Role of interferon α/β receptor chain 1 in the structure and transmembrane signaling of the interferon α/β receptor complex

Abstract

A previously cloned cDNA encodes one subunit of the human interferon α/β receptor (IFNαR), denoted IFNαR1. To study the expression and signaling of IFNαR1, we used monoclonal antibodies (mAbs) generated against the baculovirus-expressed ectodomain of IFNαR1. Immunoprecipitation and immunoblotting of lysates from a variety of human cell lines showed that IFNαR1 has an apparent molecular mass of 135 kDa. Binding analysis with 125I-labeled mAb demonstrated high levels of cell surface expression of IFNαR1 in human cells and in mouse cells transfected with IFNαR1 cDNA, whereas no cross-reactivity was observed in control mouse L929 cells expressing only the endogenous mouse receptor. The subunit was rapidly down- regulated by IFNα (80% decrease within 2 hr) and degraded upon internalization. The IFNαR1 chain appeared to be constitutively associated with the 115-kDa subunit of the IFNα/β receptor, since the mAbs coprecipitated this protein. IFNα/β treatment induced tyrosine phosphorylation of IFNαR1 within 1 min, with kinetics paralleling that of the IFN-activated protein-tyrosine kinases Jak1 and Tyk2. Ligand-induced tyrosine phosphorylation of IFNαR1 was blocked by the kinase inhibitors genistein or staurosporine. Although IFNαR1 cDNA-transfected mouse cells expressed high levels of this subunit when compared with empty vector- transfected cells, the number of binding sites for human IFNα (50-75 sites per cell) was not increased. Human IFNα induced the expression of a mouse IFNα/β-responsive gene (the 204 gene) in mouse L929 cells transfected with the IFNαR1 cDNA, but not in mock-transfected cells. These results suggest that the IFNαR1 subunit acts as a species-specific signal transduction component of the IFNα/β receptor complex.