Cloning of the human heparan sulfate-N-deacetylase/N-sulfotransferase gene from the Treacher Collins syndrome candidate region at 5q32-q33.1

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.

Natural Products Containing a Nitrogen-Sulfur Bond

Only about 100 natural products are known to contain a nitrogen-sulfur (N-S) bond. This review thoroughly categorizes N-S bond-containing compounds by structural class. Information on biological source, biological activity, and biosynthesis is included, if known. We also review the role of N-S bond functional groups as post-translational modifications of amino acids in proteins and peptides, emphasizing their role in the metabolism of the cell.

The glomerular basement membrane as a model system to study the bioactivity of heparan sulfate glycosaminoglycans

The glomerular basement membrane and its associated cells are critical elements in the renal ultrafiltration process. Traditionally the anionic charge associated with several carbohydrate moieties in the glomerular basement membrane are thought to form a charge selective barrier that restricts the transmembrane flux of anionic proteins across the glomerular basement membrane into the urinary space. The charge selective function, along with the size selective component of the basement membrane, serves to limit the efflux of plasma proteins from the capillary lumen. Heparan sulfate glycosaminoglycans are anionically charged carbohydrate structures attached to proteoglycan core proteins and have a role in establishing the charge selective function of the glomerular basement membrane. Although there are a large number of studies in the literature that support this concept, the results of several recent studies using molecular genetic approaches to minimize the anionic charge of the glomerular basement membrane would suggest that the role of heparan sulfate glycosaminoglycans in the glomerular capillary wall are still not yet entirely resolved, suggesting that this research area still requires new and novel exploration.

Sulfotransferase Ndst1 is needed for mandibular and TMJ development

Heparan sulfate proteoglycans (HS-PGs) regulate several developmental processes, but their possible roles in mandibular and TMJ formation are largely unclear. To uncover such roles, we generated mice lacking Golgi-associated N-sulfotransferase 1 (Ndst1) that catalyzes sulfation of HS-PG glycosaminoglycan chains. Ndst1-null mouse embryos exhibited different degrees of phenotypic penetrance. Severely affected mutants lacked the temporomandibular joint and condyle, but had a mandibular remnant that displayed abnormal tooth germs, substandard angiogenesis, and enhanced apoptosis. In mildly affected mutants, the condylar growth plate was dysfunctional and exhibited thicker superficial and polymorphic cell zones, a much wider distribution of Indian hedgehog signaling activity, and ectopic ossification along its lateral border. Interestingly, mildly affected mutants also exhibited facial asymmetry resembling that seen in individuals with hemifacial microsomia. Our findings indicate that Ndst1-dependent HS sulfation is critical for mandibular and TMJ development and allows HS-PGs to exert their roles via regulation of Ihh signaling topography and action.

Mice deficient in heparan sulfate N-deacetylase/N-sulfotransferase 1

Ndsts (N-deacetylase/N-sulfotransferases) are enzymes responsible for N-sulfation during heparan sulfate (HS) and heparin biosynthesis. In this review, basic features of the Ndst1 enzyme are covered and a brief description of HS biosynthesis and its regulation is presented. Effects of Ndst1 deficiency on embryonic development are described. These include immature lungs, craniofacial dysplasia and eye developmental defects, branching defect during lacrimal gland development, delayed mineralization of the skeleton, and reduced pericyte recruitment during vascular development. A brief account of the effects of Ndst1 deficiency in selective cell types in adult mice is also given.

Protease-proteoglycan complexes of mouse and human mast cells and importance of their beta-tryptase-heparin complexes in inflammation and innate immunity

Approximately 50% of the weight of a mature mast cell (MC) consists of varied neutral proteases stored in the cell's secretory granules ionically bound to serglycin proteoglycans that contain heparin and/or chondroitin sulfate E/diB chains. Mouse MCs express the exopeptidase carboxypeptidase A3 and at least 15 serine proteases [designated as mouse MC protease (mMCP) 1-11, transmembrane tryptase/tryptase gamma/protease serine member S (Prss) 31, cathepsin G, granzyme B, and neuropsin/Prss19]. mMCP-6, mMCP-7, mMCP-11/Prss34, and Prss31 are the four members of the chromosome 17A3.3 family of tryptases that are preferentially expressed in MCs. One of the challenges ahead is to understand why MCs express so many different protease-proteoglycan macromolecular complexes. MC-like cells that contain tryptase-heparin complexes in their secretory granules have been identified in the Ciona intestinalis and Styela plicata urochordates that appeared approximately 500 million years ago. Because sea squirts lack B cells and T cells, it is likely that MCs and their tryptase-proteoglycan granule mediators initially appeared in lower organisms as part of their innate immune system. The conservation of MCs throughout evolution suggests that some of these protease-proteoglycan complexes are essential to our survival. In support of this conclusion, no human has been identified that lacks MCs. Moreover, transgenic mice lacking the beta-tryptase mMCP-6 are unable to combat a Klebsiella pneumoniae infection effectively. Here we summarize the nature and function of some of the tryptase-serglycin proteoglycan complexes found in mouse and human MCs.

Endothelial inflammation: the role of differential expression of N-deacetylase/N-sulphotransferase enzymes in alteration of the immunological properties of heparan sulphate

Heparan sulphate N-deacetylase/N-sulphotransferase (NDST) enzymes catalyse the reaction that initiates sulphation and subsequent modification of the oligosaccharide, heparan sulphate (HS). The extent and distribution of sulphate substitution on HS plays a vital role in regulation of the binding of a range of proteins, including IFN-gamma, several interleukins and most chemokines. In this study, the expression of NDST transcripts was found to be non-uniform between a range of cell types, suggesting that different cells produce characteristic HS species. It was found that stimulation of the HMEC-1 microvascular endothelial cell line with the pro-inflammatory cytokines IFN-gamma and TNF-alpha caused a transient decrease in the level of NDST-1 and -2 transcripts after 4 hours (P < 0.05 and P < 0.01 respectively), but the expression of NDST-1 increased above control levels after 16 hours (P < 0.01). The change in NDST expression was concurrent with an increase in the abundance of sulphated HS epitopes on the cell surface; this was not caused by variation in the expression of proteoglycans or by changes in the rate of GAG turnover. Cytokine-stimulated endothelial cells also showed an increase in their potential to bind RANTES (CCL5); this was abrogated by chlorate blockade of sulphotransferase activity or by heparitinase cleavage of cell surface HS. Monolayers of cytokine-stimulated HMEC-1 also supported an enhanced leukocyte chemotactic response towards RANTES. This study demonstrated that pro-inflammatory cytokines can increase NDST expression leading to increased sulphation of HS and a corresponding increase in sequestration of functional RANTES at the apical surface of endothelial cells. This may enhance leukocyte extravasation at sites of inflammation.

Sulfonation and molecular action

The sulfonation of endogenous molecules is a pervasive biological phenomenon that is not always easily understood, and although it is increasingly recognized as a function of fundamental importance, there remain areas in which significant cognizance is still lacking or at most minimal. This is particularly true in the field of endocrinology, in which the sulfoconjugation of hormones is a widespread occurrence that is only partially, if at all, appreciated. In the realm of steroid/sterol sulfoconjugation, the discovery of a novel gene that utilizes an alternative exon 1 to encode for two sulfotransferase isoforms, one of which sulfonates cholesterol and the other pregnenolone, has been an important advance. This is significant because cholesterol sulfate plays a crucial role in physiological systems such as keratinocyte differentiation and development of the skin barrier, and pregnenolone sulfate is now acknowledged as an important neurosteroid. The sulfonation of thyroglobulin and thyroid hormones has been extensively investigated and, although this transformation is better understood, there remain areas of incomplete comprehension. The sulfonation of catecholamines is a prevalent modification that has been extensively studied but, unfortunately, remains poorly understood. The sulfonation of pituitary glycoprotein hormones, especially LH and TSH, does not affect binding to their cognate receptors; however, sulfonation does play an important role in their plasma clearance, which indirectly has a significant effect on biological activity. On the other hand, the sulfonation of distinct neuroendocrine peptides does have a profound influence on receptor binding and, thus, a direct effect on biological activity. The sulfonation of specific extracellular structures plays an essential role in the binding and signaling of a large family of extracellular growth factors. In summary, sulfonation is a ubiquitous posttranslational modification of hormones and extracellular components that can lead to dramatic structural changes in affected molecules, the biological significance of which is now beginning to be appreciated.

Decreased glomerular expression of agrin in diabetic nephropathy and podocytes, cultured in high glucose medium

AIM

A decrease in glomerular heparan sulfate (HS) proteoglycan (PG), without apparent decrease in HSPG core protein expression, has been reported to occur in diabetic nephropathy (DN). In most studies however, agrin, the major HSPG core protein in the glomerular basement membrane, has not been studied. This prompted us to study the glomerular expression of agrin in parallel to the expression of HS-glycosaminoglycans (GAG) in biopsies of patients with DN. Furthermore, the influence of glucose on agrin production in cultured podocytes and the expression of agrin in fetal kidneys was investigated.

METHODS

Cryostat sections of renal biopsies from patients with DN (n = 8) and healthy controls (HC, n = 8), were stained for agrin and HS-GAG. Sections of fetal kidneys were double stained for agrin and CD35 or CD31. Stainings were performed by indirect immunofluorescence (IIF). The production of agrin by cultured human podocytes was tested by ELISA and IIF.

RESULTS

The expression of agrin, detected by AS46, was significantly reduced in biopsies from patients with DN compared to HC (p < 0.01). Similar findings were observed when monoclonal antibody JM72 was used (p < 0.05). In addition, a significant reduction in the glomerular expression of HS-GAG was detected with JM403 in these patients (p < 0.01). Agrin is expressed in cultured podocytes, the expression hereof was reduced when the cells were cultured in the presence of 25 mM D-glucose (p < 0.01). In biopsies of human fetal kidneys, glomerular expression of agrin coincided with the expression of CD31. In early stages of glomerular differentiation there was a strong staining for agrin and CD31 while CD35 was only slightly positive.

CONCLUSIONS

Our data argue against a selective dysregulation in HSPG sulfation in DN, but suggest a pivotal role for hyperglycemia in the downregulation of agrin core protein production.

Multiple isozymes of heparan sulfate/heparin GlcNAc N-deacetylase/GlcN N-sulfotransferase. Structure and activity of the fourth member, NDST4

We report the cloning and partial characterization of the fourth member of the vertebrate heparan sulfate/heparin: GlcNAc N-deacetylase/GlcN N-sulfotransferase family, which we designate NDST4. Full-length cDNA clones containing the entire coding region of 872 amino acids were obtained from human and mouse cDNA libraries. The deduced amino acid sequence of NDST4 showed high sequence identity to NDST1, NDST2, and NDST3 in both species. NDST4 maps to human chromosome 4q25-26, very close to NDST3, located at 4q26-27. These observations, taken together with phylogenetic data, suggest that the four NDSTs evolved from a common ancestral gene, which diverged to give rise to two subtypes, NDST3/4 and NDST1/2. Reverse transcription-polymerase chain reaction analysis of various mouse tissues revealed a restricted pattern of NDST4 mRNA expression when compared with NDST1 and NDST2, which are abundantly and ubiquitously expressed. Comparison of the enzymatic properties of the four murine NDSTs revealed striking differences in N-deacetylation and N-sulfation activities; NDST4 had weak deacetylase activity but high sulfotransferase, whereas NDST3 had the opposite properties. Molecular modeling of the sulfotransferase domains of the murine and human NDSTs showed varying surface charge distributions within the substrate binding cleft, suggesting that the differences in activity may reflect preferences for different substrates. An iterative model of heparan sulfate biosynthesis is suggested in which some NDST isozymes initiate the N-deacetylation and N-sulfation of the chains, whereas others bind to previously modified segments to fill in or extend the section of modified residues.

Ocular colobomata

Ocular colobomata present diagnostic and therapeutic challenges in patients of all ages, but especially in young children. The "typical" coloboma, caused by defective closure of the fetal fissure, is located in the inferonasal quadrant, and it may affect any part of the globe traversed by the fissure from the iris to the optic nerve. Ocular colobomata are often associated with microphthalmia, and they may be idiopathic or associated with various syndromes. Types and severity of complications vary depending on the location and size of the colobomata. This article reviews the pathogeneses, categorization, genetic bases, differential diagnoses and management of ocular coloboma.

Human protein tyrosine phosphatase-like gene: expression profile, genomic structure, and mutation analysis in families with ARVD

The mouse protein tyrosine phosphatase-like gene (Ptpla) was recently cloned and data suggested that it plays a role in myogenesis and cardiogenesis. The human homologue (PTPLA) was mapped to chromosome 10p13-14, a region where we have mapped a locus responsible for arrhythmogenic right ventricular dysplasia (ARVD). As a positional candidate gene, we characterized PTPLA by determining its tissue expression, its genomic structure, and we also screened for mutations in the ARVD patients. Northern analysis demonstrated PTPLA is preferentially expressed in both adult and fetal heart. A much lower expression was detected in skeletal and smooth muscle tissues. Virtually no expression was observed in other tissues. The protein-encoding sequences of PTPLA consist of seven exons. A sequence variation (Lys64Gln) was found in all the affecteds in a large ARVD family. However, the same variant was also detected in normal control subjects (three alleles/100 chromosomes). Thus, the variant (Lys64Gln) is not responsible for ARVD in our family and is a benign polymorphism. Nevertheless, its tissue-specific expression in the developing and adult heart suggest PTPLA has a role in regulating cardiac development, differentiation, or other cellular events. The genomic structure and intragenic polymorphism of PTPLA should be useful for further clinical and genetic studies such as gene targeting of PTPLA.

Cancer-associated alternative usage of multiple promoters of human GalCer sulfotransferase gene

The galactosylceramide sulfotransferase (cerebroside sulfotransferase, CST) (EC 2.8.2.11) gene is highly expressed in human renal cancer cells. To elucidate the regulatory mechanism of its gene expression, we have determined the genomic organization of the human CST gene. The gene comprises at least four exons and spans about 20 kb. The coding region is located in exons 3 and 4. To determine the transcription initiation sites, 5'-rapid amplification of cDNA ends analysis was performed using mRNA obtained from four human renal cancer cell lines, SMKT-R1-R4, and normal human renal proximal tubular cells. We found four transcription initiation sites and alternative usage of six exons corresponding to the 5'-untranslated region in cancer cells. On the other hand, the only transcript beginning at exon 1a was observed in normal cells. Using reverse transcriptase-PCR analysis, we confirmed that all of the exons 1a-d, especially exons 1c and 1d, are used as a transcription initiation site in cancer cells, whereas only exons 1a and 1b, mostly 1a, are utilized in normal cells. Analyzing the protein production from the mRNA variants with different 5'-UTRs, we found that all the transcripts examined produced the identical proteins. These observations suggest that the aberrant usage of transcription initiation sites flanked with promoters/enhancers is involved in the cancer-associated expression of the CST gene. Furthermore, this gene was assigned to human chromosome 22q12 by means of fluorescence in situ hybridization.

The heparin-binding proteins apolipoprotein E and lipoprotein lipase enhance cellular proteoglycan production

Apolipoprotein E (apoE) and lipoprotein lipase (LPL), key proteins in the regulation of lipoprotein metabolism, bind with high affinity to heparin and cell-surface heparan sulfate proteoglycan (HSPG). In the present study, we tested whether the expression of apoE or LPL would modulate proteoglycan (PG) metabolism in cells. Two apoE-expressing cells, macrophages and fibroblasts, and LPL-expressing Chinese hamster ovary (CHO) cells were used to study the effect of apoE and LPL on PG production. Cellular PGs were metabolically labeled with (35)[S]sulfate for 20 hours, and medium, pericellular PGs, and intracellular PGs were assessed. In all transfected cells, PG levels in the 3 pools increased 1.6- to 3-fold when compared with control cells. Initial PG production was assessed from the time of addition of radiolabeled sulfate; at 1 hour, there was no difference in PG synthesis by apoE-expressing cells when compared with control cells. After 1 hour, apoE-expressing cells had significantly greater production of PGs. Total production assessed with [(3)H]glucosamine was also increased. This was due to an increase in the length of the glycosaminoglycan chains. To assess whether the increase in PGs was due to a decrease in PG degradation, a pulse-chase experiment was performed. Loss of sulfate-labeled pericellular PGs was similar in apoE and control cells, but more labeled PGs appeared in the medium of the apoE-expressing cells. Addition of exogenous apoE and anti-human apoE antibody to both non-apoE-expressing and apoE-expressing cells did not alter PG production. Moreover, LPL addition did not alter cell-surface PG metabolism. These results show that enhanced gene expression of apoE and LPL increases cellular PG production. We postulate that such changes in vascular PGs can affect the atherogenic potential of arteries.

Molecular cloning and characterization of a human uronyl 2-sulfotransferase that sulfates iduronyl and glucuronyl residues in dermatan/chondroitin sulfate

A partial-length human cDNA with a predicted amino acid sequence homologous to a previously described heparan sulfate iduronyl 2-sulfotransferase (Kobayashi, M., Habuchi, H., Yoneda, M., Habuchi, O., and Kimata, K. (1997) J. Biol. Chem. 272, 13980-13985) was obtained by searching the expressed sequence-tagged data bank. Northern blot analysis was performed using this homologous cDNA as a probe, which demonstrated ubiquitous expression of messages of 5.1 and 2.0 kilobases in a number of human tissues and in several human cancer cell lines. Since the human lymphoma Raji cell line had the highest level of expression, it was used to isolate a full-length cDNA clone. The full-length cDNA was found to contain an open reading frame that predicted a type II transmembrane protein composed of 406 amino acid residues. The cDNA in a baculovirus expression vector was expressed in Sf9 insect cells, and cell extracts were then incubated together with 3'-phosphoadenosine 5'-phospho[35S]sulfate and potential glycosaminoglycan acceptors. This demonstrated substantial sulfotransferase activity with dermatan sulfate, a small degree of activity with chondroitin sulfate, but no sulfotransferase activity with desulfated N-resulfated heparin. Analysis of [35S]sulfate-labeled disaccharide products of chondroitin ABC, chondroitin AC, and chondroitin B lyase treatment demonstrated that the enzyme only transferred sulfate to the 2-position of uronyl residues, which were preponderantly iduronyl residues in dermatan sulfate, but some lesser transfer to glucuronyl residues of chondroitin sulfate.

Apolipoprotein E containing high density lipoprotein stimulates endothelial production of heparan sulfate rich in biologically active heparin-like domains. A potential mechanism for the anti-atherogenic actions of vascular apolipoprotein e

Reduced heparin and heparan sulfate (HS) proteoglycans (PG) have been observed in both inflammation and atherosclerosis. Methods to increase endogenous heparin and heparan sulfate are not known. We found that incubation of endothelial cells with 500-1,000 micrograms/ml high density lipoprotein (HDL) increased 35SO4 incorporation into PG by 1.5-2.5-fold. A major portion of this increase was in HS and was the result of increased synthesis. Total PG core proteins were not altered by HDL; however, the ratio of 35SO4 to [3H]glucosamine was increased by HDL, suggesting increased sulfation of glycosaminoglycans. In addition, HDL increased the amount of highly sulfated heparin-like HS in the subendothelial matrix. HS from HDL-treated cells bound 40 +/- 5% more 125I-antithrombin III (requires 3-O sulfated HS) and 49 +/- 3% fewer monocytes. Moreover, the HS isolated from HDL-treated cells inhibited smooth muscle cell proliferation (by 83 +/- 5%) better than control HS (56 +/- 6%) and heparin (42 +/- 6%). HDL isolated from apolipoprotein E (apoE)-null mice did not stimulate HS production unless apoE was added. ApoE also stimulated HS production in the absence of HDL. ApoE did not increase 35SO4 incorporation in macrophages and fibroblasts, suggesting that this is an endothelial cell-specific process. Receptor-associated protein inhibited apoE-mediated stimulation of HS only at higher (20 micrograms/ml) doses, suggesting the involvement of a receptor-associated protein-sensitive pathway in mediating apoE actions. In summary, our data identify a novel mechanism by which apoE and apoE-containing HDL can be anti-atherogenic. Identification of specific apoE peptides that stimulate endothelial heparin/HS production may have important therapeutic applications.

Multiple isoforms of heparan sulfate D-glucosaminyl 3-O-sulfotransferase. Isolation, characterization, and expression of human cdnas and identification of distinct genomic loci

3-O-Sulfated glucosaminyl residues are rare constituents of heparan sulfate and are essential for the activity of anticoagulant heparan sulfate. Cellular production of the critical active structure is controlled by the rate-limiting enzyme, heparan sulfate D-glucosaminyl 3-O-sulfotransferase-1 (3-OST-1) (EC 2.8.2.23). We have probed the expressed sequence tag data base with the carboxyl-terminal sulfotransferase domain of 3-OST-1 to reveal three novel, incomplete human cDNAs. These were utilized in library screens to isolate full-length cDNAs. Clones corresponding to predominant transcripts were obtained for the 367-, 406-, and 390-amino acid enzymes 3-OST-2, 3-OST-3A, and 3-OST-3B, respectively. These type II integral membrane proteins are comprised of a divergent amino-terminal region and a very homologous carboxyl-terminal sulfotransferase domain of approximately 260 residues. Also recovered were partial length clones for 3-OST-4. Expression of the full-length enzymes confirms the 3-O-sulfation of specific glucosaminyl residues within heparan sulfate (Liu, J., Shworak, N. W., Sinaÿ, P., Schwartz, J. J. Zhang, L., Fritze, L. M. S., and Rosenberg, R. D. (1999) J. Biol. Chem. 274, 5185-5192). Southern analyses suggest the human 3OST1, 3OST2, and 3OST4 genes, and the corresponding mouse isologs, are single copy. However, 3OST3A and 3OST3B genes are each duplicated in humans and show at least one copy each in mice. Intriguingly, the entire sulfotransferase domain sequence of the 3-OST-3B cDNA (774 base pairs) was 99.2% identical to the same region of 3-OST-3A. Together, these data argue that the structure of this functionally important region is actively maintained by gene conversion between 3OST3A and 3OST3B loci. Interspecific mouse back-cross analysis identified the loci for mouse 3Ost genes and syntenic assignments of corresponding human isologs were confirmed by the identification of mapped sequence-tagged site markers. Northern blot analyses indicate brain exclusive and brain predominant expression of 3-OST-4 and 3-OST-2 transcripts, respectively; whereas, 3-OST-3A and 3-OST-3B isoforms show widespread expression of multiple transcripts. The reiteration and conservation of the 3-OST sulfotransferase domain suggest that this structure is a self-contained functional unit. Moreover, the extensive number of 3OST genes with diverse expression patterns of multiple transcripts suggests that the novel 3-OST enzymes, like 3-OST-1, regulate important biologic properties of heparan sulfate proteoglycans.

Molecular cloning and expression of a third member of the heparan sulfate/heparin GlcNAc N-deacetylase/ N-sulfotransferase family

N-Deacetylation and N-sulfation of N-acetylglucosamine residues in heparan sulfate and heparin initiate a series of chemical modifications that ultimately lead to oligosaccharide sequences with specific ligand binding properties. These reactions are catalyzed by GlcNAc N-deacetylase/N-sulfotransferase (NDST), a monomeric enzyme with two catalytic activities. Two genes encoding NDST isozymes have been described, one from rat liver (NDST1) and another from murine mastocytoma (NDST2). Both isozymes are expressed in tissues in varying amounts, but their relative contribution to heparan sulfate formation in any one tissue is unknown. We now report the identification of a third member of the NDST family, designated NDST3. A full-length cDNA clone (3.2 kilobase pairs) encoding a 873-amino acid protein was obtained from a human fetal/infant brain cDNA library. Human NDST3 (hNDST3) has a nucleotide sequence homologous but not identical to hNDST1 and NDST2. The deduced amino acid sequence shows 70% and 65% amino acid identity to that of hNDST1 and NDST2, respectively. A soluble chimera of hNDST3 and protein A exhibited both N-deacetylase and N-sulfotransferase activity, confirming its enzymatic identity. Northern blot analysis of human fetal brain poly(A)+ RNA showed a single transcript of 6.4 kilobase pairs. Reverse transcription polymerase chain reaction analysis revealed more restricted tissue expression of hNDST3 than hNDST1 and NDST2, and high levels in brain, liver, and kidney. Analysis of Chinese hamster ovary cells revealed expression of NDST1 and NDST2, but not NDST3. In a Chinese hamster ovary cell mutant exhibiting reduced N-sulfotransferase activity and reduced sulfation of heparan sulfate (Bame, K. J., and Esko, J. D. (1989) J. Biol. Chem. 264, 8059-8065), expression of NDST1 was greatly reduced, but NDST2 was expressed normally, suggesting that both enzymes are involved in heparan sulfate assembly. The discovery of multiple NDST isozymes suggests that the assembly of heparan sulfate is much complicated than previously appreciated.

Carbohydrate sulfotransferases: mediators of extracellular communication

Sulfated carbohydrates mediate diverse extracellular recognition events in both normal and pathological processes. The sulfotransferases that generate specific carbohydrate 'sulfoforms' have recently been recognized as key modulators of these processes and therefore represent potential therapeutic targets.

A role of Lys614 in the sulfotransferase activity of human heparan sulfate N-deacetylase/N-sulfotransferase

An active sulfotransferase (ST, residues 558-882) domain of the human heparan sulfate N-deacetylase/N-sulfotransferase (hHSNST) has been identified by aligning the amino acid sequence of hHSNST to that of mouse estrogen sulfotransferase (EST). The bacterially expressed ST domain transfers the 5'-sulfuryl group of 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to only deacetylated heparin with an efficiency similar to that previously reported for the purified rat HSNST. Moreover, the K(m,PAPS) (2.1 microM) of the ST domain is also similar to that of the rat enzyme. Lys48 is a key residue in mEST catalysis. The residue corresponding to Lys48 is conserved in all known heparan sulfate sulfotransferases (Lys614 in the ST domain of hHSNST). Mutation of Lys614 to Ala abolishes N-sulfotransferase activity, indicating an important catalytic role of Lys614 in the ST domain. Crystals of the ST domain have been grown (orthorhombic space group P2(1)2(1)2) with diffraction to 2.5 A resolution.

cDNA cloning, genomic organization and chromosomal localization of human heparan glucosaminyl N-deacetylase/N-sulphotransferase-2

The cDNA and gene encoding human heparan glucosaminyl N-deacetylase/N-sulphotransferase-2 have been cloned. The cDNA encoded a protein of 883 amino acids that was 94% similar to heparan N-sulphotransferase-2 from mouse mast cells. Comparison of the deduced amino acid sequences of human heparan N-sulphotransferase-1 and -2 showed that the enzymes were 70% similar; greater than 90% of the amino acids between residues 418 and 543 were identical. The least conserved amino acids were found in the N-terminus/putative transmembrane regions of the two enzymes. The human heparan N-sulphotransferase-2 gene was localized to chromosome arm 10q (band 10q22) by in situ fluorescent hybridization. The gene contains 13 exons spanning 6.5 kb, ranging in size from 88 bp (exon 2) to >1 kb (exon 1), and 12 introns, which were found to occur at similar sites within the coding sequence of the human heparan N-sulphotransferase-1 gene. The structure of the two genes differed in that the heparan N-sulphotransferase-1 gene contained one additional intron. The similarity of the heparan N-sulphotransferase-1 and -2 proteins and their similar exon-intron organization suggest that they derive from a common ancestral gene.

Identification and expression in mouse of two heparan sulfate glucosaminyl N-deacetylase/N-sulfotransferase genes

The biosynthesis of heparan sulfate/heparin is a complex process that requires the coordinate action of a number of different enzymes. In close connection with polymerization of the polysaccharide chain, the modification reactions are initiated by N-deacetylation followed by N-sulfation of N-acetylglucosamine units. These two reactions are carried out by a single protein. Proteins with such dual activities were first purified and cloned from rat liver and mouse mastocytoma. The mouse mastocytoma enzyme is encoded by an approximately 4-kilobase (kb) mRNA, whereas the rat liver transcript contains approximately 8 kb. In the present study, the primary structure of the enzyme encoded by the mouse 8-kb transcript is described. It is demonstrated that both the 4-and 8-kb transcripts have a wide tissue distribution and that they are encoded by separate genes. Characterization of the gene encoding the 4-kb transcript demonstrates that it spans a region of about 8 kb and that it contains at least 14 exons. The similarity of this gene and the previously characterized human gene for the 8-kb transcript is discussed.

Molecular characterization and expression of heparan-sulfate 6-sulfotransferase. Complete cDNA cloning in human and partial cloning in Chinese hamster ovary cells

Heparan-sulfate 6-sulfotransferase (HS6ST) catalyzes the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate to position 6 of the N-sulfoglucosamine residue of heparan sulfate. The enzyme was purified to apparent homogeneity from the serum-free culture medium of Chinese hamster ovary (CHO) cells (Habuchi, H., Habuchi, O., and Kimata, K. (1995) J. Biol Chem. 270, 4172-4179). From the amino acid sequence data of the purified enzyme, degenerate oligonucleotides were designed and used as primers for the reverse transcriptase-polymerase chain reaction using poly(A)+ RNA from CHO cells as a template. The amplified cDNA fragment was then used as a probe to screen a cDNA library of CHO cells. The cDNA clone thus obtained encoded a partial peptide sequence composed of 236 amino acid residues that included the sequences of six peptides obtained after endoproteinase digestion of the purified enzyme. This cDNA clone was applied to the screening of a human fetal brain cDNA library by cross-hybridization. The isolated cDNA clones contained a whole open reading frame that predicts a type II transmembrane protein composed of 401 amino acid residues. No significant amino acid sequence identity to any other proteins, including heparan-sulfate 2-sulfotransferases, was observed. When the cDNA for the entire coding sequence of the protein was inserted into a eukaryotic expression vector and transfected into COS-7 cells, the HS6ST activity increased 7-fold over the control. The FLAG fusion protein purified by anti-FLAG affinity chromatography showed the HS6ST activity alone. Northern blot analysis revealed the occurrence of a single transcript of 3.9 kilobases in both human fetal brain and CHO cells. The results, together with the ones from our recent cDNA analysis of heparan-sulfate 2-sulfotransferase (Kobayashi, M., Habuchi, H., Yoneda, M., Habuchi, O., and Kimata, K. (1997) J. Biol. Chem. 272, 13980-13985), suggest that at least two different gene products are responsible for 6- and 2-O-sulfations of heparan sulfate.

Localization of human heparan glucosaminyl N-deacetylase/N-sulphotransferase to the trans-Golgi network

In order to determine the intracellular location of heparan N-deacetylase/N-sulphotransferase, cDNAs encoding human heparan glucosaminyl N-deacetylase/N-sulphotransferase were cloned from human umbilical vein endothelial cells. The deduced amino acid sequence was identical to that of the human heparan N-sulphotransferase cloned previously [Dixon, Loftus, Gladwin, Scambler, Wasmuth and Dixon (1995) Genomics 26, 239-244]. RNA blot analysis indicated that two heparan N-sulphotransferase transcripts of approx. 8.5 and 4 kb were produced in all tissues. Expression was most abundant in heart, liver and pancreas. A cDNA encoding a Flag-tagged human heparan N-sulphotransferase (where Flag is an epitope with the sequence DYKDDDDK) was transfected into mouse LTA cells. Immunofluorescence detection using anti-Flag monoclonal antibodies demonstrated that the enzyme was localized to the trans-Golgi network. A truncated Flag-tagged heparan N-sulphotransferase was also retained in the Golgi, indicating that, as for many other Golgi enzymes, the N-terminal region of heparan N-sulphotransferase is sufficient for retention in the Golgi apparatus.

Molecular cloning and expression of Chinese hamster ovary cell heparan-sulfate 2-sulfotransferase

Heparan-sulfate 2-sulfotransferase (HS2ST), which catalyzes the transfer of sulfate from 3'-phosphoadenosine 5'-phosphosulfate to L-iduronic acid at position 2 in heparan sulfate, was purified from cultured Chinese hamster ovary (CHO) cells to apparent homogeneity (Kobayashi, M., Habuchi, H., Habuchi, O., Saito, M., and Kimata, K. (1996) J. Biol. Chem. 271, 7645-7653). The internal amino acid sequences were obtained from the peptides after digestion of the purified protein with a combination of endoproteinases. Mixed oligonucleotides based on the peptide sequences were used as primers to obtain a probe fragment by reverse transcriptase-polymerase chain reaction using CHO cell poly(A)+ RNA as template. The clone obtained from a CHO cDNA library by screening with the probe is 2.2 kilobases in size and contains an open reading frame of 1068 bases encoding a new protein composed of 356 amino acid residues. The protein predicts a type II transmembrane topology similar to other Golgi membrane proteins. Messages of 5.0 and 3.0 kilobases were observed in Northern analysis. Evidence that the cDNA clone corresponds to the purified HS2ST protein is as follows. (a) The predicted amino acid sequence contains all five peptides obtained after endoproteinase digestion of the purified protein; (b) the characteristics of the predicted protein fit those of the purified protein in terms of molecular mass, membrane localization, and N-glycosylation; and (c) when the cDNA containing the entire coding sequence of the enzyme in a eukaryotic expression vector was transfected into COS-7 cells, the HS2ST activity increased 2.6-fold over controls, and the FLAG-HS2ST fusion protein purified by affinity chromatography showed the HS2ST activity alone.

European Gene Mapping Project (EUROGEM): breakpoint panels for human chromosomes based on the CEPH reference families. Centre d'Etude du Polymorphisme Humain

Meiotic breakpoint panels for human chromosomes 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14, 15, 17, 18, 20 and X were constructed from genotypes from the CEPH reference families. Each recombinant chromosome included has a breakpoint well-supported with reference to defined quantitative criteria. The panels were constructed at both a low-resolution, useful for a first-pass localization, and high-resolution, for a more precise placement. The availability of such panels will reduce the number of genotyping experiments necessary to order new polymorphisms with respect to existing genetic markers. This paper shows only a representative sample of the breakpoints detected. The complete data are available on the World Wide Web (URL http:/(/)www.icnet.uk/axp/hgr/eurogem++ +/HTML/data.html) or by anonymous ftp (ftp.gene.ucl.ac.uk in/pub/eurogem/maps/breakpoints).

Treacher Collins syndrome

Treacher Collins syndrome is an autosomal dominant disorder of craniofacial development, the features of which include conductive hearing loss and cleft palate. In the absence of a candidate gene, a positional cloning approach has been used to isolate the mutated gene which maps to chromosome 5q31.3-32. Flanking markers were identified and a yeast artificial chromosome and cosmid contig of the region defined by these markers was created as a prelude to the creation of a transcript map of the region. Analysis of genes isolated using this approach resulted in the identification of the mutated gene. While the function of the gene remains unknown, the identification of 20 mutations spread throughout the gene, all of which would result in the insertion of a premature termination codon into the reading frame, suggests that the mechanism underlying the disease is haploinsufficiency.

Positional cloning of a gene involved in the pathogenesis of Treacher Collins syndrome. The Treacher Collins Syndrome Collaborative Group

Treacher Collins syndrome is an autosomal dominant disorder of craniofacial development, which has been localized to chromosome 5q32-33.1. In the present study, the isolation of new polymorphic markers has allowed the identification of overlapping recombination events in two affected individuals. Extension of the transcription map of the critical region proximally has resulted in the isolation of a new gene (which has been named Treacle) of unknown function. The identification of different mutations in five unrelated families, all of which would result in premature termination of the predicted protein, indicates that the Treacher Collins syndrome gene has been positionally cloned.

Transcriptional map of the Treacher Collins candidate gene region

Treacher Collins syndrome (TCOF1) is a dominant disorder of craniofacial development that has been linked previosuly to a region of chromosome 5q31.3-32. Identification of recombination events in affected individuals has reduced the candidate gene region to a 0.5-Mb area between the loci RPS14 (proximal) and ANX6 [distal]. A transcriptional map of this candidate gene region, generated by analysis of exon amplification clones, has identified the genomic location of four genes, heparan sulfate-N-sulfotransferase-N-deacetylase, glutathione peroxidase, as well as two novel, previously uncharacterized genes. Each of these genes, based on their location, must be considered candidates for TCOF1 locus.