title: EXTL2, a member of the EXT family of tumor suppressors, controls glycosaminoglycan biosynthesis in a xylose kinase-dependent manner.
abstract: Mutant alleles of EXT1 or EXT2, two members of the EXT gene family, are causative agents in hereditary multiple exostoses, and their gene products function together as a polymerase in the biosynthesis of heparan sulfate. EXTL2, one of three EXT-like genes in the human genome that are homologous to EXT1 and EXT2, encodes a transferase that adds not only GlcNAc but also N-acetylgalactosamine to the glycosaminoglycan (GAG)-protein linkage region via an α1,4-linkage. However, both the role of EXTL2 in the biosynthesis of GAGs and the biological significance of EXTL2 remain unclear. Here we show that EXTL2 transfers a GlcNAc residue to the tetrasaccharide linkage region that is phosphorylated by a xylose kinase 1 (FAM20B) and thereby terminates chain elongation. We isolated an oligosaccharide from the mouse liver, which was not detected in EXTL2 knock-out mice. Based on structural analysis by a combination of glycosidase digestion and 500-MHz (1)H NMR spectroscopy, the oligosaccharide was found to be GlcNAcα1-4GlcUAβ1-3Galβ1-3Galβ1-4Xyl(2-O-phosphate), which was considered to be a biosynthetic intermediate of an immature GAG chain. Indeed, EXTL2 specifically transferred a GlcNAc residue to a phosphorylated linkage tetrasaccharide, GlcUAβ1-3Galβ1-3Galβ1-4Xyl(2-O-phosphate). Remarkably, the phosphorylated linkage pentasaccharide generated by EXTL2 was not used as an acceptor for heparan sulfate or chondroitin sulfate polymerases. Moreover, production of GAGs was significantly higher in EXTL2 knock-out mice than in wild-type mice. These results indicate that EXTL2 functions to suppress GAG biosynthesis that is enhanced by a xylose kinase and that the EXTL2-dependent mechanism that regulates GAG biosynthesis might be a "quality control system" for proteoglycans.
authors: Department of Biochemistry, Kobe Pharmaceutical University, 4-19-1 Motoyamakita-machi, Higashinada-ku, Kobe 658-8558, Japan.
authors: Satomi
authors: S
authors: Nadanaka
authors: Shaobo
authors: S
authors: Zhou
authors: Shoji
authors: S
authors: Kagiyama
authors: Naoko
authors: N
authors: Shoji
authors: Kazuyuki
authors: K
authors: Sugahara
authors: Kazushi
authors: K
authors: Sugihara
authors: Masahide
authors: M
authors: Asano
authors: Hiroshi
authors: H
authors: Kitagawa
mesh_terms: D000483:Alleles; D000818:Animals; D003001:Cloning, Molecular; D005347:Fibroblasts / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D016147:Genes, Tumor Suppressor; D023281:Genomics; D006025:Glycosaminoglycans / Q000378:metabolism*; D016695:Glycosyltransferases / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008099:Liver / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism*; D011509:Proteoglycans / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D014994:Xylose / Q000737:chemistry*
chemical_list: D006025:Glycosaminoglycans; D008565:Membrane Proteins; D011509:Proteoglycans; D012333:RNA, Messenger; D014994:Xylose; D016695:Glycosyltransferases; C110834:EXTL2 protein, human; C581320:EXTL2 protein, mouse; D017351:N-Acetylglucosaminyltransferases; D010770:Phosphotransferases
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