any known islet-enriched transcription factor. However, data derived from gel retardation assays, a modified ligation-mediated polymerase chain reaction in situ footprinting technique and a SDS-polyacrylamide separation/renaturation procedure led to the hypothesis that this protein might be Pax-6, a conclusion that was confirmed by gel supershift assays. Additional experiments revealed a second non-consensus Pax-6 binding site in the -306/-274 IGRP promoter region. Pax-6 binding to these elements is unusual in that it appears to require both its homeo and paired domains. Interestingly, loss of Pax-6 binding to the -273/ -246 element is compensated by Pax-6 binding to the -306/-274 element and vice versa. Gel retardation assays revealed that another islet-enriched transcription factor, namely Pdx-1, binds four non-consensus elements in the IGRP promoter. However, mutation of these elements has little effect on IGRP fusion gene expression. Although chromatin immunoprecipitation assays show that both Pax-6 and Pdx-1 bind to the IGRP promoter within intact cells, in contrast to the critical role of these factors in beta cell-specific insulin gene expression, IGRP gene transcription appears to require Pax-6 but not Pdx-1.

Selective stimulation of G-6-Pase catalytic subunit but not G-6-P transporter gene expression by glucagon in vivo and cAMP in situ

We recently compared the regulation of glucose-6-phosphatase (G-6-Pase) catalytic subunit and glucose 6-phosphate (G-6-P) transporter gene expression by insulin in conscious dogs in vivo (Hornbuckle LA, Edgerton DS, Ayala JE, Svitek CA, Neal DW, Cardin S, Cherrington AD, and O'Brien RM. Am J Physiol Endocrinol Metab 281: E713-E725, 2001). In pancreatic-clamped, euglycemic conscious dogs, a 5-h period of hypoinsulinemia led to a marked increase in hepatic G-6-Pase catalytic subunit mRNA; however, G-6-P transporter mRNA was unchanged. Here, we demonstrate, again using pancreatic-clamped, conscious dogs, that glucagon is a candidate for the factor responsible for this selective induction. Thus glucagon stimulated G-6-Pase catalytic subunit but not G-6-P transporter gene expression in vivo. Furthermore, cAMP stimulated endogenous G-6-Pase catalytic subunit gene expression in HepG2 cells but had no effect on G-6-P transporter gene expression. The cAMP response element (CRE) that mediates this induction was identified through transient transfection of HepG2 cells with G-6-Pase catalytic subunit-chloramphenicol acetyltransferase fusion genes. Gel retardation assays demonstrate that this CRE binds several transcription factors including CRE-binding protein and CCAAT enhancer-binding protein.

Up-regulation of matrix metalloproteinase-1 expression in U937 cells by low-density lipoprotein-containing immune complexes requires the activator protein-1 and the Ets motifs in the distal and the proximal promoter regions

We reported previously that low-density lipoprotein (LDL)-containing immune complexes (LDL-IC) stimulated matrix metalloproteinase-1 (MMP-1) expression in U937 histiocytes through Fc gamma receptor (FcgammaR)-mediated extracellular signal-regulated kinase pathway. The present study has explored the transcriptional mechanisms involved in the stimulation. Deletion analysis showed that LDL-IC stimulated MMP-1 promoter activity in cells transfected with the Construct 1 that contained a 4,334-bp MMP-1 promoter fragment, but had no effect in cells transfected with other constructs that had shorter MMP-1 promoter (2685-bp or less), suggesting that cis-acting elements located between -4334 and -2685 are required for the promoter stimulation. The mutation study further indicated that the activator protein-1 (AP-1) (-3471) or Ets (-3836) motifs in this distal region were essential for the LDL-IC-stimulated MMP-1 expression. Moreover, although above deletion analysis showed that LDL-IC did not stimulate MMP-1 promoter activity in cells transfected with constructs that contained the proximal AP-1 (-72) and Ets (-88) in the promoter fragments that are 2685-bp or less, the mutations of the -72 AP-1 or the -88 Ets motif in the construct 1 abolished the stimulation of MMP-1 expression by LDL-IC, suggesting that a long promoter sequence is required for the -72 AP-1 and -88 Ets motifs to be involved in the stimulation. Finally, electrophoretic mobility shift assay showed that LDL-IC stimulated the activities of transcription factors AP-1 and Ets. In conclusion, the present study shows that both the distal and proximal AP-1 and Ets motifs are required for LDL-IC-stimulated MMP-1 expression in U937 histiocytes.

Upstream stimulatory factor (USF) and neurogenic differentiation/beta-cell E box transactivator 2 (NeuroD/BETA2) contribute to islet-specific glucose-6-phosphatase catalytic-subunit-related protein (IGRP) gene expression

Islet-specific glucose-6-phosphatase (G6Pase) catalytic-subunit-related protein (IGRP) is a homologue of the catalytic subunit of G6Pase, the enzyme that catalyses the final step of the gluconeogenic pathway. The analysis of IGRP-chloramphenicol acetyltransferase (CAT) fusion-gene expression through transient transfection of islet-derived beta TC-3 cells revealed that multiple promoter regions, located between -306 and -97, are required for maximal IGRP-CAT fusion-gene expression. These regions correlated with trans -acting factor-binding sites in the IGRP promoter that were identified in beta TC-3 cells in situ using the ligation-mediated PCR (LMPCR) footprinting technique. However, the LMPCR data also revealed additional trans -acting factor-binding sites located between -97 and +1 that overlap two E-box motifs, even though this region by itself conferred minimal fusion-gene expression. The data presented here show that these E-box motifs are important for IGRP promoter activity, but that their action is only manifest in the presence of distal promoter elements. Thus mutation of either E-box motif in the context of the -306 to +3 IGRP promoter region reduces fusion-gene expression. These two E-box motifs have distinct sequences and preferentially bind NeuroD/BETA2 (neurogenic differentiation/beta-cell E box transactivator 2) and upstream stimulatory factor (USF) in vitro, consistent with the binding of both factors to the IGRP promoter in situ, as determined using the chromatin-immunoprecipitation (ChIP) assay. Based on experiments using mutated IGRP promoter constructs, we propose a model to explain how the ubiquitously expressed USF could contribute to islet-specific IGRP gene expression.

Induction of matrix metalloproteinase gene transcription by nitric oxide and mechanisms of MMP-1 gene induction in human melanoma cell lines

Expression of 12 matrix metalloproteinases (MMPs) after exposure of human melanoma cell lines C32TG and Mewo to nitric oxide (NO) was investigated by the reverse transcription-polymerase chain reaction. Expression of the mRNA of MMP-1, -3, -10 and -13 in C32TG cells was transcriptionally enhanced in a dose-dependent manner by exposure to an NO donor, S-nitroso-N-acetyl-DL-penicillamine (SNAP) and mRNA expression of MMP-1 and -10 was similarly enhanced in Mewo cells. Exposure of C32TG cells to NO increased the MMP-1 protein concentration in the culture medium. Testing with the luciferase gene fused to the 1.5 Kbp 5'-flanking region of the human MMP-1 gene showed that exposure to NO upregulated MMP-1 promoter activity in C32TG cells. Endogenous NO production after introduction of inducible NO synthase cDNA also enhanced MMP-1 promoter activity in C32TG cells. Deletion and mutational analysis identified a critical AP-1 binding site required for NO regulation of MMP-1. A neighboring Ets motif from the AP-1 site in the promoter region acted as an accessory to enhance MMP-1 expression. Electromobility shift analysis using the AP-1 binding site showed that NO enhanced the AP-1 binding ability of nuclear factors in C32TG cells. PD98059, a selective MEK inhibitor and SB202190, a p38 MAPK inhibitor, attenuated the MMP-1 mRNA expression enhanced by NO. Thus, MMP-1 was transcriptionally enhanced by NO via MAPK (ERK and p38) pathways. The results of our study suggest that the increased expression of MMPs in response to NO may be associated with tumor progression under inflammation.

Hepatocyte nuclear factor-4 alpha mediates the stimulatory effect of peroxisome proliferator-activated receptor gamma co-activator-1 alpha (PGC-1 alpha) on glucose-6-phosphatase catalytic subunit gene transcription in H4IIE cells

It has recently been shown that adenoviral-mediated expression of peroxisome proliferator-activated receptor gamma co-activator-1 alpha (PGC-1 alpha) in hepatocytes stimulates glucose-6-phosphatase catalytic subunit (G6Pase) gene expression. A combination of fusion gene, gel retardation and chromatin immunoprecipitation assays revealed that, in H4IIE cells, PGC-1 alpha mediates this stimulation through an evolutionarily conserved region of the G6Pase promoter that binds hepatocyte nuclear factor-4 alpha.

Deletion of the homeobox gene PRX-2 affects fetal but not adult fibroblast wound healing responses

The phenotype of fibroblasts repopulating experimental wounds in vivo has been shown to influence both wound healing responses and clinical outcome. Recent studies have demonstrated that the human homeobox gene PRX-2 is strongly upregulated in fibroblasts within fetal, but not adult, mesenchymal tissues during healing. Differential homeobox gene expression by fibroblasts may therefore be important in mediating the scarless healing exhibited in early fetal wounds. RNase protection analysis demonstrated that murine Prx-2 expression was involved in fetal but not adult wound healing responses in vitro. Using fibroblasts established from homozygous mutant (Prx-2-/-) and wild-type (Prx-2+/+) murine skin tissues it was demonstrated that Prx-2 affected a number of fetal fibroblastic responses believed to be important in mediating scarless healing in vivo; namely cellular proliferation, extracellular matrix reorganization, and matrix metalloproteinase 2 and hyaluronic acid production. These data demonstrate how Prx-2 may contribute to the regulation of fetal, but not adult, fibroblasts and ultimately the wound healing phenotype. This study provides further evidence for the importance of homeobox transcription factors in the regulation of scarless wound healing. A further understanding of these processes will, it is hoped, enable the targeting of specific therapies in wound healing, both to effect scarless healing and to stimulate healing in chronic, nonhealing wounds such as venous leg ulcers.

Accessory elements, flanking DNA sequence, and promoter context play key roles in determining the efficacy of insulin and phorbol ester signaling through the malic enzyme and collagenase-1 AP-1 motifs

Insulin stimulates malic enzyme (ME)-chloramphenicol acetyltransferase (CAT) and collagenase-1-CAT fusion gene expression in H4IIE cells through identical activator protein-1 (AP-1) motifs. In contrast, insulin and phorbol esters only stimulate collagenase-1-CAT and not ME-CAT fusion gene expression in HeLa cells. The experiments in this article were designed to explore the molecular basis for this differential cell type- and gene-specific regulation. The results highlight the influence of three variables, namely promoter context, AP-1 flanking sequence, and accessory elements that modulate insulin and phorbol ester signaling through the AP-1 motif. Thus, fusion gene transfection and proteolytic clipping gel retardation assays suggest that the AP-1 flanking sequence affects the conformation of AP-1 binding to the collagenase-1 and ME AP-1 motifs such that it selectively binds the latter in a fully activated state. However, this influence of ME AP-1 flanking sequence is dependent on promoter context. Thus, the ME AP-1 motif will mediate both an insulin and phorbol ester response in HeLa cells when introduced into either the collagenase-1 promoter or a specific heterologous promoter. But even in the context of the collagenase-1 promoter, the effects of both insulin and phorbol esters, mediated through the ME AP-1 motif are dependent on accessory factors.

HER2/Neu-mediated activation of the ETS transcription factor ER81 and its target gene MMP-1

In this study, we show that the ETS transcription factor ER81 directly binds to and activates the promoter of the matrix metalloproteinase gene, MMP-1. Further, the oncoprotein HER2/Neu synergizes with ER81 to stimulate MMP-1 transcription. The activation of ER81 by HER2/Neu is mediated by MAP kinases, which phosphorylate ER81 in its N-terminal activation domain. Four respective phosphorylation sites have been identified. Blocking phosphorylation at these sites decreases ER81 transcriptional activity, which can be further diminished by abolishment of phosphorylation at two non-MAP kinase sites. Altogether, our results reveal mechanisms of how phosphorylation of ER81 regulates the expression of target genes such as MMP-1, which may be important for many physiological processes from embryogenesis to adulthood as well as for tumor metastasis.

Protein kinase A phosphorylates hepatocyte nuclear factor-6 and stimulates glucose-6-phosphatase catalytic subunit gene transcription

Glucose-6-phosphatase is a multicomponent system that catalyzes the terminal step in gluconeogenesis. To examine the effect of the cAMP signal transduction pathway on expression of the gene encoding the mouse glucose-6-phosphatase catalytic subunit (G6Pase), the liver-derived HepG2 cell line was transiently co-transfected with a series of G6Pase-chloramphenicol acetyltransferase fusion genes and an expression vector encoding the catalytic subunit of cAMP-dependent protein kinase A (PKA). PKA markedly stimulated G6Pase-chloramphenicol acetyltransferase fusion gene expression, and mutational analysis of the G6Pase promoter revealed that multiple cis-acting elements were required for this response. One of these elements was mapped to the G6Pase promoter region between -114 and -99, and this sequence was shown to bind hepatocyte nuclear factor (HNF)-6. This HNF-6 binding site was able to confer a stimulatory effect of PKA on the expression of a heterologous fusion gene; a mutation that abolished HNF-6 binding also abolished the stimulatory effect of PKA. Further investigation revealed that PKA phosphorylated HNF-6 in vitro. Site-directed mutation of three consensus PKA phosphorylation sites in the HNF-6 carboxyl terminus markedly reduced this phosphorylation. These results suggest that the stimulatory effect of PKA on G6Pase fusion gene transcription in HepG2 cells may be mediated in part by the phosphorylation of HNF-6.

CREB binding protein recruitment to the transcription complex requires growth factor-dependent phosphorylation of its GF box

Growth factors such as epidermal growth factor (EGF) and insulin regulate development and metabolism via genes containing both POU homeodomain (Pit-1) and phorbol ester (AP-1) response elements. Although CREB binding protein (CBP) functions as a coactivator on these elements, the mechanism of transactivation was previously unclear. We now demonstrate that CBP is recruited to these elements only after it is phosphorylated at serine 436 by growth factor-dependent signaling pathways. In contrast, p300, a protein closely related to CBP that lacks this phosphorylation site, binds only weakly to the transcription complex and in a growth factor-independent manner. A small region of CBP (amino acids 312-440), which we term GF box, contains a potent transactivation domain and mediates this effect. Direct phosphorylation represents a novel mechanism controlling coactivator recruitment to the transcription complex.

Characterization of the mouse islet-specific glucose-6-phosphatase catalytic subunit-related protein gene promoter by in situ footprinting: correlation with fusion gene expression in the islet-derived betaTC-3 and hamster insulinoma tumor cell lines

Glucose-6-phosphatase (G6Pase) is a multicomponent system located in the endoplasmic reticulum comprising a catalytic subunit and transporters for glucose-6-phosphate, inorganic phosphate, and glucose. We have recently cloned a novel gene that encodes an islet-specific G6Pase catalytic subunit-related protein (IGRP) (Ebert et al., Diabetes 48:543-551, 1999). To begin to investigate the molecular basis for the islet-specific expression of the IGRP gene, a series of truncated IGRP-chloramphenicol acetyltransferase (CAT) fusion genes were transiently transfected into the islet-derived mouse betaTC-3 and hamster insulinoma tumor cell lines. In both cell lines, basal fusion gene expression decreased upon progressive deletion of the IGRP promoter sequence between -306 and -66, indicating that multiple promoter regions are required for maximal IGRP-CAT expression. The ligation-mediated polymerase chain reaction footprinting technique was then used to compare trans-acting factor binding to the IGRP promoter in situ in betaTC-3 cells, which express the endogenous IGRP gene, and adrenocortical Y1 cells, which do not. Multiple trans-acting factor binding sites were selectively identified in betaTC-3 cells that correlate with regions of the IGRP promoter identified as being required for basal IGRP-CAT fusion gene expression. The data suggest that hepatocyte nuclear factor 3 may be important for basal IGRP gene expression, as it is for glucagon, GLUT2, and Pdx-1 gene expression. In addition, binding sites for several trans-acting factors not previously associated with islet gene expression, as well as binding sites for potentially novel proteins, were identified.

Ets target genes: past, present and future

Ets is a family of transcription factors present in species ranging from sponges to human. All family members contain an approximately 85 amino acid DNA binding domain, designated the Ets domain. Ets proteins bind to specific purine-rich DNA sequences with a core motif of GGAA/T, and transcriptionally regulate a number of viral and cellular genes. Thus, Ets proteins are an important family of transcription factors that control the expression of genes that are critical for several biological processes, including cellular proliferation, differentiation, development, transformation, and apoptosis. Here, we tabulate genes that are regulated by Ets factors and describe past, present and future strategies for the identification and validation of Ets target genes. Through definition of authentic target genes, we will begin to understand the mechanisms by which Ets factors control normal and abnormal cellular processes.

Insulin responsiveness of the glucagon gene conferred by interactions between proximal promoter and more distal enhancer-like elements involving the paired-domain transcription factor Pax6

Regulation of gene transcription is an important aspect of insulin's action. However, the mechanisms involved are poorly understood. Insulin inhibits glucagon gene transcription, and insulin deficiency is associated with hyperglucagonemia that contributes to hyperglycemia in diabetes mellitus. Transfecting glucagon-reporter fusion genes into a glucagon-producing pancreatic islet cell line, a 5'-, 3'-, and internal deletion analysis, and oligonucleotide cassette insertions failed in the present study to identify a single insulin-responsive element in the glucagon gene. They rather indicate that insulin responsiveness depends on the presence of both proximal promoter elements and more distal enhancer-like elements. When the paired domain transcription factor Pax6 binding sites within the proximal promoter element G1 and the enhancer-like element G3 were mutated into GAL4 binding sites, the expression of GAL4-Pax6 and GAL4-VP16 restored basal activity, whereas only GAL4-Pax6 restored also insulin responsiveness. Likewise, GAL4-CBP activity was inhibited by insulin within the glucagon promoter context. The results suggest that insulin responsiveness is conferred to the glucagon gene by the synergistic interaction of proximal promoter and more distal enhancer-like elements, with Pax6 and its potential coactivator the CREB-binding protein being critical components. These data thereby support concepts of insulin-responsive element-independent mechanisms of insulin action to inhibit gene transcription.

Platelet-derived growth factor induces collagenase 3 transcription in osteoblasts through the activator protein 1 complex

Platelet-derived growth factor (PDGF) BB is a mitogen that stimulates bone resorption and increases collagenase 3 transcription in osteoblasts, although the mechanisms involved are as yet unknown. We examined the effect of PDGF BB on collagenase 3 transcription in cultures of osteoblasts from fetal rat calvariae (Ob cells). PDGF BB increased the activity of collagenase 3 promoter fragments transiently transfected into Ob cells. Deletion analysis of the collagenase promoter revealed three regions that impaired the induction of collagenase 3 by PDGF BB. A construct spanning base pair -53 to +28 collagenase 3 sequences, in relation to the start site of transcription +1, was fully responsive to PDGF BB and was studied in detail. Targeted mutations of an AP-1 site in this fragment decreased basal collagenase promoter activity and the responsiveness to PDGF BB, whereas mutations of Stat3 and Ets binding sites did not alter the response to PDGF. Electrophoretic mobility shift assay, using nuclear extracts from control and treated cells, revealed AP-1 nuclear protein complexes that were enhanced in extracts from PDGF BB-treated Ob cells. Supershift assays revealed that antibodies to c-Fos, Fos B, Fra-2, c-Jun, Jun B, and Jun D shifted the binding of nuclear extracts from cells treated with PDGF BB to AP-1 sequences. In conclusion, PDGF BB induces collagenase 3 transcription in osteoblasts by regulating nuclear proteins interacting with AP-1 sequences.

Allele-specific regulation of matrix metalloproteinase-12 gene activity is associated with coronary artery luminal dimensions in diabetic patients with manifest coronary artery disease

Both the processes of atherosclerosis and plaque rupture are indicated to be influenced by matrix metalloproteinase (MMP) activity. We therefore searched for common functional variation in the matrix metalloelastase (MMP-12) gene locus that may be implicated in coronary artery disease. Single-strand conformation polymorphism analysis of DNA from healthy individuals detected a common polymorphism within the MMP-12 gene promoter (an A-to-G substitution at position -82). The frequency of the G allele was 0. 19. The polymorphism influences the binding of the transcription factor activator protein-1 (AP-1) in electromobility shift assay. A higher binding affinity of AP-1 to the A allele was associated with higher MMP-12 promoter activity in vitro in transient transfection studies in U937 and murine lung macrophage (MALU) cells. Phorbol 12-myristate 13-acetate (PMA) and insulin, 2 known activators of AP-1, increased the binding of AP-1 to the MMP-12 promoter, with higher affinity for the A allele. In transfection experiments, both the A and the G alleles responded to insulin and PMA, the A allele showing higher promoter activity than the G allele. Furthermore, Western blot analysis demonstrated that insulin increased MMP-12 protein production. To analyze whether the -82 A/G polymorphism is associated with coronary artery disease, 367 consecutive patients who underwent percutaneous transluminal coronary angiography with stent implantation were genotyped. In patients (n=71) with diabetes, the A allele was associated with a smaller luminal diameter. In conclusion, a common functional polymorphism within the MMP-12 promoter influences coronary artery luminal dimensions in diabetic patients with manifest coronary artery disease.

Differential role of hepatocyte nuclear factor-1 in the regulation of glucose-6-phosphatase catalytic subunit gene transcription by cAMP in liver- and kidney-derived cell lines

In liver and kidney, the terminal step in gluconeogenesis is catalyzed by glucose-6-phosphatase. To examine the effect of the cAMP signal transduction pathway on transcription of the gene encoding the catalytic subunit of glucose-6-phosphatase (G6Pase), G6Pase-chloramphenicol acetyltransferase (CAT) fusion genes were transiently transfected into either the liver-derived HepG2 or kidney-derived LLC-PK cell line. Co-transfection of an expression vector encoding the catalytic subunit of cAMP-dependent protein kinase (PKA) markedly stimulated G6Pase-CAT fusion gene expression, and mutational analysis of the G6Pase promoter revealed that multiple regions are required for this PKA response in both the HepG2 and LLC-PK cell lines. A sequence in the G6Pase promoter that resembles a cAMP response element is required for the full PKA response in both HepG2 and LLC-PK cells. However, in LLC-PK cells, but not in HepG2 cells, a hepatocyte nuclear factor-1 (HNF-1) binding site was critical for the full induction of G6Pase-CAT expression by PKA. Changing this HNF-1 motif to that for the yeast transcription factor GAL4 reduces the PKA response in LLC-PK cells to the same degree as deleting the HNF-1 site. However, co-transfection of this mutated construct with chimeric proteins comprising the GAL4-DNA binding domain ligated to the coding sequence for HNF-1alpha, HNF-1beta, HNF-3, or HNF-4 completely restored the PKA response. Thus, we hypothesize that, in LLC-PK cells, HNF-1 is acting as an accessory factor to enhance PKA signaling through the cAMP response element by altering G6Pase promoter conformation or accessibility rather than specifically affecting some component of the PKA signal transduction pathway.

Constitutive expression and regulation of collagenase-3 in human breast cancer cells

Matrix metalloproteinases (MMPs) are a family of secreted or transmembrane proteins that have been implicated in multiple physiological and pathological processes related to extracellular matrix turnover. Recent evidence strongly suggests a role for collagenase-3 (MMP-13) in tumor metastasis and invasion. We report here that collagenase-3 is constitutively expressed in the breast cancer cell line MDA-MB231 (MDA) and outline the molecular mechanism regulating its expression. Functional analysis of the collagenase-3 promoter showed that both the activator protein-1 (AP-1) site and the runt domain (RD) binding site were required for maximal constitutive expression of collagenase-3 in MDA cells. Determination of factors binding to those sites by Northern analysis and transient transfections identified the requirement of Fra-1, c-Jun, and Cbfa1 for basal collagenase-3 promoter activity in MDA cells.