Keywords

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Introduction

The functions of heparan sulfate (HS) are involved in various cellular processes such as proliferation, differentiation, adhesion, migration, morphology, and maintenance of stem cells (Habuchi et al. 2004; Bishop et al. 2007; Lindahl and Li 2009; Buresh et al. 2010; Shah et al. 2011; Buresh-Stiemke et al. 2012). It has been shown that HS plays some roles in various physiological phenomena such as inflammation, blood coagulation, tumor cell invasion, and malignancy. Moreover, infections of host cells with pathogens such as viruses, bacteria, and parasites have been shown to occur through the interactions with cell surface HS on host cells (Mettenleiter et al. 1990; Trybala et al. 1996; Liu and Thorp 2002). 6-O-Sulfate residues in HS are greatly involved in the above various biological and pathological processes primarily by modulating various signal transduction pathways such as fibroblast growth factors (FGFs), vascular endothelial growth factors (VEGFs), Wnts, and hedgehog. HS 6-O-sulfotransferases (HS6STs) transfer sulfate to position 6 of the N-sulfoglucosamine/N-acetylglucosamine residue in heparin/HS. Three isoforms are identified in mice and humans. All HS6STs are type II transmembrane proteins with short cytoplasmic domain at the N-terminus, followed by transmembrane and luminal domain which have 3′-phosphoadenosine 5′-phosphosulfate (PAPS) binding site and sulfotransferase activity localized at the Golgi apparatus.

Databanks

NC-IUBMB number: EC 2.8.2.

Brookhaven Protein Data Bank accession number: not available

Sequence accession numbers/codes for DNA and amino acid sequences, with binomial names of organisms are listed below.

Heparan-sulfate 6-O-sulfotransferase 1-3 (HS6ST1-3)

Species

Gene symbol

Gene symbol

NCBI reference number (protein)

UniprotKB ID

HS6ST1

    

Homo sapiens (human)

HS6ST1

NM_004807.2

NP_004798.3

O60243

Mus musculus (mouse)

Hs6st1

NM_015818.2

NP_056633.2

Q9QYK5

Rattus norvegicus (rat)

Hs6st1

NM_001108210.1

NP_001101680.1

D4A6E6

Gallus gallus (chicken)

HS6ST1

NM_204482.1

NP_989813.1

Q76KB2

Danio rerio (zebrafish)

hs6st1a

NM_001020508.2

NP_001018344.2

Q56UJ5

HS6ST2

    

Homo sapiens (human)

HS6ST2

NM_001077188.1

NP_001070656.1

Q96MM7

 

NM_147175.3

NP_671704.3

 

Mus musculus (mouse)

Hs6st2

NM_001077202.1

NP_001070670.1

Q80UW0

 

NM_015819.3

NP_056634.3

 

Rattus norvegicus (rat)

Hs6st2

NM_001191726.1

NP_001178655.1

D3ZEK5

   

D3ZBS5

Gallus gallus (chicken)

HS6ST2

NM_204490.1

NP_989821.1

Q76LW2

Danio rerio (zebrafish)

hs6st2

NM_194421.1

NP_919402.1

Q800H9

Q800H9

    

Homo sapiens (human)

HS6ST3

NM_153456.3

NP_703157.2

Q8IZP7

Mus musculus (mouse)

Hs6st3

NM_015820.3

NP_056635.2

Q9QYK4

Rattus norvegicus (rat)

Hs6st3

NM_001271404.1

NP_001258333.1

 

Gallus gallus (chicken)

HS6ST3

XM_003640546.1

XP_003640594.1

F1NDE4

Danio rerio (zebrafish)

hs6st3b

NM_001080194.1

NP_001073663.1

A0MGZ7

HS6ST

    

Drosophila melanogaster (fruit fly)

Hs6st

NM_079685.2

NP_524409.2

Q9VDR6

Caenorhabditis elegans (nematode)

hst-6

NM_076494.3

NP_508895.2

G5EFN7

Name and History

Name: Heparan sulfate 6-O-sulfotransferase

HS6STs transfer sulfate to position 6 of the N-sulfoglucosamine/N-acetylglucosamine residue in heparin/HS. Habuchi et al. found that heparan sulfate 6-O-sulfotransferase protein was secreted into the serum-free culture medium of CHO cells and purified the enzyme to an apparent homogeneity (Habuchi et al. 1995). The purified enzyme transferred sulfate to position 6 of the N-sulfoglucosamine residue when completely desulfated and N-resulfated heparin (CDSNS-heparin) was used as acceptor, but did not transfer sulfate to the amino group of glucosamine residue or to position 2 of the iduronic acid residue. HS also was served as an acceptor; however, chondroitin and chondroitin sulfate were not. The optimal pH of the enzyme was around 6.3. The enzyme was inhibited by dithiothreitol and stimulated strongly by protamine. From the partial amino acid sequence data of the purified enzyme, the cDNA was isolated by the reverse transcriptase-polymerase chain reaction followed by the screening of a cDNA library of CHO cells and the human fetal brain cDNA library by cross-hybridization (Habuchi et al. 1998). The isolated cDNA clones had a whole open reading frame that predicts a type II transmembrane protein composed of 401 amino acid residues. Then the new mouse and human isoforms of HS6ST, HS6ST2, which is a homologue to the original human HS6ST (HS6ST1) and subsequently the third HS6ST (HS6ST3), were cloned (Habuchi et al. 2000).

Structure

All three HS6STs are predicted to have type II transmembrane protein topology with short cytoplasmic domain at the N-terminus, followed by transmembrane and luminal domain which have PAPS binding site and sulfotransferase activity localized at the Golgi apparatus (Nagai et al. 2004; Kotani et al. 2005).

Enzyme Activity Assay and Substrate Specificity

HS6STs transfer sulfate to position 6 of the N-sulfoglucosamine residue in heparan sulfate but not to the N-acetylglucosamine residues.

$$ \mathrm{nPAP}\mathrm{S}+{\left(\mathrm{IdoA}\alpha 1\kern-0.12em -\kern-0.12em 4{\mathrm{GlcNSO}}_3\upalpha 1\kern-0.12em -\kern-0.12em 4\right)}_{\mathrm{n}}\to \mathrm{nPAP}+{\left[\mathrm{IdoA}\alpha 1\kern-0.12em -\kern-0.12em 4{\mathrm{GlcNSO}}_3\left({6\mathrm{SO}}_4\right)\upalpha 1\kern-0.12em -\kern-0.12em 4\right]}_{\mathrm{n}} $$

where PAPS is 3′-phosphoadenosine 5′-phosphosulfate, and PAP is 3′-phosphoadenosine 5′-phosphate.

The sulfotransferase activities were determined as follows: The standard reaction mixture (50 μL) contained 2.5 μmol of imidazole-HCl (pH 6.8), 3.75 μg of protamine chloride, 25 nmol (as hexosamine) of acceptor GAGs, 50 pmol of [35S]PAPS (approx. 5 × 105 c.p.m) and enzyme. After incubation for 20 min at 37 °C, the reaction was stopped by heating at 100 °C for 1 min. Chondroitin sulfate A (0.1 μmol as GlcA) was added to the reaction mixture as a carrier, and the 35S-labelled polysaccharides were precipitated with ethanol containing 1.3 % (w/v) potassium acetate and 0.5 mM EDTA, followed by gel chromatography on a fast desalting column to remove [35S]PAPS and its degradation products. The radioactivity incorporated to high molecular weight fractions was counted by scintillation counter. The amounts of enzymes added to the reaction mixture were chosen so as to obtain a linear incorporation of [35S] sulfate. The amount of enzyme activity required to transfer 1 pmol of sulfate/min to CDSNS-heparin was defined as one unit.

The HS6ST1 activity was also detected in mouse and human serum (Habuchi et al. 1998). All HS6STs transferred sulfate to CDSNS-heparin, N-sulfated heparosan, heparin, and heparan sulfate. Almost no activity was observed toward completely desulfated and N-acetylated (CDSNAc) heparin, suggesting that N-desulfated heparin is a poor acceptor. None of the isoforms showed significant activity toward chondroitin, any types of chondroitin sulfate, and keratan sulfate. Each isoform showed a different specificity toward the isomeric hexuronic acid adjacent to the targeted N-sulfated glucosamine; HS6ST1 appeared to prefer iduronic acid residues adjacent to the N-sulfoglucosamine, whereas HS6ST2 had a different preference, depending on the substrate concentrations (it preferred the glucuronic acid residue at high concentrations but the iduronic acid residue at low concentrations). The preference of HS6ST-3 was intermediate between those of HS6ST1 and HS6ST2. These three isoforms could also transfer sulfate to position 6 of N-sulfoglucosamine residue adjacent to the reducing side of iduronic acid 2-sulfate. Besides, there are two forms of HS6ST2, the original form and a short form with 40 amino acids deleted (HS6ST2-S) (Habuchi et al. 2003). HS6ST2-S also transferred the sulfate groups, but their preferences for sulfation sites in HS substrates were different. HS6ST-2 appeared to have a preference to transfer sulfate to position 6 of GlcNSO3 residues in the IdoA(2SO4)-GlcNSO3 unit. HS6ST-2S transferred sulfate groups to position 6 of GlcNSO3 residues in the GlcA-GlcNO3 in addition to IdoA(2SO4)-GlcNSO3.

Preparation

Habuchi et al. purified HS6ST1 from the serum-free cultured medium of CHO cells as follows (Habuchi et al. 1995). All purification steps were performed at 4 °C. First, 0.1 volume (2 mL) of the medium fraction was applied to a column of heparin-sepharose CL-6B (20 × 65 mm, 20 mL) equilibrated with 0.15 M NaCl in buffer A (10 mM Tris-HCl, pH 7.2, 0.1 % (w/v) Triton X-100, 10 mM MgCl2, 2 mM CaCl2, 20 % (v/v) glycerol) at the flow rate of 70 mL/h. The column was washed with 10 column volumes (200 mL) of buffer A and then eluted with five column volumes (100 mL) of buffer A-1.0 M NaCl. The chromatography was repeated ten times. All eluates were combined, concentrated to 100 mL with polyethylene glycol 20,000 (molecular weight 15,000–25,000), and dialyzed against buffer A-0.05 M NaCl. Next, the 3′, 5′-ADP-agarose (14 × 90 mm, 1.9 μmol of 3′,5′-ADP/mL of gel) column was equilibrated with buffer A-0.05 M NaCl. Half of the fraction (50 mL) was applied at a flow rate of 13 mL/h, and the column was washed with 120 mL of buffer A-0.05 M NaCl. The sulfotransferase activity was eluted with a linear gradient of 0–0.2 mM 3′, 5′-ADP in buffer A-0.05 M NaCl of total volume (150 mL). The fractions containing sulfotransferase activity were pooled. The chromatography was performed twice, and the fractions containing the activity were combined. Finally, the heparin-sepharose CL-6B column (16 × 35 mm, 5 mL) was equilibrated with buffer A-0.15 M NaCl. The fraction was applied at the flow rate of 13 mL/h, and the column was washed with 50 mL of buffer A-0.25 M NaCl. The sulfotransferase activity was eluted with a linear gradient from 0.25 to 1.2 M NaCl in buffer A (total volume, 150 mL). The fractions containing sulfotransferase activity were pooled, dialyzed against buffer A-0.15 M NaCl, and stored at −20 °C.

Biological Aspects

Expression Pattern

From the EST profile database, mouse Hs6st1 is expressed rather ubiquitously; Hs6st2 primarily in connective tissue, heart, and spleen; and Hs6st3 slightly in brain and eye. Human HS6ST1 is also ubiquitously expressed with especially high expression observed in salivary gland. HS6ST2 is expressed primarily in bladder, brain, testis, and thyroid and HS6ST3 slightly in brain, connective tissue, and kidney. These results suggest that the expression of these isoforms may be regulated in tissue-specific manners and that each isoform may be involved in the synthesis of HS with tissue-specific structures and functions (Habuchi et al. 2000; Sedita et al. 2004; Cadwallader and Yost 2006; Buresh-Stiemke et al. 2012).

Signal Transduction

HS are important modulators for optimizing signal transduction of many pathways (Ebner et al. 2002; Kamimura et al. 2006; Lindahl and Li 2009; Kleinschmit et al. 2010; Qu et al. 2011; Kamimura et al. 2011; Song et al. 2011; Townley and Bulow 2011; Tran et al. 2012). The expression patterns of chick HS6ST1 transcripts were preferentially localized at the anterior proximal region, while HS6ST2 transcripts were localized mainly in the posterior proximal region and weakly in the anterior region (Nogami et al. 2004). Kobayashi et al. showed that the disruption of chick HS6ST1 and HS6ST2 in the prospective limb region by short hairpin RNA resulted in different decreasing patterns of 6-O-sulfation in HS in chick limb buds (Kobayashi et al. 2010). They performed an immunostaining with 10E4 antibody that specifically recognizes N-sulfated and 6-O-sulfated HS to show the level of 6-O-sulfation in the limb bud.10E4 staining was not observed in the anterior part of the mesenchyme in HS6ST1 RNAi-treated limbs and decreased both in the anterior and posterior part of the limbs treated with HS6ST2 RNAi. Staining with anti-HS antibody 3G10 that recognizes the HS stub regions generated by heparitinase digestion was not influenced by HS6ST1 nor HS6ST2 RNAi treatments, suggesting that HS polysaccharide synthesis was not affected. The expression levels of Fgf-8 and Shh in HS6ST1 RNAi limb buds were significantly decreased compared with control limb buds. The expression of Fgf-8 decreased more in the anterior region where HS6ST1 expression was preferentially observed. Significant decrease of Fgf-10 expression in the mesoderm and concomitant upregulation of Fgf-8 in the AER in the anterior region was observed in HS6ST1 RNAi limb buds. In contrast, dramatic decrease of Fgf-8, Shh, and Fgf-10 expression was observed in HS6ST2 RNAi limb buds. When the HS6ST1-RNAi vectors were injected in the anterior or middle but not the posterior regions of the developing limb buds, the truncation was observed at a high frequency. Some truncation was also observed in limb buds at similar frequency when the HS6ST2-RNAi vector was injected in the anterior, middle, and posterior regions. The results suggest that Fgf-8, Shh, and Fgf-10 expressions and signalings are regulated by 6-O-sulfation of HS regionally in chick limb buds, and thus, the 6-O-sulfation affects the limb pattern formation.

Chen et al. reported that hs6st2 was expressed in the region around the caudal vein in zebrafish Danio rerio embryos, and the morpholino hs6st2 antisense knockdown exhibited abnormalities in the branching morphogenesis of the caudal vein during embryonic development (Chen et al. 2005). In contrast, no vascular defects were observed in embryos injected with the hs6st1 morpholino. Co-injection of morpholinos against hs6st2 and vegf-a into embryos resulted in synergistic increase in the frequency of caudal vein branching defects, suggesting that Hs6st2 and Vegf-a interact in vivo during caudal vein formation. Bink et al. showed that hs6st morpholino-injected embryos displayed the phenotype of convergent-extension defects, which was reminiscent of knypek (kny)/glypican zebrafish mutants (Bink et al. 2003). Somite development was most affected in hs6st morphant embryos. In weakly affected embryos, muscle cells spanned across the somitic boundary. In more severe cases, breakdown of intersomitic boundaries was observed. Expression of myoD, a bHLH transcription factor involved in muscle differentiation, was downregulated in wild-type embryos. However, in hs6st morphants, myoD expression was maintained at high level suggesting that 6-O-sulfate residues of HS may be involved in the muscle cell differentiation.

RNAi of Drosophila Hs6st gene produced defective branching in the tracheal system, a developmental system that shares many of the signaling components required for vertebrate angiogenesis (Kamimura et al. 2001). Highly specific expression of dHs6st mRNA was detected in tracheal precursor cells, and its expression pattern was similar to that of breathless (btl), a Drosophila FGF receptor. 94 % of the dHs6st dsRNA-injected embryos survived to stage 17, the final stage of embryogenesis, and died prior to the point immediately before hatching. They showed that tracheal branch formation was disordered in dHs6st dsRNA-injected embryos without affecting tracheal cell differentiation. In dHs6st dsRNA-injected embryos, downstream of FGF signaling MAPK was not activated, indicating that 6-O-sulfation of HS was required for FGF signaling in Drosophila during tracheal development.

Knockout Mice and Transgenic Mice

Disruption of the Hs6st1 gene (Habuchi et al. 2007; Izvolsky et al. 2008; Habuchi and Kimata 2010) resulted in growth retardation and developmental abnormalities, with most embryos dying between the E15.5 and perinatal stages. Compared with their wild-type littermates, the Hs6st1 knockout mice littermates showed an ∼50 % reduction in the number of fetal microvessels in the labyrinthine zone of the placenta. VEGF-A mRNA and protein level was reduced to ∼60 and 75 % in the placenta of Hs6st1 knockout embryos. Disaccharide analysis showed a marked reduction of GlcNAc(6SO4) and HexA-GlcNSO3(6SO4) levels in Hs6st1 knockout embryos. Wnt-2 showed a decreased affinity to HS isolated from the knockout embryonic placenta. Alveolar enlargement was seen in the knockout mice, and when intra-alveolar distance was measured, mean linear intercept of the knockout mice was significantly increased, compared with the heterozygous mice (40 ± 5 versus 30 ± 4 μm, 7-day-old and 42 ± 6 versus 29 ± 4 μm, adult), indicating impaired alveolarization.

Recent studies indicate the important roles for HS in axon targeting (Irie et al. 2002; Conway et al. 2011). Different axon navigation phenotypes were observed in two HS sulfotransferase mutant mouse embryos, Hs2st −/− and Hs6st1 −/−. Hs2st −/− embryos displayed axon disorganization at the chiasm, with axons growing up the ventral midline (Pratt et al. 2006). Large number of retinal ganglion cell (RGC) axons in Hs6st1 −/− embryos grew up the contralateral optic nerve and innervated the opposite eye, which resembled the phenotype of Slit1 −/−; Slit2 −/− embryos (Plump et al. 2002). Quantitative RT-PCR analysis showed that both Hs2st and Hs6st1 were expressed in the optic chiasm. High levels of Hs6st1 expression were seen at the point at which RGC axons made errors. Retinal explants from wild-type and Hs6st1 −/− knockout mice were cultured in collagen gels on a bed of a collagen gel containing Slit2 expressing COS7 cells. RGC axons from wild-type explants showed a significant lower contact to COS7 cells expressing Slit2. In contrast, Hs6st1 −/− RGC axons showed no difference in contact to COS7 cells whether they were expressing Slit2 or not. Thus, the ability of RGC growth cones to avoid Slit2 is HS6ST1 dependent.

Sugaya et al. examined the effects of HS 6-O-sulfation in growth factor signaling using fibroblasts derived from Hs6st1- and/or Hs6st2-deficient mice (6ST1-KO, 6ST2-KO, and double knockout (dKO)) (Sugaya et al. 2008). HS compositional analysis from mouse embryonic fibroblasts (MEF) prepared from E14.5 dKO mice showed that GlcNAc6SO4 residue, HexA-GlcNSO3(6SO4) unit, and HexA(2SO4)-GlcNSO3(6SO4) unit were hardly detectable. In contrast, 2-O-sulfation in HS was increased 1.9-fold. HS6ST activity in the dKO-MEF was hardly detected, and HS2ST activity was 1.6-fold higher than that in wild-type MEFs. Neither the chain length nor the amount and composition of chondroitin sulfate (CS) were altered in dKO-MEFs. Although the expression levels of mRNAs encoding FGF receptors were similar between WT- and dKO-MEFs, FGF-4- and FGF-2-dependent signalings in dKO-MEFs were reduced to ∼30 and 60 % of WT-MEFs, respectively, and FGF-1-dependent signaling was moderately reduced, compared with that of WT-MEFs. Surface plasmon resonance biosensor analysis demonstrated that the apparent affinity of dKO-HS for FGF-4 was markedly reduced to one-fifth. The Kd value of FGF-1 affinity to HS isolated from dKO-MEFs was 2.8-fold higher than that of HS isolated from WT-MEFs. In contrast, the FGF-2 affinity to HS from dKO-MEFs was 2.5-fold higher than that of HS from WT-MEFs, probably reflecting the higher content of 2-O-sulfate groups in HS from dKO-MEFs. Thus, 6-O-sulfate in HS may regulate the signalings of multiple FGFs by affecting the interactions between ligands and their receptors.

Human Disease

As many signaling systems utilize HS for their efficient signal transduction, it is convincing that HS is involved in various disease processes (Li and Rossman 2001; Backen et al. 2007; Kato et al. 2007; Labbe et al. 2007; Waaijer et al. 2012). Papers reporting that HS6ST and 6-O-sulfation of HS participate in the pathogenesis of some diseases are summarized below.

Tornberg et al. reported that missense mutations in HS6ST1 were identified in families with idiopathic hypogonadotropic hypogonadism (IHH) with variable degrees of olfactory dysfunction and gonadotropin-releasing hormone (GnRH) deficiency (Tornberg et al. 2011). IHH is a condition characterized by failure to undergo puberty in the setting of low sex steroids and low gonadotropins as a result of defects in gonadotropin-releasing hormone neuron development or function. In Kallmann syndrome, anosmia (loss of the sense of smell) is associated with IHH. HS6ST1 mutations associated with IHH exhibited reduced sulfotransferase activity in vitro and in vivo, suggesting that HS6ST1 and the 6-O-sulfations of HS are critical for IHH pathogenesis. KAL1 gene encodes anosmin-1 protein, and the mutation is associated in some individuals with Kallmann syndrome. Mutations of KAL1 affected the normal development of the olfactory system and migration of the neurons secreting GnRH. Transgenic expression of C. elegans kal1 in AIY interneurons elicited an axon branching phenotype, which was suppressed to near-background levels by loss-of-function mutations in hst6, the single HS6ST in C. elegans. The suppression of the axonal branching phenotype was rescued by transgenic expression of a wild-type HS6ST1 cDNA. Expression of the mutant HS6ST1 cDNAs identified in IHH showed reduced capacity for transgenic rescue of the hst6 loss-of-function phenotype. HS6ST1 mutations were found in patients who had IHH with wide spectrum of severity. Two patients had microphallus, one of whom also had unilateral cryptorchidism. Three patients presented with absent puberty, whereas three male patients showed some spontaneous testicular development. Some carriers of HS6ST1 mutations did not always manifest IHH. Though the same genetic mutation was observed, there were clinical variability in patients both within and across families, indicating that HS6ST1 mutations display incomplete penetrance and variable expressivity of the IHH phenotype. Additional genetic factors may contribute to the clinical variability. In fact, mutations were found in other IHH-associated genes, FGFR1, and NELF in two different families. Thus, other genetic lesions are likely involved in this digenic or oligogenic disease in addition to HS6ST1 mutations. HS6ST2 or HS6ST3 gene may be the possible candidate.

Osteoarthritis (OA) is a disease characterized by degeneration of cartilage that leads to pain and joint stiffness. The specific causes of osteoarthritis are unknown, but age, obesity, injury and physical activity, and other factors are believed to be risk factors for OA. Kashin–Beck disease (KBD) is a chronic, endemic osteochondropathy, which is mainly distributed in China and other countries of Asia. Using suppression subtractive hybridization technique, Wang et al. screened the genes that were differentially expressed in OA cartilage and found that HS6ST2 expression was downregulated in OA and KBD at both mRNA and protein levels (Wang et al. 2011). C28/I2 chondrocytes were transfected with three different HS6ST2 siRNA oligonucleotides. They found that in HS6ST2-siRNA-transfected cells, cell viability was significantly decreased at 48 h after transfection. The mRNA expression of SOX9 and AGC1 (encoding the core protein of aggrecan) was remarkably decreased in HS6ST2-siRNA-treated cells at 24 and 48 h after transfection, respectively. At 72 h after transfection, HS6ST2-RNAi-treated cells were less stained by toluidine blue, suggesting that the aggrecan protein level was lower than in control RNAi-treated cells. When the mRNA expression levels of MMP3, ADAMTS4, and ADAMTS5, which are relevant to the degradation of aggrecan in cartilage, were examined, MMP3 expression was found to increase significantly at 24 h after HS6ST2-siRNA transfection, ADAMTS5 expression was to decrease significantly at 48 h after transfection, and ADAMTS4 expression was to show no significant difference both at 24 and 48 h after transfection. These findings suggest that HS6ST2 may participate in the pathogenesis of OA and KBD by affecting aggrecan metabolism.

Premature ovarian failure (POF) is a condition characterized by amenorrhea, infertility, sex steroid deficiency, and elevated gonadotropin serum levels in women before the age of 40. POF is frequently associated with X chromosome abnormalities ranging from various Xq deletions to complete loss of one of the X chromosomes. Two critical regions on the long arm of the X chromosome, at Xq13-q21 and Xq26-27, were identified (Davison et al. 2000). Bioinformatics analysis of those regions identified putative candidate genes for ovarian failure on the X chromosome or on autosomes that were involved in the translocation event (Baronchelli et al. 2012). Two isoforms of HS6ST gene were identified in two chromosomal breakpoints: HS6ST1 gene at 2q21 (−216Kb) and HS6ST2 gene at Xq26.2 (+720Kb). Although the definitive evidence for the involvement of HS6STs on POF is further needed, they are potent candidate genes, since HS6ST2 was expressed preferentially in the ovary and the mutation might influence oocyte development by disturbing a proper interaction with follicular growth factors, and further, the HS6ST1 gene mutations have recently been associated with IHH as described above, and these genes possibly play some roles in gonadal fertility.

Future Perspectives

In many diseases including infection and cancer, intracellular signaling systems are disturbed. Most studies tend to focus on the signaling molecule itself, but it should be considered that HS and its biosynthetic enzymes including 6-O-sulfotransferases might regulate the onset, the progression, and the severity of various diseases since HS serves as a modulator in the wide range of signaling systems and biological processes. It is becoming more important to gain a better insight into the role of HS in diseases, for example, by using mutant mice as model animals.

Cross-References

Exostoses (Multiple)-Like 1-3 (EXTL1-3)

Exostosin 1,2 (EXT1,2)

Heparan Sulfate 2-O-Sulfotransferase (HS2ST)

Heparan Sulfate (Glucosamine) 3-O-Sulfotransferase 1-6 (HS3ST1-6)

Heparin-Heparansulfate Related GlcA C5-Epimerase

N-Deacetylase/N-Sulfotransferase (Heparan Glucosaminyl) 1 (NDST1)

N-Deacetylase/N-Sulfotransferase (Heparan Glucosaminyl) 2 (NDST2)

N-Deacetylase/N-Sulfotransferase (Heparan Glucosaminyl) 3,4 (NDST3,4)

Further Reading

For review of the biological role of the zebrafish and the Drosophila Hs6st

  • Nakato and Kimata (2002)

  • Habuchi et al. (2004)

For review of the biosynthesis and biological roles of HS

  • Kusche-Gullberg and Kjellen (2003)

  • Habuchi et al. (2006)

  • Stringer (2006)

  • Bishop et al. (2007)

  • Lindahl and Li (2009)