N4BP1 acts as a potent negative regulator of IL-17 signaling by blocking the translation of Act1 mRNA.

BACKGROUND

Interleukin 17 (IL-17) is a primary pathogenic cytokine, and antibodies blocking its function are clinically approved for treating psoriasis. Although Act1 (TRAF3IP2) is an essential multifunctional adaptor in IL-17 signaling, its regulatory mechanisms remain poorly understood. In this study, the role of endoribonuclease N4BP1 in regulating the IL-17 signaling pathway was characterized.

METHODS

N4BP1 was knocked out in both in vivo and in vitro experimental models to detect alterations in the IL-17 signaling pathway. Moreover, the specific mechanism by which N4BP1 exerts its regulatory effect was explored by examining the stability, degradation rate, transcription and translation rate of key proteins.

RESULTS

N4BP1 deficiency markedly enhanced IL-17-induced expression of proinflammatory mediators, including CXCL1, CCL20, and MMP9. Unexpectedly, the mRNA stability of CXCL1, CCL20, and MMP9 was largely unaffected by N4BP1 knockout. Further investigation revealed that N4BP1-deficient cells exhibited elevated MAPK phosphorylation, particularly of p38. Pharmacological inhibition of p38 substantially reduced CXCL1, CCL20, and MMP9 levels in N4BP1-deficient cells. This hyperactivation of MAPKs was attributed to an increased protein level of Act1 in N4BP1-deficient cells. Silencing of Act1 with shRNAs in N4BP1-deficient cells greatly diminished the upregulation of CXCL1, CCL20 and MMP9. The elevated Act1 protein level in N4BP1-deficient cells was not due to enhanced Act1 mRNA stability. Instead, polysome profiling demonstrated a pronounced enrichment of Act1 mRNA in the translationally active polysome fraction in N4BP1-deficient cells. In vivo, under pathological stimuli such as IMQ or aging, N4BP1-deficient mice exhibited increased Act1 protein, MAPK phosphorylation, and increased expression of IL-17 downstream genes, including CXCL1, CCL20, and MMP9. Pharmacological inhibition of Act1 ameliorates IMQ-induced skin damage, with a more pronounced therapeutic effect observed in N4BP1 KO mice.

CONCLUSIONS

These findings collectively establish that N4BP1 is a potent negative regulator of IL-17 signaling that suppresses the translation of Act1 mRNA.