J Biol Chem, Vol. 274, Issue 27, 18957-18964, July 2, 1999

CD44, a Cell Surface Chondroitin Sulfate Proteoglycan, Mediates Binding of Interferon- and Some of Its Biological Effects on Human Vascular Smooth Muscle Cells

From the Wallenberg Laboratory for Cardiovascular Research, Göteborg University, Göteborg 413 45, Sweden and ^§ Astra Hässle, Mölndal S-431 83, Sweden

Several cytokines and growth factors act on cells after their association with the glycosaminoglycan (GAG) moiety of cell surface proteoglycans (PGs). Interferon- (IFN-) binds to GAG; however, the relevance of this interaction for the biological activity of IFN- on human cells remains to be established. Human arterial smooth muscle cells (HASMC), the main cells synthesizing PG in the vascular wall, respond markedly to IFN-. We found that treatment of HASMC with chondroitinase ABC, an enzyme that degrades chondroitin sulfate GAG, reduced IFN- binding by more than 50%. This treatment increased the affinity of ¹²⁵I-IFN- for cells from a K_d value of about 93 nM to a K_d value of about 33 nM. However, the total binding was reduced from 9.3 ± 0.77 pmol/µg to 3.0 ± 0.23 pmol/mg (n = 4). Interestingly, pretreatment with chondroitinase ABC reduced significantly the cellular response toward IFN-. The interaction of IFN- with chondroitin sulfate GAG was confirmed by affinity chromatography of isolated cell-associated ³⁵S-, ³H-labeled PG on a column with immobilized IFN-. The cell-associated PG that binds to IFN- was a chondroitin sulfate PG (CSPG). This CSPG had a core protein of approximately 110 kDa that was recognized by anti-CD44 antibodies on Western blots. High molecular weight complexes between IFN- and chondroitin 6-sulfate were observed in gel exclusion chromatography. Additions of chondroitin 6-sulfate to cultured HASMC antagonized the antiproliferative effect and expression of major histocompatibility complex II antigens induced by IFN-. These results indicate that IFN- binds with low affinity to the chondroitin sulfate GAG moiety of the cell surface CSPG receptor CD44. This interaction may increase the local concentration of IFN- at the cell surface, thus facilitating its binding to high affinity receptors and modulating the ability of IFN- to signal a cellular response.