Two different negative and one positive regulatory factors interact with a short promoter segment of the alpha 1 (I) collagen gene

Pro-remodeling peptides modulate collagen α1(I) promoter activity in rat cardiac myofibroblasts

Previous studies have extensively demonstrated the effect of endothelin-1 (ET-1), angiotensin II (Ang II), and TGF-β1 on the stimulation of collagen type I expression in cardiac myofibroblasts. However, the role of pro-remodeling peptides in the transcriptional regulation of the collagen promoter remains unclear. Thus, the purpose of this study was to investigate the net regulatory effects of pro-remodeling peptides on collagen type I promoter activity. Constructs of various lengths (300 bp, 1.1 kbp, 1.7 kbp, 2.3 kbp and 3.5 kbp) of the rat collagen α1(I) promoter were transfected into cardiac myofibroblasts in vitro and promoter activity was measured using chloramphenicol acetyl transferase (CAT) assays. Reduced promoter activity occurred across all treatments in myofibroblasts transfected with the 1.7 kbp construct. ET-1 was unable to increase promoter activity with constructs 300, 1.1, and 1.7 kbp, but induced promoter activity in cells with the 2.3 kbp construct. Additionally, while a combination of pro-remodeling peptides induced promoter activity across constructs, the resultant increase in the 2.3 and 3.5 kbp constructs were comparable to that observed from ET-1 treatment alone. Lastly, cells transfected with the entire promoter sequence had the lowest promoter activity. This data suggests that the collagen promoter is tightly regulated and that pro-remodeling factors produce an overall net effect on collagen expression, rather than additive.

Sp1 and Sp3 transcription factors mediate leptin-induced collagen α1(I) gene expression in primary culture of male rat hepatic stellate cells

Mechanisms by which leptin stimulates collagen α(1)(I) [Col1a(I)] gene expression are unclear. The purposes of this study were to identify the trans-acting factors and cis-acting elements in Col1a(I) promoter involved in this effect as well as the pathways that are implicated. In primary cultures of rat hepatic stellate cells (HSCs), we measured the effects of leptin on Col1a(I) gene and protein expression and on the binding of nuclear proteins to the Col1a(I) promoter. We found that leptin increased Col1a(I) gene and protein expression in activated HSCs. Transient transfections showed that leptin exerted its effects through elements located between -220 and -112 bp of the Col1a(I) promoter. Gel retardation assays demonstrated that leptin induced the binding of transcription factors specific protein (Sp)-1 and Sp3 to two elements located between -161 and -110 bp of the Col1a(I) promoter. Leptin-induced Sp1/Sp3 phosphorylation, but this effect was suppressed by inhibiting or silencing Janus kinase-2, phosphatidylinositol-3-kinase, nonphagocytic adenine dinucleotide phosphate (NADPH) oxidase, or ERK1/2, by the use of antioxidants or catalase, or by preventing protein-aldehyde adduct formation. Leptin provoked oxidative stress, aldehyde-protein adduct formation, and increased gene expression of some components of the NADPH oxidase complex. In conclusion, in HSCs, leptin up-regulates Col1a(I) gene expression after activating NADPH oxidase, inducing oxidative stress, aldehyde-protein adduct formation, and ERK1/2 phosphorylation, which in turn activates Sp1/Sp3 and provokes the binding of these two factors to regulatory elements located between -161 and -110 bp of the Col1a(I) promoter. These findings may contribute to a better understanding of mechanisms involved in the leptin-induced liver fibrosis.

Myocardin-related transcription factor-A complexes activate type I collagen expression in lung fibroblasts

Pulmonary fibrosis is characterized by the excessive deposition of a collagen-rich extracellular matrix. The accumulation of collagen within the lung interstitium leads to impaired respiratory function. Furthermore, smooth muscle actin-positive myofibroblasts within the fibrotic lung contribute to disease progression. Because collagen and smooth muscle cell α-actin are coordinately expressed in the setting of fibrosis, the hypothesis was tested that specific transcriptional regulators of the myocardin family might also regulate collagen gene expression in myofibroblasts. Myocardin-related transcription factors (MRTFs), through their interaction with the serum-response factor (SRF) on CArG box regulatory elements (CC(A/T)6GG), are important regulators of myofibroblast differentiation. MRTF-A transactivated type I collagen gene reporters as much as 100-fold in lung myofibroblasts. Loss of functional MRTF-A using either a dominant negative MRTF-A isoform, shRNA targeting MRTF-A, or genetic deletion of MRTF-A in lung fibroblasts significantly disrupted type I collagen synthesis relative to controls. Analysis of the COL1A2 proximal promoter revealed a noncanonical CArG box (CCAAACTTGG), flanked by several Sp1 sites important for MRTF-A activation. Chromatin immunoprecipitation experiments confirmed the co-localization of MRTF-A, SRF, and Sp1 bound to the same region of the COL1A2 promoter. Mutagenesis of either the noncanonical CArG box or the Sp1 sites significantly disrupted MRTF-A activation of COL1A2. Together, our findings show that MRTF-A is an important regulator of collagen synthesis in lung fibroblasts and exhibits a dependence on both SRF and Sp1 function to enhance collagen expression.

An alpha-1 chain of type I collagen Sp1-binding site polymorphism in women suffering from stress urinary incontinence

OBJECTIVE

We examined the possible influence of G-->T substitution in transcription factor Sp1-binding site in the gene encoding alpha-1 chain of type I collagen on the risk of stress urinary incontinence.

STUDY DESIGN

The study group consisted of 50 women reporting symptoms of stress urinary incontinence. Fifty control subjects were treated for benign gynecological conditions other then stress urinary incontinence. DNA was obtained from peripheral blood leukocytes. The fragment of the first intron of the gene encoding the alpha-1 chain of type I collagen containing the Sp1-binding site was amplified by polymerase chain reaction. The analysis of restriction fragment length polymorphism was performed.

RESULTS

We found association between the GT and TT genotype and stress urinary incontinence (P = .019). The odds ratio for developing stress urinary incontinence is 4.98 (95% confidence interval 1.97 to 12.56) in subjects presenting the GT genotype and 2.23 (95% confidence interval 0.69 to 7.25) for the TT genotype.

CONCLUSION

The G-T polymorphism at the Sp1 binding site of the gene encoding alpha-1 chain of type 1 collagen is associated with increased risk of stress urinary incontinence in women.

Multiple proteins are involved in the protein–DNA complex in the proximal promoter of the human α1(III) collagen gene (COL3A1)

We have characterized the proximal promoter of the human alpha1(III) collagen gene (COL3A1). Transient transfection assays using a series of chimeric constructs linked to the luciferase gene indicated that the segment from -96 to -34 is necessary to activate transcription. Electrophoretic mobility shift assays (EMSAs) showed that the multiple proteins form the DNA-protein complex in different combinations depending on the cell types. A competition assay using mutant oligonucleotides showed that the sequence 5'-GCTCTCATATTTCAGAA-3' (-79 to -63 bp) is critical for DNA-protein complex formation. This sequence is contained in the B element of mouse alpha1(III) collagen gene (Col3a1) reported by Ruteshouse and de Crombrugghe (J. Biol. Chem., 1993). In the rhabdomyosarcoma cell line, A204, at least two proteins of 92-118 kDa and 40-52 kDa are involved in the DNA-protein complex bound to this motif.

The transcription factor CCAAT-binding factor CBF/NF-Y and two repressors regulate the core promoter of the human pro-alpha3(V) collagen gene (COL5A3)

To elucidate the mechanisms underlining alpha3(V) collagen chain expression, we performed an initial analysis of the structure and function of the core promoter of the human COL5A3 gene. The core promoter, which lacks a typical TATA motif and has a high GC content, was defined within the -129 bp immediately upstream from the major transcription start site by transient transfection experiments. In this region, we identified four DNA-protein complexes, named A, B, C, and D, by a combination of DNase I footprinting and electrophoretic mobility shift assays. Electrophoretic mobility shift assays using mutant oligonucleotide revealed that the complexes A, B, C, and D bind to -122 to -117, the -101 to -96, the -83 to -78, and the -68 to -57 bp, respectively. The competition assays using consensus oligonucleotides and supershift assays with specific antibodies showed that complex A consists of CBF/NF-Y. In a chromatin immunoprecipitation assay, CBF/NF-Y protein directly bound to this region, in vivo. Functional analysis showed that CBF/NF-Y activated the gene, whereas the proteins of complexes B and C repressed its activity. Furthermore, overexpression of a mutant form of the CBF-B/NF-YA subunit, which forms CBF/NF-Y with CBF-A/NF-YB and CBF-C/NF-YC subunits, inhibited promoter activity.

Identification of a functional CBF-binding CCAAT-like motif in the core promoter of the mouse pro-α1(V) collagen gene (Col5a1)

We used structure-function analysis of the core promoter region to elucidate the transcriptional features of the mouse alpha 1(V) collagen gene (Col5a1). The core promoter, which lacks a typical TATA motif and has a high GC content, was defined within the 231 bp immediately upstream from the major transcription start site by transient transfection experiments. In this region, we identified three nuclear-factor binding sites by electrophoretic mobility shift assay: BS1 (-195 to -167), BS2 (-134 to -106), and BS3 (-110 to -80). Oligonucleotide competition and supershift assays revealed that Sp1, CBF, and Sp1-related protein specifically bind to BS1, BS2, and BS3, respectively. The CCAAT-like motif, CAAAT, and flanking sequences are conserved between the mouse and human gene. CBF, which recognizes this motif, activated the Col5a1 promoter, as previously reported for Col1a1 and Col1a2. Furthermore, overexpression of a wild-type and mutant forms of CBF-B subunit altered this activity. These results suggest that CBF is a key factor in the coordinated expression of type I and V collagen genes.

Transcriptional activation of alpha 1(III) procollagen gene in Tsk2/+ dermal fibroblasts

Transient transfection experiments into Tsk2/+ and normal dermal fibroblasts were performed using four successively shorter Col3a1 promoter deletion constructs: #103, #110, #114, and #120 fused to the chloramphenicol-acetyl-transferase (CAT) reporter gene. The transcriptional activity in Tsk2/+ and normal dermal fibroblasts driven by the three longer constructs was equal. With the shortest construct, #120 (-96 to +16bp) the transcriptional activity in Tsk2/+ fibroblasts was 25 times higher than in normal fibroblasts. Electrophoretic mobility shift assays with a labeled #120 probe revealed that increased DNA-protein binding occurred with nuclear extracts prepared from Tsk2/+ fibroblasts and that this binding was displaced by consensus Sp1 and NF-1 oligonucleotide sequences. These data indicate that sequences from -96 to +16bp of the Col3a1 promoter play an important role in the upregulated expression of this gene in Tsk2/+ fibroblasts and that the promoter contains sequences which bind the trans-acting nuclear factors, Sp1(like) and NF-1(like).

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.

Sp1 and Sp3 transcription factors mediate malondialdehyde-induced collagen alpha 1(I) gene expression in cultured hepatic stellate cells

Malondialdehyde, the end product of lipid peroxidation, has been shown to stimulate collagen alpha1(I) (Col1a1) gene expression. However, mechanisms of this effect are unclear. The purpose of this study was to clarify these mechanisms. Rat hepatic stellate cells were cultured in the presence of 200 microm malondialdehyde, and the effects on collagen gene expression and the binding of nuclear proteins to the col1a1 promoter were analyzed. Malondialdehyde treatment induced an increase in the cellular levels of col1a1 mRNA that was abrogated by pretreating cells with cycloheximide, p-hydroxymercuribenzoate, pyridoxal 5'-phosphate, and mithramycin. Transient transfections showed that malondialdehyde exerted its effect through regulatory elements located between -220 and -110 bp of the col1a1 promoter. Gel retardation assays demonstrated that malondialdehyde increased the binding of nuclear proteins to two elements located between -161 and -110 bp of the col1a1 promoter. These bindings were supershifted with Sp1 and Sp3 antibodies. Finally, malondialdehyde increased cellular levels of the Sp1 and Sp3 proteins and Sp1 mRNA. Our data indicated that treatment of hepatic stellate cells with malondialdehyde stimulated col1a1 gene expression by inducing the synthesis of Sp1 and Sp3 and their binding to two regulatory elements located between -161 and -110 bp of the col1a1 promoter.

Mouse alpha1(I)-collagen promoter is the best known promoter to drive efficient Cre recombinase expression in osteoblast

Cell- and time-specific gene inactivation should enhance our knowledge of bone biology. Implementation of this technique requires construction of transgenic mouse lines expressing Cre recombinase in osteoblasts, the bone forming cell. We tested several promoter fragments for their ability to drive efficient Cre expression in osteoblasts. In the first mouse transgenic line, the Cre gene was placed under the control of the 2.3-kb proximal fragment of the alpha1(I)-collagen promoter, which is expressed at high levels in osteoblasts throughout their differentiation. Transgenic mice expressing this transgene in bone were bred with the ROSA26 reporter (R26R) strain in which the ROSA26 locus is targeted with a conditional LacZ reporter cassette. In R26R mice, Cre expression and subsequent Cre-mediated recombination lead to expression of the LacZ reporter gene, an event that can be monitored by LacZ staining. LacZ staining was detected in virtually all osteoblasts of alpha1(I)-Cre;R26R mice indicating that homologous recombination occurred in these cells. No other cell type stained blue. In the second line studied, the 1.3-kb fragment of osteocalcin gene 2 (OG2) promoter, which is active in differentiated osteoblasts, was used to drive Cre expression. OG2-Cre mice expressed Cre specifically in bone. However, cross of OG2-Cre mice with R26R mice did not lead to any detectable LacZ staining in osteoblasts. Lastly, we tested a more active artificial promoter derived from the OG2 promoter. The artificial OG2-Cre transgene was expressed by reverse transcriptase-polymerase chain reaction in cartilage and bone samples. After cross of the artificial OG2-Cre mice with R26R mice, we detected a LacZ staining in articular chondrocytes but not in osteoblasts. Our data suggest that the only promoter able to drive Cre expression at a level sufficient to induce recombination in osteoblasts is the alpha1(I)-collagen promoter.

Factors involved in the regulation of type I collagen gene expression: implication in fibrosis

Type I collagen, the major component of extracellular matrix in skin and other tissues, is a heterotrimer of two alpha1 and one alpha2 collagen polypeptides. The synthesis of both chains is highly regulated by different cytokines at the transcriptional level. Excessive synthesis and deposition of collagen in the dermal region causes thick and hard skin, a clinical manifestation of scleroderma. To better understand the causes of scleroderma or other tissue fibrosis, it is very important to investigate the molecular mechanisms that cause upregulation of the Type I collagen synthesis in these tissues. Several cis-acting regulatory elements and trans-acting protein factors, which are involved in basal as well as cytokine-modulated Type I collagen gene expression, have been identified and characterized. Hypertranscription of Type I collagen in scleroderma skin fibroblasts may be due to abnormal activities of different positive or negative transcription factors in response to different abnormally induced signaling pathways. In this review, I discuss the present day understanding about the involvement of different factors in the regulation of basal as well as cytokine-modulated Type I collagen gene expression and its implication in scleroderma research.

Activation of fibroblast procollagen alpha 1(I) transcription by mechanical strain is transforming growth factor-beta-dependent and involves increased binding of CCAAT-binding factor (CBF/NF-Y) at the proximal promoter

During normal developmental tissue growth and in a number of diseases of the cardiopulmonary system, adventitial and interstitial fibroblasts are subjected to increased mechanical strain. This leads to fibroblast activation and enhanced collagen synthesis, but the underlying mechanisms involved remain poorly understood. In this study, we have begun to identify and characterize mechanical strain-responsive elements in the rat procollagen alpha 1(I) (COL1A1) gene and show that the activity of COL1A1 promoter constructs, transiently transfected into cardiac fibroblasts, was increased between 2- and 4-fold by continuous cyclic mechanical strain. This was accompanied by an approximately 3-fold increase in the levels of total active transforming growth factor-beta (TGF-beta) released into the medium. Inclusion of a pan-specific TGF-beta neutralizing antibody inhibited strain-induced COL1A1 promoter activation. Deletion analysis revealed the presence of two potential strain response regions within the proximal promoter, one of which contains an inverted CCAAT-box overlapping a GC-rich element. Both mechanical strain and exogenously added TGF-beta1 enhanced the binding activity of CCAAT-binding factor, CBF/NF-Y, at this site. Moreover, this element was sufficient to confer strain-responsiveness to an otherwise unresponsive SV40 promoter. In summary, this study demonstrates that strain-induced COL1A1 promoter activation in cardiac fibroblasts is TGF-beta-dependent and involves increased binding of CCAAT-binding factor at the proximal promoter. Furthermore, these findings suggest a novel and potentially important TGF-beta response element in the rat COL1A1 gene.

YY1 is a positive regulator of transcription of the Col1a1 gene

Both cell-specific and ubiquitous transcription factors in fibroblasts have been identified as critical for expression of the Col1a1 gene, which encodes the alpha1 chain of type I collagen. Here, we report that Yin Yang 1 (YY1) binds to the Col1a1 promoter immediately upstream of the TATA box, and we examine the functional implications of YY1 binding for regulation of Col1a1 gene expression in BALBc/3T3 fibroblasts. The Col1a1 promoter region spanning base pairs (bp) -56 to -9 bound purified recombinant YY1 and the corresponding binding activity in nuclear extracts was supershifted using a YY1-specific antibody. Mutation of the TATA box to TgTA enhanced YY1 complex formation. Mutation analysis revealed two YY1 core binding sites at -40/-37 bp (YY1A) and, on the reverse strand, at -32/-29 bp (YY1B) immediately adjacent to the TATA box. In transfections using Col1a1-luciferase constructs, mutation of YY1A decreased activity completely (wild-type p350 (p350wt), -222/+113 bp) or partially (p130wt, -84 bp/+13 bp), whereas mutation of YY1B blocked the expression of both promoter constructs. Cotransfection with pCMV-YY1 increased p350wt and p130wt activities by as much as 10-fold, whereas antisense YY1 decreased constitutive expression and blocked the increased activity due to pCMV-YY1 overexpression. The mTgTA constructs were devoid of activity, arguing for a requirement for cognate binding of the TATA box-binding protein (TBP). Electrophoretic mobility shift assays performed under conditions permitting TBP binding showed that recombinant TBP/TFIID and YY1 could bind to the -56/-9 bp fragment and that YY1B was the preferred site for YY1 binding. Our results indicate that YY1 binds to the Col1a1 proximal promoter and functions as a positive regulator of constitutive activity in fibroblasts. Although YY1 is not sufficient for transcriptional initiation, it is a required component of the transcription machinery in this promoter.

delta Ef1 binds to a far upstream sequence of the mouse pro-alpha 1(I) collagen gene and represses its expression in osteoblasts

The transcription of type I collagen genes is tightly regulated, but few cis-acting elements have been identified that can modulate the levels of expression of these genes. Generation of transgenic mice harboring various segments of the mouse pro-alpha1(I) collagen promoter led us to suspect that a repressor element was located between -10.5 and -17 kilobase pairs. Stable and transient transfection experiments in ROS17/2.8 osteoblastic cells confirmed the existence of such a repressor element at about -14 kilobase pairs and showed that it consisted in an almost perfect three-time repeat of a 41-base pair sequence. This element, which we named COIN-1, contains three E2-boxes, and a point mutation in at least two of them completely abolished its repressor effect. In gel shift assays, COIN-1 bound a DNA-binding protein named delta EF1/ZEB-1, and mutations that abolished the repressor effect of COIN-1 also suppressed the binding of delta EF1. We also showed that the repressor effect of COIN-1 was not mediated by chromatin compaction. Furthermore, overexpression of delta EF1 in ROS17/2.8 osteoblastic cells enhanced the inhibitory effect of COIN-1 in a dose-dependent manner and repressed the expression of the pro-alpha 1(I) collagen gene. Thus, delta EF1 appears to repress the expression of the mouse pro-alpha 1(I) collagen gene, through its binding to COIN-1.

The Y-box binding protein YB-1 suppresses collagen alpha 1(I) gene transcription via an evolutionarily conserved regulatory element in the proximal promoter

Appropriate expression of collagen type I, a major component of connective tissue matrices, is dependent on tight transcriptional control and a number of trans-activating and repressing factors have been characterized. Here we identify the Y-box binding protein-1 (YB-1) as a novel repressor of the collagen type alpha1(I) (COL1A1) gene. Collagen type I mRNA and protein levels decreased upon overexpression of YB-1 by transfection in NRK fibroblasts. The human, rat, and mouse COL1A1 promoter -220/+115 contains three putative Y-boxes, one of these sites, designated collagen Y-box element (CYE), includes a Y-box plus an adjacent 3' inverted repeat. DNase-I footprinting and Southwestern blotting with fibroblast nuclear extract demonstrated binding of several nuclear proteins across the CYE, one of which was identified as YB-1. Recombinant YB-1 bound the CYE sequence in gel shift assays with a preference for single-stranded templates. The entire sequence (-88/-48) was required for high affinity binding. Complex formation of endogenous YB-1 with the CYE was established by supershift studies. COL1A1 promoter-reporter constructs were suppressed up to 80% by cotransfection with YB-1 in a variety of cell types. In addition, CYE conferred YB-1 responsiveness on two heterologous promoters further demonstrating the importance of this repressor region. Mung bean nuclease sensitivity analysis suggested that repression is most likely exerted through changes in DNA conformation.

Identification of an SAS (Sp1c adjacent site)-like element in the distal 5'-flanking region of the rat lutropin receptor gene essential for cyclic adenosine 3',5'-monophosphate responsiveness

One of the hallmarks of the differentiation of granulosa cells is the estradiol and FSH/cAMP-dependent induction of the LH receptor (LHR). Previous studies using granulosa cells isolated from diethylstilbestrol-pretreated immature rats identified a novel cAMP-responsive element termed the SAS site (Sp1c adjacent site) in the promoter region of the rat (r) LHR gene. The studies presented herein show that there is an additional distal site located at nucleotide (nt) -933/-924 that appears to interact with the same transcription factor that binds to the promoter SAS site. Similar to the SAS site, the complex formed between granulosa cell nuclear extracts and this distal site is enhanced by cAMP treatment of the granulosa cells. The core sequence required for the formation of the DNA/protein complex at this distal rLHR site was determined to be AGTGG(A)GGGG. With the exception of adenine at -928, substitution of any residue within this sequence prevented formation of this complex. The core sequence of this distal site differs from that of the proximal SAS site, which is GGGGG, and hence the distal site has been termed a SAS-like site. Reporter gene assays using constructs containing the -2,109/-1 region of the rLHR demonstrate that mutation of the distal SAS-like site abolishes the cAMP-induced transcription of the rLHR gene in rat granulosa cells, underscoring the functional significance of this site. Given the lack of sequences in the 5'-flanking region of the rLHR gene consistent with known cAMP-responsive elements, the identification of the novel SAS and SAS-like sites in the rLHR gene provides important clues toward understanding the mechanisms by which the rLHR gene is induced by FSH/cAMP.

Cbfa1 contributes to the osteoblast-specific expression of type I collagen genes

Type I collagen is composed of two chains, alpha1(I) and alpha2(I), encoded by two distinct genes, the alpha1(I) and alpha2(I) collagen genes, that are highly expressed in osteoblasts. In most physiological situations, alpha1(I) and alpha2(I) collagen expression is coregulated, suggesting that identical transcription factors control their expression. Here, we studied the role of Cbfa1, an osteoblast-specific transcription factor, in the control of alpha1(I) and alpha2(I) collagen expression in osteoblasts. A consensus Cbfa1-binding site, termed OSE2, is present at the same location in the alpha1(I) collagen promoter at approximately -1347 base pairs (bp) of the rat, mouse, and human genes. Cbfa1 can bind to this site, as demonstrated by electrophoretic mobility shift assay (EMSA) and supershift experiments using an anti-Cbfa1 antibody. Mutagenesis of the alpha1(I) collagen OSE2 at -1347 bp reduced the activity of a alpha1(I) collagen promoter fragment 2- to 3-fold. Moreover, multimers of this OSE2 at -1347bp confer osteoblast-specific activity to a minimum alpha1(I) collagen promoter fragment in DNA transfection experiments as well as in transgenic mice. An additional Cbfa1-binding element is present in the alpha1(I) collagen promoter of mouse, rat, and human at approximately position -372. This site binds Cbfa1 only weakly and does not act as a cis-acting activator of transcription when tested in DNA transfection experiments. Similar to alpha1(I) collagen, the mouse alpha2(I) collagen gene contains multiple OSE2 sites, of which one is conserved across multiple species. In EMSA, Cbfa1 binds to this site and multimers of this alpha2(I) OSE2 element confer osteoblast-specific activity to the minimum alpha1(I) collagen promoter in DNA transfection experiments. Thus, our results suggest that Cbfa1 is one of the positive regulators of the osteoblast-specific expression of both type I collagen genes.

The promoter of the long variant of collagen XVIII, the precursor of endostatin, contains liver-specific regulatory elements

The endostatin precursor collagen XVIII is expressed at high levels in human livers, the main source being hepatocytes. We have studied the regulatory elements in the promoter 2 of the Col18a1 gene that directs the transcription of the NC1-517 variant of collagen alpha1(XVIII), which is the main form expressed in the liver. The 5'-flanking region of Col18a1 gene was cloned, and a series of 5'-deletions from -3286 bp to +285 bp were linked to the luciferase reporter gene. Transfection experiments in HepG2 cells allowed to identify a silencer-like element containing putative HNF1 and HNF3 sites and activator elements containing stretches of GC-rich sequences. Another putative HNF3 site in close apposition to a NF1/CTF site was localized upstream of the silencer-like element. Cotransfection experiments showed that the Col18a1 promoter 2 was transactivated by Sp1 and HNF3alpha. Gel-shift analyses showed that HNF3, NF1/CTF, and Sp1-like sites specifically recognized nuclear factors. Super-shift experiments indicated that HNF3beta was the major form of HNF3 interacting with the HNF3/NF1 site. The well-differentiated hepatoma cell line mhATFS315 transfected with a truncated form of HNF3beta, which competitively blocks HNF3 transactivating activity, expressed the Col18a1gene at a very low level. Taken together, these data strongly suggest that Col18a1 is a liver-specific gene. Furthermore, gel-shift analyses performed with nuclear factors prepared from well-differentiated hepatocellular carcinomas showed increased HNF3/NF1 binding activity compared with normal livers. Consequently, the precursor of endostatin might be differently expressed according to the differentiated and/or transformed state of hepatocytes.

A novel cyclic adenosine 3',5'-monophosphate-responsive element involved in the transcriptional regulation of the lutropin receptor gene in granulosa cells

The induction of the lutropin receptor (LHR) in granulosa cells by FSH is mediated, at least in part, by cAMP. However, the classic cAMP-responsive element (CRE) is not present in the 5'-flanking region of the rat LHR gene. Previous studies from our laboratory had shown that three Sp1 sites within the promoter region of the rat LHR (rLHR) bind Sp1 and Sp3 and are involved in the basal and cAMP-mediated transcription of the rLHR gene. In the present studies we show that the rLHR promoter region forms a complex (designated complex A) with nuclear extracts from rat granulosa cells, and the abundance of complex A is markedly increased when using cells that had been pretreated with 8-bromo (Br)-cAMP. We have localized the binding of the protein(s) in complex A to a DNA sequence immediately upstream and partially overlapping with the Sp1c binding site. The core site (designated SAS for Sp1c adjacent sequence) is localized to nucleotide (nt) -146 to -142 and contains the sequence GGGGG. The consensus sequence for the core portion of this element appears to be (G/T)GGGG. Mutations of the SAS site, but not SP1c site, abolish complex A formation. Experiments utilizing rat granulosa cells transfected with luciferase reporter genes driven by the 5'-flanking region of the rLHR gene demonstrate a functional role for the SAS site in the cAMP responsiveness of the rLHR gene.

NF-Y and Sp1 cooperate for the transcriptional activation and cAMP response of human tissue inhibitor of metalloproteinases-2

The balance between matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) is a key determinant in the homeostasis of the extracellular matrix. We have identified two cis-acting elements involved in the transcriptional regulation of TIMP-2. The first is an inverted CCAAT box located at position -73 to -69 in the TIMP-2 promoter that binds the transcription factor NF-Y. The second is a GAGGAGGGGG motif located at position -107 to -98, that binds the transcription factors Sp1 and Sp3. NF-Y and Sp1 cooperate for the basal transcription activity of the promoter. We then determined that TIMP-2 is transcriptionally up-regulated by cAMP analogs. Up-regulation of TIMP-2 by dibutyryl cAMP is a delayed response that requires de novo protein synthesis and does not affect RNA stability. The NF-Y and the Sp1 binding site are both involved in cAMP-dependent up-regulation of TIMP-2. Whereas NF-Y is essential for cAMP mediated regulation, Sp1 alone is not sufficient but enhances the activity of NF-Y. Dibutyryl cAMP has no effect on the expression of MMP-2 and MMP-9 and switches the MMP-TIMP balance in favor of the inhibitor.

Collagen alpha1(I) gene contains an element responsive to tumor necrosis factor-alpha located in the 5' untranslated region of its first exon

The aims of the present study were to identify the cis-acting element through which tumor necrosis factor-alpha (TNFalpha) inhibits collagen alpha1(I) gene transcription and the trans-acting factors involved in this effect in cultured hepatic stellate cells. Deletion analysis of the collagen alpha1(I) promoter demonstrated that TNFalpha inhibited gene expression through an element located between -59 and + 116 bp relative to the transcription start site. DNase I protection assays revealed a footprint between +68 and +86 bp of the collagen first exon, the intensity of which decreased when the DNA probe was incubated with nuclear protein from TNFalpha-treated hepatic stellate cells. This footprint contained a G+C-rich box. Transfection experiments demonstrated that mutations in this G+C-rich element abrogated the inhibitory effect of TNFalpha on the collagen alpha1(I) promoter. Gel retardation experiments using a radiolabeled oligonucleotide containing sequences of this region confirmed that TNFalpha treatment decreased the formation of two complexes between nuclear proteins and DNA. These complexes were efficiently blocked with an oligonucleotide containing an Spl-binding site and were supershifted with specific Spl and Sp3 antibodies. These results suggest that TNFalpha inhibits collagen alpha1(I) gene expression by decreasing the binding of Spl to a G+C-rich box in the 5' untranslated region of its first exon.

Expression and characterization of Xenopus type I collagen alpha 1 (COL1A1) during embryonic development

A cDNA encoding Xenopus type I collagen alpha 1 (Xenopus COL1A1) has been isolated from an ovary cDNA library. The COL1A1 cDNA is approximately 5.7 kb pairs and encodes 1447 amino acids. The putative COL1A1 polypeptide shares high identities of amino acid sequence with other vertebrate COL1A1 proteins. The level of Xenopus COL1A1 transcripts was increased markedly in the posterior region of the embryo at the tail-bud stage, then gradually spread to the anterior region. Histological observations of the tail-bud embryos showed that COL1A1 was mainly expressed in the inner layer of the posterior dorsal epidermis exposed to the somite mesoderm, except for in the dorsal fin. Less intense signals were also detected in the outer layer of the dorsal epidermis and dermatome. The expression of COL1A1 was increased in posteriorized embryos resulting from treatment with retinoic acid but decreased in hyper-dorsalized embryos resulting from lithium chloride treatment. These results suggest that COL1A1 is a major component of the dorsal dermis exposed to the somite in Xenopus embryos, but its expression is not related to the temporal sequence of somite segregation.

Interaction of Ap1, Ap2, and Sp1 with the regulatory regions of the human pro-alpha1(I) collagen gene

In the pro-alpha1(I) collagen gene a number of cis-regulatory elements, which interact with a variety of trans-acting factors, are present in the promoter and first intron. We have undertaken a comprehensive study of Sp1, Ap1, and Ap2 binding in the region spanning -442 to +1697 nt. DNase I footprinting analysis revealed these factors bind with varying affinities to some of the potential sites: Sp1 binds to 16 of 34 potential sites, Ap2 binds to 22 of 40 potential binding sites, and Ap1 binds to its only potential site. The Sp1 sites were mostly clustered in the intron region, while the Ap2 sites were clustered in the promoter region. Transmission electron microscopic analysis of DNA-protein complexes not only confirmed these results, but also clearly showed that heterologous and/or homologous protein-protein interactions between Sp1 and/or Ap2 bring the promoter and intron in contact with each other, with the resulting looping out of the intervening DNA. This strongly suggests that the DNA-looping model is an explanation for the orientation preference of the enhancing element in the first intron as these interactions possibly create an optimum environment for the binding of the rest of the transcriptional machinery.

Competition analysis of the human alpha2(I) collagen promoter using synthetic oligonucleotides

Previous studies have identified four cis-response elements which mediate the basal transcriptional activity of the human alpha2(I) collagen gene. One of these elements, a pyrimidine-rich region (TCCCCC motif), was shown to be a repressor site, and the other three elements were shown to be activator sites. Furthermore, the repressor site and two of the activator sites were found to constitute binding sites for the transcription factors Sp1 and Sp3. In this study, we further determined the affinity and specificity of the binding of Sp1 and Sp3 to the human alpha2(I) collagen promoter and investigated the function of the pyrimidine-rich region which contains the TCCCCC motif. Functional analyses of Sp1 and Sp3 in Drosophila cells confirmed that Sp1 and Sp3 activate the human alpha2(I) collagen promoter via the GC boxes and the TCCTCC motif, but that binding of Sp1 or Sp3 to the repressor site does not activate or repress the collagen promoter activity. Com- petitive analyses using DNA mobility shift assays showed that the TCCCCC motif which constitutes the repressor site abolished the binding of Sp1 or Sp3 to the GC boxes or the TCCTCC motif, but not the binding of CCAAT-binding factor to the fourth cis-response element (CCAAT-binding factor site). Furthermore, the affinity of Sp1 or Sp3 for the TCCTCC motif was shown to be greater than that of the Sp1 consensus oligonucleotide. In vitro transcription analysis revealed that the addition of each activator site oligonucleotide or repressor site oligonucleotide had an inhibitory effect on the transcription of the collagen gene. These results suggest that the repressor site regulates the transcription of the collagen gene by taking away Sp1 or Sp3 from the activator sites.

Sp family of transcription factors is involved in iron-induced collagen alpha1(I) gene expression

The purpose of this study was to identify the cis-acting elements and the trans-acting factors involved in the iron-induced expression of the collagen alpha1(I) (COL1aI) gene. Rat hepatic stellate cells were cultured in the presence of 50 microM ferric chloride, 50 microM ascorbic acid, and 250 microM citric acid (Fe/AA/CA), and the effects on collagen gene expression and the binding of nuclear proteins to the COL1aI promoter were measured. The Fe/AA/CA treatment induced a time- and dose-dependent increase in the cellular levels of COL1aI mRNA that was abrogate by pretreating cells with cycloheximide, antioxidants, and inhibitors of aldehyde-protein adduct formation. Transient transfection experiments showed that Fe/AA/CA exerted its effect through regulatory elements located between -220 and -110 bp of the COL1aI promoter. Gel retardation assays showed that Fe/AA/CA increased the binding of nuclear proteins to two elements located between -161 and -110 bp of the COL1aI promoter. These bindings were blocked by unlabeled consensus Sp1 oligonucleotide and supershifted with Sp1 and Sp3 antibodies. Finally, Fe/AA/CA increased cellular levels of the Sp1 and Sp3 proteins and Sp1 mRNA. Treatment with Fe/AA/CA stimulates COL1aI gene expression by inducing the synthesis of Sp1 and Sp3 and their binding to two regulatory elements located between -161 and -110 bp of the COL1aI promoter.

Parathyroid hormone inhibits collagen synthesis and the activity of rat col1a1 transgenes mainly by a cAMP-mediated pathway in mouse calvariae

We examined the effect of parathyroid hormone and various signaling molecules on collagen synthesis and chloramphenicol acetyltransferase activity in cultured transgenic mouse calvariae carrying fusion genes of the rat Col1a1 promoter and the chloramphenicol acetyltransferase reporter. After 48 h of culture, parathyroid hormone, forskolin, dibutyryl cAMP, 8-bromo cAMP, and phorbol myristate acetate inhibited transgene activity, while the calcium ionophore ionomycin had no effect. Pretreatment of calvariae with the phosphodiesterase inhibitor isobutylmethylxanthine potentiated the inhibitory effect of 1 nM parathyroid hormone on transgene activity and collagen synthesis. Parathyroid hormone further inhibited transgene activity and collagen synthesis in the presence of phorbol myristate acetate. Parathyroid hormone inhibition of transgene activity and collagen synthesis was not affected by indomethacin or interleukin-6. After 48 h of culture, parathyroid hormone inhibited chloramphenicol acetyltransferase activity by 50-85% in cultured calvariae carrying transgenes having progressive 5' upstream deletions of promoter DNA down to -1683 bp. These data show that the inhibitory effect of parathyroid hormone on Col1a1 expression in mouse calvariae is mediated mainly by the cAMP signaling pathway. Prostaglandins and IL-6 are not local mediators of the parathyroid hormone response in this model. Finally, regions of the Col1a1 promoter downstream of -1683 bp are sufficient for parathyroid hormone inhibition of the Col1a1 promoter.

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.

Transcriptional activation of the alpha1(I) procollagen gene and up-regulation of alpha1(I) and alpha1(III) procollagen messenger RNA in dermal fibroblasts from tight skin 2 mice

OBJECTIVE

To investigate the levels of expression of type I and type III collagen genes in dermal fibroblasts from tight skin 2 (Tsk2) and normal mice and to examine the transcriptional regulation of the alpha1(I) procollagen gene (COL1A1) in these cells.

METHODS

Dermal fibroblasts from Tsk2 mice and from normal age- and sex-matched control mice were studied. Steady-state levels of alpha1(I) and alpha1(III) procollagen messenger RNA (mRNA) were evaluated by Northern and dot-blot hybridization analyses. The transcriptional regulation of COL1A1 was examined by transient transfection experiments with deletion constructs containing portions of the COL1A1 promoter ligated to the chloramphenicol acetyltransferase reporter gene. To identify DNA binding proteins that interact with regulatory elements within the COL1A1 promoter, gel mobility shift assays were performed with nuclear extracts prepared from normal and Tsk2 dermal fibroblasts.

RESULTS

Synthesis of collagen was almost 100% higher in Tsk2 dermal fibroblasts than in control fibroblasts. Up-regulation of mRNA for 2 extracellular matrix proteins was observed in the Tsk2 dermal fibroblasts compared with the normal cells: the alpha1(I) procollagen mRNA steady-state levels were 50% higher, and those of the alpha1(III) procollagen mRNA 100% higher, in Tsk2 cells. The results of transient transfection experiments with COL1A1 promoter constructs demonstrated that the elevated levels of alpha1(I) collagen mRNA in Tsk2 cells were largely due to increased transcriptional activity of the corresponding gene. Electrophoretic mobility shift assays performed with a probe encompassing a relevant COL1A1 promoter region revealed increased DNA-protein binding activities in nuclear extracts prepared from Tsk2 fibroblasts compared with normal fibroblasts. Competition experiments using consensus Spl and nuclear factor 1 (NF-1) oligonucleotides and supershift experiments using anti-Sp1 and anti-NF-1 antibodies indicated that at least 2 transcription factors, Sp1 and NF-1, or their homologs are involved in the up-regulated transcriptional activity of the COL1A1 promoter in Tsk2 fibroblasts.

CONCLUSION

Dermal fibroblasts from Tsk2 mice display increased collagen synthesis and up-regulation of alpha1(I) and alpha1(III) procollagen mRNA in vitro. The data also directly demonstrate the transcriptional activation of COL1A1 in dermal fibroblasts from Tsk2 mice and suggest that the transcription factors Sp1 and NF-1 or their homologs play an important role in the upregulated expression of this gene in Tsk2 fibroblasts. These findings are similar to those described for fibroblasts from humans with systemic sclerosis and validate the use of Tsk2 as a model for the study of the connective tissue alterations in this disease.

Identification of elements in the promoter region of the alpha1(I) procollagen gene involved in its up-regulated expression in systemic sclerosis

OBJECTIVE

To identify regulatory elements in the promoter region of the alpha1(I) procollagen gene (COL1A1) involved in the transcriptional activation of this gene in systemic sclerosis (SSc), and to identify the transcription factors interacting with these regulatory elements.

METHODS

Dermal fibroblasts from 6 patients with diffuse SSc of recent onset and from 6 healthy individuals were studied. The transcriptional regulation of COL1A1 was examined by transient transfections with deletion constructs containing portions of the COL1A1 promoter. The DNA binding activity of nuclear proteins recognizing the regulatory regions in the COL1A1 promoter was examined by gel mobility shift assays. A procedure was established to allow the quantitative determination of the amount of DNA binding proteins interacting with the COL1A1 promoter, employing DNA binding protein and DNA titration experiments analyzed by gel mobility shift assays.

RESULTS

Maximal chloramphenicol acetyltransferase activity was observed with a -174-bp to +42-bp COL1A1 promoter construct in both normal and SSc cells; however, the activity driven by this construct was 70-260% higher in SSc fibroblasts. Most of the transcriptional activity of the COL1A1 promoter was contained in a minimal promoter region encompassing -174 bp to -84 bp. Electrophoretic mobility shift assays performed with oligonucleotides corresponding to the regions spanning -129/-107 bp and -104/-78 bp of the COL1A1 promoter revealed marked increases in the intensities of DNA-protein complexes formed with both oligonucleotides in nuclear extracts prepared from each of the SSc cell lines in comparison with normal fibroblasts. Competition experiments showed that each of these regions contained elements recognized by Sp1 and nuclear factor 1 (NF-1) binding proteins. A quantitative determination of DNA binding activity recognizing the Sp1 binding element within the -129/-107-bp region showed that it was 23.6 nM in SSc fibroblasts compared with 6.9 nM in normal fibroblasts.

CONCLUSION

The results demonstrate that a short region in the proximal promoter of COL1A1 containing 2 tandem NF-1/Sp1 elements displays up-regulated transcriptional activity in SSc fibroblasts, and that SSc fibroblasts contain 3.4-fold greater DNA binding activity recognizing these elements than normal cells.

An RNA oligonucleotide corresponding to the polypyrimidine region of the rat alpha 1(I) procollagen promoter forms a stable triplex and inhibits transcription

In this report we demonstrate formation of a triplex structure by an antiparallel RNA oligonucleotide corresponding to the 21 bp polypurine-pyrimidine stretch from -141 to -162 of the rat alpha 1(I) procollagen promoter with a Kd of 0.1-0.2 microM. The formation of triplexes by the triplex forming oligoribonucleotide (ORN) was also observed under physiological conditions. In vitro transcription run-off experiments showed that triplex formation results in inhibited transcription from the rat alpha 1(I) procollagen gene. Our results demonstrate a novel approach for down-regulation of procollagen gene transcription in vivo.

Transcription factor ZBP-89 regulates the activity of the ornithine decarboxylase promoter

Appropriate cellular levels of polyamines are required for cell growth and differentiation. Ornithine decarboxylase is a key regulatory enzyme in the biosynthesis of polyamines, and precise regulation of the expression of this enzyme is required, according to cellular growth state. A variety of mitogens increase the level of ornithine decarboxylase activity, and, in most cases, this elevation is due to increased levels of mRNA. A GC box in the proximal promoter of the ornithine decarboxylase gene is required for basal and induced transcriptional activity, and two proteins, Sp1 and NF-ODC1, bind to this region in a mutually exclusive manner. Using a yeast one-hybrid screening method, ZBP-89, a DNA-binding protein, was identified as a candidate for the protein responsible for NF-ODC1 binding activity. Three lines of evidence verified this identification; ZBP-89 copurified with NF-ODC1 binding activity, ZBP-89 antibodies specifically abolished NF-ODC1 binding to the GC box, and binding affinities of 12 different double-stranded oligonucleotides were indistinguishable between NF-ODC1, in nuclear extract, and in vitro translated ZBP-89. ZBP-89 inhibited the activation of the ornithine decarboxylase promoter by Sp1 in Schneider's Drosophila line 2, consistent with properties previously attributed to NF-ODC1.

Halofuginone: a novel antifibrotic therapy

1. Fibrosis is characterized by extracellular matrix deposition, of which collagen type I is the major constituent. The progressive accumulation of connective tissue resulted in destruction of normal tissue architecture and function. 2. Fibrosis is a common response to various insults or injuries and can be the outcome of any perturbation in the cellular function of any tissue. 3. Halofuginone was found to inhibit collagen alpha 1(I) gene expression and collagen synthesis in a variety of cell cultures including human fibroblasts derived from patients with excessive skin collagen type I synthesis. 4. Halofuginone was found to inhibit collagen alpha 1(I) gene expression and collagen synthesis in animal models characterized by excessive deposition of collagen. In these models, fibrosis was induced in various tissues such as skin, liver, lung, etc. Halofuginone was injected intraperitoneally, added to the foodstuff or applied locally. 5. Halofuginone decreased skin collagen in a chronic graft-versus-host disease patient. 6. The ability of extremely low concentrations of halofuginone to inhibit collagen alpha 1(I) synthesis specifically and transiently at the transcriptional level suggests that this material fulfills the criteria for a successful and effective anti-fibrotic therapy.

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.

Cloning and characterization of hcKrox, a transcriptional regulator of extracellular matrix gene expression

cKrox is a novel zinc finger-containing transcription factor that binds to the alpha1(I) and alpha2(I) collagen gene promoters. The gene coding for cKrox is a new member of a family of early growth response genes, that play important roles in development. In the mouse, cKrox is expressed, beginning at 9.5 days of gestation and at 10.5 days in regions destined to become skin. In adult animals, expression is predominantly in skin, one of the two major organs where type I collagen is expressed. We have isolated cDNA clones for human cKrox. Theoretical translation of the nucleic acid sequence reveals 90% conservation of amino acids between the mouse and human proteins; however, the human gene product contains a 117-amino-acid N-terminal extension. The amino acid sequences of the zinc-finger DNA binding domains of mouse and human cKrox are identical. RT-PCR analysis of human fibroblasts indicates constitutive low-level expression of cKrox which can be transiently elevated by treatment with retinoic acid. Transient transfection assays indicate that hcKrox represses transcription of the alpha1(I) procollagen promoter, and electrophoretic mobility shift assays demonstrate that hcKrox binds to both the human and murine promoter DNA. Deletion derivatives of hcKrox demonstrate transcription-activating potential that is promoter-dependent. NIH3T3 cells permanently expressing hcKrox demonstrate a threefold and 10-fold decrease in alpha1(I) procollagen and fibronectin mRNA levels, respectively, compared to control cells. Consistent with this finding, a fibronectin promoter reporter construct is repressed more than 80% by hcKrox. These data suggest that hcKrox represses collagen transcription directly, and it may function as a repressor of fibronectin and possibly other matrix genes.

Halofuginone, a specific inhibitor of collagen type I synthesis, prevents dimethylnitrosamine-induced liver cirrhosis

BACKGROUND/AIMS

Hepatic cirrhosis is characterized by excessive deposition of collagen, resulting from an increase in type I collagen gene transcription. We evaluated the effect of halofuginone-a specific inhibitor of collagen type alpha 1(I) gene expression-on dimethylnitrosamine (DMN)-induced liver fibrosis/cirrhosis in rats.

METHODS

Fibrosis was induced by intraperitoneal injection of DMN. Halofuginone (5 mg/kg) was added to the diet. Collagen was stained with Sirius red and collagen alpha 1(I) gene expression was evaluated by in situ hybridization.

RESULTS

In control rats, a low level of collagen alpha 1(I) gene expression was observed. A high dose of DMN (1%) caused severe fibrosis, as indicated by induction of collagen alpha 1(I) gene expression and increased liver collagen content. Addition of halofuginone before the onset of fibrosis, almost completely prevented the increase in collagen type I gene expression and resulted in lower liver collagen content. Moreover, halofuginone partially prevented the marked decrease in liver weight and reduced the mortality rate. At a lower dose of DMN (0.25%), which causes mild fibrosis, halofuginone prevented the increase in collagen alpha 1(I) gene expression, prevented the increase in liver collagen deposition and reduced plasma alkaline phosphatase activity, all of which are characteristic of liver fibrosis/ cirrhosis.

CONCLUSIONS

These results suggest that halofuginone can be used as an important tool to understand the regulation of the collagen alpha 1(I) gene and may become a novel and promising antifibrotic agent for liver fibrosis/ cirrhosis.

Cloning and characterization of a transcription factor that binds to the proximal promoters of the two mouse type I collagen genes

We have used the yeast one-hybrid system to clone transcription factors that bind to specific sequences in the proximal promoters of the type I collagen genes. We utilized as bait the sequence between -180 and -136 in the pro-alpha2(I) collagen promoter because it acts as a functional promoter element and binds several DNA-binding proteins. Three cDNA clones were isolated that encoded portions of the mouse SPR2 transcription factor, whereas a fourth cDNA contained a potential open reading frame for a polypeptide of 775 amino acids and was designated BFCOL1. Recombinant BFCOL1 was shown to bind to the -180 to -152 segment of the mouse pro-alpha2(I) collagen proximal promoter and to two discrete sites in the proximal promoter of the mouse pro-alpha1(I) gene. The N-terminal portion of BFCOL1 contains its DNA-binding domain. DNA transfection experiments using fusion polypeptides with the yeast GAL4 DNA-binding segment indicated that the C-terminal part of BFCOL1 contained a potential transcriptional activation domain. We speculate that BFCOL1 participates in the transcriptional control of the two type I collagen genes.

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.

Identification of negative and positive regulatory elements in the rat alpha 1(I) collagen gene promoter

Type I collagen is the main constituent of extracellular matrix found in various organs including the heart. Under some pathological conditions accumulation of excess type I collagen in the interstitium leads to organ dysfunction. In order to identify the regulatory elements in the rat alpha 1(I) collagen gene promoter, deletions were made in the promoter region. Various plasmid constructs were transfected into different fibroblasts using LipofectAMINE. The results indicated a negative cis-element between nucleotides -310 to -440 in the rat alpha 1(I) collagen gene promoter. Presence of this sequence significantly diminished the reporter gene activity. In addition we have observed that the sequence between -220 to -330 contained a positively acting cis-element, which is highly active in rat fibroblasts. Analysis of the nuclear factors binding to the negative element by electrophoretic mobility shift assays indicated that similar or identical factors are present in different fibroblasts as well as human HeLa cells and that these factors appear to bind to a composite sequence within -325 to -400. Competition with different oligonucleotides suggested that two distinct but contiguous sequence motifs may constitute the negative regulatory element. Our results with the rat alpha 1(I) collagen promoter confirm the presence of a negative cis-element previously described for the mouse promoter and provided additional information on the bipartite nature of this element.

Basement-membrane stromal relationships: interactions between collagen fibrils and the lamina densa

Collagens, the most abundant molecules in the extracellular space, predominantly form either fibrillar or sheet-like structures-the two major supramolecular conformations that maintain tissue integrity. In connective tissues, other than cartilage, collagen fibrils are mainly composed of collagens I, III, and V at different molecular ratios, exhibiting a D-periodic banding pattern, with diameters ranging from 30 to 150 nm, that can form a coarse network in the extracellular matrix in comparison with a fine meshwork of lamina densa. The lamina densa represents a stable sheet-like meshwork composed of collagen IV, laminin, nidogen, and perlecan compartmentalizing tissue from one another. We hypothesize that the interactions between collagen fibrils and the lamina densa are crucial for maintaining tissue-tissue interactions. A detailed analysis of these interactions forms the basis of this review article. Here, we demonstrate that there is a direct connection between collagen fibrils and the lamina densa and propose that collagen V may play a crucial role in this connection. Collagen V might also be involved in regulation of collagen fibril diameter and anchoring of epithelia to underlying connective tissues.

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 regulation of the human alpha2(I) collagen gene. Combined action of upstream stimulatory and inhibitory cis-acting elements

This study identifies three regions of the human alpha2(I) collagen promoter involved in the binding of nuclear factors. These regions include sequences from -173 to -155 (footprint I), -133 to -119 (footprint II), and -101 to -72 (footprint III). A novel positive cis-element containing a TCCTCC motif was identified within footprint II. In addition, we demonstrated that a pyrimidine-rich region within footprint I is a binding site for a transcriptional repressor, and a CCAAT motif within footprint III is a binding site for a transcriptional activator. Comparative functional analysis of the cis-acting elements within the proximal 350 base pairs of this promoter, including previously characterized Sp1 binding sites at -300, indicates that constitutive activity of this promoter is regulated equivalently by the three positive cis-acting elements at -300, -125, and -80. Mutations in the repressor site at -160 increase constitutive activity by 4-6-fold. However, simultaneous mutations of the repressor site and the cis-regulatory element at either the -300 or -125 sites result in no increase in constitutive transcription activity suggesting interaction between the activators and repressor elements. In contrast, simultaneous mutation of the CCAAT motif and the repressor site results in about a 4-fold increase, suggesting that activation via the CCAAT motif may be independent of this repressor.

Inhibition of collagen type I synthesis by skin fibroblasts of graft versus host disease and scleroderma patients: effect of halofuginone

The effect of halofuginone (a plant alkaloid) on collagen alpha 1(I) gene expression and collagen synthesis was evaluated in human skin fibroblasts from patients with chronic graft-versus-host disease (cGvHD) or scleroderma and from a normal individual. Halofuginone caused a dose-dependent inhibition in collagen alpha 1(I) gene expression and collagen synthesis in all cultures tested, the cGvHD fibroblasts being the least sensitive. In normal and scleroderma fibroblasts, concentrations of halofuginone as low as 10(-10) M and 10(-9) M were sufficient to cause a significant reduction in collagen alpha 1(I) gene expression and collagen synthesis, respectively. In addition, halofuginone also inhibited the transforming growth factor beta-induced collagen synthesis. Three days after halofuginone removal, collagen gene expression returned to control levels. The reduction of collagen mRNA transcript levels by halofuginone appeared to be dependent on new protein synthesis because simultaneous treatment of fibroblasts with protein synthesis inhibitors prevents the suppressive effect of halofuginone on collagen alpha 1(I) mRNA gene expression. The ability of extremely low concentrations of halofuginone to inhibit collagen alpha 1(I) synthesis specifically and transiently at the transcriptional level suggests that this material may be an important tool for studying collagen alpha 1(I) gene regulation and may be used as a novel and promising antifibrotic therapy.

c-Krox binds to several sites in the promoter of both mouse type I collagen genes. Structure/function study and developmental expression analysis

We have previously shown that c-Krox is a zinc finger protein that can increases the transcriptional activity of the mouse alpha1(I) collagen promoter through its binding to two GC-rich sequences (Galéra, P., Musso, M., Ducy, P., and Karsenty, G. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 9372-9376). In this report we show that c-Krox can bind to an additional site in the promoter of the alpha1(I) collagen gene and to three sites in the promoter of the alpha2(I) collagen gene, the other gene coding for type I collagen. One of the binding sites present in both promoters is adjacent to the CCAAT box. We have performed a structure/function analysis of c-Krox locating the transactivation domain in the zinc finger and C-terminal domains and the dimerization domain in the C-terminal end of the protein. We also demonstrate that c-Krox is an early response gene, whose expression is detectable as early as 9.5-day postcoitum in mouse embryos. Whole-mount in situ hybridization shows that c-Krox is expressed in dermatomes, the somite derivatives that generate dermis, and section in situ hybridization shows that c-Krox and alpha1(I) collagen mRNAs colocalized in skin but not in bone during development. This result is consistent with the predominant expression of c-Krox in skin in postnatal life. Thus, our findings suggest that c-Krox is one transcription factor controlling the coordinated expression of the two type I collagen genes in skin.