Enterocytic differentiation correlates with changes in the fine structure and sulfation of perlecan in HT29 human colon carcinoma cells

3-Sulfogalactosyl-dependent adhesion of Escherichia coli HS multivalent adhesion molecule is attenuated by sulfatase activity

Bacterial adhesion to host receptors is an early and essential step in bacterial colonization, and the nature of adhesin–receptor interactions determines bacterial localization and thus the outcome of these interactions. Here, we determined the host receptors for the multivalent adhesion molecule (MAM) from the gut commensal Escherichia coli HS (MAM^HS), which contains an array of seven mammalian cell entry domains. The MAM^HS adhesin interacted with a range of host receptors, through recognition of a shared 3-O-sulfogalactosyl moiety. This functional group is also found in mucin, a component of the intestinal mucus layer and thus one of the prime adherence targets for commensal E. coli. Mucin gels impeded the motility of E. coli by acting as a physical barrier, and the barrier effect was enhanced by specific interactions between mucin and MAM^HS in a sulfation-dependent manner. Desulfation of mucin by pure sulfatase or the sulfatase-producing commensal Bacteroides thetaiotaomicron decreased binding of E. coli to mucin and increased the attachment of bacteria to the epithelial surface via interactions with surface-localized sulfated lipid and protein receptors. Together, our results demonstrate that the E. coli adhesin MAM^HS facilitates retention of a gut commensal by attachment to mucin. They further suggest that the amount of sulfatase secreted by mucin-foraging bacteria such as B. thetaiotaomicron, inhabiting the same niche, may affect the capacity of the mucus barrier to retain commensal E. coli.

Requirement of both mucins and proteoglycans in cell-cell dissociation and invasiveness of colon carcinoma HT-29 cells

Human colon carcinomas are characterized by an aberrant expression of mucins, which in some case leads to an abundant presence of mucus such as in mucinous and signet ring cell carcinomas. Cellular cloning of the human colon carcinoma cell line HT-29 (HT-29 STD), which is mainly composed of undifferentiated cells, yielded a highly mucin-secreting variant (HT-29 5M21). The latter cloned cells cultured on plastic display a polarized organization with an apical secretion of MUC5AC mucin (Lesuffleur et al., Int J Cancer 1998;76:383-92.). Our aim was to study these 2 cell-types as for the invasive and adhesive properties with regard to the function of E-cadherin. HT-29 STD cells were noninvasive in collagen type I, whereas HT-29 5M21 cells were invasive, and the latter behavior was connected to a loss of function of E-cadherin. Likewise, HT-29 5M21 cells were characterized by a cell-cell adhesion independent of E-cadherin, in contrast to the E-cadherin dependent cell-cell adhesion of HT-29 STD cells. Immunofluorescence of HT-29 5M21 cells cultured on collagen type I showed the disappearance of the polarized organization, with a redistribution of apical mucins to the entire cell surface. Treatment of HT-29 5M21 cells by 1-benzyl-2-acetamido-2-deoxy-alpha-D-galactopyranoside (GalNAcalpha-O-bn) or by beta-D-xyloside revealed that both mucins and proteoglycans were involved in the loss of E-cadherin function. The use of specific antibodies allowed to show that MUC5AC, MUC1 and heparan sulfate proteoglycans cooperated in the formation of a biological inhibitory complex towards the function of E-cadherin in this invasive HT-29 clone.

Interaction of thrombospondin-1 and heparan sulfate from endothelial cells. Structural requirements of heparan sulfate

Cell surface-associated heparan sulfate proteoglycans, predominantly perlecan, are involved in the process of binding and endocytosis of thrombospondin-1 (TSP-1) by vascular endothelial cells. To investigate the structural properties of heparan sulfate (HS) side chains that mediate this interaction, the proteoglycans were isolated from porcine endothelial cells and HS chains obtained thereof by beta-elimination. To characterize the structural composition of the HS chains and to identify the TSP-1-binding sequences, HS was disintegrated by specific chemical and enzymatic treatments. Cell layer-derived HS chains revealed the typical structural heterogeneity with domains of non-contiguously arranged highly sulfated disaccharides separated by extended sequences containing predominantly N-acetylated sequences of low sulfation. Affinity chromatography on immobilized TSP-1 demonstrated that nearly all intact HS chains possessed binding affinity, whereas after heparinase III treatment only a small proportion of oligosaccharides were bound with similar affinity to the column. Size fractioning of the bound and unbound oligosaccharides revealed that only a specific portion of deca- to tetradecasaccharides possessed TSP-1-binding affinity. The binding fraction contained over 40% di- and trisulfated disaccharide units and was enriched in the content of the trisulfated 2-O-sulfated L-iduronic acid-N-sulfated-6-O-sulfated glucosamine disaccharide unit. Comparison with the disaccharide composition of the intact HS chains and competition experiments with modified heparin species indicated the specific importance of N- and 6-O-sulfated glucosamine residues for binding. Further depolymerization of the binding oligosaccharides revealed that the glucosamine residues within the TSP-1-binding sequences are not continuously N-sulfated. The present findings implicate specific structural properties for the HS domain involved in TSP-1 binding and indicate that they are distinct from the binding sequence described for basic fibroblast growth factor, another HS ligand and a potential antagonist of TSP-1.

Human perlecan immunopurified from different endothelial cell sources has different adhesive properties for vascular cells

Perlecan, a major heparan sulfate proteoglycan of vascularized tissues, was immunopurified from media conditioned by human endothelial cells of both arterial and venous origin. The heparan sulfate moiety of perlecan from cultured arterial cells differed in amount and/or composition from that produced by a transformed cell line of venous origin. Both forms of perlecan bound basic fibroblast growth factor with Kd approximately 70 nM. In ELISA experiments, perlecan and its protein core bound to various extracellular matrix components in a manner that was strongly influenced by the format of the assay. Human vascular smooth muscle cells and human endothelial cells adhered to perlecan-coated surfaces, and both cell types adhered better to the venous cell-derived than to the arterial cell-derived perlecan. Removal of the heparan sulfate chains abolished this difference and increased the ability of both types of perlecan to adhere vascular cells. Denaturation of perlecan and its protein core also rendered each of them more adhesive, indicating the presence of conformation-independent adhesion determinants in the polypeptide sequence. Their location was investigated using recombinant perlecan domains. Overall, our results represent the first demonstration of human perlecan acting as an adhesive molecule for human vascular cells and suggest that it may play a role in vascular wound healing.