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: Satomi Nadanaka, Shaobo Zhou, Shoji Kagiyama, Naoko Shoji, Kazuyuki Sugahara, Kazushi Sugihara, Masahide Asano, Hiroshi Kitagawa
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 288 Issue 13 Pg. 9321-33 (Mar 29 2013) ISSN: 1083-351X [Electronic] United States
• PMID: 23395820 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Glycosaminoglycans
• Membrane Proteins
• Proteoglycans
• RNA, Messenger
• Xylose
• Glycosyltransferases
• EXTL2 protein, human
• EXTL2 protein, mouse
• N-Acetylglucosaminyltransferases
• Phosphotransferases

Topics

• Alleles
• Animals
• Cloning, Molecular
• Fibroblasts (metabolism)
• Gene Expression Regulation, Enzymologic
• Genes, Tumor Suppressor
• Genomics
• Glycosaminoglycans (metabolism)
• Glycosyltransferases (metabolism)
• HeLa Cells
• Humans
• Liver (metabolism)
• Membrane Proteins (metabolism)
• Mice
• Mice, Knockout
• Mutation
• N-Acetylglucosaminyltransferases (genetics, metabolism)
• Phosphotransferases (metabolism)
• Proteoglycans (metabolism)
• RNA, Messenger (metabolism)
• Xylose (chemistry)