Molecular cloning and expression of human chondroitin 6-sulfotransferase

Advances and challenges in biotechnological production of chondroitin sulfate and its oligosaccharides

Chondroitin sulfate (CS) is a member of glycosaminoglycans (GAGs) and has critical physiological functions. CS is widely applied in medical and clinical fields. Currently, the supply of CS relies on traditional animal tissue extraction methods. From the perspective of medical applications, the biggest drawback of animal-derived CS is its uncontrollable molecular weight and sulfonated patterns, which are key factors affecting CS activities. The advances of cell-free enzyme catalyzed systems and de novo biosynthesis strategies have paved the way to rationally regulate CS sulfonated pattern and molecular weight. In this review, we first present a general overview of biosynthesized CS and its oligosaccharides. Then, the advances in chondroitin biosynthesis, 3'-phosphoadenosine-5'-phosphosulfate (PAPS) synthesis and regeneration, and CS biosynthesis catalyzed by sulfotransferases are discussed. Moreover, the progress of mining and expression of chondroitin depolymerizing enzymes for preparation of CS oligosaccharides is also summarized. Finally, we analyze and discuss the challenges faced in synthesizing CS and its oligosaccharides using microbial and enzymatic methods. In summary, the biotechnological production of CS and its oligosaccharides is a promising method in addressing the drawbacks associated with animal-derived CS and enabling the production of CS oligosaccharides with defined structures.

A Chinese case of CHST3-related skeletal dysplasia and a systematic review

PURPOSE

We reported a case with carbohydrate sulfotransferase 3 (CHST3) spondyloepiphyseal dysplasia and made a systematic review of all previously reported cases.

METHODS

A 14.8-year-old boy underwent clinical, radiological, and genetic evaluations. The patients and five age-matched healthy boys accepted high-resolution peripheral quantitative computed tomography evaluation. All CHST3-related skeletal dysplasia cases from PubMed and Embase were collected and summarized. The genotype-phenotype correlation was analyzed.

RESULTS

The proband complained of aggravated joint pain and had a compression fracture of L2 during his second decade. Physical examination showed a height Z score of -4.94, short limbs, and restricted movement of the elbows and knees. X-rays showed carpal epiphyseal dysplasia, enlargement of elbow and knee joints, and subluxation of the left hip. Echocardiography showed abnormal cardiac valves. Compared with the norm, his total and trabecular volumetric bone mineral density (BMD), and the microarchitecture of the trabecular bone had trends to be worse at the distal radius and tibia. Two novel missense variants of c.1343T>G and c.761C>G in CHST3 were inherited from his father and mother, respectively. In the systematic review, short stature, limited joint extension, joint pain, and joint dislocation were the most common characteristics of this disorder. Height Z score and the proportion of hearing impairment had no significant differences between the missense and nonmissense mutations groups.

CONCLUSION

Progressive joint pain and movement restriction are the main characteristics of CHST3-related skeletal dysplasia. BMD and bone microarchitecture of this disorder needs further exploration. There is no apparent genotype-phenotype correlation in this disorder.

Identification of N-Glycoproteins of Knee Cartilage from Adult Osteoarthritis and Kashin-Beck Disease Based on Quantitative Glycoproteomics, Compared with Normal Control Cartilage

Glycoproteins are involved in the development of many diseases, while the type and content of N-glycoproteins in the cartilage of osteoarthritis (OA) and Kashin-Beck disease (KBD) are still unclear. This research aims to identify N-glycoproteins in knee cartilage patients with OA and KBD compared with normal control (N) adults. The cartilage samples were collected from gender- and age-matched OA (n = 9), KBD (n = 9) patients, and N (n = 9) adults. Glycoproteomics and label-free liquid chromatography-tandem mass spectrometry (LC-MS/MS) obtained N-glycoproteins of KBD and OA. A total of 594 N-glycoproteins and 1146 N-glycosylation peptides were identified. The identified data were further compared and analyzed with Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Protein-Protein Interactions (PPI). Pairwise comparison of the glycoproteins detected in the three groups showed that integrin beta-1 (ITGB1), collagen alpha-1 (II) chain (COL2A1), collagen alpha-1 (VII) chain (COL7A1), carbohydrate sulfotransferase 3 (CHST-3), carbohydrate sulfotransferase 4 (CHST-4), thrombospondin 2 (THBS2), bone morphogenetic protein 8A (BMP8A), tenascin-C (TNC), lysosome-associated membrane protein (LAMP2), and beta-glucuronidase (GUSB) were significantly differentially expressed. GO results suggested N-glycoproteins mainly belonged to protein metabolic process, single-multicellular and multicellular organism process, cell adhesion, biological adhesion, and multicellular organism development. KEGG and PPI results revealed that key N-glycoproteins were closely related to pathways for OA and KBD, such as phagosome, ECM-receptor interaction, lysosome, focal adhesion, protein digestion, and absorption. These results reflected glycoprotein expression for OA and KBD in the process of ECM degradation, material transport, cell-cell or cell-ECM interaction, and information transduction. These key significantly differentially expressed N-glycoproteins and pathways lead to the degeneration and degradation of the cartilage of OA and KBD mainly by disrupting the synthesis and catabolism of basic components of ECM and chondrocytes and interfering with the transfer of material or information. The key N-glycoproteins or pathways in this research are potential targets for pathological mechanisms and therapies of OA and KBD.

Preliminary study of the gene expression of sulfation and degradation enzymes for chondroitin sulfate in glycerol-treated C2C12 myoblast cells

In this study, we induced chemical damage of C2C12 myoblasts that had differentiated into myotubes with glycerol, and four sulfation enzymes for chondroitin sulfate (CS) [carbohydrate sulfotransferase (Chst) 12, Chst15 and Chst3 and uronyl 2-O-sulfotransferase (UST)] and two CS degradation enzymes [hyaluronidase (Hyal) 1 and Hyal2] were examined for changes in gene expression. Treatment of myoblasts with 5% glycerol significantly increased the expression levels of the sulfation enzymes Chst12 and Chst15 and the degradation enzymes Hyal1 and Hyal2. However, the expression levels of the other two genes (Chst3 and Ust) showed no change. Differences in the expression levels of these enzymes may help to understand the difference in responsiveness of myoblasts to glycerol after muscle injury in vivo or in vitro.

Installation of O-glycan sulfation capacities in human HEK293 cells for display of sulfated mucins

The human genome contains at least 35 genes that encode Golgi sulfotransferases that function in the secretory pathway, where they are involved in decorating glycosaminoglycans, glycolipids, and glycoproteins with sulfate groups. Although a number of important interactions by proteins such as selectins, galectins, and sialic acid–binding immunoglobulin-like lectins are thought to mainly rely on sulfated O-glycans, our insight into the sulfotransferases that modify these glycoproteins, and in particular GalNAc-type O-glycoproteins, is limited. Moreover, sulfated mucins appear to accumulate in respiratory diseases, arthritis, and cancer. To explore further the genetic and biosynthetic regulation of sulfated O-glycans, here we expanded a cell-based glycan array in the human embryonic kidney 293 (HEK293) cell line with sulfation capacities. We stably engineered O-glycan sulfation capacities in HEK293 cells by site-directed knockin of sulfotransferase genes in combination with knockout of genes to eliminate endogenous O-glycan branching (core2 synthase gene GCNT1) and/or sialylation capacities in order to provide simplified substrates (core1 Galβ1–3GalNAcα1–O-Ser/Thr) for the introduced sulfotransferases. Expression of the galactose 3-O-sulfotransferase 2 in HEK293 cells resulted in sulfation of core1 and core2 O-glycans, whereas expression of galactose 3-O-sulfotransferase 4 resulted in sulfation of core1 only. We used the engineered cell library to dissect the binding specificity of galectin-4 and confirmed binding to the 3-O-sulfo-core1 O-glycan. This is a first step toward expanding the emerging cell-based glycan arrays with the important sulfation modification for display and production of glycoconjugates with sulfated O-glycans.

An Overview of in vivo Functions of Chondroitin Sulfate and Dermatan Sulfate Revealed by Their Deficient Mice

Chondroitin sulfate (CS), dermatan sulfate (DS) and heparan sulfate (HS) are covalently attached to specific core proteins to form proteoglycans in their biosynthetic pathways. They are constructed through the stepwise addition of respective monosaccharides by various glycosyltransferases and maturated by epimerases as well as sulfotransferases. Structural diversities of CS/DS and HS are essential for their various biological activities including cell signaling, cell proliferation, tissue morphogenesis, and interactions with a variety of growth factors as well as cytokines. Studies using mice deficient in enzymes responsible for the biosynthesis of the CS/DS and HS chains of proteoglycans have demonstrated their essential functions. Chondroitin synthase 1-deficient mice are viable, but exhibit chondrodysplasia, progression of the bifurcation of digits, delayed endochondral ossification, and reduced bone density. DS-epimerase 1-deficient mice show thicker collagen fibrils in the dermis and hypodermis, and spina bifida. These observations suggest that CS/DS are essential for skeletal development as well as the assembly of collagen fibrils in the skin, and that their respective knockout mice can be utilized as models for human genetic disorders with mutations in chondroitin synthase 1 and DS-epimerase 1. This review provides a comprehensive overview of mice deficient in CS/DS biosyntheses.

Congenital Disorders of Deficiency in Glycosaminoglycan Biosynthesis

Glycosaminoglycans (GAGs) including chondroitin sulfate, dermatan sulfate, and heparan sulfate are covalently attached to specific core proteins to form proteoglycans, which are distributed at the cell surface as well as in the extracellular matrix. Proteoglycans and GAGs have been demonstrated to exhibit a variety of physiological functions such as construction of the extracellular matrix, tissue development, and cell signaling through interactions with extracellular matrix components, morphogens, cytokines, and growth factors. Not only connective tissue disorders including skeletal dysplasia, chondrodysplasia, multiple exostoses, and Ehlers-Danlos syndrome, but also heart and kidney defects, immune deficiencies, and neurological abnormalities have been shown to be caused by defects in GAGs as well as core proteins of proteoglycans. These findings indicate that GAGs and proteoglycans are essential for human development in major organs. The glycobiological aspects of congenital disorders caused by defects in GAG-biosynthetic enzymes including specific glysocyltransferases, epimerases, and sulfotransferases, in addition to core proteins of proteoglycans will be comprehensively discussed based on the literature to date.

Chondroitin sulfate in tissue remodeling: Therapeutic implications for pulmonary fibrosis

Fibrosis is characterized by the deposition of extracellular matrix (ECM) proteins, while idiopathic pulmonary fibrosis (IPF) is a chronic respiratory disease characterized by dysregulated tissue repair and remodeling. Anti-inflammatory drugs, such as corticosteroids and immunosuppressants, and antifibrotic drugs, like pirfenidone and nintedanib, are used in IPF therapy. However, their limited effects suggest that single mediators are inadequate to control IPF. Therefore, therapies targeting the multifactorial cascades that regulate tissue remodeling in fibrosis could provide alternate solutions. ECM molecules have been shown to modulate various biological functions beyond tissue structure support and thus, could be developed into novel therapeutic targets for modulating tissue remodeling. Among ECM molecules, glycosaminoglycans (GAG) are linear polysaccharides consisting of repeated disaccharides, which regulate cell-matrix interactions. Chondroitin sulfate (CS), one of the major GAGs, binds to multifactorial mediators in the ECM and reportedly participates in tissue remodeling in various diseases; however, to date, its biological functions have drawn considerably less attention than other GAGs, like heparan sulfate. In the present review, we discuss the involvement and regulation of CS in tissue remodeling and pulmonary fibrotic diseases, its role in pulmonary fibrosis, and the therapeutic approaches targeting CS.

Research and Application of Chondroitin Sulfate/Dermatan Sulfate-Degrading Enzymes

Chondroitin sulfate (CS) and dermatan sulfate (DS) are widely distributed on the cell surface and in the extracellular matrix in the form of proteoglycan, where they participate in various biological processes. The diverse functions of CS/DS can be mainly attributed to their high structural variability. However, their structural complexity creates a big challenge for structural and functional studies of CS/DS. CS/DS-degrading enzymes with different specific activities are irreplaceable tools that could be used to solve this problem. Depending on the site of action, CS/DS-degrading enzymes can be classified as glycosidic bond-cleaving enzymes and sulfatases from animals and microorganisms. As discussed in this review, a few of the identified enzymes, particularly those from bacteria, have wildly applied to the basic studies and applications of CS/DS, such as disaccharide composition analysis, the preparation of bioactive oligosaccharides, oligosaccharide sequencing, and potential medical application, but these do not fulfill all of the needs in terms of the structural complexity of CS/DS.

Role of Chondroitin Sulfation Following Spinal Cord Injury

Traumatic spinal cord injury produces long-term neurological damage, and presents a significant public health problem with nearly 18,000 new cases per year in the U.S. The injury results in both acute and chronic changes in the spinal cord, ultimately resulting in the production of a glial scar, consisting of multiple cells including fibroblasts, macrophages, microglia, and reactive astrocytes. Within the scar, there is an accumulation of extracellular matrix (ECM) molecules—primarily tenascins and chondroitin sulfate proteoglycans (CSPGs)—which are considered to be inhibitory to axonal regeneration. In this review article, we discuss the role of CSPGs in the injury response, especially how sulfated glycosaminoglycan (GAG) chains act to inhibit plasticity and regeneration. This includes how sulfation of GAG chains influences their biological activity and interactions with potential receptors. Comprehending the role of CSPGs in the inhibitory properties of the glial scar provides critical knowledge in the much-needed production of new therapies.

Reconstruction of the Carbohydrate 6-O Sulfotransferase Gene Family Evolution in Vertebrates Reveals Novel Member, CHST16, Lost in Amniotes

Glycosaminoglycans are sulfated polysaccharide molecules, essential for many biological processes. The 6-O sulfation of glycosaminoglycans is carried out by carbohydrate 6-O sulfotransferases (C6OSTs), previously named Gal/GalNAc/GlcNAc 6-O sulfotransferases. Here, for the first time, we present a detailed phylogenetic reconstruction, analysis of gene synteny conservation and propose an evolutionary scenario for the C6OST family in major vertebrate groups, including mammals, birds, nonavian reptiles, amphibians, lobe-finned fishes, ray-finned fishes, cartilaginous fishes, and jawless vertebrates. The C6OST gene expansion likely started early in the chordate lineage, giving rise to four ancestral genes after the divergence of tunicates and before the emergence of extant vertebrates. The two rounds of whole-genome duplication in early vertebrate evolution (1R/2R) only contributed two additional C6OST subtype genes, increasing the vertebrate repertoire from four genes to six, divided into two branches. The first branch includes CHST1 and CHST3 as well as a previously unrecognized subtype, CHST16 that was lost in amniotes. The second branch includes CHST2, CHST7, and CHST5. Subsequently, local duplications of CHST5 gave rise to CHST4 in the ancestor of tetrapods, and to CHST6 in the ancestor of primates. The teleost-specific gene duplicates were identified for CHST1, CHST2, and CHST3 and are result of whole-genome duplication (3R) in the teleost lineage. We could also detect multiple, more recent lineage-specific duplicates. Thus, the vertebrate repertoire of C6OST genes has been shaped by gene duplications and gene losses at several stages of vertebrate evolution, with implications for the evolution of skeleton, nervous system, and cell-cell interactions.

[Hereditary Skeletal and Skin Disorders Caused by Defects in the Biosynthesis of Chondroitin/Dermatan Sulfate, and Molecular Mechanisms of Pulmonary Metastasis]

The roles of chondroitin sulfate (CS) and dermatan sulfate (DS) have been demonstrated in various biological events such as the construction of the extracellular matrix, tissue development, and cell signaling through interactions with extracellular matrix components, morphogens, and growth factors. Human genetic diseases, including skeletal abnormalities, connective tissue diseases, and heart defects, were reported to be caused by mutations in the genes encoding glycosyltransferases, epimerases, and sulfotransferases that are responsible for the biosynthesis of CS and DS. Glycobiological approaches revealed that mutations in CS- and DS-biosynthetic enzymes led to reductions in their enzymatic activities and in the levels of CS and DS. Furthermore, CS at the surface of tumor cells plays a key role in pulmonary metastasis. A receptor for advanced glycation end-products (RAGE) was predominantly expressed in the lung, and was identified as a functional receptor for CS chains. CS and anti-RAGE antibodies inhibited the pulmonary metastasis of not only Lewis lung carcinoma but also B16 melanoma cells. Hence, RAGE and CS are potential targets of drug discovery for pulmonary metastasis and a number of other pathological conditions involving RAGE in the pathogenetic mechanism. This review provides an overview of glycobiological studies on characterized genetic disorders caused by the impaired biosynthesis of CS, as well as DS, and on the pulmonary metastasis of Lewis lung carcinoma cells involving CS and RAGE.

Sulfation pattern of chondroitin sulfate in human osteoarthritis cartilages reveals a lower level of chondroitin-4-sulfate

Chondroitin sulfates (CS) account for more than 80% of the glycosaminoglycans of articular cartilage, which impart its physiological functions. We quantified the absolute concentration of the CS components of the full thickness cartilages from the knees of patients with terminal-phase osteoarthritis. Osteochondrol biopsies were removed from the medial femoral condyle and lateral femoral condyle of sixty female patients received total knee arthroplasty, aged from 58 to 83 years old. We found the total CS concentrations and chondroitin-4-sulfate disaccharide were significantly lowered in osteoarthritic samples. Microstructure analysis indicated while chondroitin-0-sulfate was equally distributed across different zones of the osteoarthritic cartilages, chondroitin-4-sulfate is significantly less in the deep zones. Down-regulation of sulfotransferases, the enzymes responsible for CS sulfation, in the lesion site of cartilage were observed. Our study suggested chondroitin-4-sulfate down-regulation can be a diagnostic marker for degraded osteoarthritis cartilage, with potential implications in cartilage regeneration.

Interaction of receptor type of protein tyrosine phosphatase sigma (RPTPσ) with a glycosaminoglycan library

Receptor type of protein tyrosine phosphatase sigma (RPTPσ) functions as a glycosaminoglycan (GAG) receptor of neuronal cells in both the central and peripheral nervous systems. Both chondroitin sulphate (CS) and heparan sulphate (HS) are important constituents of GAG ligands for RPTPσ, although they have opposite effects on neuronal cells. CS inhibits neurite outgrowth and neural regeneration through RPTPσ, whereas HS enhances them. We prepared recombinant RPTPσ N-terminal fragment containing the GAG binding site and various types of biotin-conjugated GAG (CS and HS) with chemical modification and chemo-enzymatic synthesis. Then interaction of the RPTPσ N-terminal fragment was analysed using GAG-biotin immobilized on streptavidin sensor chips by surface plasmon resonance. Interaction of RPTPσ with the CS library was highly correlated to the degree of disulphated disaccharide E unit, which had two sulphate groups at C-4 and C-6 positions of the N-acetylgalactosamine residue (CSE). The optimum molecular mass of CSE was suggested to be approximately 10 kDa. Heparin showed higher affinity to RPTPσ than the CS library. Our GAG library will not only contribute to the fields of carbohydrate science and cell biology, but also provide medical application to regulate neural regeneration.

Sequence determination of synthesized chondroitin sulfate dodecasaccharides

Chondroitin sulfate (CS) is a linear acidic polysaccharide composed of repeating disaccharide units of glucuronic acid and N-acetyl-d-galactosamine. The polysaccharide is modified with sulfate groups at different positions by a variety of sulfotransferases. CS chains exhibit various biological and pathological functions by interacting with cytokines and growth factors and regulating their signal transduction. The fine structure of the CS chain defines its specific biological roles. However, structural analysis of CS has been restricted to disaccharide analysis, hampering the understanding of the structure-function relationship of CS chains. Here, we chemo-enzymatically synthesized CS dodecasaccharides having various sulfate modifications using a bioreactor system of bacterial chondroitin polymerase mutants and various CS sulfotransferases. We developed a sequencing method for CS chains using the CS dodecasaccharides. The method consists of (i) labeling a reducing end with 2-aminopyridine (PA), (ii) partial digestion of CS with testicular hyaluronidase, followed by separation of PA-conjugated oligosaccharides with different chain lengths, (iii) limited digestion of these oligosaccharides with chondroitin lyase AC II into disaccharides, followed by labeling with 2-aminobenzamide, (iv) CS disaccharide analysis using a dual-fluorescence HPLC system (reversed-phase ion-pair and ion-exchange chromatography), and (v) estimation of the composition by calculating individual disaccharide ratios. This CS chain sequencing allows characterization of CS-modifying enzymes and provides a useful tool toward understanding the structure-function relationship of CS chains.

Chondroitin / dermatan sulfate modification enzymes in zebrafish development

Chondroitin/dermatan sulfate (CS/DS) proteoglycans consist of unbranched sulfated polysaccharide chains of repeating GalNAc-GlcA/IdoA disaccharide units, attached to serine residues on specific proteins. The CS/DS proteoglycans are abundant in the extracellular matrix where they have essential functions in tissue development and homeostasis. In this report a phylogenetic analysis of vertebrate genes coding for the enzymes that modify CS/DS is presented. We identify single orthologous genes in the zebrafish genome for the sulfotransferases chst7, chst11, chst13, chst14, chst15 and ust and the epimerase dse. In contrast, two copies were found for mammalian sulfotransferases CHST3 and CHST12 and the epimerase DSEL, named chst3a and chst3b, chst12a and chst12b, dsela and dselb, respectively. Expression of CS/DS modification enzymes is spatially and temporally regulated with a large variation between different genes. We found that CS/DS 4-O-sulfotransferases and 6-O-sulfotransferases as well as CS/DS epimerases show a strong and partly overlapping expression, whereas the expression is restricted for enzymes with ability to synthesize di-sulfated disaccharides. A structural analysis further showed that CS/DS sulfation increases during embryonic development mainly due to synthesis of 4-O-sulfated GalNAc while the proportion of 6-O-sulfated GalNAc increases in later developmental stages. Di-sulfated GalNAc synthesized by Chst15 and 2-O-sulfated GlcA/IdoA synthesized by Ust are rare, in accordance with the restricted expression of these enzymes. We also compared CS/DS composition with that of heparan sulfate (HS). Notably, CS/DS biosynthesis in early zebrafish development is more dynamic than HS biosynthesis. Furthermore, HS contains disaccharides with more than one sulfate group, which are virtually absent in CS/DS.

The multi-protein family of sulfotransferases in plants: composition, occurrence, substrate specificity, and functions

All members of the sulfotransferase (SOT, EC 2.8.2.-) protein family transfer a sulfuryl group from the donor 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to an appropriate hydroxyl group of several classes of substrates. The primary structure of these enzymes is characterized by a histidine residue in the active site, defined PAPS binding sites and a longer SOT domain. Proteins with this SOT domain occur in all organisms from all three domains, usually as a multi-protein family. Arabidopsis thaliana SOTs, the best characterized SOT multi-protein family, contains 21 members. The substrates for several plant enzymes have already been identified, such as glucosinolates, brassinosteroids, jasmonates, flavonoids, and salicylic acid. Much information has been gathered on desulfo-glucosinolate (dsGl) SOTs in A. thaliana. The three cytosolic dsGl SOTs show slightly different expression patterns. The recombinant proteins reveal differences in their affinity to indolic and aliphatic dsGls. Also the respective recombinant dsGl SOTs from different A. thaliana ecotypes differ in their kinetic properties. However, determinants of substrate specificity and the exact reaction mechanism still need to be clarified. Probably, the three-dimensional structures of more plant proteins need to be solved to analyze the mode of action and the responsible amino acids for substrate binding. In addition to A. thaliana, more plant species from several families need to be investigated to fully elucidate the diversity of sulfated molecules and the way of biosynthesis catalyzed by SOT enzymes.

Human genetic disorders and knockout mice deficient in glycosaminoglycan

Glycosaminoglycans (GAGs) are constructed through the stepwise addition of respective monosaccharides by various glycosyltransferases and maturated by epimerases and sulfotransferases. The structural diversity of GAG polysaccharides, including their sulfation patterns and sequential arrangements, is essential for a wide range of biological activities such as cell signaling, cell proliferation, tissue morphogenesis, and interactions with various growth factors. Studies using knockout mice of enzymes responsible for the biosynthesis of the GAG side chains of proteoglycans have revealed their physiological functions. Furthermore, mutations in the human genes encoding glycosyltransferases, sulfotransferases, and related enzymes responsible for the biosynthesis of GAGs cause a number of genetic disorders including chondrodysplasia, spondyloepiphyseal dysplasia, and Ehlers-Danlos syndromes. This review focused on the increasing number of glycobiological studies on knockout mice and genetic diseases caused by disturbances in the biosynthetic enzymes for GAGs.

Metabolism of cartilage proteoglycans in health and disease

Cartilage proteoglycans are extracellular macromolecules with complex structure, composed of a core protein onto which a variable number of glycosaminoglycan chains are attached. Their biosynthesis at the glycosaminoglycan level involves a great number of sugar transferases well-orchestrated in Golgi apparatus. Similarly, their degradation, either extracellular or intracellular in lysosomes, involves a large number of hydrolases. A deficiency or malfunction of any of the enzymes participating in cartilage proteoglycan metabolism may lead to severe disease state. This review summarizes the findings regarding this topic.

Chondroitin 6-O-sulfate ameliorates experimental autoimmune encephalomyelitis

Chondroitin sulfate proteoglycans (CSPGs) are the main component of the extracellular matrix in the central nervous system (CNS) and influence neuroplasticity. Although CSPG is considered an inhibitory factor for nerve repair in spinal cord injury, it is unclear whether CSPG influences the pathogenetic mechanisms of neuroimmunological diseases. We induced experimental autoimmune encephalomyelitis (EAE) in chondroitin 6-O-sulfate transferase 1-deficient (C6st1(-/-)) mice. C6ST1 is the enzyme that transfers sulfate residues to position 6 of N-acetylgalactosamine in the sugar chain of CSPG. The phenotypes of EAE in C6st1(-/-) mice were more severe than those in wild-type (WT) mice were. In adoptive-transfer EAE, in which antigen-reactive T cells from WT mice were transferred to C6st1(-/-) and WT mice, phenotypes were significantly more severe in C6st1(-/-) than in WT mice. The recall response of antigen-reactive T cells was not significantly different among the groups. Furthermore, the number of pathogenic T cells within the CNS was also not considerably different. When EAE was induced in C6ST1 transgenic mice with C6ST1 overexpression, the mice showed considerably milder symptoms compared with those in WT mice. In conclusion, the presence of sulfate at position 6 of N-acetylgalactosamine of CSPG may influence the effecter phase of EAE to prevent the progression of pathogenesis. Thus, modification of the carbohydrate residue of CSPG may be a novel therapeutic strategy for neuroimmunological diseases such as multiple sclerosis.

Alterations in the chondroitin sulfate chain in human osteoarthritic cartilage of the knee

OBJECTIVE

To determine whether the structure of chondroitin sulfate (CS) in cartilage is reflected by the degree of cartilage degeneration in patients with osteoarthritis (OA) of the knee and to determine how CS biosynthesis affects cartilage degeneration.

DESIGN

Two osteoarthritic cartilage samples were obtained from medial femoral condyle (MFC) and lateral femoral condyle (LFC) of 24 knees with end-stage OA. The samples were assigned to two groups as follows: lesion and remote cartilage were adjacent to and remote from the osteoarthritic cartilage, respectively. Histological grade was determined according to the Mankin score. The CS concentration and chain length were determined using high-performance liquid chromatography (HPLC) and gel filtration chromatography, respectively. Expression of the gene encoding CS glycosyltransferase was evaluated using a real-time quantitative polymerase chain reaction (qPCR) assay. These results were compared between lesion and remote cartilage.

RESULTS

The Mankin score indicated that lesion cartilage was more degraded compared with remote cartilage. Although the CS levels varied among individuals, the mean CS concentration and chain length were significantly lower and shorter in lesion cartilage than in remote cartilage, respectively (concentration: 12.04 vs 14.84 μg/mg wet weight, P = 0.021; chain length: 5.36 vs 6.19 kDa, P = 0.026). Three genes encoding CS glycosyltransferases (CHPF, CSGALNACT1, CSGALNACT2) were expressed at lower levels in lesion cartilage.

CONCLUSIONS

In the osteoarthritic knee, the CS concentration and chain length were reduced closer to the more degraded cartilage with decreasing CS glycosyltransferase gene expression. Inhibition of CS glycosyltransferase gene expression may reduce CS chain length, which may contribute to OA progression.

Human genetic disorders caused by mutations in genes encoding biosynthetic enzymes for sulfated glycosaminoglycans

A number of genetic disorders are caused by mutations in the genes encoding glycosyltransferases and sulfotransferases, enzymes responsible for the synthesis of sulfated glycosaminoglycan (GAG) side chains of proteoglycans, including chondroitin sulfate, dermatan sulfate, and heparan sulfate. The phenotypes of these genetic disorders reflect disturbances in crucial biological functions of GAGs in human. Recent studies have revealed that mutations in genes encoding chondroitin sulfate and dermatan sulfate biosynthetic enzymes cause various disorders of connective tissues. This minireview focuses on growing glycobiological studies of recently described genetic diseases caused by disturbances in biosynthetic enzymes for sulfated GAGs.

Construction of a chondroitin sulfate library with defined structures and analysis of molecular interactions

Chondroitin sulfate (CS) is a linear acidic polysaccharide, composed of repeating disaccharide units of glucuronic acid and N-acetyl-D-galactosamine and modified with sulfate residues at different positions, which plays various roles in development and disease. Here, we chemo-enzymatically synthesized various CS species with defined lengths and defined sulfate compositions, from chondroitin hexasaccharide conjugated with hexamethylenediamine at the reducing ends, using bacterial chondroitin polymerase and recombinant CS sulfotransferases, including chondroitin-4-sulfotransferase 1 (C4ST-1), chondroitin-6-sulfotransferase 1 (C6ST-1), N-acetylgalactosamine 4-sulfate 6-sulfotransferase (GalNAc4S-6ST), and uronosyl 2-sulfotransferase (UA2ST). Sequential modifications of CS with a series of CS sulfotransferases revealed their distinct features, including their substrate specificities. Reactions with chondroitin polymerase generated non-sulfated chondroitin, and those with C4ST-1 and C6ST-1 generated uniformly sulfated CS containing >95% 4S and 6S units, respectively. GalNAc4S-6ST and UA2ST generated highly sulfated CS possessing ∼90% corresponding disulfated disaccharide units. Sequential reactions with UA2ST and GalNAc4S-6ST generated further highly sulfated CS containing a mixed structure of disulfated units. Surprisingly, sequential reactions with GalNAc4S-6ST and UA2ST generated a novel CS molecule containing ∼29% trisulfated disaccharide units. Enzyme-linked immunosorbent assay and surface plasmon resonance analysis using the CS library and natural CS products modified with biotin at the reducing ends, revealed details of the interactions of CS species with anti-CS antibodies, and with CS-binding molecules such as midkine and pleiotrophin. Chemo-enzymatic synthesis enables the generation of CS chains of the desired lengths, compositions, and distinct structures, and the resulting library will be a useful tool for studies of CS functions.

Baculovirus envelope protein ODV-E66 is a novel chondroitinase with distinct substrate specificity

Chondroitin sulfate is a linear polysaccharide of alternating D-glucuronic acid and N-acetyl-D-galactosamine residues with sulfate groups at various positions of the sugars. It interacts with and regulates cytokine and growth factor signal transduction, thus influencing development, organ morphogenesis, inflammation, and infection. We found chondroitinase activity in medium conditioned by baculovirus-infected insect cells and identified a novel chondroitinase. Sequence analysis revealed that the enzyme was a truncated form of occlusion-derived virus envelope protein 66 (ODV-E66) of Autographa californica nucleopolyhedrovirus. The enzyme was a novel chondroitin lyase with distinct substrate specificity. The enzyme was active over a wide range of pH (pH 4-9) and temperature (30-60 °C) and was unaffected by divalent metal ions. The ODV-E66 truncated protein digested chondroitin most efficiently followed by chondroitin 6-sulfate. It degraded hyaluronan to a minimal extent but did not degrade dermatan sulfate, heparin, and N-acetylheparosan. Further analysis using chemo-enzymatically synthesized substrates revealed that the enzyme specifically acted on glucuronate residues in non-sulfated and chondroitin 6-sulfate structures but not in chondroitin 4-sulfate structures. These results suggest that this chondroitinase is useful for detailed structural and compositional analysis of chondroitin sulfate, preparation of specific chondroitin oligosaccharides, and study of baculovirus infection mechanism.

Chondroitin sulfates play a major role in breast cancer metastasis: a role for CSPG4 and CHST11 gene expression in forming surface P-selectin ligands in aggressive breast cancer cells

Introduction

We have previously demonstrated that chondroitin sulfate glycosaminoglycans (CS-GAGs) on breast cancer cells function as P-selectin ligands. This study was performed to identify the carrier proteoglycan (PG) and the sulfotransferase gene involved in synthesis of the surface P-selectin-reactive CS-GAGs in human breast cancer cells with high metastatic capacity, as well as to determine a direct role for CS-GAGs in metastatic spread.

Methods

Quantitative real-time PCR (qRT-PCR) and flow cytometry assays were used to detect the expression of genes involved in the sulfation and presentation of chondroitin in several human breast cancer cell lines. Transient transfection of the human breast cancer cell line MDA-MB-231 with the siRNAs for carbohydrate (chondroitin 4) sulfotransferase-11 (CHST11) and chondroitin sulfate proteoglycan 4 (CSPG4 ) was used to investigate the involvement of these genes in expression of surface P-selectin ligands. The expression of CSPG4 and CHST11 in 15 primary invasive breast cancer clinical specimens was assessed by qRT-PCR. The role of CS-GAGs in metastasis was tested using the 4T1 murine mammary cell line (10 mice per group).

Results

The CHST11 gene was highly expressed in aggressive breast cancer cells but significantly less so in less aggressive breast cancer cell lines. A positive correlation was observed between the expression levels of CHST11 and P-selectin binding to cells (P < 0.0001). Blocking the expression of CHST11 with siRNA inhibited CS-A expression and P-selectin binding to MDA-MB-231 cells. The carrier proteoglycan CSPG4 was highly expressed on the aggressive breast cancer cell lines and contributed to the P-selectin binding and CS-A expression. In addition, CSPG4 and CHST11 were over-expressed in tumor-containing clinical tissue specimens compared with normal tissues. Enzymatic removal of tumor-cell surface CS-GAGs significantly inhibited lung colonization of the 4T1 murine mammary cell line (P = 0.0002).

Conclusions

Cell surface P-selectin binding depends on CHST11 gene expression. CSPG4 serves as a P-selectin ligand through its CS chain and participates in P-selectin binding to the highly metastatic breast cancer cells. Removal of CS-GAGs greatly reduces metastatic lung colonization by 4T1 cells. The data strongly indicate that CS-GAGs and their biosynthetic pathways are promising targets for the development of anti-metastatic therapies.

A versatile polyacrylamide gel electrophoresis based sulfotransferase assay

Background

Sulfotransferases are a large group of enzymes that regulate the biological activity or availability of a wide spectrum of substrates through sulfation with the sulfur donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS). These enzymes are known to be difficult to assay. A convenient assay is needed in order to better understand these enzymes.

Results

A universal sulfotransferase assay method based on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) is described. This assay has been successfully applied to substrates as small as α-naphthol and as big as proteoglycans. As examples, we present the assays for recombinant human CHST4, TPST1, CHST3 and HS6ST1. In order to assess whether a small molecule can be applicable to this type of assay, a method to estimate the relative mobility of a molecule to PAPS is also presented. The estimated relative mobilities of various sulfated small molecules generated by SULT1A1, SULT1E1, SULT2A1 and CHST4 are in the range of ± 0.2 of the actual relative mobilities.

Conclusion

The versatility of the current method comes from the ability that SDS-PAGE can separate proteins and small molecules according to different parameters. While mobilities of proteins during SDS-PAGE are inversely related to their sizes, mobilities of small molecules are positively related to their charge/mass ratios. The predicted relative mobility of a product to PAPS is a good indicator of whether a sulfotransferase can be assayed with SDS-PAGE. Because phosphorylation is most similar to sulfation in chemistry, the method is likely to be applicable to kinases as well.

Gene silencing of EXTL2 and EXTL3 as a substrate deprivation therapy for heparan sulphate storing mucopolysaccharidoses

Neurological pathology is characteristic of the mucopolysaccharidoses (MPSs) that store heparan sulphate (HS) glycosaminoglycan (gag) and has been proven to be refractory to systemic therapies. Substrate deprivation therapy (SDT) using general inhibitors of gag synthesis improves neurological function in mouse models of MPS, but is not specific to an MPS type. We have investigated RNA interference (RNAi) as a method of targeting SDT to the HS synthesising enzymes, EXTL2 and EXTL3. Multiple shRNA molecules specific to EXTL2 or EXTL3 were designed and validated in a reporter gene assay, with four out of six shRNA constructs reducing expression by over 90%. The three EXTL2-specific shRNA constructs reduced endogenous target gene expression by 68, 32 and 65%, and decreased gag synthesis by 46, 50 and 27%. One EXTL3-specific shRNA construct reduced endogenous target gene expression by 14% and gag synthesis by 39%. Lysosomal gag levels in MPS IIIA and MPS I fibroblasts were also reduced by EXTL2 and EXTL3-specific shRNA. Incorporation of shRNAs into a lentiviral expression system reduced gene expression, and one EXTL2-specific shRNA reduced gag synthesis. These results indicate that deprivation therapy through shRNA-mediated RNAi has potential as a therapy for HS-storing MPSs.

Sulfation of the galactose residues in the glycosaminoglycan-protein linkage region by recombinant human chondroitin 6-O-sulfotransferase-1

6-O-Sulfated galactose residues have been demonstrated in the glycosaminoglycan-protein linkage region GlcUAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-Ser isolated from shark cartilage chondroitin 6-sulfate (Sugahara, K., Ohi, Y., Harada, T., de Waard, P., and Vliegenthart, J. F. G. (1992) J. Biol. Chem. 267, 6027-6035). In this study, we investigated whether a recombinant human chondroitin 6-sulfotransferase-1 (C6ST-1) catalyzes the sulfation of C6 on both galactose residues in the linkage region using structurally defined acceptor substrates. The C6ST-1 was expressed as a soluble protein A chimeric form in COS-1 cells and purified using IgG-Sepharose. The purified C6ST-1 utilized the linkage tri-, tetra-, penta-, and hexasaccharide-serines and hexasaccharide alditols, including GlcUAbeta1-3GalNAc(4-O-sulfate)beta1-4GlcUAbeta1-3Gal(4-O-sulfate)beta1-3Galbeta1-4Xylbeta1-O-Ser and DeltaGlcUAbeta1-3GalNAc(6-O-sulfate)beta1-4GlcUAbeta1-3Galbeta1-3Gal(6-O-sulfate)beta1-4Xyl-ol. Identification of the reaction products obtained with the linkage tetra-, penta-, and hexasaccharide-serines revealed that the C6ST-1 catalyzed the sulfation of C6 on both galactose residues in the linkage region. Notably, the linkage tetrasaccharide-peptide GlcUAbeta1-3Galbeta1-3Galbeta1-4Xylbeta1-O-(Gly)Ser-(Gly-Glu) was a good acceptor substrate for the C6ST-1, suggesting that the sulfation of the galactose residues can occur before the transfer of the first N-acetylhexosamine residue to the linkage tetrasaccharide. In contrast, no incorporation was observed into DeltaGlcUAbeta1-3GalNAc(4-O-sulfate)beta1-4GlcUAbeta1-3Gal(4-O-sulfate)beta1-3Galbeta1-4Xyl-ol, indicating that an intact xylose is necessary for the transfer of a sulfate to the second sugar residue Gal from the reducing end. These findings clearly demonstrated that the recombinant C6ST-1 catalyzes the sulfation of C6 on both galactose residues in the linkage region in vitro. This is the first identification of the sulfotransferase responsible for the sulfation of galactose residues in the glycosaminoglycan-protein linkage region.

DNA hypermethylation contributes to incomplete synthesis of carbohydrate determinants in gastrointestinal cancer

BACKGROUND & AIMS

It has long been known that malignant transformation is associated with abnormal expression of carbohydrate determinants. The aim of this study was to clarify the cause of cancer-associated abnormal glycosylation in gastrointestinal (GI) cancers.

METHODS

We compared the expression levels of "glyco-genes," including glycosyltransferases and glycosidases, in normal GI mucosa and in gastric and colorectal cancer cells. To examine the possibility that DNA hypermethylation contributed to the down-regulation of these genes, we treated GI cancer cells with 5-aza-2'-deoxycytidine (5-aza-dC), an inhibitor of DNA methyltransferase.

RESULTS

The silencing of some of these glyco-genes, but not up-regulation of certain molecules, was observed. The Sd(a) carbohydrate was abundantly expressed in the normal GI mucosa, but its expression was significantly decreased in cancer tissues. When human colon and gastric cancer cells were treated with 5-aza-dC, cell surface expression of Sd(a) and the transcription of B4GALNT2, which catalyzes the synthesis of the Sd(a), were induced. The promoter region of the human B4GALNT2 gene was heavily hypermethylated in many of the GI cancer cell lines examined as well as in gastric cancer tissues (39 out of 78 cases). In addition, aberrant methylation of the B4GALNT2 gene was strongly correlated with Epstein-Barr virus-associated gastric carcinomas and occurred coincidentally with hypermethylation of the ST3GAL6 gene.

CONCLUSIONS

Epigenetic changes in a group of glycosyltransferases including B4GALNT2 and ST3GAL6 represent a malignant phenotype of gastric cancer caused by silencing of the activity of these enzymes, which action may eventually induce aberrant glycosylation and expression of cancer-associated carbohydrate antigens.

Tissue-specific mRNA expression profiles of human carbohydrate sulfotransferase and tyrosylprotein sulfotransferase

Pairs of forward and reverse primers and TaqMan probes specific to each of 15 human sulfotransferases were prepared. The mRNA expression level of each target enzyme was analyzed in total RNA from single and pooled specimens of various human tissues (adrenal gland, bone marrow, brain, colon, heart, kidney, liver, lung, pancreas, peripheral leukocytes, placenta, prostate, salivary gland, skeletal muscle, small intestine, spinal cord, spleen, stomach, testis, thymus, thyroid gland, trachea, and uterus) by real-time reverse transcription PCR using an ABI PRISM 7700 Sequence Detection System. The mRNA expression profiles of the sulfotransferases in these 23 different human tissues were used to identify the tissues exhibiting high transcriptional activity for these enzymes. These results provide valuable information for studies concerning the human carbohydrate sulfotransferase and tyrosylprotein sulfotransferase genes in various tissues.

Chondroitin sulfate/dermatan sulfate hybrid chains in the development of cerebellum. Spatiotemporal regulation of the expression of critical disulfated disaccharides by specific sulfotransferases

Chondroitin sulfate/dermatan sulfate (CS/DS) chains regulate the development of the central nervous system in vertebrates. Previously, we demonstrated that CS/DS hybrid chains from embryonic pig brain exhibit neuritogenic and growth factor binding activities, which depended on their IdoUA content defining the DS-like structure. To elucidate the distribution of such functional sugar chains during the development of the brain, in situ hybridization was performed to examine expression of three CS/DS GalNAc 4-O-sulfotransferases, D4ST-1, C4ST-1, and C4ST-2, and a single uronyl 2-O-sulfotransferase (UST) involved in the biosynthesis of DS in addition to CS intermediates. C4ST-1 and C4ST-2 were ubiquitously expressed in the postnatal mouse brain, whereas the expression of D4ST-1 and UST was restricted in the developing cerebellum and culminated at postnatal day 14 as shown by reverse transcriptase-PCR analysis. In situ analysis of the disaccharides of CS/DS in brain sections revealed that the concentration of CS/DS increases 2-fold during development (postnatal day 7 to 7 weeks). The proportions of DS-specific, principal disaccharides, IdoUA-Gal-NAc(4-O-sulfate) (iA) and IdoUA(2-O-sulfate)-GalNAc(4-O-sulfate) (iB), produced by the sequential actions of D4ST-1 and UST, were higher in the CS/DS chains from cerebellum than those from whole brain sections. A dramatic increase (10-fold) in the proportion of iB during development was noteworthy. In contrast, GlcUA/IdoUA(2-O-sulfate)-GalNAc(6-O-sulfate) (D/iD) and GlcUA/IdoUA-GalNAc(4, 6-O-disulfate) (E/iE) decreased to 50 and 30%, respectively, in the developing cerebellum. These results suggest that the IdoUA-containing iA and iB units along with D/iD and E/iE units in the CS/DS hybrid play important roles in the formation of the cerebellar neural network during postnatal brain development.

Upregulation of chondroitin 6-sulphotransferase-1 facilitates Schwann cell migration during axonal growth

Cell migration is central to development and post-traumatic regeneration. The differential increase in 6-sulphated chondroitins during axonal growth in both crushed sciatic nerves and brain development suggests that chondroitin 6-sulphotransferase-1 (C6ST-1) is a key enzyme that mediates cell migration in the process. We have cloned the cDNA of the C6ST-1 gene (C6st1) (GenBank accession number AF178689) from crushed sciatic nerves of adult rats and produced ribonucleotide probes accordingly to track signs of 6-sulphated chondroitins at the site of injury. We found C6st1 mRNA expression in Schwann cells emigrating from explants of both sciatic nerve segments and embryonic dorsal root ganglia. Immunocytochemistry indicated pericellular 6-sulphated chondroitin products around C6ST-1-expressing frontier cells. Motility analysis of frontier cells in cultures subjected to staged treatment with chondroitinase ABC indicated that freshly produced 6-sulphated chondroitin moieties facilitated Schwann cell motility, unlike restrictions resulting from proteoglycan interaction with matrix components. Sciatic nerve crush provided further evidence of in vivo upregulation of the C6ST-1 gene in mobile Schwann cells that guided axonal regrowth 1-14 days post crush; downregulation then accompanied declining mobility of Schwann cells as they engaged in the myelination of re-growing axons. These findings are the first to identify upregulated C6st1 gene expression correlating with the motility of Schwann cells that guide growing axons through both developmental and injured environments.

Chondroitin 4-sulphotransferase-1 and chondroitin 6-sulphotransferase-1 are affected differently by uronic acid residues neighbouring the acceptor GalNAc residues

C4ST-1 (chondroitin 4-sulphotransferase-1) and C6ST-1 (chondroitin 6-sulphotransferase-1) transfer sulphate from PAPS (adenosine 3'-phosphate 5'-phosphosulphate) to positions 4 and 6 respectively of the GalNAc residues of chondroitin. We showed previously that C4ST-1 purified from rat chondrosarcoma and recombinant C4ST-1 both transfer sulphate efficiently to position 4 of the GalNAc residues of DSDS (desulphated dermatan sulphate). We report here the specificity of C4ST-1 and C6ST-1 in terms of uronic acid residue recognition around the GalNAc residue to which sulphate is transferred. When [35S]glycosaminoglycans formed from DSDS after incubation with [35S]PAPS and C4ST-1 were digested with chondroitinase ACII, a major part of the radioactivity was recovered in disaccharide fractions and the remainder distributed to tetrasaccharides and larger fractions, indicating that C4ST-1 mainly transferred sulphate to position 4 of the GalNAc residue located at the GlcA-GalNAc-GlcA sequence. Structural analysis of tetrasaccharide and larger oligosaccharide fractions indicated that C4ST-1 mainly transferred sulphate to the GalNAc residue adjacent to the reducing side of the GlcA residue. On the other hand, when [35S]glycosaminoglycans formed from DSDS after incubation with [35S]PAPS and C6ST-1 were digested with chondroitinase ACII, a major part of the radioactivity was recovered in fractions larger than hexasaccharides, indicating that C6ST-1 transferred sulphate to the GalNAc residues located in the L-iduronic acid-rich region. Structural analysis of the tetrasaccharide and larger oligosaccharide fractions indicated that C6ST-1 showed very little preference for the GalNAc residue neighbouring the GlcA residue. These results indicate that C4ST-1 and C6ST-1 differ from each other in the recognition of uronic acid residues adjacent to the targeted GalNAc residue.

Loss of chondroitin 6-O-sulfotransferase-1 function results in severe human chondrodysplasia with progressive spinal involvement

We studied two large consanguineous families from Oman with a distinct form of spondyloepiphyseal dysplasia (SED Omani type). By using a genome-wide linkage approach, we were able to map the underlying gene to a 4.5-centimorgan interval on chromosome 10q23. We sequenced candidate genes from the region and identified a missense mutation in the chondroitin 6-O-sulfotransferase (C6ST-1) gene (CHST3) changing an arginine into a glutamine (R304Q) in the well conserved 3'-phosphoadenosine 5'-phosphosulfate binding site. C6ST-1 catalyzes the modifying step of chondroitin sulfate (CS) synthesis by transferring sulfate to the C-6 position of the N-acetylgalactosamine of chondroitin. From the crystal structures of other sulfotransferases, it could be inferred that Arg-304 is essential for the structure of the cosubstrate binding site. We used recombinant C6ST-1 to show that the identified missense mutation completely abolishes C6ST-1 activity. Disaccharide composition analysis of CS chains by anion-exchange HPLC shows that both Delta HexA-GalNAc(6S) and Delta HexA(2S)-GalNAc(6S) were significantly reduced in the patient's cells and that Delta HexA-GalNAc(4S,6S), undetectable in controls, was elevated. Analysis of the patient's urine shows marked undersulfation of CS, in particular reduction in 6-O-sulfated disaccharide and an increase in the nonsulfated unit. Our results indicate that the mutation in CHST3 described here causes a specific but generalized defect of CS chain sulfation resulting in chondrodysplasia with major involvement of the spine.

Novel mutations in the carbohydrate sulfotransferase gene (CHST6) in American patients with macular corneal dystrophy

PURPOSE

To further characterize the mutations within the CHST6 gene responsible for causing macular corneal dystrophy in a cohort of affected patients from the United States.

DESIGN

Experimental study.

METHODS

Genomic DNA was extracted from buccal epithelium of 16 affected patients (14 families), 17 unaffected relatives, and 127 controls, followed by polymerase chain reaction amplification and direct sequencing of the CHST6 coding region. Subtyping of affected patients into type I and II macular corneal dystrophy was performed by measuring antigenic keratan sulfate (AgKS) serum levels. Haplotype analysis was performed in families that demonstrated common mutations.

RESULTS

CHST6 coding region analysis in 10 patients identified as having type I macular corneal dystrophy revealed 10 sequence changes: eight missense mutations, four of which are novel (Met104Val, Tyr110Cys, Gln122Pro, and Leu276Pro) and four of which have been reported previously (Ser51Leu, Pro72Ser, Cys102Gly, and Leu200Arg); one novel homozygous nonsense mutation in two patients from a single family (c. 1683C>T, Gln331X); and one frameshift mutation in a heterozygous state in a single patient (c.1744_1751dupGTGCGCTG). Mutation analysis in the four patients identified as having type II macular corneal dystrophy (serum samples were not obtained from two affected patients) revealed three patients heterozygous for either the c.923G>C, c.969C>A, or c.1519T>C sequence changes. The fourth patient was compound heterozygous for c.969C>A and c.1291T>G. None of these changes was observed in 127 control individuals. Haplotype analysis using microsatellite markers flanking the CHST6 gene did not reveal a common founder for the Leu200Arg (1291T>G) missense mutation, present in five families, identifying this position as a mutation hot-spot.

CONCLUSIONS

A variety of previously unreported mutations in the coding region of the CHST6 gene are associated with type I macular corneal dystrophy in a cohort of patients from the United States.

Differential roles of two N-acetylgalactosaminyltransferases, CSGalNAcT-1, and a novel enzyme, CSGalNAcT-2. Initiation and elongation in synthesis of chondroitin sulfate

By a tblastn search with beta 1,4-galactosyltransferases as query sequences, we found an expressed sequence tag that showed similarity in beta 1,4-glycosyltransferase motifs. The full-length complementary DNA was obtained by a method of 5'-rapid amplification of complementary DNA ends. The predicted open reading frame encodes a typical type II membrane protein comprising 543 amino acids, the sequence of which was highly homologous to chondroitin sulfate N-acetylgalactosaminyltransferase (CSGalNAcT-1), and we designated this novel enzyme CSGalNAcT-2. CSGalNAcT-2 showed much stronger N-acetylgalactosaminyltransferase activity toward glucuronic acid of chondroitin poly- and oligosaccharides, and chondroitin sulfate poly- and oligosaccharides with a beta 1-4 linkage, i.e. elongation activity for chondroitin and chondroitin sulfate, but showed much weaker activity toward a tetrasaccharide of the glycosaminoglycan linkage structure (GlcA-Gal-Gal-Xyl-O-methoxyphenyl), i.e. initiation activity, than CSGalNAcT-1. Transfection of the CSGalNAcT-1 gene into Chinese hamster ovary cells yielded a change of glycosaminoglycan composition, i.e. the replacement of heparan sulfate on a syndecan-4/fibroblast growth factor-1 chimera protein by chondroitin sulfate, however, transfection of the CSGalNAcT-2 gene did not. The above results indicated that CSGalNAcT-1 is involved in the initiation of chondroitin sulfate synthesis, whereas CSGalNAcT-2 participates mainly in the elongation, not initiation. Quantitative real-time PCR analysis revealed that CSGalNAcT-2 transcripts were highly expressed in the small intestine, leukocytes, and spleen, however, both CSGalNAcTs were ubiquitously expressed in various tissues.

Ectopic expression of a GlcNAc 6-O-sulfotransferase, GlcNAc6ST-2, in colonic mucinous adenocarcinoma

The content of sulfated glycans having 6-O-sulfated GlcNAc residues alters in the course of colonic carcinogenesis. We previously characterized two GlcNAc 6-O-sulfotransferases (SulTs), SulT-a and -b, expressed in colonic normal tissues and adenocarcinomas [Seko et al. (2000) Glycobiology, 10, 919-929]. Levels of the enzymatic activities of SulT-a in normal colonic mucosa are higher than those in colonic adenocarcinomas, and the enzymatic activities of SulT-b are detected only in mucinous adenocarcinomas. To determine which GlcNAc 6-O-SulTs cloned so far correspond to SulT-a and -b, we expressed seven enzymes of a Gal/GalNAc/GlcNAc 6-O-SulT family in COS-7 cells and examined their substrate specificities in comparison with those of SulT-a and -b. GlcNAc6ST-2 (HEC-GlcNAc6ST, LSST, or GST-3) can recognize GlcNAcbeta1-->3GalNAcalpha1-O-pNP as a good acceptor as well as other O-linked- and N-linked-type oligosaccharides, and its substrate specificity was similar to that of SulT-b. GlcNAc6ST-3(I-GlcNAc6ST or GST-4alpha) preferred Galbeta1-->3(GlcNAcbeta1-->6)GalNAcalpha1-O-pNP as an acceptor to the other oligosaccharides examined, and its specificity was similar to that of SulT-a. To confirm these correspondences, we further performed quantitative analyses of transcripts for GlcNAc6ST-2 and -3 genes by competitive RT-PCR. As a result, GlcNAc6ST-2 gene was expressed in almost all the mucinous adenocarcinomas examined and hardly expressed in normal colonic mucosa and nonmucinous adenocarcinoma. Expression levels of transcript for GlcNAc6ST-3 in normal mucosa were significantly higher than those in adenocarcinomas. From these results, it was indicated that GlcNAc6ST-2 corresponds to mucinous adenocarcinoma-specific SulT-b and that expression of GlcNAc6ST-3 is down-regulated in colonic adenocarcinomas.

Functional analysis of the chondroitin 6-sulfotransferase gene in relation to lymphocyte subpopulations, brain development, and oversulfated chondroitin sulfates

Chondroitin 6-sulfotransferase (C6ST) catalyzes the transfer of sulfate to position 6 of the N-acetylgalactosamine residue of chondroitin. To obtain direct evidence regarding the function of C6ST and its product, chondroitin 6-sulfate, in vivo, we isolated the mouse C6ST gene (C6st) and generated mice deficient in this gene (C6st(-/-)) by embryonic stem cell technology. C6st(-/-) mice were born at approximately the expected frequency and were viable through adulthood. In the spleen of C6st(-/-) mice, the level of chondroitin 6-sulfate became almost undetectable. Analyses of these knockout mice provided insights into the biosynthesis of oversulfated chondroitin sulfates in mice; chondroitin sulfate D in the brain of null mice and the cartilage and telencephalon of null embryos disappeared, whereas the chondroitin sulfate E level in the spleen and brain of the null mice was unchanged. Despite the disappearance of chondroitin sulfate D structure, brain development was normal in the C6st(-/-) mice. Further analysis revealed that the number of CD62L(+)CD44(low) T lymphocytes corresponding to naive T lymphocytes in the spleen of 5-6-week-old C6st(-/-) mice was significantly decreased, whereas those in other secondary lymphoid organs were unchanged. This finding suggested that chondroitin 6-sulfate plays a role in the maintenance of naive T lymphocytes in the spleen of young mice.

Structural analysis of sulfated N-linked oligosaccharides in erythropoietin

We previously demonstrated that high-performance liquid chromatography with electrospray ionization mass spectrometry (LC/MS) equipped with a graphitized carbon column (GCC) is useful for the structural analysis of carbohydrates in glycoproteins. Using LC/MS with GCC, sulfated N-linked oligosaccharides were found in erythropoietin (EPO) expressed in baby hamster kidney cells. Sulfation occurs in a part of the N-linked oligosaccharides in the EPO. Sulfated monosaccharide residue in the sulfated N-linked oligosaccharide was determined by exoglycosidase digestion followed by sugar mapping by LC/MS. The linkage position and branch-location of the sulfate group in the tetraantennary oligosaccharide were analyzed by (1)H-nuclear magnetic resonance. It was suggested that sulfation occurs on the C-6 position of GlcNAc located in the GlcNAcbeta1-4Manalpha1-3 branch.

Arterial wall chondroitin sulfate proteoglycans: diverse molecules with distinct roles in lipoprotein retention and atherogenesis

Chondroitin sulfate proteoglycans (CSPGs) of the arterial wall are generally considered to be atherogenic because of their ability to trap cholesterol-rich lipoproteins in vitro. Nevertheless, CSPGs are a diverse group of molecules with a long evolutionary history and distinct biologic functions. The three principal CSPGs in the arterial wall are versican, which is part of the hyalectan gene family; and decorin and biglycan, which are members of a separate gene family, the small leucine-rich proteoglycans. Importantly, there is now substantial evidence that the different molecular species of CSPGs participate unequally in lipoprotein retention, and that they exert unequal regulatory effects that are related to atherogenesis. Recently available murine models with genetic manipulations that affect CSPGs now allow causal studies of the roles of these molecules to be conducted in vivo, with occasionally surprising results. Moreover, tools are being developed to examine human genetic variations that are relevant to CSPGs, which may provide additional important insights into the human disease. The era in which proteoglycans are regarded as a nondescript backdrop, playing purely nonspecific structural roles, is over. Studies in manipulated animals and in human populations will continue to reveal precise, dynamic roles for these fascinating and ancient molecules.

Human corneal GlcNac 6-O-sulfotransferase and mouse intestinal GlcNac 6-O-sulfotransferase both produce keratan sulfate

Human corneal N-acetylglucosamine 6-O-sulfotransferase (hCGn6ST) has been identified by the positional candidate approach as the gene responsible for macular corneal dystrophy (MCD). Because of its high homology to carbohydrate sulfotransferases and the presence of mutations of this gene in MCD patients who lack sulfated keratan sulfate in the cornea and serum, hCGn6ST protein is thought to be a sulfotransferase that catalyzes sulfation of GlcNAc in keratan sulfate. In this report, we analyzed the enzymatic activity of hCGn6ST by expressing it in cultured cells. A lysate prepared from HeLa cells transfected with an intact form of hCGn6ST cDNA or culture medium from cells transfected with a secreted form of hCGn6ST cDNA showed an activity of transferring sulfate to C-6 of GlcNAc of synthetic oligosaccharide substrates in vitro. When hCGn6ST was expressed together with human keratan sulfate Gal-6-sulfotransferase (hKSG6ST), HeLa cells produced highly sulfated carbohydrate detected by an anti-keratan sulfate antibody 5D4. These results indicate that hCGn6ST transfers sulfate to C-6 of GlcNAc in keratan sulfate. Amino acid substitutions in hCGn6ST identical to changes resulting from missense mutations found in MCD patients abolished enzymatic activity. Moreover, mouse intestinal GlcNAc 6-O-sulfotransferase had the same activity as hCGn6ST. This observation suggests that mouse intestinal GlcNAc 6-O-sulfotransferase is the orthologue of hCGn6ST and functions as a sulfotransferase to produce keratan sulfate in the cornea.

Chromosomal localization and genomic organization for the galactose/ N-acetylgalactosamine/N-acetylglucosamine 6-O-sulfotransferase gene family

The galactose/N-acetylgalactosamine/N-acetylglucosamine 6-O-sulfotransferases (GSTs) are a family of Golgi-resident enzymes that transfer sulfate from 3'phosphoadenosine 5'phospho-sulfate to the 6-hydroxyl group of galactose, N-acetylgalactosamine, or N-acetylglucosamine in nascent glycoproteins. These sulfation modifications are functionally important in settings as diverse as cartilage structure and lymphocyte homing. To date six members of this gene family have been described in human and in mouse. We have determined the chromosomal localization of these genes as well as their genomic organization. While the broadly expressed enzymes implicated in proteoglycan biosynthesis are located on different chromosomes, the highly tissue specific enzymes GST-3 and 4 are encoded by genes located both in band q23.1--23.2 on chromosome 16. In the mouse, both genes reside in the syntenic region 8E1 on chromosome 8. This cross-species conserved clustering is suggestive of related functional roles for these genes. The human GST4 locus actually contains two highly similar open reading frames (ORF) that are 50 kb apart and encode two highly similar enzyme isoforms termed GST-4 alpha and GST-4 beta. All genes except GST0 (chondroitin 6-O-sulfotransferase) contain intron-less ORFs. With one exception these are fused directly to sequences encoding the 3' untranslated regions (UTR) of the respective mature mRNAs. The 5' UTRs of these mRNAs are usually encoded by a number of short exons 5' of the respective ORF. 5'UTRs of the same enzyme expressed in different cell types are sometimes derived from different exons located upstream of the ORF. The genomic organization of the GSTs resembles that of certain glycosyltransferase gene families.