Mechanisms of Differential Signal Transduction by Interferon Lambda Receptor 1 Variants.

INTRODUCTION: Lambda interferons signal through the interferon lambda receptor 1 (IFNLR1) and IL10RB heterodimer to induce interferon stimulated genes (ISGs). We previously showed that proteins derived from distinct IFNLR1 splice isoforms uniquely influence gene expression and hepatitis B virus replication in stem cell-derived hepatocytes (iHeps). Here, we evaluated signal transduction mechanisms of full-length IFNLR1 (variant 1) and a truncated variant missing part of the cytoplasmic JAK1-interacting domain (variant 2).

METHODS: We evaluated HEK293T cells, wild-type (WT), and IFNLR1 knockout (KO) iHeps with doxycycline-inducible expression of FLAG-tagged IFNLR1 variants using the Duolink proximity ligation assay, ImageStream flow cytometry, Western blotting, susceptibility to JAK1 and TYK2 inhibitors, and gene expression profiling.

RESULTS: Each variant colocalized with IL10RB after IFNL3 treatment, but variant 1 was more rapidly and extensively internalized. In WT iHeps, overexpression of variant 1 or variant 2 enabled higher IFNL-induced JAK1, TYK2, STAT1, and STAT2 phosphorylation, yet variant 2 supported less robust ISG induction. In KO iHeps, variant 2 supported less JAK1 and TYK2 phosphorylation and ISG induction than variant 1, yet supported comparable STAT1 and STAT2 phosphorylation. In iHeps expressing variant 1, WT iHeps were more resistant than KO iHeps to TYK2 inhibition of antiviral ISG induction, yet were more susceptible to TYK2 inhibition of proinflammatory ISG induction, suggesting endogenous noncanonical variants influence TYK2-signaling dependence.

CONCLUSION: IFNLR1 variants promote differential utilization of signaling mediators to influence IFNL-induced gene expression patterns, indicating a putative role in pathway regulation.