An AP-1-like motif in the first intron of human Pro alpha 1(I) collagen gene is a critical determinant of its transcriptional activity

Identification of a novel distal regulatory element of the human Neuroglobin gene by the chromosome conformation capture approach

Neuroglobin (NGB) is predominantly expressed in the brain and retina. Studies suggest that NGB exerts protective effects to neuronal cells and is implicated in reducing the severity of stroke and Alzheimer's disease. However, little is known about the mechanisms which regulate the cell type-specific expression of the gene. In this study, we hypothesized that distal regulatory elements (DREs) are involved in optimal expression of the NGB gene. By chromosome conformation capture we identified two novel DREs located -70 kb upstream and +100 kb downstream from the NGB gene. ENCODE database showed the presence of DNaseI hypersensitive and transcription factors binding sites in these regions. Further analyses using luciferase reporters and chromatin immunoprecipitation suggested that the -70 kb region upstream of the NGB gene contained a neuronal-specific enhancer and GATA transcription factor binding sites. Knockdown of GATA-2 caused NGB expression to drop dramatically, indicating GATA-2 as an essential transcription factor for the activation of NGB expression. The crucial role of the DRE in NGB expression activation was further confirmed by the drop in NGB level after CRISPR-mediated deletion of the DRE. Taken together, we show that the NGB gene is regulated by a cell type-specific loop formed between its promoter and the novel DRE.

The Molecular and Cellular Events That Take Place during Craniofacial Distraction Osteogenesis

Summary:

Gradual bone lengthening using distraction osteogenesis principles is the gold standard for the treatment of hypoplastic facial bones. However, the long treatment time is a major disadvantage of the lengthening procedures. The aim of this study is to review the current literature and summarize the cellular and molecular events occurring during membranous craniofacial distraction osteogenesis. Mechanical stimulation by distraction induces biological responses of skeletal regeneration that is accomplished by a cascade of biological processes that may include differentiation of pluripotential tissue, angiogenesis, osteogenesis, mineralization, and remodeling. There are complex interactions between bone-forming osteoblasts and other cells present within the bone microenvironment, particularly vascular endothelial cells that may be pivotal members of a complex interactive communication network in bone. Studies have implicated number of cytokines that are intimately involved in the regulation of bone synthesis and turnover. The gene regulation of numerous cytokines (transforming growth factor-β, bone morphogenetic proteins, insulin-like growth factor-1, and fibroblast growth factor-2) and extracellular matrix proteins (osteonectin, osteopontin) during distraction osteogenesis has been best characterized and discussed. Understanding the biomolecular mechanisms that mediate membranous distraction osteogenesis may guide the development of targeted strategies designed to improve distraction osteogenesis and accelerate bone regeneration that may lead to shorten the treatment duration.

Tryptase/Protease-activated receptor 2 interactions induce selective mitogen-activated protein kinase signaling and collagen synthesis by cardiac fibroblasts

The mast cell product, tryptase, has recently been implicated to mediate fibrosis in the hypertensive heart. Tryptase has been shown to mediate noncardiac fibroblast function via activation of protease-activated receptor 2 and subsequent activation of the mitogen-activated protein kinase pathway, including extracellular signal-regulated kinase 1/2. Therefore, we hypothesized that this pathway may be a mechanism leading to fibrosis in the hypertensive heart. Isolated adult cardiac fibroblasts were treated with tryptase, which induced activation of extracellular signal-regulated kinase 1/2 via protease-activated receptor 2. Blockade of protease activated receptor 2 with FSLLRY (10 μmol/L) and inhibition of the extracellular signal-regulated kinase pathway with PD98059 (10 μmol/L) prevented collagen synthesis in isolated cardiac fibroblasts stimulated with tryptase. In contrast, p38 mitogen-activated protein kinase and stress-activated protein/c-Jun N-terminal kinase were not activated by tryptase. Cardiac fibroblasts isolated from spontaneously hypertensive rats showed this same pattern of activation. Treatment of spontaneously hypertensive rats with FSLLRY prevented fibrosis in these animals, indicating the in vivo applicability of the cultured fibroblast findings. Also, tryptase induced a myofibroblastic phenotype indicated by elevations in α-smooth muscle actin and extra type III domain A (ED-A) fibronectin. Thus, the results from this study demonstrate the importance of tryptase for inducing a cardiac myofibroblastic phenotype, ultimately leading to the development of cardiac fibrosis. Specifically, tryptase causes cardiac fibroblasts to increase collagen synthesis via a mechanism involving activation of protease-activated receptor 2 and subsequent induction of extracellular signal-regulated kinase signaling.

The interaction of an impermeant cation with the sheep cardiac RyR channel alters ryanoid association

In previous studies, we have demonstrated that the interaction of ryanoids with the sarcoplasmic reticulum Ca(2+)-release channel [ryanodine receptor (RyR)] incorporated into planar lipid bilayers reduced the effectiveness of tetraethylammonium (TEA(+)) as a blocker of K(+) translocation (J Gen Physiol 117: 385-393, 2001). In the current study, we investigated both the effect of TEA(+) on [(3)H]ryanodine binding and the actions of this impermeant cation on the interaction of the reversible ryanoid 21-amino-9alpha-hydroxyryanodine with individual, voltage-clamped RyR channels. A dose-dependent inhibition of [(3)H]ryanodine binding was observed in the presence of TEA(+), suggesting that the cation and alkaloid compete for access to a common site of interaction. Single channel studies gave further insights into the mechanism of the competition between the two classes of ligands. TEA(+) decreases the association rate of 21-amino-9alpha-hydroxyryanodine with its receptor, whereas the dissociation rate of the ryanoid from the channel was unaffected. Our results demonstrate that TEA(+) inhibits both K(+) translocation through RyR, and ryanoid interaction at the high affinity ryanodine site on the channel. These actions involve binding of TEA(+) to different, but weakly interacting, sites in the RyR channel.

Similar rates but different modes of sequence evolution in introns and at exonic silent sites in rodents: evidence for selectively driven codon usage

In mammals divergence at fourfold degenerate sites in codons (K(4)) and intronic sequence (K(i)) are both used to estimate the mutation rate, under the supposition that both evolve neutrally. Does it matter which of these we use? Using either class of sequence can be defended because (1) K(4) is the same as K(i) (at least in rodents) and (2) there is no selectively driven codon usage (hence no systematic selection on third sites). Here we re-examine these findings using 560 introns (for 136 genes) in the mouse-rat comparison, aligned by eye and using a new maximum likelihood protocol. We find that the rate of evolution at fourfold sites and at intronic sites is similar in magnitude, but only after eliminating putatively constrained sites from introns (first introns and sites flanking intron-exon junctions). Any approximate congruence between the two rates is not, however, owing to an underlying similarity in the mode of sequence evolution. Some dinucleotides are hypermutable and differently abundant in exons and introns (e.g., CpGs). More importantly, after controlling for relative abundance, all dinucleotides starting with A or T are more prevalent in mismatches in exons than in introns, whereas C-starting dinucleotides (except CG) are more common in introns. Although C content at intronic sites is lower than at flanking fourfold sites, G content is similar, demonstrating that there exists a strong strand-specific preference for C nucleotides that is unique to exons. Transcription-coupled mutational processes and biased gene conversion cannot explain this, as they should affect introns and flanking exons equally. Therefore, by elimination, we propose this to be strong evidence for selectively driven codon usage in mammals.

Last intron of the chemokine-like factor gene contains a putative promoter for the downstream CKLF super family member 1 gene

The genes for chemokine-like factor (CKLF) and four chemokine-like factor super family members (CKLFSF1-4) are tightly linked on chromosome 16, with only 325 bp separating CKLF and CKLFSF1. We used Northern blotting and RT-PCR to show that these two genes are expressed independently of one another. We then used a novel computational promoter prediction method based on the interaction among transcription factor binding sites (TFBSs) to identify a putative promoter region for the CKLFSF1 gene. Our method predicted a promoter region in the last intron of the upstream gene, CKLF. We PCR amplified the predicted promoter region and used a luciferase assay to show that the region was able to drive the luciferase gene. DNA decoy experiments indicated that 214 bp fragment neighboring the TATA box markedly inhibited CKLFSF1 gene expression. Sequence analysis of the region revealed a typical TATA box (TATATAA) and multiple potential transcription factor binding sites, providing further evidence for this being a functional promoter for CKLFSF1. This work provides the first evidence of a promoter from one gene located in an intron of another.

Kallikrein gene delivery attenuates cardiac remodeling and promotes neovascularization in spontaneously hypertensive rats

Hypertension that results in left ventricular (LV) hypertrophy and/or fibrosis can lead to cardiac dysfunction. Spontaneously hypertensive rats (SHR) develop high blood pressure and LV hypertrophy at an early age and are a popular model of human essential hypertension. To investigate the role of the tissue kallikrein-kinin system in cardiac remodeling, an adenovirus containing the human tissue kallikrein gene was injected intravenously into adult SHR and normotensive Wistar-Kyoto (WKY) rats. The blood pressure of WKY rats remained unchanged throughout the experiment. Alternatively, kallikrein gene transfer reduced blood pressure in SHR for the first 2 wk, but had no effect from 3 to 5 wk. Five weeks after kallikrein gene delivery, SHR showed significant reductions in LV-to-heart weight ratio, LV long axis, and cardiomyocyte size; however, these parameters were unaffected in WKY rats. Interestingly, cardiac collagen density was decreased in both SHR and WKY rats receiving the kallikrein gene. Kallikrein gene transfer also increased cardiac capillary density in SHR, but not in WKY rats. The morphological changes after kallikrein gene transfer were associated with decreases in JNK activation as well as transforming growth factor (TGF)-beta 1 and plasminogen activator inhibitor-1 levels in the heart. In addition, kallikrein gene delivery elevated LV nitric oxide and cGMP levels in both rat strains. These results indicate that kallikrein-kinin attenuates cardiac hypertrophy and fibrosis and enhances capillary growth in SHR through the suppression of JNK, TGF-beta 1, and plasminogen activator inhibitor-1 via the nitric oxide-cGMP pathway.

Stimulation of Fos- and Jun-related genes during distraction osteogenesis

Bone cells respond to mechanical stimulation by gene expression. The molecular events involved in the translation of mechanical stimulation into cell proliferation and bone formation are not yet well understood. We looked for the expression of early-response genes of the AP-1 transcription factor complex in an in vivo bone regeneration system subjected to mechanical forces because these genes were found to be related to mechanotransduction and important for bone development. Sheep maxillary bone was distracted daily for 15 days. c-Jun and c-Fos were evaluated by Northern blotting analysis and immunohistochemistry in biopsy specimens removed at 8 and 15 days and were compared with post-osteotomy but not distracted repair tissue. Elevated levels of c-Jun and c-Fos mRNA were found after 8 days of distraction. Likewise, mesenchyme-like and fibroblast-like cells composing the 8-day distracted regeneration tissue showed increases in the intensity of immunostaining compared to cells in the corresponding non-distracted fracture repair tissue. After 15 days of distraction, when bone trabeculae start to form distally and proximally in the distracted regeneration tissue, mostly preosteoblasts and osteoblasts retained c-Fos and c-Jun immunoreactivity, similar to bone-associated cells in control non-distracted fracture repair tissue. We propose that the elevated expression of c-Jun and c-Fos is related to mechanical stimulation in this in vivo bone regeneration system.

Photoaging in Asians

The aging process of the skin can be divided into intrinsic and photoaging. Clinically, naturally aged skin is smooth, pale and finely wrinkled. In contrast, photoaged skin is coarsely wrinkled and associated with dyspigmentation and telangiectasia. Although the population of Asia is more than half the population of the Earth, no well-designed study has been undertaken to investigate the characteristics of cutaneous photodamage in Asian skin. As Asian skin is more pigmented, the acute and chronic cutaneous responses to UV irradiation seen in brown skin differ from those in white skin. The clinical characteristics of photoaging in Asian skin, such as pigmentary changes and wrinkle patterns, differ from those of Caucasian skin. This review provides an outline of the characteristic features of photoaging on the brown skin of Asians.

Identification of cJun-responsive genes in Rat-1a cells using multiple techniques: increased expression of stathmin is necessary for cJun-mediated anchorage-independent growth

cJun is a major component of the transcription factor AP-1 and mediates a diverse set of biologic properties including proliferation, differentiation, and apoptosis. To identify cJun-responsive genes, we inducibly expressed cJun in Rat-1a cells and observed two distinct phenotypes: changes in cellular morphology with adherent growth and anchorage-independent growth. The biologic effects of cJun were entirely reversible demonstrating that they require the continued presence of cJun. To determine the genes, which mediate the biologic effects of cJun, we employed multiple methods including differential gene analysis, suppression subtractive hybridization, and cDNA microarrays. We identified 38 cJun-responsive genes including three uncharacterized genes under adherent and/or nonadherent conditions. Half of the known 36 genes were cytoskeleton- and adhesion-related genes, suggesting a major role of cJun in the regulation of the genes related to cell morphology. As proof of the principle that this approach could identify genes whose upregulation was necessary for nonadherent growth, we investigated one gene, stathmin whose upregulation by cJun was observed only under these conditions. Although overexpression of stathmin did not result in nonadherent growth, inhibition of stathmin protein expression by antisense oligonucleotides in cJun-induced Rat-1a cells prevented nonadherent growth. These results suggest that stathmin plays an essential role in anchorage-independent growth by cJun and may be a potential target for specific inhibitors for AP-1-dependent processes involved in carcinogenesis.

DNase I-hypersensitive sites enhance alpha1(I) collagen gene expression in hepatic stellate cells

Liver fibrosis is characterized by a dramatic increase in the expression of type I collagen. Several deoxyribonuclease (DNase) I-hypersensitive sites (HS) have been located in the distal 5'-flanking region of the alpha1(I) collagen gene that are specific to collagen-producing cells. To assess the role of the DNase I-HS in regulating alpha1(I) collagen gene expression in hepatic stellate cells (HSCs), 3 transgenic mouse lines expressing collagen-alpha1(I) reporter genes were used (Krempen et al. Gene Expr 1999;8:151-163). The pCol9GFP transgene contains the collagen gene promoter (-3122 to +111) linked to the green fluorescent protein (GFP) reporter gene. The pCol9GFP-HS4,5 transgene contains HS4,5 and pColGFP-HS8,9 contains HS8,9 positioned upstream of the collagen promoter in pCol9GFP. HSCs isolated from transgenic mice containing pCol9GFPHS4,5 and pColGFP-HS8,9 showed earlier and higher GFP expression patterns than HSCs isolated from pCol9GFP mice. HSCs from pCol9GFP-HS4,5 showed the highest levels of GFP expression and culture-induced expression correlated with induction of the endogenous alpha1(I) collagen gene. After CCl(4) administration, pCol9GFP-HS4,5 mice showed increased GFP expression compared with pCol9GFP mice in both whole liver extracts and isolated HSCs. Several sites for DNA-protein interactions in both HS4 and HS5 were identified that included a binding site for activator protein 1. In conclusion, DNase I-HS4,5 enhance expression of the alpha1(I) collagen gene promoter in HSCs both in vitro and in vivo after a fibrogenic stimulus. The collagen-GFP transgenic mice provide a convenient and reliable model system to investigate the molecular mechanisms controlling increased collagen expression during fibrosis.

P38 and activating transcription factor-2 involvement in osteoblast osmotic response to elevated extracellular glucose

Poorly controlled or untreated type I diabetes mellitus is characterized by hyperglycemia and is associated with decreased bone mass and osteoporosis. We have demonstrated that osteoblasts are sensitive to hyperglycemia-associated osmotic stress and respond to elevated extracellular glucose or mannitol by increasing c-jun and collagen I expression. To determine whether MAPKs are involved in this response, MC3T3-E1 osteoblasts were treated with 16.5 mm glucose, mannitol, or contrast dye for 1 h. Immunoblotting of phosphorylated p38 demonstrated activation of p38 MAPK by hyperosmotic stress in vitro and in vivo. Activation peaked at 20 min, remained detectable after 24 h, and was protein kinase C-independent. Activating transcription factor-2 (ATF-2) activation followed the same pattern as phospho-p38. Transactivation of cAMP response element (CRE)- and c-jun promoter (containing a CRE-like element)-reporter constructs increased following hyperosmotic treatment. SB 203580 (a p38 MAPK inhibitor) blocked ATF-2 phosphorylation, CRE transactivation, and c-jun promoter activation. Hyperosmotic activation of collagen I promoter activity was also inhibited by SB 203580, consistent with the involvement of c-jun in collagen I up-regulation. Therefore, we propose that hyperglycemia-induced increases in p38 MAPK activity and ATF-2 phosphorylation contribute to CRE activation and modulation of c-jun and collagen I expression in osteoblasts.

Cell density dependent regulation of AP-1 activity is important for chondrogenic differentiation of C3H10T1/2 mesenchymal cells

The multipotential C3H10T1/2 mesenchymal cells undergo chondrogenic differentiation only when seeded as high-density micromass cultures, particularly upon treatment with bone morphogenetic protein-2 (BMP-2). The molecular mechanism(s) responsible for the cell density-dependent onset of cartilage-specific gene expression is presently unknown. Interestingly, a number of recent studies have indicated that activating protein-1 (AP-1), a well known downstream target of the mitogenic activated protein kinase (MAP kinase) signaling pathway, is a target of chondrogenic/osteogenic growth factors such as BMP-2, and plays a role in osteogenic gene regulation as well as in chondrogenic differentiation. The aim of this study is to examine the density-dependent alteration in the level and binding activity of AP-1 and its functional involvement in C3H10T1/2 mesenchymal chondrogenesis. To measure the activity of the AP-1 transcription factor, we generated a pool of stable C3H10T1/2 cell lines harboring a luciferase expression vector driven by a concatamer of an efficient AP-1 response element (AP1-10T1/2 cells). Luciferase activity of AP1-10T1/2 cultures was found to decrease sharply with increase in cell density, either as a function of culture time or initial cell seeding densities. In C3H10T1/2 micromass cultures undergoing chondrogenesis, AP-1 activity was further reduced and then maintained at a low, steady level for the entire 3-4 day culture period. AP-1 activity in micromass cultures was not significantly affected by BMP-2 treatment, but chondrogenesis was compromised upon competitive inhibition of AP-1 activity with a double-stranded AP-1 binding oligonucleotide. The level of AP-1 binding correlated with the activity of its response element but not with the levels of its leucine-zipper containing subunits, c-Jun and c-Fos. These findings suggest that a cell density-dependent, low but steady level of AP-1 binding and activity is required for promoting the chondrogenic potential of C3H10T1/2 cells.

Apigenin decreases expression of the myofibroblast phenotype

We investigated the effect of the dietary flavonoid apigenin on myofibroblast function. We report that in myofibroblasts treated with apigenin, proliferation and basal levels of alpha1(I) collagen and alpha-smooth muscle actin mRNAs were markedly reduced. Apigenin also attenuated the transforming growth factor-beta-stimulated increases of alpha1(I) collagen and alpha-smooth muscle actin mRNAs. Characterization of the apigenin effects indicates that apigenin reduces both the stability of the alpha1(I) collagen mRNA and the rate of transcription of the alpha1(I) collagen gene through a cycloheximide-sensitive pathway. Western blot analyses indicate that Akt activity is reduced in apigenin-treated myofibroblasts.

Chronic exposure of human mesangial cells to high glucose environments activates the p38 MAPK pathway

BACKGROUND

High glucose (HG) environments activate several protein kinase pathways in mesangial cells, including the mitogen-activated protein kinase (MAPK) pathway, ERK. The p38 MAPK pathway is activated by events that occur in the setting of diabetes, such as protein kinase C (PKC) up-regulation and cellular stresses (osmotic stress and redox changes). Substrates of activated p38 MAPK include transcription factors that are involved in the microvascular complications of diabetes. This current study investigated the mechanisms of HG-mediated activation of p38 MAPK in cultured human mesangial cells (HMCs) and the effects of p38 MAPK activation on the transcription factor activator protein-1 (AP-1).

METHODS

HMCs were cultured in 5 mmol/L D-glucose [normal glucose (NG)] or 30 mmol/L D-glucose (HG) for seven days. Cells were also treated with HG for brief periods of time (0.5 to 4 hours) to assess the acute effects of HG on p38 MAPK. Using Western blotting of HMC lysates, changes in the tyrosine and threonine phosphorylation of p38 MAPK were measured. The kinase activity of immunoprecipitated p38 MAPK was determined by an in vitro assay that measured the phosphorylation and activation of MAPKAP kinase-2, an intermediary signaling protein downstream of p38 MAPK. To investigate the role of osmotic stress in HG activation of p38 MAPK, cells were acutely treated with mannitol (25 to 250 mOsm/L x 5 to 60 min) or were grown seven days in media supplemented with mannitol at concentrations iso-osmotic to HG media. To investigate the role of PKC in HG-mediated p38 MAPK activation, HMCs were treated with the PKC inhibitors GF 109203X, Ro 32-0432, or rottlerin during the last several hours of HG treatment. HG conditioned cells were also treated with the antioxidants L-N-acetylcysteine (L-NAC) or diphenyliodonium (DPI) prior to harvest. To determine a functional significance of HG-mediated p38 MAPK activation, the DNA binding of the transcription factor complex AP-1 was measured by electrophoretic mobility shift assay.

RESULTS

The p38 MAPK pathway was not activated by the acute addition of HG to the HMCs. However, activation of p38 MAPK in HMCs grown seven days in HG was demonstrated by increased tyrosine and threonine phosphorylation of p38 MAPK proteins and increased kinase activity of immunoprecipitated p38 MAPK. As assessed by a kinase assay, p38 MAPK activity in cells grown in HG for seven days exceeded that of NG cells by more than 250%. This difference was not due to differences in the amount of p38 MAPK protein between the treatment groups. Acute osmotic activation of p38 MAPK occurred at extremely high mannitol concentrations (250 mOsm/L) that exceeded the osmotic stress of acute HG. Furthermore, in cells grown for seven days in mannitol at concentrations similar to HG, p38 MAPK activity was similar to control values. Phorbol ester (PMA) treatment stimulated a twofold increase in p38 MAPK activity. The addition of GFX or Ro 32-0432 to HG cells, at concentrations that inhibited PMA activation of p38 MAPK, did not inhibit the glucose-mediated p38 MAPK activation. Rottlerin, a PKC delta inhibitor, also failed to reverse the HG-mediated p38 MAPK activation. Treatment of HG cells with L-NAC or DPI inhibited the HG-mediated p38 MAPK phosphorylation. As we have previously shown, DNA binding of the transcription factor complex AP-1 was increased in HG cells. This binding was reversed by treatment of the HG cells with the p38 MAPK inhibitor SB 203580.

CONCLUSIONS

Chronic exposure of HMC to HG concentrations activates the p38 MAPK pathway. This activation appears to be independent of changes in the amount of total p38 MAPK produced by the cells, independent of chronic osmotic stress and independent of PKC activation. The reversal of p38 MAPK by L-NAC and DPI suggests the glucose-mediated p38 MAPK activation may occur via reactive oxygen species. The activity of AP-1, a transcription factor complex that regulates several genes involved in diabetic nephropathy, is reversed when the p38 MAPK pathway is inhibited. These findings suggest the p38 MAPK pathway may be an important pathway involved in diabetic complications.

The role of intron sequences in high level expression from CD45 cDNA constructs

Consistent expression from CD45 cDNA constructs has proven difficult to achieve. Through the use of new CD45 cDNA constructs and reporter genes, the role 5', 3', and intron sequences play in CD45 expression was determined. The CD45 polyadenylation signal sequence was fully functional in a beta-galactosidase reporter construct. Furthermore, the CD45 3'-untranslated region and downstream sequences were shown to contain no negative regulatory elements. Several new CD45 cDNA constructs were designed that contain either the cytomegalovirus promoter, the leukocyte function-associated antigen (LFA-1; CD11a) promoter, or various CD45 5' regions. Neither the cytomegalovirus nor the LFA-1 promoter was capable of generating detectable levels of expression in constructs with CD45 cDNA. However, when CD45 intron sequences between exons 3 and 9 were inserted in the cDNA construct to generate a CD45 minigene, the LFA-1 promoter was able to drive reproducible, significant expression of CD45. CD45 minigenes using the CD45 5' sequences up to 19 kilobases upstream of the transcriptional start produced very little protein. The LFA-1 CD45 minigene construct produced correct cell type-specific isoforms when expressed in T and B lymphocyte lines. Therefore, we conclude that the regulation of CD45 expression and cell type-specific splicing requires elements within the intron sequences.

Erk is essential for growth, differentiation, integrin expression, and cell function in human osteoblastic cells

Extracellular signal-regulated kinases (Erks), members of the mitogen-activated protein kinase superfamily, play an important role in cell proliferation and differentiation. In this study we employed a dominant negative approach to determine the role of Erks in the regulation of human osteoblastic cell function. Human osteoblastic cells were transduced with a pseudotyped retrovirus encoding either a mutated Erk1 protein with a dominant negative action against both Erk1 and Erk2 (Erk1DN cells) or the LacZ protein (LacZ cells) as a control. Both basal and growth factor-stimulated MAPK activity and cell proliferation were inhibited in Erk1DN cells. Expression of Erk1DN protein suppressed both osteoblast differentiation and matrix mineralization by decreasing alkaline phosphatase activity and the deposition of bone matrix proteins. Cell adhesion to collagen, osteopontin, and vitronectin was decreased in Erk1DN cells as compared with LacZ cells. Cell spreading and migration on these matrices were also inhibited. In Erk1DN cells, expression of alphabeta(1), alpha(v)beta(3), and alpha(v)beta(5) integrins on the surface was decreased. Metabolic labeling indicated that the synthesis of these integrins was inhibited in Erk1DN cells. These data suggest that Erks are not only essential for the growth and differentiation of osteoblasts but also are important for osteoblast adhesion, spreading, migration, and integrin expression.

Angiotensin blockade inhibits increased JNKs, AP-1 and NF- kappa B DNA-binding activities in myocardial infarcted rats

Inhibition of the renin-angiotensin system has been shown to prevent left ventricular remodeling after myocardial infarction. However, the effect of angiotensin on the signal transduction pathway of left ventricular remodeling after myocardial infarction is as yet unknown. The purpose of this study was to measure myocardial MAPKs and AP-1, NF- kappa B, and Sp-1 DNA-binding activities after myocardial infarction. Moreover, we evaluated the effects of angiotensin converting enzyme (ACE) inhibitor and angiotensin receptor blocker (ARB) on signal transduction pathway. Myocardial infarction was produced by ligation of the coronary artery in Wistar rats. Temocapril (ACE inhibitor) (3 and 30 mg/kg/day) and candesartan cilexitil (ARB) (1 and 10 mg/kg/day) were orally administered once a day. After ligation of the left descending coronary artery, JNKs (p46JNK and p55JNK) increased to 2.0- (P<0.01) and 2.8-fold (P<0.01) at 7 days, respectively. ERKs (p44ERK and p42ERK) and p38 activities did not increase significantly. AP-1 and NF- kappa B binding activities increased at 5 days, reached their peak 2.2- and 2.0-fold at 7 days. Sp-1 did not change. ACE inhibitor and ARB inhibited JNKs, NF- kappa B and AP-1 activities. Increased JNKs, AP-1, NF- kappa B, and Sp-1 DNA-binding activities were suppressed by both drugs in the infarcted region. Doppler-echocardiography showed that ACE inhibitor and ARB prevented the dilatation of left ventricular cavity at 14 days and improved diastolic filling pattern. JNKs, AP-1 and NF- kappa B activation in myocardial infarcted rats could be responsible for left ventricular remodeling after myocardial infarction and angiotensin may be related to the activation of these signals.

Role of activator protein 1 transcriptional activity in the regulation of gene expression by transforming growth factor beta1 and bone morphogenetic protein 2 in ROS 17/2.8 osteoblast-like cells

In osteoblastic cells, transforming growth factor beta1 (TGF-beta1) has been found to regulate the expression of a variety of proto-oncogenes including c-fos, c-jun, and junB. The c-fos in particular has been implicated in the mitogenic effect of TGF-beta1. Here, we examined the role of these early response genes in the regulation of osteoblast (OB) gene expression by two members of the TGF-beta superfamily, TGF-beta1 and bone morphogenetic protein 2 (BMP-2). In ROS 17/2.8 cells, TGF-beta1 as well as BMP-2 up-regulated the expression of junB and c-fos messenger RNAs (mRNAs), and this increase was correlated in both cases with an increase in activator protein 1 (AP-1) DNA-binding activity involving JunB and c-Fos proteins. Protein kinase C (PKC)- and protein tyrosine kinase (PTK)-dependent pathways have been implicated in both TGF-beta1 signaling and AP-1 gene regulation. Therefore, using the kinase inhibitors chelerythrine chloride and genistein, we showed that PKC and PTK activities, respectively, participated in TGF-beta1- and BMP-2-induced increases in junB mRNA levels. Similarly, these kinase activities were involved in the stimulatory effect of BMP-2 on c-fos mRNA expression. Using a natural dominant negative for AP-1 transcriptional activity in ROS 17/2.8 cells, we then showed that AP-1 transcription factors mediated TGF-beta1- and BMP-2-regulated expression of the (alpha1) collagen I gene as well as TGF-beta1-regulated expression of the parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor. Our data emphasize the role of the AP-1 transcription factor in TGF-beta1 and BMP-2 signaling and highlight the importance of this transcription factor family in the expression of OB genes.

Activation of DNA synthesis and AP-1 by profilin, an actin-binding protein, via binding to a cell surface receptor in cultured rat mesangial cells

Profilin is known to bind to actin monomers (to regulate actin polymerization) and to phosphatidylinositol-4,5-bisphosphate (to inhibit hydrolysis by unphosphorylated phospholipase C-gammal). It was recently reported that profilin is overexpressed in glomerular mesangial cells (MC) of rats with anti-Thy-1.1-induced glomerulonephritis and is accumulated in the extracellular space around MC. In this study, the biologic activities of extracellular profilin were examined. Scatchard analysis indicated the existence of a single class of cell surface binding sites, with similar equilibrium dissociation constants for purified splenic profilin and recombinant profilin, in cultured rat MC. Profilin increased [(3)H]thymidine incorporation in a dose-dependent manner and produced additive effects on platelet-derived growth factor-induced [(3)H]thymidine incorporation. Profilin increased AP-1 DNA-binding activity in a concentration-dependent (ED(50) = 30 nM) and time-dependent manner after transient c-jun gene expression, as measured using gel-shift assays and competitive reverse transcription-PCR. Pretreatment of profilin with an anti-profilin inhibitory antibody suppressed profilin-induced AP-1 activation and [(3)H]thymidine incorporation. Furthermore, profilin induced rapid transient activation of protein kinase C, and staurosporine and H-7 reduced the profilin-induced activation of AP-1, suggesting protein kinase C-dependent activation of AP-1. These findings indicate that profilin in the extracellular space can bind to cell surface receptors of MC and act as an inducer of signal transduction. These results suggest that extracellular profilin may be involved in the progression of glomerular diseases, by affecting cell growth.

Decreased extracellular-signal-regulated kinase and increased stress-activated MAP kinase activities in aged human skin in vivo

The ability of human skin to rejuvenate itself diminishes with the passage of time, resulting in increased fragility. This increased fragility reflects both reduced growth of skin cells and loss of collagenous connective tissue. Oxidative damage plays a central role in cellular aging. Cellular responses to growth signals and oxidative stress are mediated, in part, by growth-factor-activated and stress-activated MAP kinases. We report here that the extracellular-signal-regulated MAP kinase pathway is reduced and the stress-activated MAP kinase pathway is increased in old, compared with young, human skin in vivo. Extracellular-signal-regulated kinase activity was 45% lower in old skin (mean age 84.3 y) relative to young skin (mean age 23.8 y). This lower extracellular- signal-regulated kinase activity resulted from reduced activation, since total extracellular-signal-regulated kinase protein levels did not differ between young and old skin, whereas phosphorylated (i.e., activated) extracellular-signal-regulated kinase protein was reduced 60% in old skin. Cyclin D2, which is regulated by extracellular-signal-regulated kinase and functions to promote cell cycle progression, was reduced 50% in old skin compared with young skin. In contrast, stress-activated MAP kinase activity was elevated 3.4-fold in old skin compared with young skin. This increased activity resulted from enhanced activation, since total stress-activated MAP kinase protein levels were similar in old and young skin. Transcription factor c-Jun, which is activated by stress-activated MAP kinases and promotes expression of connective-tissue-degrading matrix metalloproteinases, was elevated 2-fold in old skin compared with young skin. Treatment of old skin with vitamin A (retinol) for 7 d stimulated extracellular-signal-regulated kinase activity, consistent with its demonstrated ability to stimulate cell growth in old human skin. Taken together, these data indicate that alterations in MAP kinase activities play a key role in the pathophysiology of human skin aging.

Induction of signal transduction pathways in rat gastric epithelial cells stimulated with interleukin-1beta

BACKGROUND

Interleukin-1beta (IL-1beta) participates in cell growth, differentiation and apoptosis via activation of several kinases in a variety of cells. Mitogen-activated protein (MAP) kinases are important intermediates of the signal transduction pathway from the cell surface to the nucleus, leading to activation of transcription factors. There are no reports on the effect of IL-1beta on these pathways in gastric epithelial cells.

AIM

To investigate whether IL-1beta activates MAP kinases [extracellular signal-regulated kinases (ERKs), c-Jun NH2-terminal kinases (JNKs) and p38 MAP kinase (p38 MAPK)] and nuclear factor (NF)-kappaB. a transcription factor, in gastric epithelial cells (RGM1).

METHODS

The activities of ERKs and JNKs were estimated by in-gel kinase assay, and p38 MAPK activity was measured by in vitro kinase assay at various time points (0-40 min) after addition of IL-1beta (100 pg/mL) for 20 min. The activity of NF-kappaB was analysed using gel mobility shift assay at times from 0 to 4 h after addition of IL-1beta.

RESULTS

Activity of ERKs was detectable at 10 min, peaked at 20 min, and continued at increased levels until 40 min. Activity of both JNKs and p38 MAPK were detectable during 5-20 min, and then decreased within 40 min. Activation of NF-kappaB occurred at 30 min, and increased activity continued for 6 h. Interleukin-1beta activated MAP kinases and NF-kappaB in RGM1 cells.

CONCLUSION

The activation induced by this cytokine may play an important role in the initiation of the inflammatory process in gastric mucosa.

Transcriptional regulatory sequences within the first intron of the chicken apolipoproteinAI (apoAI) gene

Previous studies demonstrated that the -82 to +87 nucleotides (nt) 5'-upstream region of the chicken apolipoprotein (apoAI) gene are necessary for maximum reporter chloramphenicol acetyl transferase (cat) gene activation in chicken hepatocarcinoma (LMH) cells [Bhattacharyya, N., Chattapadhyay, R., Oddoux, C., Banerjee, D., 1993. Characterisation of the chicken apolipoprotein A-I gene 5'-flanking region. DNA Cell Biol. 12, 597-604]. The -82 to +87nt contain the 5'-untranslated nt, part of the first intron, and the upstream regulatory sequences. In this study, we examined the role of the first intron in the transcriptional regulation of the chicken apoAI gene. Six different reporter cat gene constructs with or without part of the first intron were prepared and transfected into LMH, normal rat kidney (NRK) and human hepatocarcinoma (HepG2) cells. Cell extracts were prepared from each transfected cell line, and CAT activities were measured. All three cell-lines readily expressed CAT, indicating that transcriptional regulatory sequences are present within the first intron region of the chicken apoAI gene. In an enhancer assay, the first intron containing cat construct exhibited a 5.4-fold increase of reporter activity in NRK cells when compared to a SV 40 promoter containing cat plasmid, suggesting the presence of a moderate enhancer element within +29 to +87nt of the first intron. DNase I protection assays, electrophoretic mobility shift assays and binding experiments with nuclear proteins isolated from different chicken tissues and LMH cells showed interaction with +29 to +87nt. Nuclear proteins isolated from tissues like liver and intestine, that actively express apoAI gene, failed to interact with +29 to +87nt, whereas nuclear proteins isolated from tissues that are less active in apoAI gene expression readily interacted with this region. To show the binding of the LMH-specific trans-acting factors to the +50 to +68nt intron region, DNA-affinity chromatography step was performed by using 3H-labeled nuclear proteins. These studies demonstrate that the first intron region of the apoAI gene interacts with trans-acting proteins and plays an important role in transcriptional regulation of the apoAI gene.

Estradiol suppresses type I collagen synthesis in mesangial cells via activation of activator protein-1

BACKGROUND

Estradiol suppresses the synthesis of type I collagen by murine mesangial cells. However, neither the alpha 1(I) nor the alpha 2(I) collagen gene contains an estrogen-response element. Because estradiol modulates the transcription of several genes that lack an estrogen-response element but contain a regulatory activator protein-1 (AP-1) binding motif, we hypothesized that AP-1 may mediate estradiol-induced suppression of type I collagen synthesis.

METHODS

We measured type I collagen synthesis in murine mesangial cells exposed to estradiol, phorbol 12-myristate 13-acetate (an activator of AP-1), or curcumin (an inhibitor of AP-1). We also assessed the effects of estradiol on the steady-state level of c-fos and c-jun mRNA and on the binding of mesangial cell nuclear extracts to an AP-1 consensus binding site oligonucleotide.

RESULTS

Estradiol (10(-10) M to 10(-7) M) suppressed type I collagen synthesis by murine mesangial cells in a dose-dependent manner (10(-7) M, 43.7 +/- 8.2% of control values, P < 0.001). Phorbol 12-myristate 13-acetate (10 microM, four-hr exposure) also decreased type I collagen in the media. In contrast, curcumin (1 microM) increased type I collagen. Estradiol increased the steady-state level of c-fos mRNA twofold at 30 minutes, with a return to basal levels at one hour. This was associated with a greater than threefold increase in the binding of nuclear extracts from estradiol-treated mesangial cells to an AP-1 consensus binding site oligonucleotide. Estradiol-enhanced binding of nuclear extracts to the AP-1 oligonucleotide was reversed by cycloheximide.

CONCLUSIONS

These data suggest that estradiol suppresses collagen I synthesis by murine mesangial cells via enhanced AP-1 activity.

Chronic alcohol intake interferes with retinoid metabolism and signaling

Chronic and excessive ethanol consumption is associated with cellular proliferation, fibrosis, cirrhosis, and cancer of the liver. The critical event in early alcohol-induced hepatic injury is an alcohol-induced activation (cell proliferation and increased fibrogenesis) of hepatic stellate cells. However, the mechanisms by which alcohol causes proliferative activation in hepatic stellate cells have not been identified. An important characteristic of alcohol-induced injury is impaired vitamin A nutritional status. The demonstration that retinoic acid is the most physiologically active derivative of vitamin A and the discovery of retinoic acid receptors provide a mechanistic basis for understanding the actions of vitamin A and alcohol on hepatic cell proliferation. Recent studies have demonstrated that chronic alcohol intake can reduce hepatic retinoic acid concentrations, diminish retinoid signaling, and enhance activator protein-1 (AP-1 (c-Jun and c-Fos)) expression in rat liver. These are the possible biochemical and molecular mechanisms whereby ethanol ingestion results in hepatic stellate cell proliferative activation and hepatic fibrogenesis.

Alterations in the regulation of expression of the alpha 1(I) collagen gene (COL1A1) in systemic sclerosis (scleroderma)

At present, the mechanisms that regulate the expression of collagen genes in normal and pathologic fibroblasts are not known. Thus, the detailed study of transcriptional regulation of COL1A1 in SSc cells will increase our current understanding of the pathophysiology of fibrotic diseases. These studies will yield valuable information regarding the important biological process of regulation of collagen gene expression under normal and pathologic conditions, a process that has remained elusive despite intense recent investigations. It is now evident that persistent overproduction of collagen is responsible for the progressive nature of tissue fibrosis in SSc. Up-regulation of collagen gene expression in SSc fibroblasts appears to be a critical event in this process. The coordinate transcriptional activation of numerous collagen genes suggests a fundamental alteration in the regulatory control of gene expression in SSc fibroblasts. Trans-acting nuclear factors which bind to cis-acting elements in enhancer (intronic) and promoter regions of the genes modulate the basal and inducible transcriptional activity of the collagen genes. The identification of the nuclear transcription factors that regulate normal collagen gene expression may provide promising approaches to the therapy of this incurable disease.

Odontoblast commitment and differentiation

Histological and cytological organization confer specificity to the odontoblasts. These postmitotic, neural crest derived, polarized cells are aligned in a single layer at the periphery of the dental pulp and secrete the organic components of predentin-dentin. The developmental history of these cells demands a cascade of epigenetic signalling events comprising the acquisition of odontogenic potential by neural crest cells, their patterning in the developing jaws, the initiation of odontogenesis through interaction with the oral epithelium, commitment, and tooth-specific spatial distribution of competent preodontoblasts able to overtly differentiate. Recent experimental investigations are critically summarized, many open questions are stressed, and current hypotheses concerning the control of terminal odontoblast differentiation are outlined.Key words: odontoblast, neural crest, oral ectoderm, differentiation.

Differential activation of cardiac c-jun amino-terminal kinase and extracellular signal-regulated kinase in angiotensin II-mediated hypertension

Two subgroups of mitogen-activated protein kinases, c-jun NH2-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK), are thought to be involved in cultured cardiac myocyte hypertrophy and gene expression. To examine the in vivo activation of these kinases, we measured cardiac JNK and ERK activities in conscious rats subjected to acute or chronic angiotensin II (Ang II) infusion, by using in-gel kinase methods. About 50 mm Hg rise in blood pressure by Ang II (1000 ng . kg-1 . min-1) infusion caused larger activation of left ventricular JNK than ERK, via the AT1 receptor. In spite of short duration (about 30 minutes) of maximal blood pressure elevation by Ang II, JNK sustained the peak value (more than 5-fold increase) from 15 minutes up to at least 3 hours. Similar activation of JNK was seen in the right ventricle. Thus, cardiac JNK activation by Ang II seems to be in part mediated by its direct action via the AT1 receptor. The dose-response relationships for Ang II-induced rises in blood pressure and cardiac JNK and ERK activation indicated that cardiac JNK or ERK was not activated by a mild increase in blood pressure and that cardiac JNK was activated by Ang II-mediated hypertension in a more sensitive manner than ERK. Cardiac hypertrophy, induced by chronic Ang II infusion, was preceded by JNK activation without ERK activation. Furthermore, gel mobility shift analysis showed that cardiac JNK activation was followed by increased activator protein-1 DNA binding activity due to c-Fos and c-Jun. These results provided the first evidence for the preferential activation of cardiac JNK in Ang II-induced hypertension and suggested that JNK might play some role in Ang II-induced cardiac hypertrophic response in vivo. However, further study is needed to elucidate the role of JNK in cardiac hypertrophy in vivo.

A gene-targeting approach identifies a function for the first intron in expression of the alpha1(I) collagen gene

The role of the first intron of the Col1A1 gene in the regulation of type I collagen synthesis remains uncertain and controversial despite numerous studies that have made use of transgenic and transfection experiments. To examine the importance of the first intron in regulation of the gene, we have used the double-replacement method of gene targeting to introduce, by homologous recombination in embryonic stem (ES) cells, a mutated Col1A1 allele (Col-IntDelta). The Col-IntDelta allele contains a 1. 3-kb deletion within intron I and is also marked by the introduction of a silent mutation that created an XhoI restriction site in exon 7. Targeted mice were generated from two independently derived ES cell clones. Mice carrying two copies of the mutated gene were born in the expected Mendelian ratio, developed normally, and showed no apparent abnormalities. We used heterozygous mice to determine whether expression of the mutated allele differs from that of the normal allele. For this purpose, we developed a reverse transcription-PCR assay which takes advantage of the XhoI polymorphism in exon 7. Our results indicate that in the skin, and in cultured cells derived from the skin, the intron plays little or no role in constitutive expression of collagen I. However, in the lungs of young mice, the mutated allele was expressed at about 75% of the level of the normal allele, and in the adult lung expression was decreased to less than 50%. These results were confirmed by RNase protection assays which demonstrated a two- to threefold decrease in Col1A1 mRNA in lungs of homozygous mutant mice. Surprisingly, in cultured cells derived from the lung, the mutated allele was expressed at a level similar to that of the wild-type allele. Our results also indicated an age-dependent requirement for the intact intron in expression of the Col1A1 gene in muscle. Since the intron is spliced normally, and since the mutant allele is expressed as well as the wild-type allele in the skin, reduced mRNA stability is unlikely to contribute to the reduction in transcript levels. We conclude that the first intron of the Col1A1 gene plays a tissue-specific and developmentally regulated role in transcriptional regulation of the gene. Our experiments demonstrate the utility of gene-targeting techniques that produce subtle mutations for studies of cis-acting elements in gene regulation.

Effects of simulated solar radiation on type I and type III collagens, collagenase (MMP-1) and stromelysin (MMP-3) gene expression in human dermal fibroblasts cultured in collagen gels

Understanding the mechanisms responsible for photodamage to the skin is most important for dermatology. 3-D cultures have been used as tools to mimic the in vivo situation for several years. We irradiated such a system containing human dermal fibroblasts cultured in collagen gels, a well-known model considered to be a dermal equivalent, which reproduces the interaction between cells and the surrounding extracellular matrix. The effects of solar irradiation (315-800 nm) on the steady-state levels of the mRNAs of extracellular matrix components (type I and III collagens) and their degrading enzymes (interstitial collagenase, MMP-1 and stromelysin 1, MMP-3) were measured. Exposure to low levels of solar radiation (0-10 J cm-2 in the UVA, i.e. suberythemal UVA doses) caused a transient decrease in type I procollagen mRNA, an increase in MMP-mRNA, and no change in type III procollagen mRNA steady-state levels. These results describe the early changes in the connective tissue of the skin following exposure to low-level solar stimulation, and may help explain the long-term changes in photodamaged skin.

Role of AP-1 complex in angiotensin II-mediated transforming growth factor-beta expression and growth of smooth muscle cells: using decoy approach against AP-1 binding site

The cis element double-stranded oligodeoxynucleotides (ODN) ("decoy") approach has enabled us to clarify the responsible elements. Using this approach, we transfected AP-1 decoy ODN into VSMC cultured from WKY rats (WKY Adu) which produce latent TGF-beta, but not active TGF-beta, and Sprague-Dawley rats (CNC) which produce active and latent TGF-beta under Ang II-stimulation. AP-1, but not mismatched, decoy ODN abolished Ang II-stimulated TGF-beta gene expression and production in both Adu and CNC. However, AP-1 decoy did not alter DNA, RNA, and protein synthesis in Adu. In contrast, cell number was increased under Ang II stimulation by AP-1 decoy ODN in CNC without significant change in RNA and protein synthesis. These results showed that Ang II stimulated TGF-beta production through the AP-1 complex. In VSMC that produce active TGF-beta (CNC), the AP-1 complex stimulated by Ang II may inhibit cell growth through active TGF-beta production. Overall, this study demonstrates the utility of the decoy approach to study the specific function of cis elements in endogenous gene regulation such as Ang II-induced TGF-beta expression.

Tumor cell contact mediated transcriptional activation of the fibroblast matrix metalloproteinase-9 gene: involvement of multiple transcription factors including Ets and an alternating purine-pyrimidine repeat

The 92-kDa type IV collagenase (MMP-9) is a metalloproteinase frequently localized in both tumor stroma and in tumor cells, particularly at the tumor invasion front. To explore the factors regulating transcriptional activation of MMP-9 in stromal cells, we used a model system in which fibroblast MMP-9 expression can be upregulated by cell-cell contact with metastatic transformed rat embryo cells. Using transient transfection of reporter gene constructs containing 5'-deleted or mutated MMP-9 promoter fragments, as well as electrophoretic mobility shift assays, the upstream NFkappaB, SP-1, and Ets sites and the downstream AP-1 site and retinoblastoma binding element were shown to be necessary for basal transcriptional activity of fibroblast MMP-9. In contrast only Ets or SP-1 appeared to be involved in contact-mediated induction of MMP-9. Mutation of the upstream AP-1 site increased both basal and contact-stimulated promoter activation. Deletion of the alternating purine-pyrimidine repeat in the downstream promoter decreased transcriptional activity. Together these findings suggest that Ets and SP-1 are the central transcriptional activators of MMP-9 gene expression in fibroblasts specifically responding to tumor cell contact, and that promoter conformation may regulate MMP-9 expression.

COL1A1 transgene expression in stably transfected osteoblastic cells. Relative contributions of first intron, 3'-flanking sequences, and sequences derived from the body of the human COL1A1 minigene

Collagen reporter gene constructs have be used to identify cell-specific sequences needed for transcriptional activation. The elements required for endogenous levels of COL1A1 expression, however, have not been elucidated. The human COL1A1 minigene is expressed at high levels and likely harbors sequence elements required for endogenous levels of activity. Using stably transfected osteoblastic Py1a cells, we studied a series of constructs (pOBColCAT) designed to characterize further the elements required for high level of expression. pOBColCAT, which contains the COL1A1 first intron, was expressed at 50-100-fold higher levels than ColCAT 3.6, which lacks the first intron. This difference is best explained by improved mRNA processing rather than a transcriptional effect. Furthermore, variation in activity observed with the intron deletion constructs is best explained by altered mRNA splicing. Two major regions of the human COL1A1 minigene, the 3'-flanking sequences and the minigene body, were introduced into pOBColCAT to assess both transcriptional enhancing activity and the effect on mRNA stability. Analysis of the minigene body, which includes the first five exons and introns fused with the terminal six introns and exons, revealed an orientation-independent 5-fold increase in CAT activity. In contrast the 3'-flanking sequences gave rise to a modest 61% increase in CAT activity. Neither region increased the mRNA half-life of the parent construct, suggesting that CAT-specific mRNA instability elements may serve as dominant negative regulators of stability. This study suggests that other sites within the body of the COL1A1 minigene are important for high expression, e.g. during periods of rapid extracellular matrix production.

A minimal murine Msx-1 gene promoter. Organization of its cis-regulatory motifs and their role in transcriptional activation in cells in culture and in transgenic mice

To dissect the cis-regulatory elements of the murine Msx-1 promoter, which lacks a conventional TATA element, a putative Msx-1 promoter DNA fragment (from -1282 to +106 base pairs (bp)) or its congeners containing site-specific alterations were fused to luciferase reporter and introduced into NIH3T3 and C2C12 cells, and the expression of luciferase was assessed in transient expression assays. The functional consequences of the sequential 5' deletions of the promotor revealed that multiple positive and negative regulatory elements participate in regulating transcription of the Msx-1 gene. Surprisingly, however, the optimal expression of Msx-1 promoter in either NIH3T3 or C2C12 cells required only 165 bp of the upstream sequence to warrant detailed examination of its structure. Therefore, the functional consequences of site-specific deletions and point mutations of the cis-acting elements of the minimal Msx-1 promoter were systematically examined. Concomitantly, potential transcriptional factor(s) interacting with the cis-acting elements of the minimal promoter were also studied by gel electrophoretic mobility shift assays and DNase I footprinting. Combined analyses of the minimal promoter by DNase I footprinting, electrophoretic mobility shift assays, and super shift assays with specific antibodies revealed that 5'-flanking regions from -161 to -154 and from -26 to -13 of the Msx-1 promoter contains an authentic E box (proximal E box), capable of binding a protein immunologically related to the upstream stimulating factor 1 (USF-1) and a GC-rich sequence motif which can bind to Sp1 (proximal Sp1), respectively. Additionally, we observed that the promoter activation was seriously hampered if the proximal E box was removed or mutated, and the promoter activity was eliminated completely if the proximal Sp1 site was similarly altered. Absolute dependence of the Msx-1 minimal promoter on Sp1 could be demonstrated by transient expression assays in the Sp1-deficient Drosophila cell line cotransfected with Msx-1-luciferase and an Sp1 expression vector pPacSp1. The transgenic mice embryos containing -165/106-bp Msx-1 promoter-LacZ DNA in their genomes abundantly expressed beta-galactosidase in maxillae and mandibles and in the cellular primordia involved in the formation of the meninges and the bones of the skull. Thus, the truncated murine Msx-1 promoter can target expression of a heterologous gene in the craniofacial tissues of transgenic embryos known for high level of expression of the endogenous Msx-1 gene and found to be severely defective in the Msx-1 knock-out mice.

Transcriptional activation of the minimal human Proalpha1(I) collagen promoter: obligatory requirement for Sp1

A construct containing human Proalpha1(I) collagen gene promoter/enhancer-driven chloramphenicol acetyltransferase (CAT), pCOL-KT, failed to be expressed significantly in Sp1-deficient Schneider Drosophila line 2 (SL2) cells. However, CAT expression was induced 200-fold in SL2 cells co-transfected with pCOL-KT and pPACSp1, an Sp1-expression vector driven by the Drosophila actin 5C promoter. Elimination of the four potential Sp1-binding sites from pCOL-KT (pCOL-KTDeltaI), by removal of the first intron, did not abrogate Sp1-mediated induction of CAT. Even more significantly, a minimal Proalpha1(I) collagen promoter (-100 to +117 bp), containing a TATA box (-28 to -25 bp) and one putative Sp1-binding site (-87 to -82 bp), elicited strong Sp1-induced transactivation. Furthermore, mutation of the Sp1 motif in the minimal Proalpha1(I) collagen promoter-CAT construct abolished Sp1-induced expression of the reporter gene. Purified Sp1 protein bound specifically to DNA fragments of the Proalpha1(I) minimal promoter encompassing the putative Sp1-binding site; Sp1 binding could be competed out by a double-stranded oligonucleotide containing the wild-type Sp1 sequence, while an oligonucleotide containing a mutated Sp1 site failed to compete. Based on these results, we postulate that Sp1 plays an obligatory role in the transcriptional activation of the human Proalpha1(I) collagen gene. Additionally, we propose that a bona fide Sp1 motif, located most proximal to the TATA box, is necessary and sufficient for Sp1-mediated activation of the minimal Proalpha1(I) collagen promoter.

Expressions of c-jun and jun-B proto-oncogenes in odontoblasts during development of bovine tooth germs

c-jun and jun-B genes are among the nuclear proto-oncogenes induced by growth factors such as the TGF-beta superfamily and play important roles in cell differentiation. These gene products enhance expressions of proteins including osteocalcin, alkaline phosphatase, and collagens. On the other hand, it is well-known that the TGF-beta superfamily affects odontoblast differentiation, and that differentiated odontoblasts express extracellular and membrane proteins as described above. However, there are few reports of factors that participate in the transcriptional regulation of odontoblasts. Especially, little is known about the expression of c-jun and jun-B genes. In this study, we focused on the examination of expressions of c-jun and jun-B genes in dental papillae of bovine tooth germs. Using in situ hybridization, we found that these genes were expressed only in the odontoblastic lineage, but not in other dental papilla cells. Levels of c-jun and jun-B mRNAs increased along the gradient of differentiation of odontoblasts. These levels of c-jun mRNAs were maintained in both young and mature odontoblasts. However, unlike the c-jun gene, expression of the jun-B gene became sparse in mature odontoblasts compared with young odontoblasts. For further analysis, Northern hybridization of total RNA extracted from differentiated odontoblasts was performed for the examination of levels of jun-B mRNAs, indicating that levels of jun-B mRNAs of mature odontoblasts were clearly less than those of young odontoblasts. These results suggest that c-jun and jun-B genes may participate in the transcriptional regulation of odontoblasts of bovine tooth germs, and may control the odontoblast phenotype. Furthermore, our results suggest that these genes can be markers of odontoblasts during dentinogenesis; especially, high expression of jun-B gene can be a marker of young odontoblasts that start to form the new dentin matrix.

Binding of upstream stimulatory factor to an E-box in the 3'-flanking region stimulates alpha1(I) collagen gene transcription

Since several lines of evidence implicate the 3'-flanking region in regulating alpha1(I) collagen gene transcription, we analyzed 12. 4-kilobase pairs of 3'-flanking sequence of the murine alpha1(I) collagen gene for transcriptional elements. A region of the 3'-flanking region stimulated expression of the heterologous beta-globin gene promoter in an enhancer trap plasmid and of the alpha1(I) collagen gene promoter in a collagen-luciferase reporter gene construct when located 3' to the luciferase reporter gene. DNase I footprinting analysis demonstrated the presence of three regions where DNA binding proteins specifically interact within this 3'-stimulatory region. Inspection of the DNA sequence revealed a consensus E-box, a binding site for basic helix-loop-helix proteins, in one of the protein binding sites. Mobility shift assays demonstrated that upstream stimulatory factors (USF) USF-1 and USF-2 bind to this E-box. Mutating the E-box in the context of the 3'-flanking region confirmed that it contributes to the enhancement of transcriptional activity of the alpha1(I) collagen gene promoter. Mutations in all three protein binding sites abolished transcriptional activation by the 3'-flanking region, suggesting a complex interaction among the trans-acting factors in enhancing transcriptional activity. Thus, a region of the 3'-flanking region of the alpha1(I) collagen gene stimulates transcription of the alpha1(I) collagen gene promoter, and USF-1 and USF-2 contribute to this transcriptional stimulation.

Pathogenesis of scleroderma. Collagen

It is now evident that persistent overproduction of collagen and other connective tissue macromolecules results in excessive tissue deposition, and is responsible for the progressive nature of fibrosis in SSc. Up-regulation of collagen gene expression in SSc fibroblasts appears to be a critical event in the development of tissue fibrosis. The coordinate transcriptional activation of a number of extracellular matrix genes suggests a fundamental alteration in the regulatory control of gene expression in SSc fibroblasts. Trans-acting nuclear factors that bind to cis-acting elements in enhancer and promoter regions of the genes modulate the basal and inducible transcriptional activity of the collagen genes. The identity of the nuclear transcriptional factors that regulate normal collagen gene expression remains to be firmly established, and to date, no alterations in the level or in the activity of such DNA binding factors has been demonstrated in SSc fibroblasts. In addition to important interactions between fibroblasts and the extracellular matrix, cytokines and other cellular mediators can positively and negatively influence fibroblast collagen synthesis. Some of these signaling molecules may have physiologic roles, and their aberrant expression, or altered responsiveness of SSc fibroblasts to them, may result in the acquisition of the activated phenotype. The rapid expansion of knowledge regarding the effects of cytokines on extracellular matrix synthesis has led to an appreciation of the enormous complexity of regulatory networks that operate in the physiologic maintenance of connective tissue and which may be responsible for the occurrence of pathologic fibrosis. The ubiquitous growth factor TGF beta is the most potent inducer of collagen gene expression and connective tissue accumulation yet discovered. The expression of TGF beta in activated infiltrating mononuclear cells suggests a role for this cytokine as a mediator of fibroblast activation in SSc. Furthermore, the recognition that TGF beta is capable of inducing its own expression in a variety of cell types, coupled with the demonstration that a subpopulation of SSc dermal fibroblasts produces TGF beta, indicates the existence of a possible autocrine loop whereby lymphocyte-derived TGF beta in early SSc not only signals biosynthetic activation of fibroblasts in a paracrine manner, but autoinduces endogenous TGF beta production by the target fibroblasts themselves. Such an autocrine loop involving TGF beta may explain the persistent activation of collagen gene expression in SSc fibroblasts, and could be responsible for the progressive nature of fibrosis in SSc. Numerous other cytokines, as well as cell-matrix interactions, also modify collagen gene expression and can significantly influence the effects of TGF beta. Although their physiologic function in tissue remodeling or their involvement in abnormal fibrogenesis has not yet been conclusively demonstrated, the study of the biologic effects of these cytokines may provide important clues to understanding the pathogenesis of SSc, and to the development of rational drug therapy aimed at interrupting the abnormal fibrogenic process in this disease.

Transcriptional activation of the alpha 1(I) procollagen gene in systemic sclerosis dermal fibroblasts. Role of intronic sequences

OBJECTIVE

To investigate the transcriptional regulation of the alpha 1(I) procollagen gene (COL1A1) in cultured dermal fibroblasts from patients with diffuse systemic sclerosis (SSc) of recent onset and to evaluate the role that intronic sequences may play in the upregulated expression of COL1A1 in SSc dermal fibroblasts.

METHODS

Dermal fibroblasts from 6 patients with diffuse SSc of recent onset and from 3 healthy individuals were studied. The steady-state levels of alpha 1(I) procollagen messenger RNA were evaluated by Northern hybridization analysis, and the transcriptional regulation of COL1A1 was examined by transient transfection experiments with deletion constructs containing portions of COL1A1 promoter (with 5' end points at -5.3 kb, -2.3 kb, and -804 bp and 3' end point at +42 bp) ligated to the chloramphenicol acetyltransferase (CAT) reporter gene. To examine the role of intronic sequences, constructs containing, in addition to the COL1A1 promoter, a portion of the first intron (+380 bp to +1,440 bp) cloned in front of the CAT gene were transfected. The efficiency of transfections was normalized relative to the net amount of CAT plasmid actually transfected into recipient cells, determined by a modified Southern hybridization procedure.

RESULTS

Maximal CAT activity was observed with constructs extending from -804 bp to +42 bp in both normal and SSc fibroblasts. However, the activity driven by this construct was 80-110% higher in SSc fibroblasts. The CAT activity driven by a construct with a 5' end point at -5.3 kb was only 15-20% higher in SSc cells, and the CAT activity driven by a construct with a 5' end point -2.3 kb was 35-45% higher in SSc fibroblasts. The CAT activity driven by the -804-bp promoter construct was increased up to 4-fold in SSc fibroblasts in comparison with normal cells when the intronic segment spanning +380 bp to +1,440 bp was included in the transfected construct.

CONCLUSION

The results directly demonstrate the transcriptional activation of COL1A1 in dermal fibroblasts from SSc patients. The data also indicate that first-intron sequences of COL1A1 are required for maximal transcriptional activity of the collagen gene and may play an important role in the up-regulation of its expression in SSc fibroblasts.

A downstream AP-1 element regulates in vitro lung transcription from the human pulmonary surfactant protein B promoter

We have used the human lung surfactant protein B (SP-B) gene as a template for in vitro transcription studies. Transcription factors were provided by nuclear extracts from a cultured line of human lung (type II-like) cells. Elements upstream of -50 had essentially no effect on the efficiency of the SP-B promoter in vitro. However, a deletion of the region from +8 to +8 reduced in vitro transcription by a factor of 10. The only factor whose binding was detected between +1 and +100 by footprinting, and between +12 and +38 by electrophoretic mobility shift analysis (EMSA), was a member of the AP-1 family. Mutation of 4 of 7 bases of the AP-1 site reduced transcription two-fold and ablated the AP-1 EMSA binding complex observed on the SP-B downstream region (+12 to +38). Competition with unlabeled AP-1 consensus oligonucleotide abolished the downstream footprint over the AP-1 site. Thus, the SP-B promoter is one of a very small class of RNA polymerase II promoters that are strongly dependent in vitro on sequence elements downstream of the transcription start site, and, in this case, the AP-1 consensus element and surrounding sequences.

Okadaic acid-induced transcriptional downregulation of type I collagen gene expression is mediated by protein phosphatase 2A

Expression of type I collagen genes is highly regulated and becomes abnormal in various pathological conditions, from excessive collagen production in fibrotic diseases to their downregulation in transformed cells. Some inflammatory cytokines and other ligands, capable of eliciting intracellular phosphorylation, can profoundly alter collagen gene expression. We investigated the role of serine/threonine protein phosphatases (PP) in the regulation of collagen gene expression. Biosynthesis of the endogenous type I procollagen, and expression of Pro alpha 1(I) promoter-luciferase (Luc) constructs transfected in NIH3T3 fibroblasts, were evaluated in response to PP2A and PP1 inhibitor okadaic acid (OA) and exogenously expressed PP catalytic subunits. OA suppressed type I collagen gene expression as judged by reduced rates of protein synthesis, steady state levels of Pro alpha 1(I) collagen mRNA and expression of Luc driven by Pro alpha 1 (I) collagen promoter in OA-treated cells. Co-transfection of Pro alpha 1(I)-Luc with expression vectors containing PP2A, but not PP1, stimulated collagen promoter activity. These results strongly suggest that OA acts via PP2A-mediated dephosphorylation of an unidentified transcription factor(s) or cofactor(s) needed to activate Pro alpha 1(I) collagen promoter.

Regulation of expression of the alpha 1 (I) collagen gene: a critical appraisal of the role of the first intron

The transcriptional regulation of the genes encoding the alpha 1 (I) collagen chains is necessarily complex since these genes are expressed at widely different levels, and in a cell- and tissue-specific fashion. In the case of the alpha 1 (I) gene, there is substantial, but controversial, evidence for an involvement of the first intron in the tissue-specific expression of the gene. This evidence is based largely on transfection of cells with collagen-reporter gene constructs and on studies of transgenic mice. In this review, I propose a number of reason for the conflicting data in the literature: 1) the cell-specific nature of the intronic effect; thus, not all cultured, collagen-synthesizing cells will demonstrate an intronic effect by transfection; 2) the possibility that functionally equivalent regulatory elements are placed in different regions of the alpha 1 (I) gene in different species; and 3) the possibility that functionally redundant sequences exist within the alpha 1 (I) gene, which would permit other regions to substitute for the first intron.

Transcriptional repression of the alpha 1(I) collagen gene by ras is mediated in part by an intronic AP1 site

We have previously shown that transformation of fibroblasts by ras results in transcriptional inhibition of the alpha 1(I) gene. An alpha 1(I)-hGH chimeric plasmid containing 3.7 kb of 5' flanking and 4.4 kb of alpha 1(I) transcribed sequence was regulated appropriately by ras in a transient transfection assay. In contrast, a similar plasmid containing alpha 1(I) DNA from -220 to +500 was virtually unresponsive to ras. The regions from -3700 to -220 and +500 to +4400 contributed equally to the ras-mediated inhibition of the parental plasmid. Deletion analysis indicated that a short fragment, between +500 and +890 in the first intron of the alpha 1(I) gene, was recognized differently in ras-transformed and wild-type cells. A previously described AP1 site in this fragment stimulated alpha 1(I) transcription in Rat1 fibroblasts but was inactive in ras-transformed cells. Mobility shift assays using nuclear extracts from the two cell types demonstrated differences in binding to the alpha 1(I) AP1 site. We conclude that ras transformation suppresses the function of a cell-specific enhancer in the first intron of the alpha 1(I) collagen gene.

Increased alpha 1(I) procollagen gene expression in tight skin (TSK) mice myocardial fibroblasts is due to a reduced interaction of a negative regulatory sequence with AP-1 transcription factor

The TSK mouse, a model of fibrosis, displays exaggerated connective tissue accumulation in skin and visceral organs including the heart. To study the mechanisms of myocardial fibrosis in TSK mice, we established several strains of TSK mice myocardial fibroblasts in culture and examined the regulation of collagen gene expression in these cells. These strains displayed increased collagen gene expression in comparison with myocardial fibroblasts established from normal mice. On an average, the TSK myocardial fibroblast cultures showed a 4-fold increase in collagen synthesis and 4.4- and 3.6-fold increases, respectively, in alpha 1(I) and alpha 1(III) collagen mRNA steady state levels. The increased alpha 1(I) and alpha 1(III) collagen mRNA levels were mainly due to increased transcription rates (3.4- and 3.8-fold higher, respectively) of the respective genes. Furthermore, we showed that the up-regulation of alpha 1(I) procollagen gene transcription in TSK mice myocardial fibroblasts was due to the lack of the strong inhibitory influence of a regulatory sequence contained in the promoter region encompassing nucleotides -675 to -804. Nuclear extracts from TSK mice myocardial fibroblasts showed lower DNA binding activity to oligonucleotides spanning the mapped regulatory sequence as well as to a consensus AP-1 sequence, but not to a consensus SP-1 sequence, and supershift experiments with an AP-1 antibody confirmed the interaction of these oligonucleotides with AP-1 protein. These observations indicate that a strong negative regulatory sequence contained within -0.675 to -0.804 kilobase of the alpha 1(I) procollagen promoter binds AP-1 transcription factor and mediates inhibition of gene transcription in normal murine myocardial fibroblasts. The TSK mice myocardial fibroblasts lack this inhibitory control, due to lower available amounts and/or decreased binding activity to this inhibitory sequence, and hence display increased alpha 1(I) procollagen gene expression.

Cortisol downregulates osteoblast alpha 1 (I) procollagen mRNA by transcriptional and posttranscriptional mechanisms

Glucocorticoids decrease osteoblast proliferation and type I collagen production, and this may play a role in the development of glucocorticoid-induced osteoporosis. Osteoblast-enriched cultures derived from fetal rat calvaria were used to determine the mechanisms by which cortisol decreases alpha 1 (I) procollagen expression in bone cells. A 24 h treatment with cortisol decreased collagen synthesis in these cultures in a dose-dependent manner. Cortisol decreased alpha 1 (I) procollagen transcripts in a dose- and time-dependent manner as well. Repression of alpha 1 (I) procollagen transcripts was evident as early as 2 h of treatment and was maximal after 48 h of treatment. Nuclear run-off assays showed that cortisol downregulated transcription of the alpha 1 (I) procollagen gene. In addition, pretreatment with cortisol decreased the stability of alpha 1 (I) procollagen mRNA in transcription-arrested osteoblast cultures. The ability of cortisol to downregulate alpha 1 (I) procollagen transcripts was sensitive to cycloheximide treatment, suggesting that the gene is under "secondary control" by glucocorticoids. Since cortisol decreases alpha 1 (I) procollagen gene transcription in osteoblasts but does not affect alpha 1 (I) procollagen gene transcription in fibroblasts, we suggest that the mechanisms controlling glucocorticoid repression of collagen expression are cell-type specific.

Activation of Ito cells involves regulation of AP-1 binding proteins and induction of type I collagen gene expression

Activation of liver Ito cells is characterized by increased proliferation, fibrogenesis, loss of cellular retinoid and change of cell-shape. Here, we have described fundamental differences between freshly isolated Ito cells (FIC) and long-term cultured Ito cells (LTIC). This process of activation correlates with the absence of expression of Pro alpha 1(I) gene in FIC. LTIC expressed abundant transcripts of Pro alpha 1(I) gene. Nuclear run-off experiments showed the inability of FIC to support Pro alpha 1(I) RNA transcription while LTIC transcribed it greater than 5-fold as compared with FIC. Transforming growth factor beta (TGF beta)-treated LTIC had a preferential increase in the rate of Pro alpha 1(I) gene transcription as compared with control LTIC. A human collagen type I promoter-enhancer construct (pCOL-KT) [Thompson, Simkevich, Holness, Kang and Raghow (1991) J. Biol. Chem. 266, 2549-2556] was readily expressed in LTIC but failed to be expressed in FIC. Furthermore, TGF beta treatment of LTIC resulted in an increased expression of pCOL-KT. The deletion of an activator protein-1 (AP-1) binding site (+598 to +604) in the 360 bp enhancer region of pCOL-KT (S360) caused decreased expression of the CAT reporter gene, suggesting that this bonafide AP-1 site can, at least in part, mediate the transactivation effect of TGF beta. Using DNAase I protection, we demonstrate a single foot-print located at +590 to +625 in the S360 fragment; nuclear extracts prepared from TGF beta-treated LTIC exhibited greater activity of these AP-1 binding proteins. Gel mobility assays corroborated and extended the footprinting observation. No AP-1-binding activity was found in the nuclear extracts of FIC. Double-stranded oligonucleotides containing the consensus AP-1 motif were able to compete out the binding; consensus NF-1 motif oligonucleotides failed to do so. The preincubation of nuclear extracts from control and TGF beta-treated LTIC with antibodies against c-jun and c-fos rendered a reduced binding of AP-1 proteins to the target S360 fragment.