Brucella effector protein BspJ inhibits the NF-κB signaling pathway by targeting the Zfp740 promoter region to promote bacterial survival within macrophages

Abstract

Brucella species are responsible for the zoonotic disease brucellosis and utilize the type IV secretion system (T4SS) to introduce effector proteins into host cells, thereby modulating immune responses and sustaining intracellular infection. Notably, BspJ was identified as the first Brucella nucleomodulin. Although our previous studies demonstrated its influence on host inflammatory responses and bacterial colonization, the precise molecular mechanism remains elusive. In this study, we report novel findings that BspJ directly targets the host transcription factor Zfp740 promoter region through three critical amino acid residues (His66, Arg87, and Arg96), leading to the upregulation of Zfp740 expression. This upregulation subsequently blocks IκBα degradation and inhibits P65 phosphorylation and nuclear translocation, thereby obstructing the activation of the NF-κB signaling pathway and ultimately diminishing the production of proinflammatory cytokines. Moreover, both the BspJ deletion strain and strains with mutations in key amino acids significantly enhanced the inflammatory response and compromised the intracellular survival capacity of Brucella. In conclusion, our study systematically elucidates a novel regulatory axis, BspJ-Zfp740-P65/NF-κB, and reveals a new mechanism by which Brucella directly interferes with host transcriptional programs through a nucleus-targeting effector protein to suppress inflammation and establish persistent infection. These findings provide a significant theoretical foundation for understanding bacteria-mediated immune evasion and chronic infection and introduce new research avenues for the development of host-directed anti-Brucella strategies.