Differential Recognition of the Type I Interferon Receptor by Interferons τ and α is Responsible for Their Disparate Cytotoxicities

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 92; no. 26; pp. 12270 - 12274
• Main Authors: Subramaniam, P S, Khan, S A, Pontzer, C H, Johnson, H M
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences of the United States of America 19-12-1995; National Acad Sciences; National Academy of Sciences
• Subjects: Animals; Antibodies; Antivirals; Binding, Competitive; Biochemistry; Burkitt Lymphoma; Cattle; Cell Line; Cell lines; Cell Survival - drug effects; Cytotoxicity; DNA-Binding Proteins - isolation & purification; DNA-Binding Proteins - metabolism; Humans; Interferon; Interferon Type I - metabolism; Interferon Type I - toxicity; Interferons; Kidney; Kinetics; Membrane Proteins; Phosphorylation; Pregnancy Proteins - metabolism; Pregnancy Proteins - toxicity; Protein-Tyrosine Kinases; Proteins; Proteins - metabolism; Receptor, Interferon alpha-beta; Receptors; Receptors, Interferon - metabolism; Recombinant Proteins; Sheep; STAT1 Transcription Factor; STAT2 Transcription Factor; Toxicity; Trans-Activators - isolation & purification; Trans-Activators - metabolism; Tumor Cells, Cultured; TYK2 Kinase; Ungulates
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.92.26.12270

Interferon τ (IFNτ), originally identified as a pregnancy recognition hormone, is a type I interferon that is related to the various IFNα species (IFNαs). Ovine IFNτ has antiviral activity similar to that of human IFNαA on the Madin-Darby bovine kidney (MDBK) cell line and is equally effective in inhibiting cell proliferation. In this study, IFNτ was found to differ from IFNαA in that it was >30-fold less toxic to MDBK cells at high concentrations. Excess IFNτ did not block the cytotoxicity of IFNα A on MDBK cells, suggesting that these two type I IFNs recognize the type I IFN receptor differently on these cells. In direct binding studies,125I-IFNτ had a Kdof 3.90 × 10-10M for receptor on MDBK cells, whereas that of125I-IFNαA was 4.45 × 10-11M. Consistent with the higher binding affinity, IFNα A was severalfold more effective than IFNτ in competitive binding against125I-IFNτ to receptor on MDBK cells. Paradoxically, the two IFNs had similar specific antiviral activities on MDBK cells. However, maximal IFN antiviral activity required only fractional occupancy of receptors, whereas toxicity was associated with maximal receptor occupancy. Hence, IFNαA, with the higher binding affinity, was more toxic than IFNτ. The IFNs were similar in inducing the specific phosphorylation of the type I receptor-associated tyrosine kinase Tyk2, and the transcription factors Stat1α and Stat2, suggesting that phosphorylation of these signal transduction proteins is not involved in the cellular toxicity associated with type I IFNs. Experiments using synthetic peptides suggest that differences in the interaction at the N termini of IFNτ and IFNα with the type I receptor complex contribute significantly to differences in high-affinity equilibrium binding of these molecules. It is postulated that such a differential recognition of the receptor is responsible for the similar antiviral but different cytotoxic effects of these IFNs. Moreover, these data imply that receptors are "spare" with respect to certain biological properties, and we speculate that IFNs may induce a concentration-dependent selective association of receptor subunits.