SINGLE HIGH-AFFINITY BINDING OF INTERFERON-ALPHA-2 TO RECEPTORS ON HUMAN-LYMPHOBLASTOID CELLS - INTERNALIZATION AND INACTIVATION OF RECEPTORS

The interaction of human recombinant interferon (rIFN) .alpha.2 with its receptor on lymphoblastoid cells was studied using competitive displacement binding. The data were analyzed with the LIGAND program, which tests their fit to 1-site or mutiple binding site models. The binding at 4.degree. and 37.degree. C fits a 1-site model, with a similar KD for both IFN-sensitive and resistant cells. Binding at 37.degree. C to Daudi cells at high density fits artifactually a 2-site model only when the receptor concentration is close to that of the KD. The binding of IFN to its receptor follows a simple bimolecular interaction. IFN-sensitive and resistant cells internalize IFN at similar rates. Whether IFN receptors are also internalized and whether they subsequently recycle to the cell surface was examined. By measuring cell surface and total receptors, after 2 h treatment with IFN total receptors remain constant whereas cell surface receptors decrease. After prolonged treatment with IFN, there is a loss of total receptors. By inactivating cell surface receptors with proteinase K, a fraction of cell surface receptors becomes resistant to inactivation and is apparently internalized. Experiments which measure IFN receptors either during incubation in the presence of IFN or after IFN was removed from the medium, show that receptors do not recycle to the cell surface after internalization. The addition of monensin, a drug which was shown to inhibit receptor recycling, has no effect on the loss of IFN receptors.