Complete primary structure of human collagen alpha 1 (V) chain

Early life stress and LPS interact to modify the mouse cortical transcriptome in the neonatal period

INTRODUCTION

Preterm birth (PTB) is closely associated with atypical cerebral cortical development and cognitive impairment. Early exposure to extrauterine life often results in atypical environmental and biological experiences that co-occur, including early life stress (ELS) and systemic inflammation. Understanding how these experiences interact to shape cortical development is an essential prerequisite to developing therapeutic interventions that will work in the complex postnatal environment of the preterm infant. Here, we studied the effects of a murine model of infection and ELS on the neonatal cortex transcriptome.

METHODS

We used a mouse model of infection (1 ​mg/kg LPS at postnatal day (P)3) +/- ELS (modified maternal separation; MMS on days P4-P6) at timepoints with neurodevelopmental relevance to PTB. We used 4 groups: control, LPS, MMS and LPS ​+ ​MMS. Cortices were dissected at P6 for 3'RNA sequencing.

RESULTS

LPS exposure resulted in reduced weight gain and increased expression of inflammation-associated genes in the brain. More genes were differentially expressed following LPS (15) and MMS (29) than with LPS ​+ ​MMS (8). There was significant overlap between the LPS and MMS datasets, particularly amongst upregulated genes, and when comparing LPS and MMS datasets with LPS ​+ ​MMS. Gene Ontology terms related to the extracellular matrix and cytokine response were enriched following MMS, but not following LPS or LPS ​+ ​MMS. 26 Reactome pathways were enriched in the LPS group, none of which were enriched in the LPS ​+ ​MMS group. Finally, a rank-rank hypergeometric overlap test showed similarities, particularly in upregulated genes, in the LPS and MMS conditions, indicating shared mechanisms.

CONCLUSION

LPS and MMS interact to modify the cortical transcriptome in the neonatal period. This has important implications for understanding the neural basis of atypical cortical development associated with early exposure to extrauterine life.

A Novel Recurrent COL5A1 Genetic Variant Is Associated With a Dysplasia-Associated Arterial Disease Exhibiting Dissections and Fibromuscular Dysplasia

OBJECTIVE

While rare variants in the COL5A1 gene have been associated with classical Ehlers-Danlos syndrome and rarely with arterial dissections, recurrent variants in COL5A1 underlying a systemic arteriopathy have not been described. Monogenic forms of multifocal fibromuscular dysplasia (mFMD) have not been previously defined. Approach and Results: We studied 4 independent probands with the COL5A1 pathogenic variant c.1540G>A, p.(Gly514Ser) who presented with arterial aneurysms, dissections, tortuosity, and mFMD affecting multiple arteries. Arterial medial fibroplasia and smooth muscle cell disorganization were confirmed histologically. The COL5A1 c.1540G>A variant is predicted to be pathogenic in silico and absent in gnomAD. The c.1540G>A variant is on a shared 160.1 kb haplotype with 0.4% frequency in Europeans. Furthermore, exome sequencing data from a cohort of 264 individuals with mFMD were examined for COL5A1 variants. In this mFMD cohort, COL5A1 c.1540G>A and 6 additional relatively rare COL5A1 variants predicted to be deleterious in silico were identified and were associated with arterial dissections (P=0.005).

CONCLUSIONS

COL5A1 c.1540G>A is the first recurring variant recognized to be associated with arterial dissections and mFMD. This variant presents with a phenotype reminiscent of vascular Ehlers-Danlos syndrome. A shared haplotype among probands supports the existence of a common founder. Relatively rare COL5A1 genetic variants predicted to be deleterious by in silico analysis were identified in ≈2.7% of mFMD cases, and as they were enriched in patients with arterial dissections, may act as disease modifiers. Molecular testing for COL5A1 should be considered in patients with a phenotype overlapping with vascular Ehlers-Danlos syndrome and mFMD.

Proteomic analysis of Col11a1-associated protein complexes

Cartilage plays an essential role during skeletal development within the growth plate and in articular joint function. Interactions between the collagen fibrils and other extracellular matrix molecules maintain structural integrity of cartilage, orchestrate complex dynamic events during embryonic development, and help to regulate fibrillogenesis. To increase our understanding of these events, affinity chromatography and liquid chromatography/tandem mass spectrometry were used to identify proteins that interact with the collagen fibril surface via the amino terminal domain of collagen α1(XI) a protein domain that is displayed at the surface of heterotypic collagen fibrils of cartilage. Proteins extracted from fetal bovine cartilage using homogenization in high ionic strength buffer were selected based on affinity for the amino terminal noncollagenous domain of collagen α1(XI). MS was used to determine the amino acid sequence of tryptic fragments for protein identification. Extracellular matrix molecules and cellular proteins that were identified as interacting with the amino terminal domain of collagen α1(XI) directly or indirectly, included proteoglycans, collagens, and matricellular molecules, some of which also play a role in fibrillogenesis, while others are known to function in the maintenance of tissue integrity. Characterization of these molecular interactions will provide a more thorough understanding of how the extracellular matrix molecules of cartilage interact and what role collagen XI plays in the process of fibrillogenesis and maintenance of tissue integrity. Such information will aid tissue engineering and cartilage regeneration efforts to treat cartilage tissue damage and degeneration.

Characterization of the six zebrafish clade B fibrillar procollagen genes, with evidence for evolutionarily conserved alternative splicing within the pro-alpha1(V) C-propeptide

Genes for tetrapod fibrillar procollagen chains can be divided into two clades, A and B, based on sequence homologies and differences in protein domain and gene structures. Although the major fibrillar collagen types I-III comprise only clade A chains, the minor fibrillar collagen types V and XI comprise both clade A chains and the clade B chains pro-alpha1(V), pro-alpha3(V), pro-alpha1(XI) and pro-alpha2(XI), in which defects can underlie various genetic connective tissue disorders. Here we characterize the clade B procollagen chains of zebrafish. We demonstrate that in contrast to the four tetrapod clade B chains, zebrafish have six clade B chains, designated here as pro-alpha1(V), pro-alpha3(V)a and b, pro-alpha1(XI)a and b, and pro-alpha2(XI), based on synteny, sequence homologies, and features of protein domain and gene structures. Spatiotemporal expression patterns are described, as are conserved and non-conserved features that provide insights into the function and evolution of the clade B chain types. Such features include differential alternative splicing of NH(2)-terminal globular sequences and the first case of a non-triple helical imperfection in the COL1 domain of a clade B, or clade A, fibrillar procollagen chain. Evidence is also provided for previously unknown and evolutionarily conserved alternative splicing within the pro-alpha1(V) C-propeptide, which may affect selectivity of collagen type V/XI chain associations in species ranging from zebrafish to human. Data presented herein provide insights into the nature of clade B procollagen chains and should facilitate their study in the zebrafish model system.

Equal and local-load-sharing micromechanical models for collagens: quantitative comparisons in response of non-diabetic and diabetic rat tissue

Chemical crosslinks in collagens resulting from binding of advanced glycation end-products, have long been presumed to alter the stiffness and permeability of glycated tissues. Recently, we developed a stochastic mechanical model for the response and failure of uniaxially deformed sciatic nerve tissue from diabetic and control rats. Here, we use our model to determine the likely correlation of fibril glycation with failure response, by quantifying statistical differences in their response. Our four-parameter model describes both the non-linear toe region and non-linear failure region of these tissues; the four parameters consist of (1) collagen fibril alignment, (2) fiber bundle waviness, (3) Weibull shape parameter for fibrillar strength, and (4) modulus-normalized Weibull scale parameter for fibrillar strength. Using an equal load sharing model we find that diabetic and control tissues had shape parameters of 9.88+/-5.50 and 4.33+/-3.67 (p=0.043), respectively, and scale parameters of 0.28+/-0.07 and 0.58+/-0.25 (p=0.033), respectively, implying that the diabetic tissue behaves in a more brittle manner, consistent with more highly crosslinked fibrils. We conclude that biochemical crosslinking directly affects measured mechanical properties. Further, this mechanical characterization may prove useful in mapping alterations in stiffness and permeability observed in glycated tissues.

Collagen type V enhances matrix contraction by human periodontal ligament fibroblasts seeded in three-dimensional collagen gels

Extracellular matrix components play an important role in modulating cellular activity. To study such capacities of the matrix, fibroblasts are frequently cultured in a three-dimensional gel and contraction is assessed as a measure of cellular activity. Since a connective tissue contains several types of collagen, we investigated the effect of gels composed of collagen I alone or in combination with 10% collagen III and/or 5% collagen V on contraction by human periodontal ligament fibroblasts. Gels containing collagen V contracted much faster than those without this type of collagen. Blocking of the integrin beta1-subunit with an activity-blocking antibody delayed (gels with collagen V) or almost completely blocked (gels without collagen V) contraction. Use of an antibody directed against integrin alpha2beta1 resulted in delay of gel contraction for gels both with and without collagen V. Anti-integrin alpha v beta3 or RGD peptides partially blocked contraction of gels containing collagen V, but had no effect on gels consisting of collagen I alone. The beta1-containing integrins are involved in the basal contraction by fibroblasts that bind to collagens I and III. The enhanced contraction, stimulated by collagen V, appears to be mediated by integrin alpha v beta3. We conclude that collagen V may play an important modulating role in connective tissue contraction. Such a modulation may occur during the initial stages of wound healing and/or tissue regeneration.

Developmental roles of the BMP1/TLD metalloproteinases

The astacin family (M12A) of the metzincin subclan MA(M) of metalloproteinases has been detected in developing and mature individuals of species that range from hydra to humans. Functions of this family of metalloproteinase vary from digestive degradation of polypeptides, to biosynthetic processing of extracellular proteins, to activation of growth factors. This review will focus on a small subgroup of the astacin family; the bone morphogenetic protein 1 (BMP1)/Tolloid (TLD)-like metalloproteinases. In vertebrates, the BMP1/TLD-like metalloproteinases play key roles in regulating formation of the extracellular matrix (ECM) via biosynthetic processing of various precursor proteins into mature functional enzymes, structural proteins, and proteins involved in initiating mineralization of the ECM of hard tissues. Roles in ECM formation include: processing of the C-propeptides of procollagens types I-III, to yield the major fibrous components of vertebrate ECM; proteolytic activation of the enzyme lysyl oxidase, necessary to formation of covalent cross-links in collagen and elastic fibers; processing of NH2-terminal globular domains and C-propeptides of types V and XI procollagen chains to yield monomers that are incorporated into and control the diameters of collagen type I and II fibrils, respectively; processing of precursors for laminin 5 and collagen type VII, both of which are involved in securing epidermis to underlying dermis; and maturation of small leucine-rich proteoglycans. The BMP1/TLD-related metalloproteinases are also capable of activating the vertebrate transforming growth factor-beta (TGF-beta)-like "chalones" growth differentiation factor 8 (GDF8, also known as myostatin), and GDF11 (also known as BMP11), involved in negative feedback inhibition of muscle and neural tissue growth, respectively; by freeing them from noncovalent latent complexes with their cleaved prodomains. BMP1/TLD-like proteinases also liberate the vertebrate TGF-beta-like morphogens BMP2 and 4 and their invertebrate ortholog decapentaplegic, from latent complexes with the vertebrate extracellular antagonist chordin and its invertebrate ortholog short gastrulation (SOG), respectively. The result is formation of the BMP signaling gradients that form the dorsal-ventral axis in embryogenesis. Thus, BMP1/TLD-like proteinases appear to be key to regulating and orchestrating formation of the ECM and signaling by various TGF-beta-like proteins in morphogenetic and homeostatic events.

Biosynthetic Processing of the Pro-α1(V)Pro-α2(V)Pro-α3(V) Procollagen Heterotrimer

Type V collagen is a quantitatively minor fibrillar collagen comprised of different chain compositions in different tissues. The most widely distributed form, an alpha1(V)2alpha2(V) heterotrimer, regulates the physical properties of type I/V heterotypic collagen fibrils via partially processed NH2-terminal globular sequences. A less characterized alpha1(V)alpha2(V)alpha3(V) heterotrimer has a much more limited distribution of expression and unknown function(s). We characterized the biosynthetic processing of pro-alpha1(V)2pro-alpha2(V) procollagen previously and showed it to differ in important ways from biosynthetic processing of the major fibrillar procollagens I-III. Here we have successfully produced recombinant pro-alpha1(V)pro-alpha2(V)pro-alpha3(V) heterotrimers. We use these, and mouse embryo fibroblasts doubly homozygous null for the Bmp1 gene, which encodes the metalloproteinase bone morphogenetic protein-1 (BMP-1), and for a gene encoding the closely related metalloproteinase mammalian Tolloid-like 1, to characterize biosynthetic processing of pro-alpha1(V)pro-alpha2(V)pro-alpha3(V) heterotrimers, thus completing characterization of type V collagen biosynthetic processing. Whereas pro-alpha1(V) and pro-alpha2(V) processing in pro-alpha1(V)pro-alpha2(V)pro-alpha3(V) heterotrimers is similar to that which occurs in pro-alpha1(V)2pro-alpha2(V) heterotrimers, the processing of pro-alpha3(V) by BMP-1 occurs at an unexpected site within NH2-terminal globular sequences. We also demonstrate that, despite similarities in NH2-terminal domain structures, pro-alpha2(V) NH2-terminal globular sequences are not cleaved by ADAMTS-2, the metalloproteinase that cleaves the N-propeptides of the major fibrillar procollagen chains.

Characterization of Whole Fibril-Forming Collagen Proteins of Types I, III, and V from Fetal Calf Skin by Infrared Matrix-Assisted Laser Desorption Ionization Mass Spectrometry

Fibril-forming collagen proteins of the types I, III, and V were extracted from fetal calf skin, purified by differential salt precipitation, and analyzed by infrared matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (IR-MALDI-TOF-MS). Glycerol was used as liquid IR-MALDI matrix. Noncovalently bound triple helices of the types I and V were detected from the NaCl precipitate. After heating at 43 degrees C for 10 min, resulting in the dissociation of the triple helix, the single alpha-chain subunits were detected. For type I, mass spectra acquired from molecular sieve chromatography fractions revealed the presence of further substructures of dimeric type and of supramolecular complexes up to the tetramer. Triple helices of type III, stabilized by covalent disulfide bonds, were detected from the total protein precipitate also after heat treatment. For type III, even hexamer and nonamer structures with molecular weights close to 600 and 900 kDa were recorded. For comparison, ultraviolet (UV-)MALDI-MS measurements with 2,5-dihydroxybenzoic acid as matrix were carried out with some of the samples. Here, only the single alpha-chains were detected with significantly reduced sensitivity.

Collagen XXIV, a vertebrate fibrillar collagen with structural features of invertebrate collagens: selective expression in developing cornea and bone

Tissue-specific assembly of fibers composed of the major collagen types I and II depends in part on the formation of heterotypic fibrils, using the quantitatively minor collagens V and XI. Here we report the identification of a new fibrillar-like collagen chain that is related to the fibrillar alpha1(V), alpha1(XI), and alpha2(XI) collagen polypeptides and which is coexpressed with type I collagen in the developing bone and eye. The new collagen was designated the alpha1(XXIV) chain and consists of a long triple helical domain flanked by typical propeptide-like sequences. The carboxyl propeptide is classic, with 8 conserved cysteine residues. The amino-terminal peptide contains a thrombospodin-N-terminal-like (TSP) motif and a highly charged segment interspersed with several tyrosine residues, like the fibril diameter-regulating collagen chains alpha1(V) and alpha1(XI). However, a short imperfection in the triple helix makes alpha1(XXIV) unique from other chains of the vertebrate fibrillar collagen family. The triple helical interruption and additional select features in both terminal peptides are common to the fibrillar chains of invertebrate organisms. Based on these data, we propose that collagen XXIV is an ancient molecule that may contribute to the regulation of type I collagen fibrillogenesis at specific anatomical locations during fetal development.

Order of intron removal influences multiple splice outcomes, including a two-exon skip, in a COL5A1 acceptor-site mutation that results in abnormal pro-alpha1(V) N-propeptides and Ehlers-Danlos syndrome type I

Ehlers-Danlos syndrome (EDS) type I (the classical variety) is a dominantly inherited, genetically heterogeneous connective-tissue disorder. Mutations in the COL5A1 and COL5A2 genes, which encode type V collagen, have been identified in several individuals. Most mutations affect either the triple-helical domain of the protein or the expression of one COL5A1 allele. We identified a novel splice-acceptor mutation (IVS4-2A-->G) in the N-propeptide-encoding region of COL5A1, in one patient with EDS type I. The outcome of this mutation was complex: In the major product, both exons 5 and 6 were skipped; other products included a small amount in which only exon 5 was skipped and an even smaller amount in which cryptic acceptor sites within exon 5 were used. All products were in frame. Pro-alpha1(V) chains with abnormal N-propeptides were secreted and were incorporated into extracellular matrix, and the mutation resulted in dramatic alterations in collagen fibril structure. The two-exon skip occurred in transcripts in which intron 5 was removed rapidly relative to introns 4 and 6, leaving a large (270 nt) composite exon that can be skipped in its entirety. The transcripts in which only exon 5 was skipped were derived from those in which intron 6 was removed prior to intron 5. The use of cryptic acceptor sites in exon 5 occurred in transcripts in which intron 4 was removed subsequent to introns 5 and 6. These findings suggest that the order of intron removal plays an important role in the outcome of splice-site mutations and provide a model that explains why multiple products derive from a mutation at a single splice site.

Bone morphogenetic protein-1 (BMP-1) mediates C-terminal processing of procollagen V homotrimer

The processing of the fibrillar procollagen precursors to mature collagens is an essential requirement for fibril formation. The enzymes involved in these events are known as the procollagen N and C proteinases. The latter, which cleaves the C-propeptides of the fibrillar procollagens I-III, is identical to the previously described bone morphogenetic protein-1 (BMP-1). Surprisingly, unlike the other fibrillar collagens, the processing of the C-propeptide domain of the procollagen V homotrimer was found to be mediated by furin rather than BMP-1. However, the presence of putative BMP-1 cleavage sites in the alpha1(V) C-propeptide sequence prompted us to reconsider the procollagen V C-propeptide cleavage by BMP-1. Using a recombinant system to produce substantial amounts of the proalpha1(V) homotrimer, we have previously shown that the C-propeptide is spontaneously released in the culture medium. The trimeric C-propeptide fragment, resulting from the furin cleavage, still encompassed the predicted BMP-1 cleavage sites. It was purified and tested as a substrate for BMP-1. In parallel, the release of the C-propeptide in the culture medium was inhibited by the addition of a specific furin inhibitor, allowing the re-examination of BMP-1 activity on the intact molecule. We showed that BMP-1 does cleave both substrates at one of the two predicted C-proteinase cleavage sites. Our results favor a role for PCP/BMP-1 in physiological C-terminal processing of procollagen V and imply a general mechanism for fibrillar collagen C-terminal processing.

Structure of a full-length cDNA clone for the pro-alpha1(V/XI) collagen chain of red seabream

The cDNA of type V/XI collagen alpha1 (rsCOL) chain has been isolated from cells established from eyed-period eggs of red seabream, Pagrus major, and sequenced. The amino acid sequence deduced from red seabream alpha1(V/XI) chain resembles that of type XI collagen alpha1 chain. On the other hand, tissue distribution of rsCOL resembles that of type V collagen based on RT-PCR analysis. This is the first report of the cloning of the full-length cDNA of type V/XI collagen alpha1 chain from fish.

Stimulation of protein (collagen) synthesis in sponge cells by a cardiac myotrophin-related molecule from Suberites domuncula

The body wall of sponges (Porifera), the lowest metazoan phylum, is formed by two epithelial cell layers of exopinacocytes and endopinacocytes, both of which are associated with collagen fibrils. Here we show that a myotrophin-like polypeptide from the sponge Suberites domuncula causes the expression of collagen in cells from the same sponge in vitro. The cDNA of the sponge myotrophin was isolated; the potential open reading frame of 360 nt encodes a 120 aa long protein (Mr of 12,837). The sequence SUBDOMYOL shares high similarity with the known metazoan myotrophin sequences. The expression of SUBDOMYOL is low in single cells but high after formation of primmorph aggregates as well as in intact animals. Recombinant myotrophin was found to stimulate protein synthesis by fivefold, as analyzed by incorporation studies using [3H] lysine. In addition, it is shown that after incubation of single cells with myotrophin, the primmorphs show an unusual elongated, oval-shaped appearance. It is demonstrated that in the presence of recombinant myotrophin, the cells up-regulate the expression of the collagen gene. The cDNA for S. domuncula collagen was isolated; the deduced aa sequence shows that the collagenous internal domain is rather short, with only 24 G-x-y collagen triplets. We conclude that the sponge myotrophin causes in homologous cells the same/similar effect as the cardiac myotrophin in mammalian cells, where it is involved in initiation of cardial ventricular hypertrophy. We assume that an understanding of sponge molecular cell biology will also contribute to a further elucidation of human diseases, here of the cardiovascular system.

Unraveling the amino acid sequence crucial for heparin binding to collagen V

We have previously shown that a recombinant 12-kDa fragment of the collagen alpha1(V) chain (Ile(824)-Pro(950)), referred to as HepV, binds to heparin and heparan sulfate (Delacoux, F., Fichard, A., Geourjon, C., Garrone, R., and Ruggiero, F. (1998) J. Biol. Chem. 273, 15069-15076). No consensus sequence was found in the alpha1(V) primary sequence, but a cluster of 7 basic amino acids (in the Arg(900)-Arg(924) region) was postulated to contain the heparin-binding site. The contribution of individual basic amino acids within this sequence was examined by site-directed mutagenesis. Further evidence for the precise localization of the heparin-binding site was provided by experiments based on the fact that heparin can protect the alpha1(V) chain heparin-binding site from trypsin digestion. The results parallel the alanine scanning mutagenesis data, i.e. heparin binding to the alpha1(V) chain involved Arg(912), Arg(918), and Arg(921) and two additional neighboring basic residues, Lys(905) and Arg(909). Our data suggest that this extended sequence functions as a heparin-binding site in both collagens V and XI, indicating that these collagens use a novel sequence motif to interact with heparin.

COL5A1 haploinsufficiency is a common molecular mechanism underlying the classical form of EDS

We have identified haploinsufficiency of the COL5A1 gene that encodes the proalpha1(V) chain of type V collagen in the classical form of the Ehlers-Danlos syndrome (EDS), a heritable connective-tissue disorder that severely alters the collagen-fibrillar structure of the dermis, joints, eyes, and blood vessels. Eight of 28 probands with classical EDS who were heterozygous for expressed polymorphisms in COL5A1 showed complete or nearly complete loss of expression of one COL5A1 allele. Reduced levels of proalpha1(V) mRNA relative to the levels of another type V collagen mRNA, proalpha2(V), were also observed in the cultured fibroblasts from EDS probands. Products of the two COL5A1 alleles were approximately equal after the addition of cycloheximide to the fibroblast cultures. After harvesting of mRNAs from cycloheximide-treated cultured fibroblasts, heteroduplex analysis of overlapping reverse transcriptase-PCR segments spanning the complete proalpha1(V) cDNA showed anomalies in four of the eight probands that led to identification of causative mutations, and, in the remaining four probands, targeting of CGA-->TGA mutations in genomic DNA revealed a premature stop at codon in one of them. We estimate that approximately one-third of individuals with classical EDS have mutations of COL5A1 that result in haploinsufficiency. These findings indicate that the normal formation of the heterotypic collagen fibrils that contain types I, III, and V collagen requires the expression of both COL5A1 alleles.

The pro-alpha3(V) collagen chain. Complete primary structure, expression domains in adult and developing tissues, and comparison to the structures and expression domains of the other types V and XI procollagen chains

The low abundance fibrillar collagen type V is widely distributed in tissues as an alpha1(V)(2)alpha2(V) heterotrimer that helps regulate the diameters of fibrils of the abundant collagen type I. Mutations in the alpha1(V) and alpha2(V) chain genes have been identified in some cases of classical Ehlers-Danlos syndrome (EDS), in which aberrant collagen fibrils are associated with connective tissue fragility, particularly in skin and joints. Type V collagen also exists as an alpha1(V)alpha2(V)alpha3(V) heterotrimer that has remained poorly characterized chiefly due to inability to obtain the complete primary structure or nucleic acid probes for the alpha3(V) chain or its biosynthetic precursor, pro-alpha3(V). Here we provide human and mouse full-length pro-alpha3(V) sequences. Pro-alpha3(V) is shown to be closely related to the alpha1(V) precursor, pro-alpha1(V), but with marked differences in N-propeptide sequences, and collagenous domain features that provide insights into the low melting temperature of alpha1(V)alpha2(V)alpha3(V) heterotrimers, lack of heparin binding by alpha3(V) chains and the possibility that alpha1(V)alpha2(V)alpha3(V) heterotrimers are incorporated into heterotypic fibrils. In situ hybridization of mouse embryos detects alpha3(V) expression primarily in the epimysial sheaths of developing muscles and within nascent ligaments adjacent to forming bones and in joints. This distribution, and the association of alpha1(V), alpha2(V), and alpha3(V) chains in heterotrimers, suggests the human alpha3(V) gene COL5A3 as a candidate locus for at least some cases of classical EDS in which the alpha1(V) and alpha2(V) genes have been excluded, and for at least some cases of the hypermobility type of EDS, a condition marked by gross joint laxity and chronic musculoskeletal pain. COL5A3 is mapped to 19p13.2 near a polymorphic marker that should be useful in analyzing linkage with EDS and other disease phenotypes.

Mutations in the COL5A1 coding sequence are not common in patients with spontaneous cervical artery dissections

BACKGROUND AND PURPOSE

The dermal connective tissue of most patients with spontaneous cervical artery dissections (sCAD) contains abnormal collagen fibers. This suggests a predisposing connective tissue defect. The ultrastructural abnormalities in the skin of patients with sCAD have similarity with the morphological alterations in patients with Ehlers-Danlos syndrome type II, a dominant hereditary disorder that has been correlated in some patients to mutations within the genes encoding type V collagen. The aim of this study was to assess the alpha 1 chain of type V collagen (COL5A1) as a candidate gene for sCAD.

METHODS

We searched for mutations in the COL5A1 gene in cDNA from cultured fibroblasts of 19 patients with sCAD using single-strand conformational polymorphism analysis and nucleotide sequence analysis of polymerase chain reaction-amplified fragments of the whole COL5A1 coding sequence.

RESULTS

We detected 1 missense mutation leading to a predicted amino acid (192D/N) substitution within the N-terminal propeptide in 2 siblings. All other patients showed regular COL5A1 sequences with some silent polymorphisms.

CONCLUSIONS

Mutations in the COL5A1 gene do not appear to be a major factor in the etiology of sCAD.

The occurrence of two types of collagen proalpha-chain in the abalone Haliotis discus muscle

Acid-soluble collagens were prepared from connective tissues in the abalone Haliotis discus foot and adductor muscles with limited proteolysis using pepsin. Collagen preparation solubilized with 1% pepsin contained two types of alpha-chains which were different in their N-terminal amino acid sequences. Accordingly, two types of full-length cDNAs coding for collagen proalpha-chains were isolated from the foot muscle of the same animal and these proteins were named Hdcols (Haliotis discus collagens) 1alpha and 2alpha. The two N-terminal amino acid sequences of the abalone pepsin-solubilized collagen preparation corresponded to either of the two sequences deduced from the cDNA clones. In addition, several tryptic peptides prepared from the pepsin-solubilized collagen and fractionated by HPLC showed N-terminal amino acid sequences identical to those deduced from the two cDNA clones. Hdcols 1alpha and 2alpha consisted of 1378 and 1439 amino acids, respectively, showing the primary structure typical to those of fibril-forming collagens. The N-terminal propeptides of the two collagen proalpha-chains contained cysteine-rich globular domains. It is of note that Hdcol 1alpha completely lacked a short Gly-X-Y triplet repeat sequence in its propeptide. An unusual structure such as this has never before been reported for any fibril-forming collagen. The main triple-helical domains for both chains consisted of 1014 amino acids, where a supposed glycine residue in the triplet at the 598th position from the N-terminus was replaced by alanine in Hdcol 1alpha and by serine in Hdcol 2alpha. Both proalpha-chains of abalone collagens contained six cysteine residues in the carboxyl-terminal propeptide, lacking two cysteine residues usually found in vertebrate collagens. Northern blot analysis demonstrated that the mRNA levels of Hdcols 1alpha and 2alpha in various tissues including muscles were similar to each other.

Bone morphogenetic protein-1 processes the NH2-terminal propeptide, and a furin-like proprotein convertase processes the COOH-terminal propeptide of pro-alpha1(V) collagen

Bone morphogenetic protein-1 (BMP-1) plays key roles in regulating the deposition of vertebrate extracellular matrix; it is the procollagen C-proteinase that processes the major fibrillar collagen types I-III, and it may process prolysyl oxidase to the mature enzyme necessary to the formation of covalent cross-links in collagen and elastic fibers. Type V collagen is a fibrillar collagen of low abundance that is incorporated into and helps regulate the shape and diameter of type I collagen fibrils. Here we show that, in contrast to its action on procollagens I-III, BMP-1 does not cleave the C-propeptide of pro-alpha1(V) homotrimers. Instead, the single BMP-1-specific cleavage site within pro-alpha1(V) chains, lies within the large globular N-propeptide. This cleavage site is immediately upstream of a glutamine, thus redefining the specificity of cleavage for BMP-1-like enzymes. It also produces an NH2 terminus that corresponds to an equivalent NH2 terminus on the processed matrix form of the similar alpha1(XI) chain, thus suggesting physiological significance. Cleavage of the C-propeptide occurs efficiently in recombinant pro-alpha1(V) homotrimers produced in 293-EBNA human embryonic kidney cells, and this cleavage is shown to occur immediately downstream of the sequence RTRR. This is similar to sites cleaved by subtilisin-like proprotein/prohormone convertases and is shown to be specifically cleaved by the recombinant subtilisin-like proprotein/prohormone convertase furin.

cDNA sequence and expression of the mouse alpha1(V) collagen gene (Col5a1)

Several overlapping cDNA clones corresponding to the entire coding sequence of the mouse alpha1(V) collagen gene (Col5a1) were isolated. The conceptual amino acid translation indicated a high degree of sequence identity (94%) with the human alpha1(V) chain. All of the important structures previously noted in the human alpha1(V) chain were also conserved in the mouse chain. The alpha1(V) transcripts were easily detected in mouse embryos as early as 11 days post coitum (d.p.c.). The transcripts were widely distributed in non-cartilaginous and cartilaginous tissues. Finally, we calculated the ratio of transcripts of alpha1(V):alpha2(V):alpha1(XI) in the calvaria and tongue of 18 d.p.c. embryos using the competitive reverse transcription-polymerase chain reaction (RT-PCR) technique. The results raised the possibility that there are at least two different kind of types V/XI collagen heterotrimers in mouse embryonic tissues.

Basic fibroblast growth factor decreases type V/XI collagen expression in cultured bovine aortic smooth muscle cells

Vascular smooth muscle cells (SMCs), the major cellular constituent of an artery, synthesize the bulk of fibrillar collagens, including type V/XI, which regulates heterotypic collagen fibril assembly. Basic fibroblast growth factor (bFGF) is a heparin-binding polypeptide growth factor that has been implicated in important events during the development of atherosclerosis, such as early intimal SMC proliferation. Here we have investigated the effects of bFGF on aortic SMC expression of type V/XI collagen. Treatment of exponentially growing or serum-deprived subconfluent cultures of bovine aortic SMCs with bFGF decreased the steady-state levels of the mRNAs for collagen type V/XI, including alpha 1(V), alpha 2(V), and alpha 1(XI). The effect of bFGF was time dependent with a two- and a fourfold decrease in alpha 2(V) mRNA observed after treatment for 24 and 48 h, respectively. This decrease resulted from a drop in the rate of alpha 2(V) gene transcription; no change was observed in the stability of the alpha 2(V) mRNA. Furthermore, accumulation of collagen protein decreased upon bFGF treatment. As expected, treatment with bFGF increased the rate of proliferation of serum-deprived SMCs, as judged by DNA content in the cultures, thymidine incorporation, and steady-state mRNA levels of the S-phase-expressed histone H3.2. These results suggest that bFGF plays an important role in the regulation of collagen fibril structure, with potential implications for the development and organization of an atherosclerotic lesion.

Microfibrillar composition of umbilical cord matrix: characterization of fibrillin, collagen VI and intact collagen V

Ultrastructural studies made on human umbilical cord revealed that the striated collagen fibrils of the Wharton's jelly matrix are mixed with many microfibrillar structures. Microfibrils were found with a tubular cross-section of 10-12 nm diameter and were organized as beaded filaments characteristic of fibrillin-rich microfibrils. Beads had an average diameter of 25 nm and were spaced at about 50-80 nm. This ultrastructural observation was confirmed by indirect immunofluorescent staining of the jelly matrix using monoclonal antibody to fibrillin. Another constituent of the microfibrillar network was present as typical 100-nm periodic filaments of type VI collagen. Indirect immunofluorescent staining using antibodies to collagen VI showed for the first time that this collagen appeared to be distributed largely in the jelly matrix. In addition, other microfibrils with no specific banding pattern were observed. These microfibrils may constitute an organization of type V collagen different from the one which is generally assembled in heterotypic fibrils with collagen I. Among the latter heterotypic fibrils, type V collagen was studied using an anti-peptide antibody to the most N-terminal non-collagenous region of its alpha 2(V) chain. This antibody recognized a filamentous mesh decorating the bundles of collagen fibrils by immunofluorescent staining. This indicates that at least this part of alpha 2(V) chain may be accessible to the antibody at the surface of the fibrils.

Human recombinant alpha1(V) collagen chain. Homotrimeric assembly and subsequent processing

Human embryonic kidney cells (293-EBNA) have been transfected with the full-length human alpha1 chain of collagen V using an episomal vector. High yields (15 microgram/ml) of recombinant collagen were secreted in the culture medium. In presence of ascorbate, the alpha1(V) collagen is correctly folded into a stable triple helix as shown by electron microscopy and pepsin resistance. Circular dichroism data confirm the triple-helix conformation and indicate a melting temperature of 37.5 degrees C for the recombinant homotrimer. The major secreted form is a 250-kDa polypeptide (alpha1FL). N-terminal sequencing and collagenase digestion indicate that alpha1FL retains the complete N-propeptide but lacks the C-propeptide. However, alpha1FL might undergo a further N-terminal trimming into a form (alpha1TH) corresponding to the main triple-helix domain plus the major part of the NC2 domain. This processing is different from the one of the heterotrimeric (alpha1(V))2alpha2(V) and could have some physiological relevance. Analysis of cell homogenates indicates the presence of a 280-kDa polypeptide that is disulfide-linked through its C-terminal globular domain. This C-propeptide is rapidly cleaved after secretion in the medium, giving the first evidence of a C-terminal processing of recombinant fibrillar collagens. Rotary shadowing observations not only confirm the presence of a globular domain at the N-terminal end of the molecule but reveal the presence of a kink within the triple helix in a region poor in iminoacids. This region could represent a target for proteases. Together with the thermal stability data, these results might explain the low amount of (alpha1(V))3 recovered from tissues.

Cloning of an annelid fibrillar-collagen gene and phylogenetic analysis of vertebrate and invertebrate collagens

Arenicola marina possesses cuticular and interstitial collagens, which are mostly synthesised by its epidermis. A cDNA library was constructed from the body wall. This annelid cDNA library was screened with a sea-urchin-collagen cDNA probe, and several overlapping clones were isolated. Nucleotide sequencing of these clones revealed an open reading frame of 2052 nucleotides. The translation product exhibits a triple helical domain of 138 Gly-Xaa-Yaa repeats followed by a 269-residue-long C-terminal non-collagenous domain (C-propeptide). The triple helical domain exhibits an imperfection that has been previously described in a peptide produced by cyanogen bromide digestion (CNBr peptide) of A. marina interstitial collagen. This imperfection occurs at the same place in the interstitial collagen of the vestimentiferan Riftia pachyptila. This identifies the clone as coding for the C-terminal part of a fibrillar collagen chain. It was called FAm1alpha, for fibrillar collagen 1alpha chain of A. marina. The non-collagenous domain possesses a structure similar to carboxy-terminal propeptides of fibrillar pro-alpha chains. Only six conserved cysteine residues are observed in A. marina compared with seven or eight in all other known C-propeptides. This provides information on the importance of disulfide bonds in C-propeptide interactions and in the collagen-assembly process. Phylogenetic studies indicate that the fibrillar collagen 1alpha chain of A. marina is homologous to the R. pachyptila interstitial collagen and that the FAm1alpha gene evolved independently from the other alpha-chain genes. Complementary analyses indicate that the vertebrate fibrillar collagen family is composed of two monophyletic subgroups with a specific position of the collagen type-V chains.

Disproportionate micromelia (Dmm) in mice caused by a mutation in the C-propeptide coding region of Col2a1

Mice that are homozygous for the autosomal semidominant disproportionate micromelia (Dmm) mutation are characterized by disproportionate micromelia, thoracic dysplasia, and cleft palate. Chondrocytes of the epiphyseal growth plates are not organized into columns, and ultrastructural analysis reveals excessive dilation of the endoplasmic reticulum and a paucity of collagen fibrils in the extracellular matrix. To map the Dmm locus, Dmm mice were crossed with the multiple ecotropic viral (MEV) linkage testing stock. Significant linkage of Dmm to the fourteen MEV linkage markers was not observed, thereby excluding approximately 50% of the genome as candidate regions encoding Dmm. Subsequently, microsatellite markers were used to assess linkage to the nonexcluded regions of the genome, revealing tight linkage to the locus of Col2a1, the gene encoding the alpha-chains of type II collagen. alpha 1(II) collagen cDNA, synthesized with RNA from homozygotes, was cloned and sequenced, revealing a three-nucleotide deletion in the region encoding the C-propeptide globular domain. The deletion leads to the substitution of one amino acid, Asn, in the mutant for two amino acids, Lys and Thr, in the wild type. Several human chondrodysplasias with similar phenotypes to that of Dmm are associated with defects in type II collagen. Thus, mice bearing the Dmm mutation serve as a model for studying the pathogenesis of these disorders while revealing novel insights into normal skeletal morphogenesis.

Biosynthesis and processing of type XVI collagen in human fibroblasts and smooth muscle cells

The alpha 1(XVI) collagen chain, recently identified by cDNA cloning, exhibits structural similarity to a subgroup of collagens that associate with collagen fibrils. Recombinant alpha 1(XVI) collagen chains produced in embryonic kidney cells are able to form stable homotrimers, which are rapidly converted into smaller polypeptides after secretion into the culture medium. In this study, we investigated the biosynthesis of native type XVI collagen by immunoprecipitation of metabolically labeled human cells. Dermal fibroblasts and arterial smooth muscle cells were precipitated with three antibodies raised against distinct regions in the N- and C-terminal part of the human alpha 1(XVI) collagen chain. A disulfide-bonded polypeptide of 220 kDa was obtained from the culture medium, cells and extracellular matrix with all three antibodies. This polypeptide is sensitive to bacterial collagenase digestion and partially resistant to pepsin digestion, suggesting that it is the endogenous alpha 1(XVI) collagen chain. Pulse/chase experiments showed that the newly synthesized alpha 1(XVI) chains are secreted into the medium and deposited in the extracellular matrix in a time-dependent manner. Unlike the recombinant chain, the native type XVI collagen does not undergo extensive proteolytic processing upon secretion. Both cell types deposit a substantial amount of the newly synthesized alpha 1(XVI) chain into the extracellular matrix, in which the 220-kDa polypeptide is the only product immunoprecipitated. There is little evidence for the presence of another constituent chain. The data are consistent with a nomotrimeric chain composition for type XVI collagen. No apparent difference exists in the rate of synthesis and secretion between fibroblasts and smooth muscle cells. Indirect immunofluorescence microscopy showed an extracellular distribution of type XVI collagen, which is located close to cells but not associated with fibrillar structures.

An exon skipping mutation of a type V collagen gene (COL5A1) in Ehlers-Danlos syndrome

The Ehlers-Danlos syndrome (EDS) is a heterogeneous group of inherited connective tissue disorders characterised by skin hyperextensibility, joint hypermobility, easy bruising, and cutaneous fragility. Nine discrete clinical subtypes have been classified. We have investigated the molecular defect in a patient with clinical features of Ehlers-Danlos syndromes types I/II and VII. Electron microscopy of skin tissue indicated abnormal collagen fibrillogenesis with longitudinal sections showing a marked disruption of fibril packing giving very irregular outlines to transverse sections. Analysis of the collagens produced by cultured fibroblasts showed that the type V collagen had a population of alpha 1 (V) chains shorter than normal. Peptide mapping suggested a deletion within the triple helical domain. RTPCR amplification of mRNA covering the whole of this domain of COL5A1 showed a deletion of 54 bp. Although six Gly-X-Y triplets were lost, the essential triplet amino acid sequence and C-propeptide structure were maintained allowing mutant protein chains to be incorporated into triple helices. Genomic DNA analysis identified a de novo G+3-->T transversion in a 5' splice site of one COL5A1 allele. This mutation is analogous to mutations causing exon skipping in the major collagen genes, COL1A1, COL1A2, and COL3A1, identified in several cases of osteogenesis imperfecta and EDS type IV. These observations support the hypothesis that type V, although quantitatively a minor collagen, has a critical role in the formation of the fibrillar collagen matrix.

Processing of type XI collagen. Determination of the matrix forms of the alpha1(XI) chain

Type XI collagen is mainly found as a minor constituent in type II-containing fibrils and presents a alpha1(XI)alpha2(XI)alpha3(XI) stoichiometry. This molecule was shown to be partially processed in its intact tissue form. Moreover, alternative splicing has been demonstrated in the variable region of the N-terminal domain of alpha1(XI) and alpha2(XI) chains. In this work, the processing of a major intact form of alpha1(XI) from matrix laid down by chick chondrocytes in culture was identified using N-terminal sequencing and antibodies to synthetic peptides corresponding to the N-terminal propeptide cDNA-derived sequence. The results show that the fully processed form of alpha1(XI) begins at Gln254 of the N-terminal propeptide, seven residues before the end of the proline/arginine-rich protein region encoded by exon I (Zhidkova, N. I., Justice, S. K., and Mayne, R. (1995) J. Biol. Chem. 270, 9486-9493). This sequence is immediately followed by a sequence encoded by exon III. The processing takes place at an Ala-Gln sequence that corresponds to a consensus sequence for procollagen N-proteinase. The antibody raised against a sequence located within the region corresponding to exon IV (anti-P8) fails to recognize this fully processed form of the alpha1(XI) chain. It recognizes, however, two minor bands of high molecular mass. These results suggest that a major cartilage form of alpha1(XI) is the product of alternative splicing in which sequences encoded by both exons II and IV are skipped. The presence of a highly acidic subdomain encoded by exon III at the N terminus of the major form of the alpha1(XI) chain, as predicted by these data, provides potential sites for interaction of collagen XI with other molecules.

A translocation interrupts the COL5A1 gene in a patient with Ehlers-Danlos syndrome and hypomelanosis of Ito

Ehlers-Danlos syndrome (EDS) is a genetically and pathogenetically heterogeneous group of disorders of which at least 11 types have been described. All are connective tissue disorders characterized by defects of the skin, ligaments and blood vessels with the clinical spectrum ranging from innocuous findings to lethality. Mutations in the genes encoding the major fibrillar collagen types I and III have been demonstrated in EDS types VII and IV, respectively, while mutations in the lysyl hydroxylase and ATP7A genes, with roles in collagen cross-linking, are responsible for EDS types VI and IX. The biochemical and molecular bases for the most common forms of EDS (types I, II and III) are unknown. Here, we describe a balanced translocation between chromosome 9 and an X chromosome that disrupts the minor fibrillar collagen type V gene COL5A1 in a patient with both EDS type I and hypomelanosis of Ito. The breakpoint occurs at 9q34 within COL5A1 intron 24 and interestingly, within a LINE-1 (L1) element at Xp21.1. A fusion mRNA between COL5A1 and an Alu sequence is produced, but no aberrant protein is detectable. Rather, the amount of type V collagen is reduced in the patient's fibroblasts, suggesting haploinsufficiency as a cuase of the phenotype. This demonstrates that a mutation in a type V collagen gene, COL5A1, results in EDS type I, and shows the involvement of L1 sequences in a constitutional chromosomal translocation. Because collagen type V is a heteromorphic protein in which molecules may be composed of polypeptides encoded by three COL5A genes, this suggests all three genes as candidates for mutations in EDS.

B-Myb expression in vascular smooth muscle cells occurs in a cell cycle-dependent fashion and down-regulates promoter activity of type I collagen genes

The members of the Myb family of transcription factors are defined by homology in the DNA-binding domain; all bind the Myb-binding site (MBS) sequence (YG(A/G)C(A/C/G)GTT(G/A)). Here we report that cultured bovine vascular smooth muscle cells (SMCs) express B-myb. Levels of B-myb RNA found in exponential growth were reduced dramatically in serum-deprived quiescent SMCs; B-myb mRNA levels increased in the cell cycle during the late G1 to S phase transition following restimulation with serum, epidermal growth factor, or phorbol ester plus insulin-like growth factor-1. Changes in the rate of B-myb gene transcription could account for part of the observed increase following serum addition. Treatment of SMC cultures with actinomycin D indicated a >4-h half-life for B-myb mRNA during the S phase of the cell cycle. Cotransfection of either a bovine or human B-myb expression vector down-regulated the activity of a multimerized MBS element-driven reporter construct in SMCs. Putative MBS elements were detected upstream of the promoters of the two chains of type I collagen, which we have found to be expressed inversely with growth state of the SMC (Kindy, M. S., Chang, C.-J., and Sonenshein, G. E. (1988) J. Biol. Chem. 263, 11426-11430). In cotransfection experiments, B-myb expression down-regulated the promoter activity of alpha1(I) and alpha2(I) collagen constructs an average of 92 and 82%, respectively. Thus, B-myb represents a potential link in the observed inverse relationship between collagen gene expression and growth of vascular SMCs.

The evolution of fibrillar collagens: a sea-pen collagen shares common features with vertebrate type V collagen

The extracellular matrix of marine primitive invertebrates (sponges, polyps and jellyfishes) contains collagen fibrils with narrow diameters. From various data, it has been hypothesized that these primitive collagens could represent ancestral forms of the vertebrate minor collagens, i.e., types V or XI. Recently we have isolated a primitive collagen from the soft tissues of the sea-pen Veretillum cynomorium. This report examines whether the sea-pen collagen shares some features with vertebrate type V collagen. Rotary shadowed images of acid-soluble collagen molecules extracted from beta-APN treated animals, positive staining of segment-long-spacing crystallites precipitated from pepsinized collagen, Western blots of the pepsinized alpha1 and alpha2 chains with antibodies to vertebrate types I, III and V collagens, and in situ gold immunolabeling of ECM collagen fibrils were examined. Our results showed that the tissue form of the sea-pen collagen is a 340-nm threadlike molecule, which is close to the vertebrate type V collagen with its voluminous terminal globular domain, the distribution of most of its polar amino-acid residues, and its antigenic properties.

Characterization of two genes coding for a similar four-cysteine motif of the amino-terminal propeptide of a sea urchin fibrillar collagen

We report the characterization of the 5' region of the gene coding for the 2 alpha fibrillar collagen chain of the sea urchin Paracentrotus lividus. This sequence analysis identified the intron/exon organization of the region of the gene coding for the signal peptide, the cysteine-rich domain and the 12 repeats of the four-cysteine module of the unusually long amino-propeptide. This still unknown four-cysteine motif is generally encoded by one exon, which confirms that the distinct amino-propeptide structures of the fibrillar collagens arise from the shuffling of several exon-encoding modules. Moreover, Southern-blot analysis of the sea urchin genome and sequencing of selected genomic clones allowed us to demonstrate that several sea urchin genes could potentially code for the four-cysteine module. Curiously, one of these genes lacks the exons coding for four repeats of this motif while, in another gene, the same exons are submitted to an alternative splicing event.

The human COL11A2 gene structure indicates that the gene has not evolved with the genes for the major fibrillar collagens

The human COL11A2 gene was analyzed from two overlapping cosmid clones that were previously isolated in the course of searching the human major histocompatibility region (Janatipour, M., Naumov, Y., Ando, A., Sugimura, K., Okamoto, N., Tsuji, K., Abe, K., and Inoko, H. (1992) Immunogenetics 35, 272-278). Nucleotide sequencing defined over 28,000 base pairs of the gene. It was shown to contain 66 exons. As with most genes for fibrillar collagens, the first intron was among the largest, and the introns at the 5'-end of the gene were in general larger than the introns at the 3'-end. Analysis of the exons coding for the major triple helical domain indicated that the gene structure had not evolved with the genes for the major fibrillar collagens in that there were marked differences in the number of exons, the exon sizes, and codon usage. The gene was located close to the gene for the retinoic X receptor beta in a head-to-tail arrangement similar to that previously seen with the two mouse genes (P. Vandenberg and D. J. Prockop, submitted for publication). Also, there was marked interspecies homology in the intergenic sequences. The amino acid sequences and the pattern of charged amino acids in the major triple helix of the alpha 2(XI) chain suggested that the chain can be incorporated into the same molecule as alpha 1(XI) and alpha 1(V) chains but not into the same molecule as the alpha 3(XI)/alpha 1(II) chain. The structure of the carboxyl-terminal propeptide was similar to the carboxyl-terminal propeptides of the pro alpha 1(XI) chain and pro alpha chains of other fibrillar collagens, but it was shorter because of internal deletions of about 30 amino acids.

Structural analysis of cross-linking domains in cartilage type XI collagen. Insights on polymeric assembly

The collagen framework of hyaline cartilage is based on copolymers of types II, IX, and XI collagens. Previous studies have established specific covalent interactions between types II and IX collagens. The present study examined cross-linking sites in type XI collagen to define better the full heteropolymeric assembly. Pepsinsolubilized type XI collagen was purified from fetal bovine cartilage. The cross-linking amino acids in the preparation were primarily divalent, borohydride-reducible structures; pyridinoline residues were essentially absent. Individual alpha 1(XI), alpha 2(XI), and alpha 3(XI) chains were resolved by high performance liquid chromatography. Telopeptides still attached by cross-links to helical sites were released by periodate oxidation and identified by microsequencing. Analysis of cross-linked peptides isolated from trypsin digest of each alpha-chain identified the attachment helical sites for the telopeptides. A high degree of interchain specificity was evident in the cross-linking between N-telopeptides and the COOH terminus of the triple-helix, consistent with a head-to-tail interaction of molecules staggered by 4D (D = 67 nm) periods. In addition, alpha 1(II) C-telopeptide was linked to the amino-terminal site of the alpha 1(XI) triple helix. In summary, the results show that type XI collagen molecules are primarily cross-linked to each other in cartilage, implying that a homopolymer is initially formed. Links to type II collagen are also indicated, consistent with an eventual cofibrillar assembly. Analysis of cartilage extracts showed that all three chains, alpha 1(XI), alpha 2(XI), and alpha 3(XI), had at least in part retained their N-propeptides in cartilage matrix and that the alpha 3 (XI) chain was the IIB splicing variant product of the COL2A1 gene. Of particular note was the finding that the N-telopeptide cross-linking site in both alpha 1(XI) and alpha 2(XI) is located amino-terminal to the putative N-propeptidase cleavage site. This structural feature provides a potential mechanism for the proteolytic depolymerization of type XI collagen by proteases that can cleave between the cross-link and the triple helix (e.g. stromelysin).

Another look at collagen V and XI molecules

The fibrillar collagens are the most abundant proteins of extracellular matrices. Among them, collagens V and XI are quantitatively minor components which participate in the formation of the fibrillar collagen network. Since these collagens were discovered, studies have demonstrated that they may play a fundamental role in the control of fibrillogenesis, probably by forming a core within the fibrils. Another characteristic of these collagens is the partial retention of their N-propeptide extensions in tissue forms, an unusual observation in comparison to the other known fibrillar collagens. The tissue locations of collagens V and XI are different, but their structural and biological properties seem to be closely related. It has been shown that their primary structures are highly conserved at both the gene and protein levels, and that these conserved features are the bases of their similar biological properties. In particular, they are both resistant to mammalian collagenases, and surprisingly sensitive to trypsin treatment. Collagens V and XI are usually buried within the major collagen fibrils, although they have both cell adhesion and heparin binding sites which could be of crucial importance in physiological processes such as development and wound healing. It has became evident that several molecules are in fact heterotypic associations of chains from both collagens V and XI, demonstrating that these two collagens are not distinct types but a single type which can be called collagen V/XI.

Alternative mRNA processing occurs in the variable region of the pro-alpha 1(XI) and pro-alpha 2(XI) collagen chains

An analysis was performed of differential splicing of primary transcripts in the noncollagenous variable region located in the amino terminus of the pro-alpha 1(XI) and pro-alpha 2(XI) collagen chains. The results for the pro-alpha 2(XI) chain showed that human cartilage or fibroblasts in culture contain transcripts in which a single highly acidic exon encoding for 21 amino acids is present or absent. For the chicken pro-alpha 1(XI) chain a more complex pattern of alternative splicing was detected with six possible variants. Of special interest was the alternative use of two exons (called IIA and IIB) in which IIA encodes for 39 amino acids and is highly acidic (estimated pI = 3.2), whereas IIB encodes for 49 amino acids and is highly basic (estimated pI = 10.6). A similar alternative use of exon IIA or exon IIB was also observed for human chondrocytes. Northern blotting with probes specific for IIA or IIB showed that both exons are present in transcripts from cartilage but exon IIB is preferentially utilized in transcripts from tendon. Present results suggest that both the pro-alpha 1(XI) and pro-alpha 2(XI) chains of type XI collagen undergo limited processing in vivo and that the noncollagenous variable region is initially retained on the surface of the fibrils. Differential splicing in the variable region may potentially influence the interaction of collagen fibrils with other molecules of the extracellular matrix and more specifically with sulfated glycosaminoglycan chains or with hyaluronan. Such interactions may play a key role in establishing both the organization of the collagen fibrils within the extracellular matrix and in limiting the diameter of collagen fibrils.

Recombinant analysis of human alpha 1 (XVI) collagen. Evidence for processing of the N-terminal globular domain

The N-terminal non-collagenous domain NC11 of the human collagen alpha 1 (XVI) chain was obtained as a recombinant 35-kDa protein from stably transfected kidney cell clones. This form had undergone proteolytic trimming at a basic cleavage motif indicating a similar release in vivo. Domain NC11 showed a globular shape after rotary shadowing and was resistant to neutral proteases. Specific antibodies could be raised against recombinant NC11 and were used for the analysis of other cell clones transfected with the full-length alpha 1 (XVI) chain. Immunoprecipitation of detergent extracts of metabolically labelled cells demonstrated the presence of disulfide-bonded 200-kDa polypeptides possessing NC11 epitopes. This material was partially resistant to pepsin, indicating the formation of alpha 1 (XVI) chain homotrimers with a triple-helical conformation. Yet a substantial proportion of these homotrimers was degraded to fragments of variable size (35-150 kDa) when secreted into the culture medium. Several of these fragments could be obtained on a semi-preparative scale from cells grown in hollow fiber cassettes and showed substantial hydroxylation of proline, consistent with triple-helix formation. Edman degradation demonstrated the origin of some from the N-terminal and of one from a more C-terminal position of collagen XVI. This extensive degradation may be explained by the release of NC11 and by further cleavages within some of the nine interruptions of the triple-helical domain of the alpha 1(XVI) chain. Whether this process also occurs in situ remains to be shown.

Differential expression of an acidic domain in the amino-terminal propeptide of mouse pro-alpha 2(XI) collagen by complex alternative splicing

We isolated and sequenced genomic and cDNA clones encoding the complete amino-terminal portion and the 5'-untranslated region of mouse pro-alpha 2(XI) collagen mRNA. Fourteen exons encoded the amino-terminal propeptide, which was divided into three consecutive domains (a long globular domain, an amino-terminal triple helical domain, and a telopeptide domain). The long globular domain was further divided into an upstream basic subdomain and a downstream highly acidic subdomain, as is the case for the amino-terminal propeptides of pro-alpha 1(V) and pro alpha 1(XI) collagens. We also demonstrated that the primary transcript undergoes complex alternative splicing. Three consecutive exons (exons 6, 7, and 8) encoding most of the acidic subdomain showed alternative splicing which dramatically affected the structure of the amino-terminal propeptide of pro-alpha 2(XI) collagen. Using the reverse transcription-polymerase chain reaction, we analyzed the expression of these exons in various tissues and in developing limb buds of mice. The pro-alpha 2(XI) transcripts were abundant in cartilage, but most of them lacked the 3-exon sequences encoding the acidic domain. Most of other tissues also contained mRNAs that corresponded to longer splice variants, including exons 6-8. The differential expression of specific domains of pro-alpha 2(XI) collagen may be important in modulating interactions between various components of the extracellular matrix and/or may influence heterotypic collagen assembly.

Structural and functional analysis of the promoter of the human alpha 1(XI) collagen gene

In order to eventually elucidate the mechanisms regulating alpha 1(XI) collagen expression in cartilaginous and non-cartilaginous tissues, we performed an initial analysis of the structural-functional features of the promoter of the human gene (COL11A1). After cloning and sequencing the 5' portion of COL11A1, primer extension and nuclease protection assays identified several minor transcriptional start sites clustered around a major one located 318 base pairs from the ATG codon. Consistent with this finding, analysis of the upstream sequence revealed the absence of a TATA motif and the presence of several GC boxes. Transient transfection experiments delineated the smallest promoter sequence directing relatively high expression of a reporter gene in a cell type-specific manner. Nine nuclear protein-bound areas were located within this promoter sequence of the COL11A1 gene. Sequence homologies suggested that the majority of the footprints correspond to potential binding sites for ubiquitous nuclear proteins, such as AP2 and Sp1. Additional experimental evidence indicated that one of the protected areas may bind a transcriptional complex that is identical or closely related to the one that regulates tissue specificity in the coordinately expressed alpha 2(V) collagen gene.

Type XI and II collagen-induced arthritis in rats: characterization of inbred strains of rats for arthritis-susceptibility and immune-responsiveness to type XI and II collagen

To determine the relationship between susceptibility to bovine type XI and II (BXI and BII) collagen-induced arthritis, we immunized 14 inbred and one outbred strains of rats with BXI and BII. Susceptibility to BXI-arthritis corresponded largely with susceptibility, or resistance, to BII-arthritis. LEW, BB, WF, DA, and WKY were readily susceptible to BXI- and BII-arthritis. Likewise, BII-resistant F344 and BN rats were BXI-resistant. Some strains responded differently to BXI and BII. BUF and COP, which are moderately susceptible to BII, were BXI-resistant, whereas the BII-resistant rats, DA.1N and WF.1N, were partially susceptible to BXI. (F344 x BN) F1 hybrids responded to both collagens suggesting gene complementation. Arthritis occurred in all strains producing the highest titer antisera (LEW, WF and BB). Antibody responses to BXI and BII were generally commensurate within individual strains. DA were susceptible to arthritis but produced low levels of antibody comparable to BN rats which were arthritis-resistant. BXI and BII-susceptibility was variable in rats producing intermediate antibody responses. Antibodies to RXI were detected in all BXI-immunized rats, whereas antibodies to RV and RII were uniformly weaker. DTH to RXI and RII was strong in both groups of rats, correlating poorly with arthritis and antibody responses. These studies show that phenotypic susceptibility to BXI- and BII-arthritis are largely concordant among inbred rat strains but clear differences exist in certain strains; multiple genes are likely involved.

Structural characteristics of cross-linking sites in type V collagen of bone. Chain specificities and heterotypic links to type I collagen

To understand the role of type V collagen and its spatial interrelationship with type I collagen in bone matrix, the molecule's covalent intermolecular cross-links were structurally characterized. Type V collagen containing alpha 1(V), alpha 2(V) and alpha 1(XI) chains was isolated from bovine bone and reacted with NaB3H4 to label the cross-linking residues. Radiolabeled native molecules and isolated alpha chains were treated with sodium metaperiodate to cleave the divalent cross-linking bonds. Sequence analysis of the periodate-released peptides matched two of them to alpha 1(V) and alpha 1(XI) aminopropeptide domains. A third peptide was derived from the alpha 1(I) carboxytelopeptide domain of type I collagen. This latter peptide, therefore, came from a site of heterotypic cross-linking between types I and V collagens and accounted for about 15% of the total cross-linked peptides. Sequence analysis of isolated cross-linked tryptic peptides defined the helical sites of attachment of the periodate-released telopeptides and revealed that the putative aminoproteinase-cleavage sites in the alpha 1(V) and alpha 1(XI) chains are located in the molecule interior to the cross-linking residue. These data imply that type V collagen molecules in the extracellular matrix are primarily cross-linked to each other in a head-to-tail linear polymer that is linked laterally to type I collagen molecules in copolymeric fibrils.

Tyrosine-rich acidic matrix protein (TRAMP) is a tyrosine-sulphated and widely distributed protein of the extracellular matrix

Tyrosine-rich acidic matrix protein (TRAMP; 22 kDa extracellular matrix protein; dermatopontin) is a protein that co-purifies with lysyl oxidase and with dermatan sulphate proteoglycans, with possible functions in cell-matrix interactions and matrix assembly. Using a rabbit polyclonal antiserum raised against porcine TRAMP, which cross-reacts with both the human and murine forms of the protein, we show by immunoblotting that TRAMP has a widespread tissue distribution, including skin, skeletal muscle, heart, lung, kidney, cartilage and bone. In cultures of human skin fibroblasts, TRAMP incorporates both [35S]sulphate and [3H]tyrosine and is secreted into the medium, as shown by immunoprecipitation. Amino acid analysis of immunoprecipitated TRAMP demonstrates that many of the tyrosine residues in TRAMP are sulphated.