EBV-induced gene 3 augments IL-23Rα protein expression through a chaperone calnexin

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Epstein-Barr virus-induced gene 3 (EBI3) is a shared subunit of IL-27, IL-35, and IL-39 cytokines.
• The intracellular functions of EBI3 beyond its role in cytokine complexes are not well understood.

Purpose of the Study:

• To investigate the intracellular role of EBI3 in T cell function, independent of its canonical cytokine functions.
• To elucidate the mechanism by which EBI3 influences T cell responses, particularly in the context of inflammation and Interleukin-23 receptor (IL-23R) signaling.

Main Methods:

• Analysis of EBI3-deficient naive CD4+ T cells and their IFN-γ production.
• In vitro differentiation of EBI3-deficient CD4+ T cells under Th17 polarizing conditions with IL-23.
• Assessment of IL-23 receptor subunit expression (IL-23Rα and IL-12Rβ1) at both mRNA and protein levels.
• Investigation of EBI3 binding to calnexin and IL-23Rα using peptide- and glycan-dependent assays.
• Evaluation of EBI3 interaction with an IL-23Rα variant (G149R).

Main Results:

• EBI3 deficiency in naive CD4+ T cells led to reduced IFN-γ production and impaired induction of T cell-dependent colitis in mice.
• Reduced IFN-γ production was also observed in EBI3-deficient CD4+ T cells differentiated under pathogenic Th17 conditions.
• EBI3 deficiency selectively decreased IL-23Rα protein expression, but not mRNA levels, impacting IL-23 signaling.
• EBI3 augments IL-23Rα expression by binding to calnexin and IL-23Rα in a peptide-dependent manner.
• EBI3's augmentation of IL-23Rα expression was dependent on the presence of calnexin.
• EBI3 showed reduced binding to the protective IL-23Rα variant G149R, impairing its ability to augment G149R expression.

Conclusions:

• EBI3 plays a critical intracellular role in augmenting IL-23Rα protein expression, mediated through its interaction with calnexin.
• This EBI3-calnexin-IL-23Rα pathway is important for IFN-γ production and T cell-mediated inflammatory responses, particularly under inflammatory conditions.
• EBI3's function in regulating IL-23Rα expression highlights a novel mechanism contributing to T cell pathogenicity and suggests potential therapeutic targets.