CD44, a cell surface chondroitin sulfate proteoglycan, mediates binding ofinterferon-gamma and some of its biological effects on human vascular smooth muscle cells

Several cytokines and growth factors act on cells after their association w ith the glycosaminoglycan (GAG) moiety of cell surface proteoglycans (PGs). Interferon-gamma (IFN-gamma) binds to GAG; however, the relevance of this interaction for the biological activity of IFN-gamma on human cells remains to be established. Human arterial smooth muscle cells (HASMC), the main ce lls synthesizing PG in the vascular wall, respond markedly to IFN-gamma. We found that treatment of HASMC with chondroitinase ABC, an enzyme that degr ades chondroitin sulfate GAG, reduced IFN-gamma binding by more than 50%. T his treatment increased the affinity of I-125-IFN-gamma for cells from a K- d value of about 93 nM to a K-d value of about 33 nM. However, the total bi nding was reduced from 9.3 +/- 0.77 pmol/mu g to 3.0 +/- 0.23 pmol/mg (n = 4). Interestingly, pretreatment with chondroitinase ABC reduced significant ly the cellular response toward IFN-gamma. The interaction of IFN-gamma wit h chondroitin sulfate GAG was confirmed by affinity chromatography of isola ted cell-associated S-35-, H-3-labeled PG on a column with immobilized IFN- gamma. The cell-associated PG that binds to IFN-gamma was a chondroitin sul fate PG (CSPG). This CSPG had a core protein of approximately 110 kDa that was recognized by anti-CD44 antibodies on Western blots. High molecular wei ght complexes between IFN-gamma and chondroitin 6-sulfate were observed in gel exclusion chromatography. Additions of chondroitin 6-sulfate to culture d HASMC antagonized the antiproliferative effect and expression of major hi stocompatibility complex II antigens induced by IFN-gamma. These results in dicate that IFN-gamma binds with low affinity to the chondroitin sulfate GA G moiety of the cell surface CSPG receptor CD44. This interaction may incre ase the local concentration of IFN-gamma at the cell surface, thus facilita ting its binding to high affinity receptors and modulating the ability of I FN-gamma to signal a cellular response.