Transcriptional mechanisms controlling types I and III collagen genes

Structurally different RGTAs modulate collagen-type expression by cultured aortic smooth muscle cells via different pathways involving fibroblast growth factor-2 or transforming growth factor-beta1

We have engineered polymers called ReGeneraTing Agents (RGTAs), which mimic the protecting and potentiating properties of heparan sulfates toward heparin-binding growth factors (HBGF). RGTAs have been shown to optimize cell growth and regulate collagen production in vitro. Here, we studied relationships between RGTA structure and collagen-type expression in aortic smooth muscle cells by using two RGTAs, the carboxylmethylsulfate dextran RG-1503 and the carboxylmethylsulfate dextran with added benzylamide RG-1192. RG-1192 specifically induced a fivefold decrease in collagen III synthesis. This effect was abolished by FGF-2 neutralizing antibody. RG-1192 and FGF-2 acted synergistically to decrease collagen III. RG-1192 was more effective than heparin in this process. RG-1192 increased the pericellular localization of FGF-2 and protected FGF-2 from proteolysis. Surface plasmon resonance analysis indicated a Kd of 15.7 nM for the RG-1192/FGF-2 interaction (10.6 nM for the heparin/FGF-2 interaction). The structurally different RG-1503 (without benzylamide) did not interact with FGF-2 and worked synergistically with TGF-beta1 to specifically induce a twofold increase in collagen V. RGTAs with different structures exert different modulating effects on the collagen phenotype. Selection of appropriate RGTAs, which had been shown to enhance in vivo tissue repair, may provide a mean of correcting collagen abnormalities in vascular disorders and more generally in fibrotic diseases.

Identification of a novel NF-kappaB-binding site with regulation of the murine alpha2(I) collagen promoter

Hepatic fibrosis is due to the increased synthesis and deposition of type I collagen. Acetaldehyde activates type I collagen promoters. Nuclear factor kappaB (NF-kappaB) was previously shown to inhibit expression of murine alpha(1)(I) and human alpha(2)(I) collagen promoters. The present study identifies binding of NF-kappaB, present in nuclear extracts of stellate cells, to a region between -553 and -537 of the murine alpha(2)(I) collagen promoter. The NF-kappaB (p65) expression vector inhibited promoter activity. Mutation of the promoter at the NF-kappaB-binding site increased basal promoter activity and abrogated the activating and inhibitory effects of transforming growth factor beta and tumor necrosis factor alpha, respectively, on promoter activity. Acetaldehyde increased IkappaB-alpha kinase activity and phosphorylated IkappaB-alpha, NF-kappaB nuclear protein, and its binding to the promoter. However, the activating effect of acetaldehyde was not affected by the mutation of the promoter. In conclusion, although acetaldehyde increases the binding of NF-kappaB to the murine alpha(2)(I) collagen promoter, this binding does not mediate the activating effect of acetaldehyde on promoter activity. The effects of acetaldehyde in increasing the translocation of NF-kappaB to the nucleus with increased DNA binding activity may be important in mediating the effects of acetaldehyde on other genes.

Heparan mimetic regulates collagen expression and TGF-beta1 distribution in gamma-irradiated human intestinal smooth muscle cells

Radiation-induced intestinal fibrosis is characterized by collagen accumulation, a process in which TGF-beta1 plays a key role. We analyzed the effects of gamma radiation on collagen expression and TGF-beta1 distribution in human intestinal smooth muscle cells (HISM). We investigated the activity of a carboxymethylated and sulfated dextran (RG-1503), exhibiting antifibrotic properties and promoting in vivo intestinal tissue repair, on irradiated HISM. After (60)Co irradiation (10 Gy), HISM were labeled with [(3)H] proline (+/-RG-1503). Radiolabeled collagen I, III, and V were quantified by SDS-PAGE. TGF-beta1 was quantified by ELISA in culture medium, pericellular and intracellular compartments. Irradiation induced a specific 2.85-fold increase in collagen III production by HISM. Collagen V decreased by 80% 72 h after irradiation. Pericellular TGF-beta1 was increased (up to twofold) in irradiated HISM. RG-1503 added before or after irradiation reversed both mRNA and protein levels of collagen III and V to control values. RG-1503 decreased the amount of TGF-beta1 in the cell layer below the control values. Irradiation of HISM induced the development of a fibrotic phenotype in terms of collagen production and TGF-beta1 distribution. The antifibrotic RG-1503 restored HISM physiological characteristics and may represent a promising therapeutic approach for radiation-induced intestinal fibrosis.

Identification of two repressor elements in the mouse alpha 2(I) collagen promoter

We recently identified three areas of Sp1 binding located between -568 and -453 of the 5' flanking region of the murine alpha2(I) collagen promoter which are necessary for optimal activity. We now identify two additional regions of Sp1 binding located at -371 to -351 (region 4) and at -690 to -613 (region 5), which when mutated increased promoter activity in transfected rat hepatic stellate cells indicating they contain negative regulatory elements. AP-2 bound to region 4 while YY1 bound most strongly to region 5. AP-2 decreased Sp1 binding to region 4 and had a dual effect on Sp1 binding to region 5 decreasing and increasing Sp1 binding at low and high concentrations of AP-2, respectively. YY1 enhanced Sp1 binding to both regions. AP-2 inhibited or enhanced the stimulatory effect of a transfected Sp1 expression vector on the alpha2(I) collagen promoter in Drosophila cells at low or high AP-2 expression, respectively. YY1 enhanced or inhibited the activation of the promoter by low or high Sp1 expression, respectively. This study identifies two negative regulatory elements in the murine alpha2(I) collagen promoter and shows that AP-2 and YY1 interact with Sp1 at these sites and can inhibit the activating action of Sp1.

Effect of high-glucose concentrations on the expression of collagens and fibronectin by fibroblasts in culture

Extracellular matrix macromolecules such as collagen and fibronectin are progressively altered during aging and age-related diseases like diabetes. We investigated the effect of high-glucose concentration (mimicking diabetic conditions) and the influence of in vitro cell aging [comparing 4th-passage fibroblasts (P4) to 15th-passage fibroblasts (P15)] on collagen and fibronectin synthesis. Fibroblasts were incubated at postconfluency with radiolabeled precursors, [3H] proline for collagen, [35S] methionine for fibronectin. We report that in control conditions (5 mM glucose) collagen III production increased with in vitro cell aging. High glucose concentrations (10 and 15 mM) increased specifically collagen III synthesis both at the mRNA and protein levels, without alteration of collagen I production in P4 and P15 cells. Fibronectin synthesis was also increased both during in vitro cell aging and in high glucose-treated P4 fibroblasts. Taken together, these data suggest similarities between changes of phenotypic expression of collagen and fibronectin induced by in vitro cell aging and conditions imitating diabetes.

Cloning and characterization of a novel sequence-specific single-stranded-DNA-binding protein

The promoter region of the chicken alpha2(I) collagen gene contains a pyrimidine-rich element that is well conserved in different mammalian species. This sequence can also form an unusual DNA structure as shown by its sensitivity to SI nuclease in vitro and it lies in a region that is DNase I-hypersensitive only when this promoter is active. We have recently reported that fibroblast nuclear proteins, including chicken Y-box-binding protein 1, bind to this single-stranded pyrimidine-rich sequence. Here we report the isolation, from a chick embryo fibroblast cDNA expression library, of a partial cDNA clone encoding a previously unknown protein, designated SSDP (sequence-specific single-stranded DNA-binding protein), that binds this single-stranded sequence. This clone contains 1199 bp of chicken sequence and has a single long open reading frame that encodes 284 amino acid residues. The affinity-purified recombinant protein encoded by this cDNA binds sequence-specifically to the single-stranded pyrimidine sequence. This cDNA sequence lacks significant similarity to any known gene in the data banks, but it is highly conserved in expressed sequence tags derived from both mouse and human. The corresponding amino acid sequence is remarkably conserved, having 97% identity with mouse and human expressed sequences. The corresponding mRNA is approx. 1800 nt in length and is expressed in both fibroblasts and chondrocytes. The high affinity of this protein for this conserved pyrimidine-rich region suggests that it might be involved in the transcriptional regulation of the alpha2(I) collagen gene.

Effect of acetaldehyde on Sp1 binding and activation of the mouse alpha 2(I) collagen promoter

Acetaldehyde activates the mouse alpha 2(I) collagen promoter and this effect is mediated in part by increased binding of nuclear factor I (NF-I). Additional mechanisms may exist since deletions in the promoter upstream to the NF-I binding site prevented enhancement by acetaldehyde. Three adjacent areas of binding by nuclear proteins from activated hepatic stellate cells were identified at -568 to -554 (region 1), -542 to -518 (region 2), and -473 to -453 (region 3) of the promoter using DNase I protection analyses. Multiple DNA-protein complexes were formed in electrophoretic mobility shift assays with oligonucleotide probes specifying the three regions. Sp1 and NF-1 bound to all three regions, while Sp3 bound to region 2. Acetaldehyde decreased nuclear protein binding to all three regions. Mutations of regions 1, 2, and 3 reduced basal activity of the promoter and inhibited acetaldehyde stimulation in transfected stellate cells. Acetaldehyde inhibited the stimulatory effect of the Sp1 vector pPacSp1 on the promoter in transfected Drosophila cells. In conclusion, three regions of Sp1 binding were identified and are required for optimal activity of the alpha 2(I) collagen promoter. Sp1 is required for basal activity of the alpha 2(I) collagen promoter; however, the enhancing effect of acetaldehyde on the promoter is not mediated by Sp1.

Regulation of the human alpha 2(1) procollagen gene by sequences adjacent to the CCAAT box

The human, rat, mouse and chicken alpha 2(1) procollagen promoters analysed to date all contain an inverted CCAAT box at -80. In this study we have examined the binding of nuclear proteins to the proximal promotor of the human alpha 2(1) procollagen gene, where an inverted CCAAT box is flanked by a downstream GGAGG sequence and its inverted counterpart (CCTCC) on the upstream end. Each of the GGAGG sequences is separated from the inverted CCAAT box by a single pyrimidine nucleotide (5'-CCTCCCATTGGTGGAGGCCCTTTT-3'). Electrophoretic mobility-shift assays (EMSAs) revealed that two distinct DNA-protein complexes formed on this DNA sequence. Methylation interference analysis and in vitro mutagenesis studies revealed that the integrity of the sequence 5'-CCTCCCATTGG-3' (the GGAGG/CCAAT-binding element or G/CBE) was important for the binding of the CCAAT-binding factor (CBF) (complex I). Competition studies showed that complex formation on the human G/CBE could be competed by mouse CBE and nuclear factor-Y (NF-Y) oligonucleotides, suggesting that mouse CBE and human G/CBE-binding proteins belong to the same family of CCAAT box binding proteins. Furthermore, antibodies to mouse CBF specifically supershifted the G/CBE complex (complex I) in EMSAs. The downstream GGAGG and 3'-flanking sequences (5'-GGAGGCCCTTTT-3') or collagen modulating element (CME), however, were important for the formation of a novel DNA protein complex (complex III). The formation of this complex was not competed out by CBE or NF-Y oligonucleotides, nor was DNA-protein complex formation affected by the anti-CBF antibody. Functional analysis of G/CBE and CME elements subjected to mutagenesis, using promoter-chloroamphenicol acetyl transferase constructs in transient transfection assays, showed that both these elements were essential for activity of the human promoter. These experiments identified a novel regulatory element in the human alpha 2(1) procollagen gene which is not present in the rodent gene.

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.

Expression of fibronectin and interstitial collagen genes in smooth muscle cells: modulation by low molecular weight heparin fragments and serum

The effect of low M(r) heparin fragments (CY222) and fetal calf serum (FCS) on the level of fibronectin and fibrillar collagen mRNAs was investigated in smooth muscle cells (SMC) in culture. In the absence of FCS, addition of CY222 (100 micrograms/10(6) cells) to postconfluent early passage SMC resulted in a decrease in mRNA level of type III collagen. In contrast, mRNA levels coding for type I collagen, fibronectin and GAPDH (used as control of cellular activity) were not modified. Addition of 5% FCS (without CY222) to the culture medium did not affect mRNA levels of type I and type III collagens nor that of GAPDH. The level of fibronectin mRNA, however, increased in the presence of 5% FCS. In the presence of both 5% FCS and CY222, we observed a decrease in type III collagen mRNA and fibronectin mRNA levels (this level remained, however, above the control value without FCS and the level with CY222 alone). Our results demonstrate that low M(r) heparin fragments can modulate the steady-state levels of type III collagen and fibronectin mRNAs.

Acetaldehyde activates the promoter of the mouse alpha 2(I) collagen gene

The mechanism whereby ethanol ingestion results in hepatic fibrosis remains unknown. Acetaldehyde has been shown to increase alpha 1(I) collagen gene transcription in human fibroblasts and in rat myofibroblastlike cells (Ito cells) in culture. In this study, the effect of acetaldehyde was determined on the activation of the alpha 2(I) collagen promoter. A plasmid containing the mouse alpha 2(I) collagen promoter region (-2000 to 54), fused to the coding sequence of the reporter gene chloramphenicol acetyl transferase and similar plasmid constructs containing deletions in the collagen promoter, were transfected into NIH 3T3 fibroblasts in culture. Acetaldehyde (200 mumol/L) and transforming growth factor-beta 1 (5 ng/ml) activated the wild type promoter. The combination of acetaldehyde and transforming growth factor-beta 1 did not result in a greater effect than either alone. Acetaldehyde inhibited, whereas transforming growth factor-beta 1 did not activate, the promoter, with a -352 to -104 deletion. By contrast, acetaldehyde had no effect, whereas transforming growth factor-beta 1 resulted in a small decrease in the activity of the promoter, with a -501 to -352 deletion. This study shows that acetaldehyde and transforming growth factor-beta 1 independently activate the mouse alpha 2(I) collagen promoter and that this activation is mediated by the same proximal region of the promoter.

Stimulation of collagen gene expression and protein synthesis in murine mesangial cells by high glucose is mediated by autocrine activation of transforming growth factor-beta

Previous investigations have demonstrated that growing mesangial cells in high glucose concentration stimulates extracellular matrix synthesis and also increases the expression of TGF-beta. We tested whether the stimulation of extracellular matrix production is mediated by autocrine activation of TGF-beta, a known prosclerotic cytokine. Addition of neutralizing anti-TGF-beta antibody, but not normal rabbit IgG, significantly reduced the high glucose-stimulated incorporation of 3[H]proline. Denaturing SDS-PAGE revealed that mainly collagen types I and IV were stimulated by high (450 mg/dl) D-glucose. This high glucose-mediated increase in collagen synthesis was reduced by the anti-TGF-beta antibody. Treatment of mesangial cells grown in normal (100 mg/dl) D-glucose with 2 ng/ml recombinant TGF-beta 1 mimicked the effects of high glucose. Furthermore, the anti-TGF-beta antibody significantly reduced the increase in mRNA levels encoding alpha 2(I) and alpha 1(IV) collagens induced by high glucose. Thus, the high glucose-stimulated increase of collagen production in mesangial cells is mediated, at least in part, by autocrine TGF-beta activation. We postulate that the interception of the glomerular activity of TGF-beta may be an effective intervention in the management of diabetic nephropathy.

Decreased type VI collagen gene expression in cultured Werner's syndrome fibroblasts

Gene expression of collagens VI, I, and III in Werner's syndrome was studied by measuring messenger RNA (mRNA) and protein production levels in four fibroblast strains from patients with Werner's syndrome and comparing them with age-matched healthy subjects. Levels of type VI collagen mRNA were decreased in all Werner's syndrome fibroblast strains and the decreases were in parallel in all three chains (alpha 1, alpha 2, and alpha 3) of type VI collagen. A coordinate increase of the alpha 1(I) and alpha 1(III) collagen mRNA levels was observed in three of the four Werner's syndrome fibroblast strains. However, no qualitative abnormality of these mRNA transcripts in Werner's syndrome fibroblasts were found by Northern blot analysis. Changes in type VI and type I collagen mRNA correlated well with production levels of corresponding proteins, as determined by immunologic assays. These data suggest that there are changes in expression of multiple connective tissue constituents in Werner's syndrome fibroblasts.

Association of a change in chromatin structure with a tissue-specific switch in transcription start sites in the alpha 2(I) collagen gene

Chick embryonic sternal chondrocytes do not synthesize alpha 2(I) collagen until they are shifted by treatment with 5-bromo-2'-deoxyuridine (BrdUrd) to a fibroblastic phenotype, yet they transcribe this gene as rapidly as BrdUrd-treated cells. To examine further this transcription, the DNase I hypersensitive sites were mapped in the 5' region of this gene in chondrocytes, BrdUrd-treated chondrocytes, fibroblasts and three types of non-transcribing cells. A DNase I hypersensitive site at -200 bp, previously shown to be associated with the active transcription of this gene in fibroblasts, is not present in chondrocyte chromatin. The chondrocyte alpha 2(I) gene contains, however, a novel major hypersensitive site in the DNA region corresponding to the fibroblast intron 2, near the chondrocyte-specific transcription initiation site of this gene. This novel hypersensitive site is associated with the use of this alternate start site by chondrocytes, since it is lost when BrdUrd treatment causes these chondrocytes to switch to the initiation of transcription at the fibroblast start site. The BrdUrd-treated chondrocytes contain the same alpha 2(I) hypersensitive sites as fibroblasts, except that fibroblasts have an additional, previously unreported, site at -1000 bp.

Regulation of collagen gene expression by transformed human fibroblasts: decreased type I and type III collagen RNA transcription

The regulation of collagen gene expression in normal diploid human fetal fibroblasts (KMS-6 cells), and fibroblasts immortally transformed by treatment of KMS-6 with Co-60 gamma rays (KMST-6 cells) was compared to that of ones tumorigenically transformed by treatment of KMST-6 cells with Harvey murine sarcoma virus (KMST-6-Ras cells). Synthesized collagenous protein decreased to approximately 30% of that of normal fetal fibroblasts in both transformed cell lines, and the relative rate of collagen synthesis to total protein synthesis decreased about sixfold in KMST-6 cells and twelvefold in KMST-6-Ras cells. The m-RNA levels of type I collagen in both of these cell lines decreased to approximately 20% of that of the control fibroblasts, whereas type III collagen m-RNA levels decreased to only 9% of that of the control. The copy number of the collagen gene in both transformed cell lines was unaltered. The transcriptional rates of collagen alpha 1(I) and collagen alpha 1(III) in both cell lines decreased to 20% and 7% respectively of that of control. These data indicate that collagen synthesis was reduced at the transcriptional level in these transformed human fibroblasts.