Cloning and sequence analysis of a partial cDNA for chicken cartilage proteoglycan core protein

Stimulation of limb cartilage differentiation by cyclic AMP is dependent on cell density

Cyclic AMP (cAMP) has been implicated in the regulation of limb cartilage differentiation. This study represents an attempt to clarify potential mechanisms by which cAMP might regulate chondrogenesis. We have found that the ability of cAMP to stimulate limb cartilage differentiation in vitro is dependent on cell density. Dibutyryl cAMP (dbcAMP) elicits a striking increase in the accumulation of Alcian blue, pH 1.0-positive cartilage matrix, and a corresponding three- to fourfold increase in the accumulation of 35S-labeled glycosaminoglycans (GAG) by limb mesenchymal cells cultured in low serum medium at densities greater than confluence (i.e. micromass cultures established with 1-2 x 10(5) cells in 10 microliters of medium). Moreover, dbcAMP causes a striking (two- to fourfold) increase in the steady-state cytoplasmic levels of mRNAs for cartilage-characteristic type II collagen and the core protein of cartilage-specific sulfated proteoglycan in these high density, supraconfluent cultures. In contrast, cAMP does not promote the chondrogenesis of limb mesenchymal cells cultured at subconfluent densities (i.e. cultures initiated with 2.5-5 x 10(4) cells in 10 microliters of medium). In these low density cultures, dbcAMP does not promote the formation of cartilage matrix, sulfated GAG accumulation or the accumulation of cartilage-specific mRNAs. These observations suggest that cAMP may exert its regulatory effect in part by facilitating cell-cell communication during the critical condensation phase of chondrogenesis.

The human mannose-binding protein gene. Exon structure reveals its evolutionary relationship to a human pulmonary surfactant gene and localization to chromosome 10

The human mannose-binding protein (MBP) plays a role in first line host defense against certain pathogens. It is an acute phase protein that exists in serum as a multimer of a 32-kD subunit. The NH2 terminus is rich in cysteines that mediate interchain disulphide bonds and stabilize the second collagen-like region. This is followed by a short intervening region, and the carbohydrate recognition domain is found in the COOH-terminal region. Analysis of the human MBP gene reveals that the coding region is interrupted by three introns, and all four exons appear to encode a distinct domain of the protein. It appears that the human MBP gene has evolved by recombination of an ancestral nonfibrillar collagen gene with a gene that encodes carbohydrate recognition, and is therefore similar to the human surfactant SP-A gene and the rat MBP gene. The gene for MBP is located on the long arm of chromosome 10 at 10q11.2-q21, a region that is included in the assignment for the gene for multiple endocrine neoplasia type 2A.

Isolation of the N-terminal globular protein domains from cartilage proteoglycans. Identification of G2 domain and its lack of interaction with hyaluronate and link protein

The N-terminal fragment (G1-G2) of cartilage proteoglycan protein core contains two globular domains, binding region (G1) and a second globular domain (G2), G1-G2 was isolated after mild trypsin digestion of purified proteoglycan aggregates followed by chromatography first on Sepharose CL-2B under associative conditions and then on a TSK-4000 column in 4 M-guanidinium chloride. It migrated as a single band (apparent Mr 150,000) on SDS/polyacrylamide-gel electrophoresis. G2 was isolated by V8-proteinase digestion of G1-G2 followed by aggregation of the G1-containing fragments with hyaluronate and chromatography on TSK-4000. It migrated as a single band on SDS/polyacrylamide-gel electrophoresis of apparent Mr 66,000 after digestion with keratanase. G2 did not interact with proteoglycan monomer, hyaluronate, link protein or other extractable cartilage matrix proteins. A polyclonal antibody raised against G2 did not cross-react with G1 or link protein. These data show that, despite a high degree of sequence similarity, G1 and G2 do not share any functional properties nor have major antigenic sites in common.

Tetranectin immunoreactivity in normal human tissues. An immunohistochemical study of exocrine epithelia and mesenchyme

A recently discovered human plasma protein, tetranectin (TN), which has previously been demonstrated immunohistochemically within various endocrine tissues, was in this study identified in an additional number of epithelial and mesenchymal cells by two polyclonal antibodies and one monoclonal using the conventional immunoperoxidase staining technique and a modification of the CLONO-GLAD procedure. TN was found in endothelial and epithelial tissues, particularly in cells with a high turn-over or storage function such as gastric parietal and zymogenic cells, absorptive surface epithelium of the small intestine, ducts of exocrine glands and pseudostratified respiratory epithelium. Also mesenchymal cells produced a TN positive staining reaction, which was most conspicuous in mast cells, but also present in some lymphocytes, plasma cells, macrophages, granulocytes, striated and smooth muscle cells and fibroblasts. SDS-PAGE and Western blotting analysis of cultured human embryonal fibroblasts (WI-38) showed that the cells besides TN contain another protein with a molecular weight of 82,000. As this protein, however, reacted with our affinity purified antibodies it probably represents a precursor of TN or a protein with a molecular weight of approximately 60,000, which is covalently linked to TN. This and the fact that TN shows amino acid sequence homologies to the carboxyterminal part of the asialo-glycoprotein receptor and a cartilage proteoglycan core protein as well a binding affinity to plasminogen points to TN as being part of a larger molecule, which possibly has been cleaved by proteolysis at the cellular site and then passed into the blood, where it polymerizes into a tetramer.

Cartilage proteoglycans. Assembly with hyaluronate and link protein as studied by electron microscopy

Aggregates formed by the interaction of cartilage proteoglycan monomers and fragments thereof with hyaluronate were studied by electron microscopy by use of rotary shadowing [Wiedemann, Paulsson, Timpl, Engel & Heinegård (1984) Biochem. J. 224, 331-333]. The differences in shape and packing of the proteins bound along the hyaluronate strand in aggregates formed in the presence and in the absence of link protein were examined in detail. The high resolution of the method allowed examination of the involvement in hyaluronate binding of the globular core-protein domains G1, G2 and G3 [Wiedemann, Paulsson, Timpl, Engel & Heinegård (1984) Biochem. J. 224, 331-333; Paulsson, Mörgelin, Wiedemann, Beardmore-Gray, Dunham, Hardingham, Heinegård, Timpl & Engel (1987) Biochem. J. 245, 763-772]. Fragments comprising the globular hyaluronate-binding region G1 form complexes with hyaluronate with an appearance of necklace-like structures, statistically interspaced by free hyaluronate strands. The closest centre-to-centre distance found between adjacent G1 domains was 12 nm. Another fragment comprising the binding region G1 and the adjacent second globular domain G2 attaches to hyaluronate only by one globule. Also, the core protein obtained by chondroitinase digestion of proteoglycan monomer binds only by domain G1, with domain G3 furthest removed from the hyaluronate. Globule G1 shows a statistical distribution along the hyaluronate strands. In contrast, when link protein is added, binding is no longer random, but instead uninterrupted densely packed aggregates are formed.

Expression of cartilage-matrix genes and localization of their translation products in the embryonic chick eye

The presence of cartilage-matrix molecules in the embryonic chick eye was shown by means of measuring RNA expression and immunostaining studies. The molecules examined were proteoglycan core protein (PG-core), link protein (LP), cartilage-matrix protein (CMP) and type II collagen. The genes encoding these proteins are expressed in 8- to 11-day embryonic chick eyes at constant steady-state levels. Immunopositive stained tissues include sclera, choroid, cornea, lens capsule (PG-core, LP, CMP), lens epithelium, lens fibers (LP, CMP) and the membranes in the retina (LP). In addition, data from comparative studies employing the eyes from the proteoglycan core-protein-deficient mutant, nanomelia, indicate that levels of mRNA for core protein are almost absent and that CMP is reduced in the above-mentioned tissues.

A human mannose-binding protein is an acute-phase reactant that shares sequence homology with other vertebrate lectins

Mannose-binding proteins have been isolated from the liver of rats and humans and subsequently been found in the serum of rats, rabbits, and humans. We report the isolation of cDNA clones isolated from a human liver cDNA library that encodes a human mannose-binding protein. The primary structure has three domains: (a) an NH2-terminal cysteine-rich segment of 19 amino acids which appears to be involved in the formation of interchain disulfide bonds that would stabilize multimeric forms of the protein; (b) a collagen-like region consisting of 19 repeats of the sequence Gly-x-y; and (c) a COOH-terminal putative carbohydrate-binding domain consisting of 148 residues. This human mannose-binding protein bears 51% overall homology (allowing three gaps) with a rat mannose-binding protein C and 48% homology (allowing seven gaps) with a rat mannose-binding protein A. Like these homologous rat proteins, the human mannose-binding protein COOH-terminal sequences are homologous to the carbohydrate recognition portion of several other lectin-like proteins including mammalian hepatic receptors, an insect-soluble hemolymph, and a sea urchin lectin found in coelomic fluid. The apoproteins of dog and human surfactant and the human lymphocyte IgE Ec receptor have not been shown to have lectin-like properties, yet by homology are members of this family of lectin-like proteins. The human mannose-binding protein is preceded by a typical hydrophobic signal sequence and its hepatic secretion is induced as part of the acute-phase response consistent with its probable role in host defense.

Cloning of the mycobacterial epitope recognized by T lymphocytes in adjuvant arthritis

Adjuvant arthritis (AA) is a chronic disease inducible in rats by immunization with an antigen of Mycobacterium tuberculosis. After the isolation of arthritogenic T-cell lines and clones, it became possible to demonstrate that the critical M. tuberculosis antigen contained an epitope cross-reactive with a self-antigen in joint cartilage. Like AA rats, patients suffering from rheumatoid arthritis demonstrated specific T-lymphocyte reactivity to the M. tuberculosis fraction containing the cross-reactive epitope. To characterize the critical M. tuberculosis epitope we used AA T-cell clones to screen mycobacterial antigens expressed in Escherichia coli and genetically engineered truncated proteins and synthetic peptides. The AA T-cell clones recognized an epitope formed by the amino acids at positions 180-188 in the sequence of a Mycobacterium bovis BCG antigen. Administration of this antigen to rats induced resistance to subsequent attempts to produce AA.

Molecular structure of the gene and the 5'-flanking region of the human lymphocyte immunoglobulin E receptor

Overlapping clones which contain the complete gene encoding the human lymphocyte IgE receptor (MW:45kd; identical with CD23), were isolated from human genomic lambda-libraries. The gene spans approximately 13kb and comprises 11 exons. The 5'-end of the mRNA was mapped by primer extension and S1-mapping, revealing two initiation sites for transcription. Two corresponding TATA boxes were identified by sequencing the 5'-flanking region. A 188bp long inverted repeat was found which flanks the promoter region and could possibly be involved in gene regulation. Exons 9 to 11 code for the IgE-binding domain of the receptor which shows homology to several lectins, particularly to the asialoglycoprotein receptor. A comparison of the exon/intron arrangement of these genes implies that their lectin domains have evolved from a common ancestral cassette.

Extended and globular protein domains in cartilage proteoglycans

Electron microscopy after rotary shadowing and negative staining of the large chondroitin sulphate proteoglycan from rat chondrosarcoma, bovine nasal cartilage and pig laryngeal cartilage demonstrated a unique multidomain structure for the protein core. A main characteristic is a pair of globular domains (diameter 6-8 nm), one of which forms the N-terminal hyaluronate-binding region. They are connected by a 25 nm-long rod-like domain of limited flexibility. This segment is continued by a 280 nm-long polypeptide strand containing most chondroitin sulphate chains (average length 40 nm) in a brush-like array and is terminated by a small C-terminal globular domain. The core protein showed a variable extent of degradation, including the loss of the C-terminal globular domain and sections of variable length of the chondroitin sulphate-bearing strand. The high abundance (30-50%) of the C-terminal domain in some extracted proteoglycan preparations indicated that this structure is present in the cartilage matrix rather than being a precursor-specific segment. It may contain the hepatolectin-like segment deduced from cDNA sequences corresponding to the 3'-end of protein core mRNA [Doege, Fernandez, Hassell, Sasaki & Yamada (1986) J. Biol. Chem. 261, 8108-8111; Sai, Tanaka, Kosher & Tanzer (1986) Proc. Natl. Acad. Sci. 83, 5081-5085; Oldberg, Antonsson & Heinegård (1987) Biochem. J. 243, 255-259].

Gene expression of the chondroitin sulfate proteoglycan core protein PG19

We have examined genomic sequences and mRNA species hybridizing to a cDNA clone of a yolk sac carcinoma chondroitin sulfate proteoglycan designated PG19. Genomic blot hybridizations with cDNAs covering the majority of the PG19 mRNA sequence revealed 15 to 17 gene fragments. Similar analysis with probes representing either the propeptide or the combined core protein COOH-terminal domain and 3' untranslated sequences revealed single genomic fragments indicating that a single gene codes for the PG19 proteoglycan. Genomic blot analysis with cDNA sequences coding for the serine-glycine repeat of the core protein identified the same gene fragments observed with the entire PG19 cDNA, indicating that this coding region is homologous with sequences present in multiple genes. The same probes were also used to examine mRNA expression. In addition to the PG19 mRNA, several PG19-related mRNAs could be seen. These PG19-related mRNAs had homology with the serine-glycine coding sequence of the PG19 cDNA. These mRNAs may be coding for proteoglycans. The mRNA coding for PG19 appeared to be uniquely expressed in parietal yolk sac and mast cell lineages. The PG19 mRNA existed in different forms in parietal yolk sac and mast cell lines due to cell-type-specific differences in the length of the 5' untranslated sequences. These results indicate that expression of the PG19 proteoglycan gene is regulated both in terms of cell-type-specific transcription and selection of a transcriptional start site.

The partial amino acid sequence of bovine cartilage proteoglycan, deduced from a cDNA clone, contains numerous Ser-Gly sequences arranged in homologous repeats

We have determined the sequence of a partial cDNA clone encoding the C-terminal region of bovine cartilage aggregating proteoglycan core protein. The deduced amino acid sequence contains a cysteine-rich region which is homologous with chicken hepatic lectin. This lectin-homologous region has previously been identified in rat and chicken cartilage proteoglycan. The bovine sequence presented here is highly homologous with the rat and chicken amino acid sequences in this apparently globular region. A region containing clusters of Ser-Gly sequences is located N-terminal to the lectin homology domain. These Ser-Gly-rich segments are arranged in tandemly repeated, approx. 100-residue-long, homology domains. Each homology domain consists of an approx. 75-residue-long Ser-Gly-rich region separated by an approx. 25-residue-long segment lacking Ser-Gly dipeptides. These dipeptides are arranged in 10-residue-long segments in the 100-residue-long homology domains. The shorter homologous segments are tandemly repeated some six times in each 100-residue-long homology domain. Serine residues in these repeats are potential attachment sites for chondroitin sulphate chains.

Gene expression of the chondroitin sulfate proteoglycan core protein PG19

We have examined genomic sequences and mRNA species hybridizing to a cDNA clone of a yolk sac carcinoma chondroitin sulfate proteoglycan designated PG19. Genomic blot hybridizations with cDNAs covering the majority of the PG19 mRNA sequence revealed 15 to 17 gene fragments. Similar analysis with probes representing either the propeptide or the combined core protein COOH-terminal domain and 3' untranslated sequences revealed single genomic fragments indicating that a single gene codes for the PG19 proteoglycan. Genomic blot analysis with cDNA sequences coding for the serine-glycine repeat of the core protein identified the same gene fragments observed with the entire PG19 cDNA, indicating that this coding region is homologous with sequences present in multiple genes. The same probes were also used to examine mRNA expression. In addition to the PG19 mRNA, several PG19-related mRNAs could be seen. These PG19-related mRNAs had homology with the serine-glycine coding sequence of the PG19 cDNA. These mRNAs may be coding for proteoglycans. The mRNA coding for PG19 appeared to be uniquely expressed in parietal yolk sac and mast cell lineages. The PG19 mRNA existed in different forms in parietal yolk sac and mast cell lines due to cell-type-specific differences in the length of the 5' untranslated sequences. These results indicate that expression of the PG19 proteoglycan gene is regulated both in terms of cell-type-specific transcription and selection of a transcriptional start site.