Differentiation-associated modulation of heparan sulfate structure and function in CaCo-2 colon carcinoma cells

Heparan sulfate species expressed by different cell and tissue types differ in their structural and functional properties. Limited information is available on differences in regulation of heparan sulfate biosynthesis within a single tissue or cell population under different conditions. We have approached this question by studying the effect of cell differentiation on the biosynthesis and function of heparan sulfate in human colon carcinoma cells (CaCo-2). These cells undergo spontaneous differentiation in culture when grown on semipermeable supports; the differentiated cells show phenotypic similarity to small intestine enterocytes. Metabolically labeled heparan sulfate was isolated from the apical and basolateral media from cultures of differentiated and undifferentiated cells. Compositional analysis of disaccharides, derived from the contiguous N-sulfated regions of heparan sulfate, indicated a greater proportion of 2-O-sulfated iduronic acid units and a smaller amount of 6-O-sulfated glucosamine units in differentiated than in undifferentiated cells. By contrast, the overall degree of sulfation, the chain length and the size distribution of the N-acetylated regions were similar regardless the differentiation status of the cells. The structural changes were found to affect the binding of heparan sulfate to the long isoform of platelet-derived growth factor A chain but not to fibroblast growth factor 2. These findings show that heparan sulfate structures change during cell differentiation and that heparan sulfate-growth factor interactions may be affected by such changes.