Interferon Gamma Binds to Extracellular Matrix Chondroitin-Sulfate Proteoglycans, Thus Enhancing Its Cellular Response

Abstract The amino acid sequence of interferon gamma (IFN-γ) has basic amino acid clusters similar to the heparin-binding consensus sequences found in other proteins that bind to proteoglycans (PGs). We investigated whether recombinant human IFN-γ could bind to extracellular matrix (ECM) PGs secreted by human arterial smooth muscle cells (HASMCs) in vitro and whether the interaction affected the cellular response to IFN-γ. As an in vitro model of ECM we used the basement membrane from HASMCs in culture. The binding of 125I-IFN-γ to ECM was reduced significantly by pretreatment of ECM with chondroitinase ABC, an enzyme that degrades chondroitin-sulfate glycosaminoglycans. IFN-γ binding to ECM was reduced by increasing concentrations of chondroitin-6-sulfate. 125I-IFN-γ (0.05 to 2 ng/mL) binding data indicated an apparent Kd of 2×10−11 mol/L and a maximum binding of 1.6×106 IFN-γ molecules bound per square millimeter of ECM. Experiments with synthetic peptides suggested that residues 127 through 135 (AKTGKR...