Neoplastic modulation of extracellular matrix: stimulation of chondroitin sulfate proteoglycan and hyaluronic acid synthesis in co-cultures of human colon carcinoma and smooth muscle cells

An Overview of in vivo Functions of Chondroitin Sulfate and Dermatan Sulfate Revealed by Their Deficient Mice

Chondroitin sulfate (CS), dermatan sulfate (DS) and heparan sulfate (HS) are covalently attached to specific core proteins to form proteoglycans in their biosynthetic pathways. They are constructed through the stepwise addition of respective monosaccharides by various glycosyltransferases and maturated by epimerases as well as sulfotransferases. Structural diversities of CS/DS and HS are essential for their various biological activities including cell signaling, cell proliferation, tissue morphogenesis, and interactions with a variety of growth factors as well as cytokines. Studies using mice deficient in enzymes responsible for the biosynthesis of the CS/DS and HS chains of proteoglycans have demonstrated their essential functions. Chondroitin synthase 1-deficient mice are viable, but exhibit chondrodysplasia, progression of the bifurcation of digits, delayed endochondral ossification, and reduced bone density. DS-epimerase 1-deficient mice show thicker collagen fibrils in the dermis and hypodermis, and spina bifida. These observations suggest that CS/DS are essential for skeletal development as well as the assembly of collagen fibrils in the skin, and that their respective knockout mice can be utilized as models for human genetic disorders with mutations in chondroitin synthase 1 and DS-epimerase 1. This review provides a comprehensive overview of mice deficient in CS/DS biosyntheses.

Decorin in the Tumor Microenvironment

The tumor microenvironment plays a determining role in cancer development through a plethora of interactions between the extracellular matrix and tumor cells. Decorin is a prototype member of the SLRP family found in a variety of tissues and is expressed in the stroma of various forms of cancer. Decorin has gained recognition for its essential roles in inflammation, fibrotic disorders, and cancer, and due to its antitumor properties, it has been proposed to act as a "guardian from the matrix." Initially identified as a natural inhibitor of transforming growth factor-β, soluble decorin is emerging as a pan-RTK inhibitor targeting a multitude of RTKs, including EGFR, Met, IGF-IR, VEGFR2, and PDGFR. Besides initiating signaling, decorin/RTK interaction can induce caveosomal internalization and receptor degradation. Decorin also triggers cell cycle arrest and apoptosis and evokes antimetastatic and antiangiogenic processes. In addition, as a novel regulatory mechanism, decorin was shown to induce conserved catabolic processes, such as endothelial cell autophagy and tumor cell mitophagy. Therefore, decorin is a promising candidate for combatting cancer, especially the cancer types heavily dependent on RTK signaling.

Remodeling Components of the Tumor Microenvironment to Enhance Cancer Therapy

Solid tumor pathophysiology is characterized by an abnormal microenvironment that guides tumor progression and poses barriers to the efficacy of cancer therapies. Most common among tumor types are abnormalities in the structure of the tumor vasculature and stroma. Remodeling the tumor microenvironment with the aim to normalize any aberrant properties has the potential to improve therapy. In this review, we discuss structural abnormalities of the tumor microenvironment and summarize the therapeutic strategies that have been developed to normalize tumors as well as their potential to enhance therapy. Finally, we present different in vitro models that have been developed to analyze and better understand the effects of the tumor microenvironment on cancer cell behavior.

Oncosuppressive functions of decorin

The extracellular matrix is rapidly emerging as a prominent contributor to various fundamental processes of tumorigenesis. In particular, decorin, a member of the small leucine-rich proteoglycan gene family, is assuming a central role as a potent soluble tumor repressor. Decorin binds and antagonizes various receptor tyrosine kinases and inhibits downstream oncogenic signaling in several solid tumors. Among other functions, decorin evokes cell cycle arrest, apoptosis, and antimetastatic, and antiangiogenic programs. Recent work has revealed a paradigmatic shift in our understanding of the molecular mechanisms underlying its tumoricidal properties. Decorin adversely compromises the genetic signature of the tumor microenvironment and induces endothelial cell autophagy downstream of VEGFR2. Moreover, decorin selectively evokes destruction of tumor cell mitochondria downstream of Met through mitophagy. Acting as a partial agonist, decorin signals via proautophagic receptors and triggers procatabolic processes that parallel the classical tumoricidal properties of this multifaceted proteoglycan.

Muscularis mucosae in desmoplastic stroma formation of early invasive rectal adenocarcinoma

The origin of myofibroblasts or myofibroblastic cells in the desmoplastic stroma associated with carcinoma invasion has been controversial. In the early invasive area of a rectal adenocarcinoma reported here, an obvious transition between the muscularis mucosa and the bundles of eosinophilic stromal cells observed in the carcinomatous stroma was demonstrated both in morphology and in their cytoskeletal phenotype, which conceivably suggests that the smooth muscle cells of the muscularis mucosa could convert to the eosinophilic stromal cells, namely myofibroblasts. Moreover, type I procollagen was demonstrated in both protein and mRNA levels in the areas of eosinophilic stromal cells with a lesser degree of differentiated smooth muscle phenotype that showed a transition from the muscularis mucosa, implying that the myofibroblastic cells converted from smooth muscle cells of the muscularis mucosa could be responsible for type I collagen production. These findings suggest that the muscularis mucosae may not be a passive barrier through which colorectal carcinomas infiltrate into the submucosa, but may play an active role in the formation and remodeling of tumor stroma.

Association between cancer and "acid mucopolysaccharides": an old concept comes of age, finally

"Acid mucopolysaccharides" is an old name for the glycosaminoglycans. These carbohydrate polymers of the extracellular matrix provide tissue organization, cell-cell communication and a platform for signaling. They also support tumor cell proliferation, progression and invasion. Among the most prevalent is hyaluronan. Its support of cancer is an old concept, but only now is it recognized as an integral component of the cancerous state. Hyaluronan occurs not only in malignant cells, but also in peritumor stroma. Finally, it is now realized that the association between tumor and stroma must be investigated to fully understand the process of cancer growth and metastasis. Most recently, hyaluronan has been identified as essential to malignant stem cells, and a component of the cancer stem cell niche. While hyaluronan does not give up its secrets easily, recent progress justifies a review of its role in malignancy.

Myofibroblasts are responsible for collagen synthesis in the stroma of human hepatocellular carcinoma: an in vivo and in vitro study

BACKGROUND/AIMS

Marked changes in extracellular matrix occur in the stroma of hepatocellular carcinoma, as compared to normal or cirrhotic liver. The cell types responsible for extracellular matrix synthesis within hepatocellular carcinoma have not been clearly identified.

METHODS

In vivo collagen synthesis was studied by in situ hybridization and immunohistochemistry for types I, IV, V and VI collagen, together with immunolabeling of alpha-smooth muscle actin, a myofibroblast marker, and CD34, an endothelial cell marker. In vitro, extracellular matrix deposition by cultured myofibroblasts was studied by reticulin staining, immunocytochemistry and RNase protection.

RESULTS

All collagens studied were expressed in the stroma of the tumor, with a higher level of type VI and IV collagens than of type I and V. The majority of the cells expressing collagen transcripts in human hepatocellular carcinoma stroma were alpha-actin positive and CD 34 negative. In vitro experiments demonstrated that the hepatocellular carcinoma cell lines HepG2, HuH7 and Hep3B markedly increased extracellular matrix deposition by human liver myofibroblasts. This increase was mediated by a soluble mediator present in tumor cell conditioned medium. It was not explained by an increase in mRNA levels of extracellular matrix components, nor by a decrease in the secretion of matrix-degrading proteinases by myofibroblasts.

CONCLUSIONS

Myofibroblasts are the main source of collagens in the stroma of hepatocellular carcinoma. Our data also indicate that tumoral hepatocytes increase extracellular matrix deposition by cultured myofibroblasts, probably by post-transcriptional mechanisms. The generation of hepatocellular carcinoma stroma by myofibroblasts could thus be under control of tumoral cells.

Epithelial vs mesenchymal contribution to the extracellular matrix in the human intestine

The basement membrane (BM) underlying the epithelium of the intestine is generally believed to be of both epithelial and mesenchymal origin but the exact contribution of each tissue has not been directly examined in the human. In this study, we have used a newly described procedure to dissociate the human intestine into pure epithelial and corresponding mesenchymal fractions. Northern blot and RT-PCR analyses of the fractions for the presence of transcripts encoding extracellular matrix molecules revealed that the epithelium produces the formal BM molecules such as the alpha 1, alpha 2, and beta 1 chains of laminin-1 and laminin-2 and the alpha 5(IV) and alpha 6(IV) chains of collagen as well as fibronectin, a BM-associated molecule. Interestingly, the alpha 1(IV) chain of collagen, which associates with the alpha 2(IV) chain to form the main BM collagen network, as well as tenascin-C and decorin, two BM-associated molecules, was found to be exclusively of mesenchymal origin. Taken together, these data support the concept that in the human, as in experimental animals, the intestinal BM is composed of components produced from both the epithelium and the mesenchyme.

[Production of hyaluronidase by cultured human tumor cells]

The presence of hyaluronidase was detected at pH 3.8 in eight out of twelve human cancer cell line culture media. Eight cell lines derived from primary tumours and four from metastases. In three culture media the enzymatic activity was lower than 0.035 pU/cell/h. In five others (in a hepatoma cell line and in four metastasis-derived cell lines) the activity was higher than 0.057 pU/cell/h. A tumour-derived fibroblast culture was negative. The optimal activity was observed at a pH comprised between 3.6 and 4. Salt inhibition of hyaluronidase was reversible. The enzyme was denaturated by a 10-min heating at 70 degrees C. The enzyme was not strictly specific for hyaluronan hydrolysis but also digested chondroitin sulfates. PH20, a spermatozoid protein that has homologies with the bee venom hyaluronidase, was not expressed by cell lines tested.

Syndecan-1 alterations during the tumorigenic progression of human colonic Caco-2 cells induced by human Ha-ras or polyoma middle T oncogenes

The products of ras and src proto-oncogenes are frequently activated in a constitutive state in human colorectal cancer. In this study we attempted to establish whether the tumorigenic progression induced by oncogenic activation of p21ras and pp60c-src in human colonic Caco-2 cells is associated with specific alterations of syndecan-1, a membrane-anchored proteoglycan playing a role in cell-matrix interaction and neoplastic growth control. To this end, we used Caco-2 cells made highly tumorigenic by transfection with an activated (Val 12) human Ha-ras gene or with the polyoma middle T (Py-MT) oncogene, a constitutive activator of pp60c-src tyrosine kinase activity. Compared with control vector-transfected Caco-2 cells, both oncogene-transfected cell lines (1) contained smaller amounts of membrane-anchored PGs; (2) exhibited decreased syndecan-1 expression at the protein but not the mRNA level; (3) synthesized 35S-labelled syndecan-1 with decreased specific activity; (4) produced a syndecan-1 ectodomain with a lower molecular mass and reduced GAG chain size and sulphation; and (5) expressed heparanase degradative activity. These results show that the dramatic activation of the tumorigenic potential induced by oncogenic p21ras or Py-MT/pp60c-src in Caco-2 cells is associated with marked alterations of syndecan-1 expression at the translational and post-translational levels.

De novo decorin gene expression suppresses the malignant phenotype in human colon cancer cells

The rapid progress in the cloning of proteoglycan genes has enabled investigators to examine in depth the functional roles these polyhedric molecules play in the control of cell proliferation. Decorin, a leucine-rich proteoglycan expressed by most connective tissues, is a prototype molecule that regulates cellular growth via two mechanisms: modulation of growth factor activity and matrix assembly. We now provide direct evidence that human colon cancer cells stably transfected with decorin cDNA exhibit a marked suppression of the transformed phenotype: the cells have a reduced growth rate in vitro, form small colonies in soft agar, and do not generate tumors in scid/scid mice. Several independent clones are arrested in the G1 phase of the cell cycle, and their growth suppression can be restored by treatment with decorin antisense oligodeoxynucleotides. These effects are independent of growth factors and are not due to either clonal selection or integration site of the decorin gene. These findings correlate well with the observation that decorin gene expression is markedly up-regulated during quiescence. Decorin thus appears to be one component of a negative loop that controls cell growth.

Glycoconjugate profile and CD44 expression in human melanoma cell lines with different metastatic capacity

Changes in glycoconjugate production have been reported for tumor cells. In this study, we investigated the glycoconjugate expression pattern in normal human melanocytes and in a panel of 6 human melanoma cell lines with different metastatic capacity after s.c. inoculation into nude mice. Glycoconjugates were labeled in vitro with [35S] sulphate and [3H] glucosamine, purified from cells and culture medium by column chromatography and identified by treatment with specific glycosidases. Characterization of the purified glycoconjugate fractions as well as alcian-blue staining of xenograft lesions revealed that hyaluronic acid (HA) is the main glycoconjugate produced by all cell lines. Highly metastatic cell lines expressed higher levels of HA than melanocytes and than weakly metastatic or non-metastatic cell lines. In addition, a shift in dominance from chondroitin-sulphate proteoglycan to heparan-sulphate proteoglycan was observed with increasing metastatic capacity. We also studied the expression and binding activity of the HA receptor CD44. Immunoprecipitation experiments indicated high CD44 synthesis only in highly metastatic cell lines, but FACS analysis demonstrated approximately the same surface expression in melanocytes as in all cell lines. Adhesion assays to immobilized HA showed that CD44 can be present in an inactive or an active conformation. Our data suggest that a combination of increased HA production and the expression of CD44 on the cell surface may be associated with high metastatic potential of human melanoma cell lines in nude mice.

Role of mesenchymal-epithelial interactions in normal and abnormal development of the mammary gland and prostate

Development of the mammary gland (MG) and prostate occurs via mesenchymal-epithelia interactions. Epithelial MG buds are induced in ventral epidermis by mammary mesenchyme, which ultimately specifies the functional expression of the ability to produce milk. Mammary ductal branching is induced by embryonic mammary mesenchyme and is promoted by the mammary fat pad postnatally. These influences of connective tissue on the differentiation of mammary epithelium (ME) begin prenatally, but in adulthood, the connective tissue environment of adult ME profoundly influences epithelial growth, ductal branching, epithelial differentiation, and the ability of adult ME to produce milk. In a similar fashion, prostatic development occurs via mesenchymal-epithelial interactions in which urogenital sinus mesenchyme (UGM) induces epithelial morphogenesis, regulates epithelial proliferation, and evokes the expression of epithelial androgen receptors and prostate-specific secretory proteins. Although prostatic development is induced by androgens, androgenic effects on epithelial development are elicited via androgen receptors of UGM. As in MG, mesenchymal-epithelial interactions in the prostate begin during fetal periods, but continue into adulthood. The responsiveness of adult epithelial cells from various glands to stroma raises the possibility that carcinomas also may be regulated by connective tissue. Indeed, UGM can induce a rat prostatic carcinoma (Dunning tumor) to undergo striking changes in differentiation, which are accompanied by a reduction in growth rate and an apparent loss of tumorigenesis. Although the mechanism of mesenchymal-epithelial interactions remains unknown, the communication between the epithelium and stroma undoubtedly is multifactorial, involving the extracellular matrix, soluble growth or differentiation, and angiogenesis.

Altered proteoglycan gene expression and the tumor stroma

Tumor stroma is a specialized form of tissue that is associated with epithelial neoplasms. Recent evidence indicates that significant changes in proteoglycan content occur in the tumor stroma and that these alterations could support tumor progression and invasion as well as tumor growth. Our main hypothesis is that the generation of tumor stroma is under direct control of the neoplastic cells and that, via a feedback loop, altered proteoglycan gene expression would influence the behavior of tumor cells. In this review, we will focus primarily on the work from our laboratory related to the altered expression of chondroitin sulfate proteoglycan and its role in tumor development and progression. The connective tissue stroma of human colon cancer is enriched in chondroitin sulfate and the stromal cell elements, primarily colon fibroblasts and smooth muscle cells, are responsible for this biosynthetic increase. These changes can be reproduced in vitro by using either tumor metabolites or co-cultures of human colon carcinoma cells and colon mesenchymal cells. The levels of decorin, a leucine-rich proteoglycan involved in the regulation of matrix assembly and cell proliferation, are markedly elevated in the stroma of colon carcinoma. These changes correlate with a marked increase in decorin mRNA levels and a concurrent hypomethylation of decorin gene, a DNA alteration associated with enhanced gene expression. Elucidation of decorin gene structure has revealed an unexpected degree of complexity in the 5' untranslated region of the gene with two leader exons that are alternatively spliced to the second coding exon. Furthermore, a transforming growth factor beta (TGF-beta)-negative element is present in the promotor region of decorin gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered proteoglycan gene expression and the tumor stroma

Tumor stroma is a specialized form of tissue that is associated with epithelial neoplasms. Recent evidence indicates that significant changes in proteoglycan content occur in the tumor stroma and that these alterations could support tumor progression and invasion as well as tumor growth. Our main hypothesis is that the generation of tumor stroma is under direct control of the neoplastic cells and that, via a feedback loop, altered proteoglycan gene expression would influence the behavior of tumor cells. In this review, we will focus primarily on the work from our laboratory related to the altered expression of chondroitin sulfate proteoglycan and its role in tumor development and progression. The connective tissue stroma of human colon cancer is enriched in chondroitin sulfate and the stromal cell elements, primarily colon fibroblasts and smooth muscle cells, are responsible for this biosynthetic increase. These changes can be reproduced in vitro by using either tumor metabolites or co-cultures of human colon carcinoma cells and colon mesenchymal cells. The levels of decorin, a leucine-rich proteoglycan involved in the regulation of matrix assembly and cell proliferation, are markedly elevated in the stroma of colon carcinoma. These changes correlate with a marked increase in decorin mRNA levels and a concurrent hypomethylation of decorin gene, a DNA alteration associated with enhanced gene expression. Elucidation of decorin gene structure has revealed an unexpected degree of complexity in the 5' untranslated region of the gene with two leader exons that are alternatively spliced to the second coding exon.(ABSTRACT TRUNCATED AT 250 WORDS)

Human melanoma cell-derived factor(s) stimulate fibroblast glycosaminoglycan synthesis

Conditioned media from cultures of human metastatic Hs294T melanoma cells contain a factor/factors that promote(s) fibroblast-mediated contraction of collagen lattices, and stimulate(s) fibroblast glycosaminoglycan (GAG) synthesis. Complete medium from melanoma cell cultures stimulated fibroblast hyaluronate synthesis 9.3-fold, and sulphated GAG synthesis 2.6-fold, as measured by 3H-glucosamine incorporation. 35SO4 incorporation into sulphated GAGS was essentially unaltered, the net result being a decrease in the degree of sulphation. Fibroblasts synthesized hyaluronate with an increased molecular weight when grown in the presence of the melanoma-cell culture medium, while the molecular weights of heparan and chondroitin sulphates remained essentially unaltered. Our results indicate that the tumour-cell-derived factor(s) stimulate(s) changes in fibroblast glycosaminoglycan synthesis, and that these changes may facilitate tumour cell invasion in vivo.

Distribution of individual components of basement membrane in human colon polyps and adenocarcinomas as revealed by monoclonal antibodies

Double-label immunofluorescence was used to monitor basement-membrane composition and integrity in 22 human colon polyps, 36 adenocarcinomas and 2 metastases. Cryostat sections were stained with polyclonal anti-laminin anti-serum combined with monoclonal antibodies (MAbs) to all major basement-membrane components (laminin, entactin/nidogen, collagen type IV and large heparan sulfate proteoglycan), as well as to keratin 8. In all adenocarcinomas, including mucinous, basement membranes were altered more at the invasive front than in the parenchyma. The degree of this alteration was inversely correlated with the level of tumor differentiation. An uncoordinated loss of basement membrane components (dissociation of markers), previously described by us in rat colon adenocarcinomas, was also found in human tumors. In the great majority of adenocarcinomas a pronounced stromal reaction was seen. It was manifested by the presence of fibrillar deposits of basement-membrane components, mainly of collagen type IV and/or heparan sulfate proteoglycan. This reaction was never observed in polyps and may be derived from myofibroblasts reported to accumulate in colon cancer stroma. The combined use of antibodies to basement-membrane components and to a specific keratin may constitute an adequate immunohistochemical test for the presence of invasion, and may be useful in the histologic analysis of polyps, especially in dubious cases.

Modulation of collagen and fibronectin synthesis in fibroblasts by normal and malignant cells

The influence of various normal and malignant human cells on the level of collagen synthesis by human fibroblasts was tested in coculture. As revealed by immunoperoxidase staining, in cocultures with breast adenocarcinoma cells (MCF7, SA52, T47D) fibroblasts synthesized collagen while tumor cells did not. Fibroblasts displayed increased collagen production without change in the overall protein synthesis. Several other types of cells derived from normal human tissues (keratinocytes, normal mammary cells) or from fibrosarcoma, melanoma, cervical carcinoma, choriocarcinoma, or other breast adenocarcinoma (SW613, MDA, BT20) did not affect collagen synthesis of fibroblasts. Although to a lesser extent, this stimulating effect was reproduced by using the conditioned medium (CM) of the active cells but not with CM of the other cell types. A slight stimulation was also obtained when tumoral MCF7 cells and fibroblasts shared the same medium but were physically separated, suggesting that close contact was required for optimal stimulation of collagen synthesis. The collagen synthesis stimulating activity was not related to a modification of fibroblast proliferation rate. The production of collagen types I, III, and VI and fibronectin were increased in cocultures of fibroblasts with MCF7 cells. The increased synthesis of collagen types I and III and fibronectin was paralleled by similar changes in the steady-state level of their mRNAs. On the contrary, the increased production of collagen type VI appeared regulated at a post-transcriptional level.

Hypomethylation of the decorin proteoglycan gene in human colon cancer

We have previously reported that the connective tissue stroma of human colon carcinoma contains elevated amounts of decorin, a small proteoglycan involved in the regulation of matrix formation and cell proliferation. These biochemical changes were correlated with increased mRNA levels and general hypomethylation of the decorin gene in human colon cancer DNA. In this report we use a quantitative polymerase chain reaction method coupled with digestion of the DNA template by methylation-sensitive restriction endonucleases to investigate in detail the location of hypomethylated sites in decorin gene. We demonstrate that a specific site in the 3' region of the gene, encompassing codons 360-361, is specifically hypomethylated in both colon carcinoma and benign polyp. In contrast, three HpaII sites, clustered in the 5' untranslated region, show full methylation in normal and neoplastic DNA. The lack of such changes in ulcerative colitis DNA suggests that chronic inflammation alone is not sufficient to alter cytosine methylation in the decorin gene. These results suggest the possibility that the 3' region of the decorin-coding sequence may be involved in the control of decorin gene expression.

Altered deposition of basement-membrane molecules in co-cultures of colonic cancer cells and fibroblasts

Two human colon carcinoma cell lines, HT29 and Caco-2 were co-cultured with fetal rat or human skin fibroblasts. Their morphological features, ultra-structural characteristics at the heterologous cell interface, and the deposition of basement-membrane molecules [laminin, type-IV collagen, heparan sulfate proteoglycan (HSPG)] at the epithelial-stromal junction were analyzed. The 2 cell lines behaved differently. HT29 cells did not spread on the fibroblasts and grew as clusters, while Caco-2 cells formed a monolayer over the fibroblastic feeder layer. Only the latter carcinoma cells exhibited cytoplasmic processes towards the fibroblasts and, after 5 days in co-cultures, a structured basement membrane (BM). The immunocytochemical analysis of the BM constituents revealed the absence of the molecules studied at the sites of heterologous contacts in the case of HT29 cells. In contrast, in the co-cultures comprising Caco-2 cells, laminin and type-IV collagen were progressively deposited in a polar fashion at the epithelial-fibroblastic interface which, however, remained devoid of HSPG molecules. Together with earlier data indicating a dual origin of the BM molecules located at the epithelial-fibroblastic interface in normal intestine, the present study shows that the cancer cells as well as the fibroblastic ones under the influence of carcinoma cells display an altered capacity to synthesize and/or secrete BM molecules. The extent of such abnormalities correlates with the differentiation of the cells. Finally, these modifications occur concomitantly with alterations in cell interactions which vary among cell lines.

Altered methylation of versican proteoglycan gene in human colon carcinoma

We show for the first time that DNA isolated from human colon carcinoma tissue exhibits a selective hypomethylation of versican gene, which encodes a large chondroitin sulfate proteoglycan. The degree of methylation of CpG sequences of versican gene locus, as determined by isoschizomeric endonucleases and Southern hybridization, is about three times lower than that found in either normal colon or ulcerative colitis tissues. Hypomethylation can be observed in both benign and malignant colonic neoplasms; however, there is no correlation with increased expression since versican mRNA levels do not significantly vary between normal and neoplastic tissues. We further show that versican gene locus from malignant tissue, but not from normal or ulcerative colitis tissues, contains Hind III hypersensitive sites which also comprise hypomethylated CpG sequences. Analysis of versican methylation status in colon carcinoma cells and benign mesenchymal cells derived from human colon suggests that the changes observed in vivo derive from demethylating events involving host stromal cells rather than tumor cells themselves. These findings demonstrate that changes in versican gene methylation are specific for colonic neoplasms, that these changes may precede malignant transformation, and that inflammation and tissue remodelling alone are not enough to generate these changes in proteoglycan gene methylation and nuclease hypersensitivity.

Changes in glycosaminoglycan synthesis and in heparan sulfate deposition in human colorectal adenocarcinomas

Biosynthesis of glycosaminoglycans (GAGs) was studied in morphologically normal colonic mucosa, in peritumoral and tumoral areas, and in colorectal polyps of tumor-bearing patients. After GAG purification, overall biosynthesis was determined: the general trend was a decrease in GAG production in neoplastic colon, lowest GAG synthesis being observed in Dukes' stage C tumors. Separation by ion-exchange chromatography of various GAG species and further characterization revealed the presence of hyaluronic acid (HA) and heparan sulfate (HS) molecules in all specimens studied. Chondroitin-4 sulfate (CS4) was occasionally found in tumor samples. The relative proportion of HA and HS was modified in tumor tissue: i.e. increased HA and decreased HS were observed. Differences in DEAE-chromatographic behavior were obvious in pathological samples as compared to controls, the hydrodynamic form of HA and the charge density of HS being decreased. The latter could be attributed to undersulfatation of HS molecules. Immunocytochemical detection of HS proteoglycan molecules revealed regular and bright labelling at epithelial-stromal interface in control samples. In pathological samples, staining was patchy and discontinuous, showing large areas of basement membrane interruption.

Cellular interactions in metastasis

The metastatic cascade is a sequence of events that must be completed for metastases to be established. The realization that tumors are heterogeneous, consisting of many different subpopulations differing in many characteristics, and the belief that there are selective events in the metastatic process have led several laboratories to isolate and characterize variants with both high and low metastatic potential. Typically, the highly metastatic variants have been able to form distant metastases when implanted into the subcutis. Such lines have been popular for studies of metastatic mechanisms and anti-metastatic therapy, but they may be atypical examples, and thus not the best experimental models. Recent studies indicate that normal tissue influences metastasis such that many tumors metastasize only if placed in the orthotopic site. Furthermore, some cells that do not metastasize individually are able to do so in conjunction with other variant subpopulations. Thus, mixtures of tumor cells in the tissue of origin can express a more malignant character. We review possible mechanisms for such influential interactions, as well as the role of cellular interactions in generating heterogeneity and stabilizing tumor characteristics.

Heparin and endothelial cell growth factor modulate collagen and proteoglycan production in human smooth muscle cells

The effects of heparin and endothelial cell growth factor (ECGF) on extracellular matrix production were examined in human iliac smooth muscle cells. The cells were grown in (a) medium supplemented with heparin (100 micrograms/ml) and ECGF (75 micrograms/ml), (b) medium supplemented with ECGF (75 micrograms/ml) alone, or (c) unsupplemented medium. In the presence of heparin and ECGF, collagen production was inhibited 91-95% as compared to cultures incubated with ECGF alone or without both supplemental factors. In contrast, the production of proteoglycans was elevated 2.5 fold in the presence of heparin and ECGF. Enzymatic digestion of the proteoglycans indicated that both large and small molecular weight chondroitin sulfate proteoglycans were markedly elevated, while dermatan sulfate and heparan sulfate proteoglycans were increased to a lesser extent. The results suggest that the combination of heparin and ECGF elicits potent modulation of extracellular matrix production, with divergent effects on collagen and proteoglycan synthesis.