Differences in Activity between α and β Type I Interferons Explored by Mutational Analysis

Abstract

Type I interferon (IFN) subtypes ␣ and ␤ share a common multicomponent, cell surface receptor and elicit a similar range of biological responses, including antiviral, antiproliferative, and immunomodulatory activities. However, ␣ and ␤ IFNs exhibit key differences in several biological properties. For example, IFN-␤, but not IFN-␣, induces the association of tyrosine-phosphorylated receptor components ifnar1 and ifnar2, and has activity in cells lacking the IFN receptor-associated, Janus kinase tyk2. To define the structural basis for these functional differences we produced human IFN-␤ with point mutations and compared them to wild-type IFN-␤ in assays that distinguish ␣ and ␤ IFN subtypes. IFN-␤ mutants with charged residues (N86K, N86E, or Y92D) introduced at two positions in the C helix lost the ability to induce the association of tyrosine-phosphorylated receptor chains and had reduced activity on tyk2-deficient cells. The combination of negatively charged residues N86E and Y92D (homologous with IFN-␣8) increased the cross-species activity of the mutant IFN-␤s on bovine cells to a level comparable to that of human IFN-␣s. In contrast, point mutations in the AB loop and D helix had no significant effect on these subtypespecific activities. A subset of these latter mutations did, however, reduce activity in a manner analogous to IFN-␣ mutations. The effects of these mutations on IFN-␤ activity are discussed in the context of a family of related ligands acting through a common receptor and signaling pathway.The mammalian type I IFNs, 1 produced in response to viral infection and other inducers, are divided into ␣ and ␤ subtypes on the basis of their reactivity with antisera raised against IFNs derived, respectively, from leukocytes and fibroblasts (1). The human IFN-␣s are encoded by a family of at least 15 different genes, while IFN-␤ is the unique member of its subtype (2). Primary sequence comparison between the ␣ and ␤ subtypes reveal an approximately 50% amino acid homology, while the amino acid homologies between the IFN-␣ subtypes are approximately 80% (2, 3), reinforcing the division between IFN-␣ and -␤ subtypes.As the pleiotropic nature of these cytokines became apparent, with both subtypes eliciting a similar range of biological activities (3), differences between ␣ subtypes, and between IFN-␣ and -␤s, in potency and cell type specific activities were noted (4). In particular, IFN-␤ elicits a markedly higher antiproliferation response in some cell types such as (5), embryonal carcinoma, melanoma and melanocytes than do IFN-␣s (6, 7, and references therein). Higher potency of IFN-␤ in treatment of multiple sclerosis and certain cancers has been observed (7).The entire class of type I IFNs elicit their biological activities through engagement of a common cell surface receptor (8 -10). Two chains of the receptor, ifnar1 and ifnar2, both members of the type two cytokine receptor family, have been identified (11-15). Both components are necessary for function and in the absence of either there is neither...

IFN-β induces serine phosphorylation of Stat-1 in Ewing's sarcoma cells and mediates apoptosis via induction of IRF-1 and activation of caspase-7

“…These results are in agreement with published data describing the presence of speci®c functional receptors for IFN-a in a series of pediatric tumors, including Ewing's sarcoma, and in cell lines derived from these tumors (Rosolen et al, 1997). Despite the fact that all type I IFNs bind to the same receptor and activate a common set of signaling elements, there is now accumulating evidence of dierences in their signaling pathways (Croze et al, 1996;Domanski et al, 1998;Runkel et al, 1998). For instance, selective Jak-1 phosphorylation induced by IFN-b in human myocardial ®broblasts was recently reported (Grumbach et al, 1999).…”

“…IFN-a and IFN-b (type I IFNs) share a common receptor (Uze et al, 1990;Novick et al, 1994;Domanski et al, 1996); IFN-g (type II IFN) binds to a dierent cell surface receptor (Aguet et al, 1988). Recent reports showed that the subunits of its receptor engage IFN-b in a set of interactions distinct from those of IFN-a (Croze et al, 1996;Domanski et al, 1998;Runkel et al, 1998). Early events in type I IFN signaling are tyrosine phosphorylation of the type I IFN receptor subunits (IFNAR1 and IFNAR2), and the activation of the receptor-associated Tyk-2 and Jak-1 Janus kinases.…”

“…Although type I IFNs share not only the same receptor but also a common set of signaling events that ultimately regulate the expression of common biological activities, evidence is accumulating that signi®cant dierences exist between the eects of the dierent type I IFNs (Aguet et al, 1988;Uze et al, 1990;Novick et al, 1994;De Marco et al, 1995;Croze et al, 1996;Domanski et al, 1996Domanski et al, , 1998Runkel et al, 1998;Grumbach et al, 1999). Although their mechanisms of action are not completely understood, IFNs have been studied for their therapeutic ecacy in a number of pathologies including leukemia (Michalevicz et al, 1988;Gutterman, 1994;De Marco et al, 1995;Borden, 1998;Sacchi et al, 1998;Grumbach et al, 1999).…”

Dimerization of the Interferon Type I Receptor IFNaR2–2 Is Sufficient for Induction of Interferon Effector Genes but Not for Full Antiviral Activity

“…In addition, mutagenesis studies of the IFNaR2-2 chain showed differential receptor activation since (i) intracellular deletions abrogated only the IFN␤ and not the IFN␣-induced antiviral response, while activation of the JAK/Stat pathway was equal in both cases (28), and (ii) extracellular mutations created receptor complexes that showed preferential binding for each of the ligands (27). It is also possible to obtain mutations in IFN␤ that mimic IFN␣ activity (29). These data suggest that other mechanisms may be responsible for generation of signal diversity apart from utilization of cytokine-specific receptor components.…”

Regulatory Effect of IFN-κ, A Novel Type I IFN, On Cytokine Production by Cells of the Innate Immune System

“…The main question at issue is whether their activity is redundant or they are characterized by unique functions (6). Studies of the biological effects of natural IFN subtypes have shown that their activities can vary greatly (7)(8)(9)(10). IFN-␣8, for example, is the most potent antiviral protein (11), while IFN-␤ has a higher potency in inhibiting the growth of certain tumors and is used in the treatment of multiple sclerosis (12)(13)(14).…”