Structural and Functional Analyses of Xyloside-primed Glycosaminoglycans

Abstract: Glycosaminoglycans (GAGs) are polysaccharides produced by essentially all mammalian cells. Due to their enormous structural diversity, they are involved in many biological processes both in health and disease, including all stages of tumor progression. GAGs are normally attached to a core protein as a part of a proteoglycan; however, GAG biosynthesis can be induced by compounds composed of a xylose residue and an aglycon, xylopyranosides, or, more commonly, xylosides. Xylosides have been used for more than 40 years to study GAG biosynthesis and the effects of altered proteoglycan production in different cellular processes. However, little is known about the detailed structure and function of xyloside-primed GAGs. We have previously shown that the xyloside 2,6-hydroxynaphthyl β-D-xylopyranoside, XylNapOH, reduces the growth of cancer cells, but not normal cells, and suggested that the effect is related to the XylNapOH-primed GAGs. This served as a benchmark as we aimed to increase our knowledge about xylosides and xyloside-primed GAGs.We started synoptically by investigating GAG formation, proportion of heparan sulfate (HS) and chondroitin/dermatan sulfate (CS/DS), and effect on growth of breast carcinoma cells, HCC70, and normal breast fibroblasts, CCD-1095Sk cells, by xylosides where the xylose residue was separated from the aglycon by linkers of different length. Due to the apparent lack of relationship between the relative amount and composition of the xyloside-primed GAGs and the effect on cell growth, the xyloside-primed GAGs were investigated in more detail. We isolated GAGs derived from HCC70 cells and CCD-1095Sk cells primed on XylNapOH and the non-toxic 2-naphthyl β-D-xylopyranoside, XylNap, and showed that CS/DS from HCC70 cells primed on XylNapOH and XylNap had a cytotoxic effect on both HCC70 cells and CCD-1095Sk cells. Furthermore, the HS from HCC70 cells primed on XylNap inhibited this effect. In contrast, neither the CS/DS nor HS from CCD-1095Sk cells primed on XylNapOH or XylNap had any effect on cell growth. The cytotoxic effect was related to the disaccharide composition of the xyloside-primed GAGs, which differed between HCC70 cells and CCD-1095Sk cells, but was similar when the GAGs where derived from the same cell line. To further investigate the structural requirements for the cytotoxic effect, XylNap-primed GAGs from HCC70 cells and CCD-1095Sk cells were structurally characterized using a novel LC-MS/MS approach in combination with disaccharide fingerprinting and cell growth studies. The data revealed candidates for the cytotoxic effect including internal saccharides, linkage regions, and GAGs composed entirely of CS. Furthermore, the XylNap-primed GAGs were discovered to be structurally heterogeneous and to contain previously undescribed modifications. Finally, a systematic investigation of the influence of xyloside concentration, type of xyloside, and type of cell on the structure of xyloside-primed GAGs was performed, showing that it is possible to produce large quantities of xyloside-primed GAGs and to fine-tune their structure by adjusting these parameters. Our data demonstrate that xylosides and xyloside-primed GAGs may be used as tools for various biochemical and biotechnological applications, important from both the basic science and medical points of view.