Post-transcriptional inhibition of collagen and fibronectin synthesis by a synthetic homolog of a portion of the carboxyl-terminal propeptide of human type I collagen

Inflammation-mediated matrix remodeling of extracellular matrix-mimicking biomaterials in tissue engineering and regenerative medicine

Extracellular matrix (ECM)-mimicking biomaterials are considered effective tissue-engineered scaffolds for regenerative medicine because of their biocompatibility, biodegradability, and bioactivity. ECM-mimicking biomaterials preserve natural microstructures and matrix-related bioactive components and undergo continuous matrix remodeling upon transplantation. The interaction between host immune cells and transplanted ECM-mimicking biomaterials has attracted considerable attention in recent years. Transplantation of biomaterials may initiate injuries and early pro-inflammation reactions characterized by infiltration of neutrophils and M1 macrophages. Pro-inflammation reactions may lead to degradation of the transplanted biomaterial and drive the matrix into a fetal-like state. ECM degradation leads to the release of matrix-related bioactive components that act as signals for cell migration, proliferation, and differentiation. In late stages, pro-inflammatory cells fade away, and anti-inflammatory cells emerge, which involves macrophage polarization to the M2 phenotype and leukocyte activation to T helper 2 (Th2) cells. These anti-inflammatory cells interact with each other to facilitate matrix deposition and tissue reconstruction. Deposited ECM molecules serve as vital components of the mature tissue and influence tissue homeostasis. However, dysregulation of matrix remodeling results in several pathological conditions, such as aggressive inflammation, difficult healing, and non-functional fibrosis. In this review, we summarize the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. STATEMENT OF SIGNIFICANCE: Extracellular matrix (ECM)-mimicking biomaterials are effectively used as scaffolds in tissue engineering and regenerative medicine. However, dysregulation of matrix remodeling can cause various pathological conditions. Here, the review describes the characteristics of inflammatory responses in matrix remodeling after transplantation of ECM-mimicking biomaterials. Additionally, we discuss the intrinsic linkages between matrix remodeling and tissue regeneration. We believe that understanding host immune responses to matrix remodeling of transplanted biomaterials is important for directing effective tissue regeneration of ECM-mimicking biomaterials. Considering the close relationship between immune response and matrix remodeling results, we highlight the need for studies of the effects of clinical characteristics on matrix remodeling of transplanted biomaterials.

Collagen's enigmatic, highly conserved N-glycan has an essential proteostatic function

Intracellular procollagen folding begins at the protein's C-terminal propeptide (C-Pro) domain, which initiates triple-helix assembly and defines the composition and chain register of fibrillar collagen trimers. The C-Pro domain is later proteolytically cleaved and excreted from the body, while the mature triple helix is incorporated into the extracellular matrix. The procollagen C-Pro domain possesses a single N-glycosylation site that is widely conserved in all the fibrillar procollagens across humans and diverse other species. Given that the C-Pro domain is removed once procollagen folding is complete, the N-glycan might be presumed to be important for folding. Surprisingly, however, there is no difference in the folding and secretion of N-glycosylated versus non-N-glycosylated collagen type-I, leaving the function of the N-glycan unclear. We hypothesized that the collagen N-glycan might have a context-dependent function, specifically, that it could be required to promote procollagen folding only when proteostasis is challenged. We show that removal of the N-glycan from misfolding-prone C-Pro domain variants does indeed cause serious procollagen and ER proteostasis defects. The N-glycan promotes folding and secretion of destabilized C-Pro variants by providing access to the ER's lectin-based chaperone machinery. Finally, we show that the C-Pro N-glycan is actually critical for the folding and secretion of even wild-type procollagen under ER stress conditions. Such stress is commonly incurred during development, wound healing, and other processes in which collagen production plays a key role. Collectively, these results establish an essential, context-dependent function for procollagen's previously enigmatic N-glycan, wherein the carbohydrate moiety buffers procollagen folding against proteostatic challenge.

Roles of the procollagen C-propeptides in health and disease

The procollagen C-propeptides of the fibrillar collagens play key roles in the intracellular assembly of procollagen molecules from their constituent polypeptides chains, and in the extracellular assembly of collagen molecules into fibrils. Here we review recent advances in understanding the molecular mechanisms controlling C-propeptide trimerization which have revealed the importance of inter-chain disulphide bonding and a small number of charged amino acids in the stability and specificity of different types of chain association. We also show how the crystal structure of the complex between the C-propeptide trimer of procollagen III and the active fragment of procollagen C-proteinase enhancer-1 leads to a detailed model for accelerating release of the C-propeptides from procollagen by bone morphogenetic protein-1 and related proteinases. We then discuss the effects of disease-related missense mutations in the C-propeptides in relation to the sites of these mutations in the three-dimensional structure. While in general there is a good correlation between disease severity and structure-based predictions, there are notable exceptions, suggesting new interactions involving the C-propeptides yet to be characterized. Mutations affecting proteolytic release of the C-propeptides from procollagen are discussed in detail. Finally, the roles of recently discovered interaction partners for the C-propeptides are considered during fibril assembly and cross-linking.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

Novel action of FOXL2 as mediator of Col1a2 gene autoregulation

FOXL2 belongs to the evolutionarily conserved forkhead box (FOX) superfamily and is a master transcription factor in a spectrum of developmental pathways, including ovarian and eyelid development and bone, cartilage and uterine maturation. To analyse its action, we searched for proteins that interact with FOXL2. We found that FOXL2 interacts with specific C-terminal propeptides of several fibrillary collagens. Because these propeptides can participate in feedback regulation of collagen biosynthesis, we inferred that FOXL2 could thereby affect the transcription of the cognate collagen genes. Focusing on COL1A2, we found that FOXL2 indeed affects collagen synthesis, by binding to a DNA response element located about 65Kb upstream of this gene. According to our hypothesis we found that in Foxl2(-/-) mouse ovaries, Col1a2 was elevated from birth to adulthood. The extracellular matrix (ECM) compartmentalizes the ovary during folliculogenesis, (with type I, type III and type IV collagens as primary components), and ECM composition changes during the reproductive lifespan. In Foxl2(-/-) mouse ovaries, in addition to up-regulation of Col1a2, Col3a1, Col4a1 and fibronectin were also upregulated, while laminin expression was reduced. Thus, by regulating levels of extracellular matrix components, FOXL2 may contribute to both ovarian histogenesis and the fibrosis attendant on depletion of the follicle reserve during reproductive aging and menopause.

Bioactive oligopeptides in dermatology: Part I

Short sequence amino acids or oligopeptides represent a relatively new and promising area of dermatology. Oligopeptides are defined as peptide sequences ranging from 2 to 20 amino acids. This class of proteins includes potent biologically active compounds, which can modulate various cellular and molecular processes. The medical potential of short sequence peptides was initially characterized many decades ago with the identification of biological mediators such as angiotensin, vasopressin, oxytocin and bradykinin. However, the role of oligopeptides in affecting biological activity within the skin has only recently been explored. Currently, the dermatologic use of protein peptide fragments is a rapidly growing field of research. Recent studies suggest that treatment with various biologically active peptides can result in favourable clinical outcomes such as for the treatment of hyperpigmentation disorders with tyrosinase inhibitors and the use of collagen synthesis modulators to diminish skin laxity. In this review, we explore the roles of biologically active short sequence peptides as potential therapeutics through the modulation of collagen, elastin and melanin synthesis.

Cosmeceuticals and peptides

In nature, the majority of chemical reactions, biological responses, and regulatory processes are modulated in some part by specific amino acid sequences. The transfer of these interactive sequences and the biological activities they induce to short, stable, and readily synthesized peptides has created a diverse new field of modulating molecules applicable to dermatology and skin care industries. Areas such as inflammation, pigmentation, cell proliferation and migration, angiogenesis, innate immunity, and extracellular matrix synthesis have yielded peptide candidates for application to this area.

Bioactive peptides: signaling the future

Natural processes within the body are modulated almost exclusively by the interaction of specific amino acid sequences, either as peptides or as subsections of proteins. With respect to skin, proteins and peptides are involved in the modulation of cell proliferation, cell migration, inflammation, angiogenesis, melanogenesis, and protein synthesis and regulation. The creation of therapeutic or bioactive peptide analogs of specific interactive sequences has opened the door to a diverse new field of pharmaceutical and active cosmetic ingredients for the skincare industry. Here, we describe the origin of such sequences, their role in nature, their application to dermatology, as well as the advantages and challenges posed by this new technology.

Elastin peptides induced oxidation of LDL by phagocytic cells

The degradation products of one of the major component of vascular wall, elastin, have several important biological activities. Elastin peptides (KE) are mostly generated during vascular aging and the atherosclerotic process. They induce free radical and proteases production from cells, which are the major components of the atherosclerotic process. In the present study, we investigated whether the interaction between elastin peptides and neutrophils as well as monocytes contributes to low density lipoproteins (LDL) oxidation, being one of the most important initiator of the chronic inflammatory process contributing to the development of atherosclerosis. Here, we present data on the link between the elastin degradation products and LDL oxidation by the chemotactically attracted neutrophils and monocytes. The KE as well as the active epitope, the hexapeptide VGVAPG is able, in a differential concentration and time dependence, to induce the oxidation of LDL. KE is able to induce via the production of free radicals by neutrophils the oxidation of LDL very rapidly and in higher concentration compared to monocytes. These effects of KE are occurring through the stimulation of the 67 kDa elastin-laminin receptor (ELR), as demonstrated by the uncoupling effect of lactose. In our present study, the HDL was able to decrease the LDL oxidation by KE. This is a new mechanism by which elastin peptides might participate in the initiation and progression of the atherosclerotic process.

The Propeptide Domain of Lysyl Oxidase Induces Phenotypic Reversion of Ras-transformed Cells

Lysyl oxidase is an extracellular enzyme critical for the normal biosynthesis of collagens and elastin. In addition, lysyl oxidase reverts ras-mediated transformation, and lysyl oxidase expression is down-regulated in human cancers. Since suramin inhibits growth factor signaling pathways and induces lysyl oxidase in ras-transformed NIH3T3 cells (RS485 cells), we sought to investigate the effects of suramin on the phenotype of transformed cells and the role of lysyl oxidase in mediating these effects. Suramin treatment resulted in a more normal phenotype as judged by growth rate, cell cycle parameters, and morphology. beta-aminopropionitrile, the selective inhibitor of lysyl oxidase enzyme activity, was remarkably unable to block suramin-induced reversion. By contrast, ectopic antisense lysyl oxidase demonstrated that lysyl oxidase gene expression mediated phenotypic reversion. Since lysyl oxidase is synthesized as a 50 kDa precursor and processed to a 30 kDa active enzyme and 18 kDa propeptide, the effects of these two products on the transformed phenotype of RS485 cells were then directly assessed in the absence of suramin. Here we report, for the first time, that the lysyl oxidase propeptide, and not the lysyl oxidase enzyme, inhibits ras-dependent transformation as determined by effects on cell proliferation assays, growth in soft agar, and Akt-dependent induction of NF-kappaB activity. Thus, the lysyl oxidase propeptide, which is released during extracellular proteolytic processing of pro-lysyl oxidase, functions to inhibit ras-dependent cell transformation.

Interaction of Smads with collagen types I, III, and V

Ontogenesis of the mammalian orofacial region is controlled by numerous developmental signals, including those initiated by the transforming growth factors beta (TGFbetas). Targeted deletion of the genes encoding several of the TGFbetas in mice has been shown to result in clefts of the secondary palate. Members of the TGFbeta family of growth factors utilize intracellular Smads as signal transducers. Smads 2 and 3 are transcriptional regulators that bind DNA through their conserved MH1 domains and activate/inhibit transcription of TGFbeta-responsive genes through their MH2 domains. Using a yeast two-hybrid screen of a cDNA expression library constructed from fetal murine orofacial tissue, we have identified three types of collagens (types I, III, and V) that are capable of binding to the MH2 domain of Smad 3. These interactions were confirmed by glutathione S-transferase (GST) pull-down assays in which the MH2 domain of Smad 3 fused to GST interacted strongly with in vitro translated, 35S-labeled collagen types I, III, and V. Each collagen also bound to the MH2 domains of Smads 4 and 7 and, to a lesser extent, full-length Smads 1, 2, 3, and 4. Binding of Smads to collagen is a novel observation. Moreover, TGFbeta is a potent regulator of collagen synthesis and turnover during mammalian orofacial development. These data thus suggest an important means of feedback regulation of the TGFbeta signaling cascade.

Stimulation of type II collagen biosynthesis and secretion in bovine chondrocytes cultured with degraded collagen

The functional integrity of articular cartilage is dependent on the maintenance of the extracellular matrix (ECM), a process which is controlled by chondrocytes. The regulation of ECM biosynthesis is complex and a variety of substances have been found to influence chondrocyte metabolism. In the present study we have investigated the effect of degraded collagen on the formation of type II collagen by mature bovine chondrocytes in a cell culture model. The culture medium was supplemented with collagen hydrolysate (CH) and biosynthesis of type II collagen by chondrocytes was compared to control cells treated with native type I and type II collagen and a collagen-free protein hydrolysate. The quantification of type II collagen by means of an ELISA technique was confirmed by immunocytochemical detection as well as by the incorporation of (14)C-proline in the ECM after a 48 h incubation. Chondrocytes in the control group were maintained in the basal medium for 11 days. The presence of extracellular CH led to a dose-dependent increase in type II collagen secretion. However, native collagens as well as a collagen-free hydrolysate of wheat proteins failed to stimulate the production of type II collagen in chondrocytes. These results clearly indicate a stimulatory effect of degraded collagen on the type II collagen biosynthesis of chondrocytes and suggest a possible feedback mechanism for the regulation of collagen turnover in cartilage tissue.

The effects of collagen fragments on the extracellular matrix metabolism of bovine and human chondrocytes

Cartilage matrix degradation generates collagen type II fragments. The objective of this study is to explore the possibility that these collagen fragments may be part of an endogenous metabolic feedback. Initially, collagen fragments were extracted from normal or osteoarthritic cartilage, as part of a matrix fragment preparation. Later, collagen fragments were generated by digestion of bovine collagen type II with bacterial collagenase (col2f). These fragments were added to cultures of isolated chondrocytes (bovine and human) and cartilage explants (human). In a dose-dependent manner, col2f caused inhibition of cell attachment to collagen, inhibition of collagen synthesis, and induction of matrix degradation. In addition, when col2f were added to human cartilage explants, an induction of gelatinase activity was detected in the media. These data sets present first evidence that degradation products of collagen may be directly involved in the regulation of cartilage homeostasis.

Trimer carboxyl propeptide of collagen I produced by mature osteoblasts is chemotactic for endothelial cells

During the second phase of osteogenesis in vitro, rat osteoblasts secrete inducer(s) of chemotaxis and chemoinvasion of endothelial and tumor cells. We report here the characterization and purification from mature osteoblast conditioned medium of the agent chemotactic for endothelial cells. The chemoactive conditioned medium specifically induces directional migration of endothelial cells, not affecting the expression and activation of gelatinases, cell proliferation, and scattering. Directional migration induced in endothelial cells by conditioned medium from osteoblasts is inhibited by pertussis toxin, by blocking antibodies to integrins alpha(1), beta(1), and beta(3), and by antibodies to metalloproteinase 2 and 9. The biologically active purified protein has two sequences, coincident with the amino-terminal amino acids, respectively, of the alpha(1) and of the alpha(2) carboxyl propeptides of type I collagen, as physiologically produced by procollagen C proteinase. Antibodies to type I collagen and to the carboxyl terminus of alpha(1) or alpha(2) chains inhibit chemotaxis. The chemoattractant is the propeptide trimer carboxyl-terminal to type I collagen, and its activity is lost upon reduction. These data illustrate a previously unknown function for the carboxyl-terminal trimer, possibly relevant in promoting endothelial cell migration and vascularization of tissues producing collagen type I.

Carboxyl-terminal propeptide of type I collagen (c-propeptide) modulates the action of TGF-beta on MC3T3-E1 osteoblastic cells

Previously we found that the carboxyl-terminal propeptide of type I collagen (c-propeptide) is a major secretory protein of MC3T3-E1 osteoblastic cells. In this study, we found that c-propeptide suppresses collagen synthesis and alkaline phosphatase activity of MC3T3-E1 osteoblastic cells at the early-differentiated stage in a dose dependent manner. Mature osteoblasts did not respond to c-propeptide. These findings imply that c-propeptide modulates the function of osteoblasts at an early differentiation stage. Transforming growth factor-beta (TGF-beta) is stored in bone and released from bone matrix after the resorption by osteoclasts. We investigated the effect of c-propeptide on the action of TGF-beta, and found that it enhanced the effect of TGF-beta. We conclude that c-propeptide is a physiological modulator of TGF-beta in bone metabolism.

Dynamic changes of type I, III and IV collagen synthesis and distribution of collagen-producing cells in carbon tetrachloride-induced rat liver fibrosis

AIM: To find out the relationship between the gene transcription of different types of procollagen and the deposition of the relevant collagens in the liver tissue and to confirm the types of collagen producing cells in liver fibrogenesis.

METHODS: Dynamic changes of the expression of α1(I), α1(III) and α1(IV) procollagen mRNA and relevant collagens and the distribution of collagen producing cells during liver fibrogenesis of rat induced by CCl₄ (20 weeks) were investigated with Northern blot analysis, in situ hybridization and immunohistochemical techniques.

RESULTS: The increased expression of α₁(III) procollagen mRNA by Northern blot analysis was the most predominant one among the three mRNAs during fibrogenesis. However, the enhanced expression of α₁(IV) procollagen mRNA occurred very early while the expression of α1(I) mRNA was not enhanced much until the middle stage of the experiment. Desmin (Dm) positive hepatic stellate cells (HSCs) and few myofibroblasts (MFs) in and around the necrotic areas expressed α1(I), α1(III) and α1(IV) procollagen mRNA signals detected by in situ hybridization at the early stage of the experiment. All the three procollagen mRNA signals thereafter mainly localized in fibroblasts (Fbs) and MFs in fibrotic septa during the middle and late stages of fibrosis, which distributed parallel to the corresponding collagens detected by immunohistochemical study. In addition, the endothelial cells of sinusoids and the small blood vessels within the septa also showed α1(IV) procollagen mRNA and type IV collagen expression

CONCLUSION: It is considered that “HSC-MF-Fb” effect cell system is the major cellular source of collagen production in liver fibrosis, in which HSCs are collagen producing precursor cells in the early liver fibrogenesis, thereafter the synthesis of type I, III and IV collagens (Col I, Col III and Col IV) mainly derives from MFs and Fbs, which play a very important role in the progress of liver fibrosis. The endothelial cells along sinusoids, as another source of Col IV production, might participate in the capillization of liver sinusoids.

Ligand binding results in divalent cation displacement from the alpha 2 beta 1 integrin I domain: evidence from terbium luminescence spectroscopy

The alpha 2 beta 1 integrin serves as a cell surface collagen or collagen/laminin receptor. Binding of the integrin to its ligands is largely mediated by the alpha 2 subunit I domain and requires the presence of divalent cations. Terbium ion (Tb3+), a fluorescent trivalent cation that often binds divalent cation-binding sites on proteins, supported binding of the I domain to collagen with half-maximal binding occurring at 5.2 +/- 1.7 microM Tb3+. By fluorescence resonance energy transfer spectroscopy, Tb3+ showed specific and saturable binding to the recombinant I domain with a Kd of 27 +/- 4 microM. Although both Mg2+ and Mn2+ were capable of quenching Tb3+ fluorescence, Mn2+ was much more effective than Mg2+. The alpha 2 beta 1 integrin also binds the pro-alpha 1(I) collagen carboxyl-terminal propeptide in a Mg2+-dependent manner via the I domain. Recombinant propeptide was used to examine the effect of ligand on the Tb3+ binding properties of the alpha 2 integrin I domain. As propeptide bound to the I domain, Tb3+ fluorescence progressively diminished suggesting that as ligand binds to the I domain, either Tb3+ is displaced or its fluorescence is quenched. Consistent with the former possibility, little dissociation of collagen-bound I domain occurred upon the addition of EDTA and subsequent incubation. These data support a model in which (1) the divalent cation is required for initial ligand-binding activity of the I domain and (2) ligand binding results in subsequent metal ion displacement to generate a metal-free I domain-ligand complex.

Alpha2beta1 integrin recognition of the carboxyl-terminal propeptide of type I procollagen: integrin recognition and feed-back regulation of matrix biosynthesis are mediated by distinct sequences

It has recently been established that the carboxyl-terminal propeptide of type I collagen exert a feedback regulatory effect on extracellular matrix biosynthesis and that the propeptide bind to the alpha2beta1 integrin. This raises the intriguing hypothesis that the regulatory propeptide sequences exert their effects as a consequence of binding to the integrin. We show that recombinant alpha1(I) collagen chain C-terminal propeptide contains a binding site for the intact alpha2beta1 integrin and for a recombinant alpha2 integrin I domain, but not for the alpha1beta1 integrin, a structurally and functionally related collagen/laminin receptor. Additional studies employing a series of recombinant N-terminal and C-terminal deletion mutants, internal fragments of the propeptide, synthetic peptides, recombinant alpha2 integrin I domain and inhibitory monoclonal antibodies established that the previously identified sequences within the alpha1(I) C-terminal propeptide that mediate regulation of matrix biosynthesis are neither necessary nor sufficient for alpha2beta1 integrin binding. In contrast, the integrin recognition site is composed of a conformationally complex determinant located within a structurally distinct 115 amino acid region of the propeptide.

Synthesis and conformational properties of a recombinant C-propeptide of human type III procollagen

A cDNA was prepared that coded for the signal peptide of type III procollagen linked to the complete C-propeptide of the protein. The cDNA was then used to express the protein in a baculovirus recombinant system. Recombinant protein was recovered as a trimer from the medium of transfected cells in a yield of 1 to 2.5 mg per liter. Mapping of peptide fragments with and without reduction indicated that the protein contained the expected interchain disulfide bonds. Analysis by circular dichroism suggested that the conformation of the protein corresponded to the native conformation. Therefore, the protein should be appropriate for further tests of its biological function and analysis of structure by X-ray diffraction.

Identification of specific sites in the TNF-alpha molecule promoting insulin resistance in H-411E cells

Data from a number of laboratories support a potential role for tumor necrosis factor-alpha (TNF-alpha) in the loss of insulin sensitivity and the pathogenesis of insulin resistance (IR) in diabetic animal models and human patients. We designed experiments to establish a dose-response relationship for TNF-alpha and IR in H-411E cells in culture. IR was measured by inhibition of the ability of graded amounts of insulin to stimulate expression of calmodulin (CaM) mRNA in these cells. This was assessed by autoradiographs of Northern blot(s) of CaM mRNA probed with labeled oligonucleotide cDNA for rat CaM. We found that TNF-alpha at 0.1, 1.0, and 10.0 ng/ml opposed 10,000 microU/ml insulin (i.e., %IR = 20%, 67%, and 88%, respectively). At 1.0 ng/ml TNF-alpha, insulin at the concentration of 1000 microU/ml (0.006 micromol/L) stimulated CaM mRNA at a 41% level and at 10,000 microU/ml (0.06 micromol/L) at a 63% level. Furthermore, oligopeptide TNF-alpha homologs (at 1000 x the molar concentration of TNF-alpha) TNF-alpha 69-100 and TNF-alpha 133-157 conferred 66% and 101% IR, respectively, while all other peptide fragments of TNF-alpha were essentially without effect. Studies done with both monoclonal and polyclonal antibodies to the TNF-alpha receptor demonstrated blocking activity by polyclonal but not by monoclonal anti TNF-alpha receptor antibody. This supports the concept that the activity of the peptide fragments occurs through the TNF-alpha receptor and not through nonspecific translocation across the plasma membrane. These data suggest that the epitopes on TNF-alpha that mediate IR reside in two regions of the molecule spanning amino acid residues 69-100 and 133-157.

Identification of highly expressed genes in metastasis-suppressed chromosome 6/human malignant melanoma hybrid cells using subtractive hybridization and differential display

Microcell-mediated transfer of chromosome 6 into human melanoma cell lines C8161 and MelJuSo suppresses metastasis by at least 95% without affecting tumorigenicity. Subtractive hybridization and differential display were used to identify the molecule(s) responsible for suppressing metastasis in neo6/melanoma (neo6/C8161 and neo6/MelJuSo) hybrids. Seven cDNA clones exhibiting quantitatively or qualitatively higher expression in neo6/melanoma hybrids were obtained. These genes fell into 2 categories: 1) transcription-related genes (AP-2A, HMG-I(Y) and a novel isoform of nucleophosmin B23), which have previously been shown to regulate metastasis-associated genes; and 2) novel genes. One of the novel genes, designated KiSS-1, significantly suppressed metastasis of the human malignant melanoma cell lines MelJuSo and a highly metastatic subclone of C8161, C8161cl.9, following transfection and constitutive expression. Our results illustrate the power of subtractive hybridization and differential display to identify functional metastasis-controlling genes in human melanoma.

Molecular characterisation of integrin-procollagen C-propeptide interactions

The carboxyl-terminal propeptide of type I procollagen (CPP-I) plays a key role in regulation of collagen fibrillogenesis, and may exert feedback control of collagen biosynthesis. We have previously shown that CPP-I is a ligand for the integrin alpha2beta1 [Weston, S. A., Hulmes, D. J. S., Mould, A. P., Watson, R. B. & Humphries, M. J. (1994) Identification of the integrin alpha2beta1 as a cell surface receptor for the C-propeptide of type I procollagen, J. Biol. Chem. 269, 20982-20986] suggesting that some of the phenotypic effects of C-propeptides may be mediated by adhesion receptors. Here we have extended this work to study the molecular basis of this interaction. We have broadened the ligand range by demonstrating that the C-terminal propeptide of type II procollagen supports alpha2beta1-mediated binding of NHS human fibroblasts in cell attachment assays. Also, we have used function-blocking antibodies in cell attachment and solid-phase binding assays with purified integrin to expand the CPP-I receptor family, showing that integrin alpha1beta1 is also a receptor for CPP-I. Integrin alpha-subunit A-domains are known to be major ligand-binding sites and recombinant alpha1 and alpha2 subunit A-domains were able to bind CPP-I. Finally we have shown that peptides corresponding to potential integrin-binding sequences in CPP-I do not mediate integrin-CPP-I adhesion. Taken together, these studies indicate that the interactions between C-propeptides and integrins are more numerous than previously reported, that C-propeptides are a new class of molecule which bind to A-domains, and that the integrin-C-propeptide interaction does not utilise established peptide motifs.

Cleavage of type I procollagen by human mast cell chymase initiates collagen fibril formation and generates a unique carboxyl-terminal propeptide

The ability of human mast cell chymase and tryptase to process procollagen was examined. Purified human intestinal smooth muscle cell procollagen was incubated with human mast cell tryptase or human mast cell chymase. Purified chymase, but not tryptase, exhibited procollagen proteinase activity in the presence of EDTA. Addition of purified porcine heparin over a range of 0.1-100 microg/ml did not affect either the rate or the products of procollagen chymase cleavage. The cleavage site of chymase on the pro-alpha1(I) collagen carboxyl terminus was found to be in the propeptide region at Leu-1248-Ser-1249. Cleavage at this site suggested that the collagen products would form fibrils and confirmed the production of a unique carboxyl-terminal propeptide. Turbidometric fibril formation assay demonstrated de novo formation of chymase-generated collagen fibrils with characteristic lag, growth, and plateau phases. When observed by dark field microscopy, these fibrils were similar to fibrils formed by the action of procollagen proteinases. Thus, mast cell chymase, but not tryptase, exhibits procollagen peptidase-like activity as evidenced by its ability to process procollagen to fibril-forming collagen with concurrent formation of a unique carboxyl-terminal propeptide. These data demonstrate that mast cell chymase has a potential role in the regulation of collagen biosynthesis and in the pathogenesis of fibrosis.

The osteoblastic MC3T3-E1 cells synthesized C-terminal propeptide of type I collagen, which promoted cell-attachment of osteoblasts

In this study, we purified C-terminal propeptide of type I collagen (PICP) from the conditioned medium of osteoblastic MC3T3-E1 cells by chromatographic and Agarose gel extraction procedures. PICP was confirmed to be present in bone by Western blotting using a specific antibody, and was proved to be synthesized by osteoblasts with metabolic labeling. PICP promoted cell-attachment of osteoblastic MC3T3-E1 cells. We conclude that PICP is synthesized by osteoblasts and stored in bone, and that it plays a role in the maintenance of bone cells on bone matrix.

Identification of a chemotactic epitope in human transforming growth factor-beta 1 spanning amino acid residues 368-374

TGF-beta 1 plays a critical role in inflammatory and repair processes due in part to its ability to provide a potent chemotactic stimulus for inflammatory cells such as neutrophils and monocytes and for fibroblasts which initiate the fibrogenic response. In the present study, we have used synthetic oligopeptides representing the amino acid sequence of the 12.1 kDa monomer of human TGF-beta 1 in an effort to identify a chemotactic epitope on the molecule. A seven residue peptide containing residues 368-374, Val Tyr Tyr Val Gly Arg Lys, was demonstrated to be capable of inducing chemotactic migration of human peripheral blood neutrophils, monocytes, monocyte leukemia cell line THP-1, and infant foreskin fibroblasts. Furthermore, larger peptides from the carboxy-terminal portion of TGF-beta 1 that contained residues 368-374 also induced migration of these cell types. None of the peptides representing the complete amino acid of TGF-beta 1 monomer were able to compete with [125I]hrTGF-beta 1 for binding to TGF-beta cell surface receptors or fibroblasts or THP-1 cells. Implications of these observations are discussed.

Expression of the neomycin-resistance (neo) gene induces alterations in gene expression and metabolism

The amino 3'-glycosyl phosphotransferase (neo) gene is the selectable marker most widely used in stable transfection or infection protocols. Because the neo gene product has phosphotransferase activity, it might modify the phosphorylation state when introduced in mammalian cells. NIH-3T3 fibroblast cells expressing the neo gene, after either infection with retroviral vectors or transfection with plasmids, showed a 50% reduction in both fructose 2,6-bisphosphate (Fru 2,6-P2) concentration and lactate production compared with control NIH-3T3 cells, indicating that these neo-expressing cells are less glycolytic. In addition, a marked decrease in the levels of mRNA for the procollagen 1 alpha and fibronectin genes was also observed in neo-expressing NIH-3T3 cells. This decrease was concomitant with an increase in the mRNA concentration of the endogenous c-myc gene. FTO-2B rat hepatoma cells also showed modifications in gene expression when the neo gene was introduced by stable transfection or infection. In these cells an increase in both P-enolpyruvate carboxykinase (PEPCK) and tyrosine aminotransferase (TAT) mRNA was observed. These results suggest that neo gene expression may induce changes in the cells, which should be considered when neo-selected cells are used to deliver specific genes in different therapy approaches and in embryo manipulation.

Cellular localization of procollagen gene transcripts in inflammatory bowel diseases

The cellular localization of procollagen types I, III, IV, and V gene transcripts was determined in tissues from 12 patients with either Crohn's disease (CD) or ulcerative colitis (UC) and nine controls by in situ hybridization with 35S-labeled RNA probes. In CD, the signal intensity and number of labeled cells were significantly increased, particularly in deeper intestinal layers. In contrast, the labeled cells in UC were concentrated in the subepithelial intestinal layers, with an overexpression of procollagen III RNA transcripts. Immunohistological stainings for procollagen types I, III, and IV showed a weaker staining in UC than in CD, indicating that increased transcript levels in UC are unrelated to the enhanced collagen protein deposition, although the increase of procollagen messenger RNA levels correlated with the density of the inflammatory infiltrate. It was concluded that both CD and UC show highly increased procollagen RNA transcript levels but differ in collagen deposition. Thus, different posttranscriptional or posttranslational regulatory mechanisms, such as collagen degradation, may account for the observed differences.

Fibrogenesis in cirrhosis. Potential for therapeutic intervention

Liver cirrhosis is an end stage of several diseases that affect the liver chronically. It is characterized, among other things, by excess collagen deposition, distortion of liver architecture, tissue malfunction and hemodynamic alterations. Many of the complications of cirrhosis may result from excess matrix-deposition. Therefore, prevention of collagen accumulation or removal of collagen deposits could ameliorate the disease. In this article we discuss the pathophysiology of liver fibrosis and we describe various compounds with antiinflammatory and antifibrogenic activity. We discuss their possible mechanism of action and we describe animal and clinical studies in which these compounds have been utilized.

A factor from damaged rat kidney stimulates collagen biosynthesis by mesangial cells

Rats were administered CCl4, a well-defined nephrotoxin, for 20 weeks to produce glomerular sclerosis. Tubular degeneration and necrosis with interstitial fibrosis was clearly evident by histological examination. Kidneys were homogenized in phosphate-buffered saline and a collagen synthesis-stimulating factor was isolated by Sephadex G-50 gel filtration. The 5 kDa component stimulated both type I and type IV procollagen synthesis by mesangial cells and type I procollagen synthesis by rat skin fibroblasts. In each cell type, 2-6-fold increases in procollagen protein production or cell proliferation was noted. The steady-state levels of mRNA encoding for procollagen alpha 1(I) and procollagen alpha 1(IV) chains in mesangial cells were determined by by hybridization to their corresponding cDNA clones. The type I procollagen mRNA was elevated 1.4-fold compared to a 1.6-fold increase in mRNA encoding for type IV procollagen. The similar properties and chemical characteristics of this fibrogenic factor with a factor from fibrotic liver suggests they are the same and that a common endogenous collagen synthesis stimulator may be present in fibrosing organs, thus providing a driving force for collagen over-production.

Detection of procollagen biosynthesis using peptide-specific antibodies

Peptides corresponding to selected sequences of the alpha 1 chain of the COOH propeptide of type I and type III human procollagen were synthesized and used as antigens to develop polyclonal and monoclonal antibodies. The antibodies were shown to be epitope specific using a peptide-based solid phase enzyme-linked immunoadsorbent assay. The antibodies were specific for the appropriate procollagens and the COOH propeptides isolated from serum-free culture supernatants of human skin fibroblasts. The rabbit antisera directed to the type I synthetic peptide bound the intact procollagen molecule and both the procollagen alpha 1(I) and alpha 2(I) chains after the reduction of the disulfide bonds. In addition, the antisera bound intact type I COOH propeptide, generated by bacterial collagenase treatment of procollagen, and the individual chains of the propeptide after reduction. In contrast, a monoclonal antibody to the type I peptide was able to bind only to the reduced form of the COOH propeptide. Both rabbit polyclonal and murine monoclonal antibodies directed to the type III synthetic peptide bound the intact and the individual chains of type III procollagen as well as the intact and reduced forms of the type III COOH propeptide. The antibodies have been used to detect procollagen synthesis in two human osteosarcoma cell lines and the differential expression of procollagen in the culture medium of rat lung fibroblasts grown in the presence or absence of glucocorticoids.

Liver collagen mRNA and serum amino-terminal peptide of type III procollagen (PIIINP) levels in patients with alcoholic liver disease

We have investigated the alpha 1 (I), alpha 2 (I) and alpha 1 (III) liver collagen mRNA levels in 38 patients with alcoholic liver disease. The patients were divided into 3 groups according to the severity of their liver disease. Liver collagen mRNA levels were estimated by densitometric analysis after hybridization with the corresponding cDNA. Serum amino-terminal peptide of type III procollagen (PIIINP) was determined by radioimmunoassay in 30 patients. The results indicated that there was no increase but rather a decrease in the liver alpha 1 (I), alpha 2 (I) and alpha 1 (III) collagen mRNA in patients with the most severe liver lesions as compared to those with minimal changes. This decrease was significant for alpha 2 (I) and alpha 1 (III) cDNA probes. In contrast, serum PIIINP levels showed a positive correlation with the severity of the disease. Thus this study indicates that collagen accumulation in the liver as well as elevation of the serum PIIINP during the development of alcoholic liver disease probably reflects posttranscriptional events in collagen synthesis.

Kupffer cells from CC1(4)-treated rat livers induce skin fibroblast and liver fat-storing cell proliferation in culture

Conditioned media of Kupffer cells from normal rat liver produce in culture two factors that inhibit fibroblast proliferation. The inhibitory factors have molecular masses of approximately 25 and 5 kDa. In contrasts to these results, the conditioned media of Kupffer and mononuclear macrophagic cells, obtained 48 hours after CC1(4) administration to rats, contains a 17 kDa factor that stimulates fibroblast proliferation (FSF). FSF also stimulates [3H]-thymidine incorporation into DNA of cultured rat liver fat-storing cells. Two peaks with FSF activity were demonstrated after isoelectrofocusing; one with a pI of 6.1 and a second with a pI of 7.5. The fraction containing FSF is devoid of interleukin-1 (IL-1) activity and no inhibitory activity is detected in this conditioned media. Production of FSF is inhibitable by colchicine but not by indomethacin, it is thermolabile and trypsin-sensitive. In animals treated chronically with CC1(4) to produce cirrhosis, FSF activity is demonstrable from the first to the 8th week of treatment. However, the activity is lower at 8 weeks post-CC1(4) as compared with 2 weeks. The results suggest that homeostasis of cells in the liver is controlled by factors produced locally, that act by autocrine and paracrine mechanisms. When homeostasis is altered, fibroblast proliferation occurs, and excess collagen deposition leads to fibrosis. We propose that the antifibrogenic activity of colchicine is associated, in part, with its capacity to inhibit the release of FSF by Kupffer cells and liver mononuclear macrophage cells.

DNA cloning and amino acid sequence determination of a major constituent protein of mammalian nucleoli. Correspondence of the nucleoplasmin-related protein NO38 to mammalian protein B23

Using a cDNA probe encoding the nucleolar protein NO38 of Xenopus laevis, we have isolated clones that code for the corresponding mammalian protein from cDNA libraries of mouse embryonal carcinoma and fetal liver cells. The murine cDNA-derived amino acid sequence defines a polypeptide of 292 amino acids (including the initial methionine) of a total molecular weight of 32,560 and identifies a single approximately 1.5 kb mRNA on Northern blot hybridization. This polypeptide, which is highly homologous to the Xenopus protein NO38, displays an organization in three major domains: (1) an aminoterminal portion of 119 amino acids, which shows a striking homology to nucleoplasmin of Xenopus; (2) a central portion of 68 amino acids that contains two extended acidic domains, a shorter of 13 residues and a longer of 29 residues, separated by an interval enriched in positively charged amino acids; (3) a carboxyterminal portion of 105 amino acids, which is almost identical to the reported partial amino acid sequence of human and rat nucleolar protein termed B23. The sequence comparisons show that the murine protein is the mammalian counterpart to the nucleolar protein NO38 of Xenopus and is compatible with the idea that both proteins NO38 represent the amphibian and murine equivalents to the human and rat nucleolar phosphoprotein B23. Special sequence features and predicted conformations of this protein are discussed in relation to the specific localization and the possible functions of this major nucleolar protein.

Identification of small collagenous proteins with properties of procollagen alpha 1 (I) pN-propeptide in fetal porcine calvarial bone

Several small collagenous apatite binding (SCAB) proteins have been extracted from the mineralized matrix of fetal porcine calvarial bone. One protein (SCAB 3), released on demineralization of bone with 0.5 M EDTA, appears to represent the alpha 1 pN-propeptide that is normally released during proteolytic processing of type I procollagen. The 28 Kd protein, which stains blue with "Stains-all", is reduced to a 19 Kd fragment by bacterial collagenase digestion, but is not susceptible to cyanogen bromide. The amino acid composition, blocked amino-terminus and immunological properties are all consistent with properties of alpha 1 (I) pN-propeptide. Fractionation on hydroxylapatite in the presence of urea has revealed a nonbinding (SCAB 3a) and a binding (SCAB 3b) form. Extraction of the demineralized matrix of bone with 4 M GuHCl revealed a third form (G2-28) which was similar to SCAB 3a on hydroxylapatite chromatography but showed differences on FPLC "Mono Q" resin. The occurrence of these different forms of pN-propeptide in bone may be of significance in collagen fibril-associated hydroxylapatite formation and in the regulation of osteoblastic function during bone resorption.