INTERFERON RECEPTOR INTERACTION - INTERNALIZATION OF INTERFERON-ALPHA-2 AND MODULATION OF ITS RECEPTOR ON HUMAN-CELLS

Human interferon-.alpha.2 (HuIFN-.alpha.2) binds to a specific macromolecular receptor on human cells as identified by cross-linking with bifunctional cross-linking reagents and analysis by polyacrylamide gel electrophoresis. Experiments to investigate the fate of the interferon-receptor complex on the cell surface under conditions which lead to cellular response are reported. As analyzed by cross-linking and gel electrophoresis, the interferon-receptor complex, formed on incubation with 125I-IFN-.alpha.2 at 4.degree. C, persisted at the cell [Daudi human lymphoblastoid line] surface for several hours at 4.degree. C; if the cells were switched to 37.degree. C, there was a rapid decline in the complex, apparently due to a loss of the interferon receptors from the cell surface. This was associated with an internalization of the 125I-interferon as indicated by the fact that, on incubation at 37.degree. C, an appreciable fraction of the cell-associated interferon (.apprxeq. 50%) became resistant to trypsin digestion, or dissociation on incubation in growth medium or low-pH buffer. A large fraction of the trypsin-resistant (internalized) 125I-labeled material migrated as intact interferon in polyacrylamide gels, and it was immunoprecipitated by anti-(HuIFN-.alpha.)antibodies but not by anti-(HuIFN-.beta.)antibodies. The bulk of the internalized 125I-interferon was recovered in a particulate fraction and, on cross-linking with disuccinimidyl suberate, a 150,000 MW complex could be detected. Thus, interferon may be internalized as a complex with the receptor, which may account for the loss of the interferon-receptors on the cell surface. This modulation of the IFN-.alpha./.beta. receptors was induced by HuIFN-.alpha. and HuIFN-.beta., but not by HuIFN-.gamma.. The recovery of the IFN-.alpha./.beta. receptors, lost upon incubation with HuIFN-.alpha., took several hours and required protein syntehsis. The significance of the results is discussed.