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

Abstract

Expression of human ␣ and long form of the ␤ (␤ L ) subunits of type I interferon receptor (IFN-R) in mouse cells is sufficient to activate the Jak-Stat pathway and to elicit an antiviral state in response to human IFN␣2 and IFN␤. We demonstrate herein, however, that these cells respond to the antiproliferative effects of murine IFN␣␤ but not human type I IFNs. These results suggest that an unknown species-specific component is required for the antiproliferative effect of human type I IFNs. The absence of this component can be complemented by expressing the human ␤ L chain truncated at amino acid 346. Thus, the distal region of ␤ L appears to function as a negative regulator of the growth inhibitory effects of type I IFNs. Further studies looking for possible targets of the ␤ L regulatory domain demonstrated that this region associates with a tyrosine phosphatase. These results suggest that a protein associated with the negative regulatory domain of ␤ L , likely a tyrosine phosphatase, plays a role in regulating the growth inhibitory effects of human type I IFNs.The most prominent effects of type I interferons (IFN) 1 are the antiviral and antiproliferative actions (1). These effects are mediated through binding to the type I interferon receptor (IFN-R or IFN␣R), which is composed of two subunits termed ␣, or IFNAR1, and ␤, or IFNAR2 (2-10). The genes encoding the different subunits of the type I IFN-R are clustered in the q22.1 region of human chromosome 21 (6,7,(11)(12)(13)(14)(15)(16)). This region also harbors an orphan class II cytokine receptor, the CRFB-4 gene, which is encoded on human chromosome 21 between the genes for the ␤ chain of the IFN␣R and the ␤ subunit of the IFN␥R (10, 17). 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). Binding of type I IFNs to their receptor triggers rapid tyrosine phosphorylation of Tyk2 and Jak1 kinases, type I IFN-R subunits (21-25), and Stat factors (reviewed in Refs. 26 -28). Regulation of tyrosine kinase activity is mediated in most cytokine systems by protein tyrosine phosphatases (PTPs). For example, SHP1 (also named SHP, SHPTP1, HCP; PTP1C, Ref. 29), a predominantly hematopoietic tyrosine phosphatase that regulates the activity of the erythropoietin and IL-3 systems (30 -35), has also been implicated in IFN␣ signaling in hematopoietic cells (36,37). However, the role of SHP1 in other cell types is not clear since this PTP is mainly expressed in hematopoietic cells, wher...

Stat2 Binding to the Interferon-α Receptor 2 Subunit Is Not Required for Interferon-α Signaling

“…It has been proposed that an unidentified tyrosine phosphatase binds IFNaR2 near the region we have identified as a Stat2 binding site (47). Although it is conceivable that the Stat2-IFNaR2 interaction modulates the activity of such a phosphatase, we believe that this is unlikely for two reasons.…”

Impaired Antiviral Response and Alpha/Beta Interferon Induction in Mice Lacking Beta Interferon

“…In the first, IFN␣ and IFN␤ genes may be independently induced by viral infection, but IFN-␤ may specifically induce one or more genes that are required for full antiviral activity. Consistent with this possibility, there is evidence for IFN-␤-specific signalling via the alpha/beta receptor (1,6,11,28,29,33) and, in human fibrosarcoma cells at least, for a set of genes (including that encoding the double-stranded RNA-activated protein kinase, whose antiviral activity has been well studied [38]) that are preferentially or exclusively induced by IFN-␤ (10, 31). On its own, however, this model does not explain our observation, and that of others (13), that IFN-␣ induction is impaired in IFN-␤ Ϫ/Ϫ MEFs.…”

Ingested (Oral) IFN-α Represses TNF-α mRNA in Relapsing-Remitting Multiple Sclerosis

“…The IFN receptor genes IFNAR-1 and IFNAR-2 are quite diverse and may display polymorphisms, 32 and show differential negative regulation. 33 IFNAR downregulation could block Mx gene expression at higher local concentrations. 34 Another possibility is that lymphocyte subsets may have IFNAR of different affinities, one activated with low IFN␣ concentrations and others activated at higher concentrations.…”