High levels of expression of a minigene version of the human pro alpha 1 (I) collagen gene in stably transfected mouse fibroblasts. Effects of deleting putative regulatory sequences in the first intron

Status and developmental trends in recombinant collagen preparation technology

Recombinant collagen is a pivotal topic in foundational biological research and epitomizes the application of critical bioengineering technologies. These technological advancements have profound implications across diverse areas such as regenerative medicine, organ replacement, tissue engineering, cosmetics and more. Thus, recombinant collagen and its preparation methodologies rooted in genetically engineered cells mark pivotal milestones in medical product research. This article provides a comprehensive overview of the current genetic engineering technologies and methods used in the production of recombinant collagen, as well as the conventional production process and quality control detection methods for this material. Furthermore, the discussion extends to foresee the strides in physical transfection and magnetic control sorting studies, envisioning an enhanced preparation of recombinant collagen-seeded cells to further fuel recombinant collagen production.

Cosmetic Potential of a Recombinant 50 kDa Protein

Collagen and its derivative proteins have been widely used as a major component for cosmetic formulations as a natural ingredient and moisturizer. Most commercially available collagens are animal-derived collagen type I and other forms of collagen, such as type III collagen, are far less prevalent in animals, making extraction and purification extremely difficult and expensive. Here, we report the production of a 50 kDa protein produced in yeast that is 100% identical to the N-terminus of the human type III collagen. This recombinant protein has a larger molecular weight than most incumbent recombinant collagen proteins available for personal care applications. We report the industrialization of both the fermentation and purification processes to produce a final recombinant protein product. This final protein product was shown to be safe for general applications to human skin and compatible with common formulation protocols, including ethanol-based formulations. This recombinant collagen type III protein was also shown to uniquely stimulate both collagen type I and type III production and secretion by primary human dermal fibroblasts. The unique combination of biostimulation, compatibility with beauty product formulations and demonstrated commercial production, make this novel recombinant type III collagen a good candidate for broad application in the cosmetics industry.

Three Decades of Research on Recombinant Collagens: Reinventing the Wheel or Developing New Biomedical Products?

Collagens provide the building blocks for diverse tissues and organs. Furthermore, these proteins act as signaling molecules that control cell behavior during organ development, growth, and repair. Their long half-life, mechanical strength, ability to assemble into fibrils and networks, biocompatibility, and abundance from readily available discarded animal tissues make collagens an attractive material in biomedicine, drug and food industries, and cosmetic products. About three decades ago, pioneering experiments led to recombinant human collagens' expression, thereby initiating studies on the potential use of these proteins as substitutes for the animal-derived collagens. Since then, scientists have utilized various systems to produce native-like recombinant collagens and their fragments. They also tested these collagens as materials to repair tissues, deliver drugs, and serve as therapeutics. Although many tests demonstrated that recombinant collagens perform as well as their native counterparts, the recombinant collagen technology has not yet been adopted by the biomedical, pharmaceutical, or food industry. This paper highlights recent technologies to produce and utilize recombinant collagens, and it contemplates their prospects and limitations.

Two novel COL1A1 mutations in patients with osteogenesis imperfecta (OI) affect the stability of the collagen type I triple-helix

Osteogenesis imperfecta (OI) is a bone dysplasia caused by mutations in the COL1A1 and COL1A2 genes. Although the condition has been intensely studied for over 25 years and recently over 800 novel mutations have been published, the relation between the location of mutations and clinical manifestation is poorly understood. Here we report missense mutations in COL1A1 of several OI patients. Two novel mutations were found in the D1 period. One caused a substitution of glycine 200 by valine at the N-terminus of D1 in OI type I/IV, lowering collagen stability by 50% at 34 degrees C. The other one was a substitution of valine 349 by phenylalanine at the C-terminus of D1 in OI type I, lowering collagen stability at 37.5 degrees C. Two other mutations, reported before, changed amino residues in D4. One was a lethal substitution changing glycine 866 to serine in genetically identical twins with OI type II. That mutated amino acid was near the border of D3 and D4. The second mutation changed glycine 1040 to serine located at the border of D4 and D0.4, in a proband manifesting OI type III, and lowered collagen stability at 39 degrees C (2 degrees C lower than normal). Our results confirm the hypothesis on a critical role of the D1 and D4 regions in stabilization of the collagen triple-helix. The defect in D1 seemed to produce a milder clinical type of OI, whereas the defect in the C-terminal end of collagen type caused the more severe or lethal types of OI.

Recombinant microbial systems for the production of human collagen and gelatin

The use of genetically engineered microorganisms is a cost-effective, scalable technology for the production of recombinant human collagen (rhC) and recombinant gelatin (rG). This review will discuss the use of yeast (Pichia pastoris, Saccharomyces cerevisiae, Hansenula polymorpha) and of bacteria (Escherichia coli, Bacillus brevis) genetically engineered for the production of rhC and rG. P. pastoris is the preferred production system for rhC and rG. Recombinant strains of P. pastoris accumulate properly hydroxylated triple helical rhC intracellularly at levels up to 1.5 g/l. Coexpression of recombinant collagen with recombinant prolyl hydroxylase results in the synthesis of hydroxylated collagen with thermal stability similar to native collagens. The purified hydroxylated rhC forms fibrils that are structurally similar to fibrils assembled from native collagen. These qualities make rhC attractive for use in many medical applications. P. pastoris can also be engineered to secrete high levels (3 to 14 g/l ) of collagen fragments with defined length, composition, and physiochemical properties that serve as substitutes for animal-derived gelatins. The replacement of animal-derived collagen and gelatin with rhC and rG will result in products with improved safety, traceability, reproducibility, and quality. In addition, the rhC and rG can be engineered to improve the performance of products containing these biomaterials.

Correction of a mineralization defect by overexpression of a wild-type cDNA for COL1A1 in marrow stromal cells (MSCs) from a patient with osteogenesis imperfecta: a strategy for rescuing mutations that produce dominant-negative protein defects

Gene therapy for dominant-negative disorders presents a more difficult challenge than gene therapy for recessive disorders, since even partial replacement of a protein for a recessive disorder can reverse symptoms. Osteogenesis imperfecta (OI) has frequently served as a model disorder for dominant-negative defects of structural proteins. The disease is caused by mutations in type I collagen (COL1A1), the major structural component of bone, skin and other connective tissues. The severity of the phenotype is largely dependent on the ratio of normal to mutant type I procollagen synthesized by cells. Recently, attempts have been made to develop strategies for cell and gene therapies using the adult stem cells from bone marrow referred to as mesenchymal stem cells or marrow stromal cells (MSCs). In this study, we used MSCs from a patient with type III OI who was heterozygous for an IVS 41A+4C mutation in COL1A1. A hybrid genomic / cDNA construct of COL1A1 was transfected into the MSCs and the transfectants were expanded over a 200-fold. Transfected MSCs showed increased expression of the wild-type mRNA and protein. In vitro assays demonstrated that the transfected cells more efficiently differentiated into mineralizing cells. The results indicated that it is possible to overexpress COL1A1 cDNA in OI MSCs and thereby to correct partially the dominant-negative protein defect.

Endogenously Expressed Multimeric Self-Cleaving Hammerhead Ribozymes Ablate Mutant Collagen in Cellulo

Hammerhead ribozymes are small catalytic RNA molecules that can be targeted to any RNA molecule containing a putative cleavage site. We developed a vector (pCOLZ) that uses the COL1A1 promoter to drive expression of a self-cleaving multimeric ribozyme (M8Rz547) and its monomeric counterpart (Rz547). The ribozymes were stably coexpressed in MC3T3-E1 osteoblasts expressing a truncated COL1A1 target transcript. The multimeric ribozyme exhibited self-cleavage to derivative fragments, including monomers. Increased expression of ribozymes was found in cells expressing the multimeric ribozyme. A modest reduction of truncated target transcript and protein was seen in cells expressing the ribozyme monomer, while nearly complete ablation of target transcript and protein occurred in cells expressing the ribozyme multimer. A reversion to a more normal collagen phenotype, measured as an increase in fibril diameter and restored fibrillar architecture, and a decreased rate of collagen turnover were seen in cells expressing the ribozyme multimer.

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.

Phosphatidylinositol 3-kinase-dependent stabilization of alpha1(I) collagen mRNA in human lung fibroblasts

We investigated the role of phosphatidylinositol 3-kinase (PI3K) in the expression of alpha1(I) collagen mRNA. We report that the basal level of alpha1(I) collagen mRNA was reduced when PI3K activity was inhibited by either LY-294002 or wortmannin. These PI3K inhibitors also blocked increases of alpha1(I) collagen mRNA levels after the addition of transforming growth factor-beta. The effect of PI3K inhibition was abolished by the removal of the inhibitor or by the addition of cycloheximide. Inhibition of PI3K activity decreased the stability of the alpha1(I) collagen mRNA with no change in the rate of transcription of the alpha1(I) collagen gene as assessed by Northern blotting with actinomycin D-treated fibroblasts and nuclear run-on assays. Expression of a truncated alpha1(I) collagen minigene driven by a cytomegalovirus promoter in murine fibroblasts was decreased by LY-294002 treatment. These data indicate that PI3K activation results in increased stabilization of alpha1(I) collagen mRNA. In vivo, the PI3K activity in fibroblasts may regulate basal levels of alpha1(I) collagen mRNA expression.

Transgenic mice with a mutated collagen promoter display normal response during bleomycin-induced fibrosis and possess neurological abnormalities

We have previously identified a potential TGF-beta activation element (TAE) in the rat collagen alpha1(I) promoter at -1624 upstream of the transcriptional start site [Ritzenthaler et al., 1991, 1993]. To determine the importance of the TAE in vivo, we produced transgenic mice carrying 3.6 kb of the rat collagen alpha1(I) promoter linked to the reporter gene chloramphenicol acetyl transferase with and without site-directed mutations that eliminate DNA-protein binding at the TAE site. Tissue-specific expression of the reporter gene in transgenic mice with the mutated collagen promoter was similar to that of transgenic mice with the normal promoter in two genetic backgrounds as judged by in situ hybridization, reporter assays, and immunochemistry. Endotracheal instillation of bleomycin induces lung fibrosis, mediated in part by TGF-beta. Earlier studies indicated that expression of wild-type collagen-reporter gene was upregulated in transgenic mice lungs in response to endotracheal instillation of bleomycin. A similar level of reporter gene upregulation was observed in transgenic mice carrying the mutation in the TAE. Two lines of transgenic mice carrying the mutated promoter construct displayed unexpected neurological abnormalities. In the FVB genetic background, there was a higher than normal incidence of mortality, spontaneous seizures, and an inability to nurture offspring. Histological evidence demonstrated clear abnormalities, including disorderly arrangement of neurons in the hippocampus and significant laminar cortical necrosis in the cerebrum in animals after seizures. In the C57Bl/6 background, there was a high incidence of severe communicating hydrocephalus, early runting, and increased mortality similar to that in transgenic animals with astroglial overexpression of TGF-beta. These animals provide an interesting model system to investigate molecular mechanisms responsible for seizures and hydrocephalus.

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.

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

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

In vitro expression analysis of collagen biosynthesis and assembly

While the generalised pathway of collagen biosynthesis is well understood, the specific molecular interactions that drive chain recognition and assembly and the formation of tissue-specific extracellular supramolecular structures have not been elucidated. This review focuses on the use of in vitro collagen expression systems to explore some of these fundamental questions on the molecular basis of normal and mutant collagen assembly. Three in vitro expression/assembly systems are discussed. Firstly, a simple cell-free transcription/translation system to study the initial stages of collagen chain assembly. Secondly, a novel T7-driven high level expression system, using a recombinant vaccinia virus expressing T7 RNA polymerase, in transiently transfected cells which allows appropriate postranslational modification and collagen folding. Thirdly, the more complex questions of normal and mutant collagen extracellular matrix assembly are addressed by stable transfection and expression in cells which allow the formation of a 'tissue equivalent' matrix during long-term culture.

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.

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.

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.

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

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

Discordant expression of osteoblast markers in MC3T3-E1 cells that synthesize a high turnover matrix

To examine the autocrine effects that an organizing extracellular matrix has on osteoblast precursors, we created MC3T3-E1 cell lines that stably expressed pro-alpha1(I) collagen chains with a truncated triple helical domain. Cells that had incorporated the pro-alpha1(I) expression plasmid (pMG155) expressed shortened pro-alpha1(I) transcripts at high levels and efficiently secreted the expression gene products into culture media. Those cells lost over 30% of newly deposited collagenous matrix compared with virtually no loss in control cultures, and media from the abnormal cells had qualitative differences in matrix metalloprotinase production. Electron micrographs strongly suggested that type I collagen molecules containing the truncated pro-alpha1(I) chains dramatically interfered with collagen fibrillogenesis in newly forming osteoblast matrix. Abnormal collagen fibrillogenesis was also associated with altered characteristics of cellular differentiation in that abnormal cells displayed a delayed and attenuated increase in alkaline phosphatase activity. Surprisingly, synthesis of osteocalcin was more than 5-fold higher than control cultures. These findings demonstrate that osteoblasts require a normally structured collagenous matrix for up-regulation of alkaline phosphatase activity. However, in the presence of rapid turnover of osteoblast matrix, osteocalcin gene expression may be up-regulated in response to local signals by an unknown mechanism.

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

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

Abnormal differentiation in MC3T3-E1 preosteoblasts expressing a dominant-negative type I collagen mutation

To examine the effects that an organizing extracellular matrix might have on osteoblast precursors, we created MC3T3-E1 cell lines that stably incorporated a plasmid that expressed pro alpha 1 (I) collagen chains having a truncated triple helical domain. Cells that had incorporated the pro alpha 1 (I) expression plasmid (pMG155) efficiently secreted molecules with shortened pro alpha 1 (I) chains into culture media. Electron micrographs indicated that expression of the minigene dramatically interferes with normal type I collagen fibril architecture. The turnover of newly deposited collagenous matrix as measured by 3[H]-hydroxyproline release was 29% after a 14 day chase in cells expressing the minigene compared to essentially no turnover in control cultures. MC3T3-E1 cells in culture normally demonstrate a time dependent reduction of cell division followed by an increase in osteoblast characteristics. Cell number was consistently 20-25% higher than control in MC3T3-E1 cultures expressing the truncated pro alpha 1 (I) gene but ALP activity was only 45% of control. Secretion and steady state mRNA levels for osteocalcin were over fivefold higher than control cultures but expression of other extracellular matrix components was not changed. These findings demonstrate that osteoblasts require a normally structured collagenous matrix for inhibition of cellular proliferation and subsequent upregulation of ALP. However, in the presence of rapid turnover of osteoblast matrix, the gene for osteocalcin may be upregulated in response to local signals.

Tissue-specific expression of the gene for type I procollagen (COL1A1) in transgenic mice. Only 476 base pairs of the promoter are required if collagen genes are used as reporters

Inconsistent data have been reported on the size of the promoter that is necessary for high levels of tissue-specific expression of the COL1A1 gene for type I procollagen. Some of the inconsistencies may be traced to the use of reporter gene constructs. Therefore, we prepared transgenic mice with modifications of the intact gene engineered so that the level of expression of the transgene could be assayed both as mRNA and protein that were similar to the products from the endogenous COL1A1 gene. The results with a mini-COL1A1 gene lacking 41 internal exons and introns indicated that the first intron and 90% of the 3'-untranslated region were not essential for tissue-specific expression. In a hybrid COL1A1/COL2A1 construct, a 1.9-kilobase 5'-fragment from the COL1A1 gene that contained only 476 of the promoter was linked to a promoterless 29.5-kilobase fragment of the human COL2A1 gene for type II procollagen. The hybrid COL1A1/COL2A1 construct was expressed as both mRNA and protein in tissues that normally synthesize type I procollagen but not type II procollagen. Apparently, 476 base pairs of the promoter are sufficient to drive tissue-specific expression of the COL1A1 gene and totally inappropriate expression of the COL2A1 gene.

Effect of the 3'-untranslated region on the expression levels and mRNA stability of alpha 1(I) collagen gene

Changes in the synthesis of type I collagen, a major extracellular matrix component in skin and bones, are associated with both normal growth or repair processes and with several pathological conditions such as lung fibrosis and liver cirrhosis. The expression of the alpha 1(I) collagen gene is regulated by transcriptional and post-transcriptional mechanisms. Regulation at both these levels are usually utilised when extensive changes occur in collagen synthesis. We constructed plasmids carrying the whole or partially deleted 3'-UTR sequences of the alpha 1(I) collagen gene, fused to two hGH exons and to the promoter of the alpha 1(I) collagen gene. A control plasmid contained the 3'-UTR of the hGH gene. In transient transfections into Rat-1 fibroblasts, no significant differences between plasmids were found, which suggests that although 3'-end of the gene has been shown in previous studies to contain DNaseI hypersensitive sites and to bind sequence-specific nuclear proteins it does not seem to function as a transcriptional regulator. This was further supported by the finding that TGF-beta treatment induced a 2.5-fold expression of hGH mRNA from plasmids containing collagen promoter and either hGH or alpha 1(I) collagen 3'-UTR. In stable transfections, mRNAs using the first polyadenylation site were not as stable as those transcribed from the endogenous alpha 1(I) collagen gene. We suggest that the 3'-UTR alone may not be sufficient to determine the stability of the shorter alpha 1(I) collagen mRNA species.

Inhibition of collagen synthesis by prostaglandins in the immortalized rat osteoblastic cell line Py1a: structure-activity relations and signal transduction mechanisms

We previously showed that prostaglandin E2 (PGE2) can selectively inhibit collagen synthesis and gene transcription in the immortalized rat osteoblastic clonal cell line Py1a, particularly in the presence of insulin-like growth factor I (IGF-I). In the present study, we examined the structure-activity relations for this effect. PGF2 alpha was approximately 100 times more potent than PGE2. The prostaglandin F receptor (FP) selective agonist, fluprostenol, was the most potent agonist tested, significantly inhibiting incorporation of [3H]proline into both collagen and noncollagen protein at 10(-11) M, with more than 90% inhibition of collagen synthesis at 10(-8) M. The PGE2 analog, sulprostone, and PGD2 showed activity similar to that of PGE2. PGI2 and its stable analog, carbacyclin, were the least effective. Parathyroid hormone (PTH), forskolin, and isobutylmethylxanthine (IBMX) were ineffective. Phorbol myristate acetate (PMA) inhibited collagen synthesis in a manner similar to that of the prostanoids. The inhibitory effects of PGF2 alpha, fluprostenol, and PMA show a similar time course on alpha 1(I) procollagen mRNA levels. The inhibition appeared to be caused by a decrease in collagen gene transcription as measured by nuclear run-on analysis. Further evidence for a transcriptional effect was obtained with COL1A1 promoter-CAT reporter constructs, although these showed somewhat smaller effects of prostanoids on CAT activity than on mRNA levels or labeling.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific inhibition of expression of a human collagen gene (COL1A1) with modified antisense oligonucleotides. The most effective target sites are clustered in double-stranded regions of the predicted secondary structure for the mRNA

A series of antisense oligonucleotides (ASOs) were synthesized and tested to define the best target sites within an RNA transcript of collagen for effective inhibition of expression. The test system consisted of mouse NIH 3T3 fibroblasts that were stably transfected with a human minigene for procollagen I so that the cells simultaneously synthesized full-length mouse pro alpha 1 (I) chains and internally deleted human pro alpha 1 (I) chains. The sequences of the transcripts from both genes were compared, and a series of 28 ASOs were designed to target sites in which there were at least two base differences within a 20-nucleotide sequence between the human and mouse transcripts. Six of the ASOs specifically decreased the levels of pro alpha 1 (I) chain synthesized from the human gene without a decrease in the levels of pro alpha 1 (I) chains from the mouse endogenous gene. The most effective ASOs reduced the intracellular levels of human pro alpha 1 (I) chains relative to the mouse pro alpha 1 (I) chains to 37-67% of the control values. Combined addition of two effective ASOs or a second administration of the same effective ASO did not produce any additive effect. The results did not support previous suggestions that the best target sites for ASOs were sequences around initiation codons for translation, at intron-exon boundaries, or in single-stranded loops in hairpin structures. Also, the results did not support previous suggestions that the most effective ASOs are those with the highest affinities for their target sequences. Instead, the most consistent pattern in the data was that the most effective ASOs were those targeted to sequences that were predicted to form clustered double-stranded structures in RNA transcripts.

Collagen genes: mutations affecting collagen structure and expression

It is to be expected that more collagen genes will be identified and that additional heritable connective tissue diseases will be shown to arise from collagen mutations. Further progress will be fostered by the coordinated study of naturally occurring and induced heritable connective tissues diseases. In some instances, human mutations will be studied in more detail using transgenic mice, while in others, transgenic studies will be used to determine the type of human phenotype that is likely to result from mutations of a given collagen gene. Further studies of transcriptional regulation of the collagen genes will provide the prospect for therapeutic control of expression of specific collagen genes in patients with genetically determined collagen disorders as well as in a wide range of common human diseases in which abnormal formation of the connective tissues is a feature.

Restricted expression of Mov13 mutant alpha 1(I) collagen gene in osteoblasts and its consequences for bone development

Cell type-specific differences in the transcriptional control of the mouse gene coding for the alpha 1 chain of collagen type I (Col1a1) have been revealed previously with the help of the Mov13 mouse strain which carries a retroviral insert in the first intron of the gene. Transcription of this mutant Col1a1 allele is completely blocked in all mesodermal cell types tested so far, with the exception of the odontoblast where it is expressed at an apparently normal rate (Kratochwil et al. [1989] Cell 57:807-816). To define the tissue specificity of the mutant allele more precisely, we have now studied its expression in osteoblasts, another skeletogenic cell type which, like odontoblasts, produces high amounts of collagen I. Evidence for transcription of the Mov13 allele was obtained by in situ hybridization in homozygous (M/M) and heterozygous (M/+) bone tissue, in grafts as well as in vivo. The presence of mouse collagen I and the development of bone tissue were demonstrated in M/M skeletal elements grown on the chick chorioallantoic membrane (CAM). Further support for expression of the mutant gene was obtained from two 16 day M/M fetuses in vivo. Bone tissue of diverse embryological origin (vertebrae and ribs of somitic origin, long bones derived from lateral plate, calvariae from head paraxial mesoderm, and mandibulae from head neural crest) expresses the mutant allele. However, in situ hybridization experiments indicate that only a subpopulation of osteoblasts is capable of transcribing it at a high rate, resulting in severe impairment of bone development in grafts and in vivo. Therefore, osteoblasts, in comparison to odontoblasts and fibroblast-like cells, assume an intermediate position with respect to transcription of the Mov13 allele. We suggest that this diversity in the utilization of the mutant collagen gene reflects cell type-specific differences in the transcriptional regulation of the wild type (wt) Col1a1 gene.

Analysis of the Drosophila gene for the laminin B1 chain

We have isolated and sequenced a Drosophila genomic DNA that encodes the entire coding region of the laminin B1 chain. The genomic DNA sequenced spans 11,787 bp, including a 1.1-kb 5'-flanking region, 5 exons, 4 introns, and a 1.4-kb 3'-flanking region. The open reading frame is within the two largest exons, the exons 3 and 4, while the first two and the last exons are much smaller and are untranslated. The structure of the Drosophila laminin B1 gene is similar to the Drosophila laminin B2 gene. Their exon-intron lengths and Eco RI, Pst I restriction maps are quite conserved. Both of their open reading frames are very compact, and their first introns are much larger than all of the rest of the introns. These results are consistent with the suggestion that the B1 and B2 genes could be derived from an ancestral gene. The similarity of the proximal 5'-flanking regions of the Drosophila B1 and B2 genes is 46.6%. Also, similar sequences of transcriptional regulatory elements, even though not site conserved, are found in both proximal 5'-flanking regions of the B1 and B2 genes. When transfected into Drosophila SL-2 cells, pCAT plasmid containing 1,048 bp of 5'-flanking region shows a strong expression of chloramphenicol acetyltransferase (CAT) activity. The deletion clones that contain sequences between nucleotides -462 to +150, and -282 to +150 all show strong CAT activity. These results suggest that this 5'-flanking promoter region may contain DNA sequences that can promote the expression of the laminin B1 gene.

Expression of human COL1A1 gene in stably transfected HT1080 cells: the production of a thermostable homotrimer of type I collagen in a recombinant system

A recombinant system was developed for the production of homotrimeric type I collagen in stably transfected HT1080 cells. A DNA construct (COL1A1-CMV) was prepared that contained the cDNA for the human COL1A1 gene under the transcriptional control of the promoter and enhancer of the immediate early gene of CMV. The construct, which also contained a neomycin-resistance gene, was transfected into HT1080 cells, a human fibrosarcoma cell line that synthesizes type IV collagen but does not normally synthesize any of the fibrillar collagens. Cells derived from the neomycin-resistant transfectants were then screened using a polyclonal antibody specific for human pro alpha 1(I) chains in order to identify clones that secreted high levels of the pro alpha(I) chain of type I procollagen. About 2% of neomycin-resistant clones secreted procollagen that consisted of a homotrimer of pro alpha 1(I) chains. The procollagen was post-translationally over-modified as judged by slower migration on SDS-polyacrylamide gel electrophoresis of the pro alpha 1(I) chains compared to pro alpha 1(I) chains of normal type I procollagen. The procollagen was triple helical as assayed by protease digestion with a variable cleavage at 38 degrees C and a thermal transition of both the intact and partially cleaved protein of about 41 degrees C. The system provides a method of expressing genes for fibrillar procollagens so that fully recombinant proteins are generated and easily isolated.

A mouse 3T6 fibroblast cell culture model for the study of normal and protein-engineered collagen synthesis and deposition into the extracellular matrix

Mouse 3T6 fibroblasts deposited an organized collagenous extracellular matrix during long-term culture in the presence of ascorbic acid. The matrix produced by the cells had a similar distribution of collagen types as the mouse dermal matrix, comprising predominantly type I with smaller amounts of types III and V collagens. By day 8 of culture more than 70% of the collagen in the 3T6 matrix was involved in covalent crosslinkages and required pepsin digestion for extraction. Incorporation of NaB3H4 into reducible crosslinks and aldehydes directly demonstrated the involvement of the alpha 1 (I)CB6 and alpha 2(I)CB3.5 in crosslinks. The pattern of reducible crosslinks in the in vitro 3T6 matrix was similar to that in mouse skin suggesting a comparable fibril organization. Processing of procollagen to collagen occurred efficiently throughout the culture period and the rate of collagen production was unaltered during 15 days of culture, indicating that the development of a collagenous matrix does not directly play a role in procollagen processing or biosynthetic regulation. The existence of a preformed matrix did however, increase the efficiency with which newly synthesised collagen was incorporated into the pericellular matrix. At day 0, when there was no measurable matrix present, 29% of the collagen synthesised was deposited, while by day 15, 88% of the collagen was laid down in the matrix. The development of this 3T6 culture system, where collagen is efficiently incorporated into an organized extracellular matrix, will facilitate detailed studies on matrix organization and regulation and provide a system in which protein-engineered mutant collagens can be expressed to determine their effects on the production of a functional extracellular matrix.

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

The first intron of the human Pro alpha 1(I) collagen gene contains an orientation-dependent enhancer composed of both positive and negative cis-acting elements involved in the transcriptional regulation of this gene. Deletion of a 360 bp Sau 3A intronic fragment spanning nucleotide +494 to +854 (S360) resulted in dramatic down-regulation of pCOL-KT (Thompson et al., J Biol Chem 266: 2549-2556, 1991). Using a DNaseI protection assay, we demonstrate a single footprint located at +590 to +615 in the S360 fragment; nuclear extracts prepared from mesenchymal and nonmesenchymal cells exhibited similar binding characteristics. A double stranded oligonucleotide representing a consensus Ap-1 binding sequence competed with S360 for binding. In contrast to what occurred in response to S360 deletion which was always accompanied by reduced expression, the deletion of the Ap-1 binding site (+598 to +off) caused either increased or decreased expression of the reporter gene depending on the target cell. Site-directed mutations in the Ap-1-like cis-element of Pro alpha 1(I) were also tested in transient expression assays. Consistent with the paradoxical results of Ap-1 deletion, we observed that the functional consequences of mutations in the Ap-1 site also varied in different cells. In A204 cells, one point mutation, which resulted in the loss of protein binding to S360, led to increased CAT activity while another point mutant, which retained binding of the Ap-1 like trans-acting factor(s), showed decreased CAT expression. The effects of these two mutations in the HFL-1 cells were exactly opposite of what was seen for A204 cells. Based on these observations, we postulate that the Ap-1 site plays a critical role in the transcriptional activity of the human Pro alpha 1(I) gene. The implications of an apparently dual mode of regulation through a single cis-regulatory element are discussed.

A position- and orientation-dependent element in the first intron is required for expression of the mouse hprt gene in embryonic stem cells

The gene (hprt) coding for mouse HPRT (hypoxanthine phosphoribosyltransferase) is transcribed from a promoter lacking CAAT and TATAA boxes. It is expressed ubiquitously, albeit at different levels, in all tissues and cultured cells. During investigations to characterise hprt transcription control elements required in embryonic stem (ES) cells and to develop compact hprt minigenes for gene-targeting strategies, we discovered a requirement for intron-1 sequences for expression in ES cells. The essential intron-1 element, which is 420 bp long, is located 230 bp downstream from the transcription start point and is shown to increase transcription from the hprt promoter in a position- and orientation-dependent manner. We propose that this element is an integral downstream part of the hprt promoter.