Mucopolysaccharide and protein--polysaccharide of a transplantable rat chondrosarcoma

Simultaneous proteoglycans and hypoxia mapping of chondrosarcoma environment by frequency selective CEST MRI

PURPOSE

To evaluate the relevance of CEST frequency selectivity in simultaneous in vivo imaging of both of chondrosarcoma's phenotypic features, that are, its high proteoglycan concentration and its hypoxic core.

METHODS

Swarm rat chondrosarcomas were implanted subcutaneously in NMRI nude mice. When tumors were measurable (12-16 days postoperative), mice were submitted to GAG, guanidyl, and APT CEST imaging. Proteoglycans and hypoxia were assessed in parallel by nuclear imaging exploiting ^99m Tc-NTP 15-5 and ¹⁸ F-FMISO, respectively. Data were completed by ex vivo analysis of proteoglycans (histology and biochemical assay) and hypoxia (immunofluorescence).

RESULTS

Quantitative analysis of GAG CEST evidenced a significantly higher signal for tumor tissues than for muscles. These results were in agreement with nuclear imaging and ex vivo data. For imaging tumoral pH in vivo, the CEST ratio of APT/guanidyl was studied. This highlighted an important heterogeneity inside the tumor. The hypoxic status was confirmed by ¹⁸ F-FMISO PET imaging and ex vivo immunofluorescence.

CONCLUSION

CEST MRI simultaneously imaged both chondrosarcoma properties during a single experimental run and without the injection of any contrast agent. Both MR and nuclear imaging as well as ex vivo data were in agreement and showed that this chondrosarcoma animal model was rich in proteoglycans. However, even if tumors were lightly hypoxic at the stage studied, acidic areas were highlighted and mapped inside the tumor.

Simvastatin promotes restoration of chondrocyte morphology and phenotype

In this study we examined whether the action of simvastatin affects re-differentiation of passaged chondrocytes and if so, whether this was mediated via changes in cholesterol or cholesterol intermediates. Bovine articular chondrocytes, of varying passage number, human knee chondrocytes and rat chondrosarcoma chondrocytes were treated with simvastatin and examined for changes in mRNA and protein expression of markers of the chondrocyte phenotype as well as changes in cell shape, proliferation and proteoglycan production. In all three models, while still in monolayer culture, simvastatin treatment alone promoted changes in phenotype and morphology indicative of re-differentiation most prominent being an increase in SOX9 mRNA and protein expression. In passaged bovine chondrocytes, simvastatin stimulated the expression of SOX9, ACAN, BMP2 and inhibited the expression of COL1 and α-smooth muscle actin. Co-treatment of chondrocytes with simvastatin plus exogenous cholesterol-conditions that had previously reversed the inhibition on CD44 shedding, did not alter the effects of simvastatin on re-differentiation. However, the co-treatment of chondrocytes with simvastatin together with other pathway intermediates, mevalonate, geranylgeranylpyrophosphate and to a lesser extent, farnesylpyrophosphate, blocked the pro-differentiation effects of simvastatin. Treatment with simvastatin stimulated expression of SOX9 and COL2a and enhanced SOX9 protein in human OA chondrocytes. The co-treatment of OA chondrocytes with mevalonate or geranylgeranylpyrophosphate, but not cholesterol, blocked the simvastatin effects. These results lead us to conclude that the blocking of critical protein prenylation events is required for the positive effects of simvastatin on the re-differentiation of chondrocytes.

CRISPR/Cas9 knockout of HAS2 in rat chondrosarcoma chondrocytes demonstrates the requirement of hyaluronan for aggrecan retention

Hyaluronan (HA) plays an essential role in cartilage where it functions to retain aggrecan. Previous studies have suggested that aggrecan is anchored indirectly to the plasma membrane of chondrocytes via its binding to cell-associated HA. However, reagents used to test these observations such as hyaluronidase and HA oligosaccharides are short term and may have side activities that complicate interpretation. Using the CRISPR/Cas9 gene editing approach, a model system was developed by generating HA-deficient chondrocyte cell lines. HA synthase-2 (Has2)-specific single guide RNA was introduced into two different variant lines of rat chondrosarcoma chondrocytes; knockout clones were isolated and characterized. Two other members of the HA synthase gene family were expressed at very low relative copy number but showed no compensatory response in the Has2 knockouts. Wild type chondrocytes of both variants exhibited large pericellular matrices or coats extending from the plasma membrane. Addition of purified aggrecan monomer expanded the size of these coats as the proteoglycan became retained within the pericellular matrix. Has2 knockout chondrocytes lost all capacity to assemble a particle-excluding pericellular matrix and more importantly, no matrices formed around the knockout cells following the addition of purified aggrecan. When grown as pellet cultures so as to generate a bioengineered neocartilage tissue, the Has2 knockout chondrocytes assumed a tightly-compacted morphology as compared to the wild type cells. When knockout chondrocytes were transduced with Adeno-ZsGreen1-mycHas2, the cell-associated pericellular matrices were restored including the capacity to bind and incorporate additional exogenous aggrecan into the matrix. These results suggest that HA is essential for aggrecan retention and maintaining cell separation during tissue formation.

Continuous-Wave Stimulated Emission Depletion Microscope for Imaging Actin Cytoskeleton in Fixed and Live Cells

Stimulated emission depletion (STED) microscopy provides a new opportunity to study fine sub-cellular structures and highly dynamic cellular processes, which are challenging to observe using conventional optical microscopy. Using actin as an example, we explored the feasibility of using a continuous wave (CW)-STED microscope to study the fine structure and dynamics in fixed and live cells. Actin plays an important role in cellular processes, whose functioning involves dynamic formation and reorganization of fine structures of actin filaments. Frequently used confocal fluorescence and STED microscopy dyes were employed to image fixed PC-12 cells (dyed with phalloidin- fluorescein isothiocyante) and live rat chondrosarcoma cells (RCS) transfected with actin-green fluorescent protein (GFP). Compared to conventional confocal fluorescence microscopy, CW-STED microscopy shows improved spatial resolution in both fixed and live cells. We were able to monitor cell morphology changes continuously; however, the number of repetitive analyses were limited primarily by the dyes used in these experiments and could be improved with the use of dyes less susceptible to photobleaching. In conclusion, CW-STED may disclose new information for biological systems with a proper characteristic length scale. The challenges of using CW-STED microscopy to study cell structures are discussed.

Extracellular processing of the cartilage proteoglycan aggregate and its effect on CD44-mediated internalization of hyaluronan

In many cells hyaluronan receptor CD44 mediates the endocytosis of hyaluronan and its delivery to endosomes/lysosomes. The regulation of this process remains largely unknown. In most extracellular matrices hyaluronan is not present as a free polysaccharide but often is found in complex with other small proteins and macromolecules such as proteoglycans. This is especially true in cartilage, where hyaluronan assembles into an aggregate structure with the large proteoglycan termed aggrecan. In this study when purified aggrecan was added to FITC-conjugated hyaluronan, no internalization of hyaluronan was detected. This suggested that the overall size of the aggregate prevented hyaluronan endocytosis and furthermore that proteolysis of the aggrecan was a required prerequisite for local, cell-based turnover of hyaluronan. To test this hypothesis, limited C-terminal digestion of aggrecan was performed to determine whether a size range of aggrecan exists that permits hyaluronan endocytosis. Our data demonstrate that only limited degradation of the aggrecan monomer was required to allow for hyaluronan internalization. When hyaluronan was combined with partially degraded, dansyl chloride-labeled aggrecan, blue fluorescent aggrecan was also visualized within intracellular vesicles. It was also determined that sonicated hyaluronan of smaller molecular size was internalized more readily than high molecular mass hyaluronan. However, the addition of intact aggrecan to hyaluronan chains sonicated for 5 and 10 s reblocked their endocytosis, whereas aggregates containing 15-s sonicated hyaluronan were internalized. These data suggest that hyaluronan endocytosis is regulated in large part by the extracellular proteolytic processing of hyaluronan-bound proteoglycan.

New chondrosarcoma cell lines and mouse models to study the link between chondrogenesis and chemoresistance

Chondrosarcomas are cartilage-forming, poorly vascularized tumors. They represent the second malignant primary bone tumor of adults after osteosarcoma, but in contrast to osteosarcoma they are resistant to chemotherapy and radiotherapy, surgical excision remaining the only therapeutic option. Few cell lines and animal models are available, and the mechanisms behind their chemoresistance remain largely unknown. Our goal was to establish new cell lines and animal cancer models from human chondrosarcoma biopsies to study their chemoresistance. Between 2007 and 2012, 10 chondrosarcoma biopsies were collected and used for cell culture and transplantation into nude mice. Only one transplanted biopsy and one injected cell line has engrafted successfully leading to conventional central high-grade chondrosarcoma similar to the original biopsies. In culture, two new stable cell lines were obtained, one from a dedifferentiated and one from a grade III conventional central chondrosarcoma biopsy. Their genetic characterization revealed triploid karyotypes, mutations in IDH1, IDH2, and TP53, deletion in CDKN2A and/or MDM2 amplification. These cell lines expressed mesenchymal membrane markers (CD44, 73, 90, 105) and were able to produce a hyaline cartilaginous matrix when cultured in chondrogenic three-dimensional (3D) pellets. Using a high-throughput quantitative RT-PCR approach, we observed that cell lines cultured in monolayer had lost expression of several genes implicated in cartilage development (COL2A1, COMP, ACAN) but restored their expression in 3D cultures. Chondrosarcoma cells in monolayer were sensitive to several conventional chemotherapeutic agents but became resistant to low doses of mafosfamide or doxorubicin when cultured in 3D pellets, in parallel with an altered nucleic accumulation of the drug. Our results indicate that the cartilaginous matrix produced by chondrosarcoma cells may impair diffusion of several drugs and thus contribute to chemoresistance. Therefore, 3D chondrogenic cell pellets constitute a more relevant model to study chondrosarcoma chemoresistance and may be a valuable alternative to animal experimentations.

Intracellular domain fragment of CD44 alters CD44 function in chondrocytes

The hyaluronan receptor CD44 undergoes sequential proteolytic cleavage at the cell surface. The initial cleavage of the CD44 extracellular domain is followed by a second intramembranous cleavage of the residual CD44 fragment, liberating the C-terminal cytoplasmic tail of CD44. In this study conditions that promote CD44 cleavage resulted in a diminished capacity to assemble and retain pericellular matrices even though sufficient non-degraded full-length CD44 remained. Using stable and transient overexpression of the cytoplasmic domain of CD44, we determined that the intracellular domain interfered with anchoring of the full-length CD44 to the cytoskeleton and disrupted the ability of the cells to bind hyaluronan and assemble a pericellular matrix. Co-immunoprecipitation assays were used to determine whether the mechanism of this interference was due to competition with actin adaptor proteins. CD44 of control chondrocytes was found to interact and co-immunoprecipitate with both the 65- and 130-kDa isoforms of ankyrin-3. Moreover, this interaction with ankyrin-3 proteins was diminished in cells overexpressing the CD44 intracellular domain. Mutating the putative ankyrin binding site of the transiently transfected CD44 intracellular domain diminished the inhibitory effects of this protein on matrix retention. Although CD44 in other cells types has been shown to interact with members of the ezrin/radixin/moesin (ERM) family of adaptor proteins, only modest interactions between CD44 and moesin could be demonstrated in chondrocytes. The data suggest that release of the CD44 intracellular domain into the cytoplasm of cells such as chondrocytes exerts a competitive or dominant-negative effect on the function of full-length CD44.

Swarm chondrosarcoma: a continued resource for chondroblastic-like extracellular matrix and chondrosarcoma biology research

Since its first description over four decades ago, the Swarm chondrosarcoma (Swarm rat chondrosarcoma, SRC) remains a valuable tool for studies of chondroblastic-like extracellular matrix (ECM) biology and as an animal model of human chondrosarcoma of histological grades I-III. Moreover, articular joints and skeletal anomalies such as arthritis as well as cartilage regeneration, skeletal development, tissue engineering, hard tissue tumorigenesis and space flight physiology are advanced through studies in hyaline cartilage-like models. With more than 500 articles published since the first report on the characteristics of mucopolysaccharides (glycosaminoglycans) of the tumor in 1971, several transplantable tumor and cell lines have been developed by multiple laboratories worldwide. This review describes the characterization of SRC tumors and cell lines, including the use of SRC lines as a resource for isolation and characterization of several ECM elements that have become vital for the advancement of our understanding of cartilage biology. Also presented is the importance of pertubation of ECM components and the influence of the tumor microenvironment on disease progression. Therapeutic failure and currently pursued avenues of intervention utilizing the SRC lines in treatment of chondrosarcoma are also discussed.

Global demethylation of rat chondrosarcoma cells after treatment with 5-aza-2'-deoxycytidine results in increased tumorigenicity

Abnormal patterns of DNA methylation are observed in several types of human cancer. While localized DNA methylation of CpG islands has been associated with gene silencing, the effect that genome-wide loss of methylation has on tumorigenesis is not completely known. To examine its effect on tumorigenesis, we induced DNA demethylation in a rat model of human chondrosarcoma using 5-aza-2-deoxycytidine. Rat specific pyrosequencing assays were utilized to assess the methylation levels in both LINEs and satellite DNA sequences following 5-aza-2-deoxycytidine treatment. Loss of DNA methylation was accompanied by an increase in invasiveness of the rat chondrosarcoma cells, in vitro, as well as by an increase in tumor growth in vivo. Subsequent microarray analysis provided insight into the gene expression changes that result from 5-aza-2-deoxycytidine induced DNA demethylation. In particular, two genes that may function in tumorigenesis, sox-2 and midkine, were expressed at low levels in control cells but upon 5-aza-2-deoxycytidine treatment these genes became overexpressed. Promoter region DNA analysis revealed that these genes were methylated in control cells but became demethylated following 5-aza-2-deoxycytidine treatment. Following withdrawal of 5-aza-2-deoxycytidine, the rat chondrosarcoma cells reestablished global DNA methylation levels that were comparable to that of control cells. Concurrently, invasiveness of the rat chondrosarcoma cells, in vitro, decreased to a level indistinguishable to that of control cells. Taken together these experiments demonstrate that global DNA hypomethylation induced by 5-aza-2-deoxycytidine may promote specific aspects of tumorigenesis in rat chondrosarcoma cells.

Development of chondrosarcoma animal models for assessment of adjuvant therapy

Chondrosarcoma is a primary cancer of bone causing significant morbidity due to local recurrence and limited treatment options. Relatively few chondrosarcoma animal models have been developed, and the only orthotopic model is technically demanding and has limited clinical relevance. The aim of this review is to assess the features of current animal chondrosarcoma models for the purpose of developing new models in which to test adjuvant chondrosarcoma therapy. The available literature on this topic was identified using the PubMed database, and then analysed for relevance to the human chondrosarcoma disease and feasibility in testing new therapeutic agents. Animal-derived chondrosarcoma models comprise predominantly allograft tumour transplanted into the rat (Swarm rat chondrosarcoma) or the hamster. These types of models are less relevant to the human disease and have been more useful for evaluation of chondrosarcoma growth and histology than in developing novel therapeutic agents. The athymic nude mouse has enabled reliable human xenograft transplantation. A number of human chondrosarcoma cell lines have been successfully used to generate tumours in this species, including OUMS-27 and HCS-2/A. Although effective in demonstrating anti-tumour effects of a number of agents, the lack of a representative orthotopic model diminishes overall clinical relevance. More clinically relevant models of human chondrosarcoma progression are required either through transgenic mice or orthotopic human xenograft models.

Characterization of collagenous matrix assembly in a chondrocyte model system

Collagen is a major component of the newly synthesized pericellular microenvironment of chondrocytes. Collagen types II, IX, and XI are synthesized and assembled into higher ordered complexes by a mechanism in which type XI collagen plays a role in nucleation of new fibrils, and in limiting fibril diameter. This study utilizes a cell line derived from the Swarm rat chondrosarcoma that allows the accumulation and assembly of pericellular matrix. Immunofluorescence and atomic force microscopy were used to assess early intermediates of fibril formation. Results indicate that this cell line synthesizes and secretes chondrocyte-specific pericellular matrix molecules including types II, IX, and XI collagen and is suitable for the study of newly synthesized collagen matrix under the experimental conditions used. AFM data indicate that small fibrils or assemblies of microfibrils are detectable and may represent precursors of the approximately 20 nm thin fibrils reported in cartilage. Treatment with hyaluronidase indicates that the dimensions of the small fibrils may be dependent upon the presence of hyaluronan within the matrix. This study provides information on the composition and organization of the newly synthesized extracellular matrix that plays a role in establishing the material properties and performance of biological materials such as cartilage.

Isoform-specific heparan sulfate binding within the amino-terminal noncollagenous domain of collagen alpha1(XI)

Collagen type XI is a constituent of the pericellular matrix of chondrocytes and plays a role in the regulation of fibrillogenesis. The amino-terminal domain of collagen type XI alpha1 chain is a noncollagenous structure that has been identified on the surface of cartilage collagen fibrils. The biochemical composition of the amino-terminal domain varies due to alternative splicing of the primary transcript. Recombinantly expressed alpha1(XI) aminoterminal domain isoforms were used in this study to investigate potential interactions. Purified products were analyzed for heparan sulfate binding properties. The results demonstrated that two additional binding sites exist within the alpha1(XI) aminoterminal domain, one within the amino propeptide and one within the variable region of the amino-terminal domain. Analysis of relative affinities indicated that the site located within the amino propeptide (site 1) was of similar affinity to sites that exist within the major triple helix of collagen type XI. Substitution of amino acid residues 147 to 152 within the amino propeptide by site-directed mutagenesis resulted in altered affinity for heparan sulfate. The binding site located within the variable region (site 2) demonstrated significantly higher affinity than other sites within the molecule. Displacement of collagen type XI within the pericellular matrix was observed in cell culture in the presence of excess heparan sulfate and by treatment with heparinase. These studies suggest two additional binding sites located within the noncollagenous amino-terminal domain that may play a role in the function of collagen type XI. The localization of collagen type XI within the pericellular matrix may be dependent upon interactions with heparan sulfate proteoglycans, and these are likely to take place in an isoform-specific manner.

Chondroitin sulfate N-acetylgalactosaminyltransferase-1 plays a critical role in chondroitin sulfate synthesis in cartilage

Cartilage destruction leads to severe joint diseases, such as osteoarthritis and spinal disorders with back pain, and cartilage regeneration is very inefficient. A major component of the cartilage extracellular matrix is the proteoglycan aggrecan that contains approximately 100 chondroitin sulfate (CS) chains, which impart water absorption and resistance to compression. Here, we demonstrate that chondroitin sulfate N-acetylgalactosaminyltransferase-1 (CSGalNAcT-1) plays a critical role in CS biosynthesis in cartilage. By in situ hybridization and real time reverse transcription-PCR of developing cartilage, CSGalNAcT-1 exhibited the highest level of expression. Its expression in chondrogenic ATDC5 cells correlated well with that of aggrecan core protein. In heterozygote and homozygote aggrecan-null cartilage where aggrecan transcription is decreased, CSGalNAcT-1 transcription diminished accordingly. Overexpression of the enzyme in chondrocytic cells further enhanced CS biosynthesis but not that of the aggrecan core protein, indicating that the enzyme activity is not saturated in the cells and that aggrecan synthesized in the overexpressing cells is heavier than the native molecule. Analysis of the CS chains synthesized in the overexpressing cells by gel chromatography and that of disaccharide composition revealed that the CS chains had similar length and sulfation patterns. Furthermore, adenoviral gene delivery of the enzyme into intervertebral discs displayed a substantial increase in the level of CS biosynthesis. These observations indicate that CSGalNAcT-1 overexpression increases the number of CS chains attached to aggrecan core protein. Our studies may lead to a new therapeutic intervention, ameliorating the outcome of cartilage degenerative diseases.

Cytogenetics of swarm rat chondrosarcoma

The Swarm rat chondrosarcoma is a tumor tissue line derived from a tumor that arose spontaneously in a Sprague-Dawley rat. The original tissue has given rise to several tissue lines and cell lines that have been prepared in different laboratories. It has been observed that these lines differed in their growth rates and biochemical characteristics. We have characterized our Swarm rat chondrosarcoma tissue and cell lines currently in use in terms of their cytogenetic profiles and their tumorigenic properties in vivo. We found a wide variety of chromosomal abnormalities among cell lines, including translocations, deletions and polyploidy. There were also significant differences in their growth properties in vivo, giving rise to tumors of a few milligrams in the case of Ng cells, to 35 grams in the tissue line JWS. The cytogenetic complexity of the Swarm rat chondrosarcoma between and among different lines makes it very suitable to address questions about the changes that occur as a result of karyotypic abnormalities and to provide links between cytogenetic abnormalities and the dynamic oncogenic machinery.

Heterogeneity in growth properties of the rat Swarm chondrosarcoma

Chondrosarcoma remains one of the most difficult clinical conundrums of orthopaedic pathology, with wide variation in clinical course. The natural history of chondrosarcoma ranges from slow indolent growth without metastasis over years to rapid proliferation and lethal metastasis. Molecular regulatory events in the growth of these neoplasms are poorly understood. Of the Swarm rat chondrosarcoma, originating from a single neoplasm in a Sprague-Dawley rat more than thirty-five years ago, two populations were identified with different growth properties. These two Swarm chondrosarcoma lines were characterized for growth properties, histomorphometric and ultrastructural integrity, and the ability for proteoglycans to form aggregates with hyaluronan. After careful comparison, no obvious clues to the variation in growth rate were noted. Further molecular analyses may lead to better understanding of the differential growth properties of these cell lines. Understanding the mechanisms involved in differential growth rates may lead to clinically applicable clues to predict clinical behavior of chondrosarcomas in humans.

The establishment and characterization of an immortal cell line with a stable chondrocytic phenotype

A cell line was developed from the transplantable Swarm rat chondrosarcoma (RCS) and has been maintained in continuous monolayer tissue culture for a number of years. This long term-cultured (LTC) cell line exhibits the morphological and biochemical characteristics of chondrocytes and resembles the RCS tumor by electron and light microscopy. The cell line differs from the original tumor cells in that about 90% of the sulfated macromolecules are retained in the LTC extracellular matrix as compared to 30% by primary cultures of cells from the RCS tumor. An interesting and useful feature of this cell line is that it contains clonal populations of cells which differ in the quality and quantity of matrix produced. Two such clones serve to illustrate the diversity of cell types within the LTC cell line. One termed Rex accumulates an intensely staining matrix around it, while the other, Ng, accumulates a matrix, that remains virtually unstained. The chondrocytic nature and ease of cloning make these cells ideal for biochemical analysis of the chondrocyte and its extracellular matrix.

Aggrecan structure in amphibian cartilage

The structure of the large proteoglycan present in the bullfrog epiphyseal cartilage was studied by immunochemical and biochemical methods. The isolated monomer showed a polydisperse behavior on Sepharose CL2B, with a peak at Kav = 0.14. Chondroitin sulfate chains were identified by HPLC analysis of the products formed by chondroitinase digestion and mercuric acetate treatment. These chains have approximately 38 disaccharides, a Di45:Di68 ratio of 1.6 and GalNAc4S + GalNAc4,6S are the main non-reducing terminals. Keratan sulfate was identified by the use of two monoclonal antibodies in Western blots after chondroitinase ABC treatment. A keratan sulfate-rich region (approximately 110 kDa) was isolated by sequential treatment with chondroitinase ABC and proteases. We also employed antibodies in Western blotting experiments and showed that the full length deglycosylated core protein is about 300 kDa after SDS-PAGE. Domain-specific antibodies revealed the presence of immunoreactive sites corresponding to G1/G2 and G3 globular domains and the characterization of this large proteoglycan as aggrecan. The results indicate the high conservation of the aggrecan domain structure in this lower vertebrate.

A far upstream, cell type-specific enhancer of the mouse thrombospondin 3 gene is located within intron 6 of the adjacent metaxin gene

Thrombospondin 3 (TSP3) is a secreted, pentameric glycoprotein whose regulation of expression and function are not well understood. Mouse Thbs3 is located just downstream from the divergently transcribed metaxin gene (Mtx), which encodes an outer mitochondrial membrane import protein. Although Thbs3 and Mtx share a common promoter region, previous studies showed that Mtx is regulated by proximal elements that had little effect on Thbs3 expression. In this study, transient transfection of rat chondrosarcoma cells and NIH-3T3 fibroblasts demonstrated that Thbs3 is regulated in a cell type-specific manner by a position- and orientation-independent far upstream enhancer located within intron 6 of Mtx. Despite its greater proximity to the transcription start site of Mtx, the Thbs3 enhancer did not have a significant effect on Mtx expression. Two DNA-protein complexes, which were both required for activity, were identified when nuclear extracts were assayed with a probe containing the enhancer sequence. The protein in one of these complexes was identified as Sp1, while the other DNA-protein complex remains uncharacterized. A 6-kilobase pair promoter containing the enhancer was able to direct specific expression of the E. coli lacZ gene in transgenic mice, whereas a 2-kilobase pair promoter that lacked the enhancer was inactive. Thus, despite their close proximity, the genes of the Mtx/Thbs3 gene cluster are regulated independently.

Absence of cell-surface annexin V is accompanied by defective collagen matrix binding in the Swarm rat chondrosarcoma

Annexin V has been characterized as a major collagen type II binding cell-surface component of normal chondrocytes and is also called anchorin CII in chondrogenic populations. Herein we present evidence that in vitro cultured Swarm rat chondrosarcoma cells are not capable of binding collagen type II in significant quantities to their surfaces, as compared to normal rat chondrocytes. This finding coincides with a deficiency of annexin V on the surface of these cells. A small quantity of an intracellular polypeptide could be detected which is immunologically cross-reactive with annexin V but displayed a mobility in SDS-PAGE of less than 34 kD compared to the M(r) 36 kD of intact rat annexin V. By immunohistochemistry the protein could be localized in the cytoplasm of in vitro and in vivo grown tumor cells. By reverse transcription-polymerase chain reaction and Northern blot analysis, a regular-sized mRNA for annexin V could be detected in the chondrosarcoma cells that is expressed in only slightly lower quantities than in normal chondrocytes. Taken together, the data suggest a modified processing or turnover for annexin V in the chondrosarcoma excluding it from being a functionally active collagen type II binding protein. The findings support the hypothesis of cell-surface annexin V as a key component for the formation of the pericellular matrix of chondrocytes.

Mouse CD-RAP/MIA gene: structure, chromosomal localization, and expression in cartilage and chondrosarcoma

A cDNA encoding a novel protein has been previously isolated from two independent sources: melanoma cell cultures and chondrocytes. The protein from human melanoma cell lines and tumors is called melanoma inhibitory activity (MIA) (Blesch et al. [1994] Cancer Res. 54:5695-5701) and the protein from primary bovine chondrocytes and cartilaginous tissues is called cartilage-derived retinoic acid-sensitive protein (CD-RAP) (Dietz and Sandell [1996] J. Biol. Chem. 271:3311-3316). In order to investigate the gene regulation and function of CD-RAP/MIA, the mouse gene locus was isolated and analyzed. Developmental expression was determined by in situ hybridization to mouse embryos. Expression was limited to cartilaginous tissues and was initiated with the advent of chondrogenesis, remaining abundant throughout development. The mouse gene was isolated and sequenced from a 129Sv library and sequenced directly from an additional strain, B6C3Fe. The mouse CD-RAP/MIA gene is 1.5 kbp and consists of four exons. The promoter sequence of the gene contains many potential regulatory domains including 8 basic helix-loop-helix protein-binding domains and an AT-rich domain, both motifs shown to be present in the cartilage-specific enhancer of the type II procollagen gene. Other potential cis-acting motifs include binding sites for GATA-1, NF-IL6, PEA3, w-elements, NF kappa B, Zeste and Sp1. The gene, called cdrap, was localized to the end of an arm of chromosome 7 at the same site as the transforming growth factor beta 1 (Tgf-beta 1) and the glucose phosphate isomerase 1 (Gpi 1) genes. Potential mouse mutants that mapped to the same region of chromosome 7 were identified. Two of the potential mutants with skeletal phenotypes were sequenced, pudgy (pu) and extra toes with spotting (XsJ); however, no mutations were found in the coding sequence. To determine whether CD-RAP/MIA is associated with tumors of cartilage, mRNAs from a variety of rodent tissues and cell lines were screened. Expression was detected in a rodent tumor, the Swarm rat chondrosarcoma and a chondrosarcoma cell line derived from it, but not in other tissues or tumors of non-cartilage origin. Immunolocalization revealed CD-RAP/MIA protein localized in cartilage only. These results show that the normal expression of CD-RAP/MIA is limited to cartilage; however, pathologically, it is expressed both in melanoma and chondrosarcoma. The restricted expression of CD-RAP/MIA may provide an opportunity to monitor cartilage metabolic activity as well as the tumor activity of melanoma and chondrosarcoma.

SP1-binding elements, within the common metaxin-thrombospondin 3 intergenic region, participate in the regulation of the metaxin gene

Metaxin (Mtx) is an essential nuclear gene which is expressed ubiquitously in mice and encodes a mitochondrial protein. The gene is located upstream and is transcribed divergently from the thrombospondin 3 (Thbs3) gene; 1352 nucleotides separate the putative translation start sites. Although the Mtx and Thbs3 genes share a common intergenic region, transient transfection experiments in rat chondro-sarcoma cells and in NIH-3T3 fibroblasts demonstrated that the elements required for expression of the Mtx gene are situated within a short proximal promoter and have no major effect on the transcription of Thbs3. The metaxin --377 bp promoter contains four clustered GC boxes between nucleotides --146 and --58 and an inverted GT box between nucleotides --152 and --161, but does not contain TATA or CCAAT boxes. Like many genes regulated by a TATA-less promoter, the transcription start site of metaxin is heterogeneous. The major start site is only 13 bp upstream from the putative translation start site. Electrophoretic mobility shift, competition and supershift assays showed that the ubiquitous transcription factor, Sp1, and, to a lesser extent, the Sp1-related protein, Sp3, bind to four of these Sp1-binding motifs. Co-transfection of metaxin promoter-luciferase constructs and an Sp1 expression vector into Schneider Drosophila cells, which do not synthesize Sp1, demonstrated that the metaxin gene is activated by Sp1. Deletion of the four upstream Sp1-binding elements, on the other hand, demonstrated that these motifs are superfluous in context of the larger Mtx promoter. Thus, despite the potential for common regulatory mechanisms, the available evidence indicates that the Mtx minimal promoter does not significantly affect Thbs3 gene expression.

Establishment of bone morphogenetic protein 2 responsive chondrogenic cell line

A clonal cell line named RMD-1 was established from the skeletal muscle of a 20-day fetal rat. RMD-1 represents a morphologically homogeneous population of undifferentiated mesenchymal cells, expressing alpha-smooth muscle actin and type I collagen, but no cartilage-associated genes. When cultured in agarose gel containing 100 ng/ml of recombinant human bone morphogenetic protein 2 (rhBMP-2; BMP-2), RMD-1 cells formed colonies and showed chondrocyte-like features as assessed by their ultrastructure, metachromatic staining with toluidine blue, and the production of large hydrodynamic-size proteoglycans. RMD-1 cells also differentiated into chondrocytes when the cells were plated at high density (over 2.5 x 10(5) cells/cm2) on type I collagen and incubated in medium containing 0.5% fetal bovine serum and 100 ng/ml of BMP-2. This chondrogenic differentiation was evidenced by a distinct morphological change into spherical cells, an increase in the levels of sulfated glycosaminoglycans, a decrease in type I collagen mRNA and the expression of cartilage-associated genes, including type II collagen, type IX collagen, aggrecan and alkaline phosphatase. In the presence of ascorbic acid and 10% serum, RMD-1 cells increased in size and expressed type X collagen as well as high alkaline phosphatase activity, then induced matrix mineralization. Thus, RMD-1 is a unique cell line that can differentiate from undifferentiated mesenchymal cells into hypertrophic chondrocytes.

Use of a new rat chondrosarcoma cell line to delineate a 119-base pair chondrocyte-specific enhancer element and to define active promoter segments in the mouse pro-alpha 1(II) collagen gene

We show that a new rat chondrosarcoma (RCS) cell line established in long-term culture from the Swarm tumor displayed a stable differentiated chondrocyte-like phenotype. Indeed, these cells produced the collagen types II, IX, and XI and alcian blue-stainable cartilage-specific proteoglycans, but no type I or type III collagen. To functionally characterize their chondrocytic nature, the cells were stably transfected with a type II collagen/beta geo chimeric gene which confers essentially perfect chondrocyte-specific expression in transgenic mice. RCS cells expressed both beta-galactosidase and G418 resistance, in comparison with similarly transfected 10T1/2 and NIH/3T3 fibroblasts which did not. These cells were then used to perform a systematic deletion analysis of the first intron of the mouse type II collagen gene (Col2a1) using transient expression experiments to determine which segments stimulated expression of a luciferase reporter gene in RCS cells but not in 10T1/2 fibroblasts. Cloning of two tandem copies of a 156-base pair (bp) intron 1 fragment (+2188 to +2343) in a construction containing a 314-bp Col2a1 promoter caused an almost 200-fold increase in promoter activity in RCS cells but no increase in 10T1/2 cells. DNase I footprint analysis over this 156-bp fragment revealed two adjacent protected regions, FP1 and FP2, located in the 3'-half of this segment, but no differences were seen with nuclear extracts of RCS cells and 10T1/2 fibroblasts. Deletion of FP2 to leave a 119-bp segment decreased enhancer activity by severalfold, but RCS cell specificity was maintained. Further deletions indicated that sequences both in the 5' part of the 119-bp fragment and in FP1 were needed simultaneously for RCS cell-specific enhancer activity. A series of deletions in the promoter region of the mouse Col2a1 gene progressively reduced activity when these promoters were tested by themselves in transient expression experiments. However, these promoter deletions were all activated to a similar level in RCS cells by a 231-bp intron 1 fragment that included the 156-bp enhancer. The RCS cell-specific activity persisted even if the Col2a1 promoter was replaced by a minimal adenovirus major late promoter. This 231-bp intron 1 fragment also had strong enhancing activity in transiently transfected mouse primary chondrocytes. Our experiments establish the usefulness of RCS cells as an experimental system for studies of the control of chondrocyte-specific genes, provide an extensive delineation of segments in the Col2a1 first intron involved in chondrocyte-specific activity, and show that promoter sequences are dispensable for chondrocyte specificity.

Effect of ultrafilterable fragments from chondroitinase and protease-treated aggrecan on calcium phosphate precipitation in liposomal suspensions

A liposome-centered endogenous precipitation method was used to investigate the effect of ultrafilterable fragments from the enzymatic digestion of rat chondrosarcoma aggrecan on the formation of insoluble calcium phosphate salts in buffered solutions at pH 7.4 and 22 degrees C. Unlike the intact aggrecan and its major chondroitin sulfate and core protein components, disaccharide units from chondroitinase degradation of the aggrecan and small (< 3 kg/mol molecular weight) fragments from protease digestion of the core structure were found to be only weakly inhibitory toward mineral formation. Corresponding reductions in Ca(2+)-binding indicate that these fragments were unable to absorb to active sites on the apatite surface for long enough periods to significantly hinder crystal growth. The data suggest that controlled enzymatic breakdown of aggrecan may be one possible mechanism by which the calcification of growth plate cartilage is allowed to advance in vivo.

The cartilage proteoglycan aggregate: assembly through combined protein-carbohydrate and protein-protein interactions

In vitro reassembled aggregates of cartilage proteoglycan (aggrecan) were studied by glycerol spraying/rotary shadowing electron microscopy and compared to the corresponding native (i.e. never dissociated) structures. In both cases a tightly packed central filament structure was observed consisting of the hyaluronate binding region (HABR) of the proteoglycan, link protein (LP) and hyaluronate (HA). This differs from earlier results where a discontinuous central filament structure was seen after spreading proteoglycan aggregates at a water/air interphase. Binding of isolated HABR to HA is random but upon addition of link protein a clustering of the HA-binding proteins is observed, indicating a cooperativity. In a fully saturated aggregate the HA is covered by a continuous protein shell consisting of HABR and LP. When added in amounts below saturation HABR and LP bind to the HA in clusters which are interrupted by free strands of HA. The proteoglycan aggregate is thus an example for a structure where a polysaccharide forms a template for a supramolecular assembly largely stabilized by protein-protein interactions.

Structural domains in chondroitin sulfate identified by anti-chondroitin sulfate monoclonal antibodies. Immunosequencing of chondroitin sulfates

Monoclonal antibodies have been developed that recognize epitopes in native chondroitin sulfate chains. One of these antibodies, CS-56, reportedly recognizes chondroitin 4- and 6-sulfates. However, this antibody, and four other anti-chondroitin sulfate antibodies, 4C3, 4D3, 6C3 and 7D4, do not recognize epitopes in chondroitin sulfate chains from Swarm rat chondrosarcoma proteoglycan, an indication that native chondroitin sulfate epitopes are more structurally complex than the standard 0-, 4-, and 6-sulfated disaccharide repeats that constitute the backbone of chondroitin sulfate chains. A series of limited chondroitinase digestions was performed on the large aggregating proteoglycan monomer extracted from embryonic chick chondrocyte cultures to identify the digestion parameters required to release the different native chondroitin sulfate epitopes. Some epitopes were more accessible to enzymatic digestion than other epitopes. The approximate location of epitopes was determined by measuring the size of undigested oligosaccharides retained on the core protein following a limited digestion, and correlating this with the level of immunoreactivity for the different antibodies. These analyses identified the locations of three different antigenic domains. Domain 1 resides at the linkage region and contains epitopes for two of the five antibodies, and a portion of the epitopes for a third antibody. Domain 2 lies in the interior of the chain and contains epitopes for three of the five antibodies. Domain 3 resides at the non-reducing terminus and does not contain epitopes for any of the anti-chondroitin sulfate antibodies used in this study. These results indicate that specific native chondroitin sulfate epitopes are non-randomly distributed within the linear framework of chondroitin sulfate chains.

Functional characterization of chondroitin sulfate proteoglycans of brain: interactions with neurons and neural cell adhesion molecules

Ng-CAM and N-CAM are cell adhesion molecules (CAMs), and each CAM can bind homophilically as demonstrated by the ability of CAM-coated beads (Covaspheres) to self-aggregate. We have found that the extent of aggregation of Covaspheres coated with either Ng-CAM or N-CAM was strongly inhibited by the intact 1D1 and 3F8 chondroitin sulfate proteoglycans of rat brain, and by the core glycoproteins resulting from chondroitinase treatment of the proteoglycans. Much higher concentrations of rat chondrosarcoma chondroitin sulfate proteoglycan (aggrecan) core proteins had no significant effect in these assays. The 1D1 and 3F8 proteoglycans also inhibited binding of neurons to Ng-CAM when mixtures of these proteins were adsorbed to polystyrene dishes. Direct binding of neurons to the proteoglycan core glycoproteins from brain but not from chondrosarcoma was demonstrated using an assay in which cell-substrate contact was initiated by centrifugation, and neuronal binding to the 1D1 proteoglycans was specifically inhibited by the 1D1 monoclonal antibody. Different forms of the 1D1 proteoglycan have been identified in developing and adult brain. The early postnatal form (neurocan) was found to bind neurons more effectively than the adult proteoglycan, which represents the C-terminal half of the larger neurocan core protein. Our results therefore indicate that certain brain proteoglycans can bind to neurons, and that Ng-CAM and N-CAM may be heterophilic ligands for neurocan and the 3F8 proteoglycan. The ability of these brain proteoglycans to inhibit adhesion of cells to CAMs may be one mechanism to modulate cell adhesion and migration in the nervous system.

Interleukin-6 and transforming growth factor-beta synergistically stimulate chondrosarcoma cell proliferation

This study examines the regulation of Swarm rat chondrosarcoma (SRC) cell proliferation in vitro. In serum-free cultures, SRC cells showed only transient DNA synthesis and this was increased by serum. Transforming growth factor-beta (TGF-beta) was identified as an essential serum component, since the mitogenic effect of sera was related to their TGF-beta content and neutralized by antibody to TGF-beta. Among a large panel of agents tested, TGF-beta was the only factor that stimulated proliferation in serum-free media. The TGF-beta isoforms TGF-beta 1 and TGF-beta 2 induced similar dose-dependent increases with maximal 62.5-fold stimulation at 10 ng/ml. Interleukin-6 (IL-6) was identified as a new factor that stimulated SRC proliferation. IL-6 effects were serum-dependent and their magnitude correlated with the TGF-beta content in different serum preparations. In serum-free cultures where IL-6 by itself had no detectable effect it caused up to 7.6-fold increased proliferation in the presence of small doses of TGF-beta (0.01-0.1 ng/ml). This synergy was unique, since no other factor tested synergized with IL-6 or TGF-beta. In examining potential mechanisms for this synergy it was found that TGF-beta increased IL-6 receptor expression. In summary, these results identify IL-6 as a new and TGF-beta as the most potent growth factor for chondrosarcoma cells and describe novel interactions between these factors in the regulation of cell growth.

Experimental transplantation of the Swarm rat chondrosarcoma into bone: radiological and pathological studies

The Swarm rat chondrosarcoma has been the subject of extensive biochemical studies. However, to our knowledge, there are no previous reports in the literature on transplantation of this tumor into bone. This article describes the natural history of the tumor when implanted into the bone of the rat, and correlates its histological growth pattern with its radiological appearance. Our results showed that the tumor grows slowly in the bone. The rate of intramedullary growth, however, was variable and was not the same in all the animals. Its growth pattern resembles human chondrosarcoma, with extensive invasion of the marrow and cortex. In the first few weeks after implantation, the only radiological changes noted were mild medullary radiopacities. At a later stage, 12-14 weeks postimplantation, as the tumor infiltrated the bone, significant radiological abnormalities were observed in the medullary cavity and cortex. Periosteal reaction was seen after the tumor invaded the cortex with the production of a soft-tissue mass. Distant dissemination was rare; only 1 of 24 rats developed pulmonary metastases. The Swarm rat chondrosarcoma is a well-differentiated malignant tumor that histologically resembles well-differentiated human chondrosarcoma. Transplanted into bone, it may be useful as an experimental model for comparative studies with human chondrosarcoma.

The effects of long term monolayer culture on the proteoglycan phenotype of a clonal population of mature human malignant chondrocytes

Articular cartilage chondrocytes maintain biosynthetic heterogeneity in cell culture, but undergo irreversible dedifferentiation of their proteoglycan phenotype, as defined by keratan sulfate content. A recently described cell line of malignant human chondrocytes, 105KC, was the first to maintain a differentiated keratan sulfate-proteoglycan phenotype in long-term culture. A clone of 105KC, labeled KC2H3, is currently described and represents a distinct and metabolically more homogeneous population of mature chondrocytes than 105KC. KC2H3 cells universally express keratan sulfate biosynthesis, as defined by indirect immunofluorescence. In addition, KC2H3 expresses a more mature proteoglycan phenotype than 105KC, as demonstrated by the keratan sulfate content: 24% of glycosaminoglycan content of the aggregating proteoglycans of KC2H3 versus 13% for 105KC. Further reported are the effects of long term monolayer culture on the proteoglycan phenotype expressed by KC2H3. After more than 16 months in continuous monolayer, KC2H3 cells remained morphologically indistinguishable from those maintained in suspension alternating with monolayer. In addition, the proteoglycan phenotype remained mature, without a tendency towards dedifferentiation. The flattened morphology adopted by chondrocytes while in monolayer has been considered a stimulus of dedifferentiation; the present study is the first to examine the direct effects of physical state on a homogeneous and stable population of chondrocytes.

Human keratinocytes contain carbohydrates that are recognized by keratan sulfate-specific monoclonal antibodies

Monoclonal antibodies that recognize carbohydrate epitopes found in keratan sulfate glycosaminoglycan chains identified both intracytoplasmic and cell-surface carbohydrates of human keratinocytes. These carbohydrates were detected, using indirect immunoperoxidase methods, both in sections of paraffin-embedded tissues and in intact cultured keratinocytes. Of the seven anti-keratan sulfate monoclonal antibodies used in this study, five detected significant amounts of epitopes associated with keratinocytes. This indicates that only certain, specific types of keratan sulfate-like carbohydrates were expressed by these cells. The extent and localization of keratan sulfate-like carbohydrates appeared to be closely related to the differentiation status of cultured keratinocytes. These epitopes were very weakly expressed on surfaces of all monolayer keratinocytes, but flattened, suprabasal cells in high Ca++ cultures strongly expressed keratan sulfate-like carbohydrates on their surfaces. A much larger population of cultured keratinocytes expressed intracellular keratan sulfate-like carbohydrates identified by the same five antibodies that detected surface epitopes. In monolayer cells, keratan sulfate-like carbohydrates were predominantly found in a broad perinuclear zone. In addition, three of the five immunoreactive antibodies detected epitopes that appeared at cell boundaries, specifically at sites of close cell-to-cell contact. Thus, molecules bearing carbohydrates recognized by anti-keratan sulfate antibodies appear at developmentally important stages of keratinocyte differentiation, indicating that these carbohydrates may serve as markers for molecules important in the differentiation of human keratinocytes.

Monoclonal antibodies specific for keratan sulfate detect epithelial-associated carbohydrates

Monoclonal antibodies that specifically recognize epitopes on keratan sulfate glycosaminoglycans were used in this study to identify carbohydrate epitopes associated with many, but not all, types of epithelial cells. Immunoreactive cells included: keratinocytes, sebaceous gland cells, eccrine sweat gland duct cells, salivary gland excretory duct cells, colon adenocarcinoma cells, embryonic chick lung epithelial cells, embryonic chick mesonephric and metanephric kidney epithelial cells, and selected embryonic chick neural tube cells. Depending upon the type of epithelium, epitopes were located either within the cytoplasm or were located on cell surfaces. These epitopes were shared by cells from both human and chick tissues, indicating the absence of species specificity. Not all anti-keratan sulfate antibodies were equally effective in identifying epithelial-associated epitopes. One of the seven antibodies employed in this study failed to detect epitopes in almost all epithelial tissues studied. Of the remaining six antibodies, three were more effective than the others in recognizing epithelial-associated epitopes. These data indicate that carbohydrates that are typically associated with extracellular matrix can also be associated with epithelial cells, but in a form that is not necessarily related to extracellular matrix. These antibodies should prove to be useful in studies of the development of epithelial cells and tissues.

Monoclonal antibodies reacting with endo-beta-galactosidase-resistant epitopes on keratan sulfate-bearing fragments of bovine nasal cartilage proteoglycan

Six monoclonal antibody-producing cell lines were derived from mice immunized with keratan sulfate (KS)-bearing tryptic fragments of the core protein of bovine nasal cartilage proteoglycan monomer digested with KS-specific endo-beta-galactosidase. The monoclonal antibodies were characterized by solid-phase ELISA competition studies and SDS-PAGE immunoblotting. Two of them resemble previously described monoclonal antibodies that are directed to epitopes containing both KS and core protein. In contrast, the remaining four monoclonal antibodies are unprecedented in being directed to epitopes whose reactivity is unaffected or enhanced by endo-beta-galactosidase degradation of KS. SDS-PAGE immunoblots revealed two large KS-bearing tryptic fragments of cartilage proteoglycan and a heterogeneous population of smaller fragments not evident by non-immunological techniques. Some of the antibodies used react with all KS-bearing fragments, others react only with the two largest fragments.

Studies of a monoclonal antibody to skeletal keratan sulphate. Importance of antibody valency

A mouse monoclonal antibody (AN9P1) to keratan sulphate is described. In a competitive-inhibition solution-phase radioimmunoassay employing 125I-labelled intact proteoglycan, it reacts preferentially with keratan sulphate bound to the core protein of adult human articular-cartilage proteoglycan and to a much lesser degree with keratan sulphate purified from this proteoglycan. Proteolytic cleavage of the proteoglycan by pepsin and trypsin has little effect on antibody binding, but treatment with papain decreases binding considerably and more than does treatment with keratanase. An even greater decrease in binding is observed after treatment with alkaline borohydride. A comparison of binding of antibody AN9P1 with that of another previously described monoclonal antibody, 1/20/5-D-4, to keratan sulphate [Caterson, Christner & Baker (1983) J. Biol. Chem. 258, 8848-8854] revealed similar binding characteristics, both showing much diminished binding after papain digestion of proteoglycan and even less with purified skeletal keratan sulphate. Removal of the Fc piece of antibody AN9P1 had no significant effect on the differential binding of divalent F(ab')2 fragment to proteoglycan, to papain-digested proteoglycan and to keratan sulphate, although there was a small decrease in binding to papain-digested proteoglycan. Conversion of the antibody into univalent Fab fragment with removal of the Fc piece resulted in diminished binding to proteoglycan, compared with that observed with IgG, and in enhanced binding to free keratan sulphate and to papain-digested proteoglycan. These results suggest that close proximity of keratan sulphate chains on the core protein of proteoglycans favours preferential reactivity of bivalent antibody with these species through cross-bridging of chains by antibody. Conversely, much decreased binding to keratan sulphate on proteoglycan core-protein fragments and to free keratan sulphate results from a lack of close proximity of keratan sulphate. By using univalent Fab fragment in these assays these differences in binding are minimized by preventing cross-bridging and thereby enhancing detection of smaller fragments without sacrificing too much sensitivity of detection of larger proteoglycan species. The persistent preferential binding of Fab fragment to proteoglycan is probably in part the result of the increased epitope density in the intact molecule compared with keratan sulphate in a more disperse form.

Different growth rates of swarm chondrosarcoma in Lewis and Wistar rats correlate with different thyroid hormone levels

The transplantable Swarm rat chondrosarcoma grew to twice the weight in 5 weeks in Lewis strain rats (approximately 80 g) as it did in Wistar strain rats (approximately 40 g). Wistar tumor passaged into Lewis rats adopted the accelerated growth rate of the Lewis tumor on the second passage. Conversely Lewis tumor passaged into Wistar rats grew like Wistar lineage chondrosarcoma after two passages. Lewis and Wistar tumors had a similar histological appearance. The extracellular matrix composition of the two tumors was very similar. Tumor explant cultures synthesized about the same amount of 35S-proteoglycans and the same proportion of 3H-hyaluronate: 3H-chondroitin sulfate. Serum levels of growth hormone and insulin were the same in the two strains but T3 and T4 levels were 50% higher in Lewis rats compared to Wistar rats. It is likely that accelerated tumor growth in Lewis strain rats is related to the higher thyroid hormone levels.

Studies on the biosynthesis of cartilage proteoglycan in a model system of cultured chondrocytes from the Swarm rat chondrosarcoma

Biosynthesis of cartilage proteoglycan was examined in a model system of cultured chondrocytes from a transplantable rat chondrosarcoma. Extensive modification with the addition of chondroitin sulfate glycosaminoglycan, N-linked oligosaccharide, and O-linked oligosaccharide is required to convert a newly synthesized core protein precursor into a proteoglycan. Kinetic analyses revealed the presence of a large pool of core protein precursor (t 1/2 approximately 90 min) awaiting completion into proteoglycan. The large t 1/2 of this pool allowed kinetic labeling experiments with a variety of radioactive precursors to distinguish between early biosynthetic events associated primarily with the rough endoplasmic reticulum from late events associated primarily with the Golgi apparatus. The results of a series of experiments indicated that the addition of N-linked oligosaccharide chains occurs early in the biosynthetic process in association with the rough endoplasmic reticulum, whereas the initiation and completion of O-linked oligosaccharides occurs much later, at about the same time as chondroitin sulfate synthesis. This also indicated that keratan sulfate chains, when present in the completed molecule, are added in the Golgi apparatus, as they are probably built on oligosaccharide primers closely related to the O-oligosaccharide chains. Furthermore, when 3H-glucose was used as the precursor, the entry of label into xylose, the linkage sugar between the core protein and the chondroitin sulfate chain, was found to occur within 5 min of the entry of label into galactose and galactosamine in the remainder of the chondroitin sulfate chain. This indicated that the initiation and completion of the chondroitin sulfate chain occurs late in the pathway probably entirely in the Golgi apparatus. Thus, proteoglycan synthesis can be described as occurring in two stages in this system, translation and N-glycosylation of a core protein precursor which has a long half-life in the rough endoplasmic reticulum, followed by extensive rapid modification in the Golgi complex in which the majority of glycosaminoglycan and oligosaccharide chains are added to the core protein precursor with subsequent rapid secretion into the extracellular matrix.

Type II collagen from lathyritic rat chondrosarcoma: preparation and in vitro fibril formation

Intact type II collagen monomer was isolated in 10-20% yield from lathyritic rat chondrosarcoma and purified to homogeneity. On warming in neutral solution, the collagen formed a mixture of D-periodic native fibrils and thin filaments with no apparent structure. There were characteristic lag and growth phases in the turbidity profile. cooling dispersed or dissolved the fibrils leaving thin filaments. The fibrils were very wide, up to 2.0 micrometers compared to the 10 to 40 nm fibrils present in situ. They had the appearance of stiff tactoids compared to the very long and flexible fibrils obtained from type I collagen under similar conditions. Type II collagen also required higher temperatures and concentrations than type I to form fibrils. The continued presence of thin filaments when type II fibril formation was complete suggests either that filaments are in slow equilibrium with fibrils or that they may not be intermediates but rather a separate product.

Inhibition of growth of the transplantable rat chondrosarcoma by analogs of hypothalamic hormones

The Swarm chondrosarcoma is a hormone-responsive tumor whose growth is dependent on growth hormone, somatomedins, and glucocorticoids. Our previous work showed that partial functional hypophysectomy can be achieved by chronic administration of the luteinizing hormone-releasing hormone (LH-RH) analog [D-Trp(6)]LH-RH, which lowers blood levels of LH and follicle-stimulating hormone. We have also demonstrated that somatostatin (SS)-28 or analogs of SS-14 depress serum prolactin, growth hormone, and corticotropin (ACTH) levels. Consequently, we investigated the effect of subcutaneous injection of these analogs on the growth of Swarm chondrosarcoma 3 days after transplanting it into male Sprague-Dawley rats. At autopsy, tumor volume was measured and tumors and various organs were weighed. In rats treated with three different analogs of SS-14, [p-NH(2)-Phe(4)]SS, [D-5-F-Trp(8)]SS, and [D-5-MeO-Trp(8)]SS, in doses of 30 mug once or twice daily for 14-30 days, there was a significant reduction in tumor volume and/or weight as compared with control rats. The longer acting SS-28 or its analog Val-Gly-Tyr-Val-Ile-Leu-Gly-SS-28, given in doses of 30 mug/day for 22-30 days, also significantly decreased tumor weight and/or volume. In three experiments, [D-Trp(6)]LH-RH (30-60 mug/day), administered alone or together with analogs of SS-14, decreased tumor weight and/or volume. Serum growth hormone and prolactin levels in rats bearing the tumors were significantly decreased after treatment with [D-5-F-Trp(8)]SS or with [D-Trp(6)]LH-RH. The inhibition of growth of the Swarm chondrosarcoma in rats by these analogs suggests that they might lead to a new endocrine therapy for chondrosarcomas, osteosarcomas, and related hormone-dependent neoplasias.

A comparison of the proteoglycans produced by rabbit articular chondrocytes in monolayer and spinner culture and those of bovine nasal cartilage

The structural and immunological properties of the glycosaminoglycans and the core proteins of bovine nasal cartilage proteoglycan and the proteoglycans produced by rabbit articular chondrocytes in spinner and monolayer culture were compared. Culture medium with 35SO4- or 3H-serine-labeled proteoglycan was mixed with bovine nasal cartilage 4M guanidine-HCl extract and digested with trypsin. The proteoglycan fragments were then isolated by DEAE-cellulose chromatography and fractionated by dissociative CsCl density gradient centrifugation. Approximately 90% of the 35SO4 incorporated into proteoglycan by the cultured chondrocytes was in chondroitin sulfates and about 5% in keratan sulfate. Although there was considerable overlap in the Sepharose 4B elution of the tryptic proteoglycan fragments of highest buoyant density, some monolayer-produced proteoglycan fragments eluted earlier and some spinner-produced proteoglycan fragments eluted later than the proteoglycan fragments from bovine nasal cartilage. These differences in apparent fragment size could relate to differences in glycosaminoglycan chain length, since the glycosaminoglycans released by treatment with alkali from monolayer-produced proteoglycan in part eluted from Sepharose 4B earlier and those from spinner-produced proteoglycan in part eluted later than the chondroitin sulfate chains released from bovine cartilage proteoglycan. After digestion with chondroitinase ABC, 3H-serine-labeled high density tryptic proteoglycan fragments from monolayer and spinner culture yielded Sepharose 6B elution profiles which were similar to each other but did not coincide with the peaks of carbazole reactivity found with similarly treated fragments of bovine nasal cartilage proteoglycan. Cross-reactivity was demonstrated by radioimmunoautography between bovine cartilage and rabbit chondrocyte proteoglycan fragments restricted to gradient fractions of low buoyant density, but immunological cross-reactivity was not found for the antigens associated with the keratan sulfate-rich and chondroitin sulfate-bearing tryptic fragments of bovine nasal cartilage proteoglycan. These studies indicate that the proteoglycan core proteins produced by rabbit articular chondrocytes in monolayer and spinner culture are, in part, different from the core protein of bovine nasal cartilage proteoglycan and that the three proteoglycans differ in the length of some of their chondroitin sulfate chains.

The ultrastructure of cultures from the Swarm rat chondrosarcoma

When chondrocytes from the Swarm rat chondrosarcoma are isolated by trypsin and collagenase digestion and cultured in Petri dishes, they form a new extracellular matrix within 24 hours, with proteoglycan matrix granules and collagen fibrils. This rapid synthesis of new matrix, together with the biochemical and morphological characterization of the proteoglycans as typical of cartilage, demonstrates the value of these cultures as a model system for studies of synthesis, secretion, and organization of extracellular matrix.

Ultrastructure of the chondrocytes and extracellular matrix of the swarm rat chondrosarcoma

The Swarm chondrosarcoma, a transplantable tumor maintained in rats, has a structure similar to hyaline cartilage. The extracellular matrix contains narrow, banded collagen fibrils and proteoglycan matrix granules. The cells are filled with organelles typically involved in synthesis and secretion, including an extensive rough endoplasmic reticulum with dilated cisternae, a large Golgi apparatus dispersed throughout the cell, and secretory vacuoles which fill directly from Golgi saccules. There is only one class of secretory vacuoles, suggesting that the secretory products, collagen and proteoglycan, are packaged and secreted together. The cells also contain unusual endoplasmic reticulum, many coated vesicles and multivesicular bodies, and abnormal mitochondria. The large amount of tissue available from the tumor, and its characterization biochemically (Choi et al., '71; Oegema et al., '75) and morphologically as cartilage, make the tumor valuable as a model tissue for studies of synthesis and secretion of extracellular matrix materials.

Regulation of chondrosarcoma metabolism by cyclic adenosine 3'5'-monophosphate

The in vitro effects of cyclic AMP on amino acid transport and synthesis of macromolecules in the Swarm rat chondrosarcoma were investigated using the cyclic AMP analogue, N6-monobutyryl cyclic AMP (MBcAMP), and the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (MIX). Amino acid transport was assessed by measuring alpha-amino-[1-14C]isobutyrate (AIB) uptake. The synthesis of macromolecules was estimated by measuring radiolabeled precursor incorporation into total proteins, proteoglycan, and RNA. MBcAMP stimulated [14C]AIB uptake, [3H]uridine transport, and UTP formation. MBcAMP inhibited 35SO4 and [3H]leucine incorporation into proteoglycan and stimulated [3H]uridine incorporation into RNA. MIX elevated endogenous cyclic AMP levels in the Swarm rat chondrosarcoma and mimicked the effects of MBcAMP on AIB transport and radiolabeled precursor incorporation into macromolecules. For comparative purposes, the effects of MBcAMP on AIB uptake and macromolecule synthesis in rat costal cartilage segments were investigated. MBcAMP and MIX stimulated AIB uptake by costal cartilage segments, inhibited [3H]leucine incorporation into total protein and 35SO4 incorporation into proteoglycan, and had no effect on [3H]uridine incorporation into RNA.