The Src-ZNRF1 axis controls TLR3 trafficking and interferon responses to limit lung barrier damage

Type I interferons are important antiviral cytokines, but prolonged interferon production is detrimental to the host. The TLR3-driven immune response is crucial for mammalian antiviral immunity, and its intracellular localization determines induction of type I interferons; however, the mechanism terminating TLR3 signaling remains obscure. Here, we show that the E3 ubiquitin ligase ZNRF1 controls TLR3 sorting into multivesicular bodies/lysosomes to terminate signaling and type I interferon production. Mechanistically, c-Src kinase activated by TLR3 engagement phosphorylates ZNRF1 at tyrosine 103, which mediates K63-linked ubiquitination of TLR3 at lysine 813 and promotes TLR3 lysosomal trafficking and degradation. ZNRF1-deficient mice and cells are resistant to infection by encephalomyocarditis virus and SARS-CoV-2 because of enhanced type I interferon production. However, Znrf1(-/-) mice have exacerbated lung barrier damage triggered by antiviral immunity, leading to enhanced susceptibility to respiratory bacterial superinfections. Our study highlights the c-Src-ZNRF1 axis as a negative feedback mechanism controlling TLR3 trafficking and the termination of TLR3 signaling. E3 ubiquitin ligase ZNRF1 is activated by c-Src kinase following TLR3 activation and, in turn, promotes TLR3 ubiquitination and trafficking to lysosomes for degradation. This leads to properly regulated interferon production and alveolar barrier repair to prevent secondary bacterial superinfection.

Automated summary

The termination mechanism of TLR3 signaling is crucial for antiviral immunity. The E3 ubiquitin ligase ZNRF1 regulates TLR3 sorting into lysosomes, leading to the termination of TLR3 signaling and interferon production. ZNRF1-deficient mice and cells are resistant to specific viral infections but more susceptible to bacterial superinfection due to lung barrier damage.