Hereditary multiple exostoses and heparan sulfate polymerization

Glycobiology Research and Training Center, Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla 92093-0687, USA.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 01/2003; 1573(3):346-55. DOI: 10.1016/S0304-4165(02)00402-6
Source: PubMed


Hereditary multiple exostoses (HME, OMIM 133700, 133701) results from mutations in EXT1 and EXT2, genes encoding the copolymerase responsible for heparan sulfate (HS) biosynthesis. Members of this multigene family share the ability to transfer N-acetylglucosamine to a variety of oligosaccharide acceptors. EXT1 and EXT2 encode the copolymerase, whereas the roles of the other EXT family members (EXTL1, L2, and L3) are less clearly defined. Here, we provide an overview of HME, the EXT family of proteins, and possible models for the relationship of altered HS biosynthesis to the ectopic bone growth characteristic of the disease.

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    • "MO is characterized by the formation of multiple cartilaginous tumors (osteochondromas), that mainly affect the metaphyses of long bones or the surface of flat bones1415161718. Complications may involve bone and surrounding tissue deformities, fractures or mechanical joint problems, vascular compression, arterial thrombosis, aneurysm, pseudoaneurysm formation, and venous thrombosis. "
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    ABSTRACT: Multiple osteochondromatosis (MO), or EXT1/EXT2-CDG, is an autosomal dominant O-linked glycosylation disorder characterized by the formation of multiple cartilage-capped tumors (osteochondromas). In contrast, solitary osteochondroma (SO) is a non-hereditary condition. EXT1 and EXT2, are tumor suppressor genes that encode glycosyltransferases involved in heparan sulfate elongation. We present the clinical and molecular analysis of 33 unrelated Latin American patients (27 MO and 6 SO). Sixty-three percent of all MO cases presented severe phenotype and two malignant transformations to chondrosarcoma (7%). We found the mutant allele in 78% of MO patients. Ten mutations were novel. The disease-causing mutations remained unknown in 22% of the MO patients and in all SO patients. No second mutational hit was detected in the DNA of the secondary chondrosarcoma from a patient who carried a nonsense EXT1 mutation. Neither EXT1 nor EXT2 protein could be detected in this sample. This is the first Latin American research program on EXT1/EXT2-CDG.
    Full-text · Article · Sep 2014 · Scientific Reports
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    • "Heparosan (−4GlcNAcα1–4GlcAβ1–), the unmodified and non-sulfated precursor of HS and HP, has also been found as the capsular polysaccharides (CPSs) of several pathogenic bacteria (DeAngelis 2002a, b), such as Escherichia coli K5 (Vann et al. 1981), Pasteurella multocida Type D (DeAngelis et al. 2002; Rimler 1994), and Avibacterium paragallinarum genotype II (Wu et al. 2010). Glycosyltransferases and polymerases (or heparosan synthases) that are responsible for the synthesis of heparosan have been identified from different biological systems, including mammalian EXT 1 and EXT 2 (Sugahara and Kitagawa 2002; Zak et al. 2002), Drosophila TTV, SOTV, and BOTV (Bellaiche et al. 1998; Izumikawa et al. 2006), E. coli K5 KfiA (Hodson et al. 2000) and KfiC (Sugiura et al. 2010), and P. multocida PmHS1 from serotype D (DeAngelis and White 2002) and PmHS2 from serotypes A, D, and F (Deangelis and White 2004). Different from PmHS1 of 617 amino acid residues whose gene (hssA) is in the cps locus of P. multocida serotype D strains, the gene encoding PmHS2 of 651 amino acid residues (hssB) is located outside of cps locus and has been found in serotypes A, D, and F strains. "
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    ABSTRACT: The biological activities of heparan sulfate (HS) and heparin (HP) are closely related to their molecular structures. Both Pasteurella multocida heparosan synthase 2 (PmHS2) and Escherichia coli K5 KfiA have been used for enzymatic and chemoenzymatic synthesis of HS and HP oligosaccharides and their derivatives. We show here that cloning using the pET15b vector and expressing PmHS2 as an N-His6-tagged fusion protein improve its expression level in E. coli. Investigation of the donor substrate specificity of the N-acetylglucosaminyltransferase activities of P. multocida heparosan synthase 2 (PmHS2) and E. coli K5 KfiA indicates the substrate promiscuities of PmHS2 and KfiA. Overall, both PmHS2 and KfiA can use uridine 5'-diphosphate-N-acetylglucosamine (UDP-GlcNAc) and some of its C2'- and C6'-derivatives as donor substrates for their α1-4-GlcNAcT activities. Nevertheless, PmHS2 has a broader tolerance towards substrate modifications. Other than the UDP-sugars that can be used by KfiA, additional C6'-derivatives of UDP-GlcNAc, UDP-glucose, and UDP-N-acetylgalactosamine (UDP-GalNAc) are tolerable substrates for the α1-4-GlcNAcT activity of PmHS2. The substrate promiscuities of PmHS2 and KfiA will allow efficient chemoenzymatic synthesis of diverse HS and HP oligosaccharide derivatives which may have improved or altered activities compared to their natural counterparts.
    Full-text · Article · May 2013 · Applied Microbiology and Biotechnology
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    • "There is evidence that the two EXT proteins cannot localize to the Golgi apparatus independent of each other but become resident in the endoplasmic reticulum (McCormick et al. 2000; Busse et al. 2007). This would be consistent with evidence that mutations in EXT1 or EXT2 genes can lead to hereditary multiple exostoses and that deletion of either gene is lethal in the mouse (Lin et al. 2000; Zak et al. 2002; Stickens et al. 2005). Antibodies against EXT2 strongly suggest a cis-Golgi localization because there is almost perfect colocalization with the GM130 marker by confocal microscopy (Fig. 3A, B). "
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    ABSTRACT: Heparan sulfate is perhaps the most complex polysaccharide known from animals. The basic repeating disaccharide is extensively modified by sulfation and uronic acid epimerization. Despite this, the fine structure of heparan sulfate is remarkably consistent with a particular cell type. This suggests that the synthesis of heparan sulfate is tightly controlled. Although genomics has identified the enzymes involved in glycosaminoglycan synthesis in a number of vertebrates and invertebrates, the regulation of the process is not understood. Moreover, the localization of the various enzymes in the Golgi apparatus has not been carried out in a detailed way using high-resolution microscopy. We have begun this process, using well-known markers for the various Golgi compartments, coupled with the use of characterized antibodies and cDNA expression. Laser scanning confocal microscopy coupled with line scanning provides high-quality resolution of the distribution of enzymes. The EXT2 protein, which when combined as heterodimers with EXT1 comprises the major polymerase in heparan sulfate synthesis, has been studied in depth. All the data are consistent with a cis-Golgi distribution and provide a starting point to establish whether all the enzymes are clustered in a multimolecular complex or are distributed through the various compartments of the Golgi apparatus.
    Full-text · Article · Aug 2012 · Journal of Histochemistry and Cytochemistry
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