Purification and characterization of a small dermatan sulphate proteoglycan implicated in the dilatation of the rat uterine cervix

Site-specific glycosylation of proteoglycans: a revisited frontier in proteoglycan research

Proteoglycans (PGs), a class of carbohydrate-modified proteins, are present in essentially all metazoan organisms investigated to date. PGs are composed of glycosaminoglycan (GAG) chains attached to various core proteins and are important for embryogenesis and normal homeostasis. PGs exert many of their functions via their GAG chains and understanding the details of GAG-ligand interactions has been an essential part of PG research. Although PGs are also involved in many diseases, the number of GAG-related drugs used in the clinic is yet very limited, indicating a lack of detailed structure-function understanding. Structural analysis of PGs has traditionally been obtained by first separating the GAG chains from the core proteins, after which the two components are analyzed separately. While this strategy greatly facilitates the analysis, it precludes site-specific information and introduces either a "GAG" or a "core protein" perspective on the data interpretation. Mass-spectrometric (MS) glycoproteomic approaches have recently been introduced, providing site-specific information on PGs. Such methods have revealed a previously unknown structural complexity of the GAG linkage regions and resulted in identification of several novel CSPGs and HSPGs in humans and in model organisms, thereby expanding our view on PG complexity. In light of these findings, we discuss here if the use of such MS-based techniques, in combination with various functional assays, can also be used to expand our functional understanding of PGs. We have also summarized the site-specific information of all human PGs known to date, providing a theoretical framework for future studies on site-specific functional analysis of PGs in human pathophysiology.

Biochemical and biomechanical analysis of tendons of caged and penned chickens

Chickens were divided into two groups, one caged and the other penned. Superficial digital flexor tendons from penned chickens showed greater tensile strength, withstanding a greater strain before rupture than tendons from caged chickens. The tensile region of tendons from penned chickens showed more swelling in acetic acid and a higher hydroxyproline concentration compared with caged chickens, indicating the presence of large collagen amounts in the former. The tensile region of penned chickens presented higher glycosaminoglycan concentrations than the same region of caged chickens. For both groups, the predominant glycosaminoglycan in the compression regions was chondroitin sulfate, whereas dermatan sulfate was found in the tensile regions. N-terminal analysis identified the small proteoglycans fibromodulin and decorin. SDS-PAGE indicated that decorin was present in all regions and fibromodulin was mainly observed in the tensile region. These results indicate that an external condition, in this case the area available for locomotion, might influence the synthesis of extracellular matrix components and the mechanical properties of the tendon.

Super-motifs and evolution of tandem leucine-rich repeats within the small proteoglycans--biglycan, decorin, lumican, fibromodulin, PRELP, keratocan, osteoadherin, epiphycan, and osteoglycin

Leucine-rich repeats (LRRs) with 20-30 amino acids in unit length are present in many proteins from prokaryotes to eukaryotes. The LRR-containing proteins include a family of nine small proteoglycans, forming three distinct subfamilies: class I contains biglycan/PG-I and decorin/PG-II; class II: lumican, fibromodulin, PRELP, keratocan, and osteoadherin; and class III: epiphycan/PG-Lb and osteoglycin or osteoinductive factor. Comparative sequence analysis of the 34 available protein sequences reveals that these proteoglycans have two types of LRRs, which we call S and T. The type S LRR is 21 residues long and has the consensus sequence of xxaPzxLPxxLxxLxLxxNxI. The type T LRR has 26 residues; its consensus sequence is zzxxaxxxxFxxaxxLxxLxLxxNxL. In both "x" indicates variable residue; "z" is frequently a gap; "a" is Val, Leu, or Ile; and I is Ile or Leu. These type S and TLRRs are ordered into two super-motifs--STT with about 73 residues in classes I and II and ST with about 47 residues in class III. The 12 LRRs in the small proteoglycans of I and II are best represented as (STT)4; the seven LRRs of class III as (ST)T(ST)2. Our analyses indicate that classes I/II and III evolved along different paths after the establishment of the precursor ST, and classes I and II also diverged after the establishment of the precursor (STT)4.

Immortalized, cloned mouse chondrocytic cells (MC615) produce three different matrix proteoglycans with core-protein-specific chondroitin/dermatan sulphate structures

Cloned immortalized MC615 mouse chondrocytic cells were used to examine their capability to produce multiple types of matrix proteoglycans. Immunofluorescence staining indicated a uniform expression of aggrecan, biglycan and decorin by all cells. After culture with [35S]sulphate, proteo[35S]glycans secreted by the cells were found to elute in two peaks from a Sepharose CL-4B column. The first peak, at the void volume of the column, contained a large proteoglycan with an estimated average hydrodynamic mass of 10(3) kDa. The glycosaminoglycan chains of this proteoglycan had an average hydrodynamic size of 17 kDa, estimated by Sepharose CL-6B chromatography, indicating the presence of 30-70 glycosaminoglycan chains per core protein, which was consistent with the characteristics of aggrecan. Biglycan and decorin were immunoisolated from the second Sepharose CL-4B peak, and had average glycosaminoglycan hydrodynamic sizes of approx. 25 kDa and 32 kDa respectively. Glycosaminoglycan chains of the aggrecan, biglycan and decorin were treated with chondroitin ABC lyase, chondroitin AC lyase and chondroitin B lyase to determine the positions of sulphation and the degree of uronic acid epimerization. The aggrecan glycosaminoglycan chains were found to contain a 4-sulphate/6-sulphate ratio of 7:3, with no epimerization of glucuronic acid to iduronic acid. The biglycan glycosaminoglycan chains were found to contain a similar ratio of 4-sulphate/6-sulphate, but with approx. 40-45% of the glucuronic acid epimerized to iduronic acid. The decorin glycosaminoglycan chains were found to contain 4-sulphate but no detectable 6-sulphate, and approx. 30-35% epimerization of the glucuronic acid to iduronic acid. The results, using these cloned cells, indicated that a single MC615 cell is able to make all three proteoglycans with distinctive differences between the glycosaminoglycans of aggrecan, biglycan and decorin. These data indicate that a mechanism must exist for a single MC615 cell to regulate the sizes and fine structures of glycosaminoglycans on simultaneously produced, different proteoglycans in a core-protein-specific manner.

Amino-terminal deletions in the decorin core protein leads to the biosynthesis of proteoglycans with shorter glycosaminoglycan chains

Analysis of the N-terminal sequence of decorin purified from connective tissues and comparison with the sequence deduced from the cDNA indicate that the nascent proteoglycan has a 14 amino acid residue N-terminal propeptide. Mammalian expression vectors encoding wild-type decorin and decorin with deletions in the propeptide were used to transform COS and CHO cells. Cells transformed with vectors encoding deletion variants of decorin synthesize proteoglycans with shorter galactosaminoglycan chains than cells transformed with wild-type decorin. This effect on the polysaccharide chain length may be due to a lower affinity between the core protein and the glycosyltransferases synthesizing the linkage region. Alternatively, the deletions may affect the intracellular transport of decorin. An antiserum prepared against the N-terminal propeptide immunoprecipitated decorin secreted by cultured cells, showing that decorin is exported with the N-terminal region intact.

Altered proteoglycan gene expression and the tumor stroma

Tumor stroma is a specialized form of tissue that is associated with epithelial neoplasms. Recent evidence indicates that significant changes in proteoglycan content occur in the tumor stroma and that these alterations could support tumor progression and invasion as well as tumor growth. Our main hypothesis is that the generation of tumor stroma is under direct control of the neoplastic cells and that, via a feedback loop, altered proteoglycan gene expression would influence the behavior of tumor cells. In this review, we will focus primarily on the work from our laboratory related to the altered expression of chondroitin sulfate proteoglycan and its role in tumor development and progression. The connective tissue stroma of human colon cancer is enriched in chondroitin sulfate and the stromal cell elements, primarily colon fibroblasts and smooth muscle cells, are responsible for this biosynthetic increase. These changes can be reproduced in vitro by using either tumor metabolites or co-cultures of human colon carcinoma cells and colon mesenchymal cells. The levels of decorin, a leucine-rich proteoglycan involved in the regulation of matrix assembly and cell proliferation, are markedly elevated in the stroma of colon carcinoma. These changes correlate with a marked increase in decorin mRNA levels and a concurrent hypomethylation of decorin gene, a DNA alteration associated with enhanced gene expression. Elucidation of decorin gene structure has revealed an unexpected degree of complexity in the 5' untranslated region of the gene with two leader exons that are alternatively spliced to the second coding exon. Furthermore, a transforming growth factor beta (TGF-beta)-negative element is present in the promotor region of decorin gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered proteoglycan gene expression and the tumor stroma

Tumor stroma is a specialized form of tissue that is associated with epithelial neoplasms. Recent evidence indicates that significant changes in proteoglycan content occur in the tumor stroma and that these alterations could support tumor progression and invasion as well as tumor growth. Our main hypothesis is that the generation of tumor stroma is under direct control of the neoplastic cells and that, via a feedback loop, altered proteoglycan gene expression would influence the behavior of tumor cells. In this review, we will focus primarily on the work from our laboratory related to the altered expression of chondroitin sulfate proteoglycan and its role in tumor development and progression. The connective tissue stroma of human colon cancer is enriched in chondroitin sulfate and the stromal cell elements, primarily colon fibroblasts and smooth muscle cells, are responsible for this biosynthetic increase. These changes can be reproduced in vitro by using either tumor metabolites or co-cultures of human colon carcinoma cells and colon mesenchymal cells. The levels of decorin, a leucine-rich proteoglycan involved in the regulation of matrix assembly and cell proliferation, are markedly elevated in the stroma of colon carcinoma. These changes correlate with a marked increase in decorin mRNA levels and a concurrent hypomethylation of decorin gene, a DNA alteration associated with enhanced gene expression. Elucidation of decorin gene structure has revealed an unexpected degree of complexity in the 5' untranslated region of the gene with two leader exons that are alternatively spliced to the second coding exon.(ABSTRACT TRUNCATED AT 250 WORDS)

cDNA sequence for rat dermatan sulfate proteoglycan-II (decorin)

A cDNA clone for dermatan sulfate proteoglycan-II, or decorin, has been isolated from a rat uterus library and sequenced. The cDNA and deduced amino acid sequences are 79 and 77% identical to the previously reported human and bovine sequences, respectively. The rat protein contains potential attachment sites for two glycosaminoglycan chains and four N-linked oligosaccharides, six conserved cysteine residues and multiple repeats of a leucine-rich sequence, LXXLXLXXNXL/I. Overlapping the C-end of one of these repeats is an NKISK sequence, which has been implicated in binding to fibronectin.

Proteoglycan synthesis in human skin and burn scar explant cultures

The synthesis of proteoglycans (PG) by normal human skin, and normal and hypertrophic scars were compared using tissue explants in culture. Newly synthesized PG were labelled with [35S]Na2SO4. Significant differences were found in the proportion of [35S]-radio-labelled incorporation of PG in the tissue and accumulation of [35S]PG in culture medium in the different tissues. The rate of PG biosynthesis in all three tissue types occurred in two phases. There was an initial phase of PG synthesis occurring at 0-3 h and a later phase that occurred at 3-18 h [35S]-labelled PG were isolated and characterized by Sepharose CL-6B chromatography and cellulose acetate electrophoresis. The results showed that the hypertrophic scar tissue and its culture medium contained higher proportions of dermatan sulphate (DS), chondroitin sulphate (CS) and DS' PG than the normal skin fractions. These results suggest that abnormal scarring is related to a change in the level of PG synthesis during the burn injury repair process.

Effects of hormonal perturbations on the small dermatan sulfate proteoglycan and mechanical properties of the uterine cervix of late pregnant rats

Rats at 16-18 days of pregnancy were treated with various hormones in attempts to accelerate cervical softening and dilatation. Mechanical properties and biochemical components of the extracellular matrix were quantified at day 19. PGF2 alpha treatment significantly increased cervical wet weight, inner circumference, total amount and concentration of small dermatan sulfate proteoglycan, and the ratio of small proteoglycan to collagen; it decreased the concentration of collagen. Fluprostenol increased the extensibility and the rate of creep and decreased the collagen concentration. The progesterone antagonist ZK 98.734 (11 beta-(4-dimethylaminophenyl)-17 beta-hydroxy-17 alpha-(3-hydroxy-prop-(Z)- enyl)-4,9,(10)-estradiene-3-one) increased the inner circumference and the ratio of small proteoglycan to collagen; it decreased the collagen concentration. Treatment with 17 beta-estradiol increased the amount of medium-sized proteoglycans and decreased the concentration of the small proteoglycan. The results support the hypothesis advanced in our earlier study that the inner circumference of the cervix, a measure of dilatation, is dependent upon the ratio of small dermatan sulfate proteoglycan-II (decorin) to collagen. These studies also suggest that changes in the inner circumference and the extensibility of the cervix involve two distinct processes of connective tissue alteration.

The physiology of cervical ripening and cervical dilatation and the effect of abortifacient drugs

The mechanical properties of the human uterine cervix are determined mainly by the connective tissue component, whereas it is doubtful whether the scanty smooth muscle component is of any physiological importance. Histological and biochemical analyses reveal a fibrous connective tissue similar to that found in skin and tendon. Degradation of the collagen and an increase in some special dermatan sulphate proteoglycans can at least partly explain the pregnancy-associated softening of this connective tissue. Relatively high oestrogen levels seem to be an absolute condition for the process, even when it is induced pharmacologically. Treatment with progesterone-receptor blockers, PGE2, PGF2 alpha or relaxin in pregnancy induce cervical softening as well as histological and biochemical changes which cannot be distinguished from the physiological cervical softening which takes place in late pregnancy. Prostaglandins and relaxin might interact and could include cytokines such as interleukin-1 during the process. The effect of cervical tents cannot be explained only by the radial pressures they exert. Most probably stimulation of local prostaglandin synthesis is also involved.