Differential modulation of two interferon-alpha binding proteins on a human lymphoblastoid cell line

The interaction between human interferon (IFN)-alpha or IFN-beta with its receptor was originally described as the binding to a single class of high-affinity receptors. However, more recently, biphasic Scatchard plots as well as multiple IFN-alpha receptor cross-linked complexes have been reported. In this study using the Daudi B lymphoblastoid cell line, two primary IFN-alpha receptor cross-linked complexes with apparent Mr of 115 and 135 kilodaltons (kDa) were obtained. Both complexes were observed under a variety of cross-linking conditions, including the addition of a mixture of protease inhibitors throughout the binding reaction and solubilization of the cells. These two complexes appear to be caused by the binding and cross-linking of 125I-rIFN-alpha A to two separate proteins because we also observed two IFN-alpha binding proteins using a ligand-blotting technique. At low concentrations of 125I-rIFN-alpha A, it was found that the intensity of the signal in the 135-kDa cross-linked complex was greater than that of the 115-kDa complex. Addition of increasing concentrations of unlabeled rIFN-alpha A to a 4 degrees C binding reaction reversed the ratio in intensities of the two complexes. Moreover, after pretreatment of the cells at 37 degrees C with low concentrations of unlabeled rIFN-alpha A, there was preferential down-regulation of both the 135-kDa complex and the higher affinity binding component of the biphasic Scatchard plot. These results suggest that the 135-kDa complex represents the binding of 125I-rIFN-alpha A to a protein having higher affinity for IFN than the protein that gives rise to the 115-kDa complex.(ABSTRACT TRUNCATED AT 250 WORDS)