Type I, II and III interferon receptors are critically important for cells’ antiviral defenses. The three classes of interferon receptor each evoke different antiviral responses—for example, Type I interferon receptors set off a stronger but shorter response than Type III interferon receptors—but the reasons for this are unknown; a black box. In a paper published this week in the journal Science Signaling, Emily Mesev, a graduate student co-advised by MOL professors Alexander Ploss and Jared Toettcher, looked inside.

Interferon receptors receive alarm signals (in the form of certain proteins emitted by virally infected cells) and respond by spurring the production of proteins with potent antiviral powers. Type I and Type III interferon receptors differ from each other structurally and respond to different alarm signals but both mobilize a similar suite of protein partners within the cell to enact their responses. Because interferon receptors span the cell membrane, Emily and her colleagues theorized that their disparate responses could be dictated either by differences in the part of the receptor that juts outside the cell, or the part that extends inside.

To investigate this, the team replaced the cell-exterior portion of each receptor with that of a third receptor protein, the erythropoietin receptor, to create something known as a “chimeric receptor”. Whereas the chimera of Greek legend has a lion’s head and a snake’s tail, these chimeric receptors have the “head” of the erythropoietin receptor outside the cell and the “tail” of an interferon receptor inside. When expressed on cells grown in tissue culture, the chimeras are stimulated by the protein erythropoietin, but the character of their response is governed by whether their cell-internal portion is from a Type I or Type III interferon receptor. By studying cells that expressed similar amounts of Type I or Type III chimeras, the researchers ensured that any differences observed could only be due to the receptors’ interior portion.

Experiments with the chimeras revealed that the strength of their response is dictated by a region called the JAK-1 binding box: Type III chimeras could be endowed with Type I strength by swapping this region for the Type I version, and vice versa. The team theorizes that structural differences in the receptors’ JAK-1 binding boxes may dictate signaling strength by hosting alternate interactions with or activation of proteins called JAK kinases.

In contrast, the researchers observed that both Type I and Type III chimeric receptors responded to stimulation for the same duration. This suggests that the dynamics of signaling is likely under the control of the receptors’ extracellular portion; it could either depend on how many of the receptors are present on the cell’s surface or the strength with which they bind the proteins that stimulate them. These new findings could enable scientists to fine-tune interferon receptor activity and crank out improved antiviral therapies in the future.

Citation: Emily V. Mesev, Aaron E. Lin, Emma G. Guare, Brigitte L. Heller, Florian Douam,  Britt Adamson, Jared E. Toettcher, Alexander Ploss. Membrane-proximal motifs are the primary determinants of signaling strength differences between type I and III interferon receptors. 2023. Science Signaling. DOI: TBD

Funding: This work was supported by funding from the following: the National Institutes of Health (grants R01AI138797, R01AI107301, R01AI146917, R01AI15323, R01AI168048, and DP2EB04247); the Burroughs Wellcome Fund Award for Investigators in Pathogenesis; the American Cancer Society Research Scholar Award (RSG-15-048-01-MPC);  the Vallee Scholars Award ; the NSF CAREER Award (1750663); the NIGMS of the National Institutes of Health (grant T32GM007388); the Damon Runyon Postdoctoral Fellowship (DRG-2432-21); and The Princeton University Flow Cytometry Resource Facility, which is supported, in part, with funding from NCI-CCSG P30CA072720-5921.

Funders: National Institutes of Health; Burroughs Wellcome Fund Award for Investigators in Pathogenesis; American Cancer Society Research Scholar ; Vallee Scholars Award; NSF CAREER Award; NIGMS of the National Institutes of Health; Damon Runyon Postdoctoral Fellowship; National Cancer Institute.

Grant Numbers: R01AI138797, R01AI107301, R01AI146917, R01AI15323, R01AI168048, DP2EB04247, RSG-15-048-01-MPC, 1750663, T32GM007388, DRG-2432-21, NCI-CCSG P30CA072720-5921.