INTERFERON-GAMMA INDUCES RECEPTOR DIMERIZATION IN SOLUTION AND ON CELLS

The extracellular domain (ECD) of the human interferon-gamma (IFNgamma ) receptor was stably expressed in Chinese hamster ovary cells and pur ified to homogeneity. Scatchard analysis of I-125-IFNgamma binding to ECD preparations revealed the formation of a ligand-receptor complex w hich displayed a K(a) of 6.4 +/- 0.9 x 10(8) M-1. Two types of complex es were identified by sucrose density gradient ultracentrifugation. Th e stoichiometry of the major ECD-ligand complex was determined by high performance liquid chromatography gel filtration. When IFNgamma was i ncubated with a 2-fold molar excess of ECD, a 190-kDa complex was isol ated that contained 2 mol of ECD per 1 mol of IFNgamma. IFNgamma also induced dimerization of IFNgamma receptors expressed at the cell surfa ce as detected by chemically cross-linking receptor bound ligand and a nalyzing cell lysates by SDS-polyacrylamide gel electrophoresis and im munoblotting. Finally, labeled forms of ECD bound to cells preincubate d at 4-degrees-C with excess amounts of IFNgamma indicating that the l igand could associate with more than one receptor molecule in the abse nce of chemical cross-linking agents. These results demonstrate that I FNgamma effects dimerization of its receptor under physiologic conditi ons and suggest that IFNgamma receptor dimerization may be an importan t event in inducing IFNgamma-dependent biologic responses.