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

Heparan sulfate proteoglycans undergo differential expression alterations in left sided colorectal cancer, depending on their metastatic character

Background

Heparan sulfate proteoglycans (HSPGs) are complex molecules which play a role in the invasion and growth and metastatic properties of cancerous cells. In this work we analyze changes in the patterns of expression of HSPGs in left sided colorectal cancer (LSCRC), both metastatic and non-metastatic, and the results are also compared with those previously obtained for right sided tumors (RSCRCs).

Methods

Eighteen LSCRCs were studied using qPCR to analyze the expression of both the proteoglycan core proteins and the enzymes involved in heparan sulfate chain biosynthesis. Certain HSPGs also carry chondroitin sulfate chains and so we also studied the genes involved in its biosynthesis. The expression of certain genes that showed significant expression differences were also analysed using immunohistochemical techniques.

Results

Changes in proteoglycan core proteins were dependent on their location, and the main differences between metastatic and non-metastatic tumors affected cell-surface glypicans, while other molecules were quite similar. Glypicans were also responsible for the main differences between RS- and LS- malignances. Regarding the biosynthesis of heparan sulfate chains, differential alterations in transcription depending on the presence or not of metastasis affected genes involved in the modification of uronic acid (epimerization and 2-O sulfation), and some isoforms responsible for sulfation of glucosamine (NDST1, HS6ST1). Moreover, in RSCRCs differences were preferentially found in the expression of genes involved in C6 and C3 sulfation of glucosamine, but not in NDSTs or SULFs. Finally, synthesis of chondroitin sulfate showed some alterations, which affected various steps, including polimerization and the modification of chains, but the main variations dependent on the presence of metastases were epimerization and 6C sulfation; however, when compared with RSCRCs, the essential divergences affected polymerization of the chains and the 6C sulfation of the galactosamine residue.

Conclusions

We evidenced alterations in the expression of HSPGs, including the expression of cell surface core proteins, many glycosiltransferases and some enzymes that modify the GAG chains in LSCRCs, but this was dependent on the metastatic nature of the tumor. Some of these alterations are shared with RSCRCs, while others, focused on specific gene groups, are dependent on tumor localization.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4597-x) contains supplementary material, which is available to authorized users.

Heparan sulfate proteoglycans undergo differential expression alterations in right sided colorectal cancer, depending on their metastatic character

Background

Heparan sulfate proteoglycans (HSPGs) are complex molecules involved in the growth, invasion and metastatic properties of cancerous cells. This study analyses the alterations in the expression patterns of these molecules in right sided colorectal cancer (CRC), both metastatic and non-metastatic.

Methods

Twenty right sided CRCs were studied. A transcriptomic approach was used, employing qPCR to analyze both the expression of the enzymes involved in heparan sulfate (HS) chains biosynthesis, as well as the proteoglycan core proteins. Since some of these proteoglycans can also carry chondroitin sulfate (CS) chains, we include the study of the genes involved in the biosynthesis of these glycosaminoglycans. Immunohistochemical techniques were also used to analyze tissue expression of particular genes showing significant expression differences, of potential interest.

Results

Changes in proteoglycan core proteins differ depending on their location; those located intracellularly or in the extracellular matrix show very similar alteration patterns, while those located on the cell surface vary greatly depending on the nature of the tumor: glypicans 1, 3, 6 and betaglycan are affected in the non-metastatic tumors, whereas in the metastatic, only glypican-1 and syndecan-1 are modified, the latter showing opposing alterations in levels of RNA and of protein, suggesting post-transcriptional regulation in these tumors. Furthermore, in non-metastatic tumors, polymerization of glycosaminoglycan chains is modified, particularly affecting the synthesis of the tetrasaccharide linker and the initiation and elongation of CS chains, HS chains being less affected. Regarding the enzymes responsible for the modificaton of the HS chains, alterations were only found in non-metastatic tumors, affecting N-sulfation and the isoforms HS6ST1, HS3ST3B and HS3ST5. In contrast, synthesis of the CS chains suggests changes in epimerization and sulfation of the C4 and C2 in both types of tumor.

Conclusions

Right sided CRCs show alterations in the expression of HSPGs, including the expression of the cell surface core proteins, many glycosiltransferases and some enzymes that modify the HS chains depending on the metastatic nature of the tumor, resulting more affected in non-metastatic ones. However, matrix proteoglycans and enzymes involved in CS fine structure synthesis are extensively modified independetly of the presence of lymph node metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1724-9) contains supplementary material, which is available to authorized users.

Overexpression of laminin alpha1 chain in colonic cancer cells induces an increase in tumor growth

Laminins represent a growing family of glycoproteins constituting the basement membrane. They are known to direct many biological processes. With respect to carcinogenesis, laminins play an important role in cell adhesion, mitogenesis, differentiation and even metastasis. To further study the biological significance of laminin-1 (composed of alpha1, beta1 and gamma1 chains) in intestinal cell differentiation or tumorigenesis, an alpha1-laminin expression vector was introduced into the HT29 colonic cancer cells, in which laminin alpha1 chain is not expressed. Upon transfection of the alpha1 chain, the alpha1beta1gamma1 trimer was found secreted in the media along with free alpha1 chain as assessed by immunoprecipitation. The presence of the laminin alpha1 chain did not significantly modify the levels of the other laminin chains nor the integrins expressed by the HT29 cells. In spite of similar growth properties with the control cells in vitro (plastic dish, soft agar), the laminin alpha1 transfectants showed a significantly increased tumor growth when injected in nude mice. Histologic and immunohistochemic examination of the laminin alpha1-expressing tumors points to an increased recruitment of the host stromal and vascular cells, without modification in the differentiation profile and invasion potential. In parallel, a clear accumulation of laminin-10 (alpha5beta1gamma1) at the carcinoma/stromal interface and a segregation of the integrin beta4 subunit at the basal pole of the cancer cells occurred, compared to control tumors. Overall, our observations emphasize the importance of laminin-1 as a chemoattractant of both stromal and vascular cells and in epithelial/stromal cell interactions for the organization of the basement membrane and segregation of integrins leading to an epithelial cell growth signal. Such a sequence of events is reminiscent of what occurs during development.

Heparin stimulates the proliferation of intestinal epithelial cells in primary culture

Heparin is a sulphated glycosaminoglycan derived from mast cells and has a number of functions including the inhibition of proliferation in several cell types and interactions with a range of heparin-binding growth factors. We report that heparin is a trophic factor in primary cultures of rat small intestinal epithelium. Heparin elicits a dose-dependent increase in epithelial proliferation and inhibits the growth of associated mesenchyme. The trophic effect of this molecule is not reproduced by other glycosaminoglycans including heparan sulphate but is dependent upon extensive molecular sulphation. Highly sulphated polysaccharides that are structurally unrelated to heparin (e.g. dextran sulphate and pentosan polysulphate) also stimulate epithelial proliferation in primary cultures. Heparin may act by the potentiation of mesenchyme-derived heparin-binding growth factors and these data suggest an in vivo role for mast cell-derived heparin in mucosal wound regeneration.

Kinetic analysis of the effects of glycosaminoglycans and lipoproteins on urokinase-mediated plasminogen activation

The glycosaminoglycans (GAGs) heparin, heparan sulphate and chondroitin 6-sulphate stimulate the rate of urokinase activation of human plasminogen. Kinetic analysis of plasminogen activation demonstrates that heparin, heparan sulphate and chondroitin 6-sulphate increased the catalytic rate (Kcat) by 5.3-, 3.5- and 2.5-fold respectively. These stimulatory GAGs had no effect on the affinity of urokinase for plasminogen, since the Km of the reaction is unaltered by the GAGs. The GAGs may enhance the rate of plasminogen activation through an interaction with the catalytic domain of the urokinase, with dissociation constants of approx. 30 nM. Additionally, the lipoproteins, lipoprotein (a) [Lp(a)] and low-density lipoprotein (LDL) inhibit heparin and heparan sulphate stimulation of plasmin formation. Lp(a) is a competitive inhibitor (Kic 20 nM) and LDL is a mixed inhibitor of heparin-enhanced urokinase-mediated plasminogen activation (Kic 24 nM and Kiu 60 nM). These inhibition constants correlate with physiological concentrations of these lipoproteins. These data suggest that these GAGs and lipoproteins may play an important role in vivo in regulating urokinase-mediated plasmin formation.

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.