Disease relevance of EXT2

• Hereditary multiple exostoses (HME), a dominantly inherited genetic disorder characterized by multiple cartilaginous tumors, is caused by mutations in members of the EXT gene family, EXT1 or EXT2 [1].
• The sporadic osteochondroma patient carried a novel missense mutation in exon 11 of EXT2 gene, leading to an amino acid substitution [2].
• Two homologous genes, EXT1 and EXT2, responsible for the development of benign multiple cartilagenous bone tumors (exostoses) on the long bones, have been identified in the past 2 years [3].
• One sporadic chondrosarcoma demonstrated LOH for EXT1 and EXT3, while a second underwent LOH for EXT2 and chromosome 10 [4].
• Here, we have investigated the in vitro polymerization capacities of recombinant soluble EXT1, EXT2, and EXT1/2 complex on exogenous oligosaccharide acceptors derived from Escherichia coli K5 capsular polysaccharide [5].

Psychiatry related information on EXT2

• Deletion 11(p11.2p12) is a rare, yet specific, deletion syndrome involving the EXT2 locus, a gene for parietal foramina, and a mental retardation locus, and therefore can be classified as a contiguous gene deletion syndrome [6].

High impact information on EXT2

• Linkage analyses have identified three different genes for HME, EXT1 on 8q24.1, EXT2 on 11p11-13 and EXT3 on 19p (refs 6-9) [7].
• The EXT2 multiple exostoses gene defines a family of putative tumour suppressor genes [8].
• Both EXT1 and EXT2 show significant homology with one additional expressed sequence tag, defining a new multigene family of proteins with potential tumour suppressor activity [8].
• The tumor suppressors EXT1 and EXT2 are associated with hereditary multiple exostoses and encode bifunctional glycosyltransferases essential for chain polymerization of heparan sulfate (HS) and its analog, heparin (Hep) [9].
• The putative tumor suppressors EXT1 and EXT2 form a stable complex that accumulates in the Golgi apparatus and catalyzes the synthesis of heparan sulfate [10].

Biological context of EXT2

• This implies that the EXT2 gene is located at the short arm of chromosome 11, in band 11p11-p12 [11].
• The missense mutations in EXT1 and EXT2 may pinpoint crucial domains in both proteins and therefore give clues for the understanding of the pathophysiology of this skeletal disorder [12].
• We have screened 17 probands with the HME phenotype, for alterations in all translated exons and flanking intronic sequences, in the EXT1 and EXT2 genes, by conformation-sensitive gel electrophoresis [12].
• Both the EXT1 and EXT2 genes have been cloned recently and define a new family of potential tumor suppressor genes [12].
• EXT2 has an open reading frame encoding 718 amino acids with an overall homology of 30.9% with EXT1, suggesting that a family of related genes might be responsible for the development of EXT [13].

Anatomical context of EXT2

• Here, by testing a cell line with a specific defect in EXT1 in in vivo and in vitro assays, we show that EXT2 does not harbor significant glycosyltransferase activity in the absence of EXT1 [10].
• An immunohistochemical analysis on developing bones further showed that both EXT1 and EXT2 were concomitantly expressed in hypertrophic chondrocytes of forelimb bones from 1-day-old neonatal mouse, but down-regulated in maturing chondrocytes of developing cartilage from 21-day-old mouse [14].
• Here, we found that the mRNA expression of EXT2, one of the crucial enzymes for heparan sulfate-glycosaminoglycan synthesis, was markedly up-regulated in injured hypoglossal motor neurons after axotomy [15].
• These results indicate that, although multiple mutational events do not occur in the EXT1 or EXT2 genes, a complete loss of HS was found in the exostosis growth plates [16].
• The EXT1 and EXT2 genes from lymphocytes of the affected individuals were analyzed by using denaturing high-performance liquid chromatography and direct sequencing [17].

Associations of EXT2 with chemical compounds

• The EXT1 and EXT2 genes have been cloned and defined as glycosyltransferases involved in the synthesis of heparan sulfate [18].
• Although both EXT1 and EXT2 exhibit GlcNAc transferase and GlcUA transferase activities required for the HS synthesis, no HS chain polymerization has been demonstrated in vitro using recombinant enzymes [19].
• The EXT2 mutation identified in the SNU-OC15 family was a missense mutation at codon 85 of exon 2 (TGC-->CGC), resulting in an amino acid change from cysteine to arginine [20].
• In contrast, incubations with recombinant EXT2 resulted in the addition of a single glucuronic acid but no further polymerization [5].
• Reported elsewhere in detail, genetic linkage analysis mapped the causative gene to chromosome 11 and molecular studies revealed a guanine-to-thymine transversion in the ext2 gene [21].

Other interactions of EXT2

• From this analysis, we conclude that mutations in either the EXT1 or the EXT2 gene are responsible for the majority of EXT cases [22].
• Genetic analyses have revealed HME to be a multigenic disorder linked to three loci on chromosomes 8q24 (EXT1), 11p11-13 (EXT2), and 19p (EXT3) [18].
• However, in situ hybridization of sectioned embryos revealed remarkable differences in expression profiles of EXT1, EXT2, and EXTL1 [18].
• Using polymerase chain reaction and direct sequencing, we analyzed the EXT1 and EXT2 genes in three familial cases and one sporadic case of HME in Taiwanese patients [23].
• The EXT2-GalNAc-T5 interaction provides the first direct physical link between EXT proteins and known components of glycosamino-glycan synthesis [24].

Analytical, diagnostic and therapeutic context of EXT2

• In this study, we performed a mutational analysis of EXT1 and EXT2 genes in eight unrelated Korean EXT families by polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis followed by direct DNA sequencing [20].
• We investigated the expression of EXT1 and EXT2 (quantitative RT-PCR) and of different HSPGs (immunohistochemistry) in solitary and hereditary osteochondromas and in cases with malignant progression to secondary peripheral chondrosarcoma, in relation to possible mutations and promoter methylation [25].
• In order to develop an efficient screening strategy for mutations in these genes, we performed two independent blind screens of EXT1 and EXT2 in 34 unrelated patients with HME, using denaturing high-performance liquid chromatography (DHPLC) and fluorescent single-strand conformation polymorphism analysis (F-SSCP) [26].
• In patients suspected to be affected by MO, we recommend a quantitative analysis such as MLPA, followed by direct sequence analysis for the screening of the EXT1 and EXT2 genes [27].
• We also determined subcellular localization and quantitation of EXT1 and EXT2 proteins by immunocytochemistry using antibodies raised against unique peptide epitopes [28].

References