P-glycoprotein expression in cartilaginous tumors

BACKGROUND AND OBJECTIVES

Malignant cartilage tumors demonstrate chemotherapeutic resistance through undetermined mechanisms. P-glycoprotein is the protein product of the multiple drug resistance gene 1 (MDR-1) and confers multidrug chemotherapeutic resistance in a variety of malignancies.

METHODS

MDR-1 expression was examined in 55 benign and malignant cartilage tumor specimens by immunohistochemistry using C219, C494, and JSB-1 antibodies, and by in situ hybridization with an MDR-1 specific oligonucleotide cDNA probe.

RESULTS

Constitutive expression of P-glycoprotein was observed in all benign and malignant cartilage tumor specimens with a similar pattern of immunohistochemical staining present with all three antibodies. In benign tumors and low grade chondrosarcomas, the staining pattern was weak to intermediate and localized to clusters of cells. However, higher grade-tumors (Grade II and III) expressed P-glycoprotein in a higher percentage of cells and with more intense staining. P-glycoprotein expression was absent in normal human articular cartilage, but was focally present in costal and growth plate cartilage. The immunohistochemistry results were confirmed by in situ hybridization in 10 cases.

CONCLUSIONS

P-glycoprotein is expressed constitutively in cartilaginous tumors, with greatest expression in high grade malignancies. The findings may account for the resistance of cartilage tumors to chemotherapeutic agents.

[Proteoglycans and pathology--new aspects]

It is well documented that proteoglycans are involved in a wide range of pathological conditions. Recently published results in international journals provide new information on the role of proteoglycans in such conditions. A mutation in the gene encoding for a cell surface proteoglycan has been demonstrated in overgrowth syndromes. A proteoglycan has been isolated from urine and shown to induce cachexia in cancer patients. Furthermore, in both achondrogenesis and colon cancer, the reduced ability to sulphate proteoglycans is due to genetic defects in cellular sulfate transporters. Finally, fibrosis has been inhibited in glomerulonephritic mice by transferring the gene for decorin, a transforming growth factor beta-1 binding proteoglycan, into muscle tissue.

Stickler syndrome. A mutation in the nonhelical 3' end of type II procollagen gene

BACKGROUND

All of the mutations in the type II procollagen (COL2A1) gene that have been identified in families affected with Stickler syndrome have been located primarily in the triple helical region of the gene. We report what we believe is the first premature stop codon in the globular C-propeptide region encoded by the COL2A1 gene, in a family affected with Stickler syndrome.

DESIGN

Genomic DNA from affected and unaffected family members of this three-generation family was amplified using the polymerase chain reaction. The polymerase chain reaction products were directly sequenced for DNA analysis.

RESULTS

Direct sequencing showed a single base deletion in exon 50, resulting in a premature stop codon in exon 51 in the globular C-propeptide of COL2A1 gene in all affected members.

CONCLUSIONS

These results implicate premature stop codons as a common cause of Stickler syndrome. The location of this premature stop codon in the far end of the nonhelical 3' end of the gene indicates that a truncated C-propeptide of at least 84 amino acid residues is inadequate for the functional gene product.

Inherited degenerative chondropathy--an autosomal dominant new clinical entity: report two cases and follow-up of four cases

Four cases of the rare disorder, inherited degenerative chondropathy have been previously reported (Kurien et al., 1989). A five-year follow-up of these patients and two additional cases are presented in this report. The progress of this disease appears to be arrested after regular dapsone therapy and there was no other organ involvement noted during the follow-up period.

Heritable diseases of cartilage caused by mutations in collagen genes

Osteoarthritis (OA) is a heterogeneous disease resulting from multiple pathogenic mechanisms. Several forms of OA are inherited in an autosomal Mendelian pattern. Recent studies have identified a variety of mutations in the type II collagen gene, which encodes the main collagenous component of articular cartilage in some forms of familial OA and other heritable diseases of cartilage, including Stickler syndrome and the chondrodysplasias. Mutations in the type X collagen gene, which encodes a major collagen of growth plate cartilage, have been identified in the Schmid type of osteochondrodysplasias. Identification of additional mutations in cartilage collagen genes in familial OA will broaden our understanding of the pathogenesis of the disease, and may permit the preventive treatment of individuals at risk.

Localization of the expression of type I, II and III collagen genes in human normal and hypochondrogenesis cartilage canals

The expression of type I, II and III collagens genes was examined in human normal and hypochondrogenesis cartilage canals employing electrophoretic analysis, immunohistochemistry and in situ hybridization techniques. In normal cartilage, collagens type I and III were present in perichondrium, in the connective tissue surrounding the vessels of cartilage canals and in the dense fibrous tissue. However, types I and III procollagen mRNAs were detected only in fibroblasts of the perichondrium and of the canals, but not in the polymorphic cells. Type II collagen was present in the cartilage matrix and in the dense fibrous tissue, in good accordance with the localization of type II procollagen mRNAs detected in the chondrocytes and in the polymorphic cells. These data suggest that there are no transitional cells expressing type I, II and III collagen genes and that polymorphic cells are of chondrocytic origin. In the case of hypochondrogenesis, type II collagen was less abundant than in normal cartilage, whereas the corresponding mRNA level was equivalent. That suggests that a postranscriptional regulation of this protein is involved in the decrease of type II collagen production. Type I collagen, unexpectedly detected in the cartilage matrix, was synthesized by chondrocytes and polymorphic cells, suggesting a replacement of type II by type I collagen. The canal hypertrophy observed in this pathological case could thus be due to a modification in the regulation of the growth of cartilage canals caused by a defective cartilage matrix.

Molecular basis of nanomelia, a heritable chondrodystrophy of chicken

Nanomelia is a recessively inherited connective tissue disorder of chicken affecting cartilage development. Other investigators have demonstrated that it involves low aggrecan production and diminished aggrecan mRNA levels. Based on genetic linkage studies showing a high likelihood that the mutation responsible for the nanomelic phenotype lay within the aggrecan gene, a series of experiments was performed to define the molecular basis of the trait. Aggrecan mRNA was present in the nucleus of the nanomelic chondrocyte but greatly reduced in the cytoplasmic compartment, a finding suggestive of a premature stop codon within the aggrecan transcript. Since no defect in mRNA splicing could be demonstrated by ribonucleasease protection studies, direct DNA sequencing was initiated by polymerase chain reaction of the mRNA and of genomic DNA. A stop codon was demonstrated at codon 1513, which is located in the eighth repeat of the chondroitin sulfate 2 domain of the large tenth exon. The mutation creates a unique BasBI restriction site which readily distinguishes the mutant and wild-type alleles.

The chondrodystrophy, nanomelia: biosynthesis and processing of the defective aggrecan precursor

The lethal chicken mutation nanomelia leads to severe skeletal defects because of a deficiency of aggrecan, which is the largest aggregating chondroitin sulphate proteoglycan of cartilage. In previous work, we have demonstrated that nanomelic chondrocytes produce a truncated aggrecan precursor that fails to be secreted, and is apparently arrested in the endoplasmic reticulum (ER). In this study, we investigated the biosynthesis and extent of processing of the abnormal aggrecan precursor. The truncated precursor was translated directly in cell-free reactions, indicating that it does not arise post-translationally. Further studies addressed the processing capabilities of the defective precursor. We found that the mutant precursor was modified by N-linked, mannose-rich oligosaccharides and by the addition of xylose, but was not further processed; this is consistent with the conclusion that it moves no further along the secretory pathway than the ER. Using brefeldin A we demonstrated that the defective precursor can function as a substrate for Golgi-mediated glycosaminoglycan chains, but does not do so in the nanomelic chondrocyte because it fails to be translocated to the appropriate membrane compartment. These studies illustrate how combined cell biological/biochemical and molecular investigations may contribute to our understanding of the biological consequences and molecular basis of genetic diseases, particularly those involving errors in large, highly modified molecules such as proteoglycans.

Mouse cartilage matrix deficiency (cmd) caused by a 7 bp deletion in the aggrecan gene

Mouse cartilage matrix deficiency (cmd) is an autosomal recessive mutation characterized by cleft palate, short limbs, tail and snout. Heterozygous mice show normal size and phenotype, while homozygous mice die just after birth due to respiratory failure. Biochemical and immunohistochemical characterization of cmd cartilage reveals normal levels of type II collagen and link protein, but an absence of the large cartilage proteoglycan, aggrecan. Here, we have mapped the aggrecan gene to a region of mouse chromosome 7 near the cmd locus. DNA sequencing of the aggrecan gene identified a 7 bp deletion in exon 5 resulting in a severely truncated molecule. The finding of an aggrecan mutation in the cmd mouse confirms the critical role of aggrecan in cartilage formation.

Mutation in the COL2A1 gene in a patient with hypochondrogenesis. Expression of mutated COL2A1 gene is accompanied by expression of genes for type I procollagen in chondrocytes

A new dominant mutation in the COL2A1 gene was found in a 38-week-old fetus with hypochondrogenesis. Denaturing gradient gel electrophoresis was used to analyze all 44 exons coding for the triple-helical domain of COL2A1 gene and the corresponding exon-intron boundaries. The technique detected a new sequence variation in exon 35. Sequencing of exon 35 demonstrated a single base mutation that converted the codon for glycine at position 604 to a codon for alanine. Electrophoresis of pepsin-digested collagen extracted from the diseased cartilage showed a doublet band of the alpha 1(II) chain of type II collagen and the presence of alpha 1(I) and alpha 2(I) chains of type I collagen. Two-dimensional analysis of cyanogen bromide peptides from the type II collagen revealed post-translational overmodification of peptides CB12, CB11, CB8, and CB10.5, whereas peptide CB9.7 migrated normally. Microscopic examination of cartilage showed that the mutation altered the organization of the growth plate. Also, articular chondrocytes contained large cisternae of rough endoplasmic reticulum. The density of the extracellular matrix was reduced, and the intensity of the staining with an antibody to type II collagen was diminished. In contrast, a significant staining with an antibody to type I collagen was observed. In situ hybridization with cRNA probes revealed a significant level of alpha 1(I) mRNA in the cytoplasm of the patient's chondrocytes. The signal for alpha 1(II) mRNA was about the same in control samples. The results indicated, therefore, that the genes for both type I and type II procollagens were simultaneously expressed in chondrocytes from the patient.

Type II collagen mutations in rare and common cartilage diseases

Cartilage diseases include a wide variety of clinical phenotypes from common osteoarthrosis to several different types of chondrodysplasias, i.e. 'disorders of cartilage', of which more than 100 different have been described. Patients frequently suffer from various symptoms affecting their joints and/or the growth of their long bones. The amount of hyaline cartilage at articular surfaces is often diminished and structurally abnormal. The surface of the cartilage may have an irregular appearance with defects extending into the subchondral bone. The major constituents of this hyaline cartilage are collagens and proteoglycans, the most abundant protein being type II collagen. It is a homotrimer of three identical alpha-chains, which are encoded by a single gene on human chromosome 12. The gene for type II collagen therefore became a likely candidate for some forms of chondrodysplasias and cartilage degeneration. Recently, both linkages and exclusions between this gene and various cartilage diseases have been reported and a growing number of mutations within the gene have also been identified.

cDNA cloning of chick cartilage chondroitin sulfate (aggrecan) core protein and identification of a stop codon in the aggrecan gene associated with the chondrodystrophy, nanomelia

We previously reported the cloning and sequencing of a 1.5-kilobase cDNA which encoded a portion of the chondroitin sulfate domain from the chick cartilage proteoglycan core protein and the localization of a species-specific monoclonal antibody epitope. Using polymerase chain reaction amplification and primer extension, cDNA clones which code for the entire proteoglycan core protein have now been obtained from a 10-day chick embryo cDNA library. The composite sequence is 6464 nucleotides long, coding for a protein of 2109 amino acid residues with a calculated M(r) = 223,500. The overall arrangement of globular and carbohydrate-attachment domains is similar to human and rat chondrosarcoma aggrecan, but there are significant differences in detailed homology between chick and mammalian core proteins. Most significantly a highly repetitive region (19 repeat units of 20 residues each), not found in either human or rat, enlarges one of the characteristic serine-glycine containing regions (designated CS-2) while the other serine-glycine containing domain (designated CS-1) is approximately one-fourth the length of the mammalian CS-1. Analysis of a polymerase chain reaction-amplified fragment encoding the chick-specific repeat region revealed a single base mutation at position 4553 (G to T transversion) that converted the codon GAA for glutamate at amino acid 1513 to TAA, a stop codon, in nanomelic chondrocytes. Genomic DNA from nanomelic liver was also digested with restriction enzyme BsaBI to verify the G to T transversion. This single mutation leads to a shortened core protein precursor with a calculated M(r) = 158,300. The resulting phenotype, nanomelia, arises because the truncated core protein is neither processed to a mature proteoglycan, nor secreted from the chondrocyte.

Biologic and clinical significance of cytogenetic and molecular cytogenetic abnormalities in benign and malignant cartilaginous lesions

Cartilaginous neoplasms are often histologically and therapeutically challenging. Predicting biologic behavior can be difficult. In this study, 120 nonneoplastic, benign, and malignant cartilaginous lesions from 103 patients were cytogenetically analyzed in a 6-year period after short-term culture. For selected cases, fluorescent in situ hybridization (FISH) techniques using chromosome-specific probes were performed on metaphase/interphase preparations and on paraffin-embedded tissue sections. Clonal abnormalities of chromosomes 2, 3, 5, 7, 8, and 12 were most frequently observed. Involvement of chromosomes 5, 8, and 12 may be etiologically significant because of the gene localizations for the human cartilage link protein, Langer-Giedion syndrome (a rare syndrome characterized by multiple exostoses), and type II collagen (a major component of normal cartilage) respectively, to these three chromosomes. That chromosome 7 abnormalities were observed only in malignant tumors is of diagnostic value. The identity of three marker chromosomes and the significance of trisomy 7 (a finding of controversial meaning), were determined with FISH. That the presence of chromosome aberrations and increasing histologic grade strongly correlated (p = 0.001) is of prognostic importance. Moreover, complex aberrations were observed nearly exclusively in high-grade tumors (p = 0.001). The data show that nonrandom chromosome loci are aberrantly affected in cartilaginous lesions and that these abnormalities may be of significant histopathogenetic consequence. In addition, these chromosome abnormalities appear to be diagnostically and prognostically valuable in classifying and grading chondromatous neoplasms.

Heredity, genes and osteoarthritis

Human osteoarthritis (OA) is a heterogeneous and multifactorial disease with multiple pathogenetic mechanisms implicated in its development and progression. Despite its complex clinical expression, it appears that some forms of OA have a heritable component. This article briefly updates the reader on recent research that addresses the subject of heredity as one of significance in the etiology of OA.

Type II collagen defect in two sibs with the Goldblatt syndrome, a chondrodysplasia with dentinogenesis imperfecta, and joint laxity

We report on a syndrome of spondylo-epimetaphyseal dysplasia, dentinogenesis imperfecta, and ligamentous hyperextensibility in two sibs born to nonconsanguineous parents. This chondrodysplasia was characterized by severe shortness of stature and an osteoporosis without fractures. Electron microscopic examination of the cartilage documented large vacuoles of dilated rough endoplasmic reticulum within the cytoplasm of chondrocytes. Gel electrophoresis of pepsin-soluble collagen extracted from cartilage demonstrated the presence of type II collagen chains with an abnormal mobility. Prolyl and lysyl hydroxylations were slightly increased. The abnormal molecules melted at a higher temperature than the normal ones. CNBr peptide mapping of type II collagen showed an altered electrophoretic migration of peptides CB 11, CB 8, and CB 10,5 whereas CB 9,7 looked normal. In addition, two small non-collagenous proteins isolated from cartilage were not found in an age-matched control individual but were detected in a normal newborn infant. The quantitation of proline-labelled collagen synthesized by dermal fibroblasts demonstrated a 50% reduction of total collagen. This decrease essentially affected the amount of extracellular type I collagen, which was secreted less efficiently than in control cells. Nevertheless, type I collagen chains behaved normally on 5% polyacrylamide gels. The reduced mRNA levels of alpha 1I and alpha 2I chains might reflect either a transcriptional defect or a decreased stability of mRNA transcripts. We suggest that the association of both pathological chondrocytes producing altered collagen type II and decreased synthesis of type I could be responsible for this peculiar phenotype. The overmodification of alpha 1II CNBr peptides is consistent with the presence of a single-base substitution in the COL2A1 gene. Whether there is a direct causal relationship between the type II collagen defect and the underexpression of type I collagen will require clarification.

Procollagen II gene mutation in Stickler syndrome

Four affected members of a family with Stickler syndrome were found to have a single base-pair deletion resulting in a translational frameshift in exon 40 of the procollagen II (COL2A1) gene on chromosome 12. This mutation was not seen in any of five clinically unaffected family members or in any of 15 unrelated control patients. All affected members had distinctly abnormal vitreous syneresis and all had retinal perivascular pigmentation. Retinal detachments occurred in three of the four affected patients. Three of the four affected patients had peripheral cortical "wedge" cataracts, and the fourth had extensive nuclear sclerosis. Abnormalities of the soft palate were found in all four affected patients. All patients reported severe joint pains, and epiphyseal dysplasia was found radiographically in all patients.

Cartilage-hair hypoplasia in Finland: epidemiological and genetic aspects of 107 patients

Cartilage-hair hypoplasia (CHH) is an autosomal recessive form of metaphyseal chondrodysplasia characterised by short limbed short stature, hypoplastic hair growth, and impaired cell mediated immunity and erythrocyte production. The syndrome is exceptionally prevalent among the Finns and among the Old Order Amish in the United States; sporadic cases have been reported from other countries. An epidemiological and genetic study of CHH in Finland showed 107 patients, 46 males and 61 females, in 85 families. Eighteen of them had died, seven before the age of 1 year. The living patients ranged in age from 1 to 51 years, median 21 years. The incidence was estimated to be 1:23,000 live births. Consanguinity was found in two families and interfamilial relationships in 20 families. Geographical distribution of the birth places of the patients and their great grandparents showed accumulation in a small area in western Finland and regional clusters were seen in other parts of the country as well. The result of the segregation analysis was in accordance with recessive inheritance with reduced penetrance.

The control of expression of type II collagen: relevance to cartilage disease

Cartilage is a unique tissue containing only one cell type, the chondrocyte, surrounded by an extensive extracellular matrix. One of the principal components of the cartilage matrix is type II collagen. The gene coding for type II collagen is relatively large and contains several distinct sequences that function to both up-regulate and down-regulate expression by interacting with chondrocyte transcription factors. Also, there appears to be regulation of collagen II expression by differential splicing of the collagen II mRNA to form different forms of the protein. Finally, the gene is a target for mutations that result in diseases of cartilage such as chondrodysplasias and some forms of osteoarthritis.

Enhanced expression of fibronectin by cmd/cmd chondrocytes and its modulation by exogenously added proteoglycan

Cartilage matrix deficiency (cmd/cmd) in mice is a genetic disorder associated with the failure of chondrocytes to synthesize the core protein of cartilage proteoglycan monomer (cartilage-PG). Immunohistochemical and biochemical analyses revealed enhanced accumulation of fibronectin in culture of cmd/cmd chondrocytes as well as in mutant cartilage tissue in vivo. Purified cartilage-PG, when added exogenously to a culture of cmd/cmd chondrocytes, caused a reduction in abnormal accumulation of fibronectin over several subsequent days of culturing. Using a fibronectin cDNA probe, we showed that, on the basis of total RNA, the fibronectin mRNA level was four or eight times higher in cmd/cmd chondrocytes than in the normal. The level of fibronectin mRNA in cmd/cmd cells was lowered by culturing the cells in the presence of added cartilage-PG. These findings suggest that the abnormal accumulation of fibronectin in the mutant cell culture is primarily due to elevation of fibronectin mRNA level, and that cartilage-PG in the extracellular matrix may affect the regulation of fibronectin biosynthesis at the steady-state level of mRNA.

Cartilage hair hypoplasia in infancy: a misleading chondrodysplasia

Among children with recessive metaphyseal dysplasia, cartilage hair hypoplasia, as described by McKusick is often recognized only during the 2nd year or later. The early radiological changes observed in six children with cartilage hair hypoplasia demonstrate the misleading aspect of this chondrodysplasia: micromelia, massive appearance of the long bones and round inferior femoral epiphyses, without distinct metaphyseal involvement. Early diagnosis permits the organisation of clinical, immunological and orthopaedic follow up and allows for correct genetic counselling.

A new chondrodystrophy mutation in Japanese quail (Coturnix japonica)

A second form of hereditary chondrodystrophy (ch-2) has been discovered in a selected line of Japanese quail, Coturnix japonica. This form of chondrodystrophy is autosomal and recessive, characterized by an overall shortening and bending of the long bones of the wings and legs, slight dwarfing of the trunk, bulging of the eyes, flattening of the head, and a parrot beak. The shortened long bones vary in regard to the amount of bending from nearly straight to bends of up to 90 degrees in the midshaft region. In severe cases, the bend is evident as a protuberance of the skin. Affected embryos usually survive the 18-day incubation period. Several have hatched, but most survived no longer than 4 days after hatching. Only one female has survived long enough to lay eggs. Testcrosses indicated that this mutation is not allelic to micromelia.