Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Exostosin 1”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed2002

Cerebellar proteoglycans regulate sonic hedgehog responses during development.

Sonic hedgehog promotes proliferation of developing cerebellar granule cells. As sonic hedgehog is expressed in the cerebellum throughout life it is not clear why proliferation occurs only in the early postnatal period and only in the external granule cell layer. We asked whether heparan sulfate proteoglycans might regulate sonic hedgehog-induced proliferation and thereby contribute to the specialized proliferative environment of the external granule cell layer. We identified a conserved sequence within sonic hedgehog that is essential for binding to heparan sulfate proteoglycans, but not for binding to the receptor patched. Sonic hedgehog interactions with heparan sulfate proteoglycans promote maximal proliferation of postnatal day 6 granule cells. By contrast, proliferation of less mature granule cells is not affected by sonic hedgehog-proteoglycan interactions. The importance of proteoglycans for proliferation increases during development in parallel with increasing expression of the glycosyltransferase genes, exostosin 1 and exostosin 2. These data suggest that heparan sulfate proteoglycans, synthesized by exostosins, may be critical determinants of granule cell proliferation.

Amino Acid Sequence↗
PubMed2006

Three novel EXT1 and EXT2 gene mutations in Taiwanese patients with multiple exostoses.

Multiple osteochondromatosis, also known as hereditary multiple exostoses (HME), is an inherited autosomal dominant disorder characterized by the presence of multiple exostoses on the long bones. These exostoses are benign cartilaginous tumors (enchondromata). Three different exostosis (EXT) loci on chromosomes 8q (exostosin 1, EXT1), 11p (exostosin 2, EXT2) and 19p (exostosin 3, EXT3) have been reported. Recently, the EXT1 and EXT2 genes were identified by positional cloning. 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. We found three novel mutations (S277X in the EXT1 gene, and G194X and 939+1G>A in the EXT2 gene) and a known mutation (Q172X in the EXT2 gene). Mutation analysis in families with HME allows for genetic counseling and prenatal diagnosis.

DNA Mutational Analysis↗
PubMed2005

Differentiation-induced loss of heparan sulfate in human exostosis derived chondrocytes.

An exostosis or osteochondroma is an aberrant bony growth occurring next to the growth plate either as an isolated growth abnormality or as part of the Hereditary Multiple Exostosis (HME) syndrome. Mutations in either exostosin 1 (EXT1) or exostosin 2 (EXT2) gene cause the HME syndrome and also some isolated osteochondromas. The EXT1 and EXT2 genes are glycosyltransferases that function as hetero-oligomers in the Golgi to add repeating glycosaminoglycans (GAGs) to heparan sulfate (HS) chains. Previously, we demonstrated that HS is markedly diminished in the exostosis cartilage cap and that the HS proteoglycan, perlecan, has an abnormal distribution in these caps. The present studies were undertaken to evaluate which chondrocyte-specific functions are associated with diminished HS synthesis in human chondrocytes harboring either EXT1 or EXT2 mutations. Systematic evaluation of exostosis cartilage caps and chondrocytes, both in vitro and in vivo, suggests that chondrocyte-specific cell functions account for diminished HS levels. In addition, we provide evidence that perichondrial cells give rise to chondrocytes that clonally expand and develop into an exostosis. Undifferentiated EXT chondrocytes synthesized amounts of HS similar to control chondrocytes; however, EXT chondrocytes displayed very poor survival in vitro under conditions that promote normal chondrocyte differentiation with high efficiency. Collectively, these observations suggest that loss of one copy of either the EXT1 or EXT2 gene product compromises the perichondrial chondrocytes' ability to differentiate normally and to survive in a differentiated state in vitro. In vivo, these compromised responses may lead to abnormal chondrocyte growth, perhaps from a perichondrial stem cell reserve.

Cell Differentiation↗
PubMed2005

Distinct tissue-specificity of three zebrafish ext1 genes encoding proteoglycan modifying enzymes and their relationship to somitic Sonic hedgehog signaling.

Proteins of the EXT (Exostosin) 1 family are known for their role in human disease. Mutations in EXT1 cause hereditary multiple exostoses (HME), benign outgrowths of the bones, and therefore were classed as tumor suppressors. More recently, their role during embryonic development of Drosophila and mouse was addressed, revealing important functions of EXT1 genes in major signaling pathways. Here, we report the isolation of three zebrafish members of the EXT1 family, which we named ext1a, ext1b, and ext1c, respectively. They are expressed in restricted temporal and spatial domains during development. Both ext1a and ext1b are provided maternally and expressed during gastrulation: ext1a in the neurectoderm and ext1b in the embryonic midline and in the involuting mesendoderm of the germ ring. During somitogenesis stages, transcripts of all three ext genes can be found in the somitic mesoderm. Furthermore, ext1a is expressed in the dorsal neural tube. These expression domains become more pronounced at 24 hr postfertilization (hpf). At 48 hpf, ext1 genes are present in the brain, while somitic expression ceases. Zebrafish have three members of the EXT1 family, in contrast to only one EXT1 gene in mammals or Xenopus, consistent with the occurrence of partial genome duplications in the teleost lineage. Our expression analysis reveals that the three ext genes have distinct expression patterns, reflecting functional divergence after duplication. In addition, expression of ext1a and ext1c responds to elevated and reduced levels of Sonic hedgehog (shh) signaling in the somites, whereas expression of ext1b does not. This suggests a differential relationship between the shh pathway and individual ext gene function in zebrafish.

Amino Acid Sequence↗
PubMed2000

Up-regulation of PTHrP and Bcl-2 expression characterizes the progression of osteochondroma towards peripheral chondrosarcoma and is a late event in central chondrosarcoma.

Chondrosarcomas are malignant cartilage-forming tumors arising centrally in bone (central chondrosarcoma) or within the cartilaginous cap of osteochondroma (peripheral chondrosarcoma). For hereditary multiple osteochondromas, two responsible genes, EXT1 and EXT2, have been cloned. Their recently elucidated role in heparan sulfate biosynthesis and Hedgehog diffusion leads to the hypothesis that EXT inactivation affects fibroblast growth factor (FGF) and Indian Hedgehog (IHh)/parathyroid hormone-related peptide (PTHrP) signaling, two important pathways in chondrocyte proliferation and differentiation. The expression of PTHrP, PTHrP-receptor, Bcl-2, FGF2, FGFR1, FGFR3, and p21 is investigated by immunohistochemistry in osteochondromas (n = 24) and peripheral (n = 29) and central (n = 20) chondrosarcomas. IHh/PTHrP and FGF signaling molecules are mostly absent in osteochondromas. Although no somatic EXT mutations were found in sporadic osteochondromas, the putative EXT downstream targets are affected similarly in sporadic and hereditary tumors. In chondrosarcomas, re-expression of FGF2, FGFR1, PTHrP, Bcl-2, and p21 is found. Expression levels increase with increasing histological grade. Up-regulation of PTHrP and Bcl-2 characterizes malignant transformation of osteochondroma because PTHrP and Bcl-2 expression is significantly higher in borderline and grade I peripheral chondrosarcomas compared with osteochondromas. In contrast, up-regulation of PTHrP and Bcl-2 seems to be a late event in central cartilaginous tumorigenesis because expression is mainly restricted to high-grade central tumors.

Adolescent↗
PubMedDate not supplied

Herpes simplex virus: discovering the link between heparan sulphate and hereditary bone tumours.

To gain entry into the host, viruses use host cell surface molecules that normally serve as receptors for other ligands. Herpes simplex virus type 1 (HSV-1) uses heparan sulphate (HS) glycosaminoglycans (GAGs) as receptors for initial attachment to the host cell surface. HS GAGs are both ubiquitous and structurally diverse, and normally serve as critical mediators of interactions between the cell and the extracellular environment. We have used the HS binding ability of HSV-1 to identify the function of a cellular gene, EXT1, which is involved in HS polymerisation. Cellular factors that affect virus growth and replication are often key regulators of the cell cycle and EXT1 is no different-humans with inherited mutations in EXT1 have developmental defects that lead to bone tumours (hereditary multiple exostoses, HME) and sometimes chondrosarcomas. Thus, as a result of using HSV-1 as a molecular probe, a functionally orphaned disease gene now has a defined function. These findings highlight the utility of viruses for investigating important cellular processes.

Cell Line↗
PubMed2000

Molecular basis of multiple exostoses: mutations in the EXT1 and EXT2 genes.

Hereditary multiple exostoses (EXT) is an autosomal dominant disorder characterized by the formation of exostoses, which are cartilage-capped bony protuberances mainly located on long bones. Two genes, EXT1 and EXT2, and at least one other unidentified gene, are known to be involved in the formation of exostoses. To date, 49 different EXT1 and 25 different EXT2 mutations have been found in EXT patients, and there is evidence that mutations in these two genes are responsible for over 70% of the EXT cases. Among the 49 EXT1 mutations there are 9 nonsense, 21 frameshift, and 5 splice site mutations; 2 in-frame deletions of 1 and 5 amino acids respectively; and 12 missense mutations. For EXT2, 8 nonsense, 11 frameshift, 3 splice site and 3 missense mutations are described. The majority of these mutations are mutations causing loss of function, which is consistent with the presumed tumor suppressor function of the EXT genes.

Exostoses, Multiple Hereditary↗
PubMed2005

Mutation screening of EXT1 and EXT2 by direct sequence analysis and MLPA in patients with multiple osteochondromas: splice site mutations and exonic deletions account for more than half of the mutations.

Multiple osteochondromas (MO) is an autosomal dominant condition, caused by mutations in either the EXT1 or the EXT2 gene. The DNA of a cohort of 35 patients, clinically suspected to be affected with MO, was screened for mutations by a combination of direct sequence analysis and multiplex ligation-dependent probe amplification (MLPA). In this cohort, 26 pathogenic gene alterations were found (74%). With sequence analysis mutations were detected in 22 patients (63%). In total, 10 mutations were detected in the EXT1 and 12 in the EXT2 gene. The number of the splice site mutations detected was larger than expected from the literature. In addition, with the MLPA four deletions of one or more exons were found in this cohort. Two patients, of whom one had a negative family history, showed deletions of exon 1 of the EXT1 gene, which is possibly a deletion hot spot. 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.

Cohort Studies↗
PubMed1999

A direct interaction between EXT proteins and glycosyltransferases is defective in hereditary multiple exostoses.

Hereditary multiple exostoses (HME) is an autosomal dominant condition in which bony outgrowths occur from the juxtaepiphyseal regions of the long bones. In a few percent of cases these exostoses undergo malignant transformation to chondrosarcomas. HME results from mutations in one of two homologous genes, EXT1 and EXT2. These are members of a new gene family that is conserved from Caenorhabditis elegans to higher vertebrates. In humans this family comprises five genes which are most conserved at their C-termini, but they do not contain any discernible functional motifs and their function(s) is unclear. Indirect evidence suggests that EXT proteins are involved in glycosaminoglycan synthesis, act as tumor suppressors and affect hedgehog signaling. One recent study has also reported that these proteins co-purify with glycosyltransferase (GlcA and GlcNAc transferase) activity and on that basis it has been postulated that they are themselves glycosyl-transferases. We performed two-hybrid screens with a fragment of EXT2 from the region that is most highly conserved in the gene family and identified two interacting proteins: the tumor necrosis factor type 1 associated protein and a novel UDP-GalNAc:poly-peptide N -acetylgalactosaminyltransferase. Significantly, both these interactions were abrogated by a disease-causing EXT mutation, indicating that they are important in the etiology of HME. The EXT2-GalNAc-T5 interaction provides the first direct physical link between EXT proteins and known components of glycosamino-glycan synthesis.

Amino Acid Sequence↗
PubMed1997

Identification of novel mutations in the human EXT1 tumor suppressor gene.

Hereditary multiple exostoses (EXT) is a genetically heterogeneous bone disorder caused by genes segregating on human chromosomes 8, 11, and 19 and designated EXT1, EXT2 and EXT3, respectively. Recently, the EXT1 gene has been isolated and partially characterized and appears to encode a tumor suppressor gene. We have identified six mutations in the human EXT1 gene from six unrelated multiple exostoses families segregating for the EXT gene on chromosome 8. One of the mutations we detected is the same 1-bp deletion in exon 6 that was previously reported in two independent EXT families. The other five mutations, in exons 1, 6, 9, and the splice junction at the 3' end of exon 2, are novel. In each case, the mutation is likely to result in a truncated or nonfunctional EXT1 protein. These results corroborate and extend the previous report of mutations in this gene in two EXT families, and provide additional support for the EXT1 gene as the cause of hereditary multiple exostoses in families showing linkage to chromosome 8.

Alternative Splicing↗
PubMed2004

Novel mutations in the EXT1 gene in two consanguineous families affected with multiple hereditary exostoses (familial osteochondromatosis).

Multiple hereditary exostoses (HME) is an autosomal dominant developmental disorder exhibiting multiple osteocartilaginous bone tumors that generally arise near the ends of growing long bones. Here, we report two large consanguineous families from Pakistan, who display the typical features of HME. Affected individuals also show a previously unreported feature--bilateral overriding of single toes. Analysis using microsatellite markers for each of the known EXT loci, EXT1, EXT2, and EXT3 showed linkage to EXT1. In the first family, mutation analysis of the EXT1 gene revealed that affected individuals were heterozygous for an in-frame G-to-C transversion at the conserved splice donor site in intron 1. This mutation is predicted to disrupt splicing of the first intron and produce a frameshift that leads to a premature termination codon. In the second family, an insertion of an A in exon 8 is predicted to produce a frameshift at codon 555 followed by a premature termination, a further 10 codons downstream. In both families, an increased number of affected male subjects were observed. In affected females in family 2, phenotypic variability and incomplete penetrance were noted.

Base Sequence↗
PubMed1999

EXT-mutation analysis and loss of heterozygosity in sporadic and hereditary osteochondromas and secondary chondrosarcomas.

Osteochondromas occur as sporadic solitary lesions or as multiple lesions, characterizing the hereditary multiple exostoses syndrome (EXT). Approximately 15% of all chondrosarcomas arise within the cartilaginous cap of an osteochondroma. EXT is genetically heterogeneous, and two genes, EXT1 and EXT2, located on 8q24 and 11p11-p12, respectively, have been cloned. It is still unclear whether osteochondroma is a developmental disorder or a true neoplasm. Furthermore, it is unclear whether inactivation of both alleles of an EXT gene, according to the tumor-suppressor model, is required for osteochondroma development, or whether a single EXT germline mutation acts in a dominant negative way. We therefore studied loss of heterozygosity and DNA ploidy in eight sporadic and six hereditary osteochondromas. EXT1- and EXT2-mutation analysis was performed in a total of 34 sporadic and hereditary osteochondromas and secondary peripheral chondrosarcomas. We demonstrated osteochondroma to be a true neoplasm, since aneuploidy was found in 4 of 10 osteochondromas. Furthermore, LOH was almost exclusively found at the EXT1 locus in 5 of 14 osteochondromas. Four novel constitutional cDNA alterations were detected in exon 1 of EXT1. Two patients with multiple osteochondromas demonstrated a germline mutation combined with loss of the remaining wild-type allele in three osteochondromas, indicating that, in cartilaginous cells of the growth plate, inactivation of both copies of the EXT1 gene is required for osteochondroma formation in hereditary cases. In contrast, no somatic EXT1 cDNA alterations were found in sporadic osteochondromas. No mutations were found in the EXT2 gene.

Adolescent↗
PubMed2000

Association of EXT1 and EXT2, hereditary multiple exostoses gene products, in Golgi apparatus.

We prepared the specific antibodies for EXT1 and EXT2, hereditary multiple exostoses (HME) gene products, and characterized their expression, subcellular localization, and protein association among EXT members. Biochemical analyses indicate that EXT1 and EXT2 can associate and form homo/hetero-oligomers in vivo with or without HME-linked mutations, EXT1 (R340C) and EXT2 (D227N), when exogenously expressed in COS-7 cells. An immunocytochemical analysis showed that both EXT1 and EXT2 localized in Golgi apparatus, irrespective of HME mutations. 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. Taken together with the recent finding that EXTs encode for the glycosyltransferase required for the synthesis of heparan sulfate [Lind, T., Tufaro, F., McCormick, C., Lindahl, U., and Lindholt, K. (1998) J. Biol. Chem. 273, 26265-26268], our results implied a molecular basis that a HME-linked mutation found in EXT genes could interfere the physiological function(s) of EXT homo/hetero-oligomers as glycosyltransferases in the developing bones of HME patients.

Animals↗
PubMed2005

Methylation status of EXT1 and EXT2 promoters and two mutations of EXT2 in chondrosarcoma.

Germline mutation and functional loss of EXT1 or EXT2 are commonly found in multiple osteochondromas and predispose to the development of chondrosarcoma. Mutations of EXT1 and EXT2 have rarely been detected in sporadic secondary chondrosarcomas from osteochondroma; these frequently display loss of heterozygosity at the EXT1 and EXT2 loci, but primary chondrosarcomas typically do not. To evaluate promoter methylation (which is an epigenetic gene silencing mechanism) of EXT1 and EXT2, we performed methylation-specific polymerase chain reaction (PCR) for 20 chondrosarcoma cases (12 primary, 3 secondary to osteochondroma, 2 secondary to enchondromatosis, 2 extraskeletal ordinary, and 1 clear cell) and in five cell lines. In addition, mutation analysis of the EXT1 and EXT2 coding regions was performed using PCR-single-strand conformation polymorphism and sequencing analysis for 12 of the 20 chondrosarcoma cases (8 primary, 1 secondary to enchondromatosis, 1 secondary to osteochondroma, and 2 extraskeletal ordinary) and five cell lines. Promoter methylation of EXT1 and EXT2 was not detected in any of the cases, and both EXT1 and EXT2 were expressed in all cell lines. Two missense mutations in EXT2 (D227E and R299H) were detected among the chondrosarcoma cases. When considering tumor development in primary chondrosarcoma, we should include mutations in EXT2, along with the status of other members of the EXT gene family.

5' Untranslated Regions↗
PubMed1997

Mutation screening of the EXT1 and EXT2 genes in patients with hereditary multiple exostoses.

Hereditary multiple exostoses (HME), the most frequent of all skeletal dysplasias, is an autosomal dominant disorder characterized by the presence of multiple exostoses localized mainly at the end of long bones. HME is genetically heterogeneous, with at least three loci, on 8q24.1 (EXT1), 11p11-p13 (EXT2), and 19p (EXT3). Both the EXT1 and EXT2 genes have been cloned recently and define a new family of potential tumor suppressor genes. This is the first study in which mutation screening has been performed for both the EXT1 and EXT2 genes prior to any linkage analysis. 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. We found the disease-causing mutation in 12 families (70%), 7 (41%) of which have EXT1 mutations and 5 (29%) EXT2 mutations. Together with the previously described 1-bp deletion in exon 6, which is present in 2 of our families, we report five new mutations in EXT1. Two are missense mutations in exon 2 (G339D and R340C), and the other three alterations (a nonsense mutation, a frameshift, and a splicing mutation) are likely to result in truncated nonfunctional proteins. Four new mutations are described in EXT2. A missense mutation (D227N) was found in 2 different families; the other three alterations (two nonsense mutations and one frameshift mutation) lead directly or indirectly to premature stop codons. 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.

Electrophoresis, Polyacrylamide Gel↗
PubMed2005

A novel EXT1 splice site mutation in a kindred with hereditary multiple exostosis and osteoporosis.

CONTEXT: Hereditary multiple exostosis (HME) is an autosomal dominant disorder characterized by the development of benign cartilage-capped tumors at the juxta-epiphyseal regions of long bones. HME is usually caused by mutations of EXT1 or EXT2. OBJECTIVE: The objective of this study was to investigate a three-generation Austrian kindred with HME for EXT1 and EXT2 mutations and for abnormalities of bone mineral density (BMD). METHODS: DNA sequence and mRNA analyses were used to identify the mutation and its associated consequences. Serum biochemical and radiological investigations assessed bone metabolism and BMD. RESULTS: HME-affected members had a lower femoral neck BMD compared with nonaffected members (z-scores, -2.98 vs. -1.30; P = 0.011), and in those less than 30 yr of age, the lumbar spine BMD was also low (z-scores, -2.68 vs. -1.42; P = 0.005). However, they had normal mobility and normal serum concentrations of calcium, phosphate, alkaline phosphatase activity, creatinine, PTH, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, osteocalcin, and beta-crosslaps. DNA sequence analysis of EXT1 revealed a heterozygous g-->c transversion that altered the invariant ag dinucleotide of the intron 8 acceptor splice site. RT-PCR analysis using lymphoblastoid RNA showed that the mutation resulted in skipping of exon 9 with a premature termination at codon 599. DNA sequence abnormalities of the osteoprotegerin gene, which is in close proximity to the EXT1 gene, were not detected. CONCLUSIONS: A novel heterozygous acceptor splice site mutation of EXT1 results in HME that is associated with a low peak bone mass, indicating a possible additional role for EXT1 in bone biology and in regulating BMD.

Adolescent↗
PubMed1998

Structure, chromosomal location, and expression profile of EXTR1 and EXTR2, new members of the multiple exostoses gene family.

Hereditary multiple exostoses (EXT) is an autosomal dominant disorder that is characterized by the appearance of multiple outgrowths of the long bones (exostoses) at their epiphyses. Genetical heterogeneities have segregated at least on chromosome 8, 11, and 19 and been designated EXT1, EXT2, and EXT3, respectively. Recently, the responsible genes for EXT1 and EXT2 have been isolated and appeared to define a structurally related gene family. In the present study, we have identified novel genes which share significant sequence homologies with the EXT genes. The predicted protein products of the novel EXT-related genes, EXTR and EXTR2 (for EXT-related genes 1 and 2), consist of 919 and 330 amino acid residues, respectively. These genes were transcribed ubiquitously in various tissues. Based on PCR-assisted analyses of both a human/rodent mono-chromosomal hybrid cell panel and a radiation hybrid mapping panel, EXTR1 was localized to the chromosome 8p21 region, where loss of heterozygosity has been frequently observed in various tumors, and EXTR2 was assigned to the chromosome 1p21 region, where osteopetrosis, a dominant hereditary disease of bone, has been mapped by genetic linkage analysis, implying that the protein products of these two EXT-related genes, as well as of the EXT genes, have potential tumor suppressor activity.

Amino Acid Sequence↗