Nucleosomes Bind to Cell Surface Proteoglycans

Material on the surface of activated T-cells was displaced following incubation with a sulfated polysaccharide, dextrin 2-sulfate (D2S), and purified by anion-exchange chromatography. This revealed a complex comprising histones H2A, H2B, H3, and H4 and DNA fragmented into 180-base pair units characteristic of mono-, di-, tri, and polynucleosomes, a pattern of fragmentation similar to that found in apoptotic cells. An antibody raised against the purified nucleosome preparation bound to the plasma membrane of activated T-cells confirming the surface location of nucleosomes. The interaction of sulfated polysaccharides with nucleosomes was investigated using a biotinylated derivative of D2S. It was found that sulfated polysaccharides bound to nucleosomes via the N termini of histones, especially H2A and H2B. Treatment of T-cells with either heparinase or heparitinase abolished nucleosome binding to plasma membranes. This suggests that nucleosomes are anchored to the surface of T-cells by heparan sulfate proteoglycans through an ionic interaction with the basic N-terminal residues in the histones. Furthermore, nucleosomes bound to the cell surface in this manner are then able to bind other sulfated polysaccharides, such as D2S, heparin, or dextran sulfate, through unoccupied histone N termini forming a complex comprising cell surface heparan sulfate proteoglycans, nucleosomes, and sulfated polysaccharides.