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The interferon ␣␤ receptor (IFN␣R) or type I IFN-R is formed by a 110-kDa ␣ subunit or IFNAR and by a ␤ subunit, which has short and long forms (molecular masses of 55 and 95-100 kDa, respectively). In this report, we demonstrate that the IFN␣/␤R cDNA recently cloned corresponds to the 55-kDa or short form of the ␤ subunit, while the 95-100-kDa species reported here corresponds to a longer form of the IFN␣/␤R cDNA that is probably produced by alternative splicing of the same gene. Stable transfection of the ␣ subunit with either form of the ␤ subunit results in the expression of low and high affinity receptors, while expression of either form of the ␤ subunit alone only produces low affinity receptors. More important, only expression of the ␣ and long form of the human ␤ subunits in mouse L-929 cells reconstitutes the activation of the Jak kinases and the Stat factors, as well as the antiviral response to human type I IFNs.Characterization of the interferon ␣␤ receptor or type I interferon receptor (IFN␣R or IFN-R) 1 with monoclonal antibodies (mAb) has revealed that this receptor is composed of at least two chains: the ␣ and ␤ subunits (recognized by the IFNaR3 and IFNaR␤1 monoclonal antibodies, respectively) (1, 2). Using mAbs and affinity cross-linking methods, we described two forms of the type I IFN-R: normal and variant (2, 3). The "normal" receptor is expressed in most cells and is composed of ␣ and ␤ subunits with molecular masses of 110 and 100 kDa, respectively. The "variant" receptor is expressed in monocytic cell lines and normal bone marrow cells, and in contrast to the "normal" receptor, its ␤ subunit has a molecular mass of 55 kDa (2, 3). Two cDNAs encoding IFNAR (4) and IFN␣␤R (5) subunits of the type I IFN-R have been cloned. We have recently demonstrated that the ␣ subunit is encoded by the IFNAR cDNA (6), and its cytoplasmic domain directly interacts with Tyk-2 tyrosine kinase.The IFN␣␤R cDNA product (5) has a similar M r as the variant form of the ␤ subunit (2) and is proposed to form a disulfide-bonded dimer that it is only cleaved by high concentrations of reducing agents (5 Cloning of the Long Form of the ␤ Subunit-A cDNA library was made with poly(A)ϩ RNA obtained from the human myeloma U-266 cell line using a commercial cDNA kit, followed by subcloning into the pcDNA II vector (Invitrogen). Screening was performed using a IFN␣/␤R cDNA (5) probe. Positive colonies were obtained after three rounds of screening, and the inserts were mapped using restriction endonucleases and polymerase chain reaction. Both strands of the longest cDNA clone (4A1) were sequenced using an automated sequencing machine (373A DNA sequencer, Applied Science Laboratories) by the method of DyeDeoxy Terminator, Cycle Sequencing Kit (Applied). Partial sequences of shorter cDNA clones were also obtained using the same method. Expression of the Different Type I IFN-R Subunits in Mouse L-929Cells-Mouse L-929 cells were transfected using Lipofectamine Reagent (Life Technologies, Inc.) with the ␤ S , ␤ L , and ␣ subunit...

Interferon-alpha (IFN-alpha) and IFN-gamma regulate gene expression by tyrosine phosphorylation of several transcription factors that have the 91-kilodalton (p91) protein of interferon-stimulated gene factor-3 (ISGF-3) as a common component. Interferon-activated protein complexes bind enhancers present in the promoters of early response genes such as the high-affinity Fc gamma receptor gene (Fc gamma RI). Treatment of human peripheral blood monocytes or basophils with interleukin-3 (IL-3), IL-5, IL-10, or granulocyte-macrophage colony-stimulating factor (GM-CSF) activated DNA binding proteins that recognized the IFN-gamma response region (GRR) located in the promoter of the Fc gamma RI gene. Although tyrosine phosphorylation was required for the assembly of each of these GRR binding complexes, only those formed as a result of treatment with IFN-gamma or IL-10 contained p91. Instead, complexes activated by IL-3 or GM-CSF contained a tyrosine-phosphorylated protein of 80 kilodaltons. Induction of Fc gamma RI RNA occurred only with IFN-gamma and IL-10, whereas pretreatment of cells with GM-CSF or IL-3 inhibited IFN-gamma induction of Fc gamma RI RNA. Thus, several cytokines other than interferons can activate putative transcription factors by tyrosine phosphorylation.

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