Differential binding of a CCAAT DNA binding factor to the promoters of the mouse alpha 2(I) and alpha 1(III) collagen genes

Candida albicans ferric reductases are differentially regulated in response to distinct forms of iron limitation by the Rim101 and CBF transcription factors

Iron is an essential nutrient that is severely limited in the mammalian host. Candida albicans encodes a family of 15 putative ferric reductases, which are required for iron acquisition and utilization. Despite the central role of ferric reductases in iron acquisition and mobilization, relatively little is known about the regulatory networks that govern ferric reductase gene expression in C. albicans. Here we have demonstrated the differential regulation of two ferric reductases, FRE2 and FRP1, in response to distinct iron-limited environments. FRE2 and FRP1 are both induced in alkaline-pH environments directly by the Rim101 transcription factor. However, FRP1 but not FRE2 is also induced by iron chelation. We have identified a CCAAT motif as the critical regulatory sequence for chelator-mediated induction and have found that the CCAAT binding factor (CBF) is essential for FRP1 expression in iron-limited environments. We found that a hap5Delta/hap5Delta mutant, which disrupts the core DNA binding activity of CBF, is unable to grow under iron-limited conditions. C. albicans encodes three CBF-dependent transcription factors, and we identified the Hap43 protein as the CBF-dependent transcription factor required for iron-limited responses. These studies provide key insights into the regulation of ferric reductase gene expression in the fungal pathogen C. albicans.

Peroxisome proliferator-activated receptor gamma interacts with CIITA x RFX5 complex to repress type I collagen gene expression

Recent reports demonstrate that peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear receptor superfamily, acts as a repressor of type I collagen synthesis. Our data demonstrate that exogenously expressed PPARgamma down-regulates collagen expression in a dose-responsive manner in human lung fibroblast cells. Silencing PPARgamma using lentiviruses expressing short hairpin RNAs partially reverses interferon-gamma (IFN-gamma)-induced repression and activates collagen mRNA levels. Previous studies indicate that IFN-gamma represses collagen gene expression and induces major histocompatibility complex II (MHC II) expression by activating the formation of a regulatory factor for X-box 5 (RFX5) complex with class II transactivator (CIITA). This report demonstrates that PPARgamma is within the RFX5.CIITA complex as judged by co-immunoprecipitation and DNA affinity precipitation studies. Most importantly, occupancy of PPARgamma on the collagen transcription start site and MHC II promoter increases with IFN-gamma treatment. The PPARgamma agonist, troglitazone, sensitizes the cells to IFN-gamma treatment by increasing recruitment of PPARgamma to collagen gene while repressing collagen expression, and these effects are blocked by the PPARgamma antagonist T0070907. PPARgamma may mediate IFN-gamma-stimulated collagen transcription down-regulation and MHC II up-regulation by interacting with CIITA as well as regulating CIITA expression. Therefore, PPARgamma is a critical target for investigations into therapeutics of diseases involving extracellular matrix remodeling and the immune response.

Regulatory factor for X-box family proteins differentially interact with histone deacetylases to repress collagen alpha2(I) gene (COL1A2) expression

Our studies indicate that the regulatory factor for X-box (RFX) family proteins repress collagen alpha2(I) gene (COL1A2) expression (Xu, Y., Wang, L., Buttice, G., Sengupta, P. K., and Smith, B. D. (2003) J. Biol. Chem. 278, 49134-49144; Xu, Y., Wang, L., Buttice, G., Sengupta, P. K., and Smith, B. D. (2004) J. Biol. Chem. 279, 41319-41332). In this study, we examined the mechanism(s) underlying the repression of collagen gene by RFX proteins. Two members of the RFX family, RFX1 and RFX5, associate with distinct sets of co-repressors on the collagen transcription start site in vitro. RFX5 specifically interacts with histone deacetylase 2 (HDAC2) and the mammalian transcriptional repressor (mSin3B), whereas RFX1 preferably interacts with HDAC1 and mSin3A. HDAC2 cooperates with RFX5 to down-regulate collagen promoter activity, whereas HDAC1 enhances inhibition of collagen promoter activity by RFX1. Interferon-gamma promotes the recruitment of RFX5/HDAC2/mSin3B to the collagen transcription start site but decreases the occupancy by RFX1/mSin3A as manifested by chromatin immunoprecipitation assay. RFX1 binds to the methylated collagen sequence with much higher affinity than unmethylated sequence, recruiting more HDAC1 and mSin3A. The DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine, which inhibits DNA methylation, reduces RFX1/HDAC1 binding to the collagen transcription start site in chromatin immunoprecipitation assays. Finally, both RFX1 and RFX5 are acetylated in vivo. Trichostatin A stimulates the acetylation of RFX proteins and activates the collagen promoter activity. Collectively, our data strongly indicate two separate pathways for RFX proteins to repress collagen gene expression as follows: one for RFX5/HDAC2 in interferon-gamma-mediated repression, and the other for RFX1/HDAC1 in methylation-mediated collagen silencing.

Peroxisome proliferator-activated receptor gamma suppresses proximal alpha1(I) collagen promoter via inhibition of p300-facilitated NF-I binding to DNA in hepatic stellate cells

Depletion of peroxisome proliferator-activated receptor gamma (PPARgamma) represents one of the key molecular changes that underlie transdifferentiation (activation) of hepatic stellate cells in the genesis of liver fibrosis (Miyahara, T., Schrum, L., Rippe, R., Xiong, S., Yee, H. F., Jr., Motomura, K., Anania, F. A., Willson, T. M., and Tsukamoto, H. (2000) J. Biol. Chem. 275, 35715-35722; Hazra, S., Xiong, S., Wang, J., Rippe, R. A., Krishna, V., Chatterjee, K., and Tsukamoto, H. (2004) J. Biol. Chem. 279, 11392-11401). In support of this notion, ectopic expression of PPARgamma suppresses hepatic stellate cells activation markers, most notably expression of alpha1(I) procollagen. However, the mechanisms underlying this antifibrotic effect are largely unknown. The present study utilized deletion-reporter gene constructs of proximal 2.2-kb alpha1(I) procollagen promoter to demonstrate that a region proximal to -133 bp is where PPARgamma exerts its inhibitory effect. Within this region, two DNase footprints with Sp1 and reverse CCAAT box sites exist. NF-I, but not CCAAT DNA-binding factor/NF-Y, binds to the proximal CCAAT box in hepatic stellate cells. A mutation of this site almost completely abrogates the promoter activity. NF-I mildly but independently stimulates the promoter activity and synergistically promotes Sp1-induced activity. PPARgamma inhibits NF-I binding to the most proximal footprint (-97/-85 bp) and inhibits its transactivity. The former effect is mediated by the ability of PPARgamma to inhibit p300-facilitated NF-I binding to DNA as demonstrated by chromatin immunoprecipitation assay.

Major histocompatibility class II transactivator (CIITA) mediates repression of collagen (COL1A2) transcription by interferon gamma (IFN-gamma)

Interferon gamma (IFN-gamma) plays an important role during inflammation by repressing collagen and activating major histocompatibility class II (MHC-II) expression. Activation of MHC-II by IFN-gamma requires regulatory factor for X-box 5 (RFX5) complex as well as class II transactivator (CIITA). We have shown that the RFX family binds to the COL1A2 transcription start site, and the RFX5 complex represses COL1A2 gene expression during IFN-gamma response. In this report, we demonstrate that CIITA is a key mediator of COL1A2 repression by IFN-gamma. IFN-gamma up-regulates the expression of CIITA in a time-dependent manner in lung fibroblasts and promotes CIITA protein occupancy on COL1A2 transcription start site in vivo as judged by chromatin immunoprecipitation (ChIP) assays. There are coordinate decreases in the occupancy of RNA polymerase II on the collagen transcription start site with increasing CIITA occupancy during IFN-gamma treatment. In addition, we are able to specifically knockdown the IFN-gamma-stimulated expression of CIITA utilizing short hairpin interference RNA (shRNA) against CIITA. This leads to the alleviation of COL1A2 repression and MHC-II activation by IFN-gamma. RFX5 recruits CIITA to the collagen site as evidenced by DNA affinity chromatography. The presence of RFX5 complex proteins enhances the collagen repression by CIITA reaching levels occurring during IFN-gamma treatment. Co-expression of CIITA with deletion mutations and collagen promoter constructs demonstrates that CIITA represses collagen promoter mainly through its N-terminal region including the acidic domain and the proline/serine/threonine domain. Our data suggest that CIITA is a crucial member of a repressor complex responsible for mediating COL1A2 transcription repression by IFN-gamma.

Interferon gamma repression of collagen (COL1A2) transcription is mediated by the RFX5 complex

Interferon gamma (IFN-gamma) plays an important physiological role during inflammation by down-regulating collagen gene expression and activating major histocompatibility II (MHC-II) complex. The activation of MHC-II by IFN-gamma requires activation of a trimeric DNA binding transcriptional complex, RFX5 complex, containing RFXB (also called RFXANK or Tvl-1), RFXAP, as well as RFX5 protein. Previously, we demonstrated that RFX5 binds to the collagen transcription start site and represses collagen gene expression (Sengupta, P. K., Fargo, J., Smith, B. D. (2002) J. Biol. Chem. 277, 24926-24937). In this report, we have examined the role of RFXB and RFXAP proteins within the RFX5 complex to regulate collagen gene expression. The data show that all three RFX5 complex proteins are required for maximum repression. Expression of proteins with mutations known to be important for RFX5 complex formation does not repress collagen promoter activity. Two mutated forms of RFX5 act as dominant negative proteins activating collagen expression and reversing IFN-gamma down-regulation of collagen expression in human lung fibroblasts. IFN-gamma increases expression and nuclear translocation of RFX5. RFXB has a naturally occurring splice variant isoform (RFX SV). Interferon increases expression of the long form of RFXB and decreases expression of RFX SV with the same kinetics as collagen gene expression. Overexpression of the splice variant form reverses the IFN-gamma induced collagen repression in human lung fibroblasts. Finally, all three RFX5 complex proteins increase at the collagen transcription start site with IFN-gamma treatment using chromatin immunoprecipitation analysis. Thus, these studies suggest an important role for RFX5 complex in collagen repression.

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).

Transcriptional analysis in vivo of the hepatic genes, Cyp2b9 and Cyp2b10, by intravenous administration of plasmid DNA in mice

Phenobarbital (PB) responsiveness of CYP2B genes has been shown to be mediated by a PB responsive unit (PBRU). The core of the PBRU contains two nuclear receptor sites, NR-1 and NR-2, and a nuclear factor-1 (NF 1) binding site, which are required for PB responsiveness, but the importance of sequences flanking the core is not clear. We have used intravenous administration of plasmid DNA in the tail veins of mice to transfect hepatocytes in vivo and analyze sequence requirements for PB induction. In this assay PB treatment increased transactivation by the Cyp2b10 PBRU about 100-fold, which is similar to the increase in the expression of the endogenous gene while the Cyp2b9 PBRU was unresponsive. Analysis of chimeras of the two PBRUs and deletion mutants of the Cyp2b10 PBRU indicated that the core region containing the NR-1, NR-2 and NF-1 core sites is not sufficient for PB responsiveness. Additional sequence at the 3' side of the core sequence, which included a previously defined accessory factor-1 (AF-1) site, partially restored responsiveness. This region contained a binding site for NF-1 only in Cyp2b10 and not in Cyp2b9, but the intact site was not required for PB responsiveness. Purified constitutive androstane receptor (CAR)/retinoid X receptor (RXR) bound to the core NR-1 and NR-2 sites and to a third NR-3 site to the 5' side of the core in Cyp2b10. No binding of CAR/RXR to the Cyp2b9 PBRU was observed. These results indicate that changes in the NR sites which eliminate CAR/RXR binding are sufficient for the non-responsiveness to PB of Cyp2b9, but changes in sequences flanking the core independently eliminate PB responsiveness. The results demonstrate the advantages of transfection of mouse hepatocytes in vivo by tail vein injection of DNA as a method for transcriptional analysis of genes in vivo and show that sequences flanking the core region of the PBRU are required for PB induction in vivo.

Distant enhancers stimulate the albumin promoter through complex proximal binding sites

The albumin-alpha-fetoprotein locus epitomizes the main features of transcriptional regulation of fetal and adult hepatocyte-specific genes: developmentally regulated promoters and strong distant enhancers. Full enhancer activity required only a proximal albumin-promoter region containing the TATA box, hepatic nuclear factor 1 (HNF1), and nuclear factor Y (NF-Y) sites. Deletion of the HNF1 site abrogated enhancer and promoter activity, whereas methylation of the site reduced all activity by about 3-fold. Deletion of the NF-Y site attenuated activity by about half, but much of the activity could be replaced by juxtaposition of an upstream region (designated distal element IV). Gel shift and competition analysis demonstrated that binding of architectural factors overlapped NF-Y binding. Moreover, a mutation that eliminated NF-Y binding but only minimally perturbed the surrounding region did not affect enhancer function. In plasmids with a second promoter, the enhancers simultaneously stimulated both albumin and alpha-fetoprotein promoters with minimal competition, but surprisingly some mutations in the albumin promoter attenuated expression from both promoters, whereas another uncoupled their expression. With single promoters, the function of the proximal promoter region was controlled by three parameters in the following hierarchy: HNF1 binding > local architecture > NF-Y binding, but integrated two-promoter function had a much greater dependence on NF-Y.

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.

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.

The chick type III collagen gene contains two promoters that are preferentially expressed in different cell types and are separated by over 20 kb of DNA containing 23 exons

Type III collagen is present in prechondrogenic mesenchyme, but not in cartilages formed during endochondral ossification. However, cultured chick chondrocytes contain an unusual transcript of the type III collagen gene in which exons 1-23 are replaced with a previously undescribed exon, 23A; this alternative transcript does not encode type III collagen. This observation suggested that, although production of type III collagen mRNA is repressed in chondrocytes, transcription of the type III collagen gene may continue from an alternative promoter. To test this prediction, we isolated and characterized both the upstream and internal promoters of this gene and tested their ability to direct transcription in chondrocytes and skin fibroblasts. The upstream promoter is active in fibroblasts, but inactive in chondrocytes, indicating that repression of type III collagen synthesis during chondrogenesis is transcriptionally mediated. Additionally, sequences in intron 23, preceding exon 23A, function as a highly active promoter in chondrocytes; transcription from this promoter is repressed in fibroblasts. Thus transcriptional control of the type III collagen gene is highly complex, with two promoters separated by at least 20 kb of DNA that are preferentially expressed in different cell types and give rise to RNAs with different structures and functions.

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.

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.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Studies on the structure of the mouse CBF-A gene and properties of a truncated CBF-A isoform generated from an alternatively spliced RNA

CCAAT-binding factor (CBF), a heteromeric transcription factor that binds to sequences containing a CCAAT motif, is composed of three subunits, A, B and C, which are all required for DNA binding. The mouse CBF-A gene contains seven coding exons, which span 12 kb. Evidence is also presented for an additional 5' untranslated exon. The 90-amino-acid (aa) segment of CBF-A, which shows a high degree of sequence identity with the yeast transcription factor, HAP3, is split into exons 3 and 4. An alternatively spliced RNA that lacks exon 3 was identified by polymerase chain reaction. Although removal of exon 3 interrupts the CBF-A reading frame, a potential start codon at the 3' end of exon 2 is in the same reading frame as the reading frame encoding CBF-A in exons 4 to 7. A CBF-A polypeptide of the predicted 17-kDa, size, was indeed identified after in vitro transcription and translation of the DNA complementary to RNA (cDNA) corresponding to the alternatively spliced CBF-A mRNA. In contrast to full-length CBF-A, this truncated CBFA did not bind to a DNA sequence containing the CCAAT motif in the presence of the other two components of CBF. This result indicates that the segment corresponding to the exons missing in the truncated isoform of CBF-A is essential for the binding of CBF to DNA.

Purification of a novel factor which binds to the mouse alpha 2 (I) collagen promoter

We have identified and purified a DNA binding protein which specifically binds to a segment of the mouse alpha 2 (I) collagen promoter between -420 and -399 bp upstream of the start of transcription. Purification included heparin-agarose and sequence-specific DNA-affinity chromatography, followed by SDS-PAGE and renaturation of the DNA binding activity after elution from SDS-polyacrylamide gel. The DNA binding activity resides in two species of 42 kDa and 40 kDa, respectively. The levels of DNA binding activity of this factor, which has been tentatively designated as ColF1, are considerably higher in nuclear extracts of NIH-3T3 fibroblasts than in nuclear extracts from epidermal cells, lymphoid cells and transformed NIH-3T3 fibroblasts.

Developmental control of collagen gene expression in the rat lung: confirmation of early observations of lung growth

The short gestation period of the rat allows one to see rapid morphologic and biochemical changes in the lung. It has been shown that the rat lung undergoes a period of distension over the first several days of life followed by a rapid alveolar growth. Total lung collagen also increases during this time period. We have examined the changes in types I and III procollagen transcripts during the perinatal period and have compared them to the above observations. Total RNA was extracted from the lungs of offspring of time-pregnant Sprague-Dawley rats after large airways were removed. Northern hybridization was performed to determine the quality of steady-state RNA and rule out cross-hybridization while densitometric tracings of slot-blot hybridizations allowed comparative estimates of the target sequence of RNA. Immediately following birth, the steady-state mRNA procollagen levels increased and a shift to a predominant type I production occurred. These changes preceded the rapid increase of collagen content and alveolarization known to occur at three days of age. These data provide further evidence that collagen production is controlled at the level of transcription and in temporal and tissue-specific manners.

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.

The pathobiology of ozone-induced damage

Ozone remains one of the three most important air pollutants worldwide, yet little direct documented evidence of its genotoxicity exists. The interest in the pathology of ozone exposure and the molecular events that underlie its course stems from DNA damage caused by oxygen stress including hydroxyl radicals, superoxide, singlet oxygen, and hydrogen peroxide. Although the tissue damage associated with ozone inhalation occurs at both the conducting airway and the alveolus, the cellular and mechanistic processes underlying these events are less well understood. Ozone leads to the oxidative decomposition of polyunsaturated fatty acids. Ozone also depresses DNA replication in V79 Chinese hamster lung fibroblasts in a dose-dependent fashion (concentration, 1-10 ppm), which indicates that ozone or its reaction products may interact directly with DNA and inhibit replication. Ozone also linearizes circular DNA and induces ozone-sensitive mutant and pneumocytes to repair its DNA. DNA adducts have been implicated in aging, cellular transformation, mutagenesis, carcinogenesis, and cell death; DNA adducts are products of free radical damage. These events are all common in ozone exposure. Finally, DNA-binding proteins are potent positive and negative regulators, enhancers, or silencers of gene expression. Part of their action may be related to their ability to initiate the binding sequence of DNA transcription proteins and thus form complexes. Alteration of DNA-binding sites by ozone adducts may effect mRNA transcription due to altered binding by DNA-binding proteins. This altered transcription has been shown to effect growth factors involved in collagen and matrix regulation. The present review will address some of the complexities involved in ozone exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective activation of transcription by a novel CCAAT binding factor

A novel CCAAT binding factor (CBF) composed of two different subunits has been extensively purified from rat liver. Both subunits are needed for specific binding to DNA. Addition of this purified protein to nuclear extracts of NIH 3T3 fibroblasts stimulates transcription from several promoters including the alpha 2(I) collagen, the alpha 1(I) collagen, the Rous sarcoma virus long terminal repeat (RSV-LTR), and the adenovirus major late promoter. Point mutations in the CCAAT motif that show either no binding or a decreased binding of CBF likewise abolish or reduce activation of transcription by CBF. Activation of transcription requires, therefore, the specific binding of CBF to its recognition sites.

Differential regulation by glucocorticoids of mouse pro alpha 2(I) and pro alpha 1(III) DNA-binding proteins

Multiple procollagen-specific DNA-binding proteins were identified for the alpha 2(I) and the alpha 1(III) procollagen promotor containing gene fragments. The proteins are gene-specific, differing in their relative molecular weights and relative binding specificities. A major finding was the increased DNA-binding with specificity for the procollagen promoter containing DNAs by several nonhistone nuclear proteins in mouse embryo fibroblasts treated with dexamethasone. The previously reported coordinate decrease of type I and type III procollagens by glucocorticoids may involve differential regulation by glucocorticoids of procollagen gene specific DNA-binding proteins.

Human CCAAT-binding proteins have heterologous subunits

We have characterized three distinct proteins present in HeLa cell extracts that specifically recognize different subsets of transcriptional elements containing the pentanucleotide sequence CCAAT. One of these CCAAT-binding proteins, CP1, binds with high affinity to CCAAT elements present in the human alpha-globin promoter and the adenovirus major late promoter (MLP). A second protein, CP2, binds with high affinity to a CCAAT element present in the rat gamma-fibrinogen promoter. Finally, the third CCAAT-binding protein is nuclear factor I (NF-I), a cellular DNA-binding protein that binds to the adenovirus origin of replication and is required for the initiation of adenoviral replication. CP1, CP2, and NF-I are distinct activities in that each binds to its own recognition site with an affinity that is at least three orders of magnitude higher than that with which it binds to the recognition sites of the other two proteins. Surprisingly, CP1, CP2, and NF-I each appear to recognize their binding site with highest affinity as a multisubunit complex composed of heterologous subunits. In the case of CP1, two different types of subunits form a stable complex in the absence of a DNA-binding site. Moreover, both subunits are present in the CP1-DNA complex. We thus propose the existence of a family of related multisubunit CCAAT-binding proteins that are composed of heterologous subunits.

The developmentally regulated expression of two linked myosin heavy-chain genes

The organization of two linked chicken myosin heavy-chain (MHC) genes is described. Using probes derived from the 3' and 5' ends of the genes, chromosome walks were carried out, resulting in the isolation of a clone which encompassed the 5' end of one MHC gene and the 3' end of a different MHC gene. Further analysis showed that both genes (each approximately 25 kbp in length) are oriented head to tail and are separated by an intergenic region of 7.5 kbp. Despite extensive homologies, a transcript-specific probe for each of the genes could be prepared from the 5' untranslated regions. These probes were used to determine the transcriptional pattern for each of the genes. The data show that the gene located at the 5' end of the linkage pair is expressed during the neonatal stages of development, while the gene located at the 3' end of the pair is expressed predominantly during the embryonic stages of development.

Estradiol-dependent trans-acting factor binds preferentially to a dyad-symmetry structure within the third intron of the avian vitellogenin gene

The secondary activation of the avian vitellogenin II gene in isolated liver nuclei by cytoplasmatic liver extracts of estradiol-treated chicks is accompanied by the binding of a protein from the extract to the structural part of the cloned gene. Both the DNA-binding and gene-stimulatory activities, which cochromatograph on heparin-Sepharose, are apparently present only in the cytoplasmatic liver extracts of estradiol-treated roosters and in the oviduct extracts of egg-laying hens. DNA-binding competition assays combined with exonuclease III footprinting showed that the factor binds to the imperfect dyad-symmetry structure 5'GTCTTGTTCCAAAC3' within the third intron of the gene. The factor is sequence specific and binds equally well to both single-and double-stranded DNA with an estimated dissociation constant of 3.5 X 10(-10) M.

Characterization of the trans-activation-responsive element of the parvovirus H-1 P38 promoter

The parvovirus early protein NS1 positively regulates the expression of the P38 promoter for the viral capsid protein gene. We have examined the trans-activation of P38 by NS1 by using fusions of P38 to the reporter gene, chloramphenicol acetyltransferase (cat). Maximal trans-activation requires a small 5' cis element (tar) between -137 and -116. The tar element has activity in both orientations when 5' to the P38 promoter, but no activity has been detected 3' to the promoter. The wild-type P38 has a biphasic response to NS1 depending on the dosage of the NS1-expressing plasmid. Promoters lacking the tar also have a biphasic response that is reduced about 10-fold, and they can be inhibited by larger doses of the NS1 plasmid. Heterologous promoters from other viruses and the Harvey-ras oncogene promoter are inhibited by NS1. Truncated and internally deleted versions of NS1 lose the trans-activation, but some of them retain the inhibitory properties. Thus transactivation can be uncoupled from inhibition. The tar element has shown no activity with the heterologous simian virus 40 early promoter. In contrast, the P38 promoter responds to a heterologous enhancer, but the enhanced promoter loses activity to trans-activation by NS1. In summary, the P38 tar element has some of the properties of an enhancer with a high preference for a 5' position and a stringent requirement for the P38 promoter.