Copy number of a human type I alpha 2 collagen gene

Oxidative and nitrosative stress and fibrogenic response

Uncontrolled production of collagen I is the main feature of liver fibrosis. Following a fibrogenic stimulus such as alcohol, hepatic stellate cells (HSC) transform into an activated collagen-producing cell. In alcoholic liver disease, numerous changes in gene expression are associated with HSC activation, including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses for understanding the molecular basis of the collagen I gene regulation have revealed a complex process involving reactive oxygen species (ROS) as key mediators. Less is known, however, about the contribution of reactive nitrogen species (RNS). In addition, a series of cytokines, growth factors, and chemokines, which activate extracellular matrix (ECM)-producing cells through paracrine and autocrine loops, contribute to the fibrogenic response.

Transcriptional activation of the type I collagen genes COL1A1 and COL1A2 in fibroblasts by interleukin-4: analysis of the functional collagen promoter sequences

Pneumonitis followed by lung fibrosis is a frequent complication of radiation therapy of chest tumors. A hallmark of these fibrotic lesions is the excessive production and accumulation of extracellular matrix proteins such as type I collagen. In addition to TGF-beta1, IL-4 has been recognized as a potent inducer of collagen gene synthesis in fibroblasts. In this study, we analyzed the regulation of the alpha1(I) procollagen (COL1A1) promoter and the alpha2(I) procollagen (COL1A2) promoter by IL-4 in normal human lung fibroblasts. We provide evidence that the IL-4-induced transcriptional activator STAT6 binds to various sequences within the COL1A1 and COL1A2 promoter. The regulatory function of these regions was tested by reporter gene analysis using 5' deletions of the COL1A1 and COL1A2 promoter fused to the luciferase gene. Interleukin-4 treatment of human fibroblasts transiently transfected with COL1A1 promoter deletion constructs resulted in luciferase activity exceeding that of untreated fibroblasts by 25%, while luciferase activity driven by the COL1A2 promoter was enhanced by about 70% upon IL-4 treatment. A combined action of SP1, NFkappaB, and STAT6 essentially contributes to the IL-4 mediated COL1A2 gene activation. An AP2 site adjacent to the reverse orientated STAT6 consensus motif TTC N(3/4) GCT is located within 205 bases from the transcription start site and seems to support the moderate IL-4-induced COL1A1 gene activation. Interferon-gamma downregulation of transcription is mainly seen with the COL1A1 promoter.

Epidermal growth factor receptor overexpression in esophageal carcinoma. An immunohistochemical study correlated with clinicopathologic findings and DNA amplification

BACKGROUND

Many studies have reported the increased expression of epidermal growth factor receptor (EGFR) in various human malignancies and its association with the biologic behavior of the tumors.

METHODS

We performed an immunohistochemical analysis of the EGFR in 217 cases of human esophageal squamous cell carcinoma, 161 lymph node metastases and 23 foci of squamous dysplasias. The findings were correlated with clinicopathologic features, including the clinical outcome. Southern blot analysis was performed in 42 cases for the detection of DNA amplification of the EGFR gene and subsequently was correlated with EGFR immunoreactivity.

RESULTS

Epidermal growth factor receptor overexpression was detected in 71% of primary tumors and 88% of lymph node metastases, as compared to nonpathologic adjacent esophageal epithelium. Statistically significant correlations were observed between EGFR overexpression and sex, age, histologic type, and the presence of invasion. Tumor staining was classified into two patterns, homogeneous and heterogeneous, based on the distribution of EGFR-positive cells. The immunostaining patterns of primary tumors had a statistically significant correlation with histologic type, the presence of adventitial invasion, histologic stage and lymph node metastasis. There was a tendency toward a worse prognosis for those patients with EGFR overexpression in the primary tumor. Greater than 90% of the foci of squamous dysplasia demonstrated homogeneous EGFR overexpression. DNA amplification of the EGFR was observed in 21% of primary tumors, and all demonstrated immunohistochemical overexpression.

CONCLUSIONS

Immunohistochemical overexpression of the EGFR, which was more frequent than EGFR DNA amplification, appears to play an important role in biologic behavior of human esophageal squamous cell carcinomas.

Homozygous deletion, rearrangement and hypermethylation implicate chromosome region 3p14.3-3p21.3 in sporadic breast-cancer development

DNAs from 19 malignant human breast tumors and 2 benign fibroadenomas were analyzed for heterozygosity at 5 polymorphic loci on the short arm of chromosome 3. One homozygous deletion and one rearrangement were identified using probe D3S2 which maps to 3p14.3-3p21.1. This probe also detected novel hybridizing fragments of 2.0 kb and/or 3.4 kb in 6/18 (33%) of the malignant tumor samples that hybridized with the D3S2 probe following digestion with the 5'-methylcytosine-insensitive enzyme MspI. Comparisons of HpaII and MspI digestion showed that all but one of the tumor DNAs analyzed were hypermethylated. The two fibroadenoma DNAs were not as highly methylated and had hybridizing fragments of 3.4 kb after HpaII digestion. These malignant breast-tumor DNAs exhibit 3 mechanisms by which a tumor-suppressor gene hypothesized to reside at 3p14-3p21 could be inactivated: homozygous deletion, rearrangement and hypermethylation, and strongly implicate this 3p chromosome region in breast-tumor development.

Osteogenesis imperfecta type III: mutations in the type I collagen structural genes, COL1A1 and COL1A2, are not necessarily responsible

Most forms of osteogenesis imperfecta are caused by dominant mutations in either of the two genes, COL1A1 and COL1A2, that encode the pro alpha 1(I) and pro alpha 2(I) chains of type I collagen, respectively. However, a severe, autosomal recessive form of OI type III with a comparatively high frequency has been recognised in the black populations of southern Africa. We preformed linkage analyses in eight OI type III families using RFLPs associated with the COL1A1 and COL1A2 loci to determine whether mutations in the genes for type I collagen were responsible for this form of OI. Recombination between the OI phenotype and polymorphic markers at both loci was shown in three of the eight families investigated. The combined lod scores for the eight families were -10.6 for COL1A1 and -11.2 for COL1A2. Further, we examined the type I procollagen produced by skin fibroblast cultures derived from 15 affected and 12 unaffected subjects from the above eight families plus one further family. We found no evidence for defects in the synthesis, structure, secretion, or post-translational modification of the chains of type I procollagen produced by any of the family members. These results suggest that mutations within or near the type I collagen structural genes are not responsible for this form of OI.

Cytokines and growth factors positively and negatively regulate interstitial collagen gene expression in human vascular smooth muscle cells

Human atheromas accumulate extracellular matrix proteins such as collagen types I and III. We tested whether cytokines or growth factors produced by cells found in human atherosclerotic plaques alter collagen gene expression in vascular smooth muscle cells (VSMCs), which produce the blood vessel matrix. Interleukin-1 (IL-1, 1-10 ng/ml) modestly increased the synthesis of collagens I and III (measured by tritiated proline incorporation into specific electrophoretic bands), whereas transforming growth factor-beta (TGF-beta) or platelet-derived growth factor (PDGF) markedly stimulated production of these interstitial collagens. Interferon gamma (IFN-gamma), a product of activated T cells found in atheromas, selectively alters several VSMC functions. For example, this cytokine reduces growth of VSMCs, decreases alpha-actin gene expression, and induces VSMC expression of class II histocompatibility antigens. We report here that IFN-gamma also inhibits basal as well as IL-1-, PDGF-, or TGF-beta-stimulated collagen I and III synthesis by human VSMCs. TGF-beta, the most potent stimulator of collagen synthesis studied here, raised the level of collagen III mRNA in VSMCs 4.8-fold (determined by densitometry of Northern blots), whereas exposure to both TGF-beta and IFN-gamma reduced this mRNA to 0.5 of basal level. Locally produced cytokines and growth factors may thus modify matrix accumulation during atherogenesis by stimulating or suppressing expression of interstitial collagen mRNA and protein by VSMCs.

Beals syndrome: clinical and molecular investigations in a kindred of Indian descent

Eight members of a 3-generation kindred of Indian descent with congenital contractural arachnodactyly (Beals syndrome) have been appraised. Considerable variation was noted in the clinical features of affected persons, and the previously unreported associated finding of clubbing of the fingers and toes was evident in two individuals. The family was investigated using conventional serum and protein markers, and RFLP probes for type I and II collagen. No linkage in affected members could be demonstrated with type I collagen probes.

Evaluation of the use of S1 nuclease to detect small length variations in genomic DNA

A method which utilises S1 nuclease to detect small length variations in cloned and genomic DNA has been evaluated. The methodology of this technique is simple and robust, permitting the rapid analysis of 10(4) base pairs. By employing defined sequence variants, this method is shown to have a sensitivity which should enable the detection of length variations of only a few base pairs in heterozygous individuals.

Existence of malfunctioning pro alpha2(I) collagen genes in a patient with a pro alpha 2(I)-chain-defective variant of Ehlers-Danlos syndrome

Collagen synthesis was examined in skin fibroblasts from a patient with a variant of Ehlers-Danlos syndrome. The relative rate of collagen synthesis to total protein synthesis in the patient's fibroblasts was always one-half of that in fibroblasts from normal controls. Total collagen synthesis, as assessed by quantification of total hydroxyproline, was also significantly lower than that of controls, indicating that the rate of collagen synthesis by the patient's fibroblasts was decreased compared with that by normal fibroblasts. Analysis of procollagen and collagen components showed the absence of the pro alpha 2(I) chain and its derivatives. Dot-blot and Northern-blot analyses showed the patient's fibroblasts to contain less than 10% of the mRNAs for pro alpha 2(I) found in control fibroblasts. In spite of these results, Southern blot analysis of genomic DNA indicated the presence of the same number of genes for the pro alpha 2(I) collagen chain in the patient's fibroblasts as in control fibroblasts, suggesting malfunctioning pro alpha 2(I) collagen genes as the cause for failure of the patient's fibroblasts to synthesize pro alpha 2(I) collagen chains.

The gene coding for tropoelastin is represented as a single copy sequence in the haploid sheep genome

The identity of the primary in vitro translation products of fetal sheep nuchal ligament elastin mRNA was confirmed as two distinct polypeptides of 63 Kdal and 65 Kdal in both rabbit reticulocyte and wheat germ extract cell-free translation systems. Both polypeptides were co-translationally processed by a microsomal membrane signal peptidase, with the removal of 20-25 amino acid residues. A single (3,5 kb) RNA species encodes both tropoelastin polypeptides. Restriction endonuclease mapping of sheep genomic DNA by hydridization with two radiolabelled genomic DNA fragments containing sequences coding for sheep tropoelastin (pSE1-1,3 and pSE1-0.7,) indicated the presence of a single elastin gene. The elastin gene copy number was further quantitated by comparison of hybridisation of pSE1-1.3 and pSE1-0.7 to slot-blots and Southern transfers of sheep genomic DNA and to standard curves constructed with each clone. These results clearly demonstrate that each of these sequences is represented only once per haploid genome, suggesting that the two tropoelastin polypeptides are products of a single elastin gene.

The single copy gene coding for human alpha 1 (IV) procollagen is located at the terminal end of the long arm of chromosome 13

Using dual-laser sorted chromosomes and spot-blot analysis, we have previously assigned genomic DNA sequences coding for human alpha 1 (IV) procollagen to chromosome 13 (Pihlajaniemi et al. 1985). By in situ hybridization to normal chromosomes and chromosomes with 13q deletions, we now report the localization of this gene to the terminal end of the long arm of chromosome 13. In addition, Southern and slot blot hybridization analysis clearly show that these genomic sequences are present only once per haploid genome.

Mutations linked to the pro alpha 2(I) collagen gene are responsible for several cases of osteogenesis imperfecta type I

We have analysed six South African families with osteogenesis imperfecta type I using three DNA polymorphisms associated with the pro alpha 2(I) collagen gene. In four of these families linkage of the pro alpha 2(I) gene and the osteogenesis imperfecta phenotype was suggested, whereas in the remaining two families there was a lack of linkage. No distinct correlation could be made between the phenotypic features of the families studied and linkage or lack of linkage to the pro alpha 2(I) gene. Two different haplotypes were found to be associated with the mutant pro alpha 2(I) alleles. These findings suggest that molecular heterogeneity exists within osteogenesis imperfecta type I and that in a significant proportion of cases the defect is linked to the pro alpha 2(I) gene.

Length polymorphism in the pro alpha 2(I) collagen gene: an alternative explanation in a case of Marfan syndrome

A 38 base pair (bp) insertion in the pro alpha 2(I) collagen gene (COL1A2) of a patient with Marfan syndrome has been proposed to be the possible cause of the disease (Henke et al. 1985). However, analysis of this insertion in DNA from the patient in question and from random normal individuals reveals it to be a common polymorphism. We suggest that the 38 bp insertion is not related to the primary defect in this case of Marfan syndrome.

Human type III collagen gene expression is coordinately modulated with the type I collagen genes during fibroblast growth

Type III collagen is one of the major interstitial collagens and, as such, plays an important role in modulating the structure and function of most tissues. To compare the expression of the type III collagen gene to that of the type I collagen alpha 1(I) and alpha 2(I) genes, cDNAs encoding the 3' one-third of the human alpha 1(III) collagen mRNA were obtained by screening a human fetal lung fibroblast cDNA library with a cloned segment of the chicken alpha 1(III) gene. Northern blot analysis of human fetal lung fibroblast RNA demonstrated two alpha 1(III)-specific mRNAs of sizes 6.6 and 5.8 kilobases, sizes clearly different from those of the type I collagen mRNAs. Analyses of populations of dividing and nondividing human lung fibroblasts revealed that, on a per cell basis, the nondividing population contained twice as much alpha 1(III) mRNA than did the dividing population. The same was true for the type I collagen alpha 1(I) and alpha 2(I) mRNA transcripts. Similar results were obtained when alpha 1(III), alpha 1(I), and alpha 2(I) mRNA transcripts were quantified by using dot blot evaluation of total RNA, Northern analysis of total RNA, and dot blot evaluation of cytoplasmic RNA. Thus, despite the fact that the alpha 1(III) collagen gene is located on a chromosome different from the alpha 1(I) and alpha 2(I) genes, the expression of these three collagen chains appears to be coordinately controlled during periods of rapid and slow fibroblast growth.

Regulation of type I collagen synthesis. Total pro alpha 1(I) and pro alpha 2(I) mRNAs are maintained in a 2:1 ratio under varying rates of collagen synthesis

The type I collagen molecule contains two alpha 1(I) chains and one alpha 2(I) chain. Previous investigations, using embryonic chick calvaria, have indicated that the two chains are synthesized in a 2:1 ratio which is controlled at a pretranslational level, since the cells contain twice as much translatable pro alpha 1(I) mRNA as pro alpha 2(I) mRNA. The present report describes hybridization analyses of the cellular levels of total cellular RNAs coding for the pro alpha 1(I) and pro alpha 2(I) chains, using as probes two cloned cDNAs complementary to chick pro alpha 1(I) and pro alpha 2(I) mRNA, respectively. Total cellular RNA was extracted from embryonic chick calvaria, pro alpha 1(I) and pro alpha 2(I) RNA sequences were quantified by Northern hybridization using conditions ensuring that hybridization efficiency and specific radioactivity were the same for the two probes. Similar analyses were carried out on RNA extracted from calvaria with different levels of collagen synthesis after culture in the presence or absence of ascorbic acid. The results for all samples analyzed indicate that total cellular pro alpha 1(I) and pro alpha 2(I) mRNAs are present in a 2:1 ratio which is maintained even during variations in collagen synthesis rate. There is no evidence for regulation mediated by different rates of processing of mRNA precursors, although preferential degradation of the pro alpha 2(I) gene transcript cannot be excluded. Thus, the synthesis of type I procollagen chains is presumably coordinated by transcriptional control.

Polymorphism of DNA sequence in the human pro alpha 2(I) collagen gene

The human pro alpha 2(I) collagen gene was analysed for the presence of restriction fragment length polymorphisms. DNA from randomly selected unrelated persons of three Southern African populations was cleaved with one of eight different restriction enzymes, electrophoresed, blotted, and hybridised with cDNA and genomic probes specific for the pro alpha 2(I) gene. An MspI polymorphism was detected which results from the loss of a cleavage site within the 3' half of the gene. In two of the populations studied, the polymorphism occurred at significant frequencies, and should therefore prove useful as a genetic marker for the study of inherited disorders of connective tissue involving collagen structure or biosynthesis.

Two new polymorphic markers in the human pro alpha 2(1) collagen gene

Structural defects in the human type 1 collagen genes are known to be the cause of several inherited disorders of connective tissue, such as osteogenesis imperfecta. The analysis and prenatal diagnosis of these disorders would be facilitated by establishing a set of polymorphic markers at these gene loci. We have previously reported the presence of an Msp 1 restriction fragment length polymorphism in the pro alpha 2 (1) collagen genes of several Southern African populations (Grobler-Rabie et al., in press). This report describes the detection of a Bgl II and an EcoRI polymorphism in the pro alpha 2 gene of South African Blacks.

Amplification of c-Ki-ras gene and aberrant expression of c-myc in WI-38 cells transformed in vitro by gamma-irradiation

The expression of c-oncogenes was examined with normal human fibroblasts (WI-38) and the cells transformed in vitro by gamma-irradiation (CT-1). The amount of Ki-ras-specific mRNA in CT-1 cells was found to be approximately twice that in WI-38 cells. By Southern blot hybridization, the c-Ki-ras 2 gene of CT-1 cells was found to be amplified about two-fold. CT-1 cells have higher levels of c-myc mRNA than normal cells, although the gene dosage and the restriction nuclease pattern of the c-myc gene was the same. The content of c-myc mRNA in CT-1 cells was found to be constitutively high, whereas that in normal cells was increased by serum addition.

Regional chromosome mapping of human collagen genes alpha 2(I) and alpha 1(I) (COLIA2 and COLIA1)

For the assignment of the genes for the pro-alpha 2(I) (COLIA2) and the pro-alpha 1(I) (COLIA1) collagens, cDNA and genomic DNA probes were used in in situ hybridization experiments on human prometaphase chromosomes. An improved staining method is reported for the simultaneous identification of chromosomes and the autoradiographic grains after the hybridization procedures. With this procedure more cells with higher resolution could be used for the assignment of genes by in situ hybridization. Statistical analysis of the grains located on respectively 660 and 302 metaphases using pro-alpha 2(I) and pro alpha 1(I) DNA probes, confirmed the assignment of these genes to human chromosomes 7 and 17. Analysis of the grain distribution on prometaphase chromosomes showed that the location of the pro-alpha 2(I) collagen gene is in the region 7q21.3-22.1. The location of the pro-alpha 1(I) collagen gene was found to be in band 17q21.31-2205.

Copy number of the chicken type II procollagen gene

The copy number of the type II procollagen gene has been determined by quantitative hybridization of cloned DNA to Southern blots of total cellular DNA from chicken. Two different DNA probes have been used. One contains the 289 base pair exon coding for the junction between the triple helical domain and the carboxyl-terminal propeptide and the other contains an 162 base pair exon coding for amino acids 712-765 of the triple helical domain. Both fragments hybridize to single bands present at one copy per haploid genome in genomic DNA from chicken liver or sternal cartilage after these DNAs are cleaved with either HinfI of PstI. When the hybridization stringency and washing conditions were modified sufficiently to stabilize hybridization of heteroduplexes with up to 31% mismatch, no additional hybridizing fragments were detected. These results show that there is not a second copy of this gene or a pseudogene which is more closely related to the type II procollagen gene than the alpha 1 type I procollagen gene. These studies suggest that the cartilage 3 alpha collagen chain, which appears to be very similar to the alpha 1 (II) collagen chain, is encoded by the type II procollagen gene but is differently processed than the major type II gene product, and that the alpha 1 (II) Minor chain identified in bovine type II collagen preparations most likely represents an allelic form of type II collagen rather than a product of a different gene.

Transcriptionally active and inactive genes are similarly modified by chemical carcinogens or X-ray in normal human fibroblasts

Chemical carcinogens and ionizing radiation induce DNA modifications and strand breaks in cells. This damage is reported to be affected by chromatin proteins or chromatin of a higher structure order. To compare the sensitivity of transcriptionally active and inactive genes on chromatin toward DNA-damaging agents, we treated normal human fibroblasts (WI-38) cells in N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), X-ray, 4-hydroxyaminoquinoline 1-oxide or N-acetoxy-2-acetylaminofluorene, and high molecular weight DNA was isolated. After digestion with EcoRI to completion, the DNA was electrophoresed on an alkaline agarose gel, blotted on a nitrocellulose filter and hybridized with a transcriptionally active gene probe (human type I(alpha 2) procollagen gene) or an inactive gene probe (human beta-globin gene). The results show that both genes are similarly modified by these agents. Repair of DNA damage caused by MNNG also occurred similarly in collagen and beta-globin genes after removal of MNNG.

Isolation and characterization of a human pro alpha 2(I) collagen gene segment

Over 20 kilobase pairs of the human pro alpha 2(I) collagen gene have been isolated and characterized by restriction endonuclease mapping, cell-free translation of hybrid-selected RNA, and DNA sequence analysis. We have sequenced an exon and determined its length to be 108 base pairs (bp). This is consistent with the organization of chick and sheep collagen genes in that exons are multiples of 9 bp in length, frequently being 54 and 108 bp. The sequenced exon was bordered by a GT (guanine-thymine) at its 3' end and an AT (adenine-thymine) at its 5' end. This pattern has been found at all normal intron-exon junctions in eukaryotic cells. The amino acid sequence derived from DNA sequencing of this 108 bp exon revealed 88% homology compared to the amino acid sequence of bovine pro alpha 2(I). The bases encoded 12 Gly-X-Y triplets characteristic of the helical portion of collagen. A unique sequence Gly-Gly-Lys-Gly-Glu-Lys identified this fragment as alpha 2(I) collagen.

Internal deletion in a collagen gene in a perinatal lethal form of osteogenesis imperfecta

Cloned probes specific for unique genes have proven to be powerful tools in defining the nature of genetic diseases such as the thalassaemias and growth hormone deficiencies. A similar approach should be useful in defining heritable diseases of type I collagen, the heterotrimer of two alpha 1(I) chains and one alpha 2(I) chain, which is the most abundant member of the collagen family of proteins. Recently, cloned cDNAs and genomic DNAs for the two polypeptide chains of the type I collagen have become available and have been used to elucidate the chromosomal location of the corresponding genes. Here, we have used several of these cloned DNAs to demonstrate the presence of an internal deletion of about 0.5 kilobases (kb) in one allele for the pro alpha 1(I) chain in a patient with osteogenesis imperfecta (OI), a group of heritable disorders which are characterized by brittle bones but which are highly heterogeneous both phenotypically and biochemically.