Pseudomonas aeruginosa-derived DnaJ functions as a novel immunomodulator inducing IFNβ via CME–SGK1–IRF3 axis in macrophages

Type I interferons (IFNs), particularly IFNβ, play a pivotal role in coordinating innate and adaptive immune responses during microbial infections. Pseudomonas aeruginosa (P. aeruginosa), a clinically significant opportunistic pathogen, is able to induce IFNβ expression; however, the specific microbial factors responsible for this induction remain poorly characterized. In this study, we identify DnaJ, a heat shock protein 40 (HSP40) homolog derived from P. aeruginosa, as a novel microbial inducer of IFNβ expression in macrophages. Among the bacterial HSP homologs tested, DnaJ elicits the most robust IFNβ production via a mechanism dependent on Toll-like receptor 4 (TLR4) and the TRIF-TBK1-IRF3 signaling axis. Mechanistic analysis revealed that clathrin-mediated endocytosis (CME) is required for DnaJ-induced IRF3 activation, and that serum/glucocorticoid regulated kinase 1 (SGK1) functions downstream of CME to promote IRF3 phosphorylation and subsequent IFNβ expression. Consistent with these findings, human HSP40 similarly induced IFNβ expression through the conserved CME-SGK1-IRF3 pathway, indicating that both bacterial and host-derived HSP40 proteins can serve as immune modulators. Collectively, these findings identify P. aeruginosa DnaJ as a potent immunomodulatory ligand capable of inducing IFNβ expression. DnaJ may therefore represent a promising candidate for therapeutic modulation of innate immunity or as an adjuvant in antimicrobial immunotherapy.