Mechanisms of Differential Signaling by IFNLR1 Variants

We evaluated HEK293T cells, wild-type (WT), and IFNLR1 knock-out (KO) iHeps with doxycycline-inducible expression FLAG-tagged IFNLR1 variants using the Duolink proximity ligation assay, ImageStream flow cytometry, western blotting of JAK-STAT proteins, susceptibility to JAK1 and TYK2 inhibitors, and gene expression profiling. Results: Each variant demonstrated IFNL-induced colocalization with IL10RB, but variant 1 was more rapidly and extensively internalized.

In WT iHeps with intact endogenous IFNLR1, overexpression of either variant 1 or variant 2 enabled higher IFNL-induced JAK1, TYK2, STAT1 and STAT2 phosphorylation, yet variant 2 supported less robust ISG induction than variant 1. In iHeps with abrogated endogenous IFNLR1 expression, variant 2 supported less JAK1 and TYK2 phosphorylation and ISG induction than variant 1 yet was not deficient in supporting STAT1 and STAT2 phosphorylation.

Select ISGs had differential constitutive expression in IFNL-untreated variant-expressing iHeps. In iHeps expressing variant 1, WT-iHeps were more resistant than KO-iHeps to TYK2-inhibition of antiviral ISG induction yet conversely were more susceptible to TYK2-inhibition of proinflammatory ISG induction, suggesting endogenously produced noncanonical variants influence the TYK2-dependence of IFNL signaling. Conclusions: IFNLR1 variants promote differential utilization of signaling mediators to influence IFNL-induced gene expression patterns, indicating a putative role in pathway regulation.