INTERFERON-GAMMA BINDS TO EXTRACELLULAR-MATRIX CHONDROITIN-SULFATE PROTEOGLYCANS, THUS ENHANCING ITS CELLULAR-RESPONSE

The amino acid sequence of interferon gamma (IFN-gamma) has basic amin o acid clusters similar to the heparin-binding consensus sequences fou nd in other proteins that bind to proteoglycans (PGs). We investigated whether recombinant human IFN-gamma could bind to extracellular matri x (ECM) PGs secreted by human arterial smooth muscle cells (HASMCs) in vitro and whether the interaction affected the cellular response to I FN-gamma. As an in vitro model of ECM we used the basement membrane fr om HASMCs in culture. The binding of I-125-IFN-gamma to ECM was reduce d significantly by pretreatment of ECM with chondroitinase ABC, an enz yme that degrades chondroitin-sulfate glycosaminoglycans. IFN-gamma bi nding to ECM was reduced by increasing concentrations of chondroitin-6 -sulfate. I-125-IFN-gamma (0.05 to 2 ng/mL) binding data indicated an apparent K-d of 2x10(-11) mol/L and a maximum binding of 1.6x10(6) IFN -gamma molecules bound per square millimeter of ECM. Experiments with synthetic peptides suggested that residues 127 through 135 (AKTGKRKRS) are involved in the binding. The binding to chondroitin-sulfate PGs w as confirmed by affinity chromatography of isolated [S-35]chondroitin- sulfate PGs from ECM and cell-culture medium on immobilized IFN-gamma. The binding was abolished by treatment with chondroitinase ABC. ECM-b ound IFN-gamma was more effective in inducing the expression of class II major histocompatibility antigens such as HLA-DR in HASMCs and huma n arterial endothelial cells than soluble IFN-gamma. These results sug gest a role for chondroitin-sulfate PGs in immobilizing IFN-gamma in t he ECM compartment and enhancing the cellular response to IFN-gamma.