A Region of the β Subunit of the Interferon α Receptor Different from Box 1 Interacts with Jak1 and Is Sufficient to Activate the Jak-Stat Pathway and Induce an Antiviral State

Abstract

Type I interferons (IFNs) 1 bind to a multimeric receptor (type I IFN-R, IFN␣R, or IFN␣␤R) composed of at least two subunits designated as ␣ (1-5), and ␤ (6, 7). The IFN␣/␤R cDNA (8) corresponds to the short form of the ␤ subunit (␤ S ), whereas cDNAs for the long form (␤ L ) have been recently isolated by two different groups (9, 10). Transcripts and mature proteins for both ␤ S and ␤ L are found in most cell lines, although there is a large excess of ␤ L protein when compared with ␤ S .2 Lutfalla et al. (10) have also shown that the short and long forms of the ␤ subunit are generated by alternative splicing of the same gene. Interestingly, the type I IFN-binding proteins are not limited to the cellular components described above, because we and others have found a vaccinia virusencoded protein capable of binding type I IFNs as well as blocking type I IFN signaling (11,12).Coexpression of the ␣ subunit with either ␤ L or ␤ S in mouse L-929 cells reconstitutes the high affinity receptor, whereas either form of the ␤ chain expressed independently binds type I IFNs with low affinity. Additional studies using these transfectants show that the IFN␣ response can be reconstituted in mouse cells only when the ␣ chain is coexpressed with the ␤ L subunit rather than ␤ S , indicating that both the ␣ and ␤ L subunits are indispensable for IFN␣ signaling (9). Similarly, only the long form of the ␤ subunit is able to complement the mutant cell line U5A that is defective in the IFN␣ pathway (10).IFNs, cytokines, and growth factors activate the Jak-Stat pathway; more specifically, type I IFNs activate Jak1, Tyk2, Stat1, Stat2, and Stat3 (for recent reviews, see Refs. 13 and 14). Ligand binding to the cytokine receptor subunits activates tyrosine kinases of the Jak family that are constitutively associated with different cytokine receptors. It has been demonstrated that Jak2 binds to the Box 1 motif present in the membrane proximal region of the erythropoietin, prolactin, growth hormone, and granulocyte macrophage colony-stimulating factor receptors (15-21). In the case of the ␣ subunit of the type I IFN-R, there is no conserved Box 1 motif, and Tyk2 interacts with a distinct region different from that of Box 1 (22). Furthermore, in those cytokine receptors that activate Jak1, the region that interacts with this kinase has not been clearly defined. The presence of a Box 1 motif in the membrane proximal region of the ␤ L subunit of the type I IFN-R suggested a possible role for this motif in the binding and/or activation of Jak1 by this receptor subunit. We therefore sought to determine the role of the Box 1 and other domains of the ␤ L chain in type I IFN signaling using two strategies: (a) we stably cotransfected mouse L-929 cells with the wild-type ␣ subunit and various truncated forms of the ␤ L chain to study in vivo signaling processes; and (b) we produced GST fusion proteins with deletions of the ␤ L chain to demonstrate interactions in vitro. Our data indicate that a minimal region of the ␤ L subunit cytoplasmic domain,...

Two Distinct Domains Within the N-Terminal Region of Janus Kinase 1 Interact with Cytokine Receptors

“…For example, Tyk2 interacts with a domain of IFN-␣R␣, the ␣-chain of the IFN-␣R (also designated as IFNAR1 or IFN-␣R1), which has only distant homology with the box 1 or box 2 motifs (25,26). Jak1 is activated by multichain receptors such as the IL-6 group of cytokines (IL-6, leukemia inhibitory factor, ciliary neurotrophic factor, oncostatin M), IFN-␣, IFN-␥, IL-10, and those cytokine receptors that belong to the IL-2 family (IL-2, IL-4, IL-7, IL-9, and IL-15) (19,20,(27)(28)(29)(30)(31)(32)(33). The Jak1 binding site on cytokine receptors has been explored in only a few cases.…”

“…For instance, mutational analysis of the L 267 PKS 270 (leucine, proline, lysine, serine) motif of the ␣-chain of the IFN-␥R␣ (also designated as IFNGR1 or IFN-␥R1), which has only very distant similarity with the box 1, revealed that only Pro 268 was important for Jak1 binding (20). In contrast, the main Jak1 binding site on the IFN-␣R␤ L (also designated as IFNAR2 or IFN-␣R2) chain is clearly different from the box 1 (29) and more distant from the transmembrane region than the Jak1 site described for the IFN-␥R␣. In the case of the IL-2R␤ chain, a sequence with some similarity to the box 1 and a more distal region appear to be important for Jak1 binding (34,35).…”

Exploiting hepatitis C virus activation of NFκB to deliver HCV-responsive expression of interferons α and γ

“…[19][20][21][22] This receptor, on binding these type I IFNs, activates the Jak-STAT signaling cascade, to upregulate transcription of an array of cellular genes. [23][24][25] These IFNs have important effects on the immune system: they alter expression, activation, and localization of many cellular proteins, including MHC-I and -II, and TNFa, that activate and execute antiviral T and NK cell responses.…”

Identification of a Domain in the β Subunit of the Type I Interferon (IFN) Receptor That Exhibits a Negative Regulatory Effect in the Growth Inhibitory Action of Type I IFNs

“…The ␣ and ␤ subunits of the type I IFN-R associate with protein tyrosine kinases of the Jak family (4,8,18). The ␣ subunit interacts with Tyk2 (4,19,20) while the cytoplasmic domain of the ␤ L contains a docking site for Jak1 (18).…”

“…Expression of the human ␣ and long form of the ␤ chain (␤ L ) subunits in mouse L-929 cells fully reconstitutes the activation of the Jak-Stat pathway and the induction of an antiviral state in response to HuIFN␣2 and HuIFN␤ (9). Furthermore, only the first 82 amino acids of the cytoplasmic domain of the ␤ L chain are required to activate the Jak-Stat pathway and induce the antiviral effect in response to IFN␣2 (18).The ␣ and ␤ subunits of the type I IFN-R associate with protein tyrosine kinases of the Jak family (4,8,18). The ␣ subunit interacts with Tyk2 (4,19,20) while the cytoplasmic domain of the ␤ L contains a docking site for Jak1 (18).…”